multi fault rupture and successive triggering during the 2012 mw 8 6 sumatra offshore earthquake 1 on april 11 2012 a mw 8 6 strike slip earthquake struck the northern sumatra offshore region and became the largest intraplate event ever recorded there preliminary study results show a remarkably complex rupture pattern on a fault system manifested by north south trending paleo transform faults and east west striking abyssal hill fabric to image the rupture pattern of the earthquake we back projected teleseismic p wave recordings observed at three regional seismic networks eu au and f net our results indicate that the earthquake ruptured on a conjugate fault system composed of two subparallel wnw ese trending faults and a nne ssw striking fault in between for a duration of at least 120 s the rupture started at the wnw end of the first wnw ese trending fault located at the east of the conjugate fault system and propagated toward ese it then jumped to the second nne ssw trending fault located west of the first fault and first extended sswward and 15 s later nneward after its end on the second fault the rupture jumped onto the third wnw ese trending fault and continued wnwward the static coulomb stress changes calculated from the rupture of the first and then the second faults based on simplified uniform slip models suggest that initiation of the rupture on the second fault could be statically and dynamically triggered by the first fault however the third fault was primarily dynamically triggered by s or even love waves radiated from the southern branch of the second fault

glacial lake spillway incision and deposition of a coarse grained fan near watrous saskatchewan the watrous spillway was rapidly incised during a short lived outburst from glacial lake elstow in its outlet area the bed of lake elstow was composed of stagnant ice the 40 km long spillway is

the dynamics of southern ocean storm tracks abstractthe mechanisms that initiate and maintain oceanic storm tracks regions of anomalously high eddy kinetic energy are studied in a wind driven isopycnal primitive equation model with idealized bottom topography storm tracks are found downstream of the topography in regions strongly influenced by a large scale stationary meander that is generated by the interaction between the background mean flow and the topography in oceanic storm tracks the length scale of the stationary meander differs from that of the transient eddies a point of distinction from the atmospheric storm tracks when the zonal length and height of the topography are varied the storm track intensity is largely unchanged and the downstream storm track length varies only weakly the dynamics of the storm track in this idealized configuration are investigated using a wave activity flux related to the eliassen palm flux and eddy energy budgets it is found that vertical fluxes of wave activity which correspond to eddy growth

abyssal connections of antarctic bottom water in a southern ocean state estimate antarctic bottom water aabw is formed in a few locations around the antarctic continent each source with distinct temperature and salinity after formation the different aabw varieties cross the southern ocean and flow into the subtropical abyssal basins it is shown here using the analysis of lagrangian trajectories within the southern ocean state estimate sose model that the pathways of the different sources of aabw have to a large extent amalgamated into one pathway by the time it reaches 31 s in the deep subtropical basins the antarctic circumpolar current appears to play an important role in the amalgamation as 70 of the aabw completes at least one circumpolar loop before reaching the subtropical basins this amalgamation of aabw pathways suggests that on decadal to centennial time scales changes to properties and formation rates in any of the aabw source regions will be conveyed to all three subtropical abyssal basins 2013 american geophysical union all rights reserved

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

topographic enhancement of eddy efficiency in baroclinic equilibration abstractthe processes that determine the depth of the southern ocean thermocline are considered in existing conceptual frameworks the thermocline depth is determined by competition between the mean and eddy heat transport with a contribution from the interaction with the stratification in the enclosed portion of the ocean using numerical simulations this study examines the equilibration of an idealized circumpolar current with and without topography the authors find that eddies are much more efficient when topography is present leading to a shallower thermocline than in the flat case a simple quasigeostrophic analytical model shows that the topographically induced standing wave increases the effective eddy diffusivity by increasing the local buoyancy gradients and lengthening the buoyancy contours across which the eddies transport heat in addition to this local heat flux intensification transient eddy heat fluxes are suppressed away from the topography especially upstream indicating that local

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

probabilistic forecasting of earthquakes we present long term and short term forecasts for magnitude 5 8 and larger earthquakes we discuss a method for optimizing both procedures and testing their forecasting effectiveness using the likelihood function our forecasts are expressed as the rate density that is the probability per unit area and time anywhere on the earth our forecasts are for scientific testing only they are not to be construed as earthquake predictions or warnings and they carry no official endorsement for our long term forecast we assume that the rate density is proportional to a smoothed version of past seismicity using the harvard cmt catalogue this is in some ways antithetical to the seismic gap model which assumes that recent earthquakes deter future ones the estimated rate density depends linearly on the magnitude of past earthquakes and approximately on a negative power of the epicentral distance out to a few hundred kilometres we assume no explicit time dependence although the estimated rate density will vary slightly from day to day as earthquakes enter the catalogue the forecast applies to the ensemble of earthquakes during the test period it is not meant to predict any single earthquake and no single earthquake or lack of one is adequate to evaluate such a hypothesis we assume that 1 per cent of all earthquakes are surprises assumed uniformly likely to occur in those areas with no earthquakes since 1977 we have made specific forecasts for the calendar year 1999 for the northwest pacific and southwest pacific regions and we plan to expand the forecast to the whole earth we test the forecast against the earthquake catalogue using a likelihood test and present the results our short term forecast updated daily makes explicit use of statistical models describing earthquake clustering like the long term forecast the short term version is expressed as a rate density in location magnitude and time however the short term forecasts will change significantly from day to day in response to recent earthquakes the forecast applies to main shocks aftershocks aftershocks of aftershocks and main shocks preceded by foreshocks however there is no need to label each event and the method is completely automatic according to the model nearly 10 per cent of moderately sized earthquakes will be followed by larger ones within a few weeks

the sequence and timing of large late pleistocene floods from glacial lake missoula abstract glacial lake missoula formed when the purcell trench lobe of the cordilleran ice sheet dammed clark fork river in montana during the fraser glaciation marine oxygen isotope stage 2 over a period of several thousand years the lake repeatedly filled and drained through its ice dam and floodwaters coursed across the landscape in eastern washington in this paper we describe the stratigraphy and sedimentology of a significant new section of fine grained glacial lake missoula sediment and compare this section to a similar previously described sequence of sediments at ninemile creek 26 km to the northwest the new exposure which we informally term the rail line section is located near missoula montana and exposes 29 units each of which consists of many silt and clay couplets that we interpret to be varves the deposits are similar to other fine grained sediments attributed to glacial lake missoula similar varved sediments overlie gravelly flood deposits elsewhere in the glacial lake missoula basin each of the 29 units represents a period when the lake was deepening and all units show evidence for substantial draining of glacial lake missoula that repeatedly exposed the lake floor the evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake desiccation cracks that formed during exposure of the lake bottom and fluvial sand deposited as the lake began to refill the floods date to between approximately 21 4 and 13 4 cal ka ago based on regional chronological data the total number of varves at the rail line and ninemile sites are respectively 732 and 583 depending on lake refilling times each exposure probably records 1350 1500 years of time we present three new optical ages from the rail line and ninemile sites that further limit the age of the floods these ages in calendar years are 15 1 0 6 ka at the base of the ninemile exposure and 14 8 0 7 and 12 6 0 6 ka midway through the rail line exposure the sediment at the two sections was deposited during later stages of glacial lake missoula after the largest outburst events

numerical simulations of large scale cataclysmic floodwater a simple depth averaged model and an illustrative application a simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data the code aims to keep the basic equations simple and the required computational costs low which allows greater exploration of parameter space examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth averaged diffusion wave approximation in two dimensions as well as manning s empirical equation for simplification on the other hand topography is included as a boundary condition since topography plays an important role in selecting flood routes the model provides important advantages over theoretical analyses or one dimensional simulations including 1 the reproduction of complicated water flow paths such as bifurcations and reconvergences 2 the reconstruction of hydrological relationships among the water paths and 3 the direct comparison among the calculated extent of the flood inundation including floodwater depths and geological and geomorphological observations preliminary reconstructions of the missoula floods demonstrate the advantages of this new approach the method of coupling field based flood information with two dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on earth with direct bearing on the understanding of regional paleohydrological histories of mars

hematite u th he thermochronometry constrains intraplate strike slip faulting on the kuh e faghan fault central iran abstract the kuh e faghan strike slip fault system kff located to the northern edge of the lut block in central iran developed through a neogene quaternary pulsed history of eastward fault propagation and fault related exhumation this system is a consequence of the residual stresses transmitted from the arabia eurasia convergent plate boundary here we integrate structural and textural analysis with new and previously published apatite fission track aft and apatite u th he apatite he results chlorite thermomentry and hematite u th he data from hematite coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late miocene pliocene burial and exhumation associated with the propagation of the kff twenty nine hematite u th he hematite he dates from three striated hematite coated slip surfaces from the kff fault core and damage zone yield individual dates from 12 2 ma petrographic analysis and chlorite thermometry of a polyphase fossil fluid system in the kff fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal t 239 10 c fluids and hematite formation hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics no evidence of hematite comminution and similar hematite he closure temperatures 60 85 c in each sample integration of these results with thermal history modeling of aft and apatite he data shows that kff activity in the late miocene is characterized by an early stage of fault nucleation fluid circulation hematite mineralization and eastward propagation not associated with vertical movement that lasted from 12 to 7 ma hematite he aft and apatite he data track a second phase of fault system activity involving fault related exhumation initiating at 7 ma and continuing until present time our new data constrain the onset of the recognized late miocene pliocene tectonic reorganization in north central iran

paleohydraulic reconstruction of the largest glacial lake missoula draining s glacial lake missoula glm was the source of earth s largest known peak flood discharges onto the channeled scabland northwestern united states the original studies of glm were based on geomorphological mapping of lake sediments and shorelines more recently studies have emphasized the computational fluid dynamics of downstream megaflood routing and characteristics in the channeled scabland and adjacent areas however actual details of the lake draining processes glm have received little scientific attention in this paper we employ two dimensional hydraulic modelling to understand the paleoflow conditions for different scenarios of draining glm at its highest stands values are calculated for three glm drainage hydrographs 2 6 13 17 10 6 m 3 s 1 that previous studies had estimated for outlet flows consistent with regional mapping and with the original interpretation of fluvial geomorphology by other studies the modelling shows that lake silt sequences in the gorges of glm must postdate the most highly energetic outburst events from the lake this is because the flows generated in the lake by megaflood outflows are sufficiently energetic to erode any accumulated silt deposits in contrast the gravels underlying the silts in these zones include boulder sized clasts largescale cross stratification and 70e100 m high bars forms all of which indicate very high energy flood flow conditions the modelling also shows that the paleohydraulic conditions which developed in the lake basin during the largest megaflood outflows would be capable of accounting for the observed bedrock scour at rainbow lake pass various high eddy deposits eddy bars of flood gravel in gorges and the giant ripple marks subaqueous gravel dunes that were classically described in the 1940s previous studies interpreted the glacial lake silt rhythmites and related deposits such as the ninemile section as evidence for numerous fillings and drainings of glm our modelling suggests that these inferred events must have been relatively low in energy and magnitude relative to the earlier outburst s that emplaced the flood gravels subaqueous gravel dunes and scabland like erosion surfaces

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

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

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

quaternary break out flood sediments in the peshawar basin of northern pakistan the presence of horizontally bedded fining upward sequences of sands silts and clays throughout the peshawar basin of northern pakistan has previously been ascribed to pleistocene lakes within the basin close inspection of these sediments however show sedimentological properties that suggest these stacked sequences are more characteristic of deposits of periodic break out flood deposits and not lacustrine deposits exposures near the villages of piran nowshera jehingira jalala and along the kabul river show evidence of subaerial exposure mudcracks and bioturbation zones lateral continuity and fracture sets at least three distinct cycles of deposition are apparent in the basin each exhibiting slightly different structural and sedimentological properties the groupings and dimensions of the rhythmite sequences indicate that within each cycle multiple episodes of flooding occurred the absence of significant erosional and depositional features as well as the preservation of mud rip up clasts and bioturbation zones further suggests that the periods between episodes of flooding were probably on the order of 101 to 102 years evidence of ice dams and lakes in the indus drainage system is abundant cross valley moraines and lacustrine deposits that stretch many kilometers upstream are visible in the middle indus valley between the villages of sazin and shatial and skardu calculated ratios of sediment to water suggest that an upstream reservoir at least 32 km3 and perhaps as large as 128 km3 would have been required to produce the extent of rhythmites observed in the peshawar basin generating a reservoir of this size in the indus drainage system was accomplished near the villages of sazin shatial where large cross valley moraines and upstream lacustrine sediments indicate large ice dams as do the moraines and lacustrine sediments near gilgit and skardu the origin of the graded sediments in the peshawar basin however has not been correlated to the failure of a specific ice dam the temporal relationship of the graded sediments is unclear limited thermoluminescence tl analysis of the youngest set of graded sediments referred to as lake beds by previous investigators in the peshawar basin suggest an age of at least 130 000 years bp this time correlates to the yunz stage of glaciation along the middle indus valley which spans from the mid to late pleistocene to about 130 000 years bp

the schwartzwalder uranium deposit ii age of uranium mineralization and lead isotope constraints on genesis u pb isotope analyses of ores from the schwartzwalder uranium mine colorado show that these ores have high amounts of initial common pb and that the initial pb was both variable and relatively radiogenic in its pb isotope ratios 206 pb 204 pb 26 30 as a result the only useful approach to dating these ores is with u pb isochrons and even so some means of dealing with the variable initial pb isotope ratios is required because the common pb in these ores was apparently derived from sources of similar age and th u the observed 208 pb 204 pb of these th free ores can be used either to identify sample suites with similar initial pb isotope ratios or to normalize for the variable initial pb isotope ratios the resulting u pb isochrons indicate an age of mineralization for both illinois vein and titan vein ores of 69 3 or 1 1 m y suggesting that the deposit was formed during the earliest stages of laramide uplift and under at least 3 km of phanerozoic cover the initial pb isotope systematics of the ores show that the metals in the schwartzwalder ores were derived from source s of 1 730 or 130 m y age with a th u of 2 2 or 0 2 and 238 u 204 pb of 30 to 60 these restrictions on the source s of the metals rule out the possibility that the deposit could have been formed by remobilization of a proterozoic uranium deposit and both the 69 3 m y age of the ores and their initial pb isotope ratios preclude any contribution of metals to the deposit by younger volcanics such as those in the denver formation

periodic floods from glacial lake missoula into the sanpoil arm of glacial lake columbia northeastern washington at least 15 floods ascended the sanpoil arm of glacial lake columbia during a single glaciation varves between 14 of the flood beds indicate one backflooding every 35 to 55 yr this regularity suggests that the floods came from an ice dammed lake that was self dumping probably the self dumping lake was glacial lake missoula montana because the floods accord with inferred emptyings of that lake in frequency and number apparently entered lake columbia from the east and produced beds resembling backflood deposits of lake missoula floods in southern washington

reply to comment on periodic jokulhlaups from pleistocene glacial lake missoula new evidence from varved sediment in northern idaho and washington

provenance and deposition of glacial lake missoula lacustrine and flood sediments determined from rock magnetic properties abstract repeated outburst flooding from glacial lake missoula montana affected large areas of washington during marine oxygen isotope stage 2 29 14 ka we present the first high resolution rock magnetic results from two sites that are critical to interpreting these outburst floods and that provide evidence of sediment provenance glacial lake missoula the source of the floods and glacial lake columbia where floodwaters interrupted sedimentation magnetic carriers in glacial lake missoula varves are dominated by hematite whereas those in outburst flood sediments and glacial lake columbia sediments are mainly magnetite and titano magnetite stratigraphic variation of magnetic parameters is consistent with changes in lithology importantly magnetic properties highlight depositional processes in the flood sediments that are not evident in the field in glacial lake columbia hematite is present in fine silt and clay deposited near the end of each flood as fine sediment settled out of the water column this signal is only present at the end of the floods because the hematite is concentrated in the finer grained sediment transported from the floor of glacial lake missoula the only possible source of hematite 240 km away

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

magnetostratigraphic evidence from the cold creek bar for onset of ice age cataclysmic floods in eastern washington during the early pleistocene this study provides a detailed magnetostratigraphy of sediments composing the cold creek cataclysmic flood bar in the pasco basin washington our interpretation suggests onset of missoula floods or similar events prior to 1 1 myr later than previously suggested by bjornstad et al bjornstad b n fecht k r pluhar c j 2001 long history of pre wisconsin ice age cataclysmic floods evidence from southeastern washington state journal of geology 109 6 695 713 nonetheless these data suggest that channeled scabland features formed over a much longer timespan than commonly cited that continental ice sheets of the early pleistocene reached as far south as those of the late pleistocene and that similar physiography existed in eastern washington and perhaps montana to both generate and route missoula flood like events this study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the cold creek cataclysmic flood bar to our previous database of 53 samples from four boreholes resulting in a much more robust and detailed magnetostratigraphy rock magnetic studies on these sediments show pure magnetite to be the predominant remanence carrying magnetic mineral ruling out widespread remagnetization by secondary mineralization the magnetostratigraphy at eastern cold creek bar is characterized by a normal polarity interval bracketed by reversed polarities equating the normal zone with the jaramillo subchron 0 99 1 07 myr affords the simplest correlation to the magnetic polarity timescale western cold creek bar was likely deposited during the brunhes chron 0 0 78 myr since it exhibits mainly normal polarities with only two thin reversed polarity horizons that we interpret as magnetic excursions during the brunhes

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

outburst flood evolution at russell glacier western greenland effects of a bedrock channel cascade with intermediary lakes abstract glacial lake outburst floods have produced a distinctive and widespread quaternary record both onshore and offshore via widespread and intense geomorphological impacts yet these impacts remain poorly understood due to a lack of modern analogues this study therefore makes a systematic quantification of the evolution of a bedrock channelled outburst flood channel topography was obtained from digitised aerial photographs a 5 m grid resolution dem and bathymetric surveys flood inundation was measured in the field from dgps measurements flood evolution was analysed with application of a numerical model novel flood metrics including rate of rise to peak and persistence above a value of hydraulics were calculated the key findings were that outburst floods i that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level dissipated of energy due to considerable flow recirculation during the rising stage of the flood and after overtopping of the outlet are moderated in terms of peak discharge ii can have kinematic waves that are introduced to a flood via hydraulic ponding iii may develop a partitioning of flow regimes for instantaneous peak discharge bed shear stress and froude number due to time transgressive changes in channel cross section specifically between inner channel and overbank regions furthermore normalised change in cross sectional area and normalised change in channel slope can be used to suggest the relative magnitude of instantaneous peak discharge net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a time to peak value reconstructions of quaternary outburst floods should consider the importance of including intermediary lakes modern hazard mitigation studies could usefully note the potential use of reservoirs as an outburst flood alleviation resource

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

sensitivity of the ocean s deep overturning circulation to easterly antarctic winds we investigate the sensitivity of the deep meridional overturning circulation moc in the southern ocean to changes in the easterly wind stress over the antarctic continental slope the deep moc is driven by export of dense antarctic bottom water from the antarctic continental shelf and exerts a strong influence on climate by ventilating the deep ocean with oxygen and storing carbon dioxide the possibility that inter climatic modifications of the deep overturning may have been driven by changes in the atmospheric circulation has motivated the recent interest in evaluating the sensitivity of the southern ocean moc to modifications of the mid latitude westerlies using a high resolution eddy resolving model of a sector of the southern ocean we show that the deep cell of the moc is highly sensitive to the strength of the polar easterlies and relatively insensitive to the strength of the mid latitude westerlies our results highlight that determining the deep ocean ventilation in past and future climates demands an accurate evaluation of the concurrent surface wind stress throughout the southern ocean

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

erosion of the tsangpo gorge by megafloods eastern himalaya at the southeastern margin of the tibetan plateau the yarlung tsangpo river plunges through the himalaya to drop 2 km through the tsangpo gorge upstream relict glacial dams and impounded lake terraces suggest that quaternary lakes as large as 800 km 3 catastrophically drained through the gorge as megafloods we report on new megaflood deposits downstream of the gorge and use detrital zircon u pb provenance data to demonstrate that these high magnitude events originated in tibet and more effectively focused erosion in the gorge than both the extremely erosive modern peak flows and one of the largest landslide dam outburst floods ever documented our findings support the proposition that in this steep narrow gorge where hillslope angles are near the threshold angle of bedrock failure megafloods provide a mechanism to rapidly evacuate hillslope material and focus erosion on channel adjacent hillslopes although megaflood frequency remains unconstrained we demonstrate the capability of these events to contribute substantially to rapid exhumation in this region

sensitivity of the overturning circulation in the southern ocean to decadal changes in wind forcing abstractthe sensitivity of the overturning circulation in the southern ocean to the recent decadal strengthening of the overlying winds is being discussed intensely with some works attributing an inferred saturation of the southern ocean co2 sink to an intensification of the overturning circulation while others have argued that this circulation is insensitive to changes in winds fundamental to reconciling these diverse views is to understand properly the role of eddies in counteracting the directly wind forced changes in overturning here the authors use novel theoretical considerations and fine resolution ocean models to develop a new scaling for the sensitivity of eddy induced mixing to changes in winds and they demonstrate that changes in southern ocean overturning in response to recent and future changes in wind stress forcing are likely to be substantial even in the presence of a decadally varying eddy field this result has significant implications for the ocean s role in the carbon cycle and

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

the injection of zonal momentum by buoyancy forcing in a southern ocean model abstractan overturning circulation driven by prescribed buoyancy forcing is used to set a zonal volume transport in a reentrant channel ocean model with three isopycnal layers the channel is designed to represent the southern ocean such that the forced overturning resembles the lower limb of the meridional overturning circulation moc the relative contributions of wind and buoyancy forcing to the zonal circulation are examined it is found that the zonal volume transport is strongly dependent on the buoyancy forcing and that the eddy kinetic energy is primarily set by wind stress forcing the zonal momentum budget integrated over each layer is considered in the buoyancy forced wind forced and combined forcing case at equilibrium sources and sinks of momentum are balanced but the transient spinup reveals the source of momentum for the current in the buoyancy forced case the forcing creates a baroclinic shear with westward flow in the lower layer allowing topographic form stress and bottom fric

late quaternary activity of the pajarito fault rio grande rift of northern new mexico usa the pajarito fault forms the western margin of the rio grande rift in north central new mexico and lies adjacent to los alamos national laboratory a major federal research facility vertical displacement on this normal fault over the past 1 2 ma has created a 50 to 120 m high fault scarp on bandelier tuff 1 2 ma yielding a long term average slip rate of ca 0 1 mm yr in support of a laboratory wide seismic hazards assessment we excavated 14 trenches in the pajarito fault zone to determine the age of the most recent displacement event the recurrence interval between events the displacement per event and the variability in slip rate and recurrence through time the large number of trenches was required by the large height of the fault scarp and the complexity of the fault zone only about half the trenches contained significant thicknesses of holocene deposits but in those trenches there was clear evidence for an early to mid holocene displacement event the previous event was at least 20 40 ka and the average recurrence interval over the past ca 300 ka was about 20 40 kyr we infer that much of the structural relief across this fault developed soon after eruption of the bandelier tuff between 1 0 and 1 2 ma and that slip rate slowed considerably after that time d 2005 published by elsevier b v

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

statistical aspects of parkfield earthquake sequence and parkfield prediction experiment abstract this note discusses three interconnected statistical problems concerning the parkfield sequence of moderate earthquakes and the parkfield prediction experiment a is it possible that the quasi periodic parkfield sequence of characteristic earthquakes is no uncommon specific phenomenon the research hypothesis but can be explained by a preferential selection from available earthquake catalogs to this end we formulate the null hypothesis earthquakes occur according to the poisson process in time and their size follows the gutenberg richter relation we test whether the null hypothesis can be rejected as an explanation for the parkfield sequence b if the null hypothesis cannot be refuted what is the probability of magnitude m 6 earthquake occurrence in the parkfield region c the direct goal of the parkfield experiment is the registration of precursory phenomena prior to a m6 earthquake however in the absence of the characteristic earthquake can the experiment resolve which of the two competing hypotheses is true in a reasonable time statistical analysis is hindered by an insufficiently rigorous definition of the research model and inadequate or ambiguous data however we show that the null hypothesis cannot be decisively rejected the quasi periodic pattern of intermediate size earthquakes in the parkfield area is a statistical event likely to occur by chance if it has been preferentially selected from available earthquake catalogs the observed magnitude frequency curves for small and intermediate earthquakes in the parkfield area agree with the theoretical distribution computed on the basis of a modified gutenberg richter law gamma distribution using deformation rates for the san andreas fault we show that the size distribution of the parkfield characteristic earthquakes can also be attributed to selection bias according to the null hypothesis the yearly probability of a m 6 earthquake originating in the parkfield area is less than 1 signifying that several more decades of observation may be needed before the expected event occurs by its design the parkfield experiment cannot be expected to yield statistically significant conclusions on the validity of the research hypothesis for many decades

global contraction of antarctic bottom water between the 1980s and 2000s abstracta statistically significant reduction in antarctic bottom water aabw volume is quantified between the 1980s and 2000s within the southern ocean and along the bottom most southern branches of the meridional overturning circulation moc aabw has warmed globally during that time contributing roughly 10 of the recent total ocean heat uptake this warming implies a global scale contraction of aabw rates of change in aabw related circulation are estimated in most of the world s deep ocean basins by finding average rates of volume loss or gain below cold deep potential temperature surfaces using all available repeated hydrographic sections the southern ocean is losing water below 0 c at a rate of 8 2 2 6 106 m3 s 1 this bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near surface recovery apparently through a southward surge of circumpolar deep water from the north to the north smaller losses of bottom waters are see

comments on periodic jokulhlaups from pleistocene glacial lake missoula new evidence from varved sediments in northern idaho and washington by richard b waitt jr

paleomagnetic evidence for repeated glacial lake missoula floods from sediments of the sanpoil river valley northeastern washington abstract recent explanations of widespread rhythmically layered sediments in eastern washington as the result of repeated great floods from glacial lake missoula implicitly suggest a paleomagnetic test for validity if each conjectural flood layer is separated by years or decades as hypothesized a sequence of several such flood beds should record measurable secular variation in geomagnetic field direction in the sanpoil river valley where the rhythmite sequences are thought to have been deposited in glacial lake columbia the paleomagnetic test consists of measuring remanent magnetization rm directions for thick upwardly fining beds inferred to be sediments deposited by the influx of flood waters from glacial lake missoula into glacial lake columbia laboratory measurements of samples from three widely spaced sections along the sanpoil river yield rm vectors with erratic inclinations apparently affected by varying contributions of inclination error and or compaction shallowing but with declinations that generally differ statistically from one flood to the next and that show the same west to east trend at all three locations the rates of declination change inferred from these data are consistent with modern rates thus providing the first geophysical evidence supporting the timing in the tens of floods theory

status of glacial lake columbia during the last floods from glacial lake missoula abstract the last floods from glacial lake missoula montana probably ran into glacial lake columbia in northeastern washington in or near lake columbia s sanpoil arm lake missoula floods dating from late in the fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves the highest three interflood intervals each contain only one or two varves and about 200 400 successive varves conformably overlie the highest flood bed this sequence suggests that jokulhlaup frequency progressively increased until lake missoula ended and that lake columbia outlasted lake missoula the upper grand coulee lake columbia s late fraser age outlet contains a section of 13 graded beds most of them sandy and separated by varves that may correlate with the highest missoula flood beds of the sanpoil river valley the upper grand coulee also contains probable correlatives of many of the approximately 200 400 succeeding varves as do nearby parts of the columbia river valley this collective evidence casts doubt on a prevailing hypothesis according to which one or more late fraser age floods from lake missoula descended the columbia river valley with little or no interference from lake columbia s okanogan lobe dam

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

age of the mono lake excursion and associated tephra abstract the mono lake excursion mle is an important time marker that has been found in lake and marine sediments across much of the northern hemisphere dating of this event at its type locality the mono basin of california has yielded controversial results with the most recent effort concluding that the mle may actually be the laschamp excursion earth planet sci lett 197 2002 151 we show that a volcanic tephra ash 15 that occurs near the midpoint of the mle has a date not corrected for reservoir effect of 28 620 300 14c yr bp 32 400 gisp2 yr bp in the pyramid lake basin of nevada given the location of ash 15 and the duration of the mle in the mono basin the event occurred between 31 500 and 33 300 gisp2 yr bp an age range consistent with the position and age of the uppermost of two paleointensity minima in the napis 75 stack that has been associated with the mle philos trans r soc london ser a 358 2000 1009 the lower paleointensity minimum in the napis 75 stack is considered to be the laschamp excursion philos trans r soc london ser a 358 2000 1009

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

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

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

identifying the origin of the magnetic directional anomalies recorded in the datong loess profile northeastern chinese loess plateau summary to better understand the origin of short term features of palaeomagnetic signals recorded by the chinese loess detailed palaeomagnetic and magnetic fabric studies were conducted on a loess profile at datong the northeastern margin of the loess plateau which is characterized by both high sedimentation rate 18 cm ka 1 and variations of sedimentary environments it appears that the magnetic fabrics specifically the inclination of the maximum magnetic susceptibility principal axis k1 inc are robust means to identify the deposition environments our results 74 ka record four palaeodirectional anomalies referred as a d among them anomaly c with relatively normal fabrics can be correlated to the laschamp 40 ka excursion in contrast anomalies a b and d accompanying with k1 inc anomalies are interpreted to be caused by post depositional disturbances the new results improve our understanding of the origins of the natural remanent magnetization recorded by the chinese loess

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

contemporary recent extension and compression in the central andes abstract although extension in the high andes vs compression in the lowlands has already been widely discussed in the literature for the first time we recognized both extensional and contractional structures that developed contemporaneously during late pliocene quaternary times in a wide area of the central andean chain about 90 000 km 2 where crustal earthquake data are missing this area comprises north eastern chile south western bolivia and north western argentina and extends from the puna plateau to the altiplano volcanic belt late pliocene quaternary folds with hinge lines trending nne ssw to n s are mostly located along the westernmost part of the volcanic belt and the eastern part of the western cordillera locally there are coeval reverse faults parallel to the folds which reach up to the surface particularly the miscanti ridge tolocha fault and la casualidad ridge may be the morphostructural expression of tens km long fault propagation folds which locally show topographic scarps hundreds of meters high north and east of the contractional structures we found evidence of late pliocene quaternary normal faults striking n s in the southern part of the study area and nw se in the northern part well developed grabens are present in the higher areas of the volcanic belt and in the transition zone with the puna plateau the surface rupture zones of normal fault swarms range 8 24 km in length with single fault strands up to 18 km long which are typical of tectonic structures the distribution in space and time of the studied contractional and extensional structures indicates that they originated in the same time period we thus address the challenging question regarding the possible origin of the stress sources by analysing possible causes such as volcanotectonics high topography orogeny collapse and gravitational spreading of the orogen in relation also with the role played by inherited structures we finally analyse the relations between the different structures and magma upwelling and the potential for seismic hazard

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

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

tracing deep fluid source contribution to groundwater in an active seismic area central italy a combined geothermometric and isotopic δ13c perspective abstract an understanding of the origin and migration pathways of geofluids in an active seismic area is of paramount importance in terms of societal challenges such as mitigation of seismic hazards this study investigates the relationship between the stable isotope ratio 13c 12c of deep co2 and geothermometry in selected groundwater samples located close to extensional faults in central italy the temperature range is inferred from an equation based on the na li ratio and chemical geothermal modelling 113 130 c globally the calculated temperature range agrees with that resulting from deep boreholes in the northern apennines an alternative method is also included to better evaluate the difference in isotopic composition between the aqueous and gaseous 13c co2 at deep condition a review of previously published data shows that monitoring of the isotopic composition of the dissolved inorganic carbon dic in springs fed by meteoric origin located in seismically active areas must take into account mass and isotopic balance to correctly evaluate the component and the role of deep fluid during seismic events in particular the coupled and corrected isotope and geothermometrical monitoring of the springs could help to distinguish between deep gas or deep fluid contributions to shallow aquifers the results of this study indicate that faults play a crucial role in controlling the migration of crustal fluids in addition they reveal that possible evaluation of potential seismic precursors mandatorily requires a long period of monthly monitoring

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

crustal scale fluid circulation and co seismic shallow comb veining along the longest normal fault of the central apennines italy the extensional val roveto fault which is the longest exhumed potentially seismogenic structure of central apennines italy is examined to constrain earthquake related fluid circulation and fluid sources within shallow carbonate hosted faults the study focuses on fault related comb and slip parallel veins that are calcite filled and cut through the principal surface of the val roveto fault we observe multiple crack and seal events characterized by several veining episodes probably related to different slip increments along the fault plane we show that vein calcite precipitated in late pleistocene time below the present day outcrop level at a maximum depth of similar to 350 m and temperatures between 32 and 64 degrees c from meteoric derived fluids modified by reactions with crustal rocks and with a mantle contribution up to similar to 39 the observed warm temperatures are not compatible with a shallow similar to 350 m precipitation depth which in this region is dominated by circulation of cold meteoric water and or shallow groundwater based on structural geochemical data we propose that deep seated crust mantle derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co seismic comb and slip parallel fractures as comb and slip parallel veins are rather common particularly along seismogenic extensional faults we suggest that further studies are necessary to test whether these veins are often of co seismic origin if so they may become a unique and irreplaceable tool to unravel the seismic history of hazardous active faults

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

timing of lake level changes for a deep last glacial lake missoula optical dating of the garden gulch area montana usa abstract glaciolacustrine sediments in the clark fork river valley at garden gulch near drummond montana usa record highstand positions of the ice dammed glacial lake missoula and repeated subaerial exposure during these highstands the lake was at greater than 65 of its recognized maximum capacity the initial lake transgression deposited a basal sand unit subsequent cycles of lake level fluctuations are recorded by sequences of laminated and cross laminated silt sand and clay deformed by periglacial processes during intervening periods of lower lake levels optically stimulated luminescence osl dating of quartz sand grains using single aliquot regenerative dose procedures was carried out on 17 samples comparison of infrared stimulated luminescence irsl from k rich feldspar to osl from quartz for all the samples suggests that they were well bleached prior to deposition and burial ages for the basal sand and overlying glaciolacustrine exposure surfaces are indistinguishable within one standard deviation and give a weighted mean age of 20 9 1 3 ka n 11 based on sedimentological and stratigraphic analysis we infer that the initial transgression and at least six cycles of lake level fluctuation occurred over time scales of decades to 2 ka bioturbated sandy slopewash dated at 10 6 0 9 ka and 11 9 1 2 ka unconformably overlies the upper glaciolacustrine deposits the uppermost sediments above the glaciolacustrine section are younger than the glacier peak tephra 13 7 13 4 cal ka b p which was deposited across parts of the drained lake basin but has not been found at garden gulch our study indicates that glacial lake missoula reached 65 percent of maximum capacity by about 20 9 1 3 ka and either partially or completely drained twelve times from this position rapid lowering from the lake s highstand position due to ice dam failure likely led to scour in the downstream portions of the glacial lake missoula basin and megafloods in the channeled scabland

reshaping the antarctic circumpolar current via antarctic bottom water export abstractzonal momentum input into the antarctic circumpolar current acc by westerly winds is ultimately removed via topographic form stress induced by large bathymetric features that obstruct the path of the current these bathymetric features also support the export of antarctic bottom water aabw across the acc via deep geostrophically balanced northward flows these deep geostrophic currents modify the topographic form stress implying that changes in aabw export will alter the ocean bottom pressure and require a rearrangement of the acc in order to preserve its zonal momentum balance a conceptual model of the acc momentum balance is used to derive a relationship between the volume export of aabw and the shape of the sea surface across the acc s standing meanders this prediction is tested using an idealized eddy resolving acc antarctic shelf channel model that includes both the upper and lower cells of the southern ocean meridional overturning circulation using two different topographic configu

are u th dates correlated with historical records of earthquakes constraints from coseismic carbonate veins within the north anatolian fault zone u th dating of carbonate veins in connection with active tectonics has recently been used as an attractive tool for constraining the absolute timing of late quaternary crustal deformations in this study for the first time we correlate u th ages of travertine deposits in coseismic fissures along the north anatolian fault zone with records of paleoseismological studies supported by historical earthquake catalogued data u th ages are assessed in relation to the recurrence interval and the size and epicenter distance of major holocene earthquakes our statistical evaluations on age correlations indicate that the carbonate vein precipitation is concentrated in eight different periods along the north anatolian fault zone the periods are well correlated with historical earthquake records and with previous dating results of the nearby trench studies at least six of the periods correspond to the earthquakes reported in the historical catalogues the age correlations of carbonate precipitation intervals for the last millennium show a recurrence along the eastern north anatolian fault zone with a mode at 130 330 years that is consistent with a previously proposed paleoseismic recurrence interval of the fault recorded events in carbonate veins indicate a close epicenter d vi paleoearthquakes our results suggest that coseismic carbonate veins could be used to determine paleoseismic records as a supplementary tool to augment paleoseismological techniques this tool has advantages over traditional paleoseismological methods for the understanding of long term earthquake behavior particularly for prehistoric late pleistocene events which cannot be dated easily by traditional paleoseismological methods

the force balance of the southern ocean meridional overturning circulation the southern ocean so limb of the meridional overturning circulation moc is characterized by three vertically stacked cells each with a transport of about 10 sv sv 10 6 m 3 s 1 the buoyancy transport in the so is dominated by the upper and middle moc cells with the middle cell accounting for most of the buoyancy transport across the antarctic circumpolar current a southern ocean state estimate for the years 2005 and 2006 with 1 6 resolution is used to determine the forces balancing this moc diagnosing the zonal momentum budget in density space allows an exact determination of the adiabatic and diapycnal components balancing the thickness weighted residual meridional transport it is found that to lowest order the transport consists of an eddy component a directly wind driven component and a component in balance with mean pressure gradients nonvanishing time mean pressure gradients arise because isopycnal layers intersect topography or the surface in a circumpolar integral leading to a largely geostrophic moc even in the latitude band of drake passage it is the geostrophic water mass transport in the surface layer where isopycnals outcrop that accomplishes the poleward buoyancy transport

repeated sedimentation and exposure of glacial lake missoula sediments a lake level history at garden gulch montana usa abstract glaciolacustrine sediments record lake transgression regression and subaerial modification of the silty lake bottom of glacial lake missoula in the clark fork river valley the sequence preserved at garden gulch mt documents lake level fluctuations at 65 of its full pool volume twelve sedimentary cycles fine upwards from 1 very fine grained sandy silt to 2 silt with climbing ripples to 3 rhythmically laminated silt and some clay the cycles are fine grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops the gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake level lowerings periglacial wedges small rotational faults involutions and clastic dikes deform the tops of eleven cycles the wedges are 10 30 cm wide penetrate 30 70 cm deep are spaced the lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles the garden gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial lake missoula

reading a 400 000 year record of earthquake frequency for an intraplate fault our understanding of the frequency of large earthquakes at timescales longer than instrumental and historical records is based mostly on paleoseismic studies of fast moving plate boundary faults similar study of intraplate faults has been limited until now because intraplate earthquake recurrence intervals are generally long 10s to 100s of thousands of years relative to conventional paleoseismic records determined by trenching long term variations in the earthquake recurrence intervals of intraplate faults therefore are poorly understood longer paleoseismic records for intraplate faults are required both to better quantify their earthquake recurrence intervals and to test competing models of earthquake frequency e g time dependent time independent and clustered we present the results of u th dating of calcite veins in the loma blanca normal fault zone rio grande rift new mexico united states that constrain earthquake recurrence intervals over much of the past 550 ka the longest direct record of seismic frequency documented for any fault to date the 13 distinct seismic events delineated by this effort demonstrate that for 400 ka the loma blanca fault produced periodic large earthquakes consistent with a time dependent model of earthquake recurrence however this time dependent series was interrupted by a cluster of earthquakes at 430 ka the carbon isotope composition of calcite formed during this seismic cluster records rapid degassing of co2 suggesting an interval of anomalous fluid source in concert with u th dates recording decreased recurrence intervals we infer seismicity during this interval records fault valve behavior these data provide insight into the long term seismic behavior of the loma blanca fault and by inference other intraplate faults

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

quasi periodic recurrence of large earthquakes on the southern san andreas fault it has been 153 yr since the last large earthquake on the southern san andreas fault california united states but the average interseismic interval is only 100 yr if the recurrence of large earthquakes is periodic rather than random or clustered the length of this period is notable and would generally increase the risk estimated in probabilistic seismic hazard analyses unfortunately robust characterization of a distribution describing earthquake recurrence on a single fault is limited by the brevity of most earthquake records here we use statistical tests on a 3000 yr combined record of 29 ground rupturing earthquakes from wrightwood california we show that earthquake recurrence there is more regular than expected from a poisson distribution and is not clustered leading us to conclude that recurrence is quasi periodic the observation of unimodal time dependence is persistent across an observationally based sensitivity analysis that critically examines alternative interpretations of the geologic record the results support formal forecast efforts that use renewal models to estimate probabilities of future earthquakes on the southern san andreas fault only four intervals 15 from the record are longer than the present open interval highlighting the current hazard posed by this fault

long history of pre wisconsin ice age cataclysmic floods evidence from southeastern washington state abstract cataclysmic ice age floods in the pacific northwest began as early as 1 5 2 5 ma on the basis of an evaluation of surface exposures and recent borehole studies within southeastern washington field evidence suggests at least two episodes of pre wisconsin i e 130 ka glacial outburst flooding a middle pleistocene flood is identified by normal magnetic polarity calcrete capped deposits that yield maximum th u age dates from 200 to 400 ka the deposits with reversed polarity are correlated to early pleistocene 780 ka floods while exposures of pre wisconsin deposits are limited because of erosion and or burial the record of earlier pleistocene flooding is preserved within giant flood bars these bars show incremental growth representing a composite from cataclysmic floods deposited intermittently through the pleistocene in one giant flood bar up to 100 m thick deposits interpreted as matuyama age indicate that the bar had grown to half its present height by 780 ka furthermore matuy

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

paleomagnetic and tephra evidence for tens of missoula floods in southern washington paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from glacial lake missoula montana entered washington s yakima and walla walla valleys during the last glaciation in these valleys the field evidence for hiatuses between floods is commonly subtle however paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at zillah touchet and burlingame canyon display consistent secular variation that correlates serially both within and between sections the secular variation may further correlate with paleomagnetic data from fish lake oregon and mono lake california for the interval 12 000 17 000 14 c yr b p deposits of two successive floods are separated by two tephras derived from mount st helens washington the tephras differ in age by decades indicating that a period at least this long separated two successive floods the beds produced by these two floods are similar to all of the 40 beds in the slack water sediment sequence suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years

record of glacial lake missoula floods in glacial lake columbia washington abstract during the last glaciation marine oxygen isotope stage 2 outburst floods from glacial lake missoula deposited diagnostic sediments within glacial lake columbia two dominant outburst flood lithofacies are present within glacial lake columbia deposits a flood expansion bar facies and a finer grained hyperpycnite facies we conclude that the flood sediments have a glacial lake missoula source because 1 current indicators indicate westward flow through the lake and upvalley flow followed by downvalley flow in tributary valleys 2 no flood sediments are found north of a certain point 3 there is a dominance of belt purcell supergroup clasts in a flood expansion bar and 4 some of the finer grained beds have a pink colour reflective of glacial lake missoula lake bottom sediments a new radiocarbon age of 13 400 100 14c bp on plant detritus found below 37 flood beds helps constrain the timing of outburst flooding from glacial lake missoula

time dependent recurrence of strong earthquake shaking near plate boundaries a lake sediment perspective abstract accurate probabilistic seismic hazard analysis requires a good knowledge of the recurrence parameters of the strongest earthquakes in a region due to the typical short temporal span of instrumental and historical data it is often unclear whether one should adopt a time dependent or time independent poissonian recurrence model the choice of which has large repercussions on the probability estimates for new strong events the rapidly growing discipline of lacustrine paleoseismology aims at producing long continuous records of strong seismic shaking which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns the typical continuous sedimentation regime in lakes can lead to complete sensitive paleoseismic records and a reduced temporal uncertainty in recurrence intervals here i present a worldwide compilation of published long lacustrine paleoseismic records grouped per tectonic domain and statistically explore the variability of their recurrence intervals expressed by the coefficient of variation cov a cov 1 indicates a time independent process whereas cov 1 may be related to changes in the sensitivity of the lacustrine paleoseismograph or to real earthquake clustering due to e g stress transfer between neighboring faults the most useful lacustrine paleoseismic records can be retrieved in high seismicity settings where many paleoseismic events can be recorded in a relatively short time span i e

radiogenic isotopes record a drop in a bucket a fingerprint of multi kilometer scale fluid pathways inferred to drive fault valve behavior abstract minerals precipitated from fluids carry a chemical signature of fluid origin and transport history we use this concept to test the hypothesis that a subset of veins precipitated in the loma blanca fault zone rio grande rift nm usa record fault valve behavior previous studies of this site show syntectonic calcite veins formed in response to post seismic fluid discharge following repeated ground rupturing earthquakes u th ages on veins constrain the timing of fault slip over a period of 400 000 years the radiogenic isotope sr pb and u data we report here demonstrate that a cluster of earthquakes that occurred at 430 ka when fault slip frequency increased by nearly one order of magnitude corresponds with a brief period of particularly large and rapid variations in post seismic fluid chemistry isotopic variations are consistent with fluid input from the socorro magma body a large active mid crustal basalt intrusion 19 km below the surface the short duration of the earthquake cluster

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr