seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

potential for larger earthquakes in the east san francisco bay area due to the direct connection between the hayward and calaveras faults the hayward and calaveras faults two strike slip faults of the san andreas system located in the east san francisco bay area are commonly considered independent structures for seismic hazard assessment we use interferometric synthetic aperture radar to show that surface creep on the hayward fault continues 15 km farther south than previously known revealing new potential for rupture and damage south of fremont the extended trace of the hayward fault also illuminated by shallow repeating micro earthquakes documents a surface connection with the calaveras fault at depths greater than 3 5 km repeating micro earthquakes located 10 km north of the surface connection highlight the 3 d wedge geometry of the junction our new model of the hayward and calaveras faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7 posing a higher seismic hazard to the east san francisco bay area than previously considered

diurnal tides near the yermak plateau recent current measurements obtained from drifting platforms over the yermak plateau in the eastern arctic ocean confirm that the plateau is a region of greatly enhanced diurnal tidal currents modulation of the diurnal currents is clearly related to the plateau topography as has been previously proposed we show however that temporal variability due to spring neap modulation must also be considered in interpreting records from drifting platforms we review simple models of tidal current amplification in this region and find that the previous assumption of near resonant barotropic shelf waves propagating around the plateau s entire perimeter is inconsistent with the true topography instead we propose that the diurnal variability is due to topographic shelf waves at the k1 and o1 tidal frequencies that are generated at points on the plateau s perimeter where the waves group velocities are near zero observed cross slope variations in ellipticity orientation and magnitude of tidal oscillations are consistent with the presence of topographic waves generated in this manner the topographic enhancement of the diurnal tide near the yermak plateau has important consequences for the sea ice cover hydrography and general circulation of this region for example the stress divergence applied by the tidal currents at the ice base greatly exceeds the typical divergence of the surface wind stress and tides may therefore be important to local ice deformation the strong cross slope tidal currents also appear to be responsible for the production of high frequency internal wave packets which are associated with energetic diapycnal mixing in the pycnocline we also consider the possibility that tidal rectification is responsible for a mean current transporting atlantic water clockwise around the plateau

ball and socket tectonic rotation during the 2013 mw7 7 balochistan earthquake abstract the september 2013 m w 7 7 balochistan earthquake ruptured a 200 km long segment of the curved hoshab fault in southern pakistan with 10 0 2 m of peak sinistral and 1 7 0 8 m of dip slip this rupture is unusual because the fault dips 60 15 towards the focus of a small circle centered in northwest pakistan and despite a 30 increase in obliquity along strike the ratios of strike and dip slip remain relatively uniform surface displacements and geodetic and teleseismic source inversions quantify a bilateral rupture that propagated rapidly at shallow depths from a transtensional jog near the northern end of the rupture static friction prior to rupture was unusually weak 0 05 and friction may have approached zero during dynamic rupture here we show that the inward dipping hoshab fault defines the northern rim of a structural unit in southeast makran that rotates akin to a 2 d ball and socket joint counter clockwise in response to india s penetration into the eurasian plate this rotation accounts for complexity in the chaman fault system and in principle reduces seismic potential near karachi nonetheless these findings highlight deficiencies in strong ground motion equations and tectonic models that invoke anderson byerlee faulting predictions

zeolitic diagenesis of late quaternary fluviolacustrine sediments and associated calcrete formation in the lake bogoria basin kenya rift valley late quaternary fluviolacustrine siltstones mudstones and claystones loboi silts on the northern margins of the saline alkaline lake bogoria in the kenya rift valley contain up to c 40 authigenic analcime and minor natrolite the zeolitic sediments are reddish brown and up to 1 m thick the amount of analcime increases upward in the profile but decreases with distance from the lake the altered sediments show many pedogenic features including zeolitic root mats rootmarks concretions and carbonate rhizoliths residual patches of calcrete locally cap the zeolitic rocks the profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake the analcime occurs as submicroscopic 0 5 2 5 m subhedral and euhedral crystals which have an average si a 1 ratio of 2 33 as determined by x ray microanalysis or 2 18 d value of 639 analcime peak the analcime formed in lake marginal sediments soils by reaction of silicate detritus with na2co3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration poorly ordered clay minerals were probably the main reactants authigenic illite may have been a by product of the reactions chemical analyses suggest that pore waters supplied some of na and possibly k and sio2 the associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration the ca2 may have originated from infiltrating dilute runoff and groundwater authigenic smectite was precipitated in open porosity following analcime formation the zeolitic alteration at lake bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline alkaline lake sediments

long term monitoring of creep rate along the hayward fault and evidence for a lasting creep response to 1989 loma prieta earthquake we present results from over 30 yr of precise surveys of creep along the hayward fault along most of the fault spatial variability in long term creep rates is well determined by these data and can help constrain 3d models of the depth of the creeping zone however creep at the south end of the fault stopped completely for more than 6 years after the m7 1989 loma prieta earthquake lpeq perhaps delayed by stress drop imposed by this event with a decade of detailed data before lpeq and a decade after it we report that creep response to that event does indeed indicate the expected deficit in creep

paleoclimatic signature in terrestrial flood deposits large scale process simulation was used to reconstruct the geologic evolution during the past 600 000 years of an alluvial fan in northern california in order to reproduce the sedimentary record the simulation accounted for the dynamics of river flooding sedimentation subsidence land movement that resulted from faulting and sea level changes paleoclimatic trends induced fluctuations in stream flows and dominated the development of the sedimentary deposits the process simulation approach serves as a quantitative means to explore the genesis of sedimentary architecture and its link to past climatic conditions and fault motion

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

short term surface deformation on the northern hayward fault ca and nearby landslides using polarimetric sar interferometry polinsar in this study we analyze 25 radarsat 2 images from ascending and descending geometries to study the creep rate on the hayward fault and landslide motions near berkeley ca we applied a coherence optimization technique from polarimetric synthetic aperture radar interferometry polinsar to increase the accuracy of the measurements we resolve 3 5 mm year of motion along the hayward fault in agreement with earlier creep estimates we identify a potential motion on secondary fault northeast and parallel to the hayward fault which is creeping at a lower rate of 1 5 mm year in addition we identify a number of landslides along the hills east of the fault that agree with earlier results from advanced interferometric synthetic aperture radar sar analysis and field investigations we investigate four particular slope instabilities one of which was marked as moderately active and three as highly active by earlier field investigations the resolved along hill slope displacement is estimated at 23 mm year our results demonstrate that polinsar is an effective method to increase the interferometric coherence and provide improved resolution of deformation features associated with natural hazards

export of nutrients from the arctic ocean 1 this study provides the first physically based mass balanced transport estimates of dissolved inorganic nutrients nitrate phosphate and silicate for the arctic ocean using an inverse model generated velocity field in combination with a quasi synoptic assemblage of hydrographic and hydrochemical data we quantify nutrient transports across the main arctic ocean gateways davis strait fram strait the barents sea opening bso and bering strait we found that the major exports of all three nutrients occur via davis strait transports associated with the east greenland current are almost balanced by transports associated with the west spitsbergen current the most important imports of nitrate and phosphate to the arctic occur via the bso and the most important import of silicate occurs via bering strait oceanic budgets show that statistically robust net silicate and phosphate exports exist while the net nitrate flux is zero within the uncertainty limits the arctic ocean is a net exporter of silicate 15 7 3 2 kmol s 1 and phosphate 1 0 0 3 kmol s 1 net 1 standard error to the north atlantic the export of excess phosphate relative to nitrate from the arctic calculated at 1 1 0 3 kmol s 1 is almost twice as large as previously estimated net transports of silicate and phosphate from the arctic ocean provide 12 and 90 respectively of the net southward fluxes estimated at 47 n in the north atlantic additional sources of nutrients that may offset nutrient imbalances are explored and the relevance and the pathway of nutrient transports to the north atlantic are discussed

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

atmospheric forcing of fram strait sea ice export a closer look fram strait is the primary region of sea ice export from the arctic and therefore plays an important role in regulating the amount of sea ice and freshwater within the arctic we investigate the variability of fram strait sea ice motion and the role of atmospheric circulation forcing using daily data during the period 1979 2006 the most prominent atmospheric driver of anomalous sea ice motion across fram strait is an east west dipole pattern of sea level pressure slp anomalies with centers of action located over the barents sea and greenland this pattern also observed in synoptic studies is associated with anomalous meridional winds across fram strait and is thus physically consistent with forcing changes in sea ice motion the association between the slp dipole pattern and fram strait ice motion is maximized at 0 lag persists year round and is strongest on time scales of 10 60 days the slp dipole pattern is the second empirical orthogonal function eof of daily slp anomalies in both winter and summer when the analysis is repeated with monthly data only the barents center of the slp dipole remains significantly correlated with fram strait sea ice motion however after removing the leading eof of monthly slp variability e g the north atlantic oscillation the full east west dipole pattern is recovered no significant slp forcing of fram strait ice motion is found in summer using monthly data even when the leading eof is removed our results highlight the importance of high frequency atmospheric variability in forcing fram strait sea ice motion

geochemistry and origin of the şaphane alunite deposit western anatolia turkey ore geology reviews 26 2005 39 50 reply

controls on timing and amount of right lateral offset on the east bay fault system san francisco bay region california the distribution of offset correlated rock units relative position of northward younging volcanic rocks and distribution of units not offset together reveal the history of strike slip deformation along the east bay fault system the system accumulated 175 km of right lateral offset since 12 ma but of this amount only 25 km was accumulated between 12 and 10 ma and only 75 km between 12 and 6 ma the westernmost hayward fault zone is responsible for more than half 100 km of the total and it too has undergone more offset 60 km after 6 ma than before the activity on any single fault zone in the system has been sporadic and alternating periods of activity and inactivity have been recorded on at least some of the fault zones

a record of large earthquakes on the southern hayward fault for the past 500 years the hayward fault a major branch of the right lateral san andreas fault system traverses the densely populated eastern san francisco bay region california we conducted a paleoseismic investigation to better understand the hayward fault9s past earthquake behavior the site is near the south end of tyson9s lagoon a sag pond formed in a right step of the fault in fremont because the hayward fault creeps at the surface we identified paleoseismic events using features that we judge to be unique to ground ruptures or the result of strong ground motion such as the presence of fault scarp colluvial deposits and liquefaction we correlate the most recent event evidence e1 to the historical 1868 m 6 9 earthquake that caused liquefaction in the pond and recognize three additional paleoruptures since a d 1470 110 yr event ages were estimated by chronological modeling which incorporated historical and stratigraphic information and radiocarbon and pollen data modeled mean age and 95 percentile ranges of the three earlier events are a d 1730 1650 1790 yr e2 a d 1630 1530 1740 yr e3 and a d 1470 1360 1580 e4 the ages of these paleoearthquakes yield a mean recurrence of 130 40 yr although the mean recurrence is well determined for the period a d 1470 1868 individual intervals are less well determined e1 e2 140 80 70 yr e2 e3 100 90 100 yr and e3 e4 150 130 110 yr

horizontal polarization of ground motion in the hayward fault zone at fremont california dominant fault high angle polarization and fault induced cracks summary we investigate shear wave polarization in the hayward fault zone near niles canyon fremont ca waveforms of 12 earthquakes recorded by a seven accelerometer seismic array around the fault are analysed to clarify directional site effects in the fault damage zone the analysis is performed in the frequency domain through h v spectral ratios with horizontal components rotated from 0 to 180 and in the time domain using the eigenvectors and eigenvalues of the covariance matrix method employing three component records the near fault ground motion tends to be polarized in the horizontal plane at two on fault stations where the local strike is n160 ground motion polarization is oriented n88 19 and n83 32 respectively at a third on fault station the motion is more complex with horizontal polarization varying in different frequency bands however a polarization of n86 7 similar to the results at the other two on fault stations is found in the frequency band 6 8 hz the predominantly high angle polarization from the fault strike at the hayward fault is consistent with similar results at the parkfield section of the san andreas fault and the val d agri area a quaternary extensional basin in italy in all these cases comparisons of the observed polarization directions with models of fracture orientation based on the fault movement indicate that the dominant horizontal polarization is near orthogonal to the orientation of the expected predominant cracking direction the results help to develop improved connections between fault mechanics and near fault ground motion

the mission link between the hayward and calaveras faults the left stepover between the calaveras and hayward faults gives rise to compressive strain that is accommodated by vertical deformation producing the highest hills bordering the east side of san francisco bay monument peak to mission peak the projection of the active trace of the hayward fault is separated 3 5 km from the junction of the northern and southern segments of the calaveras fault at calaveras reservoir for pure strike slip on the hayward and calaveras faults the stepover region is compressed in area at a rate given by the separation times the long term slip rate of 9 mm yr on the hayward fault assuming a seismogenic depth of 10 km the horizontal compression accumulated over 150 years is equivalent to a dip slip seismic moment of 2 8 1018 n m this moment if released in a single event would generate an earthquake of magnitude 6 3 due to dip slip alone dip slip may occur on buried faults throughout the stepover region the base of the southwest face of monument peak suggests a buried thrust or reverse fault dipping northeast the prominent scarp on mission peak has the same strike and sense of slip current microearthquakes between the calaveras and hayward faults align parallel to the mission fault but show only horizontal slip on a vertical fault plane a dipping fault is needed to satisfy the geometric constraint of the convergence therefore the mission fault zone must consist of two or more fault surfaces inclined at different dip angles as is observed in the san andreas fault zone in the loma prieta area horizontal slip is building up stress on the inclined fault which is currently locked growing compressive stress will increasingly impede horizontal slip until a thrust or reverse slip event occurs allowing then more horizontal slip to be transferred from the calaveras to the hayward fault the dip slip fault might be the unstable element governing slip in the larger system

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

early spring oceanic heat fluxes and mixing observed from drift stations north of svalbard abstract from several drifting ice stations north of svalbard norway observations were made in early spring of the ocean turbulent characteristics in the upper 150 m using a microstructure profiler and close to the under ice surface using eddy correlation instrumentation the dataset is used to obtain average heat fluxes at the ice water interface in the mixed layer across the main pycnocline as well over different water masses in the region the results are contrasted with proximity to the branches of the warm and saline atlantic water current the west spitsbergen current wsc which is the main oceanic heat and salinity source both to the region and to the arctic ocean hydrographic properties show that the surface water mass modification is typically due to atmospheric cooling with relatively less influence of ice melting surface heat fluxes of o 100 w m 2 are found within the branches of the wsc and over shelf areas with elevated levels of mixing due to strong tides away from the shelves and

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

arctic warming through the fram strait oceanic heat transport from 3 years of measurements we present estimates of volume and heat transport through fram strait for the period 1997 to 2000 from data of moored instruments full depth volume transports at 78 55 n were in the order of 10 sv both northwards and southwards with an annual mean net transport between 2 and 4 sv to the south the temperature of the northward flow of atlantic water had a strong seasonality with a minimum in winter nevertheless the northward heat transport was highest in winter caused by the winter maximum of northward volume transport during the three years of observation the heat transport in the west spitsbergen current increased from 28 to 46 tw as a result of both increased speed and temperature in contrast to the west spitsbergen current the volume and heat transport of east greenland current remained fairly constant an integration over a subsection of the east greenland current showed similar values of volume transport to that obtained by measurements in the 1980s foldvik et al 1988 the southward heat transport through modified atlantic water weakened slightly between 1997 and 1999 despite increased temperatures

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

geodetic constraints on san francisco bay area fault slip rates and potential seismogenic asperities on the partially creeping hayward fault 1 the hayward fault in the san francisco bay area sfba is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes imaging the spatial variation in interseismic fault creep on the hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the sfba where the relative motion between the pacific plate and the sierra block is partitioned across closely spaced subparallel faults to estimate spatially variable creep on the hayward fault we interpret geodetic observations with a three dimensional kinematically consistent block model of the sfba fault system resolution tests reveal that creep rate variations with a length scale of 15 km are poorly resolved below 7 km depth in addition creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models differential microplate motions result in a slip rate of 6 7 0 8 mm yr on the hayward fault and we image along strike variations in slip deficit rate at 15 km length scales shallower than 7 km depth similar to previous studies we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm yr on the central hayward fault that is spatially correlated with the mapped surface trace of the 1868 mw 6 9 7 0 hayward earthquake and adjacent to gabbroic fault surfaces

alunite and the role of magmatic fluids in the tambo high sulfidation deposit el indio pascua belt chile the tambo high sulfidation deposit located within the el indio pascua belt in chile produced almost 25 t 0 8 m oz of gold from altered tertiary rhyodacitic volcanic rocks episodic magmatic hydrothermal activity in the district occurred over at least 4 my and is characterized by several stages of acid sulfate alteration including magmatic hydrothermal magmatic steam steam heated and apparent supergene assemblages two stages of aufag mineralization are recognized and are hosted in barite and alunite within hydrothermal breccias and veins isotopic compositions of fluid in alunite show a dominant magmatic signature with only a variable 18 o enriched meteoric water component throughout the entire hydrothermal process alunite 40 ar 39 ar ages constrain the timing of alteration and the duration of the hydrothermal system pre ore alteration occurred at about 10 to 11 ma and was contemporaneous with the volcanism of the tambo formation alunite from this stage of alteration occurs in the matrix of barren breccias and as fine intergrowths of alunite quartzfclays that selectively replaced feldspars and pumice fragments the textural relationships combined with stable isotope systematics suggest a magmatic hydrothermal origin for the alunite with a local magmatic steam overprint early ore stage alunite 8 7f0 2 ma occurs with barite and goldfwalthierite within open spaces of the breccia matrix and has d 34 s values 24 27x typical of magmatic hydrothermal alunite reflecting equilibrium between aqueous h2s and so4 fluid inclusion ratios of h2s so2 approximately 6 are consistent with ratios determined from stable isotope data and indicate reduced fluid conditions during ore deposition vaporphase transport of au and deposition from condensed magmatic vapor rising from the brittle ductile transition is inferred late gold coprecipitated with a third stage of alunite 8 2f0 2 ma that is characterized by nearly uniform chemical compositions and d 34 s values 1x similar to those for associated enargite reflecting disequilibrium between h2s and so4 this third stage of alunite is isotopically and chemically similar to that of post ore coarse banded alunitefhematite quartz veins that crosscut the breccias in the tambo area analyses of fluid inclusion gas from alunite in these veins indicate high so2 and disequilibrium co2 co ch4 h2 species consistent with a magmatic steam origin the gases are also depleted in he and the late goldbearing alunite was probably precipitated from rapidly ascending so2 rich vapors that were flashed from condensed magmatic

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

seismic reflection evidence for a northeast dipping hayward fault near fremont california implications for seismic hazard 1 a 1 6 km long seismic reflection profile across the creeping trace of the southern hayward fault near fremont california images the fault to a depth of 650 m reflector truncations define a fault dip of about 70 degrees east in the 100 to 650 m depth range that projects upward to the creeping surface trace and is inconsistent with a nearly vertical fault in this vicinity as previously believed this fault projects to the mission seismicity trend located at 4 10 km depth about 2 km east of the surface trace and suggests that the southern end of the fault is as seismically active as the part north of san leandro the seismic hazard implication is that the hayward fault may have a more direct connection at depth with the calaveras fault affecting estimates of potential event magnitudes that could occur on the combined fault surfaces thus affecting hazard assessments for the south san francisco bay region

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

freshwater fluxes in the east greenland current a decade of observations 1 over a decade of mooring measurements in the western fram strait at 78 50 n shows that the annual mean liquid freshwater flux fwf in the east greenland current is relatively constant at 1274 453 km3 yr 1 40 4 14 4 msv despite the fact that the annual mean total volume transport of the egc has more than doubled since 2001 this is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest fw content is present on the east greenland shelf and not in the core of the egc in order to capture the fwf on the shelf modeling results of naosim are included showing that a mean contribution of fwf on the shelf of at least 807 357 km3 yr 1 25 6 11 3 msv should be added to the fwf obtained for the egc when compared to the extra input of freshwater required to account for the 1960 1990 freshening of the northern north atlantic the observed variations in the 1998 2008 egc liquid freshwater fluxes are small

subsurface structure and kinematics of the calaveras hayward fault stepover from three dimensional vp and seismicity san francisco bay region california the calaveras and hayward faults are major components of the san andreas fault system in the san francisco bay region dextral slip is presumed to transfer from the calaveras fault to the hayward fault in the mission hills region an area of uplift in the contractional stepover between the two faults here the estimated deep slip rates drop from 15 to 6 mm yr on the calaveras fault and slip begins on the hayward fault at an estimated 9 mm yr a lineament of microseismicity near the mission fault links the seismicity on the calaveras and hayward faults and is presumed to be related directly to this slip transfer however geologic and seismologic evidence suggest that the mission fault may not be the source of the seismicity and that the mission fault is not playing a major role in the slip transfer we perform a joint inversion for hypocenters and the 3d p wave velocity structure of the stepover region using 477 earthquakes we find strong velocity contrasts across the calaveras and hayward faults corroborated by geologic gravity and aeromagnetic data detailed examination of two seismic lineaments in conjunction with the velocity model and independent geologic and geophysical evidence suggests that they represent the southern extension of a northeasterly dipping hayward fault that splays off the calaveras fault directly accounting for the deep slip transfer the mission fault appears to be accommodating deformation within the block between the hayward and calaveras faults thus the calaveras and hayward faults need to be considered as a single system for developing rupture scenarios for seismic hazard assessments online material 3d interactive visualizations of the mission and alum rock hypocenters

barotropic instability in the west spitsbergen current 1 barotropic instability in the shoreward branch of the west spitsbergen current is investigated on the basis of data from an array of current meter moorings along 78 83 n across the upper continental slope and shelf break west of svalbard the slowly varying background current profile is modeled as an along slope asymmetric jet anchored to the shelf break numerical linear stability analyses are performed on the idealized current profile and topography revealing the characteristic period wavelength and growth rate of unstable vorticity waves detailed analysis of the ambient current profile in 2007 2008 shows that unstable conditions are present during 40 of the 10 month measurement record depending on the localization width and amplitude of the current jet the resulting vorticity waves are localized at the shelf break and are able to exchange water masses across the oceanic arctic front typical wavelengths and periods are 20 40 km and 40 70 h respectively wavelet coherence and complex demodulation analyses of the current meter data confirm that transient signals of similar periodicity as predicted by the stability analysis exist in the data record prominently during the winter and spring months estimates of the heat loss contribution from isopycnal diffusion reach 1 4 tw during the time intervals when unstable vorticity waves are active at the shelf break implying that the dynamics of the west spitsbergen current play a significant role in the cooling process of the atlantic water on the way to the arctic ocean this cooling corresponds to an along shelf cooling rate of 0 08 c per 100 km

geodetically inferred coseismic and postseismic slip due to the m 5 4 31 october 2007 alum rock earthquake on 31 october 2007 the m 5 4 alum rock earthquake occurred near the junction between the hayward and calaveras faults in the san francisco bay area producing coseismic and postseismic displacements recorded by 10 continuously operating global positioning system gps instruments the cumulative postseismic displacements over the four months following the earthquake are linearly related to the cumulative number of aftershocks and are comparable in magnitude to the coseismic displacements the postseismic signal suggests that in addition to afterslip at seismogenic depths localized right lateral reverse slip occurred on dipping shallow fault surfaces southwest of the calaveras the spatial distribution of slip inferred by inverting the gps data is compatible with a model in which moderate calaveras fault earthquakes rupture locked patches surrounded by areas of creep afterslip and microseismicity oppenheimer et al 1990 if this model and existing calaveras fault slip rate estimates are correct a slip deficit remains on the 2007 alum rock rupture patch that may be made up by aseismic slip or slip in larger earthquakes recent studies e g manaker et al 2005 suggest that at depth the hayward and central calaveras faults connect via a simple continuous surface illuminated by the mission seismic trend mst implying that a damaging earthquake rupture could involve both faults graymer et al 2008 if this geometry is correct the combined coseismic and postseismic slip we infer for the 2007 alum rock event predicts static coulomb stress increases of 0 6 bar on the mst surface and on the northern calaveras fault 5 km northwest of the alum rock hypocenter

petrographic microchemical studies and origin of the agbaja phanerozoic ironstone formation nupe basin nigeria a product of a ferruginized ooidal kaolin precursor not identical to the minette type the campanian maastrichtian agbaja ironstone formation of the nupe basin nigeria forms a major part of the about 2 billion tons of iron ore reserves of the middle niger embayment the ironstone deposits were previously reported to be similar to the minette type ironstones because of their depositional patterns composition and inferred origin four rock types are recognized within the agbaja ironstone formation ooidal pack ironstone pisoidal pack ironstone mud ironstone and bog iron ore in the ironstones kaolinite of both the groundmass and the ooids pisoids is of lateritic origin whereas the associated quartz mica and heavy minerals are of detrital origin ooids and pisoids were formed by mechanical accretion of platy kaolinite crystals by rolling on the sea floor in a near shore environment and were subsequently transported and deposited together with a fine grained kaolinitic groundmass pyrite mainly framboidal and siderite both exclusively occurring as pseudomorphs of goethite and or hematite are diagenetic whereas goethite is post diagenetic in origin resulting from the ferruginization of the kaolinitic precursor crandallite gorxeicite goyazite bolivarite and boehmite are also post diagenetic in origin hematite was formed from the dehydration of goethite whereas gibbsite restricted to the upper part of the deposit is of recent and in situ lateritic origin the presence of newly formed authigenic pyrite and siderite now replaced by hematite and goethite are indicators of a reducing environment during diagenesis the absence of diagenetic chamositic clay minerals evidently caused by a low mg concentration suggests that fully marine conditions were not established during sedimentation this is supported by the lack of fossils brecciated shell materials and bioturbation features in the deposit reworking and redeposition of the primary constituents are inferred from broken pisoids nuclei of pisoidal ooidal fragments in pisoids and high iron concentrations present in the pisoids and ooids compared to that of the groundmass these observations indicate that the agbaja ironstone deposits of the lokoja study area exhibit some environmental and mineralogical characteristics that are markedly different from other known deposits of minette type where primary chamositic clay minerals generally form the protore for the ironstones the recognition of kaolinite as the precursor constituent and the occurrence of similar deposits of the same age late cretaceous in nigeria sudan and egypt have implications for the paleoenvironmental interpretations of phanerozoic ironstone deposits

wind driven variability of the large scale recirculating flow in the nordic seas and arctic ocean the varying depth integrated currents in the nordic seas and arctic ocean are modeled using an integral equation derived from the shallow water equations this equation assumes that mass divergence in the surface ekman layer is balanced by convergence in the bottom ekman layer the primary flow component follows contours of f h the model employs observed winds and realistic bottom topography and has one free parameter the coefficient of the linear bottom drag the data used for comparison are derived from in situ current meters satellite altimetry and a primitive equation model the current meter data come from a 4 yr record at 75 8 ni n the greenland sea the currents here are primarily barotropic and the model does well at simulating the variability the best bottom friction parameter corresponds to a spindown time of 30 60 days a further comparison with bottom currents from a mooring on the norwegian continental slope deployed over one winter period also shows reasonable correspondence the principal empirical orthogonal function obtained from satellite altimetry data in the nordic seas has a spatial structure that closely resembles f h a direct comparison of this mode s fluctuations with those predicted by the theoretical model yields linear correlation coefficients in the range 0 75 0 85 the primitive equation model is a coupled ocean ice version of the princeton ocean model for the north atlantic and arctic monthly mean depth averaged velocities are calculated from a 42 yr integration and then compared with velocities predicted from an idealized model driven by the same reanalyzed atmospheric winds in the largely ice free norwegian sea the coherences between the primitive equation and idealized model velocities are as high as 0 9 on timescales of a few months to a few years they are lower in the remaining partially or fully ice covered basins of the greenland sea and the arctic ocean presumably because ice alters the momentum transferred to the ocean by the wind the coherence in the canadian basin of the arctic can be increased substantially by forcing the idealized model with ice velocities rather than the wind estimates of the depth integrated vorticity budget in the primitive equation model suggest that bottom friction is important but that lateral diffusion is of equal or greater importance in compensating surface ekman pumping