foraminiferal inventory and lithologic description of the lower cretaceous albian hulcross shale monkman area northeastern british columbia correlation of an arenaceous microfauna of 41 species 44 subspecies from the hulcross formation of the monkman pass area with that found in the hulcross shale on the peace river has a further corroboration in matching spectra of volcanic ash beds at both localities the monkman pass equivalents of both the basalmost portion and the upper part of the hulcross beds on the peace river are in sandy to continental facies diatoms are plentiful in the monkman pass section in the shaly facies the foraminiferal genera include bathysiphon thuramminoides psammosphaera hippocrepina saccammina reophax glomospira ammodiscus psamminopelta haplophragmoides ammobaculites trochammina textulariopsis pseudobolivina verneuilinoides uvigerinammina gaudryina eggerella and dorothia only thuramminoides haplophragmoides and trochammina occur in abundance indicating water of depth around 100 m at time of deposition and of salinity close to that of normal seawater the low degree of bioturbation and the pres

abnormally strong daily cycle s1 strain tide observation and physical mechanism tidal signals are analyzed in the plate boundary observatory borehole strainmeters in western north america while the extracted diurnal strain tidal constituents except daily cycle s1 respond to the tidal forces in similar proportion the s1 strain tide exhibits an abnormally strong amplitude reaching tens to hundreds times larger than theoretical prediction the s1 strain tide exhibits phase lags and little amplitude correlations with the corresponding s1 barometric pressure tide while no phase lags are observed at the other frequencies between these two observations several mechanisms are examined and are excluded for explaining the strong s1 strain tides including integral effect of barometric pressure loading viscoelastic response to barometric pressure elastic loading of ocean water and hydrological water variation and thermal leakage from the surface to the strainmeter instruments the strong s1 strain tides can be attributed to the results of two physical mechanisms 1 elastic loading of surface barometric pressure and 2 thermoelastic deformation induced by temporally and spatially varying surface temperature the barometric pressure produces a component of elastic strain in phase with the pressure while the surface temperature induces thermoelastic strain exhibiting comparable amplitude with the pressure induced component but with various phase lags as a result the superposition of these two s1 strain tides exhibits a phase difference with respect to the corresponding s1 tides of both barometric pressure and temperature and explains the large s1 strain tides observed in the strainmeter data our results indicate the importance of thermoelastic deformation being a near surface physical process

a comparison of tidal ocean loading models using superconducting gravimeter data 1 errors in global ocean models have been shown to be larger than the accuracy of surface gravity measurements baker and bos 2001 and also new space gravity missions ray et al 2001 in this paper we compare the tidal loading estimated using 10 different ocean tide models to the surface gravity variations observed with 12 superconducting gravimeters sg belonging to the global geodynamics project crossley et al 1999 worldwide network ocean tidal gravity variations are shown to be mostly dependent on tidal sea height variations within a radius of 5000 km precise surface gravity measurements are therefore another tool for validating ocean tidal models from short to long wavelengths in addition for example to tide gauge data in this study we also compute the tidal loading using several different available computer codes as for ocean tidal models we show that the differences between tidal loading programs are frequently larger than the error estimates of sg measurements compared to previous models both recent hydrodynamical and topex poseidon derived tidal models allow a significant reduction of discrepancies between ocean tidal observations using sg and tidal loading estimates there still remains however a nonnegligible in phase discrepancy between ocean tidal loading estimates and surface gravity observations whereas the out of phase component is much smaller we have shown that the in phase disagreement does not seem to be caused by an inaccurate determination of the sg calibration

foraminifera of a joli fou shale equivalent in the lower cretaceous albian hasler formation northeastern british columbia the discovery of the arenaceous foraminifer haplophragmoides gigas cushman in the hudson hope area of northeastern british columbia indicates that the early cretaceous albian joli fou sea flooded around the north side of the peace river arch making an embayment that penetrated as far west as the rocky mountain foothills the microfauna of 25 genera and 46 species of arenaceous foraminifers is illustrated carrying bathysiphon spp hippocrepina sp hyperammina spp lituotuba sp psammosphaera spp reophax spp ammodiscus spp glomospira sp miliammina spp psamminopelta spp trochamminoides sp haplophragmoides spp ammomarginulina sp ammobaculites spp haplophragmium spp trochammina spp textulariopsis sp pseudobolivina spp plectorecurvoides sp verneuilina sp gaudryina sp uvigerinammina sp gravellina sp and eggerella sp the suite occurs in the lower part of the hasler shale of the fort st john group about 10 20 m above beds carrying a microfauna of the ammobaculites wen

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

typhoon induced ground deformation geodetic instruments now offer compelling sensitivity allowing to investigate how solid earth and surface processes interact by combining surface air pressure data nontidal sea level variations model and rainfall data we systematically analyze the volumetric deformation of the shallow crust at seven borehole strainmeters in taiwan induced by 31 tropical cyclones typhoons that made landfall to the island from 2004 to 2013 the typhoon s signature consists in a ground dilatation due to air pressure drop generally followed by a larger ground compression we show that this compression phase can be mostly explained by the mass loading of rainwater that falls on the ground and concentrates in the valleys towards the strainmeter sensitivity zone further our analysis shows that borehole strainmeters can help quantifying the amount of rainwater accumulating and flowing over a watershed during heavy rainfalls which is a useful constraint for building hydrological models

long term seafloor tidal gravity and pressure observations in the north sea testing and validation of a theoretical tidal model seafloor gravity and pressure measurements for 4d reservoir monitoring require precise models of the time varying tidal signals current seafloor instrumentation can resolve 0 003 mgal in time lapse gravity differences and 0 05 kpa 5 mm in pressure to verify model accuracy a seafloor gravimeter and pressure gauge were operated continuously for 446 days next to the troll a gas platform in the north sea 60 64227 north 3 72417 east at a depth of 303 m the seafloor gravity and pressure time series were filtered and corrected with estimates from the tidal model which predicts the solid earth tide ocean loading and direct gravitational attraction of the varying water level the rms difference between the observed tidal gravity signal and the prediction is about 0 0013 mgal during periods when there are no surface storms a slight difference is observed for the direct attraction of the water overhead as computed from the tidal prediction versus that computed from direct seafloor pressure measuremen

early cretaceous early late albian echinoderms from northeastern british columbia canada an echinoderm association is reported from the early late albian paddy member of the peace river formation of british columbia canada the association includes frasericrinus mauricensis gen et sp nov two additional distinctive crinoid column types a poorly preserved asteroid and an umbilical fragment of the cephalopod stelckiceras this is the first report of a cretaceous isocrinid from north america the echinoderm fossils are from the top of a succession of storm deposited sandstones and mudstones boulder creek formation that can be correlated southward into nearshore and terrestrial facies of the paddy member of the peace river formation the echinoderm fossils were buried and probably lived about 12 14 km from the contemporaneous shoreline in an estimated water depth of 10 20 m integration of biostratigraphic and allostratigraphic schemes suggests that the echinoderms are of earliest late albian age the association of the echinoderm fauna with ammonites of boreal affinity indicates depos

rupture across arc segment and plate boundaries in the 1 april 2007 solomons earthquake the largest earthquakes are generated in subduction zones and the earthquake rupture typically extends for hundreds of kilometres along a single subducting plate these ruptures often begin or end at structural boundaries on the overriding plate that are associated with the subduction of prominent bathymetric features of the downgoing plate here we determine uplift and subsidence along shorelines for the 1 april 2007 moment magnitude m w 8 1 earthquake in the western solomon islands using coral microatolls which provide precise measurements of vertical motions in locations where instrumental data are unavailable we demonstrate that the 2007 earthquake ruptured across the subducting simbo ridge transform and thus broke through a triple junction where the australian and woodlark plates subduct beneath the overriding pacific plate previously no known major megathrust rupture has involved two subducting plates we conclude that this event illustrates the uncertainties of predicting the segmentation of subduction zone rupture on the basis of structural discontinuities

a new sea floor gravimeter a new reservoir management application uses precise time lapse gravity measurements on the sea floor to detect seawater infiltration in offshore natural gas fields during production reservoir models for the north sea troll field predict gravity changes as large as 0 060 mgal within a 3 5 year period we have constructed and deployed a new instrument the rovdog remotely operated vehicle deployed deep ocean gravimeter system for this application because the measurements must be relocated accurately within 3 cm we required a gravimeter which could be handled by an rov and placed atop sea floor benchmarks we have built an instrument based upon the scintrex cg 3m land gravimeter motorized gimbals level the gravimeter sensor within a watertight pressure case precision quartz pressure gauges provide depth information a shipboard operator remotely controls the instrument and monitors the data the system error budget considers both instrumental and field measurement uncertainties the instrument prototy

foraminiferal zonation of the viking interval in the hasler shale albian northeastern british columbia a dominantly arenaceous foraminiferal fauna of over 33 genera and 65 species was recovered from silty shales in the mid portion of the hasler formation in the upper albian part of the fort st john group the assemblages lie stratigraphically below occurrences of neogastroplites and below the miliammina manitobensis zone the foraminifera come from above the occurrence of haplophragmoides gigas gigas although assignment of the beds is to the upper part of the h gigas zone the upper part of the haplophragmoides gigas zone may be divided into several subzones above the h gigas gigas sub zone in ascending order viz h gigas ssp a subzone reophax tundraensis subzone trochammina depressa subzone trochammina umiatensis subzone and reophax troyeri subzone the assemblages have close affinities with the faunas of both the overlying and underlying shales and are an expression of a late shallowing deepening cycle within the skull creek joli fou seaway they were penecontemporaneous with viking sandstone

mcmurray formation foraminifera within the lower albian lower cretaceous loon river shales of northern alberta early cretaceous paleogeography and biostratigraphy of western canada are reviewed in light of a reassessment of foraminiferal and microfloral data from unpublished university theses on the early a

the owles iop2b lake effect snowstorm shoreline geometry and the mesoscale forcing of precipitation abstractlong lake axis parallel llap lake effect precipitation systems that form when the flow is parallel to the long axis of an elongated body of water frequently produce intense highly localized snowfall conceptual models of these llap systems typically emphasize the role of thermally forced land breezes from the flanking shorelines with low level convergence and ascent centered near the lake axis in reality other factors such as shoreline geometry and differential surface roughness can strongly influence llap systems here a wrf model simulation is used to examine the mesoscale forcing of lake effect precipitation over lake ontario during iop2b of the ontario winter lake effect systems owles field campaign in the simulation the large scale flow shoreline geometry and differential surface heating and roughness contribute to the development of three major airmass boundaries the first is a land breeze front that forms along a bulge in the south shoreline between st catharines ontario can

snowbands over the english channel and irish sea during cold air outbreaks persistent northerly to easterly cold air outbreaks affected the uk during the winters of 2009 10 and 2010 11 with the resulting convection frequently organizing into snowbands over the english channel and irish sea sounding data and composite radar reflectivity images from the met office nimrod precipitation radar network reveal that these bands formed along the major axis of each body of water or sea when the boundary layer flow was roughly parallel to each of those axes along channel for both seas a band was present the majority of times that the 850 hpa flow was along channel of these times of along channel flow the 850 hpa wind speed and surface to 850 hpa temperature difference were significantly greater when bands were present than when they were not for the english channel only the land sea temperature difference was also significantly greater when bands were present than when they were not in a real data weather research and forecasting model wrf control simulation of a typical band over the english channel a trough develops over the water and offshore air streams from either side converge along it in the absence of surface fluxes the trough convergence and organized precipitation fail to develop altogether orography and roughness length variations are less important in band development affecting only the location and morphology

correlation between the phase of the moon and the occurrences of microearthquakes in the tamba region through point process modeling 1 we study the correlation between the phase of the moon and the occurrence of microearthquakes in the tamba region close to the fault of the 1995 kobe earthquake the existence of the correlation during the two year period following the kobe earthquake was suggested in a previous study first in this study we investigate the statistical significance of such correlation using point process modeling and aic akaike information criterion we confirm that the existence of the correlation is statistically significant second we investigate the temporal variation of the correlation during the four year period following the kobe earthquake the result of the second analysis indicates that the correlation is strongest just after the kobe earthquake and that it then becomes weaker year by year

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

seismicity on the western greenland ice sheet surface fracture in the vicinity of active moulins we analyzed geophone and gps measurements collected within the ablation zone of the western greenland ice sheet during a 35 day period of the 2011 melt season to study changes in ice deformation before during and after a supraglacial lake drainage event during rapid lake drainage ice flow speeds increased to 400 of winter values and icequake activity peaked at times 7 days after drainage this seismicity developed variability over both diurnal and longer periods 10 days while coincident ice speeds fell to 150 of winter values and showed nightly peaks in spatial variability approximately 95 of all detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagation within near surface ice 330m deep that generated rayleigh waves icequakes occurring before and during drainage frequently were collocated with the down flow west end of the primary hydrofracture through which the lake drained but shifted farther west and outside the lake basin after the drainage we interpret these results to reveal vertical hydrofracture opening and local uplift during the drainage followed by enhanced seismicity and ice flow on the downstream side of the lake basin this region collocates with interferometric synthetic aperture radar measured speedup in previous years and could reflect the migration path of themeltwater supplied to the bed by the lake the diurnal seismic signal can be associated with nightly reductions in surface melt input that increase effective basal pressure and traction thereby promoting elevated strain in the surficial ice

geodynamics and earth tides observations from global to micro scale introduction the volume collects papers submitted to pure and applied geophysics following a call on the topic geodynamics and earth tides partly the authors had participated in the 18th geodynamics and earth tides symposium held intrieste italy in june 2016 theearth tides constitute the leading thread through the book since instrumentation sensitive enough to observe them also records a broad spectrum of signals generated by earth dynamic processes

foraminifera of the middle to upper albian transition lower cretaceous northeastern british columbia throughout alberta and saskatchewan the upper albian substage lies unconformably on subjacent beds however on the peace river in northeastern british columbia 32 km below hudson hope a silty shale outcrop shows uninterrupted marine deposition across the middle upper albian substage boundary an arenaceous foraminiferal fauna of 21 genera and 57 sub generic taxa is illustrated from this outcrop of the hasler shale the collections come from above the previously illustrated microfauna of the stelckiceras liardense zone and below the occurrence of haplophragmoides gigas gigas and provide a spectrum of transitional faunules spanning the middle upper albian boundary the corresponding boundary of the ammobaculites wenonahae subzone of the gaudryina nanushukensis zone with the overlying haplophragmoides uniorbis subzone new at the base of the haplophragmoides gigas zone is defined at 73 m above the top of the cadotte sandstone by the disappearance of a wenonahae genera within the upper part of the a w

radiometric dating of a tuff bed in the middle albian hulcross formation at hudson s hope british columbia u pb rb sr and k ar methods were employed to estimate the age of a thin crystal tuff bed in the middle albian hulcross formation at hudson s hope northeastern british columbia ten different gravity fractions of altered biotite define an rb sr isochron that passes through the plotted rb sr data point for cogenetic plagioclase the biotite plagioclase isochron yields an age of 102 4 1 0 20 x mswd1l2 ma mswd is mean square weighted deviate and an initial ratio of 0 71311 0 00030 different size fractions of clear prismatic zircons define a u pb discordia line that intersects the concordia at 102 5 20 ma the four heaviest gravity fractions of biotite give a k ar age of 106 0 1 8 20 ma the most probable age of deposition of the tuff bed is estimated to be very close to or a little more than 102 ma but does not exceed 106 ma

analysis of tidal signals in surface displacement measured by a dense continuous gps array abstract we analyze the tidal displacement signals for the eight major diurnal and semidiurnal tides from global positioning system gps measurements made at the western united states over the past 16 years with 1075 independent stations by careful examinations among inland versus coastal gps data we are able to demonstrate that estimated precisions down to the level of 0 1 mm horizontal and 0 3 mm vertical have been reached for the tidal signals and that at such precisions coherent spatial patterns are revealed in the residual tidal amplitudes and phases after the removal of a priori modeled effects of body tides and ocean tidal loading otl we demonstrate the facility of modern precise gps data in not only constraining the ocean tide models but more significantly in providing source data in terms of regional complex love numbers for geophysical inference of the heterogeneities of elastic and inelastic structures in the solid earth s deep interior on tidal timescales

tidal observations on floating ice using a single gps receiver 1 we measure ocean tides as experienced by sea ice or ice shelves using a single gps receiver such a method allows for tidal measurements to be made with the same precision regardless of its distance from a gps base station since such a base station is not required single epoch observations are shown to be accurate to about 50 mm when compared with concurrent bottom pressure gauge bpg observations the differences between the gps and bpg observations are largely free from power at tidal frequencies furthermore harmonic tidal analyses show that these gps observations allow the correct determination of diurnal and semi diurnal tidal constituents meaning that observations of this type can be assimilated into numerical tide models

upper plate splay fault earthquakes along the arakan subduction belt recorded by uplifted coral microatolls on northern ramree island western myanmar burma abstract upper plate structures that splay out from the megathrusts are common features along major convergent plate boundaries however their earthquake and tsunami hazard potentials have not yet received significant attention in this study we identified at least one earthquake event that may have been produced by an upper plate splay fault offshore western myanmar based on u th ages of uplifted coral microatolls this event is likely an earthquake that was documented historically in c e 1848 with an estimated magnitude between 6 8 and 7 2 based on regional structural characteristics such magnitude is consistent with the observed co seismic uplift amount of 0 5 m although these events are smaller in magnitude than events produced by megathrusts they may produce higher earthquake and tsunami hazards for local coastal communities due to their proximity our results also indicate that earthquake events with co seismic uplift along the coast may not necessarily produce a flight of marine terraces therefore using only records of uplifted marine terraces as megathrust earthquake proxies may overlook the importance of upper plate splay fault ruptures and underestimate the overall earthquake frequency for future seismic and tsunami hazards along major subduction zones of the world

effect of error in theoretical earth tide on calibration of borehole strainmeters 1 since the installation of borehole strainmeters into the ground locally distorts the strain in the rock these strainmeters require calibration from a known source which typically is the earth tide consequently the accuracy of the observed strain changes from borehole strainmeters depends upon the calibration derived from modeling the earth tide previous work from the mid 1970s which is replicated here demonstrate that the theoretical tide can differ by 30 from the tide observed at surface mounted long baseline strainmeters in spite of possible inaccurate tidal models many of the 74 borehole strainmeters installed since 2005 can be calibrated however inaccurate tidal models affect the amplitude and phase of observed transient strain changes which needs to be considered along with the precision of the data from the inherent drift of these borehole instruments in particular the error from inaccurate tidal model dominates the error budget in the observation of impulsive sub daily strain transients

coast of departure and coast of arrival two important concepts for the formation and structure of convective snowbands over seas and lakes abstract a case with intense convective snowbands over the baltic sea is examined using the high resolution limited area model the intention is to gain a better insight into the importance of the shape of the coasts the orography and the surface roughness on the formation and evolution of the snowbands among the factors studied are the shape of the coast from which the air departs and that to which it arrives these factors are so important that two new concepts coast of departure and coast of arrival are introduced

the owles iop2b lake effect snowstorm mechanisms contributing to the tug hill precipitation maximum abstractlake effect storms frequently produce a pronounced precipitation maximum over the tug hill plateau hereafter tug hill which rises 500 m above lake ontario s eastern shore here weather research and forecasting model simulations are used to examine the mechanisms responsible for the tug hill precipitation maximum observed during iop2b of the ontario winter lake effect systems owles field program a key contributor was a land breeze front that formed along lake ontario s southeastern shoreline and extended inland and northeastward across tug hill cutting obliquely across the lake effect system localized ascent along this boundary contributed to an inland precipitation maximum even in simulations in which tug hill was removed the presence of tug hill intensified and broadened the ascent region increasing parameterized depositional and accretional hydrometeor growth and reducing sublimational losses the inland extension of the land breeze front and its contribution to precipitation enhancem

axial seamount periodic tidal loading reveals stress dependence of the earthquake size distribution b value abstract earthquake size frequency distributions commonly follow a power law with the b value often used to quantify the relative proportion of small and large events laboratory experiments have found that the b value of microfractures decreases with increasing stress studies have inferred that this relationship also holds for earthquakes based on observations of earthquake b values varying systematically with faulting style depth and for subduction zone earthquakes plate age however these studies are limited by small sample sizes despite aggregating events over large regions which precludes the ability to control for other variables that might also affect earthquake b values such as rock heterogeneity and fault roughness our natural experiment in a unique seafloor laboratory on axial seamount involves analyzing the size frequency distribution of 60 000 microearthquakes which delineate a ring fault system in a 25 km3 block of crust that experiences periodic tidal loading of 20 kpa we find that above a threshold stress amplitude b value is inversely correlated with tidal stress the earthquake b value varies by 0 09 per kpa change in coulomb stress our results support the potential use of b values to estimate small stress variations in the earth s crust

present day vertical land motion of australia from gps observations and geophysical models the secular rate of australia s vertical surface deformation due to past ice ocean loading changes is not consistent with present vertical velocities observed by a previously sparse network of global positioning system gps sites current understanding of the earth s rheology suggests that the expected vertical motion of the crust should be close to zero given that australia is located in the far field of past ice sheet loading recent gps measurements suggest that the vertical motion of the australian continent at permanent sites is between 0 and 2 mm year here we investigate if vertical deformation due to previous ice sheet loading can be recovered in the time series of australian gps sites through enlarging the number of sites compared to previous studies from 20 to more than 100 and through the application of improved data filtering we apply forward geophysical models of elastic surface displacement induced by atmospheric hydrologic nontidal ocean and ice loading and use independent component analysis as a spatiotemporal filter that includes multivariate regression to consider temporally correlated noise in gps using this approach the common mode error is identified and subsequent multivariate regression leads to an average reduction in trend uncertainty of 35 the average vertical subsidence of the australian continent is substantially different to vertical motion predicted by glacial isostatic adjustment and surface mass transport models

uplift rates from a new high density gps network in palmer land indicate significant late holocene ice loss in the southwestern weddell sea the measurement of ongoing ice mass loss and associated melt water contribution to sea level change from regions such as west antarctica is dependent on a combination of remote sensing methods a key method the measurement of changes in earth s gravity via the grace satellite mission requires a potentially large correction to account for the isostatic response of the solid earth to ice load changes since the last glacial maximum in this study we combine glacial isostatic adjustment modelling with a new gps dataset of solid earth deformation for the southern antarctic peninsula to test the current understanding of ice history in this region a sufficiently complete history of past ice load change is required for glacial isostatic adjustment models to accurately predict the spatial variation of ongoing solid earth deformation once the independently constrained effects of present day ice mass loss have been accounted for comparisons between the gps data and glacial isostatic adjustment model predictions reveal a substantial misfit the misfit is localized on the southwestern weddell sea where current ice models under predict uplift rates by approximately 2 mm yr 1 this under prediction suggests that either the retreat of the ice sheet grounding line in this region occurred significantly later in the holocene than currently assumed or that the region previously hosted more ice than currently assumed this finding demonstrates the need for further fieldwork to obtain direct constraints on the timing of holocene grounding line retreat in the southwestern weddell sea and that grace estimates of ice sheet mass balance will be unreliable in this region until this is resolved

high resolution bathymetric surveys using scanning sonars lava flow morphology hydrothermal vents and geologic structure at recent eruption sites on the juan de fuca ridge the coaxial and cleft segments of the juan de fuca ridge have isolated chronic high temperature and focused hydrothermal vent sites both segments also have experienced recent volcanic eruptions which produced extensive ephemeral low temperature and diffuse hydrothermal venting to study the geologic setting of these sites high resolution bathymetric surveys at eight locations on the coaxial and cleft segments were collected between 1993 and 1999 two 675 khz scanning sonar systems were used mesotech on the submersible alvin and imagenex on the remotely operated vehicle jason the bathymetry from these surveys can be gridded at a scale of 2 4 m and contoured at 1 m and thus can resolve many fine scale features on the seafloor that are indistinguishable in multibeam bathymetry collected at the sea surface bathymetric data at this resolution are particularly useful for identifying geologic features related to diking faulting and lava flow emplacement for example the high resolution bathymetric maps show that submarine fissure eruptions that form pillow lavas last long enough to become localized and to produce point source constructs along their length and their extrusion rate is low enough that no significant drainback occurs in contrast lobate sheet flows are formed by short lived high effusion rate eruptions in which no localization of output occurs along the eruptive fissure and inflation is quickly followed by drainback resulting in extensive collapse features however if the process of submarine lava flow inflation occurs at a slower rate and over a longer period of time it can create lava rises up to 25 m high with distinctive structure and morphology the scanning sonar data also show that fissures and grabens have formed or reactivated where dikes approach the surface adjacent to recent eruptive sites the fine scale bathymetry establishes that all the hydrothermal vent sites studied at the coaxial and cleft segments are located along prominent volcanic or tectonic extensional structures which provide the physical pathway for fluids from the subsurface to the seafloor furthermore the fine scale morphology of recent lava flows can be used as a qualitative indication of eruption duration

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

on the influence of diurnal and subdiurnal signals in the normal vector on large ring laser gyroscope observations the ring laser gyroscope rlg technique has been investigated for over 20 years as a potential complement to space geodetic techniques in measuring earth rotation however rlgs are also sensitive to changes in their terrestrial orientation therefore in this paper we review how the high frequency band i e signals shorter than 0 5 cycle per day of the known phenomena causing site deformation contribute to the rlg observable the sagnac frequency we study the impact of solid earth tides ocean tidal loading and non tidal loading phenomena atmospheric pressure loading and continental hydrosphere loading also we evaluate the differences between available models of the phenomena and the importance of the love numbers used in modeling the impact of solid earth tides finally we compare modeled variations in the instrument orientation with the ones observed with a tiltmeter our results prove that at the present accuracy of the rlg technique solid earth tides and ocean tidal loading effects have significant effect on rlg measurements and continental hydrosphere loading can be actually neglected regarding the atmospheric loading model its application might introduce some undesired signals we also show that discrepancies arising from the use of different models can be neglected and there is almost no impact arising from the use of different love numbers finally we discuss differences between data reduced with tiltmeter observations and these reduced with modeled signal and potential causes of this discrepancies

plate boundary deformation associated with the great sumatra andaman earthquake the sumatra andaman earthquake of 26 december 2004 is the first giant earthquake moment magnitude m w 9 0 to have occurred since the advent of modern space based geodesy and broadband seismology it therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events here we report estimates of the ground displacement associated with this event using near field global positioning system gps surveys in northwestern sumatra combined with in situ and remote observations of the vertical motion of coral reefs these data show that the earthquake was generated by rupture of the sunda subduction megathrust over a distance of 1 500 kilometres and a width of 150 kilometres megathrust slip exceeded 20 metres offshore northern sumatra mostly at depths shallower than 30 kilometres comparison of the geodetically and seismically inferred slip distribution indicates that 30 per cent additional fault slip accrued in the 1 5 months following the 500 second long seismic rupture both seismic and aseismic slip before our re occupation of gps sites occurred on the shallow portion of the megathrust where the large aceh tsunami originated slip tapers off abruptly along strike beneath simeulue island at the southeastern edge of the rupture where the earthquake nucleated and where an m w 7 2 earthquake occurred in late 2002 this edge also abuts the northern limit of slip in the 28 march 2005 m w 8 7 nias simeulue earthquake

interferometric water level tilt meter development in finland and comparison with combined earth tide and ocean loading models a modern third generation interferometric water level tilt meter was developed at the finnish geodetic institute in 2000 the tilt meter has absolute scale and can do high precision tilt measurements on earth tides ocean tide loading and atmospheric loading additionally it can be applied in various kinds of geodynamic and geophysical research the principles and results of the historical 100 year old michelson gale tilt meter as well as the development of interferometric water tube tilt meters of the finnish geodetic institute finland are reviewed modern earth tide model tilt combined with schwiderski ocean tide loading model explains the uncertainty in historical tilt observations by michelson and gale earth tide tilt observations in lohja2 geodynamic station southern finland are compared with the combined model earth tide and four ocean tide loading models the observed diurnal and semidiurnal harmonic constituents do not fit well with combined models the reason could be a result of the improper harmonic modelling of the baltic sea tides in those models

the tidal displacement field at earth s surface determined using global gps observations 1 we investigate the 3 d tidal displacement field on earth s surface recorded globally by 456 continuous global positioning system gps stations of igs spanning 1996 2011 for eight principal diurnal and semidiurnal tidal constituents in phase and quadrature amplitudes of the residual tidal displacements after removal of an a priori body tide model are estimated using the precise point positioning ppp technique on the daily gps data the resultant daily estimates are combined to derive final estimates for each tide at each station the results are compared with the predictions of eight recent global ocean tide models separately for coastal 307 and inland 149 stations we show that gps can provide tidal displacement estimates accurate to the level of 0 12 mm horizontal and 0 24 mm vertical for the lunar only constituents m2 n2 o1 and q1 and less favorably for solar related tidal constituents s2 k2 k1 and p1 although improved by ambiguity resolution most recent ocean tide models fit the gps estimates equally well on the global scale but do not agree well between them in certain coastal areas especially for the vertical displacements suggesting the existence of model uncertainties near shallow seas the tidal residuals for the inland stations after removing both body tides and ocean tidal loading otl furthermore show clear continental scale spatial coherence implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the earth s deep interior we assert that the gps tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the earth s structure

geophysics of sea ice in the baltic sea a review abstract with improved observation methods increased winter navigation and increased awareness of the climate and environmental changes research on the baltic sea ice conditions has become increasingly active sea ice has been recognized as a sensitive indicator for changes in climate although the inter annual variability in the ice conditions is large a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season on the basis of the ice extent the shift towards a warmer climate took place in the latter half of the 19th century on the other hand data on the ice thickness which are mostly limited to the land fast ice zone basically do not show clear trends during the 20th century except that during the last 20 years the thickness of land fast ice has decreased due to difficulties in measuring the pack ice thickness the total mass of sea ice in the baltic sea is however still poorly known the ice extent and length of the ice season depend on the indices of the arctic oscillation and north atlantic oscillation sea ice dynamics thermodynamics structure and properties strongly interact with each other as well as with the atmosphere and the sea the surface conditions over the ice covered baltic sea show high spatial variability which cannot be described by two surface types such as ice and open water only the variability is strongly reflected to the radiative and turbulent surface fluxes the baltic sea has served as a testbed for several developments in the theory of sea ice dynamics experiences with advanced models have increased our understanding on sea ice dynamics which depends on the ice thickness distribution and in turn redistributes the ice thickness during the latest decade advance has been made in studies on sea ice structure surface albedo penetration of solar radiation sub surface melting and formation of superimposed ice and snow ice a high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period a few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom in general process studies on ice ocean interaction have been rare in the future increasingly multidisciplinary studies are needed with close links between sea ice physics geochemistry and biology

ocean variability contributing to basal melt rate near the ice front of ross ice shelf antarctica basal melting of ice shelves is an important but poorly understood cause of antarctic ice sheet mass loss and freshwater production we use data from two moorings deployed through ross ice shelf 6 and 16 km south of the ice front east of ross island and numerical models to show how the basal melting rate near the ice front depends on sub ice shelf ocean variability the moorings measured water velocity conductivity and temperature for 2 months starting in late november 2010 about half of the current velocity variance was due to tides predominantly diurnal components with the remainder due to subtidal oscillations with periods of a few days subtidal variability was dominated by barotropic currents that were large until mid december and significantly reduced afterward subtidal currents were correlated between moorings but uncorrelated with local winds suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front estimated melt rate was 1 2 0 5 m a 1 at each site during the deployment period consistent with measured trends in ice surface elevation from gps time series the models predicted similar annual averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base these results show that accurately modeling the high spatial and temporal ocean variability close to the ice shelf front is critical to predicting time dependent and mean values of meltwater production and ice shelf thinning

correcting high resolution borehole strainmeter data from complex external influences and partial solid coupling the case of trizonia rift of corinth greece high resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow slip events and to estimate slow transients related to earthquake swarms however they are also sensitive to other numerous influences internal or external furthermore the quality of their coupling to the rock through cementation and the mechanical properties of the rock mass around them have a critical influence on their records many of the existing strainmeters present such problems and the correction for these effects often remains a challenge in this paper we present the analysis of the records of a high resolution borehole dilatometer sacks evertson located in the seismically active rift of corinth greece station trz in the trizonia island we show that the instrument suffers from an only partial solid coupling and that the nearby sea tides have a direct through elastic response and indirect through pore pressure diffusion effect on the dilatation signal which adds up to the solid tidal strain source we propose a methodology that allows in a first step to better separate the internal solid tide from the external air pressure sea level influences by calculating a frequency dependent transfer function outside the range of the tidal periods we then extrapolate this function in particular at the tidal periods in a second step the resulting variation with frequency of the coupling coefficients with sea level led us to estimate the proportion of instrument not solidly cemented to rock thus in contact with water pore pressure which is about 90 of the total height despite the small proportion of solid coupling the sensor resolution remains very good up to a few tens of hours of a time period thanks to the confining effects of the rocks on the local pore pressure these results allow us to correct for the external effects and reduce the associated variance by 80 90 in the period range of minutes to days the empirical correction of the sea level effect could be explained using a simple boussinesq s approximation and 1d pore pressure diffusion model which contributed to better constraint of some of the poro elastic parameters in the vicinity of the instrument after correction the solid tidal signal at the 24 h period is almost anti correlated with those of the theoretical solid tide this surprising result is consistent with a similar anti correlation observed for the longest period surface waves 200 s comparing the trz dilatometer signals to the strain measured by a nearby borehole strainmeter mok 15 km this could be related to the presence of a shallow fault close to the instrument which would creep in response to seismic wave related stress

seafloor gravity evidence for hydrothermal alteration of the sediments in middle valley juan de fuca ridge abstract gravity data collected at two different levels sea surface and seafloor are compared and interpreted to characterize the effect of hydrothermal circulation on the sediment density in middle valley a deeply sedimented spreading center on the juan de fuca ridge the sea surface gravity data constrain density variations at depth beneath the seafloor whereas sea bottom measurements are more sensitive to shallow sources at least two different types of hydrothermal signatures in the sediments can be distinguished from the gravity data short wavelength anomalies associated with sulfide deposits and broader anomalies associated with areas of lithified sediments in middle valley three distinct gravity anomalies were identified a an anomaly over a sulfide mound south of bent hill shows that the sulfide body extends to depths of 120 to 180 m and has been fed by several near surface conduits b an anomaly at the base of the fault bordering the valley to the east is interpreted as a regional anomaly combined with the local effect of lithified sediments and possibly sulfide deposits c an anomaly paralleling an intra valley fault that limits the deepest part of the graben is interpreted as indicating lithification of the upper sediment layer a high heat flow anomaly is located 1 to 2 km east of this fault suggesting that sediment lithification occurred in a wide band above the fault and eastward to the current high heat flow area due to the progressive migration of the hot fluid circulation

deformation and slip along the sunda megathrust in the great 2005 nias simeulue earthquake seismic rupture produced spectacular tectonic deformation above a 400 kilometer strip of the sunda megathrust offshore northern sumatra in march 2005 measurements from coral microatolls and global positioning system stations reveal trench parallel belts of uplift up to 3 meters high on the outer arc islands above the rupture and a 1 meter deep subsidence trough farther from the trench surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward a saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 sumatra andaman rupture the southeastern edge abuts a predominantly aseismic section of the megathrust near the equator

in situ calibration of and algorithm for strain monitoring using four gauge borehole strainmeters fgbs 1 borehole strainmeters have proved very useful in geodynamic research because the sensors are imbedded in rock their in situ calibration is of crucial importance the four gauge borehole strainmeter fgbs is a chinese invention to monitor the temporal variation in horizontal strain the four gauges in the fgbs are arranged at 45 intervals to bring about a simple self consistency equation which serves as a means of checking that the measurements obtained from the fgbs are correct the instruments currently used in china are usually placed at depths of several tens of meters to avoid disturbances at the surface while still being sufficiently near the surface for the vertical stress to be regarded as zero the premise on which the theoretical model of this observation is based in this paper an index of data credibility is established based on the self consistency equation to allow evaluation of the observations a relative in situ calibration has been developed to calculate a relative correction factor for each gauge s sensitivity termed the gauge weight and this has proven effective in enhancing data credibility parameters for deriving strain from readings are determined by a concise absolute in situ calibration with the aid of the theoretical earth tide instead of averaging four groups of solutions a simpler comprehensive algorithm is developed to transform readings into strain data from 24 chinese sites of yry 4 type fgbs are processed and evaluated to be fairly good

evidence for tidal triggering of high amplitude rapid tremor reversals and tremor streaks in northern cascadia 1 we provide a new link between tectonic tremor propagation tremor amplitude and tidal stresses by analyzing high resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays for two cascadia episodic tremor and slip events we observe repeating high amplitude rapid tremor reversals rtrs and tremor streaks they tend to occur when tremor amplitudes are highest and occur almost exclusively during periods of thrust encouraging tidally induced shear stress on the fault we speculate that thrust encouraging shear stress from tidal loading forces trigger rtrs and streaks that energetically rerupture the weakened fault behind the slow slip front the high rate and amplitude of tremor during rtrs and streaks stands in contrast to the hypothesis that activity at the leading edge of the slow slip zone is the most energetic and loudest this implies that the spatiotemportal pattern of slow earthquake slip migration is even more intricate than previously reported

uplift and subsidence associated with the great aceh andaman earthquake of 2004 rupture of the sunda megathrust on 26 december 2004 produced broad regions of uplift and subsidence we define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great m w 9 2 earthquake in the region of the andaman and nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model at the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls uplift extends from the middle of simeulue island sumatra at 2 5 n to preparis island myanmar burma at 14 9 n thus the rupture is 1600 km long the distance from the pivot line to the trench varies appreciably the northern and western andaman islands rose whereas the southern and eastern portion of the islands subsided the nicobar islands and the west coast of aceh province sumatra subsided tilt at the southern end of the rupture is steep the distance from 1 5 m of uplift to the pivot line is just 60 km our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions

gps height time series short period origins of spurious long period signals gps height time series used in geophysical studies are often formed from discrete continuous nonoverlapping 24 hour processing sessions with such a strategy unmodeled periodic ground displacements with approximately semidiurnal and diurnal periods have often been assumed to average close to zero by analyzing several years of continuous gps data from globally distributed sites at which controlled errors were not modeled this paper shows such an assumption to be erroneous it is shown that each unmodeled sub daily periodic displacement can propagate to several spurious long wavelength features in a gps height time series ranging in period from about 2 weeks to 1 year admittances ratio of amplitude of spurious long wavelength output signal in the gps height time series to amplitude of unmodeled periodic ground displacement depend on the coordinate component and the tidal constituent considered for example it is shown that an unmodeled s2 north component periodic ground displacement can propagate to a semiannual height signal with admittance of greater than 100 whereas the height admittance is around 5 10 since model errors in ocean tide loading atmospheric pressure loading and solid earth tide displacement amplitudes can be several millimeters long wavelength spurious signals of up to these amplitudes may be expected to appear in gps height time series this paper provides an indication of how such errors will propagate where such errors are greatest and hence how spurious fortnightly semiannual and in some cases annual effects may be present at some sites copyright 2007 by the american geophysical union

stelckiceras and other gastroplitinae ammonitina from the albian lower cretaceous fort st john group peace river area northeastern british columbia stelckiceras jeletzky 1980 and pseudopulchellia imlay 1961 emend j a jeletzky in 1980 are illustrated from the ammobaculites wenonahae subzone of the albian lower cretaceous hasler formation of the fort st john group on the peace river in northeastern british columbia species of gastroplites mclearn 1930 pseudopulchellia imlay 1961 pseudogastroplites jeletzky 1980 and stotticeras jeletzky 1980 are illustrated from the ammobaculites sp and haplophragmoides multiplum subzones of the subjacent cadotte member of the boulder creek formation and the underlying hulcross formation two new species gastroplites bahani and gastroplites jeletzkyi are described the presence of several arctic exotic ammonites suggests that the middle albian interior seaway was not entirely isolated from the arctic basin numerous foraminifera are known to be common to both basins and current inflow may have prevented endemic gastroplites s st and stelckiceras from migrating northward biostratigraphic conclusio

the density structure associated with oceanic crustal rifting at the hess deep a seafloor and sea surface gravity study abstract seafloor and sea surface gravity measurements provide new constraints on the lithospheric structure of the hess deep at the triple junction between the pacific cocos and nazca plates as the cocos nazca ridge propagates westward breaking into young oceanic crust created at the east pacific rise rocks attributed to the base of the crust or to the upper mantle are exposed on the seafloor at hess deep the tip of the propagator seafloor gravity data were collected along two north south profiles the western profile runs through the deepest part of the hess deep valley and the eastern profile runs over the tip of the cocos nazca neovolcanic ridge shipboard gravity track lines provide coverage of the rift valley from the northern to the southern rim bouguer gravity anomalies are negative over the deepest part of the basin and positive north of it at the intra rift ridge where gabbros and hartzburgites have been drilled seafloor and sea surface gravity data are modeled together in a 2d stochastic inversion and a 3d ideal body inversion when interpreted in the light of geologic data gravity results favor an asymmetric emplacement mode for the deep origin rocks the alteration of the mantle material playing a key role in the gravity signal in addition new magma is emplaced from the east forming a neovolcanic ridge over strongly serpentinized peridotite the density distribution shows that positive buoyancy cannot be the driving force for magma ascent through the upper crust

rapid bedrock uplift in the antarctic peninsula explained by viscoelastic response to recent ice unloading abstract since 1995 several ice shelves in the northern antarctic peninsula have collapsed and triggered ice mass unloading invoking a solid earth response that has been recorded at continuous gps cgps stations a previous attempt to model the observation of rapid uplift following the 2002 breakup of larsen b ice shelf was limited by incomplete knowledge of the pattern of ice unloading and possibly the assumption of an elastic only mechanism we make use of a new high resolution dataset of ice elevation change that captures ice mass loss north of 66 s to first show that non linear uplift of the palmer cgps station since 2002 cannot be explained by elastic deformation alone we apply a viscoelastic model with linear maxwell rheology to predict uplift since 1995 and test the fit to the palmer cgps time series finding a well constrained upper mantle viscosity but less sensitivity to lithospheric thickness we further constrain the best fitting earth model by including six cgps stations deployed after 2009 the larissa network with vertical velocities in the range 1 7 to 14 9 mm yr this results in a best fitting earth model with lithospheric thickness of 100 140 km and upper mantle viscosity of 6 10 17 2 10 18 pa s much lower than previously suggested for this region combining the larissa time series with the palmer cgps time series offers a rare opportunity to study the time evolution of the low viscosity solid earth response to a well captured ice unloading event

constraining ice mass loss from jakobshavn isbrae greenland using insar measured crustal uplift summary jakobshavn isbrae in west greenland has been undergoing dramatic thinning since 1997 applying the interferometric synthetic aperture radar insar technique to radarsat 1 sar data we measure crustal uplift near jakobshavn isbrae caused by recent ice mass loss the crustal uplift is predominantly at long spatial wavelengths larger than 10 km and thus is difficult to separate from insar orbit errors we reduce the effects of orbit errors by removing long wavelength deformation signals using conventional insar baseline fitting methods we find good agreement between the remaining short scale insar estimated deformation rates during 2004 2008 and the corresponding short scale components of a deformation model that is based on changes in ice elevation measured by nasa s airborne topographic mapper atm we are also able to use the insar measured deformation to invert for the spatial pattern of ice thinning overall our results suggest that despite the inherent difficulties of working with a signal that has significant large scale components insar measured crustal deformation can be used to study the ice mass loss of a rapidly thinning glacier and its surrounding catchment providing both a constraint on any existing model of ice mass loss and a data source that can be used to invert for ice mass loss these new applications of insar can help to better understand a glacier s rapid response to a warming climate

accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions