formation and spreading of red sea outflow water in the red sea hydrographic data chlorofluorocarbon 12 cfc 12 and sulfur hexafluoride sf6 measurements collected in march 2010 and september october 2011 in the red sea as well as an idealized numerical experiment are used to study the formation and spreading of red sea outflow water rsow in the red sea analysis of inert tracers potential vorticity distributions and model results confirm that rsow is formed through mixed layer deepening caused by sea surface buoyancy loss in winter in the northern red sea and reveal more details on rsow spreading rates pathways and vertical structure the southward spreading of rsow after its formation is identified as a layer with minimum potential vorticity and maximum cfc 12 and sf6 ventilation ages of seawater within the rsow layer calculated from the partial pressure of sf6 psf6 range from 2 years in the northern red sea to 15 years at 17 n the distribution of the tracer ages is in agreement with the model circulation field which shows a rapid transport of rsow from its formation region to the southern red sea where there are longer circulation pathways and hence longer residence time due to basin wide eddies the mean residence time of rsow within the red sea estimated from the psf6 age is 4 7 years this time scale is very close to the mean transit time 4 8 years for particles from the rsow formation region to reach the exit at the strait of bab el mandeb in the numerical experiment

sensitivity studies of the red sea eddies using adjoint method the topography data is derived from general bathymetric chart of the oceans gebco https www gebco net the open boundary conditions are extracted from the estimating the circulation and climate of the ocean ecco product https ecco jpl nasa gov products the data supporting the analysis presented here can be found at figshare https figshare com articles data for 2018jc014531r 7243184 the research reported in this manuscript is supported by king abdullah university of science and technology kaust and made use of the resources of the supercomputing laboratory and computer clusters at kaust

an oceanographic nowcast forecast system for the red sea we describe the application of a nowcast forecast system for three dimensional currents temperature and salinity to the red sea the modeling system is constructed around a high resolution 6 7 km primitive equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel it is coupled to near real time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data the temperature and salinity data are ingested into the model daily using a nudged objective analysis technique because the red sea is a relatively narrow basin bounded by typically high and complex orography a single layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40 km resolution meteorological fields by taking into account orographic steering of the low level winds in order to validate the modeling system two very complete hydrographic surveys of the red sea were undertaken and their results are described both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the red sea is variable and often composed of a series of eddies or subgyres mainly anticyclones immediately before one survey the winds tended to be along axis while just before the second they tended to be cross axis the red sea circulation was much more eddy like when the winds were cross axis by forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography when the winds are more along axis there is less interaction with the adjacent orography and consequently there are fewer eddies in the red sea

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

direct observations of seasonal exchange through the bab el mandab strait the exchange flow between the red sea and the gulf of aden indian ocean through the bab el mandab strait was measured continuously for 10 months june 1995 march 1996 adcp and temperature salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the gulf of aden and the high salinity outflow layer from the red sea the timing structure and evolution of the summer season mid depth intrusion of cold low salinity water into the red sea from the gulf of aden is measured for the complete intrusion cycle of 1995 we unexpectedly find the deep outflow still strong in june 1995 with speeds of 0 6 m sec and transport of 0 4 sv 1 sv 106 m sec from july to mid september the deep outflow persists but is attenuated to speeds of 0 2 m sec and transport of 0 05 sv the dominant summer feature the cold low salinity intermediate layer intrusion persists for 3 months occupies 70 of the water column in the strait and carries approximately 1 7 1012 m of cold nutrient rich water into the red sea the winter regime begins in mid september is fully developed by early november and continues to the end of our first observation interval in march 1996 speeds in the lower layer are 0 8 1 0 m sec and 0 4 0 6 m sec in the upper layer at maximum exchange in mid february outflow transport reaches 0 7 sv ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along channel wind forcing and perhaps to coastally trapped waves

process modeling studies of physical mechanisms of the formation of an anticyclonic eddy in the central red sea surface drifters released in the central red sea during april 2010 detected a well defined anticyclonic eddy around 23 n this eddy was 45 60 km in radius with a swirl speed up to 0 5 m s the eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross isobath shipboard ctd adcp survey around that region the unstructured grid finite volume community ocean model fvcom was configured for the red sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness the model was capable of reproducing the observed anticyclonic eddy with the same location and size diagnosis of model results suggests that the eddy can be formed in a red sea that is subject to seasonally varying buoyancy forcing with no wind but that its location and structure are significantly altered by wind forcing initial distribution of water stratification and southward coastal flow from the upstream area momentum analysis indicates that the flow field of the eddy was in geostrophic balance with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing

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

gas hydrate crystals may help build reefs during a recent cruise in the porcupine basin off southwest ireland we discovered two extensive and hitherto largely unsuspected deep water reef provinces including a giant cluster of hundreds of buried mounds the ring shapes of many reefs suggest that they are caused by an axial fluid expulsion at the sea bed a transient flow well confined in space and time we are exploring various hypotheses but a stimulating avenue for research is opened by a glacially controlled growth pulse and subsequent decay of a shallow layer of gas hydrates as a methane buffer and probably indirectly as a ground for overlying biological communities

earthquake early warning system in southern italy methodologies and performance evaluation we investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity pgv from moderate to large earthquakes occurring in the southern apennines italy simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the pgv following an evolutionary probabilistic approach the system performance is measured through the effective lead time elt i e the time interval between the arrival of the first s wave and the time at which the probability to observe the true pgv value within one standard deviation becomes stationary and the probability of prediction error ppe which provides a measure of pgv prediction error the regional maps of elt and ppe show a significant variability around the fault up to large distances thus indicating that the system s capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault

broadband simulations for mw 7 8 southern san andreas earthquakes ground motion sensitivity to rupture speed using the high performance computing resources of the southern california earthquake center we simulate broadband 0 10 hz ground motions for three m w 7 8 rupture scenarios of the southern san andreas fault the scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0 96 0 89 and 0 84 times the local shear wave velocity consistent with previous simulations a southern hypocenter efficiently channels energy into the los angeles region along the string of basins south of the san gabriel mountains however we find the basin ground motion levels are quite sensitive to the prescribed rupture speed with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15 these results have important implications for estimating seismic hazards in southern california and emphasize the need for improved understanding of earthquake rupture processes

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

comment on earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records by aldo zollo maria lancieri and stefan nielsen an early warning system should determine the loca tion and magnitude of an earthquake as rapidly as possiblein order to broadcast an alarm to regions that will undergosevere ground shaking it was recently claimed by zollo etal 2006 that earthquake size could be determined fromonly the first 2 seconds of p or s wave strong motion data this represents a fraction of the rupture time for larger m 7 events using this relatively short amount of data themethod of analysis was to find the peak ground displace ment pgd which was reported to scale with earthquakemagnitude such rapid information would play an importantand much needed role in an earthquake early warning eew system here we perform a similar analysis onstrong motion data from the kik net and k net arrays injapan and find no compelling evidence that the peak grounddisplacement during the first couple of seconds of p wave isrelated to the eventual size of a large earthquake

real time finite fault rupture detector finder for large earthquakes to provide rapid estimates of fault rupture extent during large earthquakes we have developed the finite fault rupture detector algorithm finder finder uses image recognition techniques to detect automatically surface projected fault ruptures in real time assuming a line source by estimating their current centroid position length l and strike the approach is based on a rapid high frequency near far source classification of ground motion amplitudes in a dense seismic network station spacing 50 km and comparison with a set of pre calculated templates using matching by correlation to increase computational efficiency we perform the correlation in the wavenumber domain finder keeps track of the current dimensions of a rupture in progress errors in l are typically on the same order as station spacing in the network the continuously updated estimates of source geometries as provided by finder make predicted shaking intensities more accurate and thus more useful for earthquake early warning shakemaps and related products the applicability of the algorithm is demonstrated for several recorded and simulated earthquakes with different focal mechanisms including the 2009 m w 6 3 l aquila italy the 1999 m w 7 6 chichi taiwan and the m w 7 8 shakeout scenario earthquake on the southern san andreas fault california

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

on the role of eddies and surface forcing in the heat transport and overturning circulation in marginal seas the factors that determine the heat transport and overturning circulation in marginal seas subject to wind forcing and heat loss to the atmosphere are explored using a combination of a high resolution ocean circulation model and a simple conceptual model the study is motivated by the exchange between the subpolar north atlantic ocean and the nordic seas a region that is of central importance to the oceanic thermohaline circulation it is shown that mesoscale eddies formed in the marginal sea play a major role in determining the mean meridional heat transport and meridional overturning circulation across the sill the balance between theoceaniceddyheatfluxandatmosphericcooling ascharacterizedbyanondimensionalnumber isshownto be the primary factor in determining the properties of the exchange results from a series of eddy resolving primitive equation model calculations for the meridional heat transport overturning circulation density of convective waters and density of exported waters compare well with predictions from the conceptual model over a wide range of parameter space scaling and model results indicate that wind effects are small and the mean exchange is primarily buoyancy forced these results imply that one must accurately resolve or parameterize eddy fluxes in order to properly represent the mean exchange between the north atlantic and the nordic seas and thus between the nordic seas and the atmosphere in climate models

physical and biological characteristics of the winter summer transition in the central red sea the central red sea crs lies between two distinct hydrographic and atmospheric regimes in the southern red sea seasonal monsoon reversal regulates the exchange of water between the red sea and the indian ocean in the northern red sea intermediate and occasionally deep water are formed during winter to sustain the basin s overturning circulation highly variable mesoscale eddies and the northward flowing eastern boundary current ebc determine the physical and biogeochemical characteristics of the crs ship based and glider observations in the crs between march and june 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the ebc flow less saline and relatively warmer water of indian ocean origin reaches the crs via the ebc initially an anticyclonic eddy with diameter of 140km penetrating to 150m depth with maximum velocities up to 30 35 cm s 1 prevails in the crs this anticyclonic eddy appears to block or at least redirect the northward flow of the ebc dissipation of the eddy permits the near coastal northward flow of the ebc and gives place to a smaller cyclonic eddy with a diameter of about 50km penetrating to 200m depth by the end of may as the northerly winds become stronger and persistent throughout the basin characteristic of the summer southwest monsoon wind regime the ebc and its associated lower salinity water became less evident replaced by the saltier surface water that characterizes the onset of the summer stratification in the crs

upper slope sediment waves in the cilician basin northeastern mediterranean large sediment waves have been observed within the upper slope deposits of the cilician basin northeastern mediterranean at the interfluve between two submarine canyons present offshore of the mersin shelf there are several generations of sediment waves stacked within the sedimentary sequence with the most recent bedforms found on the seabed in an area consisting of fine grained sediments the surficial sediment wave field estimated to cover an area of 55 km2 is found at water depths between 250 and 310 m the buried sediment wave fields have similar dimensions but they are located further downslope wave dimensions increase with water depth and depth in the sedimentary sequence the largest bedforms reach 40 m in height and 1 8 km in length most waves appear to have been migrating upslope i e towards the north northeast and this migration direction is mostly consistent throughout the sedimentary sequence this consistency indicates similar mechanisms of formation and maintenance over a considerable time interval the morphology and migration pattern of the observed bedforms suggests that sedimentation in the cilician basin during wave formation has been controlled by near bed flows resembling those generated by the present asia minor current although these flows may have been stronger in the past than they are at present

sensitivity of red sea circulation to monsoonal variability during the holocene an integrated data and modeling study received 20 october 2009 revised 6 march 2010 accepted 30 june 2010 published 4 november 2010 1 we used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the red sea in response to reduced sea level and modified atmospheric conditions during the holocene with holocene sea level close to the modern level the red sea was sensitive to changes in atmospheric conditions and it only shows a relatively mild response to sea level change changes in the monsoon system influence the exchange flow through the strait of bab el mandab the meridional overturning circulation of the red sea and its hydrography forced by humid conditions the modeled red sea temperature increased by 1 5 c while when arid conditions were imposed the temperature decreased by 2 5 c similar heating and cooling events during the early and late holocene are seen in a sea surface temperature record from the northern red sea derived from the temperature sensitive tex86 molecular biomarker which suggests that humid conditions prevailed during the early holocene and more arid conditions prevailed during the late holocene the gradual decline in red sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength this monsoon trend and the resulting changes in the red sea circulation are supported by the distribution of crenarchaea fossil lipids in red sea sediments from this period monsoon driven changes in the exchange flow through the strait of bab el mandab affected the crenarchaea population structure and therefore their molecular fossil distribution in the sediments of the red sea potentially provides an index for the summer monsoon strength during the holocene

the barra fan a bottom current reworked glacially fed submarine fan system abstract on the basis of sedimentary structures textures and ichofauna seven depositional facies have been recognised in cores from the barra fan region of the hebrides slope sedimentary facies are combined into three genetic groups a c that represent their primary mode of deposition a sandy to muddy contourite facies a a1 and a2 which represent an overall coarsening upward sequence caused by an increase in bottom current velocity over time b disorganised glaciomarine deposits including the glaciomarine dumpstone of facies b and facies b1 deposited as a result of ice rafting and glaciomarine sedimentation and c hemipelagite facies c and c1 which are the result of normal marine hemipelagic settling it is most likely that all contourite facies a a2 identified in this study are holocene in terms of its diverse morphological elements and varied facies this high latitude submarine fan is truly composite in nature however a broad three stage glacial to post glacial evolutionary system is recognised during which different processes and process combinations were dominant during the last glacial period low stand system tract downslope processes including debris flows and minor turbidity currents sculpted an irregular slope topography little in the way of bottom current activity was evident staged deglaciation was accompanied by rising sea level and high sedimentation rates across the region this created an unstable margin prone to extensive sliding and slumping that masked any effects of an incipient alongslope current the present high stand system tract is dominated by a strong slope current that became fully active during the early part of the holocene low sedimentation rates diminished sediment supply and strong bottom current activity led to development of the sandy contourite sheeted drift system across the mid slope region little downslope movement is evident during this period so that the slope topography is being slowly smoothed and remoulded by active bottom currents

shallow sedimentary rock as a fragile geological feature effects of clay content and hydrology on frictional strength strong long period 3 s seismic waves impose dynamic strains on the shallow subsurface the dynamic strain is the dynamic velocity divided by the phase velocity of the waves the dynamic stress is the strain times the shear modulus a testable hypothesis is that the shear modulus of the rock self organizes so that the rock barely fails in friction with typical imposed dynamic strains the predicted value of stiffness divided by depth is then independent of depth for constant rock density and constant coefficient of friction with the water table at the surface predicted stiffness divided depth deviates from constancy for finite water table depth prior laboratory studies indicate that the coefficient of friction is lower in clay rich rocks than in clay free rocks these effects provide appraisal of the concept in which hydrology and lithology are constrained four boreholes near parkfield california qualitatively exhibit the predicted effects there is some indication of the predicted effect of water table depth within accumulating sediments penetrated by borehole mcglincy mgcy in the santa clara valley of california but the effect of clay is not well resolved due to a dearth of clay rich beds

cybershake derived ground motion prediction models for the los angeles region with application to earthquake early warning real time applications such as earthquake early warning eew typically use empirical ground motion prediction equations gmpes along with event magnitude and source to site distances to estimate expected shaking levels in this simplified approach effects due to finite fault geometry directivity and site and basin response are often generalized which may lead to a significant under or overestimation of shaking from large earthquakes m 6 5 in some locations for enhanced site specific ground motion predictions considering 3 d wave propagation effects we develop support vector regression svr models from the scec cybershake low frequency 415 000 finite fault rupture scenarios 6 5 m 8 5 for southern california defined in ucerf 2 0 we use cybershake to demonstrate the application of synthetic waveform data to eew as a proof of concept being aware that these simulations are not yet fully validated and might not appropriately sample the range of rupture uncertainty our regression models predict the maximum and the temporal evolution of instrumental intensity mmi at 71 selected test sites using only the hypocentre magnitude and rupture ratio which characterizes uni and bilateral rupture propagation our regression approach is completely data driven where here the cybershake simulations are considered data and does not enforce pre defined functional forms or dependencies among input parameters the models were established from a subset 20 per cent of cybershake simulations but can explain mmi values of all 400 k rupture scenarios with a standard deviation of about 0 4 intensity units we apply our models to determine threshold magnitudes and warning times for various active faults in southern california that earthquakes need to exceed to cause at least moderate strong or very strong shaking in the los angeles la basin these thresholds are used to construct a simple and robust eew algorithm to declare a warning the algorithm only needs to locate the earthquake and to verify that the corresponding magnitude threshold is exceeded the models predict that a relatively moderate m6 5 7 earthquake along the palos verdes newport inglewood rose canyon elsinore or san jacinto faults with a rupture propagating towards la could cause very strong to severe shaking in the la basin however warning times for these events could exceed 30 s

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

a 3d seismic study of the morphology and spatial distribution of buried coral banks in the porcupine basin sw of ireland an industrial 3d seismic data volume supplemented by high resolution 2d seismics was used to study part of a province of buried mound structures in the porcupine basin southwest of ireland these magellan mounds and their associated moat structures interpreted as scour marks were mapped semi automatically from time structure and isopach maps image analysis techniques such as a tophat transformation mathematical morphology were applied for feature extraction size measures of both mounds and moats were derived from the resulting maps and summarised by means of some descriptive statistics spatial variability in mound occurrence and characteristics was investigated comparison with other mound structures in the area allowed the magellan mounds to be identified as coral banks associated with the growth of cold water deep sea coral species such as lophelia pertusa l and madrepora oculata l mound growth clearly started in a single event confined in time and space bottom currents and oceanographic characteristics of the surrounding water masses influenced this sudden process and the further mound development however the analysis of the 3d seismic data set did not allow us to identify unambiguously the actual cause for the sudden mound start up the mounds appear to have formed a dense cluster of structures of moderate size which are significantly elongated in a n s direction they are associated with even more elongated moats implying a periodically reversing n s directed current influence a spatial density of one mound per km2 was measured which remains more or less constant over the area investigated mound width and cross sectional area and moat shape gradually change across the mound province due to spatially changing environmental conditions at the initial growth stages of the mounds and during their further development interplay between current regime and sedimentation

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

physical mechanisms routing nutrients in the central red sea mesoscale eddies and boundary currents play a key role in the upper layer circulation of the red sea this study assesses the physical and biochemical characteristics of an eastern boundary current ebc and recurrent eddies in the central red sea crs using a combination of in situ and satellite observations hydrographic surveys in november 2013 autumn and in april 2014 spring in the crs 22 15 24 1 n included a total of 39 and 27 ctd stations respectively in addition high resolution hydrographic data were acquired in spring 2014 with a towed undulating vehicle scanfish in situ measurements of salinity temperature chlorophyll fluorescence colored dissolved organic matter cdom and dissolved nitrate phosphorous ratios reveal distinct water mass characteristics for the two periods an ebc observed in the upper 150 m of the water column during autumn transported low salinity and warm water from the south toward the crs patches of the low salinity water of southern origin tended to contain relatively high concentrations of chlorophyll and cdom the prominent dynamic feature observed in spring was a cyclonic anticyclonic eddy pair the cyclonic eddy was responsible for an upward nutrient flux into the euphotic zone higher chlorophyll and cdom concentrations and concomitant lower nitrate phosphorous ratios indicate the influence of the ebc in the crs at the end of the stratified summer period

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

determination of earthquake early warning parameters τ c and pd for southern california summary we explore a practical approach to earthquake early warning in southern california by determining a ground motion period parameter c and a high pass filtered displacement amplitude parameter pd from the initial 3 s of the p waveforms recorded at the southern california seismic network stations for earthquakes with m 4 0 at a given site we estimate the magnitude of an event from c and the peak ground motion velocity pgv from pd the incoming threecomponent signals are recursively converted to ground acceleration velocity and displacement the displacements are recursively filtered with a one way butterworth high pass filter with a cut off frequency of 0 075 hz and a p wave trigger is constantly monitored when a trigger occurs c and pd are computed we found the relationship between c and magnitude m for southern california and between pd and pgv for both southern california and taiwan these two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the p wave when the station density is high the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach in an ideal situation such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds

real time earthquake detection and hazard assessment by elarms across california 1 elarms is a network based methodology for rapid earthquake detection location and hazard assessment in the form of magnitude estimation and peak ground motion prediction the methodology is currently being tested as part of the real time seismic system in california leveraging the resources of the california integrated seismic network cisn and the advanced national seismic system a total of 603 velocity and acceleration sensors at 383 sites across the state stream waveform data to elarms processing modules at three network processing centers where waveforms are reduced to a few parameters these parameters are then collected and processed at uc berkeley to provide a single statewide prediction of future ground shaking that is updated every second the system successfully detected the mw 5 4 alum rock earthquake in northern california for which it generated an accurate hazard prediction before peak shaking began in san francisco it also detected the mw 5 4 chino hills earthquake in southern california the median system latency is currently 11 8 sec the median waveform data latency is 6 5 sec

real time testing of the on site warning algorithm in southern california and its performance during the july 29 2008 mw5 4 chino hills earthquake the real time performance of the c p d on site early warning algorithm currently is being tested within the california integrated seismic network cisn since january 2007 the algorithm has detected 58 local earthquakes in southern california and baja with moment magnitudes of 3 0 m w 5 4 combined with newly derived station corrections the algorithm allowed for rapid determination of moment magnitudes and modified mercalli intensity mmi with uncertainties of 0 5 and 0 7 units respectively the majority of reporting delays ranged from 9 to 16 s the largest event the july 29 2008 m w5 4 chino hills earthquake triggered a total of 60 cisn stations in epicentral distances of up to 250 km magnitude predictions at these stations ranged from m w4 4 to m w6 5 with a median of m w5 6 the closest station would have provided up to 6 s warning at los angeles city hall located 50 km to the west northwest of chino hills

observations and modeling of long period ground motion amplification across northeast china basin resonances can significantly amplify and prolong ground shaking and accurate site amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins in this work we estimate the site amplification of long period 2 10 s ground motions across northeast china for both surface waves and vertically incident shear waves the spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types however the site response of surface waves is typically twice as high as that of shear waves at most basin sites we further show that these site amplification features can be well explained by predictions based on the local one dimensional structure at each site our results highlight the importance of accounting for surface wave contributions and demonstrate the usefulness of semi analytical theory for surface wave amplification which may be broadly applicable in future seismic hazard analysis

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

on the crossover of boundary currents in an idealized model of the red sea the west to east crossover ofboundarycurrents has been seen in mean circulationschemes fromseveral past models of the red sea this study investigates the mechanisms that produce and control the crossover in an idealized eddy resolving numerical model of the red sea the authors also review the observational evidence and derive an analytical estimate for the crossover latitude the surface buoyancy loss increases northward in the idealized model and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonicgyreinthenorth in themidbasin thenorthwardsurfaceflow crossesfromthewestern boundarytothe eastern boundary numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0 b and the meridional gradient of surface buoyancy forcing in the analytical estimate which is based on quasigeostrophic b plane dynamics the crossover is predicted to lie at the latitude where the net potential vorticity advection including an eddy component is zero various terms in the potential vorticity budget can be estimated using a buoyancy budget a thermal wind balance and a parameterization of baroclinic instability

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

climatological coastal jet collision intermediate water formation and the general circulation of the red sea the authors present climatologies of a numerical model of the red sea focusing on the dynamics of winter intermediate water formation northward flowing boundary currents are identified as the major dynamical elements at the northern boundary the eastern current follows the geometry eventually turning back to the south at 268n and the western wall the two boundary currents collide at the collision site the denser eastern current subducts under the western boundary current the subduction forces the western boundary current eastward into the interior convection communicates the surface fluxes to the downwelled plume and intermediate water forms the estimated rate 0 11 sv sv 106 m3 s21 agrees with previous estimates the authors identify basin scale sea surface tilt to the north due to variable thermohaline forcings as the key dynamical variable the resultant geostrophic eastward cross channel flow interacts with the boundaries and creates upwelling and surface topography spatial patterns that drive the coastal jets upwelling induced vortex stretching dominates the vorticity balance and governs the separation of the western boundary current from the western wall the process ceases in the summer

probabilistic prediction of rupture length slip and seismic ground motions for an ongoing rupture implications for early warning for large earthquakes earthquake earlywarning eew predicts future ground shaking based on presently available data long ruptures present the best opportunities for eew since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times predicting the shaking from large earthquakes however requires some estimate of the likelihood of the future evolution of an ongoing rupture an eew system that anticipates future rupture using the present magnitude or rupture length together with the gutenberg richter frequencysize statistics will likely never predict a large earthquake because of the rare occurrence of extreme events however it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake to investigate the relationship between the slip and the eventual size of an ongoing rupture we simulate suites of 1 d rupture series from stochastic models of spatially heterogeneous slip we find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a big one the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect we conclude that aneewsystem for large earthquakes needs some mechanism for the rapid recognition of the causative fault e g from real time gps measurements and consideration of its smoothness an eew system for large earthquakes on smooth faults such as the san andreas fault could be implemented in two ways the system could issue a warning whenever slip on the fault exceeds a few metres because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault a more sophisticated eew system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions and using this information could provide probabilistic predictions of seismic ground motions along the evolving rupture the decision on whether an eew system should be realized in the first or in the second way or in a combination of both is user specific

multidecadal ocean variability and nw european ice sheet surges during the last deglaciation a multiproxy paleoceanographic record from the atlantic margin off the british isles reveals in unprecedented detail discharges of icebergs and meltwater in response to sea surface temperature increases across the last deglaciation we observe the earliest signal of deglaciation as a moderate elevation of sea surface temperatures that commenced with a weakly developed thermocline and the presence of highly ventilated intermediate waters in the rockall trough this warming pulse triggered a series of multidecadal ice rafted debris peaks that culminated with a major meltwater discharge at 17 500 years before present related to ice sheet disintegration across the nw european region the impact of meltwater caused a progressive reduction in deep water ventilation and a sea surface cooling phase that preceded the collapse of the laurentide ice sheet during heinrich event 1 by 500 1000 years a similar sequence of rapid ocean ice sheet interaction across the european continental margin is identified during the bolling allerod to younger dryas transition the strategic location of our sediment core suggests a sensitive and rapid response of ice sheets in nw europe to transient increases in thermohaline heat transport

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

benthic dynamics at the carbonate mound regions of the porcupine sea bight continental margin a brief review is given of some dynamical processes that influence the benthic dynamics within the carbonate mound provinces located at the porcupine bank sea bight margin ne atlantic the depth range of the mounds in this region 600 1 000 m marks the upper boundary of the mediterranean outflow water above which eastern north atlantic water dominates both water masses are carried northwards by the eastern boundary slope current in the benthic boundary layer both the action of internal waves and other tidal period baroclinic waves may enhance the bottom currents and add to both the residual and maximum flow strength both residual and maximum bottom currents vary at different mound locations with stronger currents found at belgica se porcupine sea bight mound and pelagia nw porcupine bank mound regions whilst weakest currents are found at the hovland and magellan mounds at the northern sea bight margin the differences may be attributed to the presence of internal waves pelagia or bottom intensified diurnal waves belgica these different dynamical regimes are likely to have implications for the distribution patterns of live coral at the different locations

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

on the origin and pathway of the saline inflow to the nordic seas insights from models the behaviours of three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are investigated in order to elucidate the routes and mechanisms by which saline water masses of southern origin provide inflows to the nordic seas an existing hypothesis is that mediterranean overflow water mow is carried polewards in an eastern boundary undercurrent and provides a deep source for these inflows this study however provides an alternative view that the inflows are derived from shallow sources and are comprised of water masses of western origin carried by branches of the north atlantic current nac and also more saline eastern north atlantic water enaw transported northwards from the bay of biscay region via a shelf edge current sec flowing around the continental margins in two of the models the mow flows northwards but reaches only as far as the porcupine bank 53 n in third model the mow also invades the rockall trough extending to 60 n however none of the models allows the mow to flow northwards into the nordic seas instead they all support the hyporthesis of there being shallow pathways and that the saline inflows to the nordic seas result from nac derived and enaw water masses which meet and partially mix in the rockall trough volume and salinity transports into the southern rockall trough via the sec are in the various models between 25 and 100 of those imported by the nac and are also a similarly significant proportion 20 75 of the transports into the nordic seas moreover the highest salinities are carried northwards by the sec these being between 0 13 and 0 19 psu more saline at the southern entrance to the trough than those in the nac derived waters this reveals for the first time the importance of the sec in carrying saline water masses through the rockall trough and into the nordic seas furthermore the high salinities found on density surfaces appropriate to the mow in the nordic seas are shown to result from the wintertime mixing of the saline near surface waters advected northwards by the sec nac system throughout we have attempted to demonstrate the extent to which the models agree or disagree with interpretations derived from observations so that the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

testing long period ground motion simulations of scenario earthquakes using the mw 7 2 el mayor cucapah mainshock evaluation of finite fault rupture characterization and 3d seismic velocity models using a suite of five hypothetical finite fault rupture models we test the ability of long period t 2 0 s ground motion simulations of scenario earthquakes to produce waveforms throughout southern california consistent with those recorded during the 4 april 2010 m w 7 2 el mayor cucapah earthquake the hypothetical ruptures are generated using the methodology proposed by graves and pitarka 2010 and require as inputs only a general description of the fault location and geometry event magnitude and hypocenter as would be done for a scenario event for each rupture model two southern california earthquake center three dimensional community seismic velocity models cvm 4m and cvm h62 are used resulting in a total of 10 ground motion simulations which we compare with recorded ground motions while the details of the motions vary across the simulations the median levels match the observed peak ground velocities reasonably well with the standard deviation of the residuals generally within 50 of the median simulations with the cvm 4m model yield somewhat lower variance than those with the cvm h62 model both models tend to overpredict motions in the san diego region and underpredict motions in the mojave desert within the greater los angeles basin the cvm 4m model generally matches the level of observed motions whereas the cvm h62 model tends to overpredict the motions particularly in the southern portion of the basin the variance in the peak velocity residuals is lowest for a rupture that has significant shallow slip 5 km depth whereas the variance in the residuals is greatest for ruptures with large asperities below 10 km depth overall these results are encouraging and provide confidence in the predictive capabilities of the simulation methodology while also suggesting some regions in which the seismic velocity models may need improvement

circulation and exchange in choked marginal seas a theory for the exchange between a rotating buoyancy forced marginal sea and an ocean is developed and tested numerically cooling over the marginal sea leads to sinking and sets up a two layer exchange flow with a warm surface layer entering from the ocean and a cool layer exiting at depth the connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled the incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies consistent with the overall heat and volume balances for the marginal sea there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait included in this family is a limiting maximal exchange solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section the state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or in some cases the ocean depending on the configuration of the exchange long wave information may be blocked from entering the strait from the marginal sea from the open ocean or both the scenario that holds determines what is predicted and what needs to be input numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill the comparison is reasonable in most cases though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values the analytical model is an alternative to the price and yang and siddall et al models of a marginal sea outflow

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

seasonal overturning circulation in the red sea 2 winter circulation author posting 0american geophysical union 2014 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 119 2014 2263 2289 doi 10 1002 2013jc009331

shallow s wave well logs as an indicator of past strong shaking from earthquakes on the newport inglewood fault numerical calculations assuming linear elasticity by bose et al 2014 indicate that an m w 7 75 earthquake on the newport inglewood fault would cause 5 m s of horizontal peak ground velocity pgv within the los angeles basin however the dynamic strain from this event would take much of the uppermost few hundred meters of basin rock beyond its frictional elastic limit stiff quartz rich beds within the basin are fragile geological features that would fail and crack before the rest of the clay rich rock mass repeated cracking would reduce the shear modulus of the quartz rich beds to the level that cracking barely occurred during strong events when interpreted in this way data from such stiff beds near the los angeles international airport indicate past pgv of 1 6 m s comparable with near field records from the strike slip 2002 denali and 1992 landers earthquakes numerical calculations capable of representing nonlinear failure within shallow bedded rocks are warranted online material digital rosrine s wave borehole logs

evaluation and optimization of seismic networks and algorithms for earthquake early warning the case of istanbul turkey earthquake early warning eew systems should provide reliable warnings as quickly as possible with a minimum number of false and missed alarms using the example of the megacity istanbul and based on a set of simulated scenario earthquakes we present a novel approach for evaluating and optimizing seismic networks for eew in particular in regions with a scarce number of instrumentally recorded earthquakes we show that while the current station locations of the existing istanbul eew system are well chosen its performance can be enhanced by modifying the parameters governing the declaration of warnings furthermore unless using ocean bottom seismometers or modifying the current eew algorithm additional stations might not lead to any significant performance increase

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

terrigenous fluxes at the celtic margin during the last glacial cycle the sedimentary sections of three cores from the celtic margin provide high resolution records of the terrigenous fluxes during the last glacial cycle a total of 21 14 c ams dates allow us to define age models with a resolution better than 100 yr during critical periods such as heinrich events 1 and 2 maximum sedimentary fluxes occurred at the meriadzek terrace site during the last glacial maximum lgm detailed x ray imagery of core md95 2002 from the meriadzek terrace shows no sedimentary structures suggestive of either deposition from high density turbidity currents or significant erosion two paroxysmal terrigenous flux episodes have been identified the first occurred after the deposition of heinrich event 2 canadian ice rafted debris ird and includes ird from european sources we suggest that the second represents an episode of deposition from turbid plumes which precedes ird deposition associated with heinrich event 1 at the end of marine isotopic stage 2 mis 2 and the beginning of mis 1 the highest fluxes are recorded on the whittard ridge where they correspond to deposition from turbidity current overflows canadian icebergs have rafted debris at the celtic margin during heinrich events 1 2 4 and 5 the highresolution records of heinrich events 1 and 2 show that in both cases the arrival of the canadian icebergs was preceded by a european ice rafting precursor event which took place about 1 1 5 kyr before two rafting episodes of european ird also occurred immediately after heinrich event 2 and just before heinrich event 1 the terrigenous fluxes recorded in core md95 2002 during the lgm are the highest reported at hemipelagic sites from the northwestern european margin the magnitude of the canadian ird fluxes at meriadzek terrace is similar to those from oceanic sites 2002 elsevier science b v all rights reserved

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

hydraulic control of three layer exchange flows application to the bab al mandab two layer hydraulic models have proven to be extremely useful in understanding a number of exchange flows through straits for example the strait of gibraltar there are though some strait flows that cannot be represented by a two layer model a very striking example is the bab al mandab in the exchange between the red sea and the gulf of aden three distinct water masses are observed in the strait during summer the wintertime flow is though very different with only two layers observed in the strait in this paper a three layer model of hydraulically controlled exchange flows is described the model can represent exchange flows that are controlled with respect to either the first or second or both internal modes a number of different examples are discussed the model is able to explain the qualitative features of the seasonal variation of the flow in the bab al mandab in particular the reversal of the direction of flow of the surface layer and the intrusion into the red sea of cold intermediate water from the gulf of aden during the summer months can be explained by upwelling in the gulf of aden forced by the southwest monsoon

rapid estimation of earthquake source and ground motion parameters for earthquake early warning using data from a single three component broadband or strong motion sensor we propose a new algorithm to rapidly determine earthquake source and ground motion parameters for earthquake early warning eew this algorithm uses the acceleration velocity and displacement waveforms of a single three component broadband bb or strong motion sm sensor to perform real time earthquake noise discrimination and near far source classification when an earthquake is detected the algorithm estimates the moment magnitude m epicentral distance and peak ground velocity pgv at the site of observation the algorithm was constructed by using an artificial neural network ann approach our training and test datasets consist of 2431 three component sm and bb records of 161 crustal earthquakes in california japan and taiwan with 3 1 m 7 6 at 115 km first estimates become available at t 0 0 25 s after the p pick and are regularly updated we find that displacement and velocity waveforms are most relevant for the estimation of m and pgv while acceleration is important for earthquake noise discrimination including site corrections reduces the errors up to 10 the estimates improve by an additional 10 if we use both the vertical and horizontal components of recorded ground motions the uncertainties of the predicted parameters decrease with increasing time window length t 0 larger magnitude events show a slower decay of these uncertainties than small earthquakes we compare our approach with the c algorithm and find that our prediction errors are around 60 smaller however in general there is a limitation to the prediction accuracy an eew system can provide if based on single sensor observations

quaternary stratigraphic stacking patterns on the continental shelves of the southern iberian peninsula their relationship with global climate and palaeoceanographic changes abstract a quaternary stratigraphic stacking pattern on the continental shelves of the southern iberian peninsula has been determined by analysing and comparing a dense network of low medium high and very high resolution mono channel and multi channel reflection seismic lines and well log data four major low resolution depositional sequences related to a 3rd order cycle at 1 4 1 6 ma have been recognised in the pliocene quaternary sedimentary record m p1 p2 p3 q i and q ii they are separated by four discontinuities corresponding to the most drastic changes in climate and palaeoceanography affecting the atlantic and mediterranean linkage and especially to the most prominent sea level falls in the messinian m at 5 5 ma in the lower pliocene at 4 2 ma in the upper pliocene at 2 4 ma and in the mid pleistocene at 900 920 ka mpr these major sequences were built up by asymmetrical sea level cycles the regressive and lowstand system tracts are the best developed deposits controlling the main progradation of the shelf basinwards as well the quaternary shelf stratigraphy can be divided into asymmetric 3rd order sequences of 800 ka q i and q ii and into 4th order asymmetric sequences of approximately 400 ka q1 q4 200 ka a h and 100 ka on low medium and high resolution seismics the overall architectural stacking of the shelf shows a change after the mpr discontinuity characterised by well differentiated sequences of shelf break wedges with progradational sigmoid configurations assumed to be related to approximately 100 ka sea level cycles this change in the configuration of the shelf wedges during the quaternary is attributed to the onset of the 100 ka eccentricity orbital cycles which abruptly increased the amplitude of sea level variations 100 120 m during the last 900 920 ka

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

finder v 2 improved real time ground motion predictions for m2 m9 with seismic finite source characterization recent studies suggest that small and large earthquakes nucleate similarly and that they often have indistinguishable seismic waveform onsets the characterization of earthquakes in real time such as for earthquake early warning therefore requires a flexible modeling approach that allows a small earthquake to become large as fault rupture evolves over time here we present a modeling approach that generates a set of output parameters and uncertainty estimates that are consistent with both small moderate m6 5 and large earthquakes m6 5 as is required for a robust parameter interpretation and shaking forecast our approach treats earthquakes over the entire range of magnitudes m2 as finite line source ruptures with the dimensions of small earthquakes being very small 100 m and those of large earthquakes exceeding several tens to hundreds of kilometres in length the extent of the assumed line source is estimated from the level and distribution of high frequency peak acceleration amplitudes observed in a local seismic network high frequency motions are well suited for this approach because they are mainly controlled by the distance to the rupturing fault observed ground motion patterns are compared with theoretical templates modeled from empirical ground motion prediction equations to determine the best line source and uncertainties our algorithm extends earlier work by bose et al for large finite fault ruptures this paper gives a detailed summary of the new algorithm and its offline performance for the 2016 m7 0 kumamoto japan and 2014 m6 0 south napa california earthquakes as well as its performance for about 100 real time detected local earthquakes 2 2 m 5 1 in california for most events both the rupture length and the strike are well constrained within a few seconds 10 s of the event origin in large earthquakes this could allow for providing warnings of up to several tens of seconds the algorithm could also be useful for resolving fault plane ambiguities of focal mechanisms and identification of rupturing faults for earthquakes as small as m2 5

dense aggregations of a hexactinellid sponge pheronema carpenteri in the porcupine seabight northeast atlantic ocean and possible causes dense aggregations of the hexactinellid sponge pheronema carpenteri were encountered in the porcupine seabight at depths between about 1000 and 1300m in restricted areas within this bathymetric range the sponges attain numerical abundances of more than 1 5m 2 and an estimated biomass of up to 372g m 2 wet weight or about 10g m 2 ash free dry weight these recently acquired samples together with historical data suggest that pheronema occurs close to but not within regions of the upper continental slope where the bottom topography is expected to result in significant enhancement of the near bottom tidal current velocities it is suggested that the sponges may not be able to withstand the enhanced currents but may nevertheless be dependent upon the resuspended or undeposited organic matter carried to them from these regions of increased tidal energy

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition