is the asthenosphere electrically anisotropic abstract two techniques for resolving the conductance of an electrically conductive asthenosphere are presented the first technique combines observatory electromagnetic data in the period range of the daily variation and longer which provides penetration depths of 400 km and deeper with laboratory data of the conductivity of upper mantle materials the conductance can be estimated by this technique but the geometry e g the exact depth is not resolved the second technique extends the classical magnetotelluric mt tensor estimation and decomposition to the period range 1000 30 000 s if an electrical asthenosphere exists then in this period range the electromagnetic field penetrates into it 1000 s but also through it 30 000 s the concept of regional strike directions which has been successfully used to obtain crustal anisotropy directions is again employed at these long periods the surprising result is that in the depth range of the asthenosphere a strong directional dependence of the conductance again occurs although large arrays will be necessary in order to prove that this is really conductivity anisotropy in the asthenosphere first field results from arrays 100 200 km in extent are encouraging the concept of a superposition of crustal and upper mantle anisotropy explains to some extent why earlier magnetotelluric determinations of the asthenosphere had little success only in the fortunate case where a mt experiment was performed not parallel to the direction of the crustal conductor but parallel to the asthenospheric one is the second structure resolved electrical anisotropy in the uppermost mantle supports the concept of intracrystalline water which allows for a contribution of hydrogen diffusity to the conductivity of olivine this diffusity is highly anisotropic with respect to the crystal axis and if the crystals are partly aligned the conductivity measured with mt is also direction dependent

enhanced mantle conductivity from sulfide minerals southern sierra nevada california petrographic studies of peridotitic xenoliths entrained in late quaternary basalts from beneath the southern sierra nevada have revealed the presence of accessory sulfide minerals along grain boundaries and fractures equilibration temperatures from the xenoliths are sufficiently high that the molten sulfides coexist with the basaltic melt sulfides are extremely conductive relative to the solid matrix or the basaltic melt so a small fraction can increase the bulk conductivity of the mantle appreciably previous estimates of 2 5 partial melt from magnetotelluric measurements can be plausibly reduced to less than 1 such low melt percentages have longer residence times in the mantle and are more consistent with the volumetrically minor late quaternary basalt flows and the primitive basalt compositions

numerical models on the influence of partial melt on elastic anelastic and electrical properties of rocks part ii electrical conductivity abstract partial melting influences both the elastic and electrical properties of mantle rocks significantly but in a different manner a set of theoretical models of the electrical conductivity of partially molten rocks is developed for different geometries of the melt distribution the models correspond to a similar set on elasticity and anelasticity presented in a preceding paper part i both model sets allow combined interpretations of seismic and geoelectric observations from anomalous hot mantle regions by a systematic variation of the melt geometry the following melt geometries are assumed in the conductivity models melt films tubes isolated ellipsoidal inclusions films and ellipsoidal inclusions with a variable degree of interconnection distributed geometries and superpositions of spheres with films and with tubes unexplored conduction mechanisms near the melting temperature film thicknesses of molecular sizes or effects of volatiles are not considered resistor network theory is utilized to account for a variable degree of interconnection and distributed geometries thereby a new possible interpretation of archie s law is found in terms of varying interconnection furthermore it is found that a reduced degree of interconnection may have an important influence on the conductivity at melt fractions characteristic for a weak to moderate decrease in seismic velocity the model results are compiled together with the elastic models of part i in a set of diagrams which may be applied systematically to observed electrical and seismic data to find constraints on the state of melting

resistance to mantle flow inferred from the electromagnetic strike of the australian upper mantle seismic anisotropy is thought to result from the strain induced lattice preferred orientation of mantle minerals especially olivine1 2 owing to shear waves propagating faster along the a axis of olivine crystals than along the other axes this anisotropy results in birefringence or shear wave splitting 3 which has been investigated in numerous studies1 4 although olivine is also anisotropic with respect to electrical conductivity5 with the a axis being most conductive few studies of the electrical anisotropy of the upper mantle have been undertaken and these have been limited to relatively shallow depths in the lithospheric upper mantle6 7 theoretical models of mantle flow have been used to infer that for progressive simple shear imparted by the motion of an overriding tectonic plate the a axes of olivine crystals should align themselves parallel to the direction of plate motion8 9 here however we show that a significant discrepancy exists between the electromagnetic strike of the mantle below australia and the direction of present day absolute plate motion10 we infer from this discrepancy that the a axes of olivine crystals are not aligned with the direction of the present day plate motion of australia indicating resistance to deformation of the mantle by plate motion

extreme value statistics for wave run up on a natural beach abstract statistics of wave run up maxima have been calculated for 149 35 minutes data runs from a natural beach during the experiment incident wave height varied from 0 4 to 4 0 m incident wave period from 6 to 16 s and beach face slope from 0 07 to 0 20 four extreme statistics were calculated the maximum run up height during each run the 2 exceedence level of shoreline elevation the 2 exceedence height for individual run up peaks and the 2 exceedence level for swash height as determined by the zero upcrossing method these statistics were best parameterized when normalized by the incident significant wave height and plotted against the iribarren number h l 0 1 2 the swash data with set up removed showed less scatter than total run up with set up included for iribarren number greater than 1 5 the run up was dominated by the incident frequencies for lower iribarren number longer period motions dominated the swash a reasonable value of wave steepness for a fully developed storm sea is 0 025 so that a storm iribarren number can be estimated as 6 3 times the beach slope using this and an offshore design wave height the included graphs may provide guidance in determining a design run up height

flow and electrical anisotropy in the upper mantle finite element models constraints on the effects of olivine crystal preferred orientation and microstructure long period magnetotelluric mt data shows that electrical conductivity in the upper mantle is highly anisotropic agreement between high electrical conductivity directions and seismic anisotropy fast directions suggests that anisotropic diffusion of hydrogen along oriented olivine crystals controls the anisotropy of electrical conductivity in the upper mantle since both seismic waves and hydrogen diffusion are faster along the 1 0 0 axis of olivine thus mt electrical anisotropy data like seismic anisotropy may be used to map flow patterns in the upper mantle however observed electrical anisotropies are significantly higher than seismic ones to quantify the influence of strain induced crystal preferred orientations of olivine on upper mantle bulk electrical conductivities we calculate the macroscopic electrical conductivity anisotropy of a series of naturally and experimentally deformed peridotites using an anisotropic finite element model these models which fully take into account the microstructure crystal and shape preferred orientations based on orientation maps obtained by indexation of electron back scattered diffraction ebsd patterns show macroscopic electrical anisotropy factors ranging from 3 to 16 the intensity of electrical anisotropy depends to first order on the intensity of the olivine crystal preferred orientations but the relation saturates for strong crystal preferred orientations in addition the spatial distribution of the various crystal orientations may significantly enhance influence the anisotropy in strongly textured mantle rocks the strongest anisotropy factors 10 occur in mantle rocks in which deformation by dislocation creep has produced not only crystal but also strong shape preferred orientations even if the latter is masked by recrystallization higher anisotropy factors 100 observed in a few mt experiments imply however an additional as yet unknown mechanism controlling electrical conduction at asthenospheric depths in these regions

morphodynamics of a macrotidal beach abstract an intensive field investigation of hydrodynamic processes processes of sediment entrainment and suspension and morphologic change was carried out on an unprotected macrotidal beach near broome in northwestern australia the spring tide range was 9 5 m waves had heights of 0 5 1 2 m and periods of 9 13 s the beach had an overall concave upward profile with low gradient and dissipative subtidal and low tidal zones and steeper more reflective mid tidal and high tidal zones direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 1 2 w m 2 of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height time averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low tidal zone and over the lower part of the high tidal zone most of the work over the low and mid tidal zones was performed by unbroken shoaling waves rather than by surf zone processes surf zone processes only dominate over the high tidal zone the nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level the growth of standing waves and infragravity surf beat oscillations as identified from spectra and cross spectra of surface elevation and currents u and v was inhibited over most of the profile however well developed secondary standing wave energy particularly at infragravity frequencies was observed over the high tidal zone at spring high tide and over the mid tidal zone at neap high tide over the low tidal and subtidal zones strong shore parallel tidal currents were subordinate only to the orbital velocities of unbroken incident waves over the subtidal zone asymmetrical tidal currents skewed toward the north attained maximum speeds of 0 5 m s 1 just after high water field measurements of suspended sediment concentration profiles under broken and unbroken waves showed very good fit to a diffusion model for wave induced sediment suspension and suggested that sediment suspension was probably attributable largely to waves northerly advection of wave suspended sediment by asymmetrical tidal currents over the subtidal and low tidal zones accounted for a net northerly longshore transport the greatest morphologic mobility of the intertidal profile occurred over the lower high tidal and upper mid tidal zones corresponding to the position of the coarsest material and secondary maximum of time averaged wave work and to a beach state intermediate between the reflective and dissipative extremes temporally the greatest mobility of the profile as a whole was observed on the short within tidal cycle time scale net changes over the longest time scale of a lunar half cycle were negligible

a video based technique for mapping intertidal beach bathymetry abstract measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research monitoring and design applications with the advent of digital imaging technology shore based video systems provide continuous and automated data collection encompassing a much greater range of time and spatial scales than were previously possible using field survey methods a new video based technique is presented that utilises full colour image information which overcomes problems associated with previous grey scale methods which work well at steep reflective sites but are less successful at flatter dissipative sites identification of the shoreline feature is achieved by the automated clustering of sub aqueous and sub aerial pixels in hue saturation value hsv colour space and applying an objective discriminator function to define their boundary i e shoreline within a time series of consecutive geo referenced images the elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information which is incorporated in a model that combines the effects of wave set up and swash at both incident and infragravity frequencies validation of the technique is achieved by comparison with dgps survey results to assess the accuracy of the detection and elevation methods both separately and together the uncertainties associated with the two sub components of the model tend to compensate for each other the mean difference between image based and surveyed shoreline elevations was less than 15 cm along 85 of the 2 km study region which corresponded to an horizontal offset of 6 m the application of the intertidal bathymetry mapping technique in support of czm objectives is briefly illustrated at two sites in the netherlands and australia

lithospheric structure of an archean craton and adjacent mobile belt revealed from 2 d and 3 d inversion of magnetotelluric data example from southern congo craton in northern namibia 1 archean cratons and the stitching proterozoic orogenic belts on their flanks form an integral part of the southern africa tectonic landscape of these virtually nothing is known of the position and thickness of the southern boundary of the composite congo craton and the neoproterozoic pan african orogenic belt due to thick sedimentary cover we present the first lithospheric scale geophysical study of that cryptic boundary and define its geometry at depth our results are derived from two dimensional 2 d and three dimensional 3 d inversion of magnetotelluric data acquired along four semiparallel profiles crossing the kalahari craton across the damara ghanzi chobe belts dgc and extending into the congo craton two dimensional and three dimensional electrical resistivity models show significant lateral variation in the crust and upper mantle across strike from the younger dgc orogen to the older adjacent cratons we find damara belt lithosphere to be more conductive and significantly thinner than that of the adjacent congo craton the congo craton is characterized by very thick to depths of 250 km and resistive i e cold lithosphere resistive upper crustal features are interpreted as caused by igneous intrusions emplaced during pan african magmatism graphite bearing calcite marbles and sulfides are widespread in the damara belt and account for the high crustal conductivity in the central zone the resistivity models provide new constraints on the southern extent of the greater congo craton and suggest that the current boundary drawn on geological maps needs revision and that the craton should be extended further south

joint inversion of long period magnetotelluric data and surface wave dispersion curves for anisotropic structure application to data from central germany geophysical datasets sensitive to different physical parameters can be used to improve resolution of earth s internal structure herein we jointly invert long period magnetotelluric mt data and surface wave dispersion curves our approach is based on a joint inversion using a genetic algorithm for a one dimensional 1 d isotropic structure which we extend to 1 d anisotropic media we apply our new anisotropic joint inversion to datasets from central germany demonstrating the capacity of our joint inversion algorithm to establish a 1 d anisotropic model that fits mt and seismic datasets simultaneously and providing new information regarding the deep structure in central germany the lithosphere asthenosphere boundary is found at approx 84 km depth and two main anisotropic layers with coincident most conductive seismic fast axis direction are resolved at lower crustal and asthenospheric depths we also quantify the amount of seismic and electrical anisotropy in the asthenosphere showing an emerging agreement between the two anisotropic coefficients

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

modeling cross shore sandbar behavior on the timescale of weeks we compare predictions of a coupled wave averaged cross shore waves currents bathymetric evolution model to observations of onshore and offshore nearshore sandbar migration the observations span a 10 and 44 day period with onshore offshore bar migration at duck north carolina and at hasaki kashima coast japan respectively a 3 5 month period of onshore bar migration at duck and a 22 day period of offshore bar migration at egmond netherlands with best fit parameter values the modeled temporal evolution of the cross shore bed profiles agrees well with the observations model skill defined as 1 minus the ratio of prediction to no change error variances ranges from 0 50 at egmond to 0 88 for the prolonged onshore bar migration at duck localized in time and space reductions in model skill coincide with alongshore variations in the observed morphology consistent with earlier observations simulated offshore bar migration takes place during storms when large waves break on the bar and is due to the feedback between waves undertow suspended sediment transport and the sandbar simulated onshore bar migration is predicted for energetic weakly to nonbreaking conditions and is due to the feedback between near bed wave skewness bedload transport and the sandbar with negligible to small effects of bound infragravity waves and near bed streaming under small waves and conditions when breaking and nonbreaking conditions alternate with the tide the sandbar is predicted to remain stationary the intersite differences in the optimum parameter values are at least partly induced by insensitivity to parameter variations parameter interdependence and errors in the offshore wave forcing

3d modelling of electrical anisotropy from electromagnetic array data hypothesis testing for different upper mantle conduction mechanisms abstract upper mantle electrical conductivities provide besides seismic velocities or thermal diffusivities another source of information on upper mantle structure and composition we present the results of a long period magnetotelluric dataset consisting of 64 sites covering an area of 300 km 400 km in central germany mapping electrical conductivities at the base of the lithosphere to seperate the effect of crustal and upper mantle structures we interprete the obtained dataset by 3d conductivity modelling we observe high conductivities and anisotropies at asthenospheric upper mantle depth with main bulk conductivities of 1 2 s m in west east and 4 1 0 3 s m in north south direction differing by about two orders of magnitude in comparing with results from laboratory measurements on electrical conductivites for various conduction mechanisms we are able to confine the conduction mechanisms possibly dominating at these depths with melt volume fractions of 1 only partial melt can be excluded as origin of the high upper mantle conductivities instead conductivity enhancement due to hydrogen diffusion along the olivine 1 0 0 axis is favoured as the dominant conduction mechanism at the base of the lithosphere

evidence of electrical anisotropic structures in the lower crust and the upper mantle beneath the rhenish shield abstract we present the results of a long period electromagnetic investigation of the crust and upper mantle beneath the rhenish shield in western germany the magnetotelluric phase data reveal a frequency dependent regional strike that varies only smoothly across the array at short periods t 1000 s there is a consistent striking in we direction which provides strong evidence of an anisotropic structure in the upper mantle too geomagnetic data were also used whereas we reference the magnetic field components of all sites to an arbitrarily chosen field site that provides a direct view of the anomalous current flow we show that in case of a non one dimensional electrical substructure of the reference site all magnetic transfer functions of the other sites can be affected by lateral conductivity contrasts beneath the reference site a simple method to remove such effects is introduced applying this method the magnetic data show a distinct anomaly in the northwestern part of the area finally we present a 3d model of the conductivity structure beneath the rhenish shield which contains a superposition of two anisotropic structures in the lower crust 2000 s and the upper mantle 20 000 s respectively and a local anomaly in the upper crust 4000 s

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

cross shore sediment transport on natural beaches and its relation to sandbar migration patterns 2 application of the field transport parameterization 1 a cross shore sediment transport parameterization shape function based on data from intensive field experiments carried out on five european beaches is incorporated into a simple time dependent model to explore its capability for reproducing sandbar generation and evolution in the medium term o months model results are compared with bar crest migration patterns observed at duck north carolina the model comprises a simple wave transformation routine that accounts for linear shoaling and assumes a saturation law for wave decay inside the surf zone second order statistics derived from the cross shore distribution of wave heights are used to scale the sediment transport parameterizations which estimate the cross shore structure of the third and fourth velocity moments cross shore gradients in sediment fluxes calculated with an energetics approach produce bed elevation changes the updated morphology affects the wave propagation in the next time step forming a fully coupled model for predicting sandbar evolution bar generation close to shore and the details of the sandbar evolution are successfully reproduced r2 0 86 over the 77 day period of the observations using default values for drag coefficients and efficiency factors in accordance with the observations the model shows rapid offshore sandbar migration in response to individual storms and weak onshore bar movement for lower energy conditions owing to its simple nature the model is not capable of reproducing the whole profile morphology especially in the trough no trough generation and it is only valid for replicating bar crest position the results suggest that a convergence of sediment near the breakpoint breakpoint hypothesis combined with morphological feedback can successfully explain the evolution of bar crest over periods of months from the details of forcing incident waves and water levels

free carbon electrical conductivity in the earth s mantle laboratory measurements indicate that solid carbon either amorphous or as graphite enhances the electrical conductivity of rocks carbon in quantities of only a few ppm providing it forms an interconnected phase could give rise to electrical conductivities of the order seen in the high conductivity layers in the earth s mantle this possibility is consistent with carbon petrology in mantle rocks and puts the formation and migration of abiogenic carbon compounds into a broader context

morphodynamic zone variability on a microtidal barred beach abstract this paper builds on the work of masselink masselink g 1993 simulating the effects of tides on beach morphodynamics j coast res si 15 180 197 on the use of the residence times of shoaling waves breaking waves and swash backwash motions across a cross shore profile to qualitatively understand temporal beach behaviour we use a data set of in situ measurements of wave parameters height and period and water depth and time exposure video images overlooking our single barred intertidal measurement array at egmond aan zee netherlands to derive boundaries between the shoaling zone the surf zone and the swash zone we find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness this contrasts with the use of constant relative wave heights or water levels in earlier work we use the obtained boundaries and a standard cross shore wave transformation model coupled to an inner surf zone bore model to show that large 5 relative tide ranges rtr defined as the ratio tide range wave height indicate shoaling wave processes across almost the entire intertidal profile with surf processes dominating on the beach face when the rtr is between 2 and 5 surf processes dominate over the intertidal bar and the lower part of the beach face while swash has the largest residence times on the upper beach face such conditions associated with surf zone bores propagating across the bar around low tide were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen for rtr values less than about 2 surf zone processes dominate across the intertidal bar while the dominance of swash processes now extends across most of the beach face the surf zone processes were now observed to lead to offshore bar migration while the swash eroded the upper beach face

pressure effect on electrical conductivity of mantle olivine abstract we report new measurements of electrical conductivity of olivine that were made in a multi anvil press using solid buffers mo moo2 to stabilize oxygen partial pressure the temperature range was 1000 c 1400 c and the pressure range was 4 10 gpa when pressure effects are interpreted as activation volumes in the arrhenius equation they yield values of order 0 6 0 6 cm3 mole values of the pre exponential factor 0 are of the order of hundreds of s m and the zero pressure activation energy is about 1 5 ev in agreement with laboratory measurements at lower pressure conditions in addition we analyzed older literature data which produced a similar result but with larger variation the common practice of assuming that the pressure effect on electrical conductivity of olivine in the earth s upper mantle depends weakly on pressure has rested on uncertain grounds these new observations suggest that for upper mantle conditions depths of 80 200 km neglecting pressure effects on olivine conductivity is justified a weak pressure effect also supports the small polaron fe3 model as the dominant conduction mechanism although the mainly positive activation volumes argue for a component of lattice deformation when applied to the depth range 200 400 km in the earth the laboratory data yield conductivities of order 10 2 s m slightly lower than the range of geophysical conductivity profiles but well within this range after allowing for probable effects of oxygen activity and temperature uncertainty

seismic and electrical anisotropies in the lithosphere across the grenville front canada the grenville front is a prominent tectonic feature of the canadian shield which has been the focus of a lithoprobe transect a strong electrical anisotropy has been detected in a frequency range of 0 1 0 01 hz 50 to 150 km the most conductive direction being oriented n80e in order to compare electrical and seismic anisotropies ten seismometers have been deployed across the grenville front to record teleseismic events s wave splitting measurements show an average delay of 1 54 0 21 s between the fast and the slow components the fast axis direction is approximately e w at all stations showing a strong coherence between the stations along the complete transect this azimuth correlates well with that of the electrical anisotropy the electrical anisotropy originates in the subcrustal lithosphere between 50 and 150 km the similarity of the magnetotelluric and seismic anisotropy directions across the grenville front is an argument in favor of an origin of the seismic anisotropy in the subcrustal lithosphere as advocated by silver and kaneshima 1993

obliquity between seismic and electrical anisotropies as a potential indicator of movement sense for ductile shear zones in the upper mantle teleseismic shear wave splitting and magnetotelluric experiments across the grenville front between the archean craton and the proterozoic grenville province in the regions of the pontiac subprovince and northwestern grenville province canada show a consistent obliquity between the polarization direction of the fast split shear wave and the most electrically conductive direction mt in the upper mantle transcurrent shear zones at all well recorded stations is nearly n103 e and mt is approximately n80 e the obliquity may be considered a potential kinematic indicator because the seismic and electrical anisotropies are thought to be controlled by lattice preferred and shape preferred orientations of mantle minerals mainly olivine respectively the dextral movement sense of the transcurrent shear zones in the mantle inferred from the observed obliquity is consistent with that inferred from surface geology of the crustal shear zones this consistency implies that deformation of the crust and the subcrustal upper mantle in the lithosphere was largely coherent in the study region

forward modeling of the development of seismic anisotropy in the upper mantle development of seismic anisotropy in response to upper mantle flow is approached through an integrated numerical model this model allows to predict the splitting parameters for a shear wave propagating across an upper mantle which deformed in response to a given geodynamic process it consists of 1 thermo mechanical modeling of the finite strain field 2 modeling olivine lattice preferred orientation lpo generated by this strain field 3 calculation of the 3 d elastic properties associated with this lpo and 4 estimation of the shear wave splitting parameters the time lag between the fast and slow split shear wave arrivals dt and the polarization azimuth of the fast wave modeled olivine lpo are constrained relative to lpo measured in naturally and experimentally deformed peridotites comparison of predicted shear wave splitting parameters with seismological data allows us to quantify the possible contribution of the modeled upper mantle flow to the measured splitting values and hence to constrain the interpretation of shear wave splitting data in terms of upper mantle flow we use this forward model to investigate the seismic anisotropy generated in ocean basins by a velocity gradient between the plate and the deep mantle fast shear wave polarizations calculated assuming a constant plate motion are in good agreement with both the sks polarization and the fast propagation direction for p and rayleigh waves observed in the pacific and indian oceans suggesting that away from mid ocean ridges seismic anisotropy in oceanic basins primarily results from asthenospheric deformation by resistive drag beneath the plate delay times are however overestimated this may be ascribed to a stronger strain localization in nature or to partial erosion of the anisotropic layer by hotspots indeed hotspot activity may explain the short length scale variations of dt in the southern pacific finally twolayer models that simulate a change in pacific plate motion as suggested by the bend in the hawaii emperor chain fail to reproduce the observed shear wave splitting this is consistent with previous suggestions that the emperor chain track may not faithfully record the pacific plate absolute motion before 43 ma 1998 elsevier science b v all rights reserved

sandbar dynamics in microtidal environments migration patterns in unprotected and bounded beaches abstract novel observations of bar features and migration patterns at three italian sandy beaches in senigallia central adriatic sea and terracina central tyrrhenian sea are presented while two of these beaches are unprotected one is artificially embayed through the presence of a concrete jetty bar locations and motions are analysed with video imagery data sets from coastal monitoring stations wave climate from the copernicus oceanographic model is used to correlate hydrodynamics and beach morphology clear net offshore migration nom patterns are identified at all beaches although exhibiting different response scales at the low slope beach of senigallia mean surf zone slope of 0 009 bars are more sensitive to seasonal changes in wave climate with offshore shifts in winter and inactivity in summer mean annual migration rates of up to 0 26 m day and 0 09 m day are observed for outer and inner bars respectively no significant response to single storms is observed except during a single nne storm no distinct erosive or accretive trend for the shoreline is evidenced at the steep beach of terracina mean surf zone slope of 0 018 conversely bars are strongly responsive to single storm events with displacements of up to 25 50 m across a single storm the mean inter annual migration rate is 0 08 m day for the single outer bar whereas a slight onshore trend 0 02 m day for the newborn inner bar is established the presence of an artificial jetty at the misa river mouth in senigallia finally leaves the bar system typically oscillating around an equilibrium position susceptible to larger seasonal oscillations and strong offshore migration due to two ese storm events numerical simulations of nearshore circulation for two storms from different directions predict the birth of longshore currents higher ratios of significant wave height to water depth and stronger bottom orbital velocities over bars in case of the ese storm suggesting a greater tendency for offshore directed sediment transport

tectonic fabric of the subcontinental lithosphere evidence from seismic magnetotelluric and mechanical anisotropy abstract knowledge of anisotropy is key to our understanding of tectonic fabrics in the lithosphere and sublithospheric mantle anisotropy provides a unique constraint on the character of past and present deformation and thus is critical to our understanding of dynamics of the plate tectonic system in particular how continents with their thick lithospheric mantle roots form stabilize and interact with underlying mantle regions improved observational methods and rapid developments of geophysical inversion techniques are contributing to more realistic earth models that include various types of anisotropy and heterogeneity a more robust characterization of anisotropic parameters can be achieved by integrating complementary datasets incorporating constraints from seismology magnetotellurics geodynamics and mineral physics valid comparisons between different measures of anisotropy however require a solid understanding of the principles and limitations of the various techniques to this end we briefly summarize a new compilation of original articles with a common focus on anisotropy of continental lithosphere including theory laboratory experiments and observations that span a range of different geophysical techniques

decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield

the electrical conductivity of lherzolite between 700oc and 1200oc and time over a period of 1700 hours are reported for a lherzolite nodule from mount porndon australia analysis of complex impedance collected at 100 hz 1 khz and 10 khz indicates that there is significant frequency dispersion in this rock at temperatures below 900oc 1000oc by choosing the resistance of an equivalent parallel rc network at the frequency having minimum phase the effect of dispersion is largely avoided conductivity as a function of time collected following changes in fo2 at 1010 and 1200oc has been analyzed to determine the diffusivity of defects relating fo2 to the electrical conduction mechanism in olivine the diffusivities so obtained are in remarkably good agreement with those determined from strain measurements during creep tests which implies that magnesium vacancies are the rate limiting step for conductivity reequilibration after fo2 changes a longer term process is observed in this rock in which the conductivity drifts upward or downward with a time constant of hundreds of hours after initial reequilibration to gas mix fo2 changes we speculate that this long term drift could be related to equilibration of the iron distribution between coexisting olivine and pyroxene as a function of fo2 the sense is an increase in conductivity olivine gains iron at low fo2 and vice versa the lherzolite conductivity data are not significantly different from measurements made on olivine single crystals and polycrystals even though the rock contains about 34 modal pyroxene this consistency of laboratory measurements of electrical conductivity of olivines from many localities and geological settings supports the use of recent models relating mantle temperature with electrical conductivity in the interpretation of mantle geo electromagnetic soundings

lithospheric anisotropy structure inferred from collocated teleseismic and magnetotelluric observations great slave lake shear zone northern canada 1 accurate interpretation of sks shear wave splitting observations requires inherently indeterminate depth information magnetotelluric electrical anisotropies are depth constrained and thereby offer possible resolution of the sks conundrum mt and teleseismic instruments deployed across the great slave lake shear zone northern canada investigated lithospheric anisotropy and tested a hypothesis that seismic and electrical anisotropy obliquity can infer mantle strain shear sense lithospheric mantle mt strike n60 e differs significantly from crustal mt strike n30 e sks splitting vectors outside the shear zone exhibit single layer anisotropy with fast axis parallel to upper mantle mt strike and oblique to present day plate motion n135 w back azimuth sensitivity at sites within the 30 km wide shear zone imply more complex layering with two layer inversion yielding an upper layer of n20 e and a lower layer of n66 e the mt data help to constrain the depth location of sks anisotropy and taken together support a model of fossil lithospheric anisotropy

the effect of dynamic recrystallization on olivine crystal preferred orientations in mantle xenoliths deformed under varied stress conditions abstract spinel peridotite xenoliths from persani mountains southeastern carpathians romania were submitted to deformation by dislocation creep accompanied by dynamic recrystallization under variable stress and temperature conditions predominance of low angle boundaries parallel to 100 with well defined 0vw rotation axes in olivine indicates that subgrain rotation is the main recrystallization mechanism and that dislocation glide occurs mainly in 100 0kl systems analysis of olivine crystal preferred orientations highlights that recrystallization results in dispersion of the orientations of recrystallized grains relatively to the parent grains this dispersion may be quantified by a dimensionless dispersion factor defined as the ratio of the random component of the 100 axis distributions between the recrystallized grains and porphyroclasts this factor is largely independent from the overall fabric strength the number of grains analyzed and the recrystallized grain size the olivine cpo strength and anisotropy at the rock scale quantified by j index are largely controlled by the volume of recrystallized grains which depends on finite strain comparison of olivine cpo in coarse and fine grained porphyroclastic peridotites shows that deviatoric stress and temperature conditions play nevertheless a role on the cpo evolution during recrystallization selective grain growth which is favored at high temperature and low stresses does counteract the dispersion produced by the nucleation processes

northeastern pacific mantle conductivity profile from long period magnetotelluric sounding using hawaii to california submarine cable data we present results of a long period magnetotelluric mt investigation of the electrical structure beneath the eastern north pacific the electric field data consist of 2 years of continuously recorded voltages across an unpowered 4000 km long submarine telephone cable haw 1 extending from point arena california to oahu hawaii the electric field measurements are coherent to some degree with magnetic field measurements from honolulu observatory at periods of 0 1 to 45 days this coherence is enhanced at long periods over that observed with point electric field sensors due to horizontal averaging of the motional electric fields of spatial scale smaller than the cable length significantly diminishing their effect robust controlled leverage mt response estimates and their jacknife confidence limits are computed for the haw 1 to honolulu data an equivalent scalar mt response obtained from honolulu magnetic variations data is used to correct the haw 1 mt response for static shift and to extend the mt response estimate to periods of 100 days the composite response function satisfies necessary and sufficient conditions for consistency with a one dimensional conductivity structure and is most sensitive to structure between 150 and 1000 km inversion of the mt response reveals a conductive zone 0 05 0 1 s m between 150 and 400 km depth and a positive gradient below 500 km these observations are consistent with previous mt studies in the north pacific this upper mantle conductivity is too high to be explained by solid state conduction in dry olivine using reasonable mantle geotherms calculations based on measurements of hydrogen solubility and diffusivity in olivine indicate that h dissolved in olivine possibly combined with a lattice preferred orientation consistent with measured seismic anisotropy provide sufficient conductivity enhancement to explain the inversion results the high conductivity may also be explained by the presence of gravitationally stable partial melt comparison of the haw 1 results with long period mt studies conducted on land reveals differences in upper mantle conductivity between different tectonic regimes in particular the upper mantle beneath the pacific ocean is considerably more conductive than that beneath the canadian shield and similar in conductivity to that beneath the basin and range

landward migration of inner bars abstract a field investigation was carried out to collect data of inner bar migration profiles were measured once or twice a week for a two year period at naka beach ibaraki prefecture japan it was found that the onshore migration of inner bars could be described by two dimensionless quantities as 5d h b max h b max gt 2 max 20d h b max where h b max is the maximum value of daily average breaker height during one interval between surveys t max is the average wave period of the day giving h b max d is the mean size of the beach sediment and g is the acceleration due to gravity analyses based on surfzone sediment dynamics yields v wd b 2 10 11 h b d 3 where v is the average speed of onshore bar migration b is the bar height h b is the average breaker height and w is the fall velocity of the beach sediment nomographs for the speed of landward migrating bars are also presented

dimensionality imprint of electrical anisotropy in magnetotelluric responses abstract dimensionality analysis of magnetotelluric data is a common procedure for inferring the main properties of the geoelectric structures of the subsurface such as the strike direction or the presence of superficial distorting bodies and enables the most appropriate modeling approach 1d 2d or 3d to be determined most of the methods currently used assume that the electrical conductivity of individual parts of a structure is isotropic although some traces of anisotropy in data responses can be recognized in this paper we investigate the imprints of anisotropic media responses in dimensionality analysis using rotational invariants of the magnetotelluric tensor we show results for responses generated from 2d synthetic anisotropic models and for field data that have been interpreted as showing the effects of electrical anisotropy in parts of the subsurface structure as a result of this study we extend the wal dimensionality criteria to include extra conditions that allow anisotropic media to be distinguished from 2d isotropic ones the new conditions require the analysis of the strike directions obtained and take into account the overall behavior of different sites in a survey

lithospheric and sublithospheric anisotropy beneath central southeastern brazil constrained by long period magnetotelluric data abstract electric anisotropy calculated from geoelectric strikes of magnetotelluric mt data and seismic anisotropy derived from shear wave splitting parameters are jointly analyzed to estimate the degree and orientation of strain in the subcontinental mantle of central southeastern brazil high quality long period mt soundings are available at 90 sites concentrated along four profiles at the southwestern and southern borders of the paleoproterozoic archean sao francisco craton this data set is complemented by a previous study of sks and skks splitting measurements available at more than 40 sites covering a slightly wider region for this study the mt data were processed with modern techniques including recovery of the undistorted em field polarizations through correction of static shift and phase mixing due to galvanic distortions three dimensional forward modelling of mt and gds geomagnetic depth soundings transfer functions supports interpretation of deep electrical anisotropy in the region magnetotelluric phase responses of orthogonal propagation modes present slight splitting at long periods for most of the sites indicative of overall electrically low mantle anisotropy to depths greater than 250 km the electrical strike azimuths are parallel to the fast nw directions of shear wave splitting along the southern borders of the sao francisco craton suggesting that the seismic anisotropy also resides within the same depth range since this direction is very different from that of present day south american westward absolute plate motion it is inferred that no significant lateral mantle flow or deformation related to the plate motion is observed under the study area either because it is absent or the rigid lithosphere is much thicker than expected to explain the prevailing electric and seismic common direction it is suggested that a mechanical coupling between lithospheric and sublithospheric mantle exists a relic strain possibly resulting from ancient continental collision processes is interpreted to have induced a general alignment of olivine down to mantle depths beneath the continental rigid plate the observed slightly enhanced conductive texture could be associated with hydrogen diffusion along the aligned olivine a axis especially within mantle patches subjected to metasomatic processes the coincidence of mantle strikes with the trend of surface deformation pattern also suggests that crust lithospheric and sublithospheric upper mantle have deformed and translated coherently preserving the regional nw direction since the tectono thermal event responsible for the deformation distinct electric azimuths from the general nw trend are observed in regions probably perturbed by cretaceous rift related intraplate magmatism and in zones of complex deep structures produced by superposed nearly simultaneous oblique neoproterozoic collisions in the southeast of the sao francisco craton

aseismic transient slip on the gofar transform fault east pacific rise oceanic transform faults display a unique combination of seismic and aseismic slip behavior including a large globally averaged seismic deficit and the local occurrence of repeating magnitude m 6 earthquakes with abundant foreshocks and seismic swarms as on the gofar transform of the east pacific rise and the blanco ridge in the northeast pacific ocean however the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults in the model strong dilatancy strengthening supported by seismic imaging that indicates enhanced fluid filled porosity and possible hydrothermal circulation down to the brittle ductile transition effectively stabilizes along strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically the modeled slow slip migrates along the barrier zones at speeds 10 to 600 m h spatiotemporally correlated with the observed migration of seismic swarms on the gofar transform our model thus suggests the possible prevalence of episodic aseismic transients in m 6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip earthquake swarms and fault zone hydromechanical properties