dimensionality and directionality effects in newmark sliding block analyses newmark sliding block analyses represent a useful and practical tool for evaluation of seismic slope stability hazards the analysis requires assumptions about material and failure surface behavior that have been well documented in the literature this paper investigates the effects of assumptions about the manner in which loading is applied on the results of the analysis the common practice of applying a one dimensional input motion parallel to the plane of the sliding block model was compared with the application of two and three dimensional input motions for sliding block models with frictional and cohesive failure surfaces the differences were found to be small for some cases and large for others in both conservative and unconservative directions the effect of slope azimuth on newmark sliding block displacements was also investigated computed displacements were found to be very sensitive to the assumed azimuthal direction of the input motion particularly for cases of high yield acceleration pro

regional scale co seismic landslide assessment using limit equilibrium analysis abstract traditionally regional assessment of seismic slope stability has been done using the infinite slope rigid sliding block analysis a major disadvantage of this approach is the resulting overestimation of the critical acceleration of the slope due to the underlying assumption of a predefined slope failure plane and consequently the underestimation of hazard areas prone to sliding in this paper we present a modified approach for assessing seismic slope instabilities using a model based on limit equilibrium analysis and circular slip surfaces with no restriction to any predefined slope failure plane for this purpose we conduct a parametric study to identify the relationship between the critical acceleration of the slope the slope angle and the slope shear strength parameters we model typical slopes in the rocscience software slide using bishop s limit equilibrium method to identify the critical accelerations that corresponds to a failure plane with factor of safety equal to one the critical accelerations were plotted against the variables in the parametric study and the best fit equations were obtained the proposed approach was developed for global application but it was tested using the well documented co seismic landslide database of the 1994 northridge ca earthquake the predicted sliding areas were compared to the inventory of landslides that were triggered in the val verde region in los angeles by the earthquake qualitative and quantitative assessments of the proposed model clearly show its advantages in predicting potential sliding areas

drained shear strength parameters for analysis of landslides this paper presents recommendations for selecting the type and magnitude of drained shear strength parameters for analysis of landslides in particular the importance existence and use of the cohesion shear strength parameter is reviewed for slope stability analyses it is recommended that the shear strength be modeled using a stress dependent failure envelope or a friction angle that corresponds to the average effective normal stress acting on the slip surface passing through that particular material instead of using a combination of cohesion and friction angle to represent soil shear strength other recommendations for stability analyses include using an effective stress cohesion of zero for residual and fully softened strength situations to facilitate selection of shear strength parameters for landslide analyses empirical relationships for the drained residual and fully softened strengths are updated from the previous empirical relationships presented by stark and eid finally the paper presents torsional ring shear test results that indicate that pre existing shear surfaces exhibit self healing that results in increased shear resistance the magnitude of healing appears to increase with increasing soil plasticity and this increase could have implications for the size timing and cost of landslide remediation

case history of landslide movement during the northridge earthquake we document a case history of northridge earthquake induced movement of a coherent landslide mass comprised principally of weathered previously sheared siltstone information on the residual shear strength of the material through which the sliding occurred is available both from backanalysis of a static rainfall induced failure on the same slope and laboratory test data postearthquake field reconnaissance data establishes the seismic slope displacements near the slope crest a yield coefficient is estimated for the slope based on residual shear strengths and measured groundwater levels at the time of the northridge earthquake this yield coefficient is used with four horizontal equivalent acceleration time histories that approximate the seismic demand within the slide mass in newmark sliding block displacement analyses the calculated displacements range from approximately 20 to 90 mm which compares well with observed displacements at the slide scarp of approximately 50 mm

empirical predictive models for earthquake induced sliding displacements of slopes earthquake induced sliding displacement is the parameter most often used to assess the seismic stability of slopes the expected displacement can be predicted as a function of the characteristics of the slope yield acceleration and the ground motion e g peak ground acceleration yet there is significant aleatory variability associated with the displacement prediction using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2 000 acceleration time histories and four values of yield acceleration these empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement with the goal of minimizing the standard deviation of the displacement prediction the combination of peak ground acceleration and peak ground velocity is the tw

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

efficiency of turbulent mixing in the abyssal ocean circulation turbulent mixing produced by breaking of internal waves plays an important role in setting the patterns of downwelling and upwelling of deep dense waters and thereby helps sustain the global deep ocean overturning circulation a key parameter used to characterize turbulent mixing is its efficiency defined here as the fraction of the energy available to turbulence that is invested in mixing efficiency is conventionally approximated by a constant value near one sixth here we show that efficiency varies significantly in the abyssal ocean and can be as large as approximately one third in density stratified regions near topographic features our results indicate that variations in efficiency exert a first order control over the rate of overturning of the lower branch of the meridional overturning circulation

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

role of overturns in optimal mixing in stratified mixing layers turbulent mixing plays a major role in enabling the large scale ocean circulation the accuracy of mixing rates estimated from observations depends on our understanding of basic fluid mechanical processes underlying the nature of turbulence in a stratified fluid several of the key assumptions made in conventional mixing parameterizations have been increasingly scrutinized in recent years primarily on the basis of adequately high resolution numerical simulations we add to this evidence by compiling results from a suite of numerical simulations of the turbulence generated through stratified shear instability processes we study the inherently intermittent and time dependent nature of wave induced turbulent life cycles and more specifically the tight coupling between inherently anisotropic scales upon which small scale isotropic turbulence grows the anisotropic scales stir and stretch fluid filaments enhancing irreversible diffusive mixing at smaller scales we show that the characteristics of turbulent mixing depend on the relative time evolution of the ozmidov length scale compared to the so called thorpe overturning scale which represents the scale containing available potential energy upon which turbulence feeds and grows we find that when the mixing is most active and efficient since stirring by the largest overturns becomes optimal in the sense that it is not suppressed by ambient stratification we argue that the high mixing efficiency associated with this phase along with observations of in oceanic turbulent patches together point to the potential for systematically underestimating mixing in the ocean if the role of overturns is neglected this neglect arising through the assumption of a clear separation of scales between the background mean flow and small scale quasi isotropic turbulence leads to the exclusion of an highly efficient mixing phase from conventional parameterizations of the vertical transport of density such an exclusion may well be significant if the mechanism of shear induced turbulence is assumed to be representative of at least some turbulent events in the ocean while our results are based upon simulations of shear instability we show that they are potentially more generic by making direct comparisons with data from ocean and lake observations which represent a much wider range of turbulence inducing physical processes

evaluation of simplified methods for predicting earthquake induced slope displacements in earth dams and embankments abstract this paper provides a review and comparison of existing simplified displacement based sliding block models analyses were performed to evaluate the relative accuracy of fifteen of these simplified models for predicting earthquake induced displacements to accomplish this task the predictive capability of the models was assessed by comparing model predictions with the actual displacements that were observed after earthquake shaking in 122 case histories of earth dams and embankments the results indicate that the model predictions of displacement were less than the observed displacement for a large majority of the case histories that were examined the difference between the observed and predicted displacements was relatively large for a significant percentage of the cases for each model that was examined the shapes and positions of the models relative error cumulative distribution functions did not change significantly if the case histories were filtered to include only those with intermediate levels of observed displacement i e 0 01 m

global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean a global estimate of the energy conversion rate from geostrophic flows into internal lee waves in the ocean is presented the estimate is based on a linear theory applied to bottom topography at o 1 10 km scales obtained from single beam echo soundings to bottom stratification estimated from climatology and to bottom velocity obtained from a global ocean model the total energy flux into internal lee waves is estimated to be 0 2 tw which is 20 of the global wind power input into the ocean the geographical distribution of the energy flux is largest in the southern ocean which accounts for half of the total energy flux the results suggest that the generation of internal lee waves at rough topography is a significant energy sink for the geostrophic flows as well as an important energy source for internal waves and the associated turbulent mixing in the deep ocean

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

spatial variation of diapycnal diffusivity estimated from seismic imaging of internal wave field gulf of mexico bright reflections are observed within the upper 1000 m of the water column along a seismic reflection profile that traverses the northern margin of the gulf of mexico independent hydrographic calibration demonstrates that these reflections are primarily caused by temperature changes associated with different water masses that are entrained into the gulf along the loop current the internal wave field is analyzed by automatically tracking 1171 reflections each of which is greater than 2 km in length power spectra of the horizontal gradient of isopycnal displacement ex are calculated from these tracked reflections at low horizontal wavenumbers kx 10 2 cpm ex kx 0 2 0 6 in agreement with hydrographic observations of the internal wave field the turbulent spectral subrange is rarely observed diapycnal diffusivity k is estimated from the observed internal wave spectral subrange of each tracked reflection using a fine scale parametrization of turbulent mixing calculated values of k vary between 10 8 and 10 4 m2 s 1 with a mean value of k 4 10 6 m2 s 1 the spatial distribution of turbulent mixing shows that k 10 7 m2 s 1 away from the shelf edge in the upper 300 m where stratification is strong mixing is enhanced by up to four orders of magnitude adjacent to the shoaling bathymetry of the continental slope this overall pattern matches that determined by analyzing nearby suites of ctd casts however the range of values recovered by spectral analysis of the seismic image is greater as a consequence of significantly better horizontal resolution

influence of enhanced abyssal diapycnal mixing on stratification and the ocean overturning circulation abstractthe meridional overturning circulation moc is composed of interconnected overturning cells that transport cold dense abyssal waters formed at high latitudes back to the surface turbulent diapycnal mixing plays a primary role in setting the rate and patterns of the various overturning cells that constitute the moc the focus of the analyses in this paper will be on the influence of sharp vertical variations in mixing on the moc and ocean stratification mixing is enhanced close to the ocean bottom topography where internal waves generated by the interaction of tides and geostrophic motions with topography break it is shown that the sharp vertical variations in mixing lead to the formation of three layers with different dynamical balances governing meridional flow specifically an abyssal bottom boundary layer forms above the ocean floor where mixing is largest and hosts the northward transport of the heaviest waters from the southern channel to the closed basins a deep layer forms above the b

landslides triggered by the 1994 northridge california earthquake abstract the 17 january 1994 northridge california earthquake m w 6 7 triggered more than 11 000 landslides over an area of about 10 000 km 2 most of the landslides were concentrated in a 1000 km 2 area that included the santa susana mountains and the mountains north of the santa clara river valley we mapped landslides triggered by the earthquake in the field and from 1 60 000 nominal scale aerial photography provided by the u s air force and taken the morning of the earthquake these mapped landslides were subsequently digitized and plotted in a gis based format most of the triggered landslides were shallow 1 to 5 m thick highly disrupted falls and slides within weakly cemented tertiary to pleistocene clastic sediment average volumes of these types of landslides were less than 1000 m 3 but many had volumes exceeding 100 000 m 3 the larger disrupted slides commonly had runout paths of more than 50 m and a few traveled as far as 200 m from the bases of steep parent slopes deeper 5 m thick rotational slumps and block slides numbered in the tens to perhaps hundreds a few of which exceeded 100 000 m 3 in volume most of these were reactivations of previously existing landslides the largest single landslide triggered by the earthquake was a rotational slump block slide having a volume of 8 10 6 m 3 analysis of the mapped landslide distribution with respect to variations in 1 landslide susceptibility and 2 strong shaking recorded by hundreds of instruments will form the basis of a seismic landslide hazard analysis of the los angeles area

energetics of a rotating wind forced horizontal convection model of a reentrant channel abstractwe present numerical results for an idealized rotating buoyancy and windforced channel as a simple model for the southern ocean branch of the meridional overturning circulation moc dif

internal tides and ocean mixing recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features a substantial amount of energy is transferred from the main ocean tides into internal tides in his perspective garrett explains how these internal waves with tidal periods propagate through the density stratified deep ocean and eventually break down into turbulence the resulting mixing affects ocean stratification and ocean circulation it thus influences climate as well as biological production the energy for the internal tides is derived from the rotational energy of the earth moon system changes of the length of the day and the distance to the moon

influence of abyssal mixing on the multilayer circulation in the south china sea abstractby parameterizing the abyssal mixing as the exchange velocity entrainment detrainment between the middle and deep layers of the south china sea scs its effects on the multilayer circul

effects of directionality and vertical component of ground motions on seismic slope displacements in newmark sliding block analysis abstract the newmark sliding block model is widely used in the evaluation of seismic slope stability when using this model the horizontal acceleration is usually considered to act parallel to the slope downslope and the vertical component of ground motions is commonly ignored this study investigates the effect of vertical accelerations on the results of sliding displacement and quantitatively compares the difference of the displacement dn calculated from the original newmark s approach with the displacement dhv calculated from a more realistic case horizontal and vertical accelerations properly considered for this purpose 4136 ground motion recordings are selected from the nga west2 database and 2000 hypothetic slopes are simulated with critical accelerations ac ranging from 0 to 0 8 g comparison of dhv and dh shows that the incorporation of vertical accelerations only slightly increases the displacement besides the calculated dhv dn ratios are generally in the range of 1 to 5 indicating that dn significantly underestimates the slope displacement due to the simplification of seismic excitations the dhv dn ratios generally increase as ac increases simple predictive models are proposed to quantify the correction factor kd kd dhv dn they can be easily used in seismic landslide hazard assessment to improve the performance of the original newmark s approach

uncertainty in seismic slope deformation model predictions in this article we examine how variability in driving and resisting force parameters together translate into uncertainty in seismic slope deformation predictions predictive uncertainty of the newmark rigid block and makdisi seed decoupled deformation based methods was evaluated by performing a series of probabilistic monte carlo simulations for two idealized slope models results from these analyses demonstrate that the highly non linear relationship between acceleration ratio and displacement associated with the deformation models dictates the way in which parametric variability is propagated through the analysis and can lead to varying degrees of uncertainty in the deformation predictions based on this observation three zones along the displacement acceleration ratio relationship were identified according to their relative degree of non linearity and correlated with their relative influence on predictive uncertainty these are i highly uncertain ii moderately uncertain and iii low uncertainty using this framework the widely held notion of a generic order of magnitude estimate for deformation predictions is a misnomer based on this it is recommended that realistic levels of parametric variability be incorporated in the seismic slope deformation analysis to establish the operating conditions of the slope system slopes identified as highly uncertain or moderately uncertain require a more robust probabilistic analyses to meaningfully interpret poorly constrained deformation predictions

developing a map of geologically defined site condition categories for california consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion the importance of amplification by soil conditions has long been recognized but though many seismic instrument sites have been characterized by their geologic conditions there has been no consistent simple classification applied to all sites as classification of sites by shear wave velocity has become more common the need to go back and provide a simple uniform classification for all stations has become apparent within the pacific earthquake engineering research center s next generation attenuation equation project developers of attenuation equations recognized the need to consider site conditions and asked that the california geological survey provide site conditions information for all stations that have recorded earthquake ground motion in california to provide these estimates we sorted the available shear wave velocity data by geologic unit generalized the geologic units and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials this new map is different from the california geological survey preliminary site conditions map of california in that 19 geologically defined categories are used rather than national earthquake hazards reduction program categories although this map does not yet cover all of california when completed it may provide a basis for more precise consideration of site conditions in ground motion calculations

regression models for estimating coseismic landslide displacement newmark s sliding block model is widely used to estimate coseismic slope performance early efforts to develop simple regression models to estimate newmark displacement were based on analysis of the small number of strong motion records then available the current availability of a much larger set of strong motion records dictates that these regression equations be updated regression equations were generated using data derived from a collection of 2270 strong motion records from 30 worldwide earthquakes the regression equations predict newmark displacement in terms of 1 critical acceleration ratio 2 critical acceleration ratio and earthquake magnitude 3 arias intensity and critical acceleration and 4 arias intensity and critical acceleration ratio these equations are well constrained and fit the data well 71 br 2 b88 but they have standard deviations of about 0 5 log units such that the range defined by the mean one standard deviation spans about an order of magnitude these regression models therefore are not recommended for use in site specific design but rather for regional scale seismic landslide hazard mapping or for rapid preliminary screening of sites 2007 elsevier b v all rights reserved

regional seismic slope assessment improvements considering slope aspect and vertical ground motion abstract seismic slope stability assessments in active fault zones are very important prior to designing and constructing large engineering structures however in most previous regional scale analyses ground motion records are either used directly or replaced by empirical regression equations in this paper we present an improved regional seismic slope stability assessment method considering the vertical slope aspect and ground motion based on limit equilibrium models and finite element models best fit equations are obtained to calculate the sliding angle and factor of safety fos then a two stage integration process is applied to obtain the permanent displacement the new model has been tested in the chenghai active fault zone china under a seismic precautionary intensity of 9 and the results of the new model are compared with those of traditional infinite slope models the results show that ignoring the vertical ground motion and slope aspect leads to underestimation of co seismic landslide hazards on regional scales and the new model provides a more accurate index to evaluate co seismic slope behaviours in large areas

the role of the geothermal heat flux in driving the abyssal ocean circulation 1 the results presented in this paper demonstrate that the geothermal heat flux ghf from the solid earth into the ocean plays a non negligible role in determining both abyssal stratification and circulation strength based upon an ocean data set we show that the map of upward heat flux at the ocean floor is consistent within a factor of 2 with the ocean floor age dependent map of ghf the observed buoyancy flux above the ocean floor is consistent with previous suggestions that the ghf acts to erode the abyssal stratification and thereby enhances the strength of the abyssal circulation idealized numerical simulations are performed using a zonally averaged single basin model which enables us to address the ghf impact as a function of the depth dependence of diapycnal diffusivity we show that ignoring this vertical variation leads to an under prediction of the influence of the ghf on the abyssal circulation independent of the diffusivity profile introduction of the ghf in the model leads to steepening of the southern ocean isopycnals and to strengthening of the eddy induced circulation and the antarctic bottom water cell the enhanced circulation ventilates the ghf derived heating to shallow depths primarily in the southern ocean

ridges seamounts troughs and bowls topographic control of the dianeutral circulation in the abyssal ocean abstractin situ observations obtained over the last several decades have shown that the intensity of turbulent mixing in the abyssal ocean is enhanced toward the seafloor consequently a new parad

simplified procedure for estimating earthquake induced deviatoric slope displacements a simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake induced deviatoric deformations is presented it utilizes a nonlinear fully coupled stick slip sliding block model to capture the dynamic performance of an earth dam natural slope compacted earth fill or municipal solid waste landfill the primary source of uncertainty in assessing the likely performance of an earth waste system during an earthquake is the input ground motion hence a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements a seismic displacement model is developed that captures the primary influence of the system s yield coefficient ky its initial fundamental period ts and the ground motion s spectral acceleration at a degraded period equal to 1 5 ts the model separates the probability of zero displacement i e 1 cm occurring from the distribution of nonzero displacement so that very low values of calculated

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

generation of internal waves in the deep ocean by tides 1 a direct computation of the tidal generation of internal waves over the global ocean is presented it is based on linear wave theory and high resolution data for the bottom topography the geographical distribution of the energy flux from tides to internal waves is determined with a spatial resolution of a few kilometers the total flux over the area with a depth greater than 500 m is found to be 1 2 tw the greatest uncertainties of the computation are due to unresolved topography and to nonlinear effects caused by supercritical bottom slope

a new characterization of the turbulent diapycnal diffusivities of mass and momentum in the ocean the diapycnal diffusivity of mass supported by turbulent events in the ocean interior plays a fundamental role in controlling the global overturning circulation the conventional representation of this diffusivity due to osborn 1980 assumes a constant mixing efficiency we replace this methodology by a generalized osborn formula which involves a mixing efficiency that varies nonmonotonically with at least two nondimensional variables using these two variables we propose dynamic parameterizations for mixing efficiency and turbulent prandtl number the latter quantifies the ratio of momentum to mass diapycnal diffusivities based on the first synthesis of an extensive direct numerical simulation of inhomogeneously stratified shear induced turbulence data from argo floats are employed to demonstrate the extent of the spatial and statistical variability to be expected in both the diapycnal diffusivities of mass and momentum we therefore suggest that previous estimates of these important characteristics of the global ocean require reconsideration

influence of spatial variability of soil strength parameters on probabilistic seismic slope displacement hazard analysis abstract permanent sliding displacement analysis is commonly used to evaluate the seismic performance of slopes specifically the fully probabilistic seismic slope displacement hazard analysis pssdha has attracted increasing attention recently since it appropriately accounts for various sources of uncertainties associated with the estimation of sliding displacement within this analysis the uncertainty of soil strength parameters e g effective cohesion c and effective internal friction angle is commonly quantified by a logic tree method in which the spatial variability of c and is simply ignored this study aims at proposing an extended pssdha framework by rigorously accounting for the spatial variability of c and and then investigating its influence on the resultant slope displacement hazard curves based on the newmark rigid block model two different approaches namely an analytical based and a simulation based method are proposed separately the results of the analytical based method are found to be consistent with those obtained by the simulation based one it is also shown that the displacement hazard would be underestimated if the spatial variability of c and is ignored such underestimation is more significant for slopes with soil parameters exhibiting weak c correlation and strong spatial variability besides it suggests that the proper configuration of logic tree framework plays an important role in developing displacement hazard curves and a relatively large range of discrete strength values is recommended to better account for the effect of the spatial variability of soil strength parameters

shaking table modeling of seismically induced deformations in slopes physical model experiments were performed on a 1 g shaking table with the principal goals of 1 investigating the mechanisms of seismically induced permanent deformations in slopes and 2 assessing the accuracy and applicability of the newmark sliding block procedure for estimating seismically induced deformations in slopes each of the clayey slope models deformed in response to strong shaking with the principal mode of deformation being deep rotational translational sliding displacement deformations were principally focused along one or more highly localized shear surfaces though a significant amount of additional deformation was also distributed over a relatively wide region of the models the newmark analyses generally provided moderately accurate although somewhat unconservative estimates of deformations displacements computed using the rigid sliding block analysis ranged from 27 to 225 of maximum measured displacements and averaged about 75 of measured displacements for the test series the newmark type analyses were most reliable for those model tests that experienced large deformations where the sliding resistance was controlled principally by postpeak to residual strengths

turbulence variability at the equator in the central pacific at the beginning of the 1991 1993 el nino a 38 day 5990 cast microstructure study on the equator performed during the onset of the 1991 1993 el nino shows the effect on small scale activity at 140 w of an equatorial kelvin wave by using two ships data were taken continuously from november 4 to december 12 1991 near the national oceanic and atmospheric administration pacific marine environmental laboratory mooring at o n 140 w the ships occupied the station sequentially with a 3 5 day overlap for intercalibration variability in currents was observed on tidal periods and periods of 4 days presumably equatorially trapped internal gravity waves 8 days cause unknown 20 days tropical instability waves and longer kelvin waves variation in water structure occurred most prominently on the timescale of kelvin waves the diurnal cycle typical of that location was observed nocturnal deepening of the surface mixed layer was accompanied by a deep cycle bursts of turbulence penetrating into the stratified region below the nighttime mixed layer during the observational period one kelvin wave trough and one crest passed through the site changes accompanying the phase change in the kelvin wave included a reversal of the near surface current a deepening of the thermocline and a change of water mass changes in small scale activity included a tenfold decrease of the thermal dissipation rate and a fourfold decrease of the rate of heat transport downward from the mixed layer the nighttime mixed layer deepened from 30 to 60 m the thickness of the stratified region in which nocturnal turbulence bursts occurred the deep cycle region thinned from 40 to 20 m because it was confined between the bottom of the nighttime mixed layer and the low shear region near the core of the undercurrent the decrease in downward heat flux observed at this passage of the downwelling kelvin wave front could explain the rapid sea surface temperature sst increase seen at el nino onsets the magnitude of the change in vertical flux is similar to the magnitude of the change in horizontal advection this process would produce a warmer sst much more quickly than could the advection of warm waters eastward

mixing dissipation rate and their overturn based estimates in a near bottom turbulent flow driven by internal tides abstractdirect numerical simulation dns and large eddy simulation les are employed to study the mixing brought about by convective overturns in a stratified oscillatory bottom layer underneath internal tides the phasing of turbulence the onset and breakdown of convective overturns and the pathway to irreversible mixing are quantified mixing efficiency shows a systematic dependence on tidal phase and during the breakdown of large convective overturns it is approximately 0 6 a value that is substantially larger than the commonly assumed value of 0 2 used for calculating scalar mixing from the turbulent dissipation rate diapycnal diffusivity is calculated using the irreversible diapycnal flux and for tall overturns of o 50 m the diffusivity is found to be almost 1000 times higher than the molecular diffusivity the thorpe overturn length scale is often used as a proxy for the ozmidov length scale and thus infers the turbulent dissipation rate from overturns the accuracy of overturn based es

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

zonal wavenumber characteristics of northern hemisphere transient eddies abstract eleven winters and twelve summers of twice daily national meteorological center nmc analyses of geopotential height and temperature at five levels for the extratropical northern hemisphere are partitioned into long wave fields with zonal wavenumbers m 5 and short wave fields with zonal wavenumbers m 6 the data are also bandpass filtered to investigate fluctuations of periods 2 5 10 days from these fields the standard deviation of 500 mb geopotential height and the poleward geostrophic transient eddy fluxes of sensible heat and zonal momentum are calculated and presented the results are compared with theoretical and numerical modeling studies of nonlinear baroclinic instability both the observations and modeling studies produce evidence that baroclinic eddies have a definite life cycle and that the strongest baroclinic eddies are of intermediate size zonal wavenumbers 6 8 some interesting differences between observations and modeling results also emerge

variations in apparent mixing efficiency in the north atlantic central water abstract microstructure data from the north atlantic tracer release experiment natre are presented providing detailed profiles of the thermal variance in the upper 360 m of the canary basin for the fall and spring seasons the osborn cox model is used to compute the diffusivity kt the diffusivity for the depth range 240 340 m is found to be 1 0 0 04 10 5 m2 s 1 in the fall and 2 2 0 1 10 5 m2 s 1 in the spring in good agreement with dye inferred diffusivities at similar depths measured turbulent kinetic energy tke dissipation rates were found to be contaminated by hydrodynamic noise so the osborn dissipation method was not used to compute k however data segments for which the tke dissipation rate e was large enough to be unaffected by noise were used to compute the apparent mixing efficiency d the computed d values are used to investigate variations in apparent mixing efficiency with respect to density ratio r and turbulence reynolds number e n2 in an attempt to eluci

how variable is mixing efficiency in the abyss author posting american geophysical union 2020 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 47 2020 e2019gl086813 doi 10 1029 2019gl086813

inclined plane studies of the newmark sliding block procedure this study considers the shaking induced displacement and dynamic response of a rigid block and deformable columns of soil on an inclined plane this work demonstrates that because of the coupled d

slope unit based approach for assessing regional seismic landslide displacement for deep and shallow failure abstract grid based approach is typically adopted to estimate the newmark type displacement for regional seismic landslide hazard assessment however the approach is limited to the assumption of infinite slope and rigid block movement which may be different from the actual behavior of slope under seismic loading in this study a slope unit based approach is proposed to quickly estimate earthquake induced displacements for finite slopes in regional scale hence regional seismic landslide hazard can be assessed by the estimated displacements the approach is advantageous as it considers slope geometry determines the failure mode automatically and considers the interaction of incident wave and slope the implementation of the approach is demonstrated by considering two areas that experience severe landslides during the chi chi and northridge earthquakes results show that the prediction rate of the proposed method is up to 73 compared with the landslide inventory given the estimated displacements