flow structure modification and drag reduction induced by sediment stratification in coastal tidal bottom boundary layers abstract the karman prandtl logarithm formula of velocity distribution has been widely used to depict flow structures and estimate parameters including bed roughness length and friction velocity in coastal tidal bottom boundary layers however the basic assumptions are of homogeneous flow but the effects of stratification should be taken into account here field observations of hydrodynamics and sediment dynamics were carried out in the well mixed area outside of the changjiang estuary china during may 31 june 2 2011 velocity profiles within the 2 m bottom layer suggest that the flow structure is prominently influenced when the gradient of suspended sediment concentration reaches o 0 1 kg m 4 the direct application of the log fit method resulted in a pronounced deviation from the actual boundary parameters the extended log fit method was used to represent the tidally averaged vertical flow structure indicating that the modification of the flow structure diminishes down to the bed and the calculated z0 based on the lowest layer close to the bed 0 22 0 38 m above the bed in the observation approaches the real value the observed data were also used to examine the modified logarithmic velocity distribution model in which the flux richardson number is modified with an empirical constant a to parameterize the stratification effects it was found that the constant a is approximately 1 which is significantly different from previous studies results of a vertical one dimensional model supported the above findings the sediment stratification effects should be taken into account and the logarithmic velocity distribution model tends to be applicable in the water layers very close to the bed

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

a three dimensional microgeodynamic model of melt geometry in the earth s deep interior 1 this article presents a three dimensional microgeodynamic model of grain melt geometry in partially molten rocks the isotropic unit cell of the partially molten rock is characterized by a face centered cubic symmetry consisting of rhombic dodecahedral grains the variation of surface tension between grain grain and grain melt contacts excites a coupled viscous flow within grains and the interstitial melt leading to a steady state grain melt geometry we obtain the fractional area of intergranular contact contiguity from these models as a function of melt volume fraction between melt fractions of 0 05 and 0 25 comparison with previous results indicates that the contiguity in three dimensional models is lower than in two dimensional models the contrast between two and three dimensional values of contiguity increases at high melt volume fractions we apply our model to the ultralow velocity zones ulvzs and the very low velocity province vlvp in the earth s core mantle boundary the observed seismic signature of the ulvz and vlvp can be explained by peridotite melt volume fractions between 0 08 and 0 12 and between 0 01 and 0 05 respectively in a matrix of elastic properties similar to the preliminary earth reference model

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

enhancement of wind driven upwelling and downwelling by alongshore bathymetric variability steady wind driven flow along a shelf of changing width is described with a frictional barotropic model valid in the limit of small rossby and burger number in these limits an alongshore wind drives enhanced onshelf transport in a coastal ocean if the shelf widens downwind and the change in shelf width only affects the flow in the direction of kelvin wave propagation downwave from the change in shelf width there is enhanced onshore transport of cold nutrient laden bottom water if the winds favor upwelling and the shelf narrows in the direction of kelvin wave propagation this enhanced transport extends a considerable distance away from the change in shelf width but becomes concentrated near the shelf break far from the change in width isobath curvature on the scale of the shelf width significantly modifies local cross shelf transport the cross shelf transport of nutrient rich water during upwelling is expected to be enhanced from point eugenia to la jolla san luis obispo to monterey and point reyes to cape mendocino on the west coast of north america

a dynamical description of fall and winter mean current profiles over the northern california shelf abstract fall and winter mean current profiles from a midshelf water depth 90 m northern california site exhibit a similar vertical structure for several different years the alongshelf flow is poleward with a maximum velocity of 5 10 cm s 1 in the middle or upper water column there is an offshore flow of about 2 cm s 1 in the upper 20 30 m an onshore flow of about 2 cm s 1 in the interior depths 35 65 m and an offshore flow of about 1 cm s 1 within 20 m of the bottom profiles are similar for averages over timescales from weeks to months mean current profiles at other midshelf sites along northern california and two sites off peru also have a similar vertical structure the vertical shear in the mean alongshelf flow is geostrophic throughout the water column that is in thermal wind balance with the cross shelf density gradient for timescales of a week or longer the thermal wind balance extends to within 1 m of the bottom and reduces the mean near bottom alongshelf flow to 1 cm s 1 or less th

a description of subtidal pressure field observations on the northern california continental shelf during the coastal ocean dynamics experiment during the coastal ocean dynamics experiment code along the northern california continental shelf in the spring and summer of 1981 and 1982 the first comprehensive effort to obtain all of the observations necessary to infer pressure fluctuations throughout the water column was made this is a description of the subtidal fluctuations in measured bottom pressure internal pressures inferred from moored conductivity and temperature observations and the water column total pressure anomalies computed from a combination of the two components the pressure field during code 2 april july 1982 is found to be more energetic than that in code 1 april july 1981 with more than 70 total pressure variance concentrated at frequencies of less than 15 days 1 the spatial structure of the pressure fluctuation field is characterized by coastal intensification and a tendency for poleward phase propagation like the pressures most of the code across shelf pressure difference variance is found at the lower frequencies with more than 60 of the total across shelf pressure difference variance at frequencies of less than 15 days 1 the code across shelf pressure differences are found to be in geostrophic balance with both alongshelf currents and the total alongshelf transport the alongshelf pressure difference variance is generally found to be concentrated at the lower frequencies much like that of the across shelf pressure differences most of the pressure and pressure difference variance is found to be highly coherent with wind stress the 20 day band pressure variability is apparently related to the response of the pressure field during so called relaxation events the barotropic component of the alongshelf geostrophic transport i e across shelf pressure difference has been found to be almost perfectly coherent with regional wind stress y and to propagate poleward within the code region at the same rate as y and the alongshelf pressure gradient is very important in accelerating the alongshelf flow the 5 day band pressure variability in the code region appears to result from local wind stress fluctuations the alongshelf pressure gradient was found to be of secondary importance relative to the wind in accelerating the alongshelf flow

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

energetics of a two phase model of lithospheric damage shear localization and plate boundary formation summary the two phase theory for compaction and damage proposed by bercovici et al 2001a j geophys res 106 8887 8906 employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a model for damage void generation and microcracking and a continuum description of weakening failure and shear localization here we examine further variations of the model which consider 1 how interfacial surface energy when averaged over the mixture appears to be partitioned between phases 2 how variability in deformational work partitioning greatly facilitates localization and 3 how damage and localization are manifested in heat output and bulk energy exchange microphysical considerations of molecular bonding and activation energy suggest that the apparent partitioning of surface energy between phases goes as the viscosity of the phases when such partitioning is used in the two phase theory it captures the melt compaction theory of mckenzie 1984 j petrol 25 713 765 exactly as well as the void damage theory proposed in a companion paper ricard bercovici submitted calculations of 1 d shear localization with this variation of the theory still show at least three possible regimes of damage and localization at low stress is weak localization with diffuse slowly evolving shear bands at higher stress strong localization with narrow rapidly growing bands exists and at yet higher shear stress it is possible for the system to undergo broadly distributed damage and no localization however the intensity of localization is strongly controlled by the variability of the deformational work partitioning with dilation rate represented by the parameter f or 1 extreme localization is allowed with sharp profiles in porosity weak zones nearly discontinuous separation velocities and effectively singular dilation rates finally the bulk heat output is examined for the 1 d system to discern how much deformational work is effectively stored as surface energy in the high stress distributed damage cases heat output is reduced as more interfacial surface energy is created yet in either the weak or strong localizing cases the system always releases surface energy regardless of the presence of damage or not and thus slightly more heat is in fact released than energy is input through external work moreover increased levels of damage represented by the maximum work partitioning f make the localizing system release surface energy faster as damage enhances phase separation and focusing of the porosity field thus yielding more rapid loss of net interfacial surface area however when cases with different levels of damage are compared at similar stages of development say the peak porosity of the localization it is apparent that increased damage causes smaller relative heat release and retards loss of net interfacial surface energy the energetics and energy partitioning of this damage and shear localization model are applied to estimating the energy costs of forming plate boundaries and generating plates from mantle convection

seasonal differences in the current and temperature variability over the northern california shelf during the coastal ocean dynamics experiment a long term moored array was maintained over the northern california continental shelf from april 1981 to april 1983 as part of the coastal ocean dynamics experiment to determine the seasonal differences in the current and water temperature characteristics the array consisted of two midshelf moorings and one upper slope mooring from april 1981 through july 1982 and one midshelf mooring from august 1982 to april 1983 the two summers were characterized by southeastward mean wind stresses upwelling favorable cold water isotherms sloping upward toward the coast and a sheared equatorward mean shelf current the intervening fall and winter were characterized by a weak mean wind stress relatively warm shelf water level isotherms and a more barotropic poleward mean shelf current in contrast to the differences in the characteristics of the means many of the characteristics of the current and temperature variability are the same for the summer and winter the vertical structure of the largest current empirical orthogonal functions eofs for each of the shelf moorings which account for more than 75 of the subtidal variance do not vary with season the current is vertically sheared oriented 15 20 clockwise relative to local isobaths near the surface and along isobaths near the bottom currents at the two shelf moorings alongshore separation 29 37 km are correlated with each other and with the local wind stress and these relationships do not exhibit a seasonal variation denser arrays of wind and current sensors during the two summers indicated that there were strong persistent variations in the wind field over relatively small scales tens of kilometers with corresponding variations in the shelf current field during the summer of 1981 but not during the summer of 1982 over the slope the largest eofs account for 56 72 of the current variance and have a vertical structure which is relatively uniform with depth during the summer fall and winter of 1981 but is strongly sheared in the upper 100 m during the summer of 1982 current observations over the slope are not correlated with either the shelf currents or the local wind stress during any season in contrast the temperature variability as described by eofs does exhibit a seasonal variation in vertical structure with the variability concentrated in the upper 20 30 m in summer and more uniform with depth in winter the near surface temperature variability over the slope is correlated with the shelf temperature variability estimates of the cross shelf heat flux due to the wind driven ekman transport accounts for a large part of the shelf temperature variability observations from the midshelf mooring maintained through the fall and winter of 1982 1983 showed evidence of the 1982 1983 el nino with persistent onshore and poleward currents and water temperatures typically above 12 c

influence of dihedral angle on the seismic velocities in partially molten rocks abstract this article reports the influence of dihedral angle in a partially molten aggregate on its effective elastic properties using theoretical techniques for a given mineral assemblage dihedral angles can vary widely depending on the composition of the melt our results indicate that wetting melts with low dihedral angles have a lower fraction of intergranular contact area contiguity reducing the effective elastic moduli an important consequence of this effect is that the seismic signature of an aggregate with a small volume fraction of a wetting melt will be similar to that of an aggregate containing a larger volume fraction of less wetting melt inferring the extent of melting in seismic ultralow velocity zones therefore needs to incorporate the influence of melt composition via the influence of dihedral angle

modeling studies of the coastal circulation off northern california statistics and patterns of wintertime flow we conduct modeling studies of the coastal circulation off northern california in the vicinity of the eel river 40 6 n the site of the 1995 2000 strata formation on margins strataform marine geology observational program using a series of nested hydrostatic primitive equation models to aid in the understanding of the shelf flow field that receives and transports sediments during the winter floods the basic objectives of our numerical studies are to model the continental shelf and slope flow and to understand the dominant dynamical processes we simulate the shelf and slope flow surrounding cape mendocino during 100 days in winter 1996 1997 using a 3 km resolution model embedded in a 9 km resolution regional model of the north pacific ocean the naval research laboratory s pacific west coast pwc model the validity of the model simulations is assessed by comparison with current measurements from a strataform shelf tripod outfitted with an acoustic doppler current profiler and with satellite altimetry good agreement is found between the amplitude and time variability of the 3 km resolution modeled and observed alongshore currents on the shelf the 3 km resolution model outperforms the 9 km resolution pwc model using statistical maps of flow variables strong alongshore variability in wintertime flow is documented the role of the forcing supplied by wind and river runoff in establishing this flow asymmetry between regions north and south of cape mendocino is examined using empirical orthogonal functions the evolution of a robust anticyclonic eddy over the shelf and slope adjacent to cape mendocino is described the eddy forms when strong poleward winds weaken and reverse direction during winter storms the important role of alongshore pressure gradients in the shelf circulation is documented

the alhama de murcia fault se spain a seismogenic fault in a diffuse plate boundary seismotectonic implications for the ibero magrebian region received 20 december 2002 revised 15 september 2003 accepted 26 september 2003 published 2 january 2004 1 the shortening between the african and the iberian plates is absorbed by a number of faults distributed over a very wide zone with very low slip rates and long periods of seismic loading thus a seismotectonic map based only on faults associated with seismicity or with expressive geomorphic features is incomplete it is possible to characterize seismogenic faults using paleoseismology first paleoseismological results based on trenching analysis in the eastern betics lorca totana segment of the alhama de murcia fault are presented the main paleoseismic parameters of this fault segment are 1 a minimum of two to three mw 6 5 7 earthquakes in the last 27 kyr shortly before 1650 a d between 830 and 2130 b c and shortly before 16 7 ka respectively with a mean recurrence period of 14 kyr and a very short elapsed time and 2 a net slip rate of 0 07 0 6 mm yr during the last 30 kyr these results were extrapolated to the rest of the known active faults in the eastern betics and were added to the slip rates of the active faults at the african margin the total slip rate of the transect which crosses de alhama de murcia fault in spain and reaches the cheliff basin algeria would represent 21 82 of the total shortening between africa and eurasia estimated from plate motion models and seismic moment summation a number of factors could account for this discrepancy 1 hidden seismogenic faults in the emerged areas 2 absence of correlation between current and late pleistocene slip rates 3 extensive small faults that are undetected and that absorb a significant amount of the deformation and 4 possible overestimation of the convergence rates index terms 7221 seismology paleoseismology 7230 seismology seismicity and seismotectonics 7215 seismology earthquake parameters 8150 tectonophysics plate boundary general 3040 keywords eastern betics alhama de murcia fault paleoseismology trenching seismotectonics plate boundary

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

scenarios for earthquake generated tsunamis on a complex tectonic area of diffuse deformation and low velocity the alboran sea western mediterranean the tsunami impact on the spanish and north african coasts of the alboran sea generated by several reliable seismic tsunamigenic sources in this area was modeled the tectonic setting is complex and a study of the potential sources from geological data is basic to obtain probable source characteristics the tectonic structures considered in this study as potentially tsunamigenic are the alboran ridge associated structures the carboneras fault zone and the yusuf fault zone we characterized 12 probable tsunamigenic seismic sources in the alboran basin based on the results of recent oceanographical studies the strain rate in the area is low and therefore its seismicity is moderate and cannot be used to infer characteristics of the major seismic sources these sources have been used as input for the numerical simulation of the wave propagation based on the solution of the nonlinear shallow water equations through a finite difference technique we calculated the maximum wave elevations and tsunami travel times using the numerical simulations the results are shown as maps and profiles along the spanish and african coasts the sources associated with the alboran ridge show the maximum potential to generate damaging tsunamis with maximum wave elevations in front of the coast exceeding 1 5 m the carboneras and yusuf faults are not capable of generating disastrous tsunamis on their own although their proximity to the coast could trigger landslides and associated sea disturbances the areas which are more exposed to the impact of tsunamis generated in the alboran sea are the spanish coast between malaga and adra and the african coast between alhoceima and melilla

pipe poiseuille flow of viscously anisotropic partially molten rock summary laboratory experiments in which synthetic partially molten rock is subjected to forced deformationprovideacontextfortestinghypothesesaboutthedynamicsandrheologyofthemantle here our hypothesis is that the aggregate viscosity of partially molten mantle is anisotropic and that this anisotropy arises from deviatoric stresses in the rock matrix we formulate a model of pipe poiseuille flow based on theory by takei holtzman and takei katz pipe poiseuille is a configuration that is accessible to laboratory experimentation but for which there are no published results we analyse the model system through linearized analysis and numerical simulations this analysis predicts two modes of melt segregation migration of melt from the centre of the pipe towards the wall and localization of melt into high porosity bands that emerge near the wall at a low angle to the shear plane we compare our results to those of takei katz for plane poiseuille flow we also describe a new approximation of radially varying anisotropy that improves the self consistency of models over those of takei katz this study provides a set of baseline quantitative predictions to compare with future laboratory experiments on forced pipe poiseuille flow of partially molten mantle

a generalized formulation of interfacial tension driven fluid migration with dissolution precipitation abstract we present an extended formulation for the interfacial tension driven melt migration by taking into account dissolution precipitation and diffusive matter transport through the liquid phase our results indicate that the melt migration is caused by two mechanisms in the first mechanism a change in melt fraction is accommodated by compaction decompaction of solid matrix and in the second mechanism a change in melt fraction is accommodated by dissolution precipitation the latter mechanism is newly introduced in this study as spatial scale decreases the dominant mechanism changes from compaction decompaction to dissolution precipitation and when the second mechanism is dominant evolution of melt fraction is governed by a nonlinear diffusion equation therefore critical scale of this transition is called diffusion length d below which melt fraction evolves primarily by diffusion diffusion length d is usually smaller than the compaction length c important roles of the new mechanism are discussed on the basis of existing experimental data on melt infiltration shear induced melt segregation into melt rich bands and rehomogenization of melt in the bands due to static annealing melt distribution in the mantle is briefly discussed on the basis of the new model

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

deceleration of a finite width stratified current over a sloping bottom frictional spindown or buoyancy shutdown abstract the deceleration of an unforced two dimensional finite width current over a sloping bottom in a stratified fluid is studied to quantify the relative importance of frictional spindown and buoyancy shutdown when both act simultaneously frictional spindown decelerates the current through ekman suction and pumping at the current edges which transmit stresses into the interior fluid buoyancy shutdown is the process by which lateral advection of density in the bottom boundary layer generates thermal wind shears that reduce the bottom stress thereby halting deceleration a theoretical model of a downwelling current suggests that buoyancy shutdown always reduces the deceleration timescale from that for frictional spindown alone and produces a nonzero steady along isobath current overlying an arrested bottom mixed layer the model is most sensitive to the burger number s n f where n is the buoyancy frequency the bottom slope and f the coriolis parameter larger s produces a stronger steady cu

wave driven inner shelf motions on the oregon coast abstract recent work by s lentz et al documents offshore transport in the inner shelf due to a wave driven return flow associated with the hasselmann wave stress the stokes coriolis force this analysis is extended using observations from the central oregon coast to identify the wave driven return flow present and quantify the potential bias of wind driven across shelf exchange by unresolved wave driven circulation using acoustic doppler current profiler adcp measurements at six stations each in water depths of 13 15 m observed depth averaged across shelf velocities were generally correlated with theoretical estimates of the proposed return flow during times of minimal wind forcing across shelf velocity profiles were vertically sheared with stronger velocities near the top of the measured portion of the water column and increased in magnitude with increasing significant wave height consistent with circulation due to the hasselmann wave stress yet velocity magnitudes and vertical shears wer

compaction around a rigid circular inclusion in partially molten rock conservation laws that describe the behavior of partially molten mantle rock have been established for several decades but the associated rheology remains poorly understood constraints on the rheology may be obtained from recently published experiments involving deformation of partially molten rock around a rigid spherical inclusion these experiments give rise to patterns of melt segregation that exhibit the competing effects of pressure shadows and melt rich bands such patterns provide an opportunity to infer rheological parameters through comparison with models based on the conservation laws and constitutive relations that hypothetically govern the system to this end we have developed software tools to simulate finite strain two phase flow around a circular inclusion in a configuration that mirrors the experiments simulations indicate that the evolution of porosity is predominantly controlled by the porosity weakening exponent of the shear viscosity and the poorly known bulk viscosity in two dimensional simulations presented here we find that the balance of pressure shadows and melt rich bands observed in experiments only occurs for bulk to shear viscosity ratio of less than about five however the evolution of porosity in simulations with such low bulk viscosity exceeds physical bounds at unrealistically small strain due to the unchecked exponential growth of the porosity variations processes that limit or balance porosity localization should be incorporated in the formulation of the model to produce results that are consistent with the porosity evolution in experiments

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

acceleration of a stratified current over a sloping bottom driven by an alongshelf pressure gradient abstract an idealized theoretical model is developed for the acceleration of a two dimensional stratified current over a uniformly sloping bottom driven by an imposed alongshelf pressure gradient and taking into account the effects of buoyancy advection in the bottom boundary layer both downwelling and upwelling pressure gradients are considered for a specified pressure gradient the model response depends primarily on the burger number s n f where n is the initial buoyancy frequency is the bottom slope and f is the coriolis parameter without stratification s 0 buoyancy advection is absent and the alongshelf flow accelerates until bottom stress balances the imposed pressure gradient the e folding time scale to reach this steady state is the friction time h r where h is the water depth and r is a linear bottom friction coefficient with stratification s 0 buoyancy advection in the bottom boundary layer produces vertical shear which prevents the bottom stress from becoming large

the seasonal alongshore pressure gradient on the west coast of the united states the long term mean steric height 0 500 dbar data of reid and mantyla 1976 are added to relative monthly mean adjusted sea level data to obtain a seasonal time series of quasi absolute large scale 300 km sea surface elevation along the west coast of the united states from 48 n to 33 n north of 38 n the elevation slope reverses sign seasonally so that the resulting pressure gradient force is southward from october to june and northward from july to september south of 38 n the pressure gradient force is northward except during january at all latitudes and during february in the interval from 38 n to 35 n maximum northward force occurs during august and september at all latitudes the relative contributions to sea level elevation slope by seasonal heating and cooling freshwater effluent effects the alongshore component of coastal wind stress and deep ocean currents are investigated both seasonal heating and cooling and freshwater contributions to large scale elevation slope are relatively insignificant 10 in every month at all latitudes wind stress forcing determined with the barotropic steady frictional model of csanady 1978 is significant north of point conception 35 n for both the long term mean slope and its seasonal oscillation remote contributions are particularly important in the pacific northwest south of san francisco 38 n empirical evidence suggests that deep ocean currents contribute significantly to coastal elevation slope in summer and fall and in the mean deep ocean currents may also affect elevation slope along the whole coast during spring causing elevated sea level toward the north

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

transport and bottom boundary layerobservations of the north atlantic deep western boundary current at the blake outer ridge abstract the north atlantic deep western boundary current dwbc was surveyed at the blake outer ridge over 14 days in july and august 1992 to determine its volume transport and to investigate its bottom boundary layer bbl this site was chosen because previous investigations showed the dwbc to be strong and bottom intensified on the ridge s flanks and to have a thick bbl the primary instrument used was the absolute velocity profiler a free falling velocity and conductivity temperature depth device in two sections across the width of the dwbc volume transports of 17 1 sv and 18 1 sv were measured for all water flowing equatorward below a potential temperature of 6 c 1 sv 1 10 6 m 3 s 1 transport values were derived using both absolute velocities and avp referenced geostrophic velocities and were the same within experimental uncertainty good agreement was found between our results and historical ones when both were similarly bounded and referenced although this was a short term survey the mean of a 9 day time series of absolute velocity profiles was the same as the means of year long current meter records at three depths in the same location a turbulent planetary bbl was found everywhere under the current the thickness of the bottom mixed layer bml where concentrations of density nutrients and suspended sediments were vertically uniform was asymmetrical across the current and up to 5 times thicker than the bbl there was no velocity shear above the bbl within the thicker bmls and the across slope density gradient was very small the extra thick bml is perhaps maintained by a combination of processes including turbulence downwelling ekman transport a weak up slope return flow above the bbl and buoyant convection from the bbl into the bml the frictional bottom stress was mostly balanced by a down stream change in the current s external potential energy evidenced by a drop in the velocity core of the current

role of grain boundaries in magma migration and storage we employ a continuous theory of two phase flow to investigate the influence of grain boundary tension on distribution and migration of melts through a viscous matrix the disaggregation melt fraction the volume fraction of partial melt at which grain boundaries are completely wetted is crucial in determining the total interfacial force per unit volume in partially molten aggregates withsmalldihedralanglesandcontaininglessmeltthanthedisaggregationfraction capillaryactionongrainboundariestendstoretain melt in tubules alongtriplegrain junctions as a consequence pulses ofbuoyantmagma decay during their ascent through the mantle stronginterfacialtensiononmatrixgrainboundariesalsoinfluencesthethicknessofaheavypartiallymoltenlayer inaggregateswith large dihedral angles strong tension on grain melt interfaces can give rise to self separation of the melt from the matrix