in situ demonstration of a passive radio sounding approach using the sun for echo detection ice sheet contributions to sea level rise present one of the greatest challenges that our society will face in the next century however models predicting sea level rise due to ice melt lack critical information regarding processes at the base of ice sheets although radio echo sounders are powerful tools that are currently used to constrain subglacial conditions existing ice penetrating radar systems are too resource intensive in terms of cost power and logistics for multiyear deployment at a large scale to address this we present passive radio sounding as a low resource approach for observing ice sheets across a range of spatial and temporal scales while passive radar has been used for target tracking and military purposes it has never been used for the sounding of ice sheets some recent work has proposed using passive radio sounding of europa s icy shell using jupiter s decametric radiation we expand on this idea by evaluating and discussing challenges and opportunities for developing a passive radio sounder using the sun as an illuminator of opportunity for echo detection here our prototype instrument sits on the side of a cliff and measures the sun s direct and reflected path off the ocean surface we then use an autocorrelation based method to extract the amplitude and delay of the reflection this serves as the first in situ demonstration of an autocorrelation based passive sounder using a compact astronomical white noise signal

a revised tsunami source model for the 1707 hoei earthquake and simulation of tsunami inundation of ryujin lake kyushu japan 1 based on many recent findings such as those for geodetic data from japan s geonet nationwide gps network and geological investigations of a tsunami inundated ryujin lake in kyushu we present a revised source rupture model for the great 1707 hoei earthquake that occurred in the nankai trough off southwestern japan the source rupture area of the new hoei earthquake source model extends further to the hyuga nada more than 70 km beyond the currently accepted location at the westernmost end of shikoku numerical simulation of the tsunami using a new source rupture model for the hoei earthquake explains the distribution of the very high tsunami observed along the pacific coast from western shikoku to kyushu more consistently a simulation of the tsunami runup into ryujin lake using the onshore tsunami estimated by the new model demonstrates a tsunami inundation process inflow and outflow speeds affect transport and deposition of sand in the lake and around the channel connecting it to the sea tsunamis from the 684 tenmu 1361 shokei and 1707 hoei earthquakes deposited sand in ryujin lake and around the channel connecting it to the sea but lesser tsunamis from other earthquakes were unable to reach ryujin lake this irregular behavior suggests that in addition to the regular nankai trough earthquake cycle of 100 150 years there is a hyperearthquake cycle of 300 500 years these greater earthquakes produce the largest tsunamis from western shikoku to kyushu

gnss r nonlocal sea state dependencies model and empirical verification global navigation satellite system reflectometry gnss r is an active bistatic remote sensing technique operating at l band frequencies gnss r signals scattered from a rough ocean surface are known to interact with longer surface waves than traditional scatterometery and altimetry signals a revised forward model for gnss r measurements is presented which assumes an ocean surface wave spectrum that is forced by other sources than just the local near surface winds the model is motivated by recent spaceborne gnss r observations that indicate a strong scattering dependence on significant wave height even after controlling for local wind speed this behavior is not well represented by the most commonly used gnss r scattering model which features a one to one relationship between wind speed and the mean square slope of the ocean surface the revised forward model incorporates a third generation wave model that is skillful at representing long waves an anchored spectral tail model and a gnss r electromagnetic scattering model in comparisons with the spaceborne measurements the new model is much better able to reproduce the empirical behavior

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

ubiquitous weakening of faults due to thermal pressurization faults weaken during earthquakes analysis of the amount of energy released during earthquakes globally suggests that heat induced pressurization of pore fluids can weaken faults during earthquakes of all sizes laboratory simulations of earthquakes show that at high slip rates faults can weaken significantly aiding rupture1 2 3 various mechanisms such as thermal pressurization and flash heating have been proposed to cause this weakening during laboratory experiments1 4 5 6 yet the processes that aid fault slip in nature remain unknown measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening known as an event s fracture energy7 8 9 here we compile new and existing8 9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes we observe a distinct transition in how fracture energy scales with event size which implies that faults weaken differently during small and large earthquakes and earthquakes are not self similar we use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms we find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes over seven orders of fault slip magnitude we conclude that thermal pressurization is a widespread and prominent process for fault weakening

early miocene marine palynology of the colombian caribbean margin biostratigraphic and paleoceanographic implications abstract dinoflagellate cysts and acritarchs are excellent proxies for biostratigraphic and paleoceanographic studies in neritic sequences however neogene marine palynological studies in tropical latitudes are scarce here we analyzed the marine palynological contents dinoflagellate cysts acritarchs foraminiferal test linings and prasinophytes of 40 samples from a well drilled in northernmost colombia southern caribbean sea spanning the late chattian late burgidalian time interval 24 1 17 3 ma we propose a biostratigraphic scheme that includes an upper chattian lower aquitanian minisphaeridium latirictum interval zone 23 9 22 0 ma an upper aquitanian achomosphaera alcicornu interval zone 22 0 20 3 ma and a burdigalian cribroperidinium tenuitabulatum interval zone 20 3 17 5 ma our results reveal several biostratigraphic events that are heterochronous compared to high latitudes furthermore the conspicuous shift from a peridinioid dominated to a gonyaulacoid dominated dinoflagellate cyst assemblage towards the aquitanian burdigalian boundary 20 7 ma indicates a reduction in marine primary productivity this paleoproductivity decline was probably driven by the initial constriction of the central american seaway

dispersed organic matter in samples from the western continental shelf of southern africa palynofacies assemblages and depositional environments of late cretaceous and younger sediments abstract the composition and distribution of dispersed microscopic organic matter particles phytoclasts and palynomorphs in sediments and sedimentary rocks reflect factors that influenced their production in their original environments transport to depositional sites burial and post depositional changes thus they can be used as proxies for reconstructing provenance temporal and spatial paleoenvironmental conditions and diagenetic changes in this study phytoclasts and palynomorphs in 55 spot samples from upper cretaceous eocene miocene and uppermost pleistocene sediments on the western continental shelf of namibia and south africa were examined they were used to test lateral depositional facies inferred from unpublished micropaleontological analysis and to decipher any stratigraphic trends in the distribution of the organic particles in the sediments thirteen types of phytoclasts and palynomorphs were identified and analyzed in two ways visually with basic quantitative techniques and statistically with two multivariate techniques three components namely amorphous organic matter wood and black debris were visually and statistically significant average linkage cluster analysis of these three components and discrete changes in the amounts of marine palynomorphs and other terrigenously derived organic material such as spores and pollen brown black fragments and plant tissues delineated seven palynofacies assemblages by contrast principal components analysis revealed two groups of samples based on the amounts of amorphous organic matter and wood five groups of samples referred to as associations were identified visually from the pattern of organic matter distribution and compared with the statistical results a palynofacies depositional model is proposed to re evaluate the fluvial to inner shelf settings previously inferred for the sediments some clear stratigraphic trends were obvious in both sets of results such as the dominance of amorphous organic matter in turonian coniacian and uppermost pleistocene sediments and higher percentages of black debris in the older sediments these trends appear to be controlled more by provenance and depositional conditions than by age the dominance of amorphous organic matter in several uppermost pleistocene sediments deposited during a global fall in sea level were attributed to in situ physical and biological degradation of mostly marine algal material in an inner shelf setting

earthquake ruptures with strongly rate weakening friction and off fault plasticity part 1 planar faults abstract observations demonstrate that faults are fractal surfaces with deviations from planarity at all scales we study dynamic rupture propagation on self similar faults having root mean square rms height fluctuations of order 10 3 to 10 2 times the profile length our 2d plane strain models feature strongly rate weakening fault friction and off fault drucker prager viscoplasticity the latter bounds otherwise unreasonably large stress concentrations in the vicinity of bends our choice of a cohesionless yield function prevents tensile stress states and thus fault opening a consequence of strongly rate weakening friction is the existence of a critical background stress level above which self sustaining rupture propagation in the form of self healing slip pulses first becomes possible around this level at which natural faults are expected to operate ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity except for shallow inclinations of the maximum compressive stress to the fault less than about 20 the fluctuations are anticorrelated with the local fault slope these accelerations and decelerations of the rupture together with naturally emerging slip heterogeneity excite waves of all wavelengths and result in ground acceleration spectra that are flat at high frequency consistent with observed strong motion records

ultralong period seismic study of the december 2004 indian ocean earthquake and implications for regional tectonics and the subduction process analysis of the earth s longest period normal modes shows that the december 2004 sumatra andaman earthquake was much larger mw 9 3 than ini tially inferred from surface wave data and involved slip on a much longer fault than initially inferred from body wave data the seismic moment and relative excitation of the normal modes indicate that the entire aftershock zone ruptured consistent with the large tsunami amplitudes in thailand sri lanka and india an apparent increase in seismic moment with period results from interference between parts of the fault the earthquake resulted from subduction of the indian plate beneath the burma microplate a sliver plate between the indian and sunda plates hence the rate and direction of convergence depends on the motion of the burma plate which is not well known convergence would be highly oblique if the rate of motion between burma and sunda is that inferred from spreading in the andaman sea and less if a slower rate is inferred from the sagaing fault the december earthquake was much larger than expected from a previously proposed relation based on the idea of seismic coupling in which such earthquakes occur only when young lithosphere subducts rapidly moreover a global reanalysis finds little support for this correlation hence we suspect that much of the apparent differences between subduction zones such as some trench segments but not others being prone to m w 8 5 events and hence oceanwide tsunamis may reflect the short earthquake history sampled this possi bility is supported by the variability in rupture mode at individual trench segments

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

late eocene sea retreat from the tarim basin west china and concomitant asian paleoenvironmental change the paleogene sediments of the southwest tarim basin along the west kunlun shan in western china include the remnants of the easternmost extent of a large epicontinental sea this shallow sea once extended across the eurasian continent before it retreated westward and eventually separated as the paratethys sea climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the tibetan plateau uplift in the aridification of the asian continental interior and the intensification of the asian monsoon system the age and paleogeography of the retreat are poorly constrained hindering the understanding of its cause and paleoenvironmental impacts this study reports litho and biostratigraphic results from two sections recording the last major regression out of the tarim basin that is expressed by a regional transition from marine clastics and limestones to continental red beds rich micro and macrofossil assemblages including benthic foraminifera ostracods bivalves calcareous nannofossils and organic walled dinoflagellate cysts dinocysts indicate a shallow proximal and marine environment strong similarity to assemblages known from central asia and europe confirms that surface ocean connections extended across eurasia from the tarim basin to the western tethys during the latest eocene moreover the recovered fossil associations date the last marine sediments as earliest priabonian in age 37 ma overlap between dinoflagellate mps interval zone and calcareous nannofossil zone cp 14 the retreat of the sea from the tarim basin is time equivalent with the sea level lowstand at the bartonian priabonian boundary but pre dates both the oligocene miocene regional uplift of the pamir mountains and kunlun shan and the major eustatic sea level falls of the eocene oligocene transition 34 ma and mid oligocene 30 ma which are usually held responsible for the sea retreat furthermore a concomitant and significant aridification step occurs at 36 6 ma top of chron c17n 1n as recorded by regional sedimentary records of the xining basin along the northeastern tibetan plateau suggesting that the tarim sea served as a significant moisture contributor for the asian interior

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

characterization of dry snow sub structure using gnss reflected signals abstract signals of global navigation satellite systems gnss bi statically reflected off pristine dry snow in dome concordia antarctica were collected during an experimental campaign with the aim of investigating the potential capabilities of these signals to remotely sense dry snow areas the data have been used to sense the sub surface structure of the snow by means of a new holographic observable the obtained reflected signals present interferometric patterns consistent with the coherent superposition of signals reflected in different layers of the snow sub structure down to a few hundred meters depth a forward model has been developed to compare the amplitude and phase behavior of the interferences with the data a new radio holographic observable is also defined to help identify the layer at which the internal reflections occur this work represents the first step towards the potential use of a space based gnss r mission for densely monitoring the depths of antarctica s thick dry snow and or complementing l band radiometric observations

allochthonous versus autochthonous organic matter in cenozoic sediments of the norwegian sea evidence for the onset of glaciations in the northern hemisphere the cenozoic sediments sampled in odp leg 104 on the voring plateau show a distinct variability of the total organic carbon content toc and the accumulation rates of toc based on the geochemical and organic petrographic characterization of the sedimentary organic matter om the allochthonous and autochthonous proportion of the om could be quantified the results clearly demonstrate that high toc percentages and toc accumulation rates in cenozoic sediment sections display a generally high input of allochthonous organic matter oxidized and partly well rounded organic particles built up the main portion of om within the miocene toc rich sediments the most probable source of this oxidized om are reworked sediments from the scandinavian shelf changes in the input of these organic particles are to some degree correlative with sea level changes the cenozoic accumulation of autochthonous om is low and does not reveal a clear variation during the miocene and early pliocene in spite of a high accumulation rate of biogenic opal during the early miocene the accumulation rate of autochthonous toc is low the autochthonous particle assemblage is dominated by relatively inert om like dinoflagellate cysts this points to an intensive biological and or early diagenetic degradation of the marine om under well oxidized bottom water conditions during the last 23 myr nevertheless a continuation of marine om degradation during later stages of diagenesis cannot be excluded a prominent dominance of allochthonous om over autochthonous is documented with the beginning of the pliocene at 2 45 ma the episodic occurrence of ice rafted thermally mature om reflects the onset of the glacial erosion of mesozoic coal and black shale bearing sediments on the scandinavian and barents sea shelves the first occurrence of these in view of the actual burial depth thermally overmature om particles is therefore a marker for the beginning of the strong scandinavian glaciation and the advance of the glacial front toward the shelves

correction of the sea state impact in the l band brightness temperature by means of delay doppler maps of global navigation satellite signals reflected over the sea surface this paper presents an efficient procedure based on 2 d convolutions to obtain delay doppler maps ddms of global navigation satellite signals reflected gnss r over the sea surface and collected by a spaceborne receiver two ddm derived observables area and volume are proposed to link the sea state induced brightness temperature to the measured normalized ddm finally the requirements to use global positioning system reflectometry to accurately correct for the sea state impact on the l band brightness temperature quantization levels decimation truncation and noise impact are analyzed in view of its implementation in the passive advanced unit instrument of the spanish earth observation satellite seosat ingenio project

phase altimetry with dual polarization gnss r over sea ice this paper evaluates the potential use of reflected signals from global navigation satellite systems as a source of opportunity for the retrieval of absolute ellipsoidal heights over sea ice accurate estimation of the surface level would be helpful for the determination of the ice thickness a key parameter for classification and characterization of sea ice masses our analysis is based on altimetric estimations from the coherent differential phase between direct and both cross and co polar reflected signals for this purpose gps waveforms have been collected from a fixed platform in greenland monitoring the complete process of sea ice formation and melting during a 7 month period the variability of coherent phase samples and polarimetric measurements are compared with in situ observations to make a realistic rough characterization of the ice cover the retrieved sea ice surface height estimates are then evaluated against an arctic tide model ice surface temperature from moderate resolution imaging spectroradiometer and the laser altimetry product from icesat

stress orientations in subduction zones and the strength of subduction megathrust faults subduction zone megathrust faults produce most of the world s largest earthquakes although the physical properties of these faults are difficult to observe directly their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them a global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward consistently making an angle of 45 to 60 with respect to the subduction megathrust fault these angles indicate that the megathrust fault is not substantially weaker than its surroundings together with several other lines of evidence this implies that subduction zone megathrusts are weak faults in a low stress environment the deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface

sea surface topography retrieved from gnss reflectometry phase data of the geohalo flight mission sea surface topography observations are deduced from an airborne reflectometry experiment a gnss global navigation satellite system receiver dedicated for reflectometry was set up aboard the german halo high altitude long range research aircraft flights were conducted over the mediterranean sea about 3500 m above sea level a signal path model divided into large and small scale contributions is used for phase altimetry the results depict geoid undulations and resolve anomalies of the sea surface topography for the whole experiment 65 tracks over the mediterranean sea are retrieved and compared with a topography model tracks differ between right handed and left handed circular polarization the difference however is not significant for this study precision and spatial resolution decrease disproportionately at low elevations eight tracks with centimeter precision are obtained between 11 and 33 of elevation at higher elevation angles the number of tracks is significantly reduced due to surface roughness in future such retrievals could contribute to ocean eddy detection

characteristics of secondary slip fronts associated with slow earthquakes in cascadia we implement an algorithm to automatically detect migrations of low frequency earthquakes at time scales between 30 min and 32 h during the 2003 2004 and 2005 slow slip events in cascadia we interpret these migrations of seismicity as a passive manifestation of secondary slip fronts ssfs that propagate faster than the main front we identify the dominant features of 383 ssfs including time location duration area propagation velocity and estimate their moment stress drop slip and slip rate we apply the same algorithm to continuous tremor detection in cascadia between 2009 and 2015 and characterize 693 ssfs at time scales between 4 h and 32 h we identify to our knowledge for the first time numerous 11 22 5 h long ssfs that propagate at velocities intermediate between slow slip events and previously reported ssfs the systematic detection of ssfs fills a gap between seismically and geodetically detectable slow earthquake processes analysis of ssf basic features indicates a wide range of stress drops and slip rates with medians of 5 8 kpa and 1 1 mm h as well as an intriguing relationship between ssf direction and duration that was observed in other contexts and could potentially help discriminate between the different physical models proposed to explain slow slip phenomena

delay doppler analysis of bistatically reflected signals from the ocean surface theory and application we present a new stochastic theory for delay doppler mapping of the ocean surface for bistatic scattering this stochastic theory should complement nicely the previous theories for the global positioning system gps reflected signals from ocean surfaces especially that of zavorotny and voronovich 2000 we quantify the doppler spread of the reflected signal before interpreting the delay our theoretical results compare very well to doppler spectra computed using data collected during an airborne campaign the bandwidth of the spectra is linked to the geometry and to the ocean roughness the bulk of the doppler spread is caused by the rms slope and not by the surface orbital velocity our stochastic theory is generalized to include the delay mapping made possible by the existence of the pseudorandom noise code on the gps l band carrier these results can be seen as a generalization of woodward s theorem for fm signals to delay doppler analysis of more complicated signals our formulation is amenable to inversion for the determination of geophysical parameters such as surface wind vector and mean sea level another novelty in our approach is the inclusion of the sea state

on the characteristics of earthquake stress release variations in japan abstract the amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process as such it represents a key parameter for improving our understanding of earthquake source physics and for reliable ground motion prediction large earthquake populations usually show variations in stress release as large as three orders of magnitude but the underlying mechanisms have remained largely elusive and particularly the dependence of stress release on earthquake size is still a matter of debate here i use a unique dataset from japan encompassing earthquakes of a wide magnitude range and spatial coverage to show that stress release variations of crustal earthquakes are strongly correlated with heat flow variations indicating that they are thermally controlled in contrast subcrustal events depict highest stress release in regions of strong subduction interface coupling and overall less pronounced variability as compared with crustal earthquakes stress release is overall only weakly dependent on earthquake size but at local scales i e within individual earthquake sequences the dependence can be very strong and apparently varies with stress regime accounting for these systematic variations reduces the stress release variability on local scale by a factor of two to three as compared with the full earthquake population a finding that is of key significance in the endeavor to reduce the uncertainties in future ground motion predictions

mega earthquakes rupture flat megathrusts the 2004 sumatra andaman and 2011 tohoku oki earthquakes highlighted gaps in our understanding of mega earthquake rupture processes and the factors controlling their global distribution a fast convergence rate and young buoyant lithosphere are not required to produce mega earthquakes we calculated the curvature along the major subduction zones of the world showing that mega earthquakes preferentially rupture flat low curvature interfaces a simplified analytic model demonstrates that heterogeneity in shear strength increases with curvature shear strength on flat megathrusts is more homogeneous and hence more likely to be exceeded simultaneously over large areas than on highly curved faults

palynostratigraphy and chronostratigraphy of baffin bay deep sea cores climatostratigraphic implications abstract palynostratigraphic considerations and 14c dates ams accelerator mass spectrometry on foraminifera samples from piston cores suggest sedimentation rates as high as ca 8 11 cm ka in deep baffin bay during the late pleistocene throughout this interval baffin bay experiences rigorous conditions and probably the extension of a dense sea ice cover unfavourable to phytoplanktonic productivity the dinocyst microflora indicates only brief episodes of higher productivity related to arctic conditions and to moderately low salinites ca 30 31 the abundance of reworked pre quaternary palynomorphs in the deposits is interpreted as a response to glacial and glacio marine activity in the northernmost areas surrounding baffin bay the dinocyst stratigraphy spanning approximately over the last ice age ca 100 ka reveals that baffin bay constituted a confined basin isolated from the north atlantic ocean prior to the present interglacial

distribution of dinoflagellate cysts in surface sediments of the northern north atlantic in relation to nutrient content and productivity in surface waters abstract analyses of dinoflagellate cyst assemblages from the surface sediments of 371 sites from the north atlantic ocean were performed in order to define relationships with nitrate phosphate silica and productivity in the upper water layer statistical analyses reveal close links between dinocyst assemblages and nitrate content in february that provide a measurement of nitrate availability amongst the taxa in the assemblages nematosphaeropsis labyrinthus which positively correlates with nutrients shows an eutrophic relationship whereas impagidinium aculeatum impagidinium patulum spiniferites ramosus spiniferites mirabilis and lingulodinium machaerophorum have a rather oligotrophic relationship on these grounds transfer functions were tested using multiple regressions and the best analogue technique to reconstruct nitrate content both methods yielded reasonable estimates and allow the reconstruction of the nitrate concentrations in february with an accuracy better than 1 45 mol m 3 at the scale of the study area there are also tenuous links between the dinocyst assemblages and productivity transfer functions were tentatively tested for the reconstruction of annual productivity and yield estimates with an accuracy of about 26 5 gc m 2 year 1 these results demonstrate that dinocyst assemblages can be used for the reconstruction of productivity and nitrates

relationship between gps signals reflected from sea surfaces and surface winds modeling results and comparisons with aircraft measurements theoretical calculations of global positioning system gps signals reflected from rough sea surfaces are discussed and compared with the aircraft measurements the theoretical model is based on the assumption that rough sea surfaces are composed of facets and the reflection of gps signals from the facets can be calculated on the basis of geometric optics in order to determine the slopes of the sea surface facets the statistical model of cox and munk 1954 for ocean surface slopes is used since much of the sea surface roughness observed is at scales much less than the gps wavelength the dependence of the mean square slopes on frequency is taken into consideration model results agree well with aircraft measurements the differences between model results and observations are within the level of experimental errors for calm sea surfaces near sea surface wind speeds 7 m s 1 the correlation powers decrease their peak values to 4 8 db significantly widen time delay responses and shift toward the delays corresponding to path lengths longer than those of specular points sensitivity tests show that there is considerable potential for current or advanced gps receiving systems to estimate near sea surface wind speeds the errors in the wind speed estimates could be smaller than 2 m s 1 for near sea surface wind directions the maximum changes in the correlation powers of the gps signals as a function of azimuth appear to be 0 5 db for current gps receiving systems which may be too small for wind direction estimation new designs of the gps receivers or a higher signal to noise ratio than that of current aircraft receivers may be needed

the dependence of ocean backscatter at k sub u band on oceanic and atmospheric parameters the jet propulsion laboratory nuscat k sub u band scatterometer successfully acquired ocean backscatter data over a wide variety of oceanic and atmospheric conditions during the surface wave dynamics experiment swade ten flights resulted in 30 h of data collection were conducted on the nasa ames c130 aircraft the swade experimental area was deployed with several buoys providing appropriate in situ measurements to correlate with the radar backscatter for incidence angles from 10 to 60 spl deg at both horizontal and vertical polarizations the nuscat swade backscatter data base was utilized in conjunction with buoy measurements to investigate ocean backscatter signatures over the range of conditions encountered during swade to account for modulations and fluctuations in incidence angles a backscatter analysis independent of a priori geophysical model functions was developed tested and implemented results for backscatter azimuth modulations in terms of upwind downwind and crosswind radar returns are compared to airborne radscat results and to sass i and ii geophysical model functions versus neutral wind speed u sub n nuscat swade results are closest overall to sass ii values fit best with sass i at 10 spl deg incidence angle and are significantly higher than radscat effects of friction velocity u wave age c sub o u and significant wave height h sub 1 3 on ocean backscatter are studied the backscatter shows a good positive sensitivity to u an inverse dependence on c sub o u and no systematic trend with h sub 1 3 excluding cases of large swells coefficients of empirical relations between backscatter and neutral wind speed friction velocity and wave age are derived for 10 40 spl deg incidence angles at both horizontal and vertical polarizations covariance studies of backscatter with the derived relations to winds show an overall deviation factor in the order of 1 db for ocean signatures including uncertainties in surface conditions

detection of arctic ocean tides using interferometric gnss r signals 1 this paper evaluates the usage of reflected gps signals for earth observations to study changes of sea level and sea ice in remote sensing in a coastal setup 670 m above disko bay greenland signals with different carriers l1 and l2 were recorded a method is presented that analyses the interferometric phase between the reflected and the direct signals and derives the height of the reflecting surface the analysis includes a ray tracing and an estimation of signal coherence it is shown that coherent reflections are related to sea ice coverage absolute heights are derived with a time interval of 30 min the altimetric results show semidiurnal tides that are validated using the aodtm 5 tide model the residual height has a mean of 9 7 cm for l1 and 22 9 cm for l2 the dispersion is not significant but a significant tropospheric bias is detected with an error of up to 20 cm

sea level monitoring and sea state estimate using a single geodetic receiver gnss reflectometry gnss r altimetry has demonstrated a strong potential for sea level monitoring interference pattern technique ipt based on the analysis of the signal to noise ratio snr estimated by a gnss receiver presents the main advantage of being applicable everywhere by using a single geodetic antenna and receiver transforming them to real tide gauges classical snr analysis method used to estimate the variations of the reflecting surface height h t has a limited domain of validity due to its variation rate dhdtt assumed to be negligible we present here a significant advance in this altimetric methodology using gnss multipath to conjointly estimate h t and dhdtt over areas characterized by high amplitudes of tides and presence of waves it drastically enhances the temporal and spatial monitoring of tides and waves inversion approach is based on a least square method lsm combining simultaneous measurements from different gnss constellations gps glonass our method is validated with snr data acquired on an offshore site of 60 meter height in conditions were assumptions of the classical snr analysis method are not valid i e with a semi diurnal tide amplitude of 4 m vertical velocity of the sea surface due to tide reaching 0 2 mm s and presence of waves with amplitude up to few meters linear correlation between the estimates with our method and tide gauges records are better than 0 97 whereas it only equals 0 82 with the classical method over the whole 3 months of acquisition our dynamic snr method allows a very good estimate of the main tide periods and permits to detect swell and waves with realistic amplitudes and periods which is not the case with tide gauges located in protected areas or classical snr analysis method

constitutive relations for fault slip and earthquake instabilities constitutive relations for fault slip are described and adopted as a basis for analyzing slip motion and its instability in the form of earthquakes on crustal faults the constitutive relations discussed include simple rate independent slip weakening models in which shear strength degrades with ongoing slip to a residual frictional strength and also more realistic but as yet less extensively applied slip rate and surface state dependent relations for the latter the state of the surface is characterized by one or more variables that evolve with ongoing slip seeking values consistent with the current slip rate models of crustal faults range from simple single degree of freedom spring slider systems to more complex continuous systems that incorporate nonuniform slip and locked patches on faults of depth dependent constitutive properties within elastic lithospheric plates that may be coupled to a viscoelastic asthenosphere

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

carrier phase delay altimetry with gps reflection occultation interferometry from low earth orbiters 1 gps signals reflected off the surface of the earth can be detected by receivers aboard occulting low earth orbiters leos in this work carrier phase interferometry between the reflected and direct occultation signals is performed to infer its relative delay at centimetric error our analysis shows that submeter sensitivity on the surface heights can formally be reached with this technique the potential applications to polar ice altimetry are discussed

the distribution and relationship between palynomorphs in aerosols and deep sea sediments off the coast of northwest africa abstract palynomorphs in eolian dust and bottom sediments from the northeastern atlantic off the coast of northwest africa were studied primary examination was for terrestrial plant detritus pollen spores opal phytoliths and freshwater diatoms but observations about marine entities were also made three distinct geographic palynofloras were detected a northern palynoflora consisting of pollen derived primarily from the mediterranean basin a central or saharan palynoflora characterized by pollen derived from desert plants and a southern tropical equatorial palynoflora composed of pollen derived from tropical plants but including up to 50 allochthonous pollen from the drier interior of west africa palynomorph distributions are related closely to both source vegetation and to atmospheric and oceanic transport mechanisms and in many cases distribution patterns in bottom sediments and aerosols are complementary the quantity of pollen and spores per gram of bottom sediment ranges from greater than 2000 off the saharan coast in mauritania to less than 50 in deep ocean basins pollen and spores in mediterranean aerosols may exceed 40 per cubic meter of air during the summer and range between 4 to 6 for tropical aerosols during the winter tropical aerosols and bottom sediments contained the greatest abundance of fungal spores the distribution of opal phytoliths and freshwater diatoms in both aerosols and bottom sediments indicates that dust storms are a major transporting agent for these entities from the interior of west africa to the gulf of guinea these storms are also an important agent for the transport of pollen to the tropical atmosphere distances of transport may exceed 5000 km for mediterranean pollen and even greater distances for palynomorphs in eolian dust from interior west africa the abundance of dinoflagellates and microforaminifera in bottom sediments is directly related to the area of upwelling off the west african coast

limitations of use of organic petrographic techniques for identification of petroleum source rocks organic petrographic and organic geochemical studies have been conducted on 58 sediment samples of differing ages and depositional environments in this study interpretations of petroleum source rock potential based on data from transmitted light microscopy show a poor correlation with those derived from chemical data this lack of correlation arises from the failure to distinguish consistently between hydrogen poor and hydrogen rich amorphous organic matter and inability to detect hydrogen rich components exinite and resinite in coal fragments interpretations based on data from reflected light microscopy show a better correlation with those derived from chemical studies but difficulties still remain these difficulties arise from inability except on the basis of luorescence intensity to distinguish hydrogen rich from hydrogen poor organic matter in a finely dispersed state

dilatant strengthening as a mechanism for slow slip events 1 the mechanics of slow slip events sse in subduction zones remain unresolved we suggest that sse nucleate in areas of unstable friction under drained conditions but as slip accelerates dilatancy reduces pore pressure p quenching instability competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast we model sse with 2 d elasticity rate state friction and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss 0 ln v v0 v is slip speed we consider two diffusion models membrane diffusion md is approximated by p p tf where p and p are shear zone and remote pore pressure and tf is a characteristic diffusion time homogeneous diffusion hd accurately models fault normal flow with diffusivity chyd for md linearized analysis defines a boundary 1 a b between slow and fast slip where f0e b p f0 a and b are friction parameters and is compressibility when 1 a b slip speeds remain quasi static for hd ep eh p defines dilatancy efficiency where h is shear zone thickness and v is plate velocity sse are favored by large eh and low effective stress the ratio ep to thermal pressurization efficiency scales with 1 p so high p favors sse consistent with seismic observations for ep 10 3 transient slip rates repeat times average slip and stress drops are comparable to field observations model updip propagation speeds are comparable to those observed along strike many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress model sse accommodate only a fraction of plate motion the remaining deficit must be accommodated during coseismic or postseismic slip

the eddy experiment gnss r speculometry for directional sea roughness retrieval from low altitude aircraft we report the retrieval of sea surface directional mean square slope from global navigation satellite system reflections gnss r delay doppler map ddm data collected during an experimental flight at 1 km altitude we emphasize the utilization of the entire ddm to more precisely infer ocean roughness directional parameters and argue that the ddm exhibits the impact of both roughness and scatterer velocity obtained estimates are analyzed and compared with jason 1 measurements ecmwf numerical weather model outputs and optical data

using ddm asymmetry metrics for wind direction retrieval from gps ocean scattered signals in airborne experiments reflectometry of signals of opportunity such as those emitted by a global navigation satellite system known as gnss r has been developed over the past years as a technique with great potential for ocean scatterometry among other applications different approaches have been proposed to use gnss r for remote sensing of ocean surface roughness one of them is based on deriving some descriptor metric from the measured delay doppler map ddm and directly relating it to a geophysical property of the scattering surface for instance different descriptors have been proposed in the literature to measure the ddm spreading caused by the increase in ocean surface mean square slopes due to surface winds in this paper a new descriptor based on the ddm is proposed for wind direction retrieval this descriptor designated as the skewness angle 1 skew measures the asymmetry in the ddm power distribution along the doppler frequency axis and it was modeled as a function of wind direction by means of a simulation study then that model was validated using real gnss r data from an airborne experiment after validation the ddm skewness model was successfully used for wind direction retrieval with a resulting rms error on the order of 20

effect of sea roughness on bistatically scattered range coded signals from the global positioning system a series of aircraft experiments was performed using a specialized gps receiver and a nadir oriented left hand circularly polarized antenna this apparatus received reflections of the gps signals from water surfaces under a variety of sea states the cross correlation between the reflected signal and a reference pseudo random noise code was recorded as a function of the relative time delay the shape of this function showed a dependence on the roughness of the reflecting surface this dependence generally followed that predicted by theory for bistatic scattering of range coded signals use of this information as a remote sensing technique for the determination of sea state is discussed

imaging shear strength along subduction faults subduction faults accumulate stress during long periods of time and release this stress suddenly during earthquakes when it reaches a threshold this threshold the shear strength controls the occurrence and magnitude of earthquakes we consider a 3 d model to derive an analytical expression for how the shear strength depends on the fault geometry the convergence obliquity frictional properties and the stress field orientation we then use estimates of these different parameters in japan to infer the distribution of shear strength along a subduction fault we show that the 2011 mw9 0 tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength this observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength with increasing constraints on the different parameters at play our approach could in the future help identify favorable locations for large earthquakes

global mapping functions for the atmosphere delay at radio wavelengths i have developed expressions for calculating the ratios mapping functions of the line of sight hydrostatic and wet atmospheric path delays to their corresponding zenith delays at radio wavelengths for elevation angles down to 3 the coefficients of the continued fraction representation of the hydrostatic mapping function depend on the latitude and height above sea level of the observing site and on the day of the year the dependence of the wet mapping function is only on the site latitude by comparing with mapping functions calculated from radiosonde profiles for sites at latitudes between 43 s and 75 n the hydrostatic mapping function is seen to be more accurate than and of comparable precision to mapping functions currently in use which are parameterized in terms of local surface meteorology when the new mapping functions are used in the analysis of geodetic very long baseline interferometry vlbi data the estimated lengths of baselines up to 10 400 km long change by less than 5 mm as the minimum elevation of included data is reduced from 12 to 3 the independence of the new mapping functions from surface meteorology while having comparable accuracy and precision to those that require such input makes them particularly valuable for those situations where surface meteorology data are not available

5 cm precision aircraft ocean altimetry using gps reflections 1 we present the first two aircraft global positioning system gps reflection altimetry measurements the most precise gps ocean altimetry measurement and demonstrate the altimetric precision and spatial resolution necessary to map mesoscale eddies our first experiment demonstrated a 14 cm precision single satellite ocean altimetry measurement while our more recent experiment demonstrates 5 cm altimetric precision with 5 km spatial resolution the new results show significant improvement over our previous effort due to improved modeling greater aircraft altitudes and velocities improved receiver positioning and better experimental control plans to further reduce speckle and refine models to obtain 5 cm altimetric accuracy are presented

scattering of gps signals from the ocean with wind remote sensing application a theoretical model that describes the power of a scattered global positioning system gps signal as a function of geometrical and environmental parameters has been developed this model is based on a bistatic radar equation derived using the geometric optics limit of the kirchhoff approximation the waveform i e the time delayed power obtained in the delay mapping technique depends on a wave slope probability density function which in turn depends on wind waveforms obtained for aircraft altitudes and velocities indicate that altitudes within the interval 5 15 km are the best for inferring wind speed in some regimes an analytical solution for the bistatic radar equation is possible this solution allows converting trailing edges of waveforms into a set of straight lines which could be convenient for wind retrieval a transition to satellite altitudes together with satellite velocities makes the peak power reduction and the doppler spreading effect a significant problem for wind retrieval based on the delay mapping technique at the same time different time delays and different doppler shifts of the scattered gps signal could form relatively small spatial cells on sea surface suggesting mapping of the wave slope probability distribution in a synthetic aperture radar sar fashion this may allow more accurate measurements of wind velocity and wind direction

2 cm gps altimetry over crater lake dierences in electromagnetic path delay be tween direct global positioning system gps signals and those reflected from the surface of crater lake have led to lake surface height estimates with 2 cm precision in 1 sec ond this is the rst high precision altimetric demonstra tion with gps from sucient altitude 480 m to probe fundamental experimental errors which bear on future air and spaceborne passive gps altimetry it also serves as the rst demonstration of a new approach to altimetric remote sensing in the coastal region an area that is poorly mea sured by conventional radar altimetry time series analy sessuggest thattroposphericandthermalnoisefluctuations dominate the altimetric error in this experiment estimat ing the dierential delay from several simultaneously visi ble satellites may enable tropospheric error estimation and correction thermal noise on the reflected signal will be reduced with fully polarimetric observations and larger an tenna apertures

the application of reflected gps signals to ocean remote sensing abstract the l band broadcast signal from the global positioning system gps reflected off of the sea surface is under study for use as a ocean coastal and wetlands remote sensing tool the reflected signal from a given gps satellite is cross correlated with the pseudorandom noise code uniquely identifying that satellite the shape of this cross correlation ordinarily a very sharp triangle when tracking a direct line of sight signal becomes wider and smoother as the mean square slope of the reflecting surface increases it is proposed that the surface wind speed can be determined by matching the recorded shape of this cross correlation to that predicted by theoretical models as a function of wind speed and direction the significance of these effects increases with altitude of the receiver experimental data have been collected using a specially modified gps receiver on aircraft and on a balloon at altitudes of up to 25 km these data compare favorably with predictions of analytical models and demonstrate the dependence of the waveform shape on surface wind speed and receiver altitude the advantages that this measurement technique has over conventional scatterometers is the small size low cost and simplicity of the receiver hardware no requirement for a transmitter and the ability to simultaneously collect data from usually 10 or more points from a low earth orbiting satellite this number could be larger if the russian global navigation satellite system satellites are also considered as additional sources of radiation furthermore the bistatic scattering geometry is complementary to the backscatter used by conventional scatterometers

slip partitioning along an idealized subduction plate boundary at deep slow slip conditions abstract below the base of many subduction seismogenic zones the plate interface periodically slips at rates 1 to 2 orders of magnitude faster than tectonic plate velocities a number of competing hypotheses exist to explain the mechanisms for these slow slip events sses but they remain incompletely tested because we do not know how deformation is partitioned across the lithologically complex plate boundary interface we use the deepest exposure of the arosa zone a 520 m thick exhumed subduction interface as a case study to evaluate the partitioning of strain between lithologic units throughout the sse cycle we review and synthesize published constitutive relations for the five lithologic units present to express shear stress as a function of deformation rate we use these results to predict 1 the shear stress across the plate boundary as a function of slip velocity and 2 the partitioning of deformation among the different lithologic units for sse and aseismic creep velocities we conduct this analysis for pore fluid pressures from hydrostatic to near lithostatic our results show that at pore fluid pressure close to hydrostatic aseismic creep and sse velocities occur by viscous deformation of calcareous and quartzose units however once the pore fluid pressure increases above 80 of lithostatic plate boundary slip migrates from the calcareous and quartzose rocks during aseismic creep to frictional deformation of talc schist during slow slip this result is insensitive to differences in the thicknesses of metasedimentary units that may be present along subduction plate boundaries and therefore may apply to subduction plate boundaries in general

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

preseismic rupture progression and great earthquake instabilities at plate boundaries we present a procedure for modeling the initially quasi static upward progression of a zone of slip from some depth in the lithosphere toward the earth s surface along a transform plate margin culminating in a great crustal earthquake stress transmission in the lithosphere is analyzed with a generalized elsasser model in which elastic lithospheric plates undergo plane stress deformation and are coupled by an elementary foundation model to a maxwellian viscoelastic asthenosphere upward progression of rupture over a finite length of plate boundary corresponding to a seismic gap along strike is analyzed by a method based on the line spring concept whereby a two dimensional antiplane analysis of the upward progression provides the relation between lithospheric thickness averaged stress and slip used as a boundary condition in the generalized elsasser plate model the formulation results in a nonlinear integral equation for the rupture progression as a function of time and distance along strike a simpler approximate single degree of freedom analysis procedure is described and shown to lead to instability results that can be formulated in terms of the slip softening slope at the boundary falling below the elastic unloading stiffness of the surroundings the results also indicate a delay of ultimate seismic instability due to the stiffer short versus long time asthenospheric response and predict a final period of self driven creep toward instability the procedures for prediction of rupture progression and instability are illustrated in detail for an elastic brittle crack model of slip zone advance and parameters of the model are chosen consistently with great earthquake slips and stress drops for example an effective crack fracture energy of the order 4 106 j m2 at the peak 7 to 10 km below surface of a gaussian bell shaped distribution of fracture energy with depth with variance of the order 5 km simulating strength build up in a seismogenic layer leads to prediction of nominal seismic stress drops of 30 to 60 bars and slips of 2 to 5 m in great strike slip earthquake ruptures breaking 100 to 400 km along strike precursory surface straining in the self driven stage is predicted to proceed at a distinctly higher rate over time intervals beginning 3 to 10 months before such an earthquake this interval being greater for longer distances along strike over which the preseismic upward rupture progression takes place

latest pleistocene holocene paleoceanographic trends on the continental margin of eastern canada foraminiferal dinoflagellate and pollen evidence micropaleontological studies were made of cores from four shelf basins on the eastern canadian margin emerald and canso basins on the scotian shelf 44 46 n notre dame channel newfoundland shelf 50 n and cartwright saddle labrador shelf 55 events were correlated using a combination of14c dates and pollen stratigraphies surface and bottom water changes were compared on the basis of dinoflagellates and benthic foraminifera respectively the results indicate significant paleoceanographic shifts along a north south gradient both prior to and during the holocene distinct late pleistocene holocene paleoceanographic events were distinguished in the emerald canso and notre dame basins these events are less obvious in cartwright saddle which is in deeper water and further off shore pleistocene glaciomarine sediments in all basins contain a fauna dominated byelphidium excavatum f clavata dinoflagellates and pollen are rare or absent the widespreadelphidium fauna probably reflects turbid glacial meltwater and or a permanent ice shelf cover from 20 000 10 000 yrs bp the notre dame core also penetrates older sediment with an outer labrador current fauna which may represent a late wisconsinian interstade at about 23 000 yrs bp from 7 000 10 000 yrs bp a cold water fauna occurred which is similar to modern outer labrador current faunas from about 5000 7000 yrs bp a warm interval is indicated by a relatively warm water calcareous benthonic foraminiferal fauna and increased representation of typical gulf stream dinoflagellates the most recent change occurred in the last 2000 years with an abrupt cooling associated with stronger flow of the arctic inner labrador current this cooling event is marked by an increase in arctic dinoflagellates and by an exclusively agglutinated benthonic foraminiferal fauna at two sites canso and notre dame these holocene paleoceanographic changes are not clearly seen in the benthic fauna of the deep northern basin cartwright saddle although dinoflagellate data at this site indicate that surface water changes have occurred that are similar to those found in shallower basins shifts in the zonal position of the gulf stream and changes in the relative mass transports of the west greenland and labrador currents are mechanisms which may account for the paleoceanographic events the glacial interstadial glacial sequence recorded in the notre dame channel in conjunction with other theories on glacial triggering mechanisms provides biostratigraphic evidence which suggests the onset of a glacial stage in the near future

strength of stick slip and creeping subduction megathrusts from heat flow observations subduction faults called megathrusts can generate large and hazardous earthquakes the mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone however the relative strength of a megathrust based on the mode of slip is far from clear the fault strength affects surface heat flow by frictional heating during slip we model heat flow data for a number of subduction zones to determine the fault strength we find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping

compressive sensing of frequency dependent seismic radiation from subduction zone megathrust ruptures megathrust earthquakes rupture a broad zone of the subducting plate interface in both along strike and along dip directions the along dip rupture characteristics of megathrust events e g their slip and energy radiation distribution reflect depth varying frictional properties of the slab interface here we report high resolution frequency dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive sensing sparse source recovery technique resolving generally low frequency radiation closer to the trench at shallower depths and high frequency radiation farther from the trench at greater depths together with coseismic slip models and early aftershock locations our results suggest depth varying frictional properties at the subducting plate interfaces the shallower portion of the slab interface above 15 km is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip deficient high frequency radiation and few early aftershocks the slab interface at intermediate depths 15 35 km is the main unstable seismogenic zone for the nucleation of megathrust quakes typically with large coseismic slip abundant early aftershocks and intermediate to high frequency radiation the deeper portion of the slab interface 35 45 km is seismically unstable however with small coseismic slip dominant high frequency radiation and relatively fewer aftershocks

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

sensitivity analysis of wind vector measurements from ocean reflected gps signals the power received by a gps receiver located on an airplane flying over the ocean and collecting the gps signal reflected off the surface is estimated for varying wind speed and wind direction platform altitude satellite elevation angle and receiver integration time by accounting for the wind induced anisotropy on the surface it is shown that the trailing edges of computed waveforms change with both wind speed and direction when the receiver integration time is properly chosen substantial differences in the waveforms at different wind directions are exhibited even at the beginning of the trailing edge particularly for reflections from high elevation satellites these differences are associated with the extent and directional properties of the scattered fields as a function of reflection angle an analysis of the interdependence of the observational geometric parameters the coherence time and the receiver integration time is presented to suggest a suitable arrangement for enhanced measurement sensitivity to the wind direction

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

the paris concept an experimental demonstration of sea surface altimetry using gps reflected signals this paper presents the passive reflectometry and interferometry system paris concept and how it originated in the european space agency esa noordwijk the netherlands in 1993 as a novel method to perform mesoscale ocean altimetry the paris concept uses signals of opportunity such as the signals from the global navigation satellite systems gnss which are reflected off the ocean surface to perform mesoscale ocean altimetry essentially the relative delay between the direct and the reflected signals received from a low earth orbit satellite provides information about sea surface height the paper describes an original experiment on sea surface altimetry using gps reflected signals the objective of the experiment was to demonstrate the potential of the paris concept this experiment is the first one ever published on performing sea surface height estimations using reflected navigation signals in a controlled environment the key result of the experiment is the demonstration of a root mean squared rms height accuracy within 5 s of 1 of the used code chip 3 m for c a code direct extrapolation of this experimental result to the 10 times higher chip rate p code signal allows us to predict a height error of 30 cm in 5 s provided adequate models are used to take into account systematic effects the paper ends presenting the potential of the paris concept for long term ocean altimetric observations in view of the current trends of the gnss systems

gps signal scattering from sea surface wind speed retrieval using experimental data and theoretical model abstract global positioning system gps signals reflected from the ocean surface have potential use for various remote sensing purposes some possibilities are measurements of surface roughness characteristics from which wave height wind speed and direction could be determined for this paper gps reflected signal measurements collected at aircraft altitudes of 2 km to 5 km with a delay doppler mapping gps receiver are used to explore the possibility of determining wind speed to interpret the gps data a theoretical model has been developed that describes the power of the reflected gps signals for different time delays and doppler frequencies as a function of geometrical and environmental parameters the results indicate a good agreement between the measured and the modeled normalized signal power waveforms during changing surface wind conditions the estimated wind speed using surface reflected gps data obtained by comparing actual and modeled waveforms shows good agreement within 2 m s with data obtained from a nearby buoy and independent wind speed measurements derived from the topex poseidon altimetric satellite

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

palaeoclimate of baffin bay from 300 000 year record of foraminifera dinoflagellates and pollen several different models1 5 have attempted to relate quaternary marine and terrestrial records of ice sheet growth in the north atlantic region the models are derived from either discontinuous terrestrial records including marine fossils in raised shorelines1 2 or from deep sea calcareous microfossils3 4 this study correlates arctic marine and terrestrial data directly by comparing 18o foraminiferal dinoflagellate and pollen records from a core taken in baffin bay the core contains an almost continuous sequence of sediments deposited during isotope stages 1 10 subarctic foraminifera and atlantic dinoflagellates in early isotope stages 2 4 6 and 8 show that subarctic water entered southern baffin bay before the glacial maxima boreal subarctic pollen suggest that atlantic air flowed into baffin bay during the ice sheet growth phases these data support models which postulate that open water in the labrador sea had an important role in supplying moisture to laurentide and greenland ice sheets

imaging short period seismic radiation from the 27 february 2010 chile mw 8 8 earthquake by back projection of p pp and pkikp waves 1 teleseismic short period 0 5 5 s p waves from the 27 february 2010 chile earthquake mw 8 8 are back projected to the source region to image locations of coherent short period seismic wave radiation several receiver array configurations are analyzed using different p wave arrivals including networks of stations in north america p japan pkikp and europe pp as well as a global configuration of stations with a broad azimuthal distribution and longer period p waves 5 20 s coherent bursts of short period radiation from the source are concentrated below the chilean coastline along the downdip portion of the megathrust the short period source region expands bilaterally with significant irregularity in the radiation comparison with finite fault slip models inverted from longer period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short period radiation a manifestation of frequency dependent seismic radiation similar to observations for the great 2011 tohoku earthquake mw 9 0 back projection of synthetic p waves generated from the finite fault models demonstrates that if the short period energy had radiated with the same space time distribution as the long period energy back projection analysis would image it in the correct location updip we conclude that back projection imaging of short period signals provides a distinct view of the seismic source that is missed by studies based only on long period seismic waves geodetic data and or tsunami observations

location of largest earthquake slip and fast rupture controlled by along strike change in fault structural maturity due to fault growth earthquake slip distributions are asymmetric along strike but the reasons for the asymmetry are unknown we address this question by establishing empirical relations between earthquake slip profiles and fault properties we analyze the slip distributions of 27 large continental earthquakes in the context of available information on their causative faults in particular on the directions of their long term lengthening we find that the largest slips during each earthquake systematically occurred on that half of the ruptured fault sections most distant from the long term fault propagating tips i e on the most mature half of the broken fault sections meanwhile slip decreased linearly over most of the rupture length in the direction of long term fault propagation i e of decreasing structural maturity along strike we suggest that this earthquake slip asymmetry is governed by along strike changes in fault properties including fault zone compliance and fault strength induced by the evolution of off fault damage fault segmentation and fault planarity with increasing structural maturity we also find higher rupture speeds in more mature rupture sections consistent with predicted effects of low velocity damage zones on rupture dynamics since the direction s of long term fault propagation can be determined from geological evidence it might be possible to anticipate in which direction earthquake slip once nucleated may increase accelerate and possibly lead to a large earthquake our results could thus contribute to earthquake hazard assessment and earthquake early warning

influence of releasing step overs on surface fault rupture and fault segmentation examples from the 17 august 1999 izmit earthquake on the north anatolian fault turkey the 17 august 1999 izmit earthquake broke four distinct structural segments of the north anatolian fault from east to west the karadere sakarya sapanca and golcuk fault segments these segments are separated from one another and the adjoining yalova and duzce fault segments to the west and east respectively by distinct right releasing step over and or gaps in the fault trace these include from east to west the eften lake step over 2 4 km wide akyazi gap 6 13 km long sapanca step over 1 2 km wide golcuk step over 1 2 km wide and karamursel step over 4 5 km wide the earthquake nucleated within or near the golcuk step over with bilateral rupture propagation to the west and east to the west about 4 5 5 m of surface rupture up to 7 m of subsurface rupture on the golcuk segment was mostly if not entirely arrested by the 4 to 5 km wide karamursel step over to the east about 3 4 m of surface rupture about 4 m of subsurface rupture propagated through the 1 to 2 km wide sapanca step over triggering up to 4 5 5 5 m of surface rupture up to 5 6 m of subsurface rupture on the sakarya segment rupture on the sakarya segment stepped across the akyazi gap triggering 1 1 5 m of rupture on the karadere segment rupture on the karadere segment was arrested by the 2 to 4 km wide eften lake step over modeling of the transient stress field associated with the rupture propagation agrees well with the field observations the modeled fault rupture of 5 m on the golcuk segment appears to decrease the transient stress on the eastern tip of the adjoining yalova segment across the 4 to 5 km wide karamursel step over even if we allow rupture on the golcuk segment to extend along the entire southern margin of the step over our model shows that regardless of the amount of slip in a generic sense it is difficult to increase stress on the tip of an adjoining fault segment across a 5 km wide step over on the other hand fault rupture of 3 m on the western tip of the sapanca fault segment significantly increases the transient stress on the adjoining sakarya segment across the 1 to 2 km wide sapanca step over allowing rupture propagation across the basin an evaluation of 30 historical strike slip earthquakes involving 59 step over basins supports our field observations and stress modeling of the izmit fault rupture historical strike slip events with small to large displacements usually propagate through step overs less than 1 2 km wide with increasing displacement larger and larger step overs can be ruptured through the empirical data generally show a ratio ranging from 2 1 to 1 1 between step over width in kilometers and strike slip displacement in meters for a through going rupture however step overs of 4 to 5 km width appear to always arrest fault rupture regardless of the amount of displacement these results therefore provide important constraints for evaluating the probability of multisegment ruptures on segmented strike slip faults manuscript received 20 august 2000

mediterranean balloon experiment ocean wind speed sensing from the stratosphere using gps reflections abstract the mediterranean balloon experiment mebex conducted in august 99 from the middle up stratosphere was designed to assess the wind retrieval sensitivity of global navigation satellite systems reflections gnssr technology from high altitudes global positioning system reflected signals gpsr collected at altitudes around 37 km with a dedicated receiver have been inverted to mean square slopes mss of the sea surface and wind speeds the theoretical tool to interpret the geophysical parameters was a bistatic model which also depends on geometrical parameters the results have been analyzed in terms of internal consistency repeatability and geometry dependent performance in addition wind velocities have been compared to independent measurements by quikscat topex ers ra and a radio sonde with an agreement better than 2 m s a numerical weather prediction model nwpm the mm5 mesoscale forecast model has also been used for comparison with varying results during the experiment the conclusion of this study confirms the capability of high altitude gpsr delay map receivers with low gain antennas to infer surface winds

marine and terrestrial environmental changes in nw europe preceding carbon release at the paleocene eocene transition environmental changes associated with the paleocene eocene thermal maximum petm 56 ma have not yet been documented in detail from the north sea basin located within proximity to the north atlantic igneous province naip the kilda basin and the northern rain belt paleolatitude 54 1n during the petm this is a critical region for testing proposed triggers of atmospheric carbon release that may have caused the global negative carbon isotope excursion cie in marine and terrestrial environments the cie onset is identified from organic matter d 13 c in exceptional detail within a