on the intermediate water masses of the faroe bank channel overflow a review of available hydrographic data from the faroe bank channel indicates that north icelandic arctic intermediate water masses are present in the passage to a larger extent than was previously believed the presently compiled statistics including results on the seasonality are discussed in relation to previous investigations finally a high quality subset of the hydrographic data is used for an analysis of the alongchannel mixing of the intermediate water masses

an elastic plate model for interseismic deformation in subduction zones geodetic observations of interseismic surface deformation in the vicinity of subduction zones are frequently interpreted using simple kinematic elastic dislocation models edm in this theoretical study we develop a kinematic edm that simulates plate subduction over the interseismic period the elastic subducting plate model espm having only 2 more degrees of freedom than the well established back slip model bsm an elastic plate thickness and the fraction of flexural stresses due to bending at the trench that are released continuously unlike the bsm in which steady state deformation in both plates is assumed to be negligible the espm includes deformation in the subducting and overriding plates owing to plate thickness while still preserving the correct sense of convergence velocity between the subducting and overriding plates as well as zero net steady state vertical offset between the two plates when integrated over many seismic cycles the espm links elastic plate flexure processes to interseismic deformation and helps clarify under what conditions the bsm is appropriate for fitting interseismic geodetic data at convergent margins we show that the espm is identical to the bsm in the limiting case of zero plate thickness thereby providing an alternative motivation for the bsm the espm also provides a consistent convention for applying the bsm to any megathrust interface geometry even in the case of nonnegligible plate thickness the deformation field predicted by the espm reduces to that of the bsm if stresses related to plate flexure at the trench are released either continuously and completely at shallow depths during the interseismic period or deep in the subduction zone below 100 km however if at least a portion of these stresses are not continuously released in the shallow portion of the subduction zone via seismic or aseismic events then the predicted surface velocities of these two models can differ significantly at horizontal distances from the trench equivalent to a few times the effective interseismic locking depth

structure of unsteady overflow in the slupsk furrow of the baltic sea 1 a data set of closely spaced ctd profiling performed aboard russian and polish research vessels during 1993 2009 and numerical modeling are applied to study the variability in the asymmetric transverse structure of salinity density in the slupsk furrow sf overflow of the baltic sea the numerical simulations show that on the one hand the overflow may be dynamically treated within the sf as a subcritical eddy producing gravity current in a wide channel and on the other at the sill displays some features peculiar to frictionally controlled rotating flows comparison between the field measurements and the simulation results indicates that the variability of the cross channel density structure is caused mainly by meandering of the gravity current and mesoscale eddies mostly above halocline cyclones and intrahalocline anticyclones the meanders and eddies are found to be strongly affected by the bottom topography and wind forcing

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

long period changes in the bottom water flowing through vema channel further details of the warming of bottom water flowing through the vema channel first reported by zenk and hogg 1996 are given because cross channel gradients of temperature are large and the channel is narrow careful analysis is required to determine whether or not the bottom water temperature minimum was adequately sampled by a particular station or cruise during a period from 1972 to 1996 at least 14 visits with quality hydrographic measurements have been made to the region of these 11 were judged successful and their data indicate an abrupt rise in potential temperature by 0 03 c from 0 18 c to 0 15 c in the early 1990s that has remained until the latest observation in the spring of 1996 although this observation is consistent with the report of warming of antarctic bottom water in the argentine basin by coles et al 1996 their associated conclusion that this water mass has also freshened by 0 008 psu on potential density surfaces is in contradiction with our finding of no measurable change

euhedral awaruite in the allende meteorite implications for the origin of awaruite and magnetite bearing nodules in cv3 chondrites

the vema channel physiography structure and sediment current interactions abstract the east flank of the vema channel in the southwestern atlantic is an opportune location for interpreting the pleistocene holocene record of deep thermohaline circulation the channel and the adjacent sediment covered rio grande rise intersect each of the principal sub thermocline water masses of the western atlantic we analyzed a suite of 25 giant gravity cores in transects extending between 1400 and 4150 m depth this interval includes the upper and lower branches of circumpolar water north atlantic deep water and antarctic bottom water the late pleistocene holocene sediments along these transects are pelagic carbonates with excellent stratigraphic continuity shallower and deeper regions are relatively unsuitable due to poor core recovery or widespread erosional unconformities extensive hydrographic and direct current observations near the location of our prime coring transect at 30 s indicate a notable cross channel asymmetry in the abyssal hydrography and velocity structure which is reflected in the underlying lithofacies distribution the near bottom flow field shows marked temporal and spatial variability on a local scale even in the channel axis where one would anticipate relatively steady uniform flow much of this variability appears to reflect the effects of transient mesoscale eddies rather than regional variations in the integrated north ward transport of aabw in spite of temporal variations in the flow field the nadw aabw transition zone appears to have remained remarkably stable over time scales of 10 5 10 6 yrs on geological evidence discussed elsewhere in this volume jones 1984 jones and johnson 1984 this observation is somewhat surprising because in the modern oceans the density contrast between nadw and aabw is relatively small if the transition zone between the two water masses has indeed remained relatively stationary then the density determining water properties t and s may also have remained relatively constant with only the rates of production changing if this interpretation proves correct upon further studies it implies that pale oceanographic interpretations of deep thermohaline flow should in some instances utilize geological indices of non conservative water properties e g co 2 13 c for monitoring paleocirculation changes

distribution of interseismic coupling along the north and east anatolian faults inferred from insar and gps data the north anatolian fault naf has produced numerous major earthquakes after decades of quiescence the mw 6 8 elazig earthquake january 24 2020 has recently reminded us that the east anatolia

hydrography of the romanche and chain fracture zones the romanche and chain fracture zones rfz and cfz are known as pathways for the lower north atlantic deep water lnadw and the antarctic bottom water aabw from the western trough to the eastern trough of the equatorial atlantic ocean across the mid atlantic ridge we report hydrographic observations describing the evolution of the lnadw and aabw properties during their transit through the equatorial fracture zones to the west of the rfz and cfz sills the lnadw and aabw cores are separated by a deep thermocline pycnocline which marks the transition between the two water masses the deep thermocline is eroded eastward and vanishes in the eastern basin this zonal asymmetry is the signature of a zonal baroclinic pressure gradient associated in each fracture zone with eastward flows of lnadw and aabw below 3800 m depth during the eastward transit through the rfz the near bottom aabw becomes less dense saltier 0 07 and warmer 0 7 c richer in oxygen 0 3 ml l 1 but less rich in silicate 30 mol l 1 simultaneously the lnadw core becomes fresher and colder at a given density and the oxygen maximum characterizing the lnadw core weakens by 0 2 ml l 1 we argue that the property changes within the aabw and lnadw are due to intense vertical mixing in addition to vertical mixing with the aabw it seems likely that isopycnal mixing of the lnadw with the eastern basin deep water contributes to the property evolution of the lnadw exiting the rfz in the cfz evidence is also given of mixing occuring within the aabw and the lnadw a sudden change in the aabw properties observed across the cfz main sill suggests the blocking of the eastward progression of the densest aabw by the cfz main sill however this dense water can reach the eastern basin by flowing northeastward through valleys the sills of which are deeper than thoses of the cfz finally a simple hydraulic control model applied to the rfz and cfz flows predicts a transport of 1 4 0 1 106 m3 s 1 of water colder than 1 9 c across the rfz cfz main sill

trans dimensional finite fault inversion summary this paper develops a probabilistic bayesian approach to the problem of inferring the spatiotemporal evolution of earthquake rupture on a fault surface from seismic data with rigorous uncertainty estimation to date uncertainties of rupture parameters are poorly understood and the effect of choices such as fault discretization on uncertainties has not been studied we show that model choice is fundamentally linked to uncertainty estimation and can have profound effects on results the approach developed here is based on a trans dimensional selfparametrizationofthefault avoidsregularizationconstraintsandprovidesrigorousuncertainty estimationthataccountsformodel selectionambiguityassociatedwiththefaultdiscretization in particular the fault is parametrized using self adapting irregular grids which intrinsically match the local resolving power of the data and provide parsimonious solutions requiring few parameters to capture complex rupture characteristics rupture causality is ensured by parametrizing rupture onset time by a rupture velocity field and obtaining first rupture times from the eikonal equation the bayesian sampling of the parameter space is implemented on a computer cluster with a highly efficient parallel tempering algorithm the inversion is applied to simulated and observed w phase waveforms from the 2010 maule chile earthquake simulation results show that our approach avoids both over and underparametrization to ensure unbiased inversion results with uncertainty estimates that are consistent with data information the simulation results also show the ability of w phase data to resolve the spatial variability of slip magnitude and rake angles in addition sensitivity to spatially dependent rupture velocities exists for kinematic slip models application to the observed data indicates that residual errors are highly correlated and likely dominated by theory error necessitating the iterative estimation of a non stationary data covariance matrix the moment magnitude for the maule earthquake is estimated to be 8 9 with slip concentrated in two zones updip of and north and south of the hypocentre respectively while this aspect of the slip distribution is similar to previous studies we show that the slip maximum in the southern zone is poorly resolved compared to the northern zone both slip maxima are higher than reported in previous studies which we speculate may be due to the lack of bias caused by the regularization used in other studies

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

spatial and temporal evolution of a long term slow slip event the 2006 guerrero slow slip event summary the guerrero 2006 slow slip event sse mexico one of the world s largest observed sses was recorded at 15 continuous gps stations this event provides the opportunity to analyse in detail the spatial and temporal evolution of slip at depth and to constrain the characteristics of a large sse we perform an inversion in two steps first we invert the cumulative gps displacements to retrieve the total slip amplitude second we invert for the initiation time and duration of the slip using a linearized least squares inversion procedure and assuming a functional form for the slip function our results show that the slip is located on a patch of 300 km 150 km parallel and perpendicular to the coast respectively and extends from the bottom of the seismogenic zone to the transition zone this slow slip event has an equivalent moment magnitude of 7 5 the maximum slip over a length scale of 25 km is 15 cm and the mean slip is 5 5 cm its lateral extension coincides with the segmentation of the subduction our inversion scheme allows us to analyse the spatial variability of the rise time rupture velocity and slip function we obtain a continuous image of the spatial and temporal variations of slip on the fault plane the rupture initiated at a depth of 40 km transition zone in the western part of the guerrero gap the rupture then propagated from the western to the eastern part of the guerrero segment with an average velocity of 0 8 km d 1 our results show that a slip dislocation pulse characterized by a symmetric ramp function can model the 2006 sse the rise time local duration of slip does not show large spatial variations and is equal to about 185 d the local slip duration is compared to the total duration 11 12 months of the event suggesting a large interaction of a large part of the fault during the dynamic process we find that our inverted slip model is well resolved on the shallow part of the fault and in the central section of the fault

late tertiary quaternary magnetostratigraphy and biostratigraphy of vema channel sediments abstract twenty one piston cores in a transect of the vema channel near 31 s were analyzed magnetostratigraphically and biostratigraphically in order to ascertain the depositional continuity in the late tertiary and quaternary the cores span a depth interval of 2941 4235 m and represent three distinct physiographic provinces each of which shows a relatively consistent accumulation pattern the deepest cores are from the broad terraces which flank the vema channel axis on both the west 3650 mm and east 4150 4250 m these cores show the highest accumulation rates in the region 20 m m y 2 and no evidence of unconformities twelve cores from the flanks of the rio grande rise 2941 3950 m show depositional continuity in the late quaternary and normal pelagic accumulation rates 5 10 m m y 2 with evidence in two of the cores for minor erosional hiatuses on a local scale perhaps due to slumping a relatively narrow transition zone between the rio grande rise flanks and the eastern terrace 3950 4150 m shows buried manganese pavements and near outcrops of miocene pliocene strata indicating intermittent erosion during the late tertiary and quaternary perhaps due to episodes of intensified aabw flow modern flow within this transition zone and over the eastern terrace is relatively weak gu 2 cm s 2 and southward the presence of well developed sediment waves on the terrace and buried erosional unconformities upslope to the east suggests substantially higher current velocities during the late tertiary than those present today

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

magnetic characteristics of cv chondrules with paleointensity implications 1 we have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the cv type 1 mokoia and 2 allende allende has been previously extensively studied and is thought to have a high potential of retaining an extra terrestrial paleofield few paleomagnetic studies of mokoia have previously been undertaken we report a range of magnetic measurements including hysteresis first order reversal curve analysis forcs demagnetization characteristics and isothermal remanent irm acquisition behavior on both mokoia and allende chondrules the mokoia chondrules displayed more single domain like behavior than the allende chondrules suggesting smaller grain sizes and higher magnetic stability the mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the allende chondrules irm acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral likely to be a feni phase taenite kamacite and or awaruite contributing to 48 of the mokoia chondrules and 42 of the allende chondrule characteristics forc analysis revealed that generally the allende chondrules displayed low field coercivity distributions with little interactions and the mokoia chondrules show clear single domain like distributions paleointensity estimates for the two meteorites using the remc and preisach methods yielded estimates between 13 and 60 t and 3 56 t respectively for allende and 3 140 t and 1 110 t respectively for mokoia from the data we suggest that mokoia chondrules carry a non primary remagnetization and while allende is more likely than mokoia to retain its primary magnetization it also displays signs of post accretionary magnetization

identification of magnetite in lunar regolith breccia 60016 evidence for oxidized conditions at the lunar surface lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the moon apollo 16 sample 60016 is an ancient feldspathic regolith breccia that was converted from a soil to a rock at 3 8 ga the breccia contains a small 70 50 m rock fragment composed dominantly of an fe oxide phase with disseminated domains of troilite fragments of plagioclase an95 97 pyroxene en74 75 fs21 22 wo3 4 and olivine fo66 67 are distributed in and adjacent to the fe oxide the silicate minerals have lunar compositions that are similar to anorthosites mineral chemistry synchrotron x ray absorption near edge spectroscopy xanes and x ray diffraction xrd studies demonstrate that the oxide phase is magnetite with an estimated fe3 fe ratio of 0 45 the presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at or above the fe magnetite or wustite magnetite oxygen buffer this discovery provides direct evidence for oxidised conditions on the moon thermodynamic modelling shows that magnetite could have been formed from oxidisation driven mineral replacement of fe metal or desulphurisation from fe sulphides troilite at low temperatures 570 c in equilibrium with h2o steam liquid or co2 gas oxidising conditions may have arisen from vapour transport during degassing of a magmatic source region or from a hybrid endogenic exogenic process when gases were released during an impacting asteroid or comet impact

motion of continental slivers and creeping subduction in the northern andes regions of intense continental deformation termed continental slivers have been identified in chile bolivia and ecuador analyses of gps data now identify another large sliver in peru the inca sliver that is moving away from a neighbouring sliver in ecuador implying that moving continental slivers control the deformation of almost the entire andean mountain range

abyssal erosion and scarp retreat deep tow observations of the blake escarpment and blake spur abstract deep tow surveys conducted at two sites at the base of the blake spur and blake escarpment serve to delineate the contact between mesozoic platform carbonates of the blake plateau and adjacent abyssal strata the continental margin in the surveyed areas consists of steep limestone cliffs and headlands with over 2 km of relief this extreme topography distorts the hydrographic structure of the water column and intensifies abyssal current flow in the surveyed areas significant lateral scarp retreat is indicated by the presence of broad nearly horizontal benches of mesozoic limestone presently exposed at the base of the blake spur and escarpment in 4 5 5 km water depth and by angular apparently truncated limestone ledges that crop out on the cliff face at the blake spur the contact between mesozoic platformal limestones and basinal tertiary strata does not occur directly at the foot of the cliff but is exposed on the abyssal plain within a 50 m deep erosional moat here strong 2 knots south flowing bottom currents occur within 100 m of the sea floor the coincidence of this vigorous current flowing within the moat near the base of the escarpment and the eroded character of the sea floor suggests that currents are an important mechanism in sculpting this abyssal headland and contributing to lateral scarp retreat similar erosional processes are indicated along the blake escarpment near 29 03 n where the relatively straight cliff face is interrupted by occasional steep walled box canyons on the headland between the canyons the mesozoic outcrop projects into the blake bahama basin for several kilometers as a broad arcuate gently sloping bench these outcropping benches of mesozoic strata at the base of the escarpment are analogous to larger scale buried benches observed in the subsurface that were formed by pre miocene erosion neogene and quaternary scarp retreat is suggested by the location of the contact between mesozoic rocks and younger strata seaward of the steeper cliff face and is probably the result of current induced erosion focused erosion may be facilitated by the presence of a thin 50 m filament of corrosive antarctic bottom water aabw that flows vigorously along the base of the cliff at both sites the recessed position of the canyons shelters them from the main flow of this abyssal current but the steepness and morphology of the canyon walls suggest that additional unidentified erosional processes are focused at the canyon heads

entrainment in shallow rotating gravity currents a modeling study abstract the physics of shallow gravity currents passing through a rotating channel at subcritical froude number is investigated here with a series of idealized numerical experiments it is found that the combined effects of friction and rotation set up a complex transverse circulation that has some crucial implications for the entrainment process a key component of this secondary circulation is a geostrophically balanced transverse jet in the interface that laterally drains fluid from the interface this effect is shown to result in a strong cross channel asymmetry and a spatial separation of the entrainment process drained interfacial fluid is partly replaced by entrained ambient fluid on the deep side of the gravity current whereas the downward mixing of buoyant fluid occurs on the shallow side these results closely corresponding to recent measurements in a shallow channelized gravity current in the western baltic sea illustrate that the description of entrainment as a strictly vertical mixing p

antarctic bottom water flow through the hunter channel the rio grande rise acts as a natural barrier for the equatorward flow of antarctic bottom water in the subtropical south atlantic in addition to the vema channel the hunter channel cuts through this obstacle and offers a separate route for bottom water import into the southern brazil basin on the occasion of the deep basin experiment a component of the world ocean circulation experiment woce the expected deep flow through the hunter channel was directly observed for the first time by an array of moored current meters and thermistor chains from december 1992 to may 1994 main results are i the hunter channel is in fact a conduit for bottom water flow into the brazil basin our new mean transport from moored current meters 2 92 1 24 106 m3 s 1 is significantly higher than earlier estimates that were based on geostrophic calculations ii during the woce observational period a tendency toward increased bottom water temperatures was observed this observation from the hunter channel is consistent with findings from the vema channel iii the overflow through the hunter channel is highly variable and puts in perspective earlier synoptic geostrophic transport estimates

fractionally modified flow in a deep ocean channel application to the vema channel the modification of the exchange flow in a deep southern hemisphere passage resembling the vema channel by frictionally induced secondary circulation is investigated numerically the hydrostatic primitive equation model is a two dimensional version of the sigma coordinate princeton ocean model the time dependent response of a stratified along channel flow forced by barotropic or baroclinic pressure gradients is examined near the bottom where the along channel flow is retarded there is cross channel ekman flux that is associated with downwelling on the eastern side and upwelling on the western side of the channel in the presence of stratification the cross channel flow rearranges the density structure which in turn acts on the along channel velocity via the thermal wind relation eventually the cross isobath ekman flux is shut down in the case of baroclinically driven flow of antarctic bottom water through the vema channel the model reproduces the observed shape of the deep temperature profiles and their cross channel asymmetry the model offers an explanation that is alternative or supplementary to inviscid multilayer hydraulic theory that was proposed in earlier studies it explains the extremely thick bottom boundary layers in the center and on the western slope of the channel the deep thermocline is spread out in the west and sharpened in the east and the coldest water is found on the eastern side of the deep trough the modified density field reduces the along channel flow near the bottom and focuses it into a narrow jet on the eastern side of the channel

variability of the deep water overflow in the luzon strait abstractthe luzon strait with its deepest sills at the bashi channel and luzon trough is the only deep connection between the pacific ocean and the south china sea scs to investigate the deep water overflow through the luzon strait 3 5 yr of continuous mooring observations have been conducted in the deep bashi channel and luzon trough for the first time these observations enable us to assess the detailed variability of the deep water overflow from the pacific to the scs on average the along stream velocity of the overflow is at its maximum at about 120 m above the ocean bottom reaching 19 9 6 5 and 23 0 11 8 cm s 1 at the central bashi channel and luzon trough respectively the velocity measurements can be translated to a mean volume transport for the deep water overflow of 0 83 0 46 sverdrups sv 1 sv 106 m3 s 1 at the bashi channel and 0 88 0 77 sv at the luzon trough significant intraseasonal and seasonal variations are identified with their dominant time scales ranging between

a mixed seismic aseismic stress release episode in the andean subduction zone in subduction zones stress is released by earthquakes and transient aseismic slip the latter falls into two categories slow slip and afterslip slow slip events emerge spontaneously during the interseismic phase and show a progressive acceleration of slip with a negligible contribution of synchronous tremors or microseismicity to the energy or moment release1 2 3 4 5 6 7 8 9 10 11 12 in contrast afterslip occurs immediately after large and moderate earthquakes decelerates over time and releases between 20 and 400 of the moment released by the preceding earthquake13 14 15 16 17 18 here we use seismic and gps data to identify transient aseismic slip that does not fit into either of these categories we document a seismic aseismic slip sequence which occurred at shallow depths along a weakly coupled part of the andean subduction zone19 in northern peru and lasted seven months the sequence generated several moderate earthquakes that together account for about 25 of the total moment released during the full sequence equivalent to magnitude 6 7 transient slip immediately followed two of the earthquakes with slip slowing at a logarithmic rate considered separately the moment released by transient slip following the second earthquake was more than 1 000 of the moment released during the earthquake itself a value incompatible with classical models of afterslip synchronous seismic swarms and aseismic slip may therefore define a stress release process that is distinct from slow slip events and afterslip

structure and evolution of the abyssal jet in the vema channel of the south atlantic the vema channel represents the only major conduit through which the deepest and coldest 0 2 c potential temperature antarctic bottom water aabw flows from the argentine into the brazil basin from 2003 to 2007 two current meter moorings were present on each side of the vema sill close to the narrowest spot of the vema channel the data from the moorings are compared with earlier current and temperature observations on average the maximum current core lies 100 m above the bottom of the sill with a mean northward speed of 0 3 m s 1 farther up in the water column where lower circumpolar deep water and north atlantic deep water prevail one finds a level of sluggish currents with a southward tendency in the sub centimeter per second range the lower boundary of a layer of no motion was observed at 3700 m depth where the mean potential temperature amounts to 1 5 c the evolution of the abyssal warming phenomenon over the last decades with notable fluctuations at the choke point between the argentine and the brazil basin differs from the more stable attitude of deep horizontal currents starting with ctd observations in 1972 we find a steady increase of temperatures of the coldest aabw in the vema channel this general trend of rising abyssal potential temperatures of almost 2 mkelvin per year is based on mostly annual ctd observations the overall warming trend is fully compatible with our three year moored temperature series in agreement with earlier records with high temporal resolution distinct frequently fluctuating horizontal current shear between the western and eastern sides of the vema sill may be explained by two different catchment areas for aabw at the mouth of the vema channel one pathway originates at the american continental rise and advects bottom water in form of the deep western boundary current a second pathway is supplied by an eastern boundary current along the mid atlantic ridge in the argentine basin both source waters merge at the channel entrance mix and their respective strengths can alternate within the sill area

the importance of aspiration and channel curvature in producing strong vertical mixing over a sill on the basis of observations of the time dependent tidally forced flow over a long sill we find that aspiration and channel curvature set the flow structure and condition the flow to allow intense vertical mixing aspiration reduces the potential energy of the water column by thinning it while maintaining its density contrast channel curvature induces a cross channel circulation that can rapidly overturn a stratified flow eighteen along channel sections of density velocity and dissipation rate of turbulent kinetic energy were collected in and around the tacoma narrows of puget sound a site suspected of driving a strong vertical circulation in adjoining main basin rapid inflow to the narrows on flood from one channel of a triple junction reduces dynamic pressure allowing dense water from below sill depth to be uplifted or aspirated into the narrows we estimate water from below 150 m 3 times the sill depth is drawn into the narrows on a 3 m flood tide once in the narrows the flow remains stratified until it passes a 50 bend where a strong secondary circulation overturns the 50 m deep water column and generates intense turbulent mixing cross channel velocities of up to 0 4 m s 1 are observed and maximum values of exceed 10 3 w kg 1 upon leaving the sill stratification is reestablished and turbulence decays a similar set of sequences occurs on ebb except that the outflow bypasses the flood inflow channel and instead discharges into colvos passage the third branch of the triple junction colvos passage ultimately discharges the ebb effluent back into main basin enhancing the impact of mixing at the narrows by discharging the mixed product far from the source scaling of the cross channel momentum equation suggests that below a threshold value of along channel velocity stratification should suppress secondary circulation for a given vertical shear radius of curvature and channel width above the threshold velocity the magnitude of the cross channel velocity is roughly consistent with predictions for unstratified flow we estimate the maximum effective eddy diffusivity that aspiration and mixing in the narrows can produce in main basin to be 10 3 m2 s 1

measuring the onset of locking in the peru chile trench with gps and acoustic measurements the subduction zone off the west coast of south america marks the convergence of the oceanic nazca plate and the continental south america plate nazca south america convergence over the past 23 million years has created the 6 km deep peru chile trench 150 km offshore high pressure between the plates creates a locked zone leading to deformation of the overriding plate the surface area of this locked zone is thought to control the magnitude of co seismic release and is limited by pressure temperature sediment type and fluid content1 here we present seafloor deformation data from the submerged south america plate obtained from a combination of global positioning system gps receivers and acoustic transponders we estimate that the measured horizontal surface motion perpendicular to the trench is consistent with a model having no slip along the thrust fault between 2 and 40 km depth a tsunami in 1996 200 km north of our site was interpreted as being the result of an anomalously shallow interplate earthquake2 seismic coupling at shallow depths such as we observe may explain why co seismic events in the peruvian subduction zone create large tsunamis

circulation and variability at the southern boundary of the brazil basin as a contribution to the woce deep basin experiment an array of current meters with individual record lengths exceeding ii years was set across the southern boundary of the brazil basin between early 1991 and early 1996 the array spanned the santos plateau the vema channel and the hunter channel all areas believed to be important for transport of antarctic bottom water between the argentine and brazil basins from the combination of geostrophic velocities computed from hydrographic stations and those directly measured the total transport of bottom water potential temperature below 2 degrees c is estimated to be about 6 9 sv sv 10 6 m 3 s 1 northward with about 4 sv coming through the vema channel and the remainder through the hunter channel properties of the eddy field are also discussed eddy energy levels and their spatial distribution are similar to comparable regimes in the north atlantic integral timescales vary from a few days to several weeks with distance from the brazil current and the western boundary the eddy heat bur is in the same direction as the heat advection by the mean flow but considerably smaller

hydraulie control and flow separation in a multi layered fluid with applications to the vema channel abstract observations from a recent field experiment in the vema channel are briefly described these show a remarkable change in the configuration of isopycnal surfaces within the channel and the development of thick nearly homogeneous regions near the bottom which are capped by sharp vertical gradients contrary to previous speculation that these bottom boundary layer result from enhanced vertical mixing a dynamical mechanism is explored this involves the hydraulic adjustment of an inertial semi geostrophic flow to the channel geometry first an active two layer flow in a rectangular geometry is studied to show that internal flow separation can occur when the flow is accelerated sufficiently by a narrowing channel almost always this separation accompanies hydraulic control the slowest upstream moving kelvin wave is stopped and upstream and downstream states are not symmetric with respect to the channel width an active three layer flow with a variable bottom profile is then presented as a more

deep lenses of circumpolar water in the argentine basin three deep anticyclonic eddies of a species only reported once before gordon and greengrove 1986 were intersected by hydrographic lines of the world ocean circulation experiment woce and south atlantic ventilation experiment save programs in the argentine basin the vortices are centered near 3500 m depth at the interface between north atlantic deep water and bottom water they have 1500 m thick cores containing lower circumpolar deep water and a dynamic influence that may span up to two thirds of the water column as one eddy was observed just downstream of the western termination of the falkland escarpment a destabilization of the deep boundary current by the sudden slope relaxation is suggested as a potential cause of eddy formation besides isopycnal interleaving at the eddy perimeters strongly eroded core properties in the upper parts of the lenses associated with low density ratios hint at double diffusion at the top of the structures as another major decay mechanism the presence of an eddy in the northern argentine basin shows the possibility for a northward drift of the vortices in this basin at least deep events in recent current measurements from the vema channel are presented that raise the question of further equatorward motion to the brazil basin

magnetite in the unequilibrated ck chondrites implications for metamorphism and new insights into the relationship between the cv and ck chondrites bulk isotopic and elemental compositions of cv and ck chondrites have led to the suggestion that both originate from the same asteroid it has been argued that magnetite compositions also support this model however magnetite has been studied almost exclusively in the equilibrated type 4 6 cks magnetite in seven unequilibrated cks analyzed here is enriched in mgo tio2 and al2o3 relative to the equilibrated cks suggesting that magnetite compositions are affected by metamorphism magnetite in cks is compositionally distinct from cvs particularly in abundances of cr2o3 nio and tio2 although there are minor similarities between cv and equilibrated ck chondrite magnetite this is contrary to what we would expect if the cvs and cks represent a single metamorphic sequence cv magnetite should resemble ck3 magnetite as both were metamorphosed to type 3 conditions oxygen fugacities and temperatures of cvox and ck chondrites are also difficult to reconcile using existing cv ck parent body models mineral chemistries which eliminate issues of bulk sample heterogeneity provide a reliable alternative to techniques that involve a small amount of sample material cv and ck chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism

from geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults thanks to advances in tectonic geodesy it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range interseismic coupling is generally observed to be spatially heterogeneous defining locked patches of stress accumulation to be released in future earthquakes or aseismic transients surrounded by creeping areas clay rich tectonites high temperature and elevated pore fluid pressure seem to be key factors promoting aseismic creep the generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate

suspended particulate matter transport through the vema channel richardson m j biscaye p e gardner w d and hogg n g 1987 suspended particulate matter transport through the vema channel mar geol 77 171 184 sixteen month time series measurements of water velocity and light scattering were coupled with hydrographic and suspended particulate matter sections to determine the flux and the variability in flux of suspended particulate matter through the vema channel the northward flux of spm through the vema channel ranged from 3 to 10 5 104 g s 1 with a mean of 6 5 104 g s 1 the largest fluxes were measured in the deepest and eastern portions of the channel with maximum fluxes of suspended particulate matter at specific sites being roughly two to four times the mean flux some of the suspended particulate matter in the channel may be eroded from the channel itself by the swift currents or eddy like features however the known manganese encrustation and hard floor of the channel suggest that the deep channel floor is not a likely source of sediment a primary source of the suspended particulate matter in the channel may be the sediment drifts in the argentine basin with their associated high standing crops of resuspended particulate matter this resuspended material would then be transported by the antarctic bottom water into and through the vema channel into the brazil basin the northward flux of suspended particulate matter through the vema channel is presently a significant but not dominant influence on sedimentation in the brazil basin

the flow of antarctic bottom water into the brazil basin the total transport of antarctic bottom water across the rio grande rise including the western boundary the vema channel and the hunter channel is estimated from hydrographic measurements across these pathways the contribution of the vema channel is greatest at 3 9 106 m3 s 1 which is very close to earlier estimates the western boundary current contribution is 2 0 106 m3 s 1 and that of the hunter channel 0 7 106 m3 s 1 the lower values outside the vema channel are offset by the important source of mass they form to the lower density classes of bottom water about 40 of the flow is concentrated in the highest density class representing the source of weddell sea deep water to the brazil basin the flow structure is characterized by horizontal and vertical recirculation

biological dissolution and activity of the allende meteorite this paper reports on the effect of the allende meteorite on the integrity of biological material and addresses the question whether it can induce cell damage via oxidative stress and cell mortality the reaction mechanisms addressed herein are studied using electron paramagnetic resonance spectroscopy epr high resolution transmission electron microscopy scanning electron microscopy and energy dispersive spectroscopy high resolution x ray diffraction and the assays for thiobarbituric acid reactive substances tbars and cell viability using 3 4 5 dimethylthiazol 2 yel 2 5 diphenyltetrazolium bromide mtt bromide as determined by the tbars assay allende specimens induced cell damage via oxidative stress the contents of tbars in suspensions containing 1000 ppm of allende and fe 1 x s were 6 8 0 7 and 5 8 0 6 nmol mg protein respectively epr experiments conducted on reaction mixtures containing allende 5 5 dimethyl 1 pyrroline n oxide dmpo and h 2 o 2 showed a quartet signal a 1 2 2 1 intensity and hyperfine coupling constants corresponding to a n 1 49 mt and a h 1 49 mt a signature of the dmpo oh adduct the intensity of the signal depended on the concentration of the solids in suspension while the formation of dmpo oh was limited by h 2 o 2 experiments were conducted to test for the production of the dmpo oh adduct from ferric ions and the plausible generation of ho the role of ethanol ch 3 ch 2 oh as scavenger of ho in allende dmpo suspensions was addressed results showed a six line spectra with hyperfine coupling constants a n 15 8 g a h 22 6 g and g 2 0059 consistent with the formation of the dmpo ch oh ch 3 adduct but not dmpo och 2 ch 3 we explain these findings as the result of formation of ho onto or in proximity to the mineral surface with ch 3 ch 2 oh competing with dmpo for ho and ferric iron playing a lesser role in dmpo transformation our findings are congruent with reported radical scavenging experiments for pyrite under anoxic conditions concluding the formation of ho at surface defect sites experiments conducted in allende desferrioxamine b dfo b suspensions showed the inhibition of the formation of ho by means of decreases in the dmpo oh adduct signal accounted for by the reaction between fe ii and ho to form fe iii and competing reaction mechanisms at the structural fe centers confirming that the production of ho radicals is associated with iron centers and contributes to mineral dissolution small sized magnetite domains present were recognized as catalytic sites for the production of ho radicals the fe 3 o 4 domains present in the allende matrix exhibited a submicron range an elongated hexagonal habit and a high degree of crystallinity supporting the presence of biogenic fe 3 o 4 cell viability was found to be susceptible to the distribution and atomic environment of structural fe

the relationship between ck and cv chondrites ck chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of fe ni metal although the group is predominately composed of equilibrated meteorites types 4 6 in recent years a significant number of new samples have been classified as being either ck3 or ck3 anomalous these unequilibrated cks often display a close affinity with members of the cv oxidized subgroup cks and cvs oxidized subgroup may therefore form a continuum and by implication could be derived from a single common parent body to investigate the relationship between these two groups a detailed study of the oxygen isotope composition opaque mineralogy and major and trace element geochemistry of a suite of cv and ck chondrites has been undertaken the results of oxygen isotope analysis confirm the close affinity between cv and ck chondrites while excluding the possibility of a linkage between the co and ck groups magnetites in both cv and ck chondrites show significant compositional similarities but high ti contents are a diagnostic feature of the latter group the results of major and trace element analysis demonstrate that both cv and ck chondrites show overlapping variation supporting evidence for a single common source for both groups comes from their similar cosmic ray exposure age distributions recent reflectance spectral analysis is consistent with both the cvs and cks being derived from eos family asteroids which are believed to have formed by the catastrophic disruption of a single large asteroid thus a range of evidence appears to be consistent with cv and ck chondrites representing samples from a single thermally stratified parent body in view of the close similarity between cv and ck chondrites some modification of the present classification scheme may be warranted possibly involving integration of the two groups one means of achieving this would be to reassigned ck chondrites to a subgroup of the oxidized cvs it is recognized that a full evaluation of this proposal may require further study of the still poorly understood ck3 chondrites

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

temperature fluctuations and current shear in antarctic bottom water at the vema sill the vema channel acts as a major conduit for the equatorward spreading of antarctic bottom water between the argentine and brazil basins for almost two years the thermal stratification above its saddle depth 4660 m called vema sill was recorded by moored thermistors and current meters the lowest 490 m of the water column was instrumented to monitor the well developed benthic boundary layer of antarctic bottom water the latter can be subdivided into weddell sea deep water on the sea bed and lower circumpolar deep water above it the data show fluctuations on various scales including periods each about 1 2 weeks long when the abyssal stratification virtually disappeared assuming a stable ratio between density and temperature time series of bulk richardson numbers are estimated from temperature and current shear data the results suggest a potential for intermittent episodes of locally generated vertical mixing

antarctic bottom water flux in the equatorial western atlantic a moored array at the equator in the western basin of the atlantic provides a 604 day time series of abyssal currents and temperatures spanning the full breadth of the antarctic bottom water aabw flowing from the brazil basin to the guiana basin mean aabw transport is estimated to be 2 0 sv sv 106 m3 s21 comprising organized westward flow of 2 24 sv and return flow of 0 24 sv the low frequency variability is dominated by a quasi annual transport cycle of amplitude 0 9 sv and a 120 day period of amplitude 0 6 sv maximum transports occur in september october while minimum transports occur in february march allowing for this quasiannual cycle and extrapolating the 604 day record to a full two years adds about 7 to the estimated mean aabw transport the array also provides limited sampling in the overlying lower north atlantic deep water lnadw where a southern boundary intensified flow of lnadw gives the strongest recorded mean speed through the array 9 9 cm s21 into the brazil basin the lnadw records also have a quasi annual cycle with strong lnadw flow episodes occurring in april may time series of temperature indicate that the lnadw aabw transition layer rises and falls in synchrony with the quasi annual aabw transport cycle uplifted transition layer during strong aabw transport periods an observed overall warming trend appears to be accompanied by a decline in aabw transport

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

topographic influence on overflow dynamics idealized numerical simulations and the faroe bank channel overflow 1 properties of the north atlantic deep water nadw depend on mixing that occurs in the denmark strait ds and the faroe bank channel fbc overflow regions how the sill s topography in those regions may affect mixing processes and downstream variability is thus investigated using a high resolution terrain following ocean model model results agree with observations that show enhanced mixing and entrainment downstream from the sill however mixing seems to occur over a longer distance downstream from the fbc sill and more abruptly downstream from the ds sill sensitivity experiments with various fbc sill widths demonstrate that the narrow sill is responsible for the enhanced mixing the downstream flow variability eddy propagation and deep water properties are affected by sill width and background stratification similar to the laboratory overflow experiments of cenedese et al 2004 three distinct mixing regimes characterized by the froude number are identified in the fbc simulations a steady subcritical flow regime upstream from the sill a supercritical wave like flow regime downstream from the sill and an irregular eddy dominated regime farther away from the sill satellite altimeter data near the fbc show cyclonic anomalies propagating along the northern slope of the channel resembling the surface eddies associated with the overflow variability in the model a cross channel circulation over the fbc sill driven by frictional bottom boundary layers resulted in convergence divergence zones near the southern northern slopes and pinching spreading of isotherms across the channel similar to the observation based mechanism proposed by johnson and sanford 1992

a non linear geodetic data inversion using abic for slip distribution on a fault with an unknown dip angle summary we have developed a method of geodetic data inversion for slip distribution on a fault with an unknown dip angle a common strategy for obtaining slip distribution in previous studies is to first determine the fault geometry by minimizing the square misfit under the assumption of a uniform slip on a rectangular fault and then apply the usual linear inversion technique to estimate a slip distribution on the determined fault it is not guaranteed however that the fault determined under the assumption of a uniform slip gives the best fault geometry for a spatially variable slip distribution the inverse problem is non linear for cases with unknown fault geometries but the non linearity of the problems is actually weak when we can assume the fault surface to be a flat plane in particular when a clear trace of coseismic faults is observed on the earth s surface only the dip angle is an unknown parameter to determine the fault geometry then we regarded the dip angle as an hyperparameter that prescribed the structure of parametric models and obtained the best estimate of the dip angle using akaike s bayesian information criterion abic with the best estimate of the dip angle we can obtain the slip distribution on the fault based on the maximum likelihood principle we applied the method to the insar data of the 1995 dinar turkey earthquake and obtained a much lower dip angle than the previous analyses

origin of magnetite in oxidized cv chondrites in situ measurement of oxygen isotope compositions of allende magnetite and olivine magnetite in the oxidized cv chondrite allende mainly occurs as spherical nodules in porphyritic olivine po chondrules where it is associated with ni rich metal and or sulfides to help constrain the origin of the magnetite we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in po chondrules of allende by an in situ ion microprobe technique five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18o values from 4 8 to 7 1 and delta 17o values from 2 9 to 6 3 seven coexisting olivine grains have oxygen isotopic compositions from 0 9 to 6 3 in delta 18o and from 4 6 to 7 9 in delta 17o the delta 17o values of the magnetite and coexisting olivine do not overlap they range from 0 4 to 2 6 and from 4 0 to 5 7 respectively thus the magnetite is not in isotopic equilibrium with the olivine in po chondrules implying that it formed after the chondrule formation the delta 17o of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas we infer that the magnetite formed on the parent asteroid by oxidation of metal by h2o which had previously experienced minor o isotope exchange with fine grained silicates

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

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

abyssal circulation in the argentine basin the abyssal water mass in the argentine basin generically called antarctic bottom water is of southern origin its source is primarily weddell sea deep water with characteristics of 0 7 to 0 2 c and salinity 34 65 34 68 which flows out of the weddell gyre into the south sandwich trench and continues north beyond the falklands escarpment into the argentine basin the abyssal water cannot have originated in the antarctic circumpolar current acc since waters colder than 0 2 c are not associated with the acc in the drake passage once the abyssal water has entered the argentine basin through gaps in the falklands escarpment or around the islas orcadas rise it is generally assumed that it turns sharply to the west in accordance with the stommel and arons 1960 theory of ocean circulation and flows along the base of the falklands escarpment before flowing north along the continental slope as a deep western boundary current off south america results from the world ocean circulation experiment woce al 1 section however suggest that the newest most cfc rich water occurs on the eastern side of the argentine basin rather than the west we therefore conclude that in addition to the western boundary current there is a more dominant anticlockwise circulation around the zapiola rise which is likely related to the migratory pattern of the acc

active tectonics of peru heterogeneous interseismic coupling along the nazca megathrust rigid motion of the peruvian sliver and subandean shortening accommodation over 100 gps sites measured in 2008 2013 in peru provide new insights into the present day crustal deformation of the 2200 km long peruvian margin this margin is squeezed between the eastward subduction of the oceanic nazca plate at the south america trench axis and the westward continental subduction of the south american plate beneath the eastern cordillera and subandean orogenic wedge continental active faults and gps data reveal the rigid motion of a peruvian forearc sliver that extends from the oceanic trench axis to the western eastern cordilleras boundary and moves southeastward at 4 5 mm yr relative to a stable south america reference frame gps data indicate that the subandean shortening increases southward by 2 to 4 mm yr in a peruvian sliver reference frame the residual gps data indicate that the interseismic coupling along the nazca megathrust is highly heterogeneous coupling in northern peru is shallow and coincides with the site of previous moderate sized and shallow tsunami earthquakes deep coupling occurs in central and southern peru where repeated large and great megathrust earthquakes have occurred the strong correlation between highly coupled areas and large ruptures suggests that seismic asperities are persistent features of the megathrust creeping segments appear at the extremities of great ruptures and where oceanic fracture zones and ridges enter the subduction zone suggesting that these subducting structures play a major role in the seismic segmentation of the peruvian margin in central peru we estimate a recurrence time of 305 40 years to reproduce the great 1746 mw 8 8 lima callao earthquake