seasonal changes in planktonic foraminifera in the northwestern north pacific ocean sediment trap experiments from subarctic and subtropical gyres abstract upper ocean environments such as seawater temperature salinity thermal structure in the water column light intensity and food supply affect the assemblage of planktonic foraminifera since detailed information on planktonic foraminifera was not available for the northwestern north pacific we examined seasonal changes in fluxes and composition of planktonic foraminifera there data were collected by sediment traps deployed at three sites site 50n 50 01 n 165 02 e site knot 43 58 n 155 03 e and site 40n 39 60 n 165 00 e in this area in order to better understand the relationship between the foraminiferal assemblage and surface ocean environments although each planktonic foraminiferal species showed specific seasonal variations in flux some exhibited similar flux profiles in order to define these more accurately correlations among species were calculated and the foraminiferal species classified into four groups 1 group a subpolar species neogloboquadrina pachyderma globigerina quinqueloba globigerina bulloides and globigerinita glutinata 2 group b subtropical and tropical species globigerinoides ruber and globigerinoides sacculifer 3 group c post upwelling species neogloboquadrina dutertrei and 4 group d deep water species globorotalia scitula and globorotalia truncatulinoides the common environments for each period based on foraminiferal production and composition were observed among the three sites based upon predominant foraminiferal groups total foraminiferal fluxes tffs organic matter om fluxes and hydrographic conditions including sea surface temperatures sst and thermal structure the surface ocean environments in the northwestern north pacific could be generalized into five types type i is characterized by a dominance of group b with low tffs under high sst and type ii is marked by a high flux of group a on the other hand type iii shows low tffs and low om fluxes due to low insolation during winter type iv represents a high flux of group a and group d at site 40n under a well mixed surface ocean and type v is characterized by a prominent peak of group c under a developed thermocline a comparison of annual mean foraminifera fluxes at 50 n between the northwestern site 50n and the northeastern north pacific station papa during the normal cold mode demonstrated higher fluxes of foraminifera at site 50n due to higher nutrient concentrations the results also showed that g bulloides is not always a proxy for upwelling and that n pachyderma is not solely controlled by seawater temperature in the northwestern pacific where the surface water is enriched in nutrients the fluxes and composition of foraminifera suggest that similar ocean environments are expected in large areas of the northern north pacific from site knot to station papa during the warm mode which is affected by el nino events

faunal and stable isotopic analyses of benthic foraminifera from the southeast seep on kimki ridge offshore southern california usa abstract we investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15 cm push core na075 092b obtained on a telepresence enabled cruise to the southeast seep on kimki ridge offshore southern california the seep core was taken at a depth of 973 m in the vicinity of a beggiatoa bacterial mat and vesicomyid clams calyptogena and compared to previously published data of living assemblages from 714 m four reference cores obtained at 1030 m and another one at 739 m all of the reference sites are also from the inner continental borderland but with no evidence of methane seepage no endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments q and r mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non seep sites the living assemblage at southeast seep was characterized by abundant takayanagia delicata cassidulina translucens and spiroplectammina biformis whereas the non seep san pedro basin reference assemblage was comprised primarily of chilostomella oolina and globobulimina pacifica density and species richness were lower at the seep site compared to the non seep site reflecting the harsher living conditions there the dead assemblage at the seep site was dominated by gyroidina turgida compared to cassidulina translucens at the 1030 m non seep site and cassidulina translucens pseudoparrella pacifica and takayanagia delicata at the 739 m non seep site density was three times lower at southeast seep than at the non seep sites of comparable water depth but species richness was 30 higher stable carbon isotopic values were considerably depleted in the seep samples compared to the non seep samples with a progression from lightest to heaviest average 13c values evident at the seep site reflecting microhabitat preference and vital effect the deep infaunal species of globobulimina the shallow infaunal species uvigerina peregrina the epifaunal species cibicidoides wuellerstorfi and the shallow infaunal but aragonite shelled species hoeglundina elegans the 13c values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr b p at southeast seep besides the continual local seepage evidence from 13c values of planktic foraminifera in the seep core suggest two pulses of methane at 3000 and 3700 cal yr b p were released that were large enough to influence much of the water column paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800 year record to induce the methane releases instead southeast seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike slip system

the okhotsk pacific seawater exchange in the viewpoint of vertical profiles of radiocarbon around the bussol strait vertical profiles for 14c values were described around the bussol strait for the first time the abnormality of 14c values at 0 400 m depth in the bussol strait was observed and expected that diapycnal mixing occurs between the sub surface water around the bussol strait and the surface water in the bussol strait the okhotsk pacific cross sections through the bussol strait of 14c and suggested the intermediate water in the sea of okhotsk 26 8 27 3 has the role of the okhotsk pacific water exchange and the deep water 27 3 between the sea of okhotsk and the pacific ocean is mixed well rapidly through the bussol strait using estimation of bomb produced 14c inventories in each water column it was suggested the quantities of the okhotsk pacific water exchange may be essentially small

lagrangian flow effects on phytoplankton abundance and composition along filament like structures abstract influence of frontal dynamics on phytoplankton distribution and composition was studied combining in situ observations and lagrangian computations from altimetry satellite derived currents four transects during the shebex cruise may 2015 over the western mediterranean were examined identifying a region with high spatial variability in the dynamical and biogeochemical properties the dynamical situation unraveled from the lagrangian analysis is dominated by filaments originated by an anticyclonic cyclonic eddy interaction that organize the transport modifying the biogeochemical properties of the water column and shaping the satellite derived surface chlorophyll a chla distribution the properties of the water column have been analyzed in relation to the dynamical properties of the filaments showing that local variation of the mixed layer and nutricline depths are correlated with the spatial variability of finite size lyapunov exponents furthermore the composition of phytoplankton community was studied regarding the path accumulated properties of the flow during the formation of the filaments in this regard new metrics accounting the lagrangian evolution of the turbulent and topological properties of the flow along fluid parcel trajectories have been developed here we provide observational evidence that fluid parcels associated with high lagrangian turbulent kinetic energy and lagrangian positive vorticity host higher presence of larger pennate diatoms i e pseudo nitzschia spp our findings indicate that the combination of these diagnostics provides an improved description of the turbulent dynamics showing that the lagrangian properties of the flow have important biological consequences for phytoplankton to high ecological levels

palaeoceanographic implications of genetic variation in living north atlantic neogloboquadrina pachyderma the shells of the planktonic foraminifer neogloboquadrina pachyderma have become a classical tool for reconstructing glacial interglacial climate conditions in the north atlantic ocean1 2 3 palaeoceanographers utilize its left and right coiling variants which exhibit a distinctive reciprocal temperature and water mass related shift in faunal abundance both at present and in late quaternary sediments1 2 4 5 recently discovered cryptic genetic diversity in planktonic foraminifers6 7 8 now poses significant questions for these studies here we report genetic evidence demonstrating that the apparent single species shell based records of right coiling n pachyderma used in palaeoceanographic reconstructions contain an alternation in species as environmental factors change this is reflected in a species dependent incremental shift in right coiling n pachyderma shell calcite 18o between the last glacial maximum and full holocene conditions guided by the percentage dextral coiling ratio our findings enhance the use of 18o records of right coiling n pachyderma for future study they also highlight the need to genetically investigate other important morphospecies to refine their accuracy and reliability as palaeoceanographic proxies

tidal exchange through the kuril straits abstract the tidal exchange between the okhotsk sea and the north pacific ocean is studied numerically with particular emphasis on the predominant k1 barotropic component the calculated harmonic constants of the k1 tide in and around the okhotsk sea agree well with those obtained from extensive tide gauge observations the features of the simulated tidal fields are similar to those reported in the literature since the k1 tide is subinertial in the okhotsk sea topographically trapped waves are effectively generated contributing to strong tidal currents with a maximum amplitude of over 1 5 m s 1 in the kuril straits the structures of tide induced mean flows in most passages of the straits are characterized by bidirectional currents in which the mean flow exhibits a reversal in direction across the passages this feature is clearly indicated in noaa infrared imagery the mean transport shows significant net exchange of water via several straits in the kuril islands a transport of about 5 0 sv 1 sv

point spread functions for interferometric imaging interferometric redatuming is a data driven method to transform seismic responses with sources at one level and receivers at a deeper level into virtual reflection data with both sources and receivers at the deeper level although this method has traditionally been applied by cross correlation accurate redatuming through a heterogeneous overburden requires solving a multidimensional deconvolution problem input data can be obtained either by direct observation for instance in a horizontal borehole by modelling or by a novel iterative scheme that is currently being developed the output of interferometric redatuming can be used for imaging below the redatuming level resulting in a so called interferometric image internal multiples from above the redatuming level are eliminated during this process in the past we introduced point spread functions for interferometric redatuming by cross correlation these point spread functions quantify distortions in the redatumed data caused by internal multiple reflections in the overburden in this paper we define point spread functions for interferometric imaging to quantify these distortions in the image domain these point spread functions are similar to conventional resolution functions for seismic migration but they contain additional information on the internal multiples in the overburden and they are partly data driven we show how these point spread functions can be visualized to diagnose image defocusing and artefacts finally we illustrate how point spread functions can also be defined for interferometric imaging with passive noise sources in the subsurface or with simultaneous source acquisition at the surface

relative dispersion of surface drifters in the benguela upwelling region abstractwe examine the relative dispersion of surface drifters deployed in groups of triplets at the boundaries of a filament in the upwelling region off namibia for both the entire ensemble and th

seasonal variations in planktonic foraminifera at three sediment traps in the subarctic transition and subtropical zones of the central north pacific ocean the distribution and flux of planktonic foraminifera in the north pacific ocean were studied for a 1 year period beginning in july 1993 using time series samples collected in three sediment traps deployed in a north south transect along 175 e longitude sediment trap locations allowed monitoring of faunas within the subarctic transition and subtropical water masses in this region seasonally high foraminiferal flux rates were recorded at the subarctic site during periods of intense stratification of surface water accompanied by high fluxes of organic matter and biogenic opal contents faunal composition dominated by sinistral forms of neogloboquadrina pachyderma and globigerina umbilicata at the latter site characterized the subarctic water mass feature data collected at the transitional and subtropical sites illustrate differences in seasonal flux rates and in relation to those recorded at the subarctic site faunal composition at the transitional water mass site was dominated by dextral phenotypes of n pachyderma whereas this taxon was absent at the subtropical site also during the period of warmest surface temperature october globigerinoides ruber became dominant at the transitional water mass site in contrast to the subtropical water mass site where globigerinoides sacculifer became dominant while associated with common occurrences of globigerinoides tenellus and globorotalia tumida much lower fluxes of planktonic foraminifera organic matter and biogenic opal also marked subtropical water the distinctive differences in faunal composition and flux rates at the transitional and subtropical sites suggest that little if any exchange of surface water occurred between these two sites and in particular in the area representing the distal kuroshio extension

control of seafloor roughness on earthquake rupture behavior earthquake rupture complexity is described for three recent large underthrusting earthquakes along the costa rican subduction zone the 1983 osa 1990 nicoya gulf and 1999 quepos events these earthquakes occurred in regions characterized by distinctly different morphologic features on the subducting plate the 1990 and 1999 events occurred along linear projections of subducting seamount chains and had fairly simple earthquake rupture histories both events are interpreted as failure of the basal contact of closely spaced isolated seamounts acting as asperities in contrast the 1983 event occurred along the subducting cocos ridge and had a complex rupture history comparison of rupture characteristics of these large underthrusting earthquakes with size and location of subducting features provides evidence that seamounts can be subducted to seismogenic depths and that variations in seafloor bathymetry of the subducting plate strongly influence the earthquake rupture process

when seamounts subduct data from an array of seismometers on the sea floor show the complex pattern of earthquakes around subducted seamounts

seasonal variation in the oxygen isotopic composition of different sized planktonic foraminifer neogloboquadrina pachyderma sinistral in the northwestern north pacific and implications for reconstruction of the paleoenvironment 1 the oxygen isotope value 18o of planktonic foraminifer shells is one of the most commonly used proxies to reconstruct the paleoenvironment neogloboquadrina pachyderma sinistral n pachyderma sin is a dominant foraminifer in subpolar and polar region that is used extensively for high latitude paleoreconstruction the present study examined seasonal variation in 18o of n pachyderma sin using sediment trap samples collected over 3 5 years in the northwestern north pacific ocean the vital offset value was about 1 which agrees with previous plankton tow studies large shell individuals 180 250 m secrete their shells in a shallower and warmer environment than small ones 125 180 m and the difference in 18o between shell size showed seasonal variation although large individuals calcify at a slower rate with slightly heavier 18o than small individuals differences between size classes mainly reflect different habitation in the water column and are related to seasonal changes in stratification during summer large individuals would calcify mainly at 25 35 m depth while small individuals calcify near the pycnocline at 45 m during winter both size classes calcify at or slightly above the weak pycnocline at 45 65 m thus the shell 18o could record the oceanographic environment around pycnocline depth and size specific differences in 18o reflect water column stratification the annual flux weighted 18o corresponded to non flux weighted mean 18o value due to the equal contribution of two flux peaks and differences between size classes also related to the stratification it suggests that fossil 18o data could represent the annual mean environment around pycnocline and past stratification

oxygen and carbon isotopic composition of living planktonic foraminifera from the northeast pacific ocean abstract stable isotopic analyses were performed on the tests of five species of living planktonic foraminifera which are important in paleoclimatic studies of high latitude late cenozoic sequences all but two of the samples used are from horizontal plankton tows of known depths between 0 500 m in the northeastern pacific ocean 50 n 145 w in situ hydrographic seawater stable isotopic and quantitative species distribution data are used in the interpretation of the results all of the species show depletions in both 18 o and 13 c in their calcite tests relative to calcite precipitated in isotopic equilibrium with ambient seawater estimates of the departures from isotopic equilibrium range from 0 35 in globigerinita glutinata to 2 24 in neogloboquadrina pachyderma sinistral with respect to 18 o and from 0 5 in orbulina universa to 4 34 globigerina bulloides with respect to 13 c the 18 o data suggest that primary test growth for individual species is not restricted to the depth interval where highest total standing crop values occur oxygen and carbon isotopic depth rankings for g bulloides n pachyderma and g glutinata reflect the relative magnitude of the vital effect in these species and not necessarily different depth habitats the vital effect for 18 o in these species remains approximately constant with changing temperature water depth while the vital effect for 13 c strongly decreases with increasing depth temperature also does not appear to directly affect the coiling ratios of g bulloides but a significant negative correlation exists between the percentage of sinistrally coiled g glutinata and water temperature

source characterization of near surface chemical explosions at safod a series of near surface chemical explosions conducted at the san andreas fault observatory at depth safod main hole were recorded by high frequency downhole receiver arrays in april 2005 these seismic recordings at depths ranging from the surface to 2 3 km constrain the shallow velocity and attenuation structure as well as the first order characteristics of the source forward modeling of the explosions indicates that a source consisting of combined explosion delayed implosion and second order moment tensor components corresponding to a distribution of vertical shear dislocations in the rock directly above the explosion is sufficient to characterize the generated seismic wave fields to first order grid searches over source parameters controlling the nonexplosive components allow for the quantification of distributed vertical shear above the source and the estimation of the moment and time delay of the implosive component relative to the explosion an estimated implosive to explosive moment ratio of 0 34 to 0 43 indicates a net static moment and positive macroscopic volume change

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

sources of tsunami and tsunamigenic earthquakes in subduction zones we classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface typical interplate events earthquakes at the outer rise within the subducting slab or overlying crust intraplate events and tsunami earthquakes that generate considerably larger tsunamis than expected from seismic waves the depth range of a typical interplate earthquake source is 10 40km controlled by temperature and other geological parameters the slip distribution varies both with depth and along strike recent examples show very different temporal change of slip distribution in the aleutians and the japan trench the tsunamigenic coseismic slip of the 1957 aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long this asperity ruptured again in the 1986 andreanof islands and 1996 delarof islands earthquakes by contrast the source of the 1994 sanriku oki earthquake corresponds to the low slip region of the previous interplate event the 1968 tokachi oki earthquake tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes tsunami hazard assessments must include such events similarity in macroseismic data from two southern kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights most moment release of tsunami earthquakes occurs in a narrow region near the trench and the concentrated slip is responsible for the large tsunami numerical modeling of the 1996 peru earthquake confirms this model which has been proposed for other tsunami earthquakes including 1896 sanriku 1946 aleutian and 1992 nicaragua

near wellbore vsp imaging without overburden in seismic exploration a complex overburden can cause defocused and distorted seismic images of deeper target areas while in surface seismic imaging it is difficult to overcome this problem vertical seismic profile vsp borehole seismic imaging with its well oriented recording geometry has proven able to circumvent the overburden s detrimental impact recently vspnear wellboresaltflankimagingwithout knowledge of the overburden has shown encouraging results in this paper we introduce another method for a more common imaging purpose imaging near wellbore horizons without knowledge of the overburden a key component of ourmethodisareverseray tracingtechniquethatusesactual vspdirect wave traveltime picks and extrapolates through a local velocity model to obtain the direct wave traveltimes in the vicinity of the well the extrapolated traveltimes then serve as references for migration of the vsp reflected data from near wellbore horizons the merits of this method are that all source side effects such as shot position and triggeringtimestaticsareavoided anditcanefficientlyandrobustly imagethenear wellborehorizonsbecauseitdoesnotneedan estimated overburden velocity model prone to errors however the image is limited to a diamond shaped area around the well whose size is proportional to the vsp array a synthetic vsp experiment on the seg eage 2d overthrust modelshowsthatthismethod withalocalevenanestimated 1d velocity model effectively images structural features suchasdipdirectionanddiscontinuitiesofthenear wellbore horizons

sediment effect on tsunami generation of the 1896 sanriku tsunami earthquake the 1896 sanriku earthquake was one of the most devastating tsunami earthquakes which generated an anomalously larger tsunami than expected from its seismic waves previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis it was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift in this paper the effect of the additional uplift to tsunami generation of the 1896 sanriku tsunami earthquake is quantified we estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges the estimated slip for the model without the additional uplift is 10 4 m and those with the additional uplift are 5 9 6 7 m this indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation

comparison of the rupture and radiation characteristics of intermediate and deep earthquakes we study the depth dependence of the rupture and radiation characteristics of earthquakes below 70 km depth by investigating the source properties of intermediate 70 300 km depth and deep 300 km depth earthquakes along the fiji and japan subducting slabs the source properties are explored by retrieval of the moment rate functions and by spectral analysis using p waves thirty two earthquakes in the period 1986 1997 with seismic moment 1 1018 n m are analyzed the main conclusions are 1 the dependence of the source duration on the scalar seismic moment m0 follows the usual one third trend on average 2 this behavior is still visible when the source durations are adjusted for the shear wave velocity and the modulus of rigidity at the hypocentral depth 3 the effective stress drop and the effective strain drop for subcrustal earthquakes in fiji and japan tend to be larger than those for the crustal ones 4 the duration and shape of the moment rate functions do not show any systematic difference between intermediate and deep events and 5 no obvious difference in the spectral properties of intermediate and deep events is seen

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

the 1996 peru tsunamigenic earthquake broadband source process we investigate the spatio temporal complexity of moment release of the february 21 1996 peru earthquake mw 7 5 we use a non linear source tomographic technique based on simulated annealing to invert surface wave source spectra for the slip distribution on a gently dipping fault plane the spectra 5 65 mhz are obtained using an empirical green s function egf method applied to first and second orbit fundamental mode rayleigh waves spectra are well fit by a 110 km bilateral rupture subparallel to the trench updip of the hypocenter with a total moment of 2 0 1020 nm the non linear inversion reveals a 30 30 km major slip patch south the onset where rupture velocities attain 1 5 2 0 km s inversions of teleseismic broadband p and sh waves 10 500 mhz indicate little or no directivity consistent with the surface wave data the average source time functions for both the surface and body wave data are similar in shape and in duration 50 s part of the slip during the 1996 peru event occurred in a region of reduced background seismicity as was the case for the 1992 nicaragua slow event suggesting that the seismogenic potential of low seismicity regions near the trench should be globally reassessed

time functions of deep earthquakes from broadband and short period stacks to constrain dynamic source properties of deep earthquakes we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic p waves from u s national seismic network terrascope and berkeley digital seismic network broadband stations we examined 42 earthquakes with depths from 100 to 660 km that occurred between july 1 1992 and july 31 1995 to directly compare time functions or to group them by size depth or region it is essential to scale them to remove the effect of moment which varies by more than 3 orders of magnitude for these events for each event we also computed short period stacks of p waves recorded by west coast regional arrays the comparison of broadband with short period stacks yields a considerable advantage enabling more reliable measurement of event duration a more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment producing scaled time functions with both correct timing and amplitude we find only subtle differences in the broadband time function shape with moment indicating successful scaling and minimal effects of attenuation at the periods considered here the average shape of the envelopes of the short period stacks is very similar to the average broadband time function the main variations seen with depth are 1 a mild decrease in duration with increasing depth 2 greater asymmetry in the time functions of intermediate events compared to deep ones and 3 unexpected complexity and late moment release for events between 350 and 550 km with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below the first two results are broadly consistent with our previous studies while the third is reported here for the first time the greater complexity between 350 and 550 km suggests greater heterogeneity in the failure process in that depth range

horizontal and vertical distributions of planktic foraminifera in the subarctic pacific abstract observations of the horizontal and vertical distributions of modern planktic foraminifera facilitate formation of ecological and geochemical inferences derived from the study of foraminiferal shells in this study we used plankton tows to collect planktic foraminifera at nine sites distributed longitudinally throughout the subarctic pacific a total of nine planktic foraminiferal species were identified the horizontal distributions of the foraminiferal assemblages could be assigned to four regions characteristics of the foraminiferal assemblages and the horizontal distributions of their shell sizes appeared to be influenced by the sea surface structure within each water mass the vertical distributions of globigerina bulloides and globigerina quinqueloba were associated with the depth of the pycnocline those of neogloboquadrina pachyderma and neogloboquadrina incompta were different and appeared to reflect a significant difference of optimum habitat temperatures based on the vertical distribution of shell sizes we found evidence of vertical migrations during shell growth of g bulloides and n incompta this information about the distribution of modern planktic foraminifera will facilitate reconstruction of past oceanographic conditions based on geochemical proxies in the subarctic pacific

tsunami earthquakes possibly widespread manifestations of frictional conditional stability 1 tsunami earthquakes shallow events that produce larger tsunamis than expected given their surface wave magnitudes ms typically have long durations and a source spectrum depleted in short period energy seven cases of underthrusting tsunami earthquakes provide information on the rupture processes but little constraint on geographic distribution or frequency we compare their rupture characteristics with smaller magnitude earthquakes on circum pacific interplate thrust faults comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes with significantly longer durations and additional source complexity than for events deeper than 15 km thus very shallow interplate earthquake ruptures are scale invariant with variable frictional properties on the plate interface controlling the depth dependent rupture process widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami generating earthquakes to occur fortunately large shallow ruptures are infrequent

cross shore transport variability in the california current ekman upwelling vs eddy dynamics abstract the low frequency dynamics of coastal upwelling and cross shelf transport in the central and southern california current system ccs are investigated using the regional ocean modeling system roms over the period 1965 2008 an ensemble of passive tracers released in the numerical model is used to characterize the effects of linear ekman upwelling and non linear mesoscale eddies circulation dynamics on the statistics of advection of coastal waters the statistics of passive tracers released in the subsurface show that the low frequency variability of coastal upwelling and cross shelf transport of the upwelled water mass are strongly correlated with the alongshore wind stress and are coherent between the central and southern ccs however the offshore transport of tracers released at the surface is not coherent between the two regions and is modulated by intrinsic mesoscale eddy activity in particular cyclonic eddies the transport of cyclonic eddies extends with depth and entrains water masses of southern origin advected by the poleward california undercurrent cuc the cuc water masses are not only entrained by eddies but also constitute a source for the central california upwelling system the interplay between intrinsic eddy activity and deterministic ekman upwelling dynamics in controlling the cross shelf exchanges in the ccs may provide an improved framework to understand and interpret nutrients and ecosystem variability

interpretation of s waves generated by near surface chemical explosions at safod a series of near surface chemical explosions conducted at the san andreas fault observatory at depth safod were recorded by high frequency downhole receiver arrays in separate experiments in november 2003 and may 2005 the 2003 experiment involved 100 kg shots detonated along a 46 km long line hole ryberg line centered on safod and recorded by 32 three component geophones in the pilot hole between 0 8 and 2 0 km depth the 2005 experiment involved 36 kg shots detonated at parkfield area seismic observatory paso stations at 1 8 km offset recorded by 80 three component geophones in the main hole between the surface and 2 4 km depth these data sample the downgoing seismic wavefield and constrain the shallow velocity and attenuation structure as well as the first order characteristics of the source using forward modeling on a velocity structure designed for the near field both observed p and s wave energy for the paso shots are identified with the travel times expected for direct and or reflected phases larger offset recordings from shots along the hole ryberg line reveal substantial sv and sh energy especially southwest of safod from the source as indicated by p to s amplitude ratios the generated sv energy is interpreted to arise chiefly from p to s conversions at subhorizontal discontinuities this provides a simple mechanism for often observed low p to s amplitude ratios from nuclear explosions in the far field as originating from strong near field wave conversions online material figures of observed and synthetic seismogram record sections snapshots of synthetic wavefields and models of crustal structure

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

arctic planktic foraminiferal assemblages implications for subsurface temperature reconstructions abstract earlier reconstructions of the inflow of atlantic water to arctic and subarctic oceans based on foraminiferal proxy data have been obstructed by uncertain quantitative reconstructions of sea surface and subsurface temperatures in this study surface sediment samples with undisturbed sediment water interface from polar north atlantic and barents sea were retrieved and prepared at the size fractions from 100 m to 1000 m the foraminiferal analyses show that neogloboquadrina pachyderma constitutes 96 99 of the fauna in arctic and polar surface water masses the same result is obtained when investigating the 150 m size fraction however in arctic areas influenced by atlantic water additional faunal information is obtained when using the smaller 100 m size fraction in these areas n pachyderma is reduced to about 50 and the relatively small species turborotalita quinqueloba becomes very frequent this also applies to the coastal water masses which are dominated by neogloboquadrina incompta and globigerinita uvula transfer functions using the current dataset based on the 100 m size fraction were developed and assessed different statistical models were tested using both seasonal and annual temperature data from 0 m 10 m 50 m and 100 m water depth the most precise reconstructions of subsurface temperatures were found when using summer temperatures from the 100 m depth level the transfer function was tested on holocene foraminiferal records and compared to previous reconstructions the results show that our new transfer function based on the 100 m fraction generally yields lower temperatures at both 10 and 100 m water depth than earlier reconstructions e g hald et al 2007 this could be due to the increased number of samples containing both small species and or the presence of more small specimens representing cold conditions

variability in vertical distributions of planktonic foraminifera in the california current relationships to vertical ocean structure 1 geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean although interpretations can be confounded by variability in foraminifera habitat depths the principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern california in winter spring and summer each species has a dynamic range of preferred habitat depth from the mixed layer to the thermocline characterized by a unique relationship with environmental properties globigerina bulloides neogloboquadrina pachyderma dextral and neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens globigerinoides ruber and orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm the shifts in habitat depth are of sufficient magnitude to affect 18o records the effects of such shifts are observed for g bulloides and n pachyderma in santa barbara basin sediments geochemical signatures from multiple species of foraminifera each with a different predicted response to environmental change can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

imaging a slow bilateral rupture with broadband seismic waves the september 2 1992 nicaraguan tsunami earthquake the spatio temporal rupture history of the september 2 1992 nicaragua tsunami earthquake ms 7 2 mw 7 6 is analyzed using long period 157 288 s rayleigh and love wave spectral inversions and an empirical green function analysis of very broadband 10 250 s body and surface waves the event has a rupture duration exceeding 110 s with a slow 0 6 2 3 km s rupture velocity and involves shallow dipping 6 10 thrust faulting at a shallow depth 10 km with the latter being primarily responsible for the strong tsunami excitation two subevents dominate the source radiation resulting from a slow asymmetric bilateral 100 160 km long rupture long period surface wave directivity reveals a predominant rupture azimuth of 140 30 consistent with asymmetric extension of the bilateral rupture at an azimuth of 125 30 resolved by the source time function analysis an inverse radon transform of the source time functions confirms the asymmetric bilateral rupture characteristics

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

fault parameters of the 1896 sanriku tsunami earthquake estimated from tsunami numerical modeling the june 15 1896 sanriku earthquake generated devastating tsunamis with the maximum run up of 25 m and caused the worst tsunami disaster in the history of japan despite its moderate surface wave magnitude ms 7 2 and weak seismic intensity this is a typical tsunami earthquake which generates anomalously larger tsunamis than expected from its seismic waves previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments in this paper we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in japan the result indicates that the tsunami source is very close to the japan trench and the fault strike is parallel to the trench axis the fault width is about 50 km suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge

interplate patchiness and subduction erosion mechanisms evidence from depth migrated seismic images at the central ecuador convergent margin prestack depth migrated seismic lines provide accurate images of the convergent ecuadorian margin where the southern flank of the carnegie ridge subducts the margin is fronted by a 5 7 km wide compressional sediment prism beneath the slope margin thinning is accomplished by gradual thinning of the lower part of the basement accompanied by pervasive seaward dipping normal faulting indicating basal subduction erosion at a low friction plate interface along the plate boundary a thin subduction channel locally thickens to form low velocity 600 m thick lenses of underthrusted fluid rich sediment supplied by slope mass wasting the contrast between the fluid rich sediment and the surrounding thinner and drier sections of the subduction channel creates a three dimensional patchiness across the plate boundary implying variations in mechanical interplate coupling the subduction channel patchiness modulates subduction erosion processes by alternately favoring margin basement weakening and material removal basement weakening would occur 1 at the base of the upper plate where enhanced reflectivity indicates basement damage by overpressured fluids from the subduction channel and 2 at the basement apex where basement breakup is caused by superposition of compressional and extensional fault systems resulting from time variable interplate mechanical coupling the detachment of rock debris in the higher coupled sections and the subsequent dragging of the fragments into the subduction channel cause tectonic erosion deeper in the subduction the subduction channel patchiness may influence processes like earthquake nucleation and rupture propagation and material recycling in the mantle

estimation of seismic moment and slip distribution of the april 1 1946 aleutian tsunami earthquake the 1946 aleutian earthquake produced a tsunami of tsunami magnitude mt 9 3 but the surface wave magnitude is only ms 7 4 making it a tsunami earthquake the discrepancy between the apparent size of the earthquake based on the seismic data and the size of the tsunami has been explained by several mechanisms including a landslide and a slow earthquake but there are few seismic data available to determine the correct mechanism we study the generating mechanism of the tsunami using tsunami waveforms recorded on tide gauges we have modeled the source of the 1946 aleutian tsunami as the result of an underthrusting earthquake we performed both forward and inverse modeling of the data using a finite difference calculation to compute synthetic tsunamis we include both vertical and horizontal deformation of the ocean bottom due to faulting in the computation the results of the inversion of the tsunami waveforms show that the slip on the fault is mainly concentrated in the shallow section of the fault near the epicenter there is little slip in the area of the aftershocks indicating that the aftershocks may represent an area of afterslip or triggered seismicity the moment estimate of the earthquake is 23 1020 n m or mw 8 2 the majority of the waveforms are well explained by this fault model and slip distribution including the honolulu waveform but the hawaiian data also suggest that other effects such as a landslide may be necessary for explaining the abnormal tsunami amplitudes in hawaii the 1946 earthquake is similar to other tsunami earthquakes such as the 1896 sanriku and 1992 nicaragua earthquakes indicating that slow shallow rupture may explain the disproportionally large tsunamis

vertical structure turbulent mixing and fluxes during lagrangian observations of an upwelling filament system off northwest iberia abstract in august 1998 a recurrent filament located near 42 n off galicia was sampled as part of the omex ii project lagrangian and other observations were made on the shelf where the filament arose and offshore in the filament itself under upwelling favourable but fluctuating winds the shelf drift experiment monitored a change from southward to weak northward net flow as the winds decreased to zero shipborne adcp measurements showed that the shelf was supplying decreasing volumes of water to the filament as the wind speeds decreased at the shelf edge the internal tide was larger than can be explained by local forcing and there were many unusually large high frequency internal waves with a quasi sinusoidal form turbulence observations revealed enhanced dissipation rates and vertical eddy diffusion coefficients within the shelf thermocline of order 1 cm 2 s 1 which appeared to be caused by the breaking of internal wave a second lagrangian experiment was executed in the filament some 120 km offshore which again coincided with a period of wind relaxation cross sections revealed a double cold core and that the offshore flow was limited to a thin surface layer substantial onshore flow occurred below 50 m in the centre of the filament while the strongest and deepest offshore flow coincided with its northern boundary turbulent kinetic energy dissipation rate measurements showed very weak mixing below 15 m in the filament core but enhanced mixing at its boundaries four mixed layer drifters released in the filament initially indicated convergence at its southern boundary marked by strong temperature and salinity contrasts after the wind became more favourable for upwelling the drifters accelerated one drifter traced the full extent of the filament while the other three escaped from it and began to circulate cyclonically over 28 days in a 100 km diameter loop back towards their release point although strong mesoscale activity linked the shelf and ocean regimes offshore transport in the filament was weak at the time of the experiment and vertical and horizontal re circulations on a variety of time scales were important there was sufficient vertical mixing in the thermocline to cause it to thicken and draw some heat into the lower layers during the summer months on the shelf the amount of heat involved was too little to have a significant impact on the development of a filament over a typical lifetime of a week

the use of vsp techniques for fault zone characterization an example from the san andreas fault vertical seismic profiling vsp technology is increasingly being used in the fields of earthquake seismology and tectonics this is motivated in part by the growing number of oil field microseismic monitoring surveys but more so by projects that involve drilling deep wells for monitoring crustal activity at depth examples of these projects are the san andreas fault observatory at depth safod the nankai trough seismogenic zone experiment the gulf of corinth rift laboratory and the taiwan chelungpu fault drilling project and other projects by the international continental and ocean drilling programs icdp and iodp these projects require instrumentation and surveying in deep and possibly hot borehole environments with higher resolution than surface seismic data images from 2d and 3d vsp data contribute to better characterization and interpretation of complex reservoirs at smaller scales the location of receivers in the low noise borehole environment yields higher signal to noise ratios higher

influence of test size water depth and ecology on mg ca sr ca δ18o and δ13c in nine modern species of planktic foraminifers abstract mg ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography however our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite mg ca is limited here we report results of a study designed to shed new light on ecological size related and very early water column diagenetic controls on mg ca in planktic foraminiferal calcite we analysed mg ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 m window sieve fractions in a core top sample from the north atlantic ocean we also analysed mg ca in four of these nine species from plankton tow samples collected from 0 to 2500 m water depth in the north atlantic ocean and arabian sea our core top study confirms that sensitivity of mg ca to change in test size is species specific but reveals an overall decrease in mg ca with increasing test size in all but one species orbulina universa for which mg ca increases with size these findings are broadly consistent with known ecological behaviour suggesting that the size related signal is largely environmentally rather than calcification rate controlled our results underscore the need to undertake mg ca palaeothermometry on narrow size fractions of planktic foraminifers particularly for shallow dwelling species such as g bulloides and g ruber where mg ca is most sensitive to test size across the size range of 200 350 m our plankton tow data from the arabian sea are in agreement with in situ temperatures in contrast our data from the north atlantic ocean reveal large variability and marked offsets to warmer values from in situ temperatures that are interpreted to reflect lateral advection from the south storm induced vertical mixing of the water column and or the influence of surface water salinity on the mg ca signal none of our plankton tow mg ca data shows any evidence of test dissolution in the water column our study provides important verification that the mg ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor thereby satisfying an important precondition of its palaeo proxy utility

importance of the mesoscale in the decadal changes observed in the northern canary upwelling system 1 analysis of sea surface temperature sst time series since 1960 from existing data bases shows a generalized warming trend in the northern canary upwelling system the field of the satellite derived sst trends off western iberia was built at the pixel scale 4 4 km for the period 1985 2008 revealing significant spatial differences in the warming rates weaker warming trends fit to the known upwelling pattern off the southern part of the western iberia pointing out the intensification of this feature since 1985 particularly during the peak summer months a more regular behavior is found further north suggesting significant decadal changes in the mesoscale patterns of the northern

frequency dependent relocation of the 1992 nicaragua slow earthquake an empirical green s function approach we present a two step empirical green s function analysis of the slow 1992 nicaragua earthquake mw 7 7 in the first step a narrow band cross correlation method recovers he relative source amplitude and phase delay spectra between the main shock and a suitable empirical green s function egf the analysis is performed at 2mhz intervals from 4 to 44mhz using first and second orbit fundamental mode rayleigh waves from the low frequency relative amplitudes we obtain the differences in mechanism and depth between the main shock and the egf and we present a method to correct for such differences in the second step we use the relative spectra to relocate the main shock relative to the egf position al a set of discrete frequencies in addition we invert the relative spectra for the relative source time functions using both a positivity and a smoothing constraint unlike standard egf deconvolution the spectral resolution achieved in our cross correlation method allows us to determine the conditions of validity of the egf approach from our analysis it appears that the centre of low frequency radiation 4 10 mhz during the slow 1 992 nicaragua earthquake is situated about 40 km trenchwards of the epicentre between 20 and 44 mhz centroids occupy intermediate positions between the low frequency points and the epicentre relative source time functions have an average duration of about 120 s they reveal a slow 1 km s1 smooth component of rupture with unilateral directivity towards the se along the trench axis a large amount of slip occurred at shallow depths at the interface between the subducted cocos plate and the caribbean plate in agreement with tsunami models of the event the low frequency radiation appears to originate from a zone devoid of teleseismic aftershocks this suggests that unusual frictional properties at the plate interface perhaps related to subducted sediments are responsible for the slow and smooth nature of the 1992 nicaragua earthquake

mixing structures in the mediterranean sea from finite size lyapunov exponents 1 we characterize horizontal mixing and transport structures in the surface circulation of the mediterranean sea as obtained from a primitive equation circulation model we calculate the finite size lyapunov exponents fsles of the velocity data set which give a direct measure of the local stirring by proper election of the fsle parameters we focus on the mesoscale structures locating a number of vortices embedded in an intricate network of high stretching lines these lines control transport in the system at the edge of the vortices a dense tangle of line intersections appears identifying strong mixing the spatial distribution of fsles averaged over one year allows to classify areas in the mediterranean basin according by their mixing activity the space average of fsles on selected geographical regions gives a measure for quantifying and comparing the mixing seasonal variability

the november 20 1960 peru tsunami earthquake source mechanism of a slow event the november 20 1960 peru earthquake excited a tsunami that was anomalously large for an earthquake of moderate magnitude m 6 75 pas body wave first motions combined with observed love to rayleigh wave spectral ratios indicate slip along a shallowly dipping thrust fault rather than a single force mechanism suggestive of a landslide deconvolution of sh waveforms shows a time function consisting of 4 subevents with a total duration of 110 s using this time function body waveform inversion yields a very shallowly dipping thrust faulting mechanism strike 0 dip 6 slip 100 and a seismic moment of 1 9 1027 dyn cm however the time function obtained from the band limited body waveforms cannot fit the surface wave data which show a large increase in amplitude with period and a moment of 3 4 1027 dyn cm both types of data can be modeled by combining the body wave time function and a 130 s cosine time function representing a longer period component this event represents the largest earthquake to occur along this relatively aseismic portion of the peruvian coast the tsunami excitation is not anomalous relative to the measured seismic moment and moment magnitude mw 7 6 the disparity between tsunami height and surface wave magnitude results from underestimation of the earthquake size by conventional magnitude scales due to the long source duration

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

migration based location of seismicity recorded with an array installed in the main hole of the san andreas fault observatory at depth safod summary we present the principles of a recently developed event location procedure and its application to seismicity recorded in the main borehole of the san andreas fault observatory at depth safod the basic idea of the location approach is the backpropagation of the recorded wavefield along rays using a gaussian beam type weighting factor in the case of a sufficient number of receivers the intersection of these rays results in a distinct maximum at the corresponding hypocentre location we have applied this technique to data recorded with an 80 level three component 3c receiver array in the safod main hole and we have located a number of events in the vicinity of the fault system a modification of the location algorithm also allowed the precise location of one of the so called target events which are the subject of recent drilling activities as well as ongoing research at safod we summarize the principles of the location method and the performed processing steps provide estimates of the uncertainties for the target event location and test the robustness of the location using six different 3 d velocity models furthermore we discuss the event locations in comparison with borehole logging data and coincident seismic reflection images and we also show identified events with highly correlated waveforms

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

potential of 3 d vertical seismic profiles to characterize seismogenic fault zones the potential of a 3 d vertical seismic profile vsp to improve resolution of seismogenic plate interfaces was explored with synthetic modeling the 3 d vsp modeled is at a proposed site for a 1 to 1 5 km deep open hole that provides background for riser drilling three dimensional vsp images could resolve 30 60 m spaced reflective horizons in a costa rican subduction zone it can record a great amount of high fidelity s wave data to invert for physical properties directions of strain and pore pressure above and below the plate interface fault a 6 km 12 km grid of shots with a surface ship will illuminate a 4 km 7 km area of the plate interface fault zone with a high data density acquisition adds 5 to 9 days to drill ship time on site and a shooting ship seismic image resolution falls between that of borehole information and 3 d surface ship seismic images a multiple kilometer 3 d volume of high fidelity s wave data is an exceptional addition not available with other techniques

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

vertical seismic wave gradiometry application at the san andreas fault observatory at depth abstractwe have developed vertical seismic wave gradiometry vswg to estimate velocity impedance and attenuation structure in the vicinity of boreholes using borehole array waveforms of check shot explosions near the borehole head we have extended wave gradiometry wg theory from a purely local relation of the wavefield and wavefield spatial gradient to one that incorporated the ray ansatz over the length of the borehole for a traveling wave in a vertically inhomogeneous medium we checked the ray assumption against acoustic full wave synthetic seismograms and it was found to yield robust measures of the medium velocity anelastic attenuation and impedance structure trade off but in cases of high anelastic attenuation realistic bounds can be placed on the seismic impedance that effectively constrains the average attenuation we have applied these methods to data collected at the san andreas fault observatory at depth borehole in central california in 2005 and we found that the wg velocity estimat

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

a 9 year time series of planktonic foraminifer fluxes and environmental change in the bering sea and the central subarctic pacific ocean 1990 1999 abstract a 9 year study of planktonic foraminifer fluxes was conducted in the bering sea station ab and in the central subarctic pacific station sa results clearly reflected variations of the water mass characteristics in the upper layers the 9 year means of total foraminifer fluxes were the same 1400 shells m 2 d 1 at both stations however total foraminifer flux at station ab tended to show its primary maximum during fall october december and its secondary maximum in spring april june whereas the primary maximum appeared in spring and the secondary maximum in fall at station sa seasonal variation was more apparent at hemipelagic station ab than at pelagic station sa planktonic foraminifers found at both stations were of six species neogloboquadrina pachyderma globigerina umbilicata globigerinita glutinata globigerina quinqueloba globorotalia wilesi and orbulina universa the foraminifer assemblages at the two stations reflected the temperature difference in the surface waters the variable g umbilicata tended to be high in the warm surface waters during the summers the temporal and geographical variation of g quinqueloba indicated that this taxon prefers regions with relatively low diatom fluxes a notable appearance of o universa occurred in 1997 at station sa during this period other measured biogenic particle fluxes such as those of diatoms were low this unusual 1997 event may be a reflection of global climatic change that happened to be observed in the central subarctic pacific ocean

the 1994 java tsunami earthquake slip over a subducting seamount on june 2 1994 a large subduction thrust earthquake ms 7 2 produced a devastating tsunami on the island of java this earthquake had a number of unusual characteristics it was the first recorded large thrust earthquake on the java subduction zone all of the aftershock mechanisms exhibit normal faulting no mechanisms are similar to the main shock also the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow shallow rupture near the trench similar to the 1992 nicaragua earthquake we first relocate the main shock and the aftershocks we then invert long period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip a dip of 12 hypocenter depth of 16 km and moment of 3 5 l020 n m mw 7 6 give the best fit to the combined seismic data and are consistent with the plate interface geometry the source spectrum obtained from both body and surface waves has a single corner frequency between 10 and 20 mhz implying a stress drop of 0 3 mpa the main energy release was preceded by a small subevent lasting 12 s the main slip occurred at 20 km depth downdip and to the nw of the hypocenter this area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount we interpret the java earthquake as slip over this subducting seamount which is a locked patch in an otherwise decoupled subduction zone we find no evidence for slow shallow rupture no thrust aftershocks are expected if the entire locked zone slipped during the main shock but extension of the subducting plate behind the seamount would promote normal faulting as observed it seems probable that such a source model could also explain the size and timing of the observed tsunami

shallow subduction zone earthquakes and their tsunamigenic potential summary we have examined the source spectra of all shallow subduction zone earthquakes from 1992 to 1996 with moment magnitude 7 0 or greater as well as some other interesting events in the period range 1 20 s by computing moment rate functions of teleseismic p waves after comparing the source spectral characteristics of tsunami earthquakes earthquakes that are followed by tsunamis greater than would be expected from their moment magnitude with regular events we identified a subclass of this group slow tsunami earthquakes this subclass consists of the 1992 nicaragua the 1994 java and the february 1996 peru earthquakes we found that these events have an anomalously low energy release in the 1 20 s frequency band with respect to their moment magnitude although their spectral drop ov is comparable to those of the other earthquakes from an investigation of the centroid and body wave locations it appears that most earthquakes in this study conformed to a simple model in which the earthquake nucleates in a zone of compacted and dehydrated sediments and ruptures up dip until the stable sliding friction regime of unconsolidated sediments stops the propagation sedimentstarved trenches e g near jalisco can produce very shallow slip because the fault material supports unstable sliding the slow tsunami earthquakes also ruptured up dip however their centroid is located unusually close to the trench axis the subduction zones in which these events occurred all have a small accretionary prism and a thin layer of subducting sediment ocean surveys show that in these regions the ocean floor close to the trench is highly faulted we suggest that the horst and graben structure of a rough subducting oceanic plate will cause contact zones with the overriding plate making shallow earthquake nucleation and up dip propagation to the ocean floor possible the rupture partly propagates in sediments making the earthquake source process slow two factors have to be considered in the high tsunami generating potential of these events first the slip propagates to shallow depths in low rigidity material causing great deformation and displacement of a large volume of water second the measured seismic moment may not represent the true earthquake displacement because the elastic constants of the source region are not taken into account in the standard cmt determination

linking synoptic forcing and local mesoscale processes with biological dynamics off ningaloo reef 1 a hydrographic survey offshore ningaloo reef north west australia in austral autumn 2010 revealed relatively stable subsurface water masses in the region despite the influence of interannual variability of the leeuwin current lc the surface water mass seems slightly more variable at seasonal time scale probably due to various contributions of the geographically distinct source waters of the lc a subsurface nitrate maximum 110 230 m a prominent feature of the ningaloo area during autumn was consistently observed within different water masses tightly coupled variations of subsurface nitrate and oxygen at small vertical scale suggest it is due to local in situ remineralization of organic matter likely to accumulate along sharp physical interfaces and possibly favored by injections of oxygenated subsurface waters offshore enhanced levels of surface chlorophyll a within the downwelling favorable lc are associated with deeper mixed layer depth eroding the shallow source of nutrients close to the continental shelf these nutrients are observed to be efficiently uplifted within the core of quasi persistent topographically trapped submesoscale cyclonic eddies dominated by nonlinear effects a wind driven coastal upwelling event occurred in autumn and was characterized by a relatively deep source 100 150 m coinciding with the subsurface maximum of nutrients thus promoting coastal productivity locally and farther north by alongshore advection within the ningaloo current

multi trace deconvolution with unknown trace scale factors omnilinear inversion of p and s waves for source time functions seismic source and wave propagation theories allow seismologists to compute long period synthetic seismograms that commonly match even subtle details of observed waveshapes but the overall trace amplitudes must be scaled by arbitrary factors to emphasize the excellent waveshape correspondence this unexplained amplitude scatter causes considerable difficulties when formally inverting observed waveforms for seismic source parameters omnilinear inversion simultaneously determines the linear model parameters and trace scaling factors to minimize the mismatch between observed and synthetic seismograms omnilinear inversion is applied to source time function deconvolution from long period p and sh waves a simulation with synthetic data shows that omnilinear inversion finds the proper scaling factors and the source time function and focal depth are better determined than for standard linear inversion omnilinear inversion is then applied to a data set of seven p waves and one sh wave from the underthrusting earthquake of july 5 1968 ms 6 6 in northern honshu japan omnilinear inversion produces a best fit focal depth of 36 km with a single pulse time function of 6 s duration and seismic moment of 4 1018 n m mw 6 4 this focal depth supports the notion that the seismically coupled plate interface extends no deeper than 40 km in northern honshu

mechanism of the 1992 nicaragua tsunami earthquake the 1992 nicaragua earthquake generated larger tsunamis than expected from its surface wave magnitude ms 7 2 and is known as a tsunami earthquake seismological studies showed that the duration was very long for its size about 100 s other studies have shown that the seismic moment estimated from tsunamis is an order of magnitude larger than that from seismic waves even after the long duration is accounted for numerical computations of tsunamis from various fault models are made to reconcile this discrepancy comparison of calculated waveforms with tide gauge records shows that the fault width is 40 km much narrower than the aftershock area and extends only into the upper 10 km of the ocean bottom slip amount on the fault is estimated to be 3 m from amplitude comparisons the fault length is estimated to be 250 km slightly longer than the aftershock area from comparison of the tsunami height distribution the rigidity around the shallow fault may be smaller than that of a standard underthrust fault and the seismic moment is estimated as 3 1020 nm consistent with the seismic observations a slow rupture on the shallow fault presumably in the subducted sediments is responsible to the unusually large tsunami excitation

seismic coupling along the chilean subduction zone underthrusting at subduction zones can cause large earthquakes at shallow depths but is accommodated by aseismic creep below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding we have determined the maximum depth of the coupled zone and its variability along the chilean subduction zone the maximum depth of seismic coupling is defined by the depth of large m 6 underthrusting earthquakes that have occurred at the downdip edge of the coupled plate interface earthquake depth is determined with omnilinear waveform inversion of long period p waves the statistical uncertainty in the depth is estimated using bootstrapping omnilinear inversion formally accounts for the scaling incompatibility between the p waveforms and decreases the uncertainty in the depth estimate we have found the depths of 27 earthquakes in the time period from 1961 to 1987 seismic coupling in chile extends down to 48 53 km there is a resolvable change in the maximum depth of coupling around 28 s the region immediately north of this latitude has a coupled zone that extends no deeper than 36 41 km while south of this latitude coupling extends down to 48 53 km this transition is not simply related to the oceanic lithospheric age and plate convergence rate but coincides with a change in several geophysical and geological phenomena with respect to shallower north and deeper south coupling there is a change from active volcanos to no volcanos the dip of the deep slab changes from steep to shallow the thickness of trench sediments changes from thin to thick and the depth of the oceanic basement changes from deeper to shallower at 28 s due to the multiplicity of changes at 28 s there is no clear unique interpretation of what physical mechanism controls the variability in the maximum depth of the seismically coupled zone in chile

boundaries of the peruvian oxygen minimum zone shaped by coherent mesoscale dynamics dissolved oxygen in sea water affects marine habitats and biogeochemical cycles oceanic zones with oxygen deficits represent 7 of the volume and 8 of the area of the oceans and are thought to be expanding one of the most pronounced lies in the region off peru where mesoscale activity in the form of fronts and eddies is strong here we study the dynamics of the peruvian oxygen minimum zone in a lagrangian framework using a coupled physical biogeochemical numerical model and finite size lyapunov exponent fields to evaluate the role of mesoscale activity we find that at depths between 380 and 600 m mesoscale structures have two distinct roles first their mean positions and paths delimit and maintain the oxygen minimum zone boundaries second their high frequency fluctuations inject oxygen across the oxygen minimum zone boundaries and eddy fluxes are one order of magnitude higher than mean oxygen fluxes we conclude that these eddy fluxes contribute to the ventilation of the peruvian oxygen minimum zone

characterization of mg ca distributions in planktonic foraminifera species by electron microprobe mapping 1 the distribution of mg ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping species include several that are commonly used for estimation of past seawater temperatures globigerinoides ruber g sacculifer neogloboquadrina incompta synonym of n pachyderma dex n dutertrei and g truncatulinoides each of the investigated species displays large variations in mg ca composition within individual tests however the pattern of mg ca variation is notably different between symbiont bearing and symbiont free species in symbiotic species cyclic mg ca compositional banding occurs that is characterized by narrow 1 3 m high mg ca typically 8 11 mmol mol bands intercalated between broader low mg ca typically 1 5 mmol mol bands this factor of 2 3 difference equates to an apparent calcification temperature change of 10 c or more such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of mg ca into the tests of symbiont bearing species these vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures symbiont free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column

isotopic composition and morphology of living globorotalia scitula a new proxy of sub intermediate ocean carbonate chemistry abundance isotopic composition and morphological imprints of the planktonic foraminifera globorotalia scitula brady were closely examined for possible use as a novel reconstruction tool of chemical environments in sub intermediate depth seawater in the past based on the mocnes plankton tow observation of dwelling depths of g scitula and the isotopic compositions together with hydrochemistry data the empirical relations between isotopic disequilibria in carbon 13c 13cg scitula 13cdic and oxygen 18o 18og scitula 18ow isotopes in the carbonate tests and the seawater 18o and 13c of dissolved inorganic carbon dic respectively are introduced the morphological information such as pore density and porosity is also examined for significant relations to carbonate chemistry shell porosity is strongly correlated saturation state of calcite the dissolution of living g scitula tests may promote the observed isotopic differences as well as the increases in porosity 18o of g scitula is found effectively to be linear function of both water temperature and calcite saturation state and thereby temperature equation for g scitula is provided while 13c of g scitula is a linear function of only calcite saturation state the equation was validated by using globorotalia scitula collected by a sediment trap in intermediate water depths satisfactory agreements were found between observed and calculated 18o from the empirical equations based on temperature and hydrochemistry data at sediment trap deployment site indicating that the equation may be useful in paleo environmental reconstruction of sub intermediate water the sediment trap observation further suggests that the abundance of g scitula does not necessarily correspond to surface water productivity and to poc flux but instead it correlates well with the supply of fine organic matter which appears to be a result of water convection thus g scitula may be an unambiguous and excellent paleo environmental recorder for carbonate chemistry and for fine organic matter transport to the depths if isotopic and morphological observations are combined