tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

fracture detection and imaging through relative seismic velocity changes using distributed acoustic sensing and ambient seismic noise abstract fracture systems are important pathways for fluid and solute transport and exert a critical influence on the hydraulic properties of aquifers and reservoirs therefore detailed knowledge of fracture locations connections and evolution is crucial for both groundwater and energy applications e g enhanced geothermal oil and gas recovery carbon sequestration and wastewater injection the innovative combination of distributed acoustic sensing das and ambient seismic noise techniques has the potential to detect and characterize fracture systems at high spatial and temporal resolution without an active source to test this we conducted a multiphysics field experiment at blue canyon dome new mexico a novel energetic material developed by sandia national laboratories was used to generate fractures in two separate stimulations ambient noise was recorded before and after each stimulation using fiber optic cables installed in the outer annulus of four boreholes surrounding the stimulation hol

morphodynamic evolution self organisation and instability of coarse clastic barriers on paraglacial coasts abstract beaches and barriers on many mid to high latitude coasts comprise mixtures of fine and coarse clastic materials forming a distinctive morphodynamic environment in many cases the sediments are derived primarily from limited glacigenic deposits and the coasts are considered paraglacial over relatively long time scales decades to centuries coarse clastic barriers on such coasts show evidence of self organisation through large scale morphological evolution and facies differentiation this process involves gradual reworking partitioning and textural sorting of material toward transport minima long intervals of slow evolution are punctuated by episodes of rapid reorganisation involving breakdown of stable barrier structures and facies patterns remixing of sediment and accelerated migration of transgressive systems drift aligned systems develop longshore cell structure sometimes leading to breaching and segmentation and may evolve toward progressively greater swash alignment under appropriate circumstances swash aligned systems may experience catastrophic transformation when appropriate environmental triggers lead to threshold exceedance in the morphodynamics of the shore system adjacent barriers may show quite different behaviour depending on the antecedent states of individual coastal cells while appropriate parameterisations and sediment budget formulations allow us to model the long term evolution of some barrier structures the non linear dynamics that appear to dominate large scale behaviour may limit predictability the identification of stability threshold criteria remains an important research priority

monitoring of phreatic eruptions using interferometry on retrieved cross correlation function from ambient seismic noise results from mt ruapehu new zealand abstract since the last major eruption in 1995 96 mt ruapehu has erupted twice on 4 october 2006 and on 25 september 2007 these events occurred without any clear precursors and were mostly phreatic explosions the technique of interferometry on retrieved cross correlation function from ambient seismic noise irccasn is used to monitor subtle temporal changes of mt ruapehu s elastic properties the computation of cross correlation functions of seismic noise recorded at several stations around the volcano allowed us to observe variations during the 2006 eruption period the comparison between a reference cross correlation function and a current cross correlation function allows us to infer relative seismic velocity variations a 0 8 decrease of relative seismic velocity in the edifice starting two days before the 2006 eruption was observed this drop is due to a reversible and ephemeral effect which can be attributed to a pressurization of a magma pocket beneath the east flank of ruapehu due to new magma entering a small reservoir this pressure increase produced an inflation of the east flank of ruapehu and opened fractures in this area leading to a localised drop of seismic velocity we conducted the same analysis for the 2007 eruption but no significant seismic velocity variation was observed this difference is possibly due to the varying time scales of pressurization for the two events and also the irccasn time resolution an analysis of the seismicity before these two eruptions allows us to propose a conceptual model which explains the velocity drop for the 2006 eruption and the lack of velocity variations for the 2007 eruption since there was no surface deformation recorded by the geonet gps network we modelled the maximum radius and pressure change for a simple mogi point source at 5 km depth that produced no deformation we inferred the maximum fresh magma volume of 0 0017 km 3 entering the reservoir as a detectability threshold for gps ground deformation measurements

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

tidal modeling of an ancient tide dominated seaway part 2 the aptian lower greensand seaway of northwest europe abstract the cretaceous lower greensand deposits of southeastern england and northern france contain abundant evidence of diurnal once daily paleotides with tidal influence increasing into the late aptian the imperial college ocean model icom is used herein to determine the amplitude origin astronomical or co oscillating and characteristics diurnal or semidiurnal of the tides in the shallow marine lower greensand seaway where these sediments were deposited a global ocean paleotidal model of the aptian predicts very low tidal ranges microtidal in the proto central atlantic ocean and boreal ocean with higher tidal amplitudes especially of the diurnal constituents predicted in the northwestern neotethys ocean this suggests that the neotethys ocean was the only significant source of oceanic tides to the lower greensand seaway herein the results of the global ocean paleotidal model are used to supply boundary conditions to a higher resolution regional paleotidal model of the lower greensand seaway the regional paleotidal model shows that the tidal range of the lower greensand seaway is largely controlled by the width of the connections to the open ocean as sea levels rose during the aptian the oceanic connections widened resulting in reduced frictional damping of the oceanic tidal wave coupled with funneling shoaling and coriolis effects this led to tidal amplification sensitivity tests using a variety of paleogeography and paleobathymetry scenarios suggest that the model predictions are robust the global to regional scale paleotidal modeling presented here strongly suggests that there was a connection through france in the aube region of the paris basin from the neotethys ocean to southeastern england however there are no time equivalent deposits in this region to validate this suggestion it is herein argued that that this is due either to postdepositional erosion or to low sediment supply coupled with strong tidal currents sweeping the seafloor to exposed bedrock

monitoring overwash using water level loggers resolves frequent inundation and run up events abstract long term months to years data on barrier island overwash are lacking but necessary for the proper parameterization of models addressing island response to rising sea levels increased storminess and anthropogenic changes here we present a method for recording overwash events that requires little maintenance and can endure storms this technique uses water level data loggers suspended in shallow wells that are anchored deeply into the ground the loggers are placed close to the highest elevation of the barrier island along a cross shore transect and record high resolution 1 cm and high frequency 2 minute water level measurements we developed a schema for differentiating between tidal fluctuations in groundwater run up overwash and inundation overwash based on the pattern of water level changes interpretations were validated using trail cameras aimed at the well and programmed to take a photograph every 5 min during daylight hours there were some data gaps in the record caused by siltation of the logger in the well repairing a corroded severed cable that was suspending the logger and limited logger data storage we constructed a year long record of overwash frequency and magnitude from october 2012 2013 that included 43 distinct overwash events at a washover fan that initially formed in august of 2011 on onslow beach nc usa the record revealed a shift in overwash intensity at the study site reflecting both changing water levels and changing barrier morphology the high number of overwash events that occurred at the washover fan 14 months after its initial formation is likely not unique to this site however overwash frequency needs to be measured along other shorelines using this method

palaeoclimatic significance of co occurring wind and water induced sedimentary structures in the last interglacial coastal deposits from bermuda and the bahamas abstract the late pleistocene stratigraphic record from the bahamas and bermuda archipelagoes includes peculiar v shaped coastal ridges and wedges of seaward dipping planar beds showing fenestral porosity up to 40 m above present sea level judging from this porosity these landforms were till now interpreted as resulting from the action of giant waves during a period of climatic instability at the end of the last interglacial period the occurrence of widespread mm thick laminae of aeolian origin subcritically climbing translatent stratification throughout these deposits does not agree with this hypothesis it rather suggests that the v shaped ridges and seaward dipping beds represent fossil parabolic and climbing aeolian dunes respectively the occurrence of fenestrae high above the intertidal zone could be related to both wave splashing and rainfall action parabolic dunes are restricted to the nw bahamas they were probably formed during a time interval ca 500 5000 yr when regional climatic conditions were dryer than today and characterized by persistently blowing ne trade winds

processes controlling river mouth lagoon dynamics on high energy mixed sand and gravel coasts abstract the river mouth lagoons of new zealand s gravel bed braided rivers are highly dynamic responding to changes in waves and river flows at timescales of hours and days to years unlike other freshwater dominated coastal wetlands and lagoons they exist along open coasts that are typically retreating with cliffed hinterlands these lagoons are common on new zealand s high energy coarse sediment coastlines and are known locally as h pua this paper employs field observations from the hurunui h pua to investigate the main processes controlling the dynamics of h pua lagoons based on two years of time lapse imagery plus concurrent wave river flow and sea level data an improved conceptual model of lagoon dynamics was developed the model describes how onshore bar migration of river sourced gravel and sand drives initial constriction offsetting of the river mouth following floods it also explains how gravel deposition in the lagoon reduces the threshold flow required to cause primary breach of the barrier opposite the point the river enters the lagoon three processes are identified which affect lagoon width wave overwashing of the gravel barrier narrows the lagoon migration of the highly dynamic lagoon outlet channel resets the barrier position to seaward and river floods occurring while the outlet channel is offset from the river flush sediment from the lagoon system eroding its bed and banks both processes affecting lagoon widening rely on lagoon outlet channel migration indicating that outlet channel dynamics are an important control on lagoon size

joint sensing of bedload flux and water depth by seismic data inversion rivers are the fluvial conveyor belts routing sediment across the landscape while there are proper techniques for continuous estimates of the flux of suspended solids constraining bedload flux is much more challenging typically involving extensive measurement infrastructure or labour intensive manual measurements seismometers are potentially valuable alternatives to in stream devices delivering continuous data with high temporal resolution on the average behaviour of a reach two models exist to predict the seismic spectra generated by river turbulence and bedload flux however these models require estimating a large number of parameters and the spectra usually overlap significantly which hinders straightforward inversion we provide three functions contained in the r package eseis that allow generic modelling of hydraulic and bedload transport dynamics from seismic data using these models the underlying monte carlo approach creates lookup tables of potential spectra which are compared against the empirical spectra to identify the best fitting solutions the method is validated against synthetic data sets and independently measured metrics from the nahal eshtemoa israel a flash flood dominated ephemeral gravel bed river our approach reproduces the synthetic time series with average absolute deviations of 0 01 0 04 m water depth ranging between 0 1 m and 0 00 0 04 kg sm bedload flux ranging between 0 4 kg sm the example flash flood water depths and bedload fluxes are reproduced with respective average deviations of 0 10 m and 0 02 kg sm our approach thus provides generic testable and reproducible routines for a quantitative description of key metrics hard to collect by other techniques in a continuous and representative manner

seismic and electrical properties of unconsolidated permafrost1 a model has been developed to relate the velocities of acoustic waves vp and vs in unconsolidated permafrost to the porosity and extent of freezing of the interstitial water the permafrost is idealized as an assemblage of spherical quartz grains embedded in a matrix composed of spherical inclusions of water in ice the wave scattering theory of kuster and toksoz is used to determine the effective elastic moduli and hence the acoustic velocities the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio the theory has been applied to laboratory measurements of vp and vs in 31 permafrost samples from the north american arctic although no direct measurements were made of the extent of freezing in these samples the data are consistent with the predictions of the model electrical resistivity measurements on the permafrost samples have demonstrated their essentially resistive behaviour the ratio of resistivity of permafrost in its frozen state to that in its unfrozen state has been related to the extent of freezing in the samples electromagnetic and seismic reflection surveys can be used together in areas of permafrost firstly an em survey to determine the extent of freezing and then the acoustic velocity model to predict the velocities in the permafrost the necessary transit time corrections can thus be made on seismic reflection records to compensate for the presence of permafrost

measurements of morphodynamic and hydrodynamic overwash processes in a large scale wave flume overwash is an important process that controls short term barrier dynamics as well as long term barrier migration but this process is difficult to study in the field due to its rare occurrence and the challenging conditions under which it occurs this paper uses data collected during the bardex ii experiment in the delta flume the netherlands where a proto type barrier was subjected to a range of wave and water level conditions the objectives of this research are to 1 compare the morphologic response to overwash on a gravel barrier bardex 2008 experiment with that on a sandy barrier bardex ii 2 understand the influence of wave period on overwash characteristics and sediment transport and 3 improve current knowledge of overwash hydrodynamics the comparative analysis shows that barrier overwash can be affected by negative feedback that stabilises the barrier through barrier crest accretion on gravel barriers and by submerged bar development on sandy barriers an increase in the wave period induced a reduction in overwash frequency over the crest but no significant relation was found between wave peak period and overwash discharge nevertheless overall water discharge during an overwash episode significantly correlates with overall overwash sediment transport rate overwash flow depths during the experiment were relatively shallow and velocities were similar compared to those measured during previous studies and reported in the literature despite the controlled laboratory conditions collection of reliable and accurate measurements of overwash velocities remains challenging

submarine permafrost depth from ambient seismic noise permafrost inundated since the last glacial maximum is degrading potentially releasing trapped or stabilized greenhouse gases but few observations of the depth of ice bonded permafrost ibp below the seafloor exist for most of the arctic continental shelf we use spectral ratios of the ambient vibration seismic wavefield together with estimated shear wave velocity from the dispersion curves of surface waves for estimating the thickness of the sediment overlying the ibp peaks in spectral ratios modeled for three layered 1 d systems correspond with varying thickness of the unfrozen sediment seismic receivers were deployed on the seabed around muostakh island in the central laptev sea siberia we derive depths of the ibp between 3 7 and 20 7 m 15 increasing with distance from the shoreline correspondence between expected permafrost distribution modeled response and observational data suggests that the method is promising for the determination of the thickness of unfrozen sediment

geological constraints on the precambrian history of earth s rotation and the moon s orbit over the past decade the analysis of sedimentary cyclic rhythmites of tidal origin i e stacked thin beds or laminae usually of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided information on earth s paleorotation and the evolving lunar orbit for precambrian time before 540 ma depositional environments of tidal rhythmites range from estuarine to tidal delta with a wave protected distal ebb tidal delta setting being particularly favorable for the deposition and preservation of long detailed rhythmite records the potential sediment load of nearshore tidal currents and the effectiveness of the tide as an agent of sediment entrainment and deposition are related directly to tidal range or maximum tidal height and consequent current speed hence the thickness of successive laminae deposited by tidal currents can be a proxy tidal record with paleotidal and paleorotational values being determined by analysis of measured records of lamina and cycle thickness the validity of the findings can be investigated by testing the primary observed values for internal self consistency through application of the laws of celestial mechanics paleotidal and paleorotational values provided by late neoproterozoic 620 ma tidal rhythmites in south australia are validated by these tests and indicate 13 1 0 1 synodic lunar months yr 400 7 solar days yr a length of day of 21 9 0 4 h and a relative earth moon distance a a0 of 0 965 0 005 the mean rate of lunar recession since that time is 2 17 0 31 cm yr which is little more than half the present rate of lunar recession of 3 82 0 07 cm yr obtained by lunar laser ranging the late neoproterozoic data militate against significant overall change in earth s moment of inertia and radius at least since 620 ma cyclicity displayed by paleoproterozoic 2450 ma banded iron formation in western australia may record tidal influences on the discharge and or dispersal of submarine hydrothermal plumes and suggests 14 5 0 5 synodic months yr and a a0 0 906 0 029 the combined rhythmite data give a mean rate of lunar recession of 1 24 0 71 cm yr during most of the proterozoic 2450 620 ma suggesting that a close approach of the moon did not occur during earlier time concentrated study of precambrian tidal rhythmites promises to illuminate the evolving dynamics of the early earth moon system and may permit the lunar orbit to be traced back to near the time of the moon s origin

seismic cone penetration test and seismic tomography in permafrost two high resolution multi offset vertical seismic profile vsp surveys were carried out in a permafrost mound near umiujaq in northern quebec canada while performing seismic cone penetration tes

quantifying the oldest tidal record the 3 2 ga moodies group barberton greenstone belt south africa comment and reply eriksson and simpson 2000 1 claimed that the moodies tidal data demonstrate the potential for constraining the lunar orbital periods and orbital shape during the archean their claim however will remain undersubstantiated until the following issues are clarified first figure 5a of

cannibalisation of holocene gravel beach ridge plains northern tierra del fuego argentina abstract gravel beach ridge plains form where there is sufficient availability of gravels and wave energy competent to transport the gravel even though beach ridge plains are formed on coasts where sea level has risen during the holocene they occur extensively on stable or emergent coasts unfortunately the holocene evolution of these plains is hard to decipher because of the lack of datable material and their reworked character minimum age the rollover of barriers is expected on submerging coasts on falling sea level coasts the beach ridge plains are in a punctuated process of progradation cannibalisation is common in both settings that is sediment is eroded to maintain longshore growth we present morphological and sedimentological data from three gravel beach ridge plains san sebastian rio chico and cabo penas of the northern coast of tierra del fuego these beach complexes occupy embayments that were infilled during the last 5000 yr under different environmental conditions depth flooded area local oceanographic processes and sediment availability in the evolution of bahia san sebastian a strong control was imposed by high waves originating within the bay due to the strong westerlies the rio chico beach ridge plain evolved during different stages of beach progradation cannibalisation spit growth and saltmarsh development the cabo penas beach ridge plain evolved in opposite directions due to wave refraction caused by rocky reefs and cannibalisation also took place

sedimentology of proterozoic cratonic sheet sandstones of the eastern canadian shield sims formation labrador canada abstract the upper lower proterozoic to middle proterozoic sims formation rests unconformably on lower proterozoic strata of the knob lake group of the labrador trough sequence the 700 m thick sims formation consists of basal fluvial arkoses and conglomerates about 100 m and an upper sheet like sand body about 600 m thick composed of quartz arenites and minor quartz clast conglomerates this upper unit is interpreted as beach shoreface tidal and shallow shelf deposits the lowest 70 m of the quartz arenite unit appear to be of fluvial origin but probably were formed by reworking of quartzose sands produced in coastal environments during a period of elevated sea level the lower sims formation probably represents molasse shed from either the hudson or labrador orogens rivers flowed northwest away from these upland areas the upper part of the sims formation records deposition during a period of slow steady sea level rise in an ocean that deepened to the west the sims formation outliers are remarkably similar to outliers of the sakami formation of northern quebec a unit that has a poorly constrained early to middle proterozoic age if these units are correlative a hypothesis supported mainly by identical facies and facies sequences then the transgressive quartz arenites would originally have covered an area of at least 200 000 km2

importance of infragravity waves for the generation of washover deposits abstract washover deposits are among the most remarkable sedimentary signatures of dune breaching and coastal inundation overwash of the barrier leading to washover development can be related either to storms or tsunamis but the distinction between these two processes based on the depositional record is still a matter of debate hence studying recent well documented washover deposits combining sedimentological and hydrodynamic investigations is a key approach to identify the processes governing the washover deposition and to analyze their sediment record within the washover during the winter of 2013 2014 the coasts of the bay of biscay experienced an exceptional wave climate leading to dune breaching and washover deposition at many locations including the gatseau spit south of oleron island france field observations aerial photographs topographic measurements gpr investigations trenches and cores grain size analysis and magnetic fabric measurements were carried out and complemented with hydrodynamic modeling of tides storm surges short waves and infra gravity waves in order to compute maximum runup during the winter of 2013 2014 such an interdisciplinary approach led to propose that 1 large overwash events occurring during the winter of 2013 2014 were mainly driven by infra gravity ig waves combined with high tides 2 the washover elongated outer shape was strongly controlled by the antecedent morphology of the back barrier area 3 one overwash flow driven by one ig wave is recorded by one normally graded lamina composed of quartz sand at base and heavy minerals enriched sand at top 4 dominant settling of the particles from a suspension during sedimentation occurred in the end of each overwash flow in response to flow velocity decrease 5 laminae can be grouped in laminasets generally composed of thinning upward laminae related to overwash flow depth decrease during falling tide and to erosion of basal laminae by highest overwash flows occurring more likely around the high tide 6 the number of laminasets in a proximal position is in the same order of magnitude as the number of modeled highest runup events offering an almost complete record of overwash events that occurred during the winter 2013 2014

lunar nodal tide and distance to the moon during the precambrian the pace of tidal evolution for the past 450 myr implies an earth moon collision some 1 500 2 000 myr bp see ref 1 an event for which there is no corroborating evidence here we present the first direct determination of the lunar distance in the precambrian we interpret a 23 3 0 3 yr periodicity preserved in a 2 500 myr bp australian banded iron formation bif 2 as reflecting the climatic influence of the lunar nodal tide which has been detected with its modern 18 6 yr periodicity in some modern climate records3 10 the lunar distance at 2 500 myr bp would then have been about 52 earth radii the implied history of precambrian tidal friction is in accord with both the more recent palaeontological evidence and the long term stability of the lunar orbit the length of the milankovitch cycles that modulate the ice ages today11 13 also evolve with the earth moon system their detection in the precambrian sedimentary record would then permit an independent determination of the lunar distance

characterization of shallow geology by high frequency seismic noise tomography summary to study the applicability of the passive seismic interferometry technique to near surface geological studies seismic noise recordings from a small scale 2 d array of seismic stations were performed in the test site of nauen germany rayleigh wave green s functions were estimated for different frequencies a tomographic inversion of the traveltimes estimated for each frequency from the green s functions is then performed allowing the laterally varying 3 d surface wave velocity structure below the array to be retrieved at engineering geotechnical scales furthermore a 2 d s wave velocity cross section is obtained by combining 1 d velocity structures derived from the inversion of the dispersion curves extracted at several points along a profile where other geophysical analyses were performed it is shown that the cross section from passive seismic interferometry provides a clear image of the local structural heterogeneities that are in excellent agreement with georadar and geoelectrical results such findings indicate that the interferometry analysis of seismic noise is potentially of great interest for deriving the shallow 3 d velocity structure in urban areas

monitoring a temporal change of seismic velocity in a volcano application to the 1992 eruption of mt merapi indonesia multiplets i e events with similar waveforms are selected from shallow earthquakes recorded on merapi volcano indonesia before the eruption of february 2nd 1992 two multiplet families are found with their sources close to the summit their seismograms are analyzed using the moving window cross spectrum technique which measures the precise time delay between seismic phases in the entire seismogram for both families of multiplets a gradual decrease in the arrival times of coda waves is observed as a function of the date prior to the eruption coda waves are becoming progressively faster up to 1 2 per cent as the time interval to the eruption shortens this observation is interpreted as the consequence of an increase in the seismic velocity inside the volcano the increase in velocity started in may 1991 and was observed until september 1991 4 months before the eruption this velocity increase may be related to an increase in pressure in the magma chamber or in the conduits and to the resulting closure of the surrounding cracks

the effect of the extent of freezing on seismic velocities in unconsolidated permafrost we develop a model to relate velocities of seismic waves in unconsolidated permafrost is idealized as an assemblage of spherical quartz grains imbedded in a matrix composed of spherical water inclusions in ice the theory of kuster and toksoz based on wave scattering considerations is used to determine the effective elastic moduli and hence the wave speeds the hasin shtrikman theoretical bounds on the elastic moduli of heterogeneous materials and considerations establish the plausibility of the model the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio and the ratio vp vs to be an increasing function of these two parameters the theory is then applied to laboratory measurements of shear and compressional wave velocities in 23 permafrost samples from different sites in the beaufort sea mackenzie river valley and canadian arctic islands although no direct measurements were made of the extents of freezing in these samples the data are consistent w

early tides response to varga et al abstract tidal cycling has been causally implicated at the origin of life but the speed of early tides has not been established the rotation period of the earth is the dominant parameter and a length of day lod of under 6 h at 3 9 ga was inferred by regression from present values lathe r 2004 icarus 168 18 22 however this would imply critical lunar proximity at that time in their commentary varga et al instead argue for a more distant moon proposing lod 16 8 h the debate is accentuated because regression from current values requires an earth moon juxtaposition at around 2 ga for which there is no evidence a smooth retreat from a moon forming impact at 4 5 ga is also irreconcilable with the weight of paleotidal evidence an inflection in the lunar recession curve is required to reconcile current and recent earth moon values with a 4 5 ga origin requiring a change in tidal friction during the evolution of the earth moon system depending on whether this took place at 2 2 5 ga before present or more recently 0 8 0 2 ga lod values are estimated at between 12 and 16 h suggesting a compromise figure of lod 14 h with tides every 7 h at 3 9 ga

seismic surface waves in a suburban environment active and passive interferometric methods seismic interferometry refers to a new range of methods where inter receiver wavefields those that would have been recorded if one of each pair of receivers had been a source can be estimated by cross correlation of wavefields recorded at each of the receivers these methods have found many applications in different fields of seismology including creating virtual sources in wells under complex overburdens computational full wavefield modelling and passive construction of surface wave waveforms from background noise in the earth curtis et al 2006 provide an overview of various applications of seismic interferometry referred to herein and more in depth works can be found in the special supplement on seismic interferometry in the july august issue of geophysics

morphology and stratigraphy of small barrier lagoon systems in maine abstract the coast of maine contains over 200 individual barrier lagoon systems most quite small with an aggregate length of nearly 100 km although they represent less than 5 of the tidally influenced coastline of maine they are widely distributed and occur in a variety of dynamic regimes and physiographic regions their morphology and backbarrier stratigraphy are different from better studied coastal plain systems and provide important clues to the holocene evolution of the maine coast in a study of geomorphic form and backbarrier stratigraphy inlet processes and holocene sea level rise have been identified as the principal controls on coarse grained barrier stratigraphy barriers in maine are found in five distinct geomorphic forms identified herein as barrier spits pocket barriers double tombolos cuspate barriers and looped barriers the few long sandy beaches in southwestern maine are mostly barrier spits the remainder of the barrier types is composed primarily of gravel or mixed sand and gravel the barriers protect a variety of backbarrier environments fresh and brackish ponds lagoons and fresh and saltwater marshes the barriers may or may not have inlets normal wave action coarse grain size and a deeply embayed coast result in barriers with steep reflective profiles several meters above mhw occasional storm events completely wash over the barriers building steep lobate gravel fans along their landward margin few if any extensive storm layers are recognized as extending into the distal backbarrier environments however during sea level rise and landward barrier retreat this abrupt storm generated transition zone inters the backbarrier sediments statistical comparisons of barrier morphology location and backbarrier environment type with backbarrier stratigraphy show that holocene backbarrier stratigraphy is best predicted by the modern backbarrier environment type this in turn is influenced most by the absence or presence and long term stability or instability of a tidal inlet geomorphic barrier form and location in coastal geomorphic compartments show little or no correlation with backbarrier stratigraphy in contrast to previous classifications of barrier lagoon systems based primarily on sandy coastal plain examples in maine the shape or origin of the backbarrier system is relatively unimportant the presence or absence of a tidal inlet is of paramount importance in shaping the holocene stratigraphy of the backbarrier region

tidal friction in the earth moon system modern computers enable us to obtain realistic values for the present tidal torque between the moon and the oceans those values agree with the observations in principle computations for distant geological epochs are possible as well and have been performed however the very complex eigenperiod spectrum of the oceans today precludes a continuous reconstruction of the tidal torque for an essential part of the earth s history hence the original state of the earth moon system is still uncertain we emphasize the importance of results for intermediate timescales

crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast carnsore point southeast ireland abstract storm sedimentation on a fringing sandy gravel barrier system in southeast ireland is examined recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation this is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern united states beach crest overtopping occurs at heights up to 6 m mhws and is related to the development of upper beach swash ramps that are plastered against storm wave eroded dune scarps located at the barrier crest ramp sediments comprise coarse basal beach gravels overlain by coarsening upward units and finally topped by distinctive seawarddipping fine grit coarse sand couplets in places where ramps reach the dune cre t overtopping swash has deposited a fine marine gravel veneer

precambrian length of day and the validity of tidal rhythmite paleotidal values paleotidal records obtained from sedimentary tidal rhythmites may be systematically abbreviated and so may give incorrect paleotidal and paleorotational values the validity of determined values including past length of day l o d can be assessed by testing for internal self consistency through application of the laws of celestial mechanics three independent values obtained from the 620 ma elatina reynella rhythmites in south australia 14 1 sidereal months year 401 sidereal days year and 19 5 years for the lunar nodal period when employed in different equations that make allowance for lunar and solar tidal effects each give a lunar semimajor axis in the range of 96 5 96 9 of the present figure such self consistency strongly supports the validity of the derived l o d of 21 9 hours at 620 ma the validity of the estimated l o d of 20 9 hours at 900 ma revised value big cottonwood rhythmites utah and of 17 1 18 9 hours at 2 5 ga weeli wolli rhythmites western australia cannot be assessed in that way because each data set has only one directly determined value the derived mean rate of lunar retreat of 2 16 cm year since 620 ma averts a close approach of the moon at least since 3 ga and a lower rate of retreat seems likely during the proterozoic

short term morphodynamics of non storm overwash abstract overwash is an important process in barrier island evolution and its effects on the barrier morphology and sedimentology have been widely studied however the short term sediment dynamics of overwash processes are not well known due to the lack of specific field studies this paper presents field data that clarify the sedimentary dynamics of overwash processes on different washover morphologies and determine the factors leading to non storm overwash occurrence two fieldwork campaigns were undertaken during overwash events go 1 winter of 2001 and go 3 winter of 2003 on western barreta island algarve portugal the fieldwork included measurements of oceanographic conditions overwash flows morphology variations mixing depth and sediment transport paths using tracers the sediment dynamics induced by overwash varied according to the washover morphology washover plain versus washover lobe the sediment transport inside the washover plain was different for the two fieldwork campaigns average mixing depth of 13 cm for go 1 and 6 cm for go 3 however it had similar main stages stage 1 crest accretion stage 2 onshore transport and stage 3 dynamic equilibrium the sediment transport inside the washover lobe can be characterised by one onshore flow stage with erosion of the mouth and channel and accretion on the washover fan the main factors governing the occurrence of non storm overwash in the study area were the combined occurrence of 1 typical winter waves 2 spring high tides 3 washover crest below the high tide level 2 m and 4 absence of prominent beach berm this study proved that when the proper conditions are generated non storm overwash has sediment transport comparable to storm overwash and therefore may be significant for barrier evolution further field studies of overwash are needed principally for more detailed overwash flow velocity measurements high frequency morphologic surveys and barrier groundwater measurements

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

late proterozoic and paleozoic tides retreat of the moon and rotation of the earth the tidal rhythmites in the proterozoic big cottonwood formation utah united states the neoproterozoic elatina formation of the flinders range southern australia and the lower pennsylvanian pottsville formation alabama united states and mansfield formation indiana united states indicate that the rate of retreat of the lunar orbit is dxi dt approximately k2 sin 2delta where xi is the earth moon radius vector k2 is the tidal love number and delta is the tidal lag angle and that this rate has been approximately constant since the late precambrian when the contribution to tidal friction from the sun is taken into account these data imply that the length of the terrestrial day 900 million years ago was approximately18 hours

overwash threshold for gravel barriers abstract this paper uses results obtained from the large scale bardex experiments undertaken in the delta flume to investigate the morphological response of a prototype gravel barrier to wave and tidal forcing during overwash conditions gravel barrier behaviour depends upon a number of factors such as sediment properties porosity permeability grainsize geological setting and wave climate since overwash processes are known to control short term gravel barrier dynamics and long term barrier migration the development of a robust quantitative method to define the critical conditions leading to gravel barrier overwashing is important both for scientific and practical management purposes it is known that when wave runup exceeds the barrier crest elevation three outcomes are possible 1 insignificant morphological change when wave runup just overtops the barrier crest and flow velocities are very weak 2 overtopping resulting in accretion on the barrier crest region and barrier stabilisation and 3 overwashing resulting in erosion lowering of the crest region and ultimately to barrier inundation this study provides an insight into the critical conditions that distinguish these two possible outcomes and to the different mechanisms that provide the required positive and negative feedbacks to the sediment dynamics in order to define the overwash threshold condition and to predict the morphological outcome of particular overwash events use is made here of the overwash potential op defined as the difference between the wave runup and the barrier crest elevation to make effective use of op it is necessary to identify a reliable runup predictor following tests using 12 runup equations the stockdon et al stockdon h f holman r a howd p a sallenger a h 2006 empirical parameterization of setup swash and runup coast eng 53 573 588 approach has been identified as the best predictor of runup conditions necessary to generate positive values of op with overtopping and overwashing predicted to occur for average op values of 0 2 m and 0 5 m respectively the use of op values provides a practical means by which to identify potential coastal hazards associated with gravel barrier overwash processes and is considered to have a range of practical coastal management applications

assessment of resolution and accuracy of the moving window cross spectral technique for monitoring crustal temporal variations using ambient seismic noise summary temporal variations in the elastic behaviour of the earth s crust can be monitored through the analysis of the earth s seismic response and its evolution with time this kind of analysis is particularly interesting when combined with the reconstruction of seismic green s functions from the cross correlation of ambient seismic noise which circumvents the limitations imposed by a dependence on the occurrence of seismic events in fact because seismic noise is recorded continuously and does not depend on earthquake sources these cross correlation functions can be considered analogously to records from continuously repeating doublet sources placed at each station and can be used to extract observations of variations in seismic velocities these variations however are typically very small of the order of 0 1 per cent such accuracy can be only achieved through the analysis of the full reconstructed waveforms including later scattered arrivals we focus on the method known as moving window cross spectral analysis that has the advantage of operating in the frequency domain where the bandwidth of coherent signal in the correlation function can be clearly defined we investigate the sensitivity of this method by applying it to microseismic noise cross correlations which have been perturbed by small synthetic velocity variations and which have been randomly contaminated we propose threshold signal to noise ratios above which these perturbations can be reliably observed such values are a proxy for cross correlation convergence and so can be used as a guideline when determining the length of microseismic noise records that are required before they can be used for monitoring with the moving window cross spectral technique

reliability of lunar orbital periods extracted from ancient cyclic tidal rhythmites abstract ancient tidal periods extracted from the geologic record are useful to constrain and calibrate theoretical models of the evolution of the earth moon system analysis of rocks that contain such tidal periodicities termed cyclic rhythmites have tended to concentrate on long series and have focused on the more obvious periods for example neap spring periods have been the most widely discussed such information can be reliably extracted from bedform thickness series measured within laterally accreted tidal bundles and vertically accreted tidal laminae other lunar orbital data is also encoded in cyclic rhythmites however this additional information has been much less extensively applied to earth moon models herein short segments of well formed cyclic rhythmites are examined to determine how reliably the various tidal periods can be extracted via harmonic analysis rhythmite series analyzed here exhibit well formed neap spring tidal periods and also exhibit a prominent fortnightly inequality or a variation in the height of successive spring tides this inequality is related to the elliptical nature of the lunar orbit anomalistic month and it is demonstrated that this period can also be reliably extracted from cyclic rhythmites tropical periods which reflect the changing lunar declination that occurs during a tropical month have also been reported from cyclic rhythmites unlike synodic and anomalistic periods the apparent tropical periods extracted from some cyclic rhythmites do not always accurately correspond to the expected values in only a few cases can this period be reliably extracted from short segments of cyclic tidal rhythmite data this period is commonly only poorly encoded in rhythmites because 1 it tends to be masked by higher amplitude synodic periods and 2 it is not well expressed within predominantly semidiurnal tidal systems samples selected from the proterozoic and phanerozoic tend to be more common during specific intervals of geologic time these intervals were characterized by glacio eustatic flux and in some cases by unique continental configurations understanding these basic controls on rhythmite occurrences should aid in the discovery of additional examples

monitoring changes in velocity and q using non physical arrivals in seismic interferometry application of seismic interferometry to records from receivers at the earth s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface when the wavefields experience intrinsic losses during propagation non physical arrivals ghosts would appear in the retrieved result these ghosts appear due to waves that reflect inside a subsurface layer thus a ghost contains information about the seismic properties of the specific layer we show how such ghosts can be used to monitor layer specific changes in the velocity and intrinsic losses in the subsurface we show how to identify the ghosts using numerical modelling results from a vertical well and how to estimate the layer specific velocity and quality factor changes using numerical modelling results from a horizontal well as well as ultrasonic s wave laboratory data

a rock physics investigation of unconsolidated saline permafrost p wave properties from laboratory ultrasonic measurements abstractsaline permafrost is sensitive to thermal disturbances and is prone to subsidence which renders it a major source of geohazard in arctic coastal environments seismic methods could be used to map and monitor saline permafrost at scales of geotechnical interests because of the ice content dependencies of seismic properties we have developed a comprehensive study of the ultrasonic p wave properties i e velocity and attenuation of synthetic saline permafrost samples for a range of salinities and temperatures and measurements conducted on a fine grained permafrost core obtained from barrow alaska the resulting data consist of p wave properties presented as functions of temperature and salinity notable observations include the following p wave velocities showed marked reductions in the presence of dissolved salts and complex variations resulting from the water to ice phase transitions strong p wave attenuation was present in the temperature intervals in which the samples were partially froz

real time monitoring of relative velocity changes using ambient seismic noise at the piton de la fournaise volcano la reunion from january 2006 to june 2007 we present the results of a real time method based on coda wave interferometry from seismic noise cross correlation functions for relative seismic velocity variations monitoring on a volcanic edifice the ambient seismic noise at the piton de la fournaise volcano on la reunion island is analyzed from january 2006 to june 2007 during this period five eruptions occurred showing a great diversity in eruption duration intensity and eruptive fissure location two different methods are used to compute the velocity variations in order to compare their stability in quasi real time routine we compare the obtained velocity variations with the surface deformation observed by gps and extensometers networks this allows us to identify and quantify three major processes at the origin of seismic wave velocity variations in the edifice firstly the observed pre eruptive summit inflation is accompanied by a decrease in seismic velocity secondly the edifice deflation following the opening of an eruptive fissure is characterized by an increase of the velocity finally the summit caldera collapse generates a strong velocity drop coda wave interferometry from seismic noise cross correlation functions in quasi real time may allow us to forecast eruption and constrain the processes taking place in the volcanic plumbing system

late precambrian tidal rhythmites in south australia and the history of the earth s rotation sedimentary rhythmites of siltstone and fine sandstone from late precambrian c 650 800 ma glaciogenic formations in south australia are interpreted as distal ebb tidal deposits that record variability in the velocity and range of palaeo ebb tides variations in lamina thickness encode a full spectrum of palaeotidal cycles including semidiurnal diurnal fortnightly and monthly tidal cycles as well as the lunar apsides perigee and nodal cycles a half yearly oscillation is attributable largely to a beat between the fortnightly tidal cycles of luni solar conjunction and lunar declination the lunar nodal cycle is discernible as an amplitude modulation of this beat oscillation the data allow determination of the earth9s palaeorotation and the past dynamics of the earth moon system with an accuracy previously unattainable for the precambrian the late precambrian c 650 ma year contained 13 1 0 5 lunar months and c 400 20 days and the late precambrian lunar month c 30 5 1 5 days these values suggest an average equivalent phase lag near 3 since late precambrian time rather than the present value of 6 the period of 19 5 0 5 years determined for the lunar nodal cycle c 650 ma ago indicates a lunar distance 96 9 1 7 of the present distance the low rate of lunar recession since late precambrian time revealed by the rhythmite data militates against a close approach of the moon during the proterozoic precambrian sedimentary rhythmites may hold a key to the early history of the earth9s rotation

a global carbon isotope excursion spice during the late cambrian relation to trilobite extinctions organic matter burial and sea level abstract the steptoean positive carbon isotope excursion spice marks a global oceanographic event that confirms intercontinental correlations between different biogeographic realms based on agnostids and other blue water trilobites the spice excursion is documented from sections in laurentia kazakhstan china and australia where it begins with the mass extinction at the base of the pterocephaliid biomere steptoean stage in laurentia and at coeval extinction horizons in gondwana and perigondwana terranes the peak of spice 5 coincided with a time of maximum regression in laurentia spice is similar in this regard to excursions that coincide with glacio eustatic falls such as in the late ordovician a plausible scenario involves the transformation of ocean circulation between two states which led to enhanced coastal upwelling and benthic extinctions the lack of evidence for glaciation indicates that the coeval sea level fall sauk ii sauk iii event resulted from tectonic or hydrologic changes that remain poorly understood at this time

seismic and ultrasonic velocities in permafrost we calculate the compressional and shear wave velocities of permafrost as a function of unfrozen water content and temperature unlike previous theories based on simple slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids solid and ice matrices and a liquid unfrozen water the compressional velocity for unconsolidated sediments obtained with this theory is close to the velocity computed with wood s model since biot s theory involves a wood averaging of the moduli of the single constituents moreover the model gives lower velocities than the well known slowness averaging theory wyllie s equation for consolidated berea sandstone the theory underestimates the value of the compressional velocity below 0 c computing the average bulk moduli by slowness averaging the ice and solid phases and wood averaging the intermediate moduli with the liquid phase yields a fairly good fit of the experimental data the proportion of unfrozen water and temperature are closely related fitting the wave velocity at a given temperature allows the prediction of the velocity at the whole range of temperatures provided that the average pore radius and its standard deviation are known