residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

the burgess shale and associated cambrian formations west of the fossil gully fault zone on mount stephen british columbia west of the fossil gully fault zone on mount stephen the three lowest members only of the burgess shale formation are preserved the kicking horse shale the yoho river limestone and the campsite cliff shale the formation rests unconformably upon the takakkaw tongue formation whose dark basinal limestones conformably overlie paler shelf like limestones of the mount whyte formation mapping has resolved a long standing problem and shown that the stratigraphical position of the famous mount stephen trilobite beds lies within the campsite cliff shale it has also revealed some of the complexities of the fossil gully fault zone among which different periods and directions of component fault movements are indicated faunal evidence shows that the plagiura kochaspis to albertella and albertella to glossopleura zonal boundaries lie within the takakkaw tongue sequence within the burgess shale three distinct soft bodied communities occur at different stratigraphical levels on this mountain slope the oldest

decadal changes of wind stress over the southern ocean associated with antarctic ozone depletion using 40 yr ecmwf re analysis era 40 data and in situ observations the positive trend of southern ocean surface wind stress during two recent decades is detected and its close linkage with spring antarctic ozone depletion is established the spring antarctic ozone depletion affects the southern hemisphere lower stratospheric circulation in late spring early summer the positive feedback involves the strengthening and cooling of the polar vortex the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients the acceleration of the circumpolar westerlies and the reduction of the upward wave flux this feedback loop together with the ozone related photochemical interaction leads to the upward tendency of lower stratospheric zonal wind in austral summer in addition the stratosphere troposphere coupling facilitated by ozone related dynamics and the southern annular mode cooperates to relay the zonal wind anomalies to the upper troposphere the wave mean flow interaction and the meridional circulation work together in the form of the southern annular mode which transfers anomalous wind signals downward to the surface triggering a striking strengthening of surface wind stress over the southern ocean

stability of the atlantic meridional overturning circulation and stratification in a zonally averaged ocean model effects of freshwater flux southern ocean winds and diapycnal diffusion the atlantic meridional overturning circulation amoc is a crucial component of the global climate system in this study using a zonally averaged ocean model we reexamine the sensitivity of this circulation and ocean density structure in general to several types of external forcing the basin of the model extends from northern high latitudes to antarctica and includes an implicit representation of a circumpolar channel in the south and ocean circulation is driven by surface buoyancy fluxes and wind forcing in contrast to earlier two dimensional studies of the amoc our approach involves a careful treatment of the residual mean circulation comprising the eulerian mean and eddy induced flows which is especially important for the southern ocean dynamics using boundary conditions consistent with present day observations the model reproduces realistic ocean stratification and meridional overturning the structure intensity and stability of the overturning are then extensively studied using three control parameters the strength of westerly wind stress over the southern ocean the magnitude of freshwater fluxes imposed on the northern atlantic and ocean diapycnal diffusivity in a realistic parameter range we estimate the amoc sensitivity to changes in the southern ocean winds on the order of 1 sv per 20 increase in the wind stress the overturning also increases with diapycnal diffusivity but the dependence is weaker than in the absence of the winds the model can undergo a shutdown of the overturning subject to a hysteresis when either the freshwater forcing gradually increases or the wind stress decreases the hysteresis loop disappears for large values of isopycnal diffusivity changes in the amoc intensity are accompanied by changes in the volume transport of the antarctic circumpolar current specifically the amoc collapse leads to a strengthening of this transport ultimately our calculations produce stability maps for the steady states of the meridional overturning circulation and provide a general framework that potentially can be used to compare different models or to understand past abrupt climate changes related to reorganization of the amoc

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

a new middle cambrian radiodont from north china implications for morphological disparity and spatial distribution of hurdiids abstract hurdiidae a clade of radiodonta that has attracted widespread attention in recent years is notable for their massive tripartite cephalic carapace and a wide variety of feeding habits although the hurdiidae has a cosmopolitan distribution in the cambrian their miaolingian occurrences are restricted to laurentia here we describe a new hurdiid radiodont cordaticaris striatus gen et sp nov based on well preserved specimens from the middle cambrian miaolingian drumian zhangxia formation in shandong province north china this new taxon is characterized by a heart shaped central element with linear ornament frontal appendages equipped with nine blade like endites including seven subequal elongate endites a node bearing peytoia type oral cone and a trunk covered with rows of setal structures cordaticaris not only enriches the taxonomic diversity of hurdiidae but also further documents the great morphological disparity of hurdiid sclerotized body elements the discovery of soft bodied fossils in the zhangxia formation also stresses the great potential of the miaolingian strata of north china for the preservation of non biomineralized organisms

jet structure and scaling in southern ocean models abstract the jet structure of the antarctic circumpolar current acc simulated by two general circulation models gcms fram fine resolution antarctic model and pop parallel ocean program is examined in relation to the bottom topography field despite differences in configuration both gcms display similar behavior the model acc consists of a number of distinct current cores superimposed on broader scale flow the jets display temporal and spatial including vertical coherence with maximum velocities occurring at the surface it is shown that multiple jets can arise in wind forced baroclinic quasigeostrophic flow the main factors influencing the number and spacing of jets are found to be the bottom topography and the proximity of lateral boundaries the meridional spacing of jets on a flat bottomed plane is consistent with the rhines scaling criterion for barotropic plane turbulence with a small modification due to baroclinicity and the presence of meridional boundaries when a zonally orient

a barotropic model of eddy saturation abstracteddy saturation refers to a regime in which the total volume transport of an oceanic current is insensitive to the wind stress strength baroclinicity is currently believed to be the key to

long term earthquake prediction in the circum pacific convergent belt investigation of the time dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering duration extending to several years which follow a power law time distribution mainshocks however interevent times of the order of decades show a quasiperiodic behaviour and follow the regional time and magnitude predictable seismicity model this model is expressed by the following formulas begin gathered log t t 0 19 m min 0 33 m p 0 39 log m 0 q hfill m f 0 73 m min 0 28 m p 0 40 log m 0 m hfill end gathered which relate the interevent time tt in years and the surface wave magnitude mf of the following mainshock with the magnitude mmin of the smallest mainshock considered the magnitude mp of the preceded mainshock and the moment rate m0 in dyn cm yr 1 in a seismogenic region the values of the parametersq andm vary from area to area the basic properties of this model are described and problems related to its physical significance are discussed

minimal change in antarctic circumpolar current flow speed between the last glacial and holocene relatively little is known about the dynamics of the antarctic circumpolar current during the last glacial period estimates of current speeds over the past 20 000 years based on sediment grain size suggest that average flow speeds during the last glacial were comparable to modern speeds but not in the areas with overlying winter sea ice

dependence of earthquake recurrence times and independence of magnitudes on seismicity history the fulfillment of a scaling law for earthquake recurrence time distributions is a clear indication of the importance of correlations in the structure of seismicity in order to characterize these correlations we measure conditional recurrence time and magnitude distributions for worldwide seismicity as well as for southern california during stationary periods disregarding the spatial structure we conclude that the relevant correlations in seismicity are those of the recurrence time with previous recurrence times and magnitudes in the latter case the conditional distribution verifies a scaling relation depending on the difference between the magnitudes of the two events defining the recurrence time in contrast with our present resolution magnitude seems to be independent on the history contained in the seismic catalogs except perhaps for southern california for very short time scales less than about 30 min for the magnitude ranges analyzed

on the transport and angular momentum balance of channel models of the antarctic circumpolar current abstract angular momentum balances are discussed both in general as well as in the context of simple channel models of the antarctic circumpolar current acc particular emphasis is placed on the close relationship between the angular momentum balance and the meridional circulation it is found that topographic form drag is established very early in the integration whereas interfacial form drag can take much longer to develop restrictions on the geostrophic portion of the meridional circulation imposed by zonally reconnecting potential vorticity contours in the upper ocean allow derivation of an estimate for the steady state transport the estimate assumes there to be little or no circumpolar flow at great depth an assumption that stems from the belief that the band of zonally reconnecting geostrophic contours in the southern ocean does not extend to the ocean floor the predicted transport is proportional to the strength of the stratification and compares favorably with numerical results in the lite

southern ocean fronts controlled by wind or topography 1 the location of fronts has a direct influence on both the physical and biological processes in the southern ocean here we explore the relative importance of bottom topography and winds for the location of southern ocean fronts using 100 years of a control and climate change simulation from the high resolution coupled climate model higem topography has primary control on the number and intensity of fronts at each longitude however there is no strong relationship between the position or spacing of jets and underlying topographic gradients because of the effects of upstream and downstream topography the southern hemisphere westerlies intensify and shift south by 1 3 in the climate change simulation but there is no comparable meridional displacement of the antarctic circumpolar current s acc path or the fronts within its boundaries even over flat topography instead the current contracts meridionally and weakens north of the acc the subtropical front stf shifts south gradually even over steep topographic ridges we suggest the stf reacts more strongly to the wind shift because it is strongly surface intensified in contrast fronts within the acc are more barotropic and are therefore more sensitive to the underlying topography an assessment of different methods for identifying jets reveals that maxima of gradients in the sea surface height field are the most reliable approximating the position of fronts using sea surface temperature gradients is ineffective at high latitudes while using sea surface height contours can give misleading results when studying the temporal variability of front locations

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

topographic influences on wind driven stratified flow in a β plane channel an idealized model for the antarctic circumpolar current abstract topographic influences are examined in an eddy resolving model of oceanic channel flow forced by steady zonal winds with small explicit lateral friction transient eddies generated by the baroclinic instability of the mean flow transfer momentum downward to the bottom layer in the flat bottom case bottom friction is the only efficient sink of eastward momentum when bottom topography is present the topographic form stress can replace the bottom friction sink in the momentum budget and a large decrease of the zonal transport results large wale topography of the scale of the forcing provides the largest form stress topographic effects decay with height as suggested by the prandit scaling and therefore only topographic scales larger than the rossby radius can affect the whole water column in that case the interfaces are deformed by standing eddies on topographic length scales and standing eddies replace transient eddies in transferring momentum downward the bottom layer mean streamfunc

on the dynamics of wind driven circumpolar currents the factors controlling the transport of the antarctic circumpolar current acc have recently been a topic of heated debate at the latitudes of drake passage potential vorticity contours are uninterrupted by coastlines and large amplitude flows are possible even with weak forcing and dissipation the relationship between the dynamics of circumpolar currents and inertial recirculations in closed basins is discussed in previous studies sverdrup balance and baroclinic adjustment theories have both been proposed as theories of the acc transport these theories predict the circumpolar transport as various simple functions of the surface wind stress a series of experiments is performed with a simple channel model with different wind strengths and different idealized basin geometries to investigate the relationship between wind strength and circumpolar transport the results show that baroclinic adjustment theories do predict transport in the special case of a periodic channel with no topographic variations or when the wind forcing is very weak more generally the transport is determined by a complex interplay between wind forcing eddy fluxes and topographic effects there is no support for the idea that sverdrup balance determines the transport through drake passage

flow past a cylinder on a β plane with application to gulf stream separation and the antarctic circumpolar current abstract the classical problem of flow past a cylinder is revisited in the context of understanding two oceanographic phenomena separation of the gulf stream from the north american coastline at cape hatteras and the interaction of the antarctic circumpolar current with topographic obstacles numerical solutions are presented for eastward barotropic flow past a cylinder in a plane channel the solutions are dependent on two nondimensional parameters the reynolds number re and a nondimensional parameter in line with previous studies increasing reduces the separation downstream of the cylinder but introduces a blocked stagnant region upstream of the cylinder flanked by two inertial jets the large limit is relevant to the interaction of the antarctic circumpolar current with topographic obstacles such as the kerguelen plateau however a new regime is obtained for high reynolds number re 200 and moderate parameter 10 100 with two separated jets downstream of the cylinder

meridional transport across a zonal channel topographic localization experiments are performed using a two layer isopycnic numerical model in a zonal channel with a large meridional topographic ridge in the lower layer the model is forced only by a steady meridional volume transport in the upper layer and develops a current structure similar to the antarctic circumpolar current meridional volume flux across time mean geostrophic streamlines is found to be due to a combination of the geostrophic eddy bolus flux and the lateral reynolds stress the proportion of each depends on the strength of the forcing the reynolds stress increases with the forcing while the bolus flux is relatively constant topography localizes the eddy fluxes at and downstream of the topography where eddy energies are greatest the strength of the zonal transport is governed by the onset of baroclinic instability and so is relatively insensitive to the strength of the meridional transport

where do winds drive the antarctic circumpolar current the strength of the antarctic circumpolar current acc is believed to depend on the westerly wind stress blowing over the southern ocean although the exact relationship between winds and circumpolar transport is yet to be determined here we show based on theoretical arguments and a hierarchy of numerical modeling experiments that the global pycnocline depth and the baroclinic acc transport are set by an integral measure of the wind stress over the path of the acc taking into account its northward deflection our results assume that the mesoscale eddy diffusivity is independent of the mean flow while the relationship between wind stress and acc transport will be more complicated in an eddy saturated regime our conclusion that the acc is driven by winds over the circumpolar streamlines is likely to be robust

the longer it has been since the last earthquake the longer the expected time till the next we adopt a iognormal distribution for earthquake interval times and we use a locally determined rather than a generic coefficient of variation to estimate the probability of occurrence of characteristic earthquakes we extend previous methods in two ways first we account for the aseismic period since the last event the seismic drought in updating the parameter estimates second in calculating the earthquake probability we allow for uncertainties in the mean recurrence time and its variance by averaging over their likelihood both extensions can strongly influence the calculated earthquake probabilities especially for long droughts in regions with few documented earthquakes as time passes the recurrence time and variance estimates increase if no additional events occur leading eventually to an affirmative answer to the question in the title the earthquake risk estimate begins to drop when the drought exceeds the estimated recurrence time for the parkfield area of california the probability of a magnitude 6 event in the next 5 years is about 34 per cent much lower than previous estimates furthermore the estimated 5 year probability will decrease with every uneventful year after 1988 for the coachella valley segment of the san andreas fault the uncertainties are large and we estimate the probability of a large event in the next 30 years to be 9 per cent again much smaller than previous estimates on the mojave pallett creek segment the catalog includes 10 events and the present drought is just approaching the recurrence interval so the estimated risk is revised very little by our methods

potential vorticity constraints on the dynamics and hydrography of the southern ocean abstract constraints on the hydrography and geostrophic velocity shear of the southern ocean implicit in its potential vorticity field are discussed and illustrated by diagnostic study of observed and modeled potential vorticity fields a stress driven thermodynamically inactive eddy resolving quasigeostrophic model of the southern ocean suggests that through the systematic erosion of potential vorticity gradients by geostrophic eddies the large scale flow equilibrates toward a state in which interior potential vorticity gradients are small observations of the large scale isopycnal distribution of potential vorticity ipv deduced from climatological hydrographic data reveal a much richer structure the most striking feature of the ipv field is the presence of large near surface gradients of ipv a vortocline coinciding with the axis of the antarctic circumpolar current acc to the south of this front potential vorticity pv is large to its north pv has low values and relative to those foun

a morphological and taxonomic appraisal of the oldest anomalocaridid from the lower cambrian of poland material previously referred to as cassubia infercambriensis was re examined and found to represent a composite fossil of a peytoia like anomalocaridid frontal appendage and an arthropod of uncertain affinities comparable to some bivalved arthropod taxa the frontal appendage is referred to the genus peytoia based on the presence of elongated ventral spines bearing a single row of auxiliary spines as well as representing the oldest example of an anomalocaridid in the fossil record series 2 stage 3 peytoia infercambriensis is also the only record of this group from the east european craton therefore extending both the temporal and geographic range of the anomalocaridid family hurdiidae

causes of large scale sea level variations in the southern ocean analyses of sea level and a barotropic model 1 we analyze a decade of sea surface height ssh measurements in the southern ocean from the topex poseidon and ers altimeters with a focus on the variability at timescales 2 years among the different processes contributing to large scale ssh variations the barotropic response to the winds dominates poleward of 50 s while thermosteric processes dominate equatorward except for resonant basins for the barotropic modes and regions of intense eddy activity a finite element barotropic model has been developed to analyze the vorticity budget the ssh from the model agrees well with observations the leading barotropic mode which is annular and is confined near antarctica is responsible for most of the barotropic circumpolar transport it is coherent with the zonally integrated eastward wind stress consistent with a free mode response although previously evidenced in bottom pressure data this mode is only partially seen in altimeter data because of ice coverage it nevertheless distinctly appears above the pacific ridges where it expands meridionally up to midlatitudes in the rest of the domain several regions coherent with the local wind stress curl are found these are regions isolated by f h contours mostly deep basins an analysis of the vorticity budget shows that generally topographic sverdrup balance is the leading process for periods 50 days but in some regions resonant basins diffusive and nonstationary terms are important a model experiment shows that transients redistribute energy along f h waveguides contributing to drain resonant regions as was hypothesized in previous works

the middle cambrian burgess shale and its relationship to the stephen formation in the southern canadian rocky mountains the burgess shale has been an anomalous geologic unit ever since walcott named it in 1911 as the geographic equivalent of the ogygopsis shale in the middle cambrian stephen formation of southeastern british columbia but it has never been recognized outside of its type locality so its status relative to the stephen formation remained uncertain the geologic setting of the burgess shale was determined by aitken and fritz in 1968 when they recognized the cathedral escarpment and divided the stephen formation into a thin platformal succession on top of the escarpment and a thick basinal succession which included walcott s burgess shale in front fieldwork by royal ontario museum parties between 1982 and 1997 has now demonstrated that the thin and thick stephen successions lie within different facies belts and should be regarded as separate formations the stephen shale formation is part of the middle carbonate belt succession whereas the name burgess shale formation is applied to the thick basinal

circulation of the pacific ocean seen in a global ocean model ocean circulation and climate advanced modelling project occam this paper compares observations made in the pacific ocean and the 8 12 year climatology of a global numerical model meridional mass and heat transports and their divergences are calculated and zonal averages compared with the air sea exchange values of doney et al 1998 with mixed success the large scale distribution of sea surface height and near surface currents are shown to be well reproduced by the model but their variance is underestimated severely so in areas of weak variability synoptic wind forcing enhances the latter though only slightly while higher model resolution improves agreement in areas of strong variability model mean transports in the east australian current in the vitiaz strait and in the kuroshio exceed measurements by 10 0 18 sv respectively and variability is underestimated by factors between 2 and 4 near 1000 m and in strong currents the flow is overestimated but over most of the ocean model output does not match either the magnitude or the spatial variability of the observations in contrast the inflow of bottom water and its spreading path throughout both south and north pacific is well described good agreement is found with measured transport through the samoan passage but at 32 s east of the tonga kermadec ridge the model yields only 60 of the observed value the sverdrup balance is shown to hold widely in the model interior utilizing the complete depth integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents

configuration of a southern ocean storm track abstractdiagnostics of ocean variability that reflect and influence local transport properties of heat and chemical species vary by an order of magnitude along the southern ocean s antarctic circumpolar current acc topographic hotspots are important regions of localized transport anomalies this study uses a primitive equation channel model to investigate the structure of eddy kinetic energy eke one measure of variability in an oceanic regime a storm track approach emphasizes the importance of stationary eddies which result from flow interactions with topography on setting eke distributions the influence of these interactions extends far downstream of the topography and impacts eke patterns through localized convergence and divergence of heat unlike for zonal averages local contributions to the stationary fluxes from terms that integrate to zero in a zonal average are important the simulations show a strong sensitivity of the zonal structure as well as the distribution and amplitude of sta

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

acceleration of the antarctic circumpolar current by wind stress along the coast of antarctica the influence of wind forcing on variability of the antarctic circumpolar current acc is investigated using a series of eddy permitting ocean sea ice models at interannual and decadal time scales the acc transport is sensitive to both the mean strength of westerly winds along the acc circumpolar path consistent with zonal momentum balance theories and sensitive to the wind stresses along the coast of antarctica consistent with the free mode theory of hughes et al a linear combination of the two factors explains differences in acc transport across 11 regional quasi equilibrium experiments repeated single year global experiments show that the acc can be robustly accelerated by both processes across an ensemble of simulations with realistic forcing over the second half of the twentieth century interannual acc transport variability owing to the free mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3 5 and 5 to one while the acc transport may not accelerate significantly owing to projected increases in along acc winds in future decades significant changes in transport could still occur because of changes in the stress along the coast of antarctica

an exploration of the role of transient eddies in determining the transport of a zonally reentrant current the meridional ekman transport in a zonally reentrant channel may be balanced by diabatic circulations standing eddies associated with topography or by lagrangian mean eddy mass fluxes a simple model is used to explore the interaction between these mechanisms a key assumption of this study is that diabatic forcing in the poleward edge of the channel acts to create lighter fluid as is the case with net freshwater fluxes into the southern ocean for weak wind forcing or strong diabatic constraint a simple scaling argument accurately predicts the level of baroclinic shear however given our understanding of the relative magnitudes of ekman flux and deep upwelling this is not the appropriate parameter range for the antarctic circumpolar current with stronger wind stresses eddies are prominent with baroclinic instability initially developing in the vicinity of large topography arguments have been advanced by a number of authors that baroclinic instability should limit the velocity shear leading to a stiff upper limit on the transport of the current however in the simulations presented here baroclinic instability is largely confined to the region of topographic highs and the approach to a current that is independent of the wind stress occurs gradually several recent parameterizations of transient eddy fluxes do not reproduce key features of the observed behavior

stress transfer in earthquakes hazard estimation and ensemble forecasting inferences from numerical simulations abstract observations indicate that earthquake faults occur in topologically complex multi scale networks driven by plate tectonic forces we present realistic numerical simulations involving data mining pattern recognition theoretical analyses and ensemble forecasting techniques to understand how the observable space time earthquake patterns are related to the fundamentally inaccessible and unobservable dynamics numerical simulations can also help us to understand how the different scales involved in earthquake physics interact and influence the resulting dynamics our simulations indicate that elastic interactions stress transfer combined with the nonlinearity in the frictional failure threshold law lead to the self organization of the statistical dynamics producing 1 statistical distributions for magnitudes and frequencies of earthquakes that have characteristics similar to those possessed by the gutenberg richter magnitude frequency distributions observed in nature and 2 clear examples of stress transfer among fault activity described by stress shadows in which an earthquake on one group of faults reduces the coulomb failure stress on other faults thereby delaying activity on those faults in this paper we describe the current state of modeling and simulation efforts for virtual california a model for all the major active strike slip faults in california noting that the working group on california earthquake probabilities wgcep uses statistical distributions to produce earthquake forecast probabilities we demonstrate that virtual california provides a powerful tool for testing the applicability and reliability of the wgcep statistical methods furthermore we show how the simulations can be used to develop statistical earthquake forecasting techniques that are complementary to the methods used by the wgcep but improve upon those methods in a number of important ways in doing so we distinguish between the official forecasts of the wgcep and the research quality forecasts that we discuss here finally we provide a brief discussion of future problems and issues related to the development of ensemble earthquake hazard estimation and forecasting techniques

forecasting where larger crustal earthquakes are likely to occur in italy in the near future a forecast of future occurrences of larger m 5 9 crustal earthquakes in italy is made on the basis of historic and instrumental seismicity and following a seismotectonic regionalization recently derived on the basis of geological evidence combined with earthquake epicenters and focal mechanisms completeness problems in the seismic catalog allow one to study only 20 regions out of 58 large crustal seismicity within each seismogenic region is modeled as either a periodic gauss process or a random poisson process according to the experimental coefficient of variation of the series of past occurrences in each region return times are estimated directly from the series of m 4 5 earthquakes if they are sufficient in number or from the gutenberg richter law applied to lower magnitude seismicity m 4 5 otherwise the immediate probability of an m 5 9 crustal seismic event is esti mated to be very low in all regions except southeastern sicily and appennino abrnz zese in the near future next 20 yr the estimated probability is high above 65 also in the appennino forlivese and naso capo d orlando regions in addition to detailed seismic risk reevaluations these regions represent the best bet for a program of intensive monitoring to gather a record of the process of strain accumulation and seismic release

the role of closed gyres in setting the zonal transport of the antarctic circumpolar current abstracteddy permitting simulations are used to show that basinlike gyres can be observed in the large scale barotropic flow of a wind driven channel with a meridional topographic ridge this is confirmed using both two layer quasigeostrophic and 25 level primitive equation models at high horizontal resolution comparing results from simulations with and without the topographic ridge it is shown that the zonal baroclinic transport in the channel increases with increasing wind stress when the bottom topography is flat but not when there is a meridional ridge the saturation of transport for increasing wind occurs in conjunction with the development of recirculating gyres in the large scale barotropic streamfunction this suggests that the total circulation can be thought of as a superposition of a gyre mode which has zero circumpolar transport and a free circumpolar mode which contains all of the transport basinlike gyres arise in the channel because the topography steers the barotropic streamlines a

the dynamics of the antarctic circumpolar current abstract the dynamics of the antarctic circumpolar current acc in a near eddy resolving model of the southern ocean fram are investigated a streamwise coordinate system is used rather than a more conventional approach of considering zonally averaged quantities the motivation for this approach is the large deviation from a purely zonal flow made by the current comparisons are made with a zonal mean analysis of the same model it is found that the topographic form drag is the main sink of the momentum that is input by the wind however in contrast to a zonal mean analysis other terms namely horizontal mixing bottom friction and advection of momentum are no longer negligible the total effect of transient eddies is to produce a drag on the mean flow again in contrast to the zonally averaged case the vertical penetration of stress is considered a generalized formula is derived for the interfacial form stress averaged along a convoluted path and that includes nonquasigeostrophic effects the i

seismic quiescence at parkfield an independent indication of an imminent earthquake the parkfield segment of the san andreas fault midway between san francisco and los angeles has experienced six moderate sized earthquakes since 1850 with an average recurrence time of about 22 years based on this regular behaviour and the occurrence of the most recent earthquake in 1966 a shock of local magnitude ml 5 7 is expected to occur by 19931 2 here we suggest that a current lack of small earthquakes on this segment could be a precursory anomaly to the next characteristic parkfield earthquake only four earthquakes of m 2 5 have occurred on the segment since january 1986 whereas twenty would have been expected extrapolating from the mean background rate comparison with other cases of precursory quiescence suggests that the m 5 7 earthquake should occur in the next two years rupturing the same 35 km fault segment that ruptured in 19663

eddy saturation of the southern ocean a baroclinic versus barotropic perspective eddy saturation is the regime in which the total time mean volume transport of an oceanic current is relatively insensitive to the wind stress forcing and is often invoked as a dynamical descript

new sites of chengjiang fossils crucial windows on the cambrian explosion soft bodied and lightly sclerotized chengjiang fossils have been found at more than ten new localities in the lower cambrian qiongzhusi and canglangpu formations of east central yunnan at the same time three different fossil assemblages have been recognized i e kunmingella isoxys naraoia assemblage at chengjiang kunmingella cricocosmia assemblage at haikou and kunmingella wutingaspis obolus assemblage at anning and wuding these sites yield new and striking specimens such as a new tentacular animal brachiopods with pedicles preserved and the enigmatic xidazoon having mixed phyla characters which are significant in our understanding of animal phylogeny above all the appearance of diverse chordates and agnathans vertebrates greatly expands our knowledge of the cambrian explosion the discovery of soft bodied fossils at many new localities and the very wide distribution of the qiongzhusi formation suggest that many more localities remain to be discovered here a new early form of tentaculate cambrotentacus sanwuia gen et sp nov perhaps related to lophophorates and entoprocts is described

water mass transformations driven by ekman upwelling and surface warming in subpolar gyres abstractthe sverdrup relationship when applied to the southern ocean suggests that some isopycnals that are deep in the eastern pacific will shoal in the atlantic cold waters surfacing in the south atlantic at midlatitudes would be warmed by the atmosphere the potential for water mass transformations in this region is studied by applying a three layer planetary geostrophic model to a wide ocean basin driven by the ekman upwelling typical of the southern ocean surface winds the model uses a simple physically based parameterization of the entrainment of mass into the surface layer with zonally symmetric atmospheric surface fields to find steady state subpolar gyre solutions the solutions are found numerically by specifying suitable boundary conditions and integrating along characteristics with reasonable parameter settings transformations of more than 10 sverdrups sv 1 sv 106 m3 s 1 of water between layers are obtained the water mass transformations are sensitive to the strength of the wind stre

multiple jets of the antarctic circumpolar current south of australia abstract maps of the gradient of sea surface height ssh and sea surface temperature sst reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments the braided and patchy nature of the gradient fields seems at odds with the traditional view derived from hydrographic sections that the acc is made up of three continuous circumpolar fronts by applying a nonlinear fitting procedure to 638 weekly maps of ssh gradient ssh it is shown that the distribution of maxima in ssh i e fronts is strongly peaked at particular values of absolute ssh i e streamlines the association between the jets and particular streamlines persists despite strong topographic and eddy mean flow interactions which cause the jets to merge diverge and fluctuate in intensity along their path the ssh values corresponding to each frontal branch are nearly constant over the sector of the southern ocean between 100 e and 180 the front positions inferred from ssh agree closely with

irregular recurrence of large earthquakes an analysis of historic and paleoseismic catalogs assessment of a region s seismic hazard requires knowledge of the repeat times and the regularity of earthquake recurrence for most areas the earthquake catalog is too short to determine recurrence parameters reliably using a large set of events for many regions however it should be possible to constrain the average characteristics of earthquake recurrence behavior this study compiles a set of the most complete historic and paleoseismic series of m 7 earthquakes from the middle american trench alaska chile japan and the san andreas fault the 52 recurrence series show a large average aperiodicity that is variations in recurrence time are larger than 40 of the average recurrence interval aperiodicity may decrease with increasing magnitude neither the use of different magnitude thresholds the exclusion of foreshocks and aftershocks the type of statistics normal or lognormal used nor the choice of segmentation results in a significantly smaller aperiodicity the irregular recurrence behavior exhibited by the data implies that earthquakes are more unpredictable than often assumed in hazard analyses

modeling earthquake recurrence in the himalayan seismic belt using time dependent stochastic models implications for future seismic hazards interest in and pertinent studies related to the seismic hazard in the himalayan region have increased significantly since the instrumental era and each damaging earthquake encourages its reestimation in the work presented herein the non poissonian probabilities of exceedance of magnitudes in a specified time in the future were investigated for different elapsed times based on the recurrence time intervals of past earthquakes in the himalaya using the weibull log normal gamma and inverse gaussian stochastic models the whole himalayan arc is divided into four seismogenic source zones viz the northwestern himalayas zone 1 the central seismic gap region zone 2 the eastern nepal and sikkim zone 3 and the eastern himalayas zone 4 by considering approximately 380 years of seismological data the suitability of each stochastic model for each zone was estimated using the kolmogorov smirnov k s test to describe the different physical processes responsible for earthquake occurrence the results show that the gamma inverse gaussian log normal and inverse gaussian models were most suitable for zones 1 4 respectively for m 6 0 the cumulative probability of recurrence intervals reaches up to 90 in 30 years for zones 1 and 2 49 years for zone 3 and 41 years for zone 4 the estimated conditional probability reaches 90 in 30 years in zone 1 35 years in zone 2 and 50 years in zones 3 and 4 the most suitable models for m 7 0 were found to be the log normal for zones 1 2 and 3 and gamma for zone 4 the cumulative probability for m 7 0 reaches 90 in 85 years in zone 1 86 years in zone 2 93 years in zone 3 and 148 years in zone 4 the estimated conditional probabilities reach 90 in 80 years in zone 1 90 years in both zone 2 and 3 and 150 years in zone 4 it is strongly recommended that model suitability be evaluated in complex regions such as the himalaya before proceeding with seismic hazard assessments the heterogeneous and complex tectonics of the himalayas differentiated plate motions different stress release patterns spatially and temporally and locking unlocking of faults thrusts are some of the reasons responsible for the different probabilistic models describing the earthquake occurrence phenomena in these four zones

wind driven flow over topography in a zonal β plane channel a quasi geostrophic model of the antarctic circumpolar current abstract the paper gives a detailed account of the dynamical balance of a wind driven zonally unbounded flow over topography the problem is investigated with a quasi geostrophic plane channel with two layers and eddy resolution the channel has a width of 1500 km and a zonal periodicity of 4000 km apart from the dimensions the model structure is similar to the one used by mcwilliams et al the experiments with this model address the problem of the relative role of transient and standing eddies as well as bottom friction and topographic form stress in the balance of a current driven by a steady surface windstress the response of the system is investigated for different values of the friction parameter and various locations of topographic obstacles in the bottom layer of the channel the principal momentum balance emerging from these experiments supports the concept of munk and palmen for the dynamics of the antarctic circumpolar current which proposes that the momentum input by windstress is transfe

basin and channel contributions to a model antarctic circumpolar current the idea that basinlike dynamics may play a major role in determining the antarctic circumpolar current acc transport is revisited a simple analytic model is developed to describe the relationship between the wind stress and transport at very low wind stress a nonzero minimum is predicted this is followed by two distinct dynamical regimes for stronger forcing 1 a stommel regime in which transport increases linearly with forcing strength and 2 a saturation regime in which the transport levels off the baroclinic structure of the sverdrup flux into the drake passage latitude band is central to the analytic model and the geometry of characteristics or geostrophic contours is key to predicting the transition between the two regimes a robustness analysis is performed using an eddy permitting quasigeostrophic model in idealized geometries many simulations were carried out in large domains across a range of forcing strengths the simulations agree qualitatively with the analytic model with two main discrepancies being related to zonal jet structures and to a western boundary inertial recirculation eddy fluxes associated with zonal jets modify the baroclinic structure and lower the saturation transport value inertial effects increase the transport although this effect is mainly limited to smaller domains

on the origins of the variability of the malvinas current in a global eddy permitting numerical simulation 1 this article investigates the origins of the variability of the malvinas current mc transport using the results of an eddy permitting ocean general circulation model first the dynamical links between the variabilities of the mc and the antarctic circumpolar current acc transports at the drake passage are established time series analyses indicate that the connection between the transport variations of the acc and the mc is masked by high frequency oscillations although a substantial portion of this highfrequency variability is produced and dissipated locally there are also anomalies that propagate between those regions the most conspicuous of these signals has an average speed of 6 7 cm s 1 and a period of 150 days second the contribution of the wind forcing to the variability of the acc and the mc is determined from principal estimator patterns analysis the analysis indicates that the variance of the transport of both currents is more directly related to the variability of the wind stress than to the wind stress curl the transport variability is particularly sensitive to zonal wind stress anomalies in the latitudinal range of the drake passage that extends farther north over the south indian ocean a rather counterintuitive result of our analysis is that the wind stress forcing over the south atlantic ocean is unimportant to the variability of the mc transport

sensitivity of antarctic circumpolar current transport and eddy activity to wind patterns in the southern ocean abstractthe southern hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode sam however the response of the antarctic circumpolar current acc transport and eddy field to wind forcing remains a topic of debate this study uses global eddy permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening the response of the barotropic and baroclinic transports and eddy field of the acc is found to depend on the spatial pattern of the changes in wind forcing in isolation an enhancement of the westerlies over the acc belt leads to an increase of both barotropic and baroclinic transport within the acc envelope with lagged enhancement of the eddy kinetic energy eke in contrast an increase in wind forcing near antarctica drives a largely barotropic change in transport along closed f h contours free mode with little change in eddy activity under

comparing idealized and complex topographies in quasigeostrophic simulations of an antarctic circumpolar current abstractthe circumpolar transport of a wind driven quasigeostrophic antarctic circumpolar current is considered simple theory suggests transport in a strongly forced regime the focus of this study is largely determined by a partitioning of the southward sverdrup flux into drake passage latitudes some streamlines feed a basin contribution to the circumpolar transport and others feed a large scale recirculation gyre simulations assuming an idealized scotia ridge topography are considered to test for sensitivity to resolution considerable sensitivity to both vertical and horizontal resolution is found and associated with this is a tight stationary eddy trapped on the western flank of the ridge that is this eddy is sensitive to resolution and exerts an influence that acts to reduce the circumpolar transport simulations using the scotia ridge like topography are also compared to others using more realistic topography in the idealized ridge topography experiments there is only a single ridge again

implementation of a geometrically informed and energetically constrained mesoscale eddy parameterization in an ocean circulation model abstractthe global stratification and circulation as well as their sensitivities to changes in forcing depend crucially on the representation of the mesoscale eddy field in a numerical ocean circ

the role of ocean gateways in the dynamics and sensitivity to wind stress of the early antarctic circumpolar current the date of inception of the antarctic circumpolar current is debated due to uncertainty in the relative opening times of drake passage and the tasman seaway using an idealized eddy resolving numerical ocean model we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current we find that overlapping continental barriers do not impede a circumpolar transport in excess of 50sv as long as a circumpolar path can be traced around the barriers however the presence of overlapping barriers does lead to an increased sensitivity of the current s volume transport to changes in wind stress this change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress specifically when the pressure drop across continents is the main balancing sink of momentum the zonal volume transport is sensitive to changes in wind stress changes in zonal volume transport take place via altering the depth independent part of the circumpolar transport rather than that arising from thermal wind shear in such a scenario isopycnals continue to slope steeply across the model southern ocean implying a strong connection between the deep and surface oceans this may have consequences for the meridional overturning circulation and its sensitivity to wind stress

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

time intervals between characteristic earthquakes and correlations with smaller events an analysis based on a mechanical model of a fault certain correlations between characteristic events and smaller events are studied in the context of a spatially homogeneous mechanical model for a fault the model satisfies a one dimensional quasi linear wave equation in which the key nonlinearity is associated with the slipstick friction force at the interface between tectonic plates we find that the model gives rise to slipping events of all sizes the smaller events are consistent with the gutenberg richter statistical law whereas the characteristic events have a separate statistical distribution the crossover from smaller events to characteristic events coincides with a correlation length which sets the scale for clustering of smaller events before the characteristic rupture numerical results and scaling arguments relate the features of the distribution of characteristic events to the corresponding features of the distribution of smaller events as well as the length of the fault the distribution of time intervals between characteristic events has the distinguishing features of asymmetry and a finite upper cutoff the mean t and standard deviation of the time interval distribution are found to be related to features of the magnitude versus frequency distribution of smaller events and the coefficient of variation t is independent of the driving rate because this analysis relates properties of characteristic earthquakes to statistical features of smaller more numerous events as well as geometric features of the fault it may ultimately be useful for long term earthquake prediction

recurrence time and frequency slip statistics of slip events on the creeping section of the san andreas fault in central california summary an important question in seismic hazard assessments is the frequency size and recurrence interval statistics at a point on a fault does a point on a fault obey the same statistics as earthquakes in a region do this is a difficult question to answer because the number of repetitive earthquakes on a particular fault that have been observed is small in order to overcome this difficulty we consider slip events on the creeping section of the san andreas fault in central california sequences of up to 100 events are obtained from creepmeter records we compare the statistical distribution of recurrence times with the brownian passage time lognormal and weibull distributions and using goodness of fit tests find that the weibull is the preferred distribution we also consider the frequency amplitude distribution of slip events we find that the data clearly do not obey a gutenberg richter distribution instead there is a uniform distribution of event sizes for a large fraction of events

earthquake recurrence on the south hayward fault is most consistent with a time dependent renewal process 1 elastic rebound and stress renewal are important components of earthquake forecasting because if large earthquakes can be shown to be periodic then rupture probability is time dependent while renewal models are used in formal forecasts it has not been possible to exclude the alternate view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration here a consistency test between time dependent and time independent recurrence distributions is made using a monte carlo method to replicate the paleoseismic series on the south hayward fault time dependent distributions with recurrence interval of 210 years and coefficient of variation of 0 6 reproduce the event series on the south hayward 5 times more often than any exponential distribution a highly significant difference as determined using a two tailed z test for relative proportions therefore large hayward fault earthquakes are quasi periodic and are most consistent with a stress renewal process

influence of wind stress wind stress curl and bottom friction on the transport of a model antarctic circumpolar current abstracteddy permitting simulations of a wind driven quasigeostrophic model in an idealized southern ocean setting are used to attempt to describe what sets the wind driven circumpolar transport of the antarctic circumpolar current acc for weak forcing the transport is well described as a linear sum of channel and basin components the authors main focus is on stronger forcing in this regime an eddy driven recirculation appears in the abyssal layer and all time mean circumpolar streamlines are found to stem from a sverdrup like interior the sverdrup flux into drake passage latitudes can then be thought of as the sum of one part that feeds the circumpolar current and another that is associated with the recirculation the relative fractions of this partitioning depend on the bottom drag the midchannel wind stress and the wind stress curl increasing the strength of the bottom drag reduces the recirculation and increases circumpolar transport increasing a zero curl eastward wind stress reduces th

test and application of the time and magnitude predictable model to the intermediate and deep focus earthquakes in the subduction zones of the circum pacific belt abstract the test and application of the time and magnitude predictable model in the subduction zones around the circum pacific belt is performed each subduction zone was separated in several seismogenic regions on the basis of tectonic and geometrical features of the subducting lithosphere and for three different depth ranges the data derived from these seismogenic regions were used in order to check the suitability of the regional time and magnitude predictable model as this model was defined for shallow events the results obtained in the present study confirm that this model appropriately describes the behavior of deep seismicity in these regions since a positive c 0 31 0 003 and a negative c 0 13 0 047 dependence were found for the logarithm of the interevent times and the magnitude of following mainshock respectively on the magnitude of the preceding mainshock moreover the slip predictable model was rejected since a negative dependence was found e 0 19 between the interevent times and the magnitudes of the following mainshock probabilities of occurrence of the future strong m 7 0 events in each seismogenic region have been determined for the next decade conditioned on the previous occurrence of such events the magnitudes of the expected events have also been estimated statistical tests for the estimated probabilities exhibit a good correlation with the occurrence rate of such events furthermore the statistical significance of the model has been studied through additional tests the results of this study demonstrate the validity of the regional time and magnitude predictable model in the areas examined

on the catalytic role of high baroclinic modes in eddy driven large scale circulations abstract this paper investigates the tridimensional consistency of the resolution of eddy scales in simulating large scale flows the generation of classical wind forced eddy driven double gyre circulation is investigated with a multilayered quasi geostrophic model six layers on the vertical have been chosen to assure the convergence of the baroclinic instability emphasis is on the resolution of the high baroclinic modes and its effects on the dynamics of the midlatitude jet several eddy resolving experiments identical except for the horizontal resolution which can be low 20 km or high 10 km are compared in every experiment the scales associated with the first and second baroclinic modes are well resolved but those associated with the third and higher baroclinic modes are so only in 10 km experiments for a better illustration of the importance of the high vertical modes three layer experiments having configurations equivalent to that of the six layer experiments have been conducted note th

what sets the mean transport through drake passage twelve experiments with two coarse resolutions of a global ocean model using a variety of surface forcings are analyzed to address the question of what sets the mean transport through drake passage seven of the experiments do not have an active sea ice model but the remaining five do previous theories have suggested that the drake passage transport is governed by the cape horn sverdrup transport or alternatively is proportional to the square root of the meridional ekman transport at the latitude of drake passage the results presented here do not support either of these theories the drake passage transport depends quite strongly on the isopycnal diffusivity parameter in the model and less strongly on the background vertical diffusivity and horizontal viscosity parameters however when the magnitudes of these parameters are fixed the results show a very strong correlation between drake passage transport and both the strength of the meridional ekman transport at the latitude of drake passage and the thermohaline circulation off the antarctic shelf the relationships are monotonic but not linear the best estimate is that the meridional ekman transport drives 100 sv of drake passage transport while the remaining 30 sv are driven by the global thermohaline circulation

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

a new burgess shale type assemblage from the thin stephen formation of the southern canadian rockies a new burgess shale type assemblage from the stephen formation of the southern canadian rocky mountains is described herein it occurs near stanley glacier in kootenay national park 40 km southeast of the type area near field british columbia while at least a dozen burgess shale localities are known from the thick stephen formation the stanley glacier locality represents the first discovery of burgess shale type fossils from the thin stephen formation the cathedral escarpment an important regional paleotopographic feature has been considered important to the paleoecologic set ting and the preservation of the burgess shale biota however the stanley glacier assemblage was preserved in a distal ramp setting in a region where no evidence of an escarpment is present the low diversity assemblage contains eight new soft bodied taxa including the anomalocaridid stanleycaris hirpex n gen n sp new genus new species pelagic or nektobenthic predators represent the most diverse group whereas in relative abundance the assemblage is dominated by typical cambrian shelly benthic taxa the low diversity of both the benthic taxa and the ichnofauna which includes diminutive trace fossils associated with carapaces of soft bodied arthropods suggests a paleoenvironment with restrictive conditions the stanley glacier assemblage expands the temporal and geographic range of the burgess shale biota in the southern canadian rockies and suggests that burgess shale type assemblages may be common in the thin ste phen formation which is regionally widespread

semi adiabatic model of the deep stratification and meridional overturning abstractan analytical model of the atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the southern ocean and the midlatitude gyres the model expressed here in terms of the two and a half layer framework predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface the approach is based on the classical elements of large scale circulation theory ideal thermocline inertial western boundary currents and eddy controlled antarctic circumpolar current acc models which are combined to produce a consistent three dimensional view of the global overturning the analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes the time mean and eddy induced isopycnal advection of buoyancy the mean stratification of the lower thermocline is determined by the surface fo

structure of earthquake occurrence in space time and magnitude distributions of time between consecutive earthquakes verify an approximately universal scaling law for stationary seismicity the shape of these distributions is shown to arise as a mixture of one distribution for short distance events and an exponential distribution for far off events the distinction from short and long distances being relative to the size of the region studied the distributions of consecutive distances show a double power law decay and verify an approximate scaling law which guarantees the simultaneous fulfillment of the scaling laws for time the interplay between space and time can be seen as well by looking at the distribution of distances for a fixed time separation these results suggest that seismicity can be understood as a series of intertwined independent continuous time random walks with power law distributed waiting times and levy flight jumps however a simple model based on these ideas does not capture the invariance of seismicity under renormalization

geostrophic circulation in a rectangular basin with a circumpolar connection abstract a simple theory is presented for steady geostrophic circulation of a stratified fluid in a rectangular basin with a circumpolar connection the interior flow obeys the plane sverdrup vorticity balance and the circulation is closed by geostrophic boundary currents the circulation is forced by surface thermal gradients and wind driven ekman transport near the latitudes of the circumpolar connection a thermal circumpolar current arises in response to imposed surface thermal gradients and northward ekman transport across the gap latitudes the transport of this model circumpolar current depends on the imposed surface thermal gradients and the gap geometry but not on the strength of the wind forcing in contrast the circulation induced in a related reduced gravity model by sverdrup transport into the gap latitudes has zero zonally integrated zonal transport the thermal current arises as a consequence of the geostrophic constraint which requires that the northern region fill with warm fluid un

location of the antarctic polar front from amsr e satellite sea surface temperature measurements abstract the location of the southern ocean polar front pf is mapped from the first 3 yr of remotely sensed advanced microwave scanning radiometer for the earth observing system amsr e sea surface temperature sst measurements in agreement with previous studies the mean path of the antarctic pf and its standard deviation are strongly influenced by bottom topography however the mean pf path diverges slightly from previous studies in several regions where there is high mesoscale variability although the sst and sst gradient at the pf show spatially coherent seasonal variations with the highest temperature and the lowest temperature gradient during summer the seasonal variations in the location of the pf are not spatially coherent the temporal mean sst at the pf corresponds well to the mean pf path the temperature is high in the atlantic and indian ocean sections and is low in the pacific ocean section where the pf has a more southerly position the relationship of the wind field with the antar

why is probabilistic seismic hazard analysis psha still used abstract even though it has never been validated by objective testing probabilistic seismic hazard analysis psha has been widely used for almost 50 years by governments and industry in applications with lives and property hanging in the balance such as deciding safety criteria for nuclear power plants making official national hazard maps developing building code requirements and determining earthquake insurance rates psha rests on assumptions now known to conflict with earthquake physics many damaging earthquakes including the 1988 spitak armenia event and the 2011 tohoku japan event have occurred in regions relatively rated low risk by psha hazard maps no extant method including psha produces reliable estimates of seismic hazard earthquake hazard mitigation should be recognized to be inherently political involving a tradeoff between uncertain costs and uncertain risks earthquake scientists engineers and risk managers can make important contributions to the hard problem of allocating limited resources wisely but government officials and stakeholders must take responsibility for the risks of accidents due to natural events that exceed the adopted safety criteria

topographic control of southern ocean gyres and the antarctic circumpolar current a barotropic perspective abstractin the southern ocean the antarctic circumpolar current is significantly steered by large topographic features and subpolar gyres form in their lee the geometry of topographic features in

variations in the malvinas current volume transport since october 1992 1 we present a set of new current meter measurements collected to monitor the malvinas current mc near its merger with the brazil current at 40 41 s from december 2001 to february 2003 below a jason 1 altimeter track these measurements are compared to former measurements obtained 8 years earlier at the same location they also provide new information on the core of the mc on the continental slope above the 1000 m isobath where a mooring had been previously lost there most of the velocity variation is along isobath 80 of the variance and shows a significant annual cycle the two data sets provide coherent means and statistical parameters on the vertical structure of the flow a 14 year long time series of mc volume transport is derived using satellite altimetry the good correlation between the altimetry derived transport and the transport estimated from the current meter data persists in time over 0 7 for each measurement period a spectacular shift in the spectral composition of transport variations was observed from 1992 until the end of 1997 transport variations occurred at rather short periods 50 90 days and to some degree around 180 days whereas after year 2000 longer periods including a seasonal cycle predominated altimetry derived anomalies of surface geostrophic velocities along the core of the mc show a similar shift in spectral composition suggesting a remote forcing origin

standing eddies in the meridional overturning circulation abstractthe role of standing eddies for the meridional overturning circulation moc is discussed the time mean isopycnal meridional streamfunction is decomposed into a time and zonal mean part a standing eddy part and a transient eddy part it turns out that the construction of an isopycnal moc with an exactly vanishing standing eddy part has to be performed by zonal integration along depth dependent horizontal isolines of time mean density in contrast zonal integration along time mean geostrophic streamlines generally only leads to an isopycnal moc with a reduced standing eddy part a generalized approach of constructing meridional transport streamfunctions by two tracer fields and the generalized way to neutralize the corresponding standing eddy part is given to summarize the discussion using the results of an idealized southern ocean model it is demonstrated that neglecting the depth dependence of the zonal integration paths by integrating along density contours or geostrophic streamlines of a

fixed recurrence and slip models better predict earthquake behavior than the time and slip predictable models 1 repeating earthquakes 1 the behavior of individual events in repeating earthquake sequences in california taiwan and japan is better predicted by a model with fixed inter event time or fixed slip than it is by the time and slip predictable models for earthquake occurrence given that repeating earthquakes are highly regular in both inter event time and seismic moment the time and slip predictable models seem ideally suited to explain their behavior taken together with evidence from the companion manuscript that shows similar results for laboratory experiments we conclude that the short term predictions of the time and slip predictable models should be rejected in favor of earthquake models that assume either fixed slip or fixed recurrence interval this implies that the elastic rebound model underlying the time and slip predictable models offers no additional value in describing earthquake behavior in an event to event sense but its value in a long term sense cannot be determined these models likely fail because they rely on assumptions that oversimplify the earthquake cycle we note that the time and slip of these events is predicted quite well by fixed slip and fixed recurrence models so in some sense they are time and slip predictable while fixed recurrence and slip models better predict repeating earthquake behavior than the time and slip predictable models we observe a correlation between slip and the preceding recurrence time for many repeating earthquake sequences in parkfield california this correlation is not found in other regions and the sequences with the correlative slip predictable behavior are not distinguishable from nearby earthquake sequences that do not exhibit this behavior

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

quasi periodic occurrence of earthquakes in the 1978 1986 bishop mammoth lakes sequence eastern california abstract in december 1984 ryall and hill noted that the five principal events in the bishop mammoth lakes earthquake sequence occurred at intervals of about 1 5 yr with a standard deviation for an individual event of 0 25 yr some data selection was involved in identifying the principal events although the choices seemed reasonable the recent chalfant valley earthquake m l 6 4 21 july 1986 followed the last prior principal event in the bishop mammoth lakes sequence by 1 65 yr and no important activity intervened except one aftershock from the prior event thus the chalfant valley earthquake could have been forecast from the observed periodicity however the precision of the forecast 0 8 yr for the 95 per cent confidence interval is not sufficient to furnish convincing evidence that the bishop mammoth lakes sequence is quasi periodic extrapolation of the trend established by the six previous events suggests that the next event in the bishop mammoth lakes sequence would be expected in december 1987 0 7 yr 95 per cent confidence interval the regularity of the bishop mammoth lakes sequence is comparable to that of the parkfield california sequence average interevent interval 20 8 yr with a standard deviation for an individual interval of 6 2 yr both sequences consist of six events there is a plausible physical explanation for the periodicity observed at parkfield such an explanation for the bishop mammoth lakes sequence is lacking

the regional time and magnitude predictable model and its application to the alpine himalayan belt abstract the regional time and magnitude predictable model has been introduced and has been shown to be appropriate to describe the behaviour in the occurrence of mainshocks the model implies that the magnitude of the preceding mainshock in a seismogenic region that is the largest earthquake during a seismic excitation governs the time of occurrence and the magnitude of the expected mainshock in this region this model has been applied in 149 seismogenic regions of the alpine himalayan seismic belt the model probability for the occurrence of the next very strong main shock ms 6 5 during the decade 1993 2002 as well as the magnitude of this shock in each of these regions have been calculated furthermore two tests have been performed to check the validity of this model these tests have shown the reliability of the model and its superiority compared to the classical time independent model

southern ocean response to relative velocity wind stress forcing an eddy resolving quasigeostrophic model of the southern ocean coupled to a dynamic atmospheric mixed layer is used to compare the performance of two different wind stress parameterization schemes the first is the standard quadratic drag law based on atmospheric velocity alone whereas the second more exact formulation is based on the difference between ocean and atmosphere velocities the two different schemes give very similar magnitudes of mean stress however the relative velocity scheme has substantially lower power input resulting in a weaker eddy field and consequently greater circumpolar transport these results are explored in terms of the existing theories of the antarctic circumpolar current including eddy saturation and eddy damping and the implications for modeling the southern ocean are discussed

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing

suppression of baroclinic instability in horizontally sheared flows abstract baroclinic instability in the presence of a meridionally sheared barotropic component to the basic flow is studied using a two level model the inclusion of a linear shear results in merldionally confined normal modes with growth rates much reduced compared to the unsheared case similar results hold for more complicated situations such as a baroclinic jet with barotropic shear the results are applied to life cycle calculations in which it is shown that the nonlinear decay phase of a baroclinic disturbance sets up barotropic shears whichtend to suppress further baroclinic developments an example of the southern hemisphere winter mean flow is found to be strongly stabilized by virtue of a strong sheared barotropic part of the zonal flow