on the wave number spectrum of oceanic mesoscale variability observed by the seasat altimeter variations of sea surface height measured by the seasat altimeter in nearly repeat orbits during the last 24 days of the mission are used to compute the wave number spectrum of mesoscale variability in various parts of the oceans the instrument noise level 150 cm2 cycles km has limited the resulting oceanic spectrum to wavelengths longer than 100 km we found that the characteristics of the oceanic spectrum are dependent on the energy level of the mesoscale variability in the high energy areas close to major current systems most of the energy is contained at wavelengths longer than 250 km at wavelengths shorter than 250 km the spectrum basically follows a k 5 k is wave number dependence in the low energy areas remote from major current systems the spectrum follows a k 1 dependence at wave lengths from 100 to 1000 km based on the assumption of horizontal isotropy of mesoscale variability scalar wave number spectra of sea surface height and geostrophic kinetic energy are also presented dynamical implications of these spectra are discussed the effects of residual geoid and atmospheric water vapor on the computed oceanic spectra have been rigorously examined it was found that the general characteristics of the oceanic spectra were not significantly affected by them

metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet staurolite muscovite schists in central qiangtang tibet subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological geochemical and geophysical observations at modern convergent plate margins so far not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion here we first revealed metamorphic records for a subduction erosion process based on our study of the late paleozoic garnet staurolite muscovite schists in the central qiangtang block tibet provenance analyses suggest that the protoliths of garnet staurolite muscovite schists have the northern qiangtang affinity and were deposited in an active continental margin setting mineral inclusion data show that the early metamorphic stage m1 recorded blueschist facies pressure temperature p t conditions of 0 8 1 1 gpa and 402 441 c indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high pressure low temperature metamorphism the peak metamorphic stage m2 recorded amphibolite facies p t conditions of 0 3 0 5 gpa and 470 520 c the 40ar 39ar cooling ages 263 259 ma yielded from muscovite suggest the amphibolite facies metamorphism 263 ma occurred at oceanic subduction stage the distinctly staged metamorphism defines a clockwise and warming decompression p t t path which reveals an underplating process following the early subduction erosion during the tectonic process the eroded low density material escaped from the cold subduction channel and rise upward into the warm middle lower crust of the upper plate undergoing amphibolite facies metamorphism our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the paleo tethys ocean

low friction along the high slip patch of the 2011 mw 9 0 tohoku oki earthquake required from the wedge structure and extensional splay faults we analyze the mechanical properties needed to account for the large shallow slip during the 2011 tohoku oki earthquake and the activation of landward normal faulting within the forearc we show that the morphology and internal structure of the forearc follows closely the prediction of the critical coulomb wedge in horizontal compression implying a high internal pore pressure ratio 0 7 0 14 0 48 and a low effective basal friction eff b 0 14 0 18 0 04 we then show that the activation of the normal fault requires a lower effective basal friction beneath the outer wedge than beneath the inner wedge outer 0 015 possibly due to transient dynamic weakening associated to the seismic rupture forearc normal faults could be considered as evidence for very efficient dynamic weakening along the megathrust and typify megathrust with high tsunamigenic potential

spirit mars rover mission to the columbia hills gusev crater mission overview and selected results from the cumberland ridge to home plate this paper summarizes the spirit rover operations in the columbia hills of gusev crater from sols 513 to 1476 and provides an overview of selected findings that focus on synergistic use of the athena payload and comparisons to orbital data results include discovery of outcrops voltaire on husband hill that are interpreted to be altered impact melt deposits that incorporated local materials during emplacement evidence for extensive volcanic activity and aqueous alteration in the inner basin is also detailed including discovery and characterization of accretionary lapilli and formation of sulfate silica and hematite rich deposits use of spirit s data to understand the range of spectral signatures observed over the columbia hills by the mars reconnaissance orbiter s compact reconnaissance imaging spectrometer crism hyperspectral imager 0 4 4 m is summarized we show that crism spectra are controlled by the proportion of ferric rich dust to ferrous bearing igneous minerals exposed in ripples and other wind blown deposits the evidence for aqueous alteration derived from spirit s data is associated with outcrops that are too small to be detected from orbital observations or with materials exposed from the shallow subsurface during rover activities although orbital observations show many other locations on mars with evidence for minerals formed or altered in an aqueous environment spirit s data imply that the older crust of mars has been altered even more extensively than evident from orbital data this result greatly increases the potential that the surface or shallow subsurface was once a habitable regime

the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

finding fault in fault zones what controls the location and size of seismic rupture along the 43 500 km of the world s subduction faults two reports in this issue based on seismological observations emphasize the key role of the structural evolution of faults on page 207 dean et al 1 propose that a structural flaw of the sedimentary formation brought into the sumatra subduction zone may facilitate rupture propagation on page 210 kimura et al 2 propose that fracturing of the downward going plate beneath the kanto area in central japan causes the subduction interface to be diverted to a deeper position and change its seismogenic behavior

light toned salty soils and coexisting si rich species discovered by the mars exploration rover spirit in columbia hills 1 light toned soils were exposed through serendipitous excavations by spirit rover wheels at eight locations in the columbia hills their occurrences were grouped into four types on the basis of geomorphic settings at three major exposures the light toned soils are hydrous and sulfate rich the spatial distributions of distinct types of salty soils vary substantially with centimeter scaled heterogeneities at paso robles dead sea shredded and champagne penny a well mixed nature for light toned soils occurring near and at the summit of husband hill and relatively homogeneous distributions in the two layers at the tyrone site aeolian fumarolic and hydrothermal fluid processes are suggested to be responsible for the deposition transportation and accumulation of these light toned soils in addition a change in pancam spectra of tyrone yellowish soils was observed after being exposed to current martian surface conditions for 175 sols this change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface si rich nodules and soils were observed near the major exposures of s rich soils they possess a characteristic feature in pancam visible near infrared vis nir spectra that may be diagnostic of hydrated species and this spectral feature can be used to search for additional si rich species the exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the neutron spectrometer on mars odyssey

tectonic erosion of the peruvian forearc lima basin by subduction and nazca ridge collision 1 subsidence of lima basin part of the peruvian forearc is controlled by tectonic erosion by the subducting nazca plate multichannel seismic reflection data coupled with age and paleowater depth constraints derived from ocean drilling program odp coring now allow the rates of erosion to be reconstructed through time in trenchward locations the forearc has experienced limited recent relative uplift 700 850 m likely due to preferential basal erosion under the center of lima basin long term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench since 47 ma eocene up to 148 km of the plate margin have been lost at an average rate of up to 3 1 km myr 1 appoximately 110 km of that total appears to be lost since 11 ma implying much faster average rates of trench retreat 10 km myr 1 since collision of the nazca ridge with the lima basin at 11 ma although there is no clear subsidence event at odp site 679 during the time at which nazca ridge was subducting beneath this part of the forearc 4 11 ma the more trenchward odp sites 682 and 688 show significant deepening after 11 ma indicating that subduction of the ridge accelerates tectonic erosion long term rates of crustal erosion in the region of lima basin are greater than estimates of regional arc magmatic productivity implying that such margins are net sinks of continental crust

runaway slip to the trench due to rupture of highly pressurized megathrust beneath the middle trench slope the tsunamigenesis of the 2011 tohoku earthquake off the east coast of northern japan abstract the gigantic 2011 march 11 mw 9 tohoku earthquake is examined from the viewpoint of the pre seismic forearc structure the seismic reflection properties of a megathrust around the usual up dip limit of the seismogenic zone the thermal state of a shallow subduction zone and the dehydration of underthrust sediments at the japan trench the pacific plate is subducting westward beneath northeast japan at a dip angle of 4 6 the middle and lower slopes of the landward side dip eastward at angles of 2 5 and 8 0 respectively the forearc prism beneath the middle and lower slopes is inferred to be in extensionally and compressively critical states respectively based on the presence of clear internal deformation features and on the occurrence of aftershock earthquakes the rapid uplift of the forearc that caused the 2011 tohoku tsunami may have been associated with this internal deformation of the prism the critical state of the prism indicates that the effective basal friction b of the plate boundary megathrust is 0 08 for the lower prism the megathrust especially under the middle slope is characterized by a prominent reflector with negative polarity one of multiple possible explanations is that the megathrust hosts highly pressurized fluids underthrust sediments in this part of the japan trench are dominated by pelagic and siliceous vitric diatomaceous silt with clay the dehydration kinetics of opal a to quartz the clay transformation of smectite illite and the thermal structure of the japan trench suggest that maximum dehydration of the sediments would take place at 50 60 km horizontally from the deformation front where the temperature along the megathrust is 100 120 c the zone of maximum dehydration coincides with the prominent seismic reflector that has negative polarity we hypothesize a possible free slip along this portion of the megathrust during the 2011 tohoku earthquake caused by anomalously high fluid pressure resulting from fluid accumulation over centuries

global statistical space time scales of oceanic variability estimated from the topex poseidon altimeter data four years of the topex poseidon altimeter data are used to produce estimates of statistical space time scales of ocean variabilities for the sea surface height a three dimensional space time correlation function with an anisotropic directional dependence is assumed the function has gaussian distributions in radial directions in the space time coordinates and ellipsoidal contour surfaces the function can reveal the space time scales and propagations of the variabilities and statistical errors in the altimeter data we evaluated the space time scales using the best fit correlation function to the altimeter data the scales show geographical differences this means that dominant variabilities depend on regions we show an optimum interpolation oi method as an example of the application of the fitted correlation function the oi is applied to the altimeter data in the space time domain to make grid point data with higher accuracy than those obtained from a usual spatial two dimensional oi 2 d oi the values of the correlation function are used for the correlation coefficients of the first guess error in the oi a propagation diagram obtained from the space time oi 3 d oi shows clear propagations of planetary disturbances with larger amplitude the grid point values from the 3 d oi show better correspondences with sea levels from tide gauges than those from the 2 d oi the advantage is due to the data of the different cycles being additionally adopted and the correlation function reflecting propagation of the ocean variabilities

the signature of mesoscale eddies on the air sea turbulent heat fluxes in the south atlantic ocean abstract by collocating 10 years 1999 2009 of remotely sensed surface turbulent heat uxes withsatellite altimetry data we investigate the impact of oceanic mesoscale eddies on the latent and sensibleheat uxesinthesouthatlanticocean instronglyenergeticregions suchasthebrazil malvinascon uenceand the agulhas current retro ection eddies explain up to 20 of the total variance in the surfaceturbulent heat uxes with averaged anomalies of 10 20 w m 2 cyclonic anticyclonic respectively eddies are associated with negative positive heat ux anomalies that tend to cool warm the marineatmospheric boundary layer a composite analysis of the turbulent heat ux anomalies inside the eddiesrevealsadirectrelationshipbetweeneddyamplitudeandtheintensityofsuchanomalies inaddition theseanomaliesarestrongerneartheeddycenter decayingradiallytoreachminimumvaluesoutsidetheeddies 1 introduction the ocean atmosphere system is primarily turbulent in the mesoscale band oceanic eddies play a crucialrole in transporting heat salt momentum and biogeochemical tr acersalongtheirtrajectories signi cantlyimpactingtheoceandynamicsand uxes olson 1991 wunsch 1999 morrowetal 2003 mesoscaleeddiesare coherent rotating features with typical horizontal scales of 50 300 km and time scales ranging fromweeks to months cheltonetal 2011a theyalsoexhibitparticularthermohalineverticalstructuresassoci ated with strong dynamical perturbations of the density and pressure elds olson 1991 chaigneau et al 2011 kurian et al 2011 zhang et al 2013 roullet et al 2014 these perturbations extend up to the seasurface leadingtoanomaliesonseasurfaceheight seasurfacetemperature sst andwindstress amongothers frengeretal 2013 souzaetal 2014 asaresult itisexpectedthateddiesimpacttheair sea uxesandtheoverlayingatmosphericcirculation frengeretal 2013 the turbulent latent lhf and sensible shf heat uxes are the primary processes by which the oceanreleases heat to the atmosphere cayan 1992 both the lhf and shf can be derived from bulk formulaelinking oceanic and atmospheric parameters such as air speci c humidity sst and wind speed to theheat exchanged at the air sea interface liu et al 1979 fairall et al 2003 large and yeager 2009 theanomalies caused by mesoscale eddies in some of these parameters have been recently investigated e g white and annis 2003 hausmann and czaja 2012 frenger et al 2013 souza et al 2014 chelton and xie 2010 although there is ample evidence that oceanic mesoscale features have a signi cant impact onair seaproperties thereisstillalackofknowledgeabouttheirsignatureonthesurfaceturbulentheat uxesandtheirpotentialcontributionstothenetsurfaceheatbudget the recent release of daily satellite based data from the french research institute for exploitation of thesea ifremer bentamy et al 2013 has su cient resolution to estimate the lhf and shf associatedwith mesoscale processes the present work merges satellite altimetry sea level anomaly sla data withremotely sensed surface heat uxes to investigate the impact of mesoscale ocean eddies on the lhf andshfinthesouthatlanticocean sa the sa encompasses both quiescent areas and two regions of intense energetic variability associated withthe presence of large mesoscale eddies figure 1a namely the agulhas current retro ection agr olsonand evans 1986 goni et al 1997 andthebrazil malvinascon uence bmc garzoli and garra o 1989 olson et al 1988 more speci cally we aim i to assess the mean lhf and shf anomalies induced bycyclonicandanticycloniceddiesinthesa ii todescribethespatialvariationsoftheheat uxanomaliesinvillasboasetal

do eddies ride on rossby waves both vortices and baroclinic rossby waves show up as westward propagating features in the sea surface height anomaly ssha records when displayed in the form of zonal temporal or hovmoller diagrams a chain of filters was used to separate the ssha into orthogonal components each of the filtered components was then reassembled as a set of maps in the maps of individual components we clearly see westward propagating rossby waves our most striking findings are i limited within their critical latitudes the wave extrema coincide with a significant number of vortices ii eddy wave coincidence occurs at a preferred latitude that depends on the wave period iii among the vortices that at some point of their existence coincide with a wave a relatively large percentage of them remained their whole lifetime with the wave and iv a mechanism is proposed to explain why eddies tend to remain over the wave extrema crests and troughs our answer to the title question is yes they often do

pathways of eddies in the south atlantic ocean revealed from satellite altimeter observations 1 the majority of the kinetic energy of ocean currents is contained in the mesoscale eddies the pathways of ocean eddies which are the weather of ocean circulation are mapped from space using a decade long record of sea surface height measured by two simultaneously flying satellite radar altimeters the speed and direction of the propagation of eddies in the south atlantic ocean are presented in the paper the patterns of the eddy propagation velocity reveal the effects of the interaction between mean flow and eddies with strong influence of bottom topography the information describes a unique property of the ocean general circulation and serves as a basis for testing ocean models

structure and tectonics of the erosional convergent margin off antofagasta north chile 23 30 s subduction erosion has dominated the evolution of the north chile convergent continental margin since at least the mesozoic we investigate the structure of the antofagasta 23 s sector of this margin along a transect using coincident wide angle and near vertical seismic profiling and gravity data a 2 d velocity field of the overriding and subducting plates was obtained using joint refraction and reflection travel time tomography a velocity derived density distribution was used to model marine gravity data and substantiate the velocity model the gravity and velocity models imply that the overriding plate is mainly made of arc type igneous basement the upper plate is constructed of two main rock bodies separated by a subhorizontal layer defined by a velocity inversion the top coincident with a reflection in near vertical seismic images the seismic boundary is interpreted as a detachment separating an upper extended domain with large scale normal faulting from a lower domain apparently undergoing a different type of deformation velocity derived porosity indicates that the front of the margin is probably fluid saturated and disaggregated by fracturation as a consequence of frontal subduction erosion fluids carried into the subduction channel within slope debris filling underthrusting grabens reduce basal friction and probably induce hydrofracturing and basal erosion along the underside of the overriding plate at depths greater than 20 km porosity and density values imply that most fluids have been exhausted and the lower part of the upper plate is structurally coherent and little fractured the change in physical properties leads to increased mechanical coupling along the plate boundary and occurs at the updip limit of the distribution of aftershocks of the 1995 antofagasta earthquake m w 8 0 defining the seismogenic zone

characterization of westward propagating signals in the south atlantic from altimeter and radiometer records abstract radar altimeter data from topex poseidon and jason 1 and microwave radiometer data from trmm tmi are used to investigate the large scale variability between 10 5 s and 35 5 s in the south atlantic ocean the proposed method for the analysis of the longitude time diagrams of the cross correlation between ssh and sst anomalies shows that the variability in mid latitudes is a blend of first mode baroclinic rossby waves and propagating mesoscale eddy like structures the estimated phase speed of the wave cp and propagation speed of the eddies cv are similar in 70 of the cases the absolute difference between cp and cv is less than 11 in 40 of the cases this difference is less than 5 statistical results indicate that in the case of eddies as the thermocline deepens the sea surface temperature rises and vice versa however planetary waves show more complex yet self consistent results in lower latitudes 10 5 s 15 5 s the shallower thermocline and the weak thermal gradients impose a zero phase lag between temperature and height similar to eddies poleward of those latitudes sea surface temperature and height are in quadrature of phase this indicates that geostrophic advection of the relatively stronger thermal gradient is performed by rossby waves

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

evidence for episodic aseismic slip across the subduction seismogenic zone off costa rica cork borehole pressure observations at the subduction prism toe abstract slow slip events or silent earthquakes may relieve a significant amount of stress at many subduction plate boundaries both downdip of the limit of seismogenesis and within the seismogenic zone itself in cases where seismic energy release accounts for only a fraction of the plate tectonic displacement rate schwartz and rokosky 2007 slow slip has been identified in several instances downdip of the landward limit of the seismogenic zone and is often accompanied by seismic tremor or low frequency earthquake activity along and above the plate interface referred to as episodic tremor and slip or ets little is known however about the spatial distribution and history of slip between great earthquakes along the seismogenic thrust interface itself which lies mostly offshore in this article we present formation pressure transients observed in two deep sea boreholes near the toe of the subduction prism off nicoya peninsula costa rica which followed ets events observed on shore by 1 2 weeks the signatures of the transients are consistent with local slip on the shallow part of the thrust interface with the underthrusting plate experiencing relaxation and the outer prism experiencing contraction the delay between the tremor activity and the pressure transients observed c 100 km seaward at the prism toe suggests either slow propagation across the seismogenic zone or delayed deformation at the outer part of the prism triggered by the slip beneath nicoya such slip may serve generally to relieve stress at subduction zones but also to increase stress in parts of the plate boundary where interseismic slip does not occur

ocean color observations of eddies during the summer in the gulf of california 1 using seawifs ocean color satellite images collected during 1997 2001 a series of eddies have been observed in the gulf of california these eddies are not clearly seen in the summertime sea surface temperature images the surface circulation between the midriff islands and the mouth of the gulf appears to be dominated by this series of eddies that have an alternating sense of rotation an eddy pair is observed to extend from cabo lobos in each of the three years suggesting that the eddies are topographically locked the formation mechanism of the eddies remains unknown however we suspect the most likely mechanism includes baroclinic instabilities along the coast produced by interactions between coastally trapped waves and local wind driven currents

material transfer and subduction channel segmentation at erosive continental margins insights from scaled analogue experiments abstract whereas tectonically erosive convergent margins make up nearly 60 of all present day convergent margins processes and amounts of material transfer and recycling remain enigmatic removal of material from the frontal forearc leaves no features which could be imaged seismically or probed through drilling only a few scaled laboratory analogue experiments have analyzed material transfer at convergent margins characterized by long term subduction erosion and none has focused on processes and amounts of material transfer and recycling therefore in this study we attempt to identify potentially relevant parameters controlling material transfer in brittle tectonically erosive forearcs this is addressed by a series of sandbox experiments performed with granular materials we here mainly focus on the amount of sediment that can be transported downdip through the subduction channel sc we analyzed our experiments with regard to the evolution of internal and basal material transfer material transfer mode patterns wedge geometry and sc evolution to achieve a truly erosive scenario we built a large initial wedge representing the brittle forearc featuring a moderately high friction basal detachment and composed of strong granular material there was no incoming material the slope of the wedge initially had a critical taper through opening a subduction gap sg the wedge was subject to rear material loss our observations point to a close interaction between sc segmentation and wedge deformation basal erosion mainly took place beneath the middle upper slope our experiments confirmed the strong influence of the sc on the wedge evolution a larger amount of material loss led to the development of a sc with an inhomogeneous distribution of velocities along the base of the wedge segmenting the sc and slope geometry the latter was comparable to observations in natural forearcs which are segmented into lower middle and upper slopes

aftershocks near the updip end of the 2011 tohoku oki earthquake abstract the march 2011 m w 9 0 tohoku oki earthquake activated shallow aftershocks with normal faulting focal mechanisms near the trench axis to investigate stress state in the shallow subduction zone near the trench axis we used ocean bottom seismographs obss to record earthquakes from august to october 2011 we estimated hypocenter locations and focal mechanisms of the recorded earthquakes by using a grid search method in a 2 d velocity model based on an active seismic survey the results show that most of the earthquakes occurred within both the overriding and subducting plates with very few on the plate interface and none in the most seaward 45 km of the overriding plate aseismic wedge the low seismicity along the plate interface is consistent with the nearly complete stress drop on the megathrust fault in the m w 9 0 earthquake focal mechanisms indicate that trench normal tension is pre dominant in both plates and extends to a depth of about 30 km at least on the other hand several trench normal compressional earthquakes were located at the landward end of the aseismic wedge these earthquakes suggest horizontal compression of the overriding prism that may be caused by a strengthening of the shallowest part of the megathrust

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

the 2007 m7 7 tocopilla northern chile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behavior 1 in 2007 a m7 7 earthquake occurred near the town of tocopilla within the northern chile seismic gap main shock slip derived from coseismic surface deformation was confined to the depth range between 30 and 55 km we relocated 1100 events during six months before and one week after the main shock aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of mejillones peninsula mp waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock however a few events appear to occur in the upper plate some with extensional mechanisms juxtaposing the tocopilla aftershocks with those following the neighboring 1995 antofagasta earthquake produces a striking symmetry across an ew axis in the center of mp events seem to skirt around mp probably due to a shallower moho there we suggest that the seismogenic coupling zone in northern chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable for both earthquake sequences aftershocks agglomerate in the conditionally stable region whereas maximum inter seismic slip deficit and co seismic slip occurs in the unstable region the boundary between the unstable and conditionally stable zones parallels the coastline we identify a similar segmentation for other earthquakes in chile and peru where the offshore segments break in great m 8 earthquakes and the onshore segments in smaller m 8 earthquakes using critical taper analysis we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate dependency of friction

crustal dynamics and active fault mechanics during subduction erosion application of frictional wedge analysis on to the north chilean forearc abstract the forearc region of the non accreting south american plate margin in northern chile is characterised by subduction erosion and regional uplift neotectonic deformation structures reflect simultaneous extensional and contractional fault kinematics in the outer forearc where the brittle crust directly overlies the subducting nazca plate the stress regime changes from extension in the upper part to compression at the base of the forearc wedge as seen in neotectonic surface structures and seismic data in the inner forearc surface structures indicate a compressional stress regime also affecting the western rim of the magmatic arc this stress regime is limited to a brittle crustal wedge segment which overlies the ductile part of the inner forearc lithosphere the shape of the two brittle forearc wedges at the leading edge of the south american plate is controlled by exogenetic surface processes internal deformation processes contemporaneous basal tectonic erosion and underplating mechanical parameter sets controlling and reflecting the recent tectonic processes and geometrical wedge segmentation within the forearc system are evaluated and applied to general frictional wedge models the states of stress within the crustal wedges are controlled by spatial variations of the basal mechanical parameters in the down dip direction of the forearc wedge base the new models illustrate the fundamental kinematics and dynamic processes of coulomb type basal tectonic erosion and mass transfer modes along active non accretive convergent margins the frictional wedge models explain the dynamics of the simultaneous and contrary deformation processes affecting the forearc crust at the north chilean convergent margin shaped by active basal tectonic erosion

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

mesoscale eddy detection in satellite imagery of the oceans using the radon transform abstract the present study proposes a new methodology to identify mesoscale eddies that are ubiquitous in the ocean and can be observed in a variety of satellite images our focus is on eddies with mean diameter of 100 500 km the proposed methodology uses an algorithm based on the radon transform the basic premise is that the inverse radon transform of a circularly symmetric feature is angle independent therefore the more constant the radon transform of an image is with respect to the rotation angle the more circularly symmetric the image is although our method is based on circular symmetry it is able to detect non symmetric eddies using a sensitivity parameter that quantifies the deformation our method is effective to determine how circular a feature observed in a satellite image is and suggest whether it is an eddy or not based on geometric criteria a series of tests with synthetic data were performed to assess the sensitivity to spectral content and aspect ratio detectable by the method another sequence of tests was carried out with images of chlorophyll a concentration sea surface temperature and sea surface height in the three cases five areas of 100 50 pixels were selected and filtered with exactly the same algorithm and parameters the two sets of tests indicate that the proposed method was able to identify eddies in a single time series of satellite images and in multiple series of different variables the main advantage of this method in comparison with either automatic ones based on dynamics and geometry or manual methods is its ability to observe eddies in multiple data sets of different variables

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

geological record of fluid flow and seismogenesis along an erosive subducting plate boundary a fossil erosive subduction channel the shear zone marking the plate boundary preserved in the northern apennines of italy is identified the fossil zone records the presence of two decollements which seem to have been simultaneously active at the top and base of the subduction channel in modern subduction zones the onset of seismic activity is believed to occur at 150 c however in the fossil channel the onset seems to have occurred at colder temperatures tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the earth s subduction zones1 2 in situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone until now a fossil erosive subduction channel the shear zone marking the plate boundary3 has not been recognized in the field so that seismic observations have provided the only information on plate boundary processes at erosive margins here we show that a fossil erosive margin is preserved in the northern apennines of italy it formed during the tertiary transition from oceanic subduction to continental collision and was preserved by the late deactivation and fossilization of the plate boundary the outcropping erosive subduction channel is 500 m thick it is representative of the first 5 km of depth with its deeper portions reaching 150 c the fossil zone records several surprises two decollements were simultaneously active at the top and base of the subduction channel both deeper basal erosion and near surface frontal erosion occurred at shallow depths extension was a key deformation component within this erosive convergent plate boundary and slip occurred without an observable fluid pressure cycle at depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast co seismic and slow inter seismic slip in the deepest portions of the outcropping subduction channel extension is finally overprinted by compressional structures in modern subduction zones the onset of seismic activity is believed to occur at 150 c but in the fossil channel the onset occurred at cooler palaeo temperatures

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

structure of the kuril trench from seismic reflection records three multichannel seismic reflection records across the kuril convergent margin provide the first deep data in this area the records are located across the southern tip of kamchatka the central kuril arc and the northern extension of hokkaido island platform which show three distinct tectonic regimes the lower slope contains a wedge shaped buttress surrounded by low velocity sediments underplating sediment uplifts the buttress as indicated by faults that displace its upper surface the middle slope is a block of acoustic basement which has a rough surface with significant arcward dipping faults the middle slope is separated from the upper slope along a steep arcward dipping reflection the middle slope boundary the upper slope structure off kamchatka is different from that off hokkaido off kamchatka a regular stratified sediment section has been uplifted tilted and dips seaward off hokkaido stronger uplift has tilted regional blocks seaward and arcward along the southern line north of hokkaido well studied nonthrust earthquakes with lateral motions occur beneath the middle slope boundary and on the boundary of the subducting plate thrust earthquakes occur under the middle and upper slope whereas tsunami earthquakes occur under the lower slope high amplitude reflections along the lower boundary of the wedge shaped buttress and along the active decollement indicate high fluid concentrations which reduce the friction along the tectonic units so that through the weak coupling slow rupture may extend up to the seafloor from a tsunami earthquake

effects of frictional behavior and geometry of subduction fault on coseismic seafloor deformation abstract the seismogenic zone of subduction faults appears to have an updip limit seaward of which the fault exhibits velocity strengthening behavior we use a two dimensional finite element model including a frictional subduction fault to explore how coseismic strengthening of the updip segment affects seafloor deformation for a stress drop of a few mpa along the seismogenic zone strengthening of the updip segment by a comparable amount can prevent the rupture from breaking the trench the resultant seafloor uplift is much larger than that predicted by a model of equal seismic moment or maximum fault slip in which the seismogenic zone extends to the trench with a curved fault geometry although a lower degree of coseismic strengthening of the updip segment leads to greater slip in the shallowest part of the fault it produces smaller seafloor uplift contrary to a popular belief given the paucity of direct observations of the coseismic behavior of the updip segment the models yield important information for understanding rupture mechanics of subduction faults and tsunami generation we also illustrate how the results may be used to guide fault slip parameterization in analytical dislocation models

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north ecuador south colombia oceanic margin 1 splay faults within accretionary complexes are commonly associated with the updip limit of the seismogenic zone prestack depth migration of a multichannel seismic line across the north ecuador south colombia oceanic margin images a crustal splay fault that correlates with the seaward limit of the rupture zone of the 1958 mw 7 7 tsunamogenic subduction earthquake the splay fault separates 5 6 6 km s velocity inner wedge basement rocks which belong to the accreted gorgona oceanic terrane from 4 to 5 km s velocity outer wedge rocks the outer wedge is dominated by basal tectonic erosion despite a 3 km thick trench fill subduction of 2 km high seamount prevented tectonic accretion and promotes basal tectonic erosion the low velocity and poorly reflective subduction channel that underlies the outer wedge is associated with the aseismic decollement thrust subduction channel fluids are expected to migrate upward along splay faults and alter outer wedge rocks conversely duplexes are interpreted to form from and above subducting sediment at 14 to 15 km depths between the overlapping seismogenic part of the splay fault and the underlying aseismic decollement coeval basal erosion of the outer wedge and underplating beneath the apex of inner wedge control the margin mass budget which comes out negative intraoceanic basement fossil listric normal faults and a rift zone inverted in a flower structure reflect the evolution of the gorgona terrane from cretaceous extension to likely eocene oblique compression the splay faults could have resulted from tectonic inversion of listric normal faults thus showing how inherited structures may promote fluid flow across margin basement and control seismogenesis

the seismogenic zone in the central costa rican pacific margin high quality hypocentres from an amphibious network transition from subduction of normal to thickened oceanic crust occurs in the central portion of the costa rican margin where large interplate earthquakes m 7 and abundant interseismic seismicity have been associated with subduction of bathymetric highs we relocated 1 300 earthquakes recorded for 6 months by a combined on and offshore seismological network using probabilistic earthquake relocation in a 3d p wave velocity model most of the seismicity originated at the seismogenic zone of the plate boundary appearing as an 18 dipping planar cluster from 15 to 25 30 km depth beneath the continental shelf several reverse focal mechanisms were resolved within the cluster the upper limit of this interseismic interplate seismicity seems to be controlled primarily by the overlying plate thickness and coherency which in turn is governed by the erosional processes and fluid release and escape at temperatures lower than 100 to 120 c along the plate boundary the downdip limit of the stick slip behaviour collocates with relative low temperatures of 150 to 200 c suggesting that it is controlled by serpentinization of the mantle wedge the distribution of the interseismic interplate seismicity is locally modified by the presence of subducted seamounts at different depths unlike in northern costa rica rupture of large earthquakes in the last two decades seems to coincide with the area defined by the interseismic interplate seismicity

does permanent extensional deformation in lower forearc slopes indicate shallow plate boundary rupture abstract seismic rupture of the shallow plate boundary can result in large tsunamis with tragic socio economic consequences as exemplified by the 2011 tohoku oki earthquake to better understand the processes involved in shallow earthquake rupture in seismic gaps where megathrust earthquakes are expected and investigate the tsunami hazard it is important to assess whether the region experienced shallow earthquake rupture in the past however there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture with the exception of mechanical studies on subducted fault rocks here we combine new swath bathymetric data unpublished seismic reflection images and inter seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the northern chile seismic gap allows inferences on past earthquake behavior while the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the north chilean margin we document permanent extensional deformation of the lower slope localized to the region 20 8 s 22 s critical taper analyses the comparison of permanent deformation to inter seismic seismicity and plate coupling models as well as recent observations from other subduction zones including the area that ruptured during the 2011 tohoku oki earthquake suggest that the normal faults at the lower slope may have resulted from shallow possibly near trench breaking earthquake ruptures in the past in the adjacent margin segments the 1995 antofagasta 2007 tocopilla and 2014 iquique earthquakes were limited to the middle and upper slope and the terrestrial forearc and so are upper plate normal faults our findings suggest a seismo tectonic segmentation of the north chilean margin that seems to be stable over multiple earthquake cycles if our interpretations are correct they indicate a high tsunami hazard posed by the yet un ruptured southern segment of the seismic gap

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

horizontal principal stress orientation in the costa rica seismogenesis project crisp transect from borehole breakouts the costa rica seismogenesis project crisp drilled the pacific margin of the middle america trench just north of where the cocos ridge enters the subduction zone resulting in basal erosion of the upper plate here we report the orientations of the maximum horizontal principal stress shmax from borehole breakouts detected by logging while drilling and wireline downhole measurements all shmax directions were estimated in the sediment cover of the margin above the deeper rocks of the deformed margin wedge we observe three overall shmax orientations nne ssw 25 azimuth in the deepest interval drilled at the upper slope site u1379 ene wsw 82 in the rest of site u1379 and in site u1413 also drilled in the upper slope and nnw sse 157 in the mid slope site u1378 our preferred interpretation is that the deepest interval of site u1379 records the stress conditions in the underlying margin wedge as shmax is parallel to the direction of the cocos caribbean plate convergence and of the compressional axes of plate boundary fault earthquakes the variable shmax directions observed elsewhere are likely due to the effect of a network of normal faults that subdivide the sediment cover into a number of independently deforming blocks in addition the observed shmax directions may be influenced by the subducting cocos ridge which acts as an indenter causing oblique deformation and by the transition to seismogenic subduction along the plate boundary fault

tsunamigenic earthquake simulations using experimentally derived friction laws abstract seismological tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre stress and frictional conditions a wealth of earthquakes of different sizes and different source features e g rupture duration can be generated in subduction zones including tsunami earthquakes some of which can produce extreme tsunamigenic events here we offer a geological perspective principally accounting for depth dependent frictional conditions while adopting a simplified distribution of on fault tectonic pre stress we combine a lithology controlled depth dependent experimental friction law with 2d elastodynamic rupture simulations for a tohoku like subduction zone cross section subduction zone fault rocks are dominantly incohesive and clay rich near the surface transitioning to cohesive and more crystalline at depth by randomly shifting along fault dip the location of the high shear stress regions asperities moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological geodetic and tsunami observations as an effect of depth dependent friction in our model slip is confined to the high stress asperity at depth near the surface rupture is impeded by the rock clay transition constraining slip to the clay rich layer however when the high stress asperity is located in the clay to crystalline rock transition great thrust earthquakes can be generated similar to the mw 9 tohoku 2011 earthquake

subduction erosion crustal structure and an evolutionary model of the northern yap subduction zone new observations from the latest geophysical survey the yap subduction zone is a distinctive erosive margin with an extremely slow convergence rate the high relief of the subducting plate generated by horst and graben structures and seamounts leads to attenuation of the crust in this study we present the latest geophysical data collected by the chinese research vessel kexue to investigate subduction erosion at the yap subduction zone and develop subduction models for yap subduction zone structures we show an anomalous distance between the yap trench and the adjacent volcanic arc the steep slope of the trench arcward a frontal prism and rare sediment in the trench all typical features of erosive margins we propose that the high relief subducting plate has led to erosion of the overlying plate and that different subduction processes controlled locally by the topography of the subducting plate have modified the yap subduction zone numerous normal faults increase the relief of the seafloor entering the trench and an anomalously large slope angle along the trench reflects uplift of the fore arc high via seamount subduction in addition the thin crust of the subducted horst and graben structures along with the normal faults might have eroded the fore arc crust and subsequently eroded the yap arc crust during subduction these subduction erosional processes at the yap trench provide one of the best cases of an erosive margin in the world particularly for a subduction zone with an extremely slow convergence rate

the thermal stability of near surface ground ice on mars the existence of subsurface water ice on mars has been predicted in several theoretical studies1 5 but there are no definitive observations of its present distribution geomorphic features on the surface of mars have been widely interpreted as evidence for the presence of ground ice6 12 but many of these features are found at near equatorial latitudes where thermal models have predicted that near surface water ice should not be stable under present climate conditions3 13 14 here i present the results of thermal calculations which show that observed geographic variations in the thermal and reflectance properties of martian soils significantly affect subsurface temperatures my results indicate that in certain regions ground ice deposits could exist much closer to the surface and much closer to the equator than previously thought in the future these deposits could be a valuable resource for human exploration15

quantifying arc migration and the role of forearc subduction erosion in the central aleutians abstract the active aleutian arc is currently classified as an accreting margin as most of the arc has a well developed frontal accretionary prism that formed in the plio pleistocene we focus on the central aleutian island arc where the arc massif was built to near its current size by the late eocene and has since seen limited growth and endured episodic erosion prior to the development of the accretionary prism as a result the volcanic front has migrated northwards tens of kilometers since inception along with previous mapping dating and geochemical data sixteen new 40ar 39ar dates and new geochemical data for volcanic rocks on several central aleutian islands supplement recent geochronologic data from six other islands in this region and facilitate an attempt to understand how and where aleutian arc volcanism has migrated with time long term average arc migration rates range from 0 6 to 5 km ma in three distinct locations the arc migration rate increases to the west and is greatest over the last five million years as the arc migrated from a 7 5 ma volcanic front to its current location arc migration and erosion during this most recent period may have been expedited by either the subduction of the kula ridge which ceased spreading in the early eocene or clockwise rotation of the pacific plate in the late miocene some central aleutian lavas and plutonic rocks have elevated la yb sm yb and sr yb most of which were emplaced during times of arc migration or in the waning stages of a peak in magmatic activity the strongly fractionated trace element patterns are similar to the basaltic andesites to dacites from the western aleutian seafloor which are interpreted to be the result of residual garnet during partial melting of eclogite in the subducting oceanic crust however the existing subduction parameters coupled with the timing of the central aleutian adakite like lavas favors a model in which significant subduction erosion of the mafic forearc including erosion and subsequent melting of the trapped kula plate i e morb like oceanic crust as well as early aleutian arc basalts in the mid crust may be partly responsible for the eclogitic component observed in central aleutian magmas

a recent phase of accretion along the southern costa rican subduction zone abstract in 2011 we acquired a 3d seismic reflection volume across the costa rica margin nw of the osa peninsula to investigate the complex structure and the development of the seismogenic zone within the costa rican subduction zone in the vicinity of recent international ocean drilling program iodp drilling in contrast to previous interpretations these newly acquired seismic images show that the margin wedge is composed of a layered fabric that is consistent with clastic sediments similar to materials recovered from iodp drilling that have been thrust and thickened into thrust bounded folded sequences these structures are consistent with a balanced sequence that has been frontally accreted in the context of an accretionary model we interpret these sequences as sediment originally deposited on the subducting crust in a trench basin created by the southward migration of the cocos nazca caribbean triple junction and accreted during recent margin subduction that also accelerated with passage of the triple junction the margin is composed of relatively rapidly accreted sediment that was added to the margin during a phase of accretion within the last 5 ma that was probably preceded throughout the neogene by periods of non accretion or erosion

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

nonlinear variations of the physical properties along the southern ecuador subduction channel results from depth migrated seismic data abstract we use two high quality pre stack depth migrated multichannel seismic profiles acquired to quantify physical properties variations of underthrust sediments along the first 30 km of subduction off the erosional southern ecuadorian margin seismic data show three zones along the subduction channel referred to as zones i ii and iii characterized by distinct velocity and velocity derived physical properties which are in agreement with values estimated from experimental results of deformation in granular media these three zones result from transformational changes of underthrust sediments governed by fundamentally different physical processes that control their mechanical behavior at increasing confining pressures based on our observations and its comparison with experimental results we argue that the transformations undergone by underthrust sediments as they dip into the subduction zone are the following within zone i progressively increasing velocity and decreasing velocity derived porosity indicates continuous sediment compaction which must be accompanied by effective fluid drainage along the decollement and or across the accretionary wedge the underthrust material is here unconsolidated from a mechanical point of view laboratory experiments indicate that the dominant processes at this range of pressures are grain rolling particle rotation and frictional slip at grain contacts within zone ii velocity and porosity remains constant for 16 km sis 72 and 12 km sis 18 this suggests undrained conditions resulting in growing fluid overpressure at the subduction channel grain deformation is similar to zone i within zone iii velocity increases and porosity falls rapidly indicating sediment compaction and subsequent release of over pressured fluids where grain deformation is likely to be elastic this might be the dominant process until the grains attain their crushing strength resulting in granular cataclasis and eventually in the collapse of the system we suggest that over pressured fluid release may induce hydrofracturation and it is likely to increase inter plate coupling down from zone iii

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

long baroclinic rossby waves detected by topex poseidon residual sea surface height anomaly fields are obtained over the north atlantic basin from topex poseidon altimeter data evidence of westward propagating anomalies characterized as first mode baroclinic rossby waves is presented the phase speeds are obtained from the analysis of the autocorrelation matrices of the residual surface height anomaly in three dimensions on a 5 5 grid periods are calculated by least squares fitting a sinusoidal function to the time series at each grid point zonal and meridional wavelengths are obtained from the phase speed and period and are least squares fit to the data as a consistency check zonally averaged westward phase speeds vary between 1 and 27 km d between 50 and 5 n increasing southward phase speeds are directed to the southwest north of approximately 25 n and to the northwest south of this latitude the sea surface height signal is divided into two spectral bands the first with periods between 280 and 450 days and the second with periods between 120 and 280 days for the first band the average of the periods taken over the whole basin is 370 days in the second band a signal of period between 6 and 7 months is evident also throughout the basin the zonally averaged zonal wavelengths associated with the first band are in the range of 400 4600 km between 50 and 5 n and for the second band are in the range 270 2500 km between 45 and 5 n longer wavelengths are found close to the southern boundaries shorter wavelengths are found in the northern portion of the basin comparison with results from numerical models suggests that the baroclinic waves observed at midlatitudes are generated at the eastern boundary by fluctuations of the wind stress curl waves observed south of 20 n support the hypothesis of direct wind forcing

mineralogic constraints on sulfur rich soils from pancam spectra at gusev crater mars 1 the mars exploration rover mer spirit excavated sulfur rich soils exhibiting high albedo and relatively white to yellow colors at three main locations on and south of husband hill in gusev crater mars the multispectral visible near infrared properties of these disturbed soils revealed by the pancam stereo color camera vary appreciably over small spatial scales but exhibit spectral features suggestive of ferric sulfates spectral mixture models constrain the mineralogy of these soils to include ferric sulfates in various states of hydration such as ferricopiapite fe2 32 fe43 so4 6 oh 2 20 h2o hydronium jarosite h3o fe3 3 so4 2 oh 6 fibroferrite fe3 so4 oh 5 h2o rhomboclase hfe3 so4 2 4 h2o and paracoquimbite fe3 2 so4 3 9 h2o

characterization of traverse slippage experienced by spirit rover on husband hill at gusev crater spirit rover experienced significant slips traversing husband hill this paper analyzes the slippage spirit experienced from sol 154 to sol 737 slippage with respect to terrain type and slope is computed using data downlinked from the rover rover position and orientation estimations from visual odometry vo and photogrammetry based bundle adjustment ba method accumulated slippage reached a maximum of 83 86 m on sol 648 however as spirit descended into the inner basin the direction of slippage reversed and accumulated slippage approached zero by the end of the entire traverse eight local regions with significant slips and nineteen traverse segments have been analyzed slippage was found to be highly correlated to slope direction and magnitude the reverse of slope directions in the ascending and descending portions of the traverse proves to be the main contributor to the observed cancellation of slippage while the horizontal component of the slippage almost canceled out the difference in elevation continually accumulated mainly during the ascent in general long traverse segments created more slips than short ones this is reflected in both the accumulated and individual slippages in considering the four major mars terrain types spirit performed best on bedrock managing to drive on slopes close to 30 fine grain surfaces were the most challenging though progress was made on slopes up to 15 slippages of over 100 more slippage than distance traveled occurred for short segments the results of this work can be incorporate into a traverse planning framework in which rover slippage is minimized results can be employed in landed planetary missions for precision navigation to avoid potentially dangerous regions by considering expected slippage

hanging wall deformation of a seismogenic megasplay fault in an accretionary prism the nobeoka thrust in southwestern japan the structure and occurrence of deformation within the hanging wall of the nobeoka thrust in kyushu japan was investigated to understand the dynamic aspects of splay faulting in relation to seismic events from field observations hanging wall is suggested to have undergone four phases of deformation the first phase involved horizontal shortening as documented by folding and thrusting followed by a phase of vertical loading shown by the development of horizontal slaty cleavages pressure solution and cleavage parallel mineral vein precipitation a third phase involved shearing and deformation along cleavage restricted to near the nobeoka thrust while the fourth phase produced widespread brittle fracturing associated with the development of pseudotachylyte bearing faults and tension crack filling veins high angle to cleavage these four phases can be explained as follows during the inter seismic period an extensionally stable taper was maintained in the inner wedge of the accretionary prism by dominant vertical loading 1 in combination with a lesser amount of horizontal compression 2 related to the locking of the mega thrust elastic strain energy in the hanging wall of the inner wedge was co seismically released by slip on the mega thrust and horizontal shortening in the outer wedge associated with dynamic ductile weakening of the fault plane this sudden release of elastic strain caused brittle fracturing with 1 at a high angle to the shear surface of the nobeoka thrust most of the displacement resulting from deformation of the footwall

the java convergent margin structure seismogenesis and subduction processes the java margin is characterized by a distinct variation in lower to upper plate material transfer and recurring catastrophic tsunamogenic earthquakes both processes are closely linked to the subduction of oceanic basement relief resulting in varying degrees of fore arc deformation tomographic models of refraction seismic profiles and reflection seismic lines in combination with high resolution multibeam bathymetric data reveal the variability in the deep structure and deformation of the java fore arc shallow subduction processes are governed by the sediment supply in the trench as well as by the nature and fabric of the oceanic lithosphere the deep structure of the fore arc reveals a shallow upper plate crust mantle transition present along the entire java margin section the serpentinized fore arc mantle wedge governs the depth extent of the seismogenic zone here which is narrower compared to its sumatran analogue in addition offshore central java high relief oceanic basement features potentially act as asperities as well as barriers to seismic rupture limiting the possible magnitude of subduction thrust earthquakes however the potential for geohazards in particular tsunamis is high along the entire margin this results from tsunamogenic earthquakes ubiquitous splay faults and potentially tsunamogenic landslides which further increase the risk of future tsunamis

in situ and experimental evidence for acidic weathering of rocks and soils on mars experimental data for alteration of synthetic martian basalts at ph 0 1 indicate that chemical fractionations at low ph are vastly different from those observed during terrestrial weathering rock surface analyses from gusev crater are well described by the relationships apparent from low ph experimental alteration data a model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at gusev this zone is not chemically fractionated to a large degree from the underlying rock interior indicating that the rock surface alteration process has occurred at low water to rock ratio the geochemistry of natural rock surfaces analyzed by apxs is consistent with a mixture between adhering soil dust and the leached alteration zone the chemistry of rock surfaces analyzed after brushing with the rat is largely representative of the leached alteration zone the chemistry of rock surfaces analyzed after grinding with the rat is largely representative of the interior of the rock relatively unaffected by the alteration process occurring at the rock surface elemental measurements from the spirit opportunity pathfinder and viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low ph low water to rock ratio alteration relationships developed for gusev rocks soils are affected principally by mobility of fe and mg consistent with alteration of olivine bearing basalt and subsequent precipitation of fe and mg bearing secondary minerals as the primary control on soil geochemistry copyright 2006 by the american geophysical union

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

sea surface structure of north brazil current rings derived from shipboard and moored acoustic doppler current profiler observations 1 in the western tropical atlantic the north brazil current retroflection periodically sheds large anticyclonic rings which then propagate northwestward between 1998 and 2000 the north brazil current rings experiment sampled a large number of these rings by shipboard and moored acoustic doppler current profiler ten of the sampled rings are analyzed in this study focusing on their sea surface dynamic properties the rings exhibit a radial structure consisting of two regimes an inner core region in near solid body rotation and an outer ring regime with an approximately exponentially decaying structure the observations show a sharp change in vorticity at the regime transition and the presence of a strong opposite vorticity shield bounding the inner solid body core we show that gaussian models commonly used to represent the surface expression of these and other rings are adequate for determining the sea surface height anomaly but tend to poorly estimate other properties such as the maximum swirl velocity therefore we propose a new two part model as a better approximation of the rings radial structure according to the cyclogeostrophic balance approximation the sea surface height distribution across the inner ring has a parabolic shape while the outer ring has an exponential structure similar to the velocity field interestingly many of the observed rings have an intensity very close to the theoretical limit for anticyclones at these latitudes which is believed to be due to inertial instability

stress and displacement fields in the outer wedge induced by megathrust earthquakes we model plate boundary slip at the outer oceanward segment of the megathrust wedge as slip at the base of a two dimensional elastic wedge subject to gravity force with a sloping seafloor at the top and drag at the bottom from a rigid plate in frictional contact the stress and displacement fields in the wedge are given analytically as functions of basal frictional coefficient e unlike either conventional dislocation models constant slip or crack models constant stress drop our wedge model constant e drop does not show a stress singularity at the updip toe of the plate boundary the slip increases but the stress drop decreases updip along the fault toward the trench axis there is a minimum stress difference state in the wedge when e is varied by referring to this state e ec the stress state is separated into a horizontally tensile regime e ec slip associated with a e drop in the range e ec occurs toward increasing horizontal tension and shear energy such earthquakes include tsunami earthquakes occurring in the outer segment and the 2011 great tohoku oki earthquake which involved both the outer and inner segments with much larger slip in the outer segment these earthquakes are characterized by an almost complete drop of basal stress which brings the wedge into the maximum tensile state leading to the rare occurrence of thrust aftershocks at the base of the wedge and frequent occurrence of normal fault aftershocks within the wedge

episodic subsidence and active deformation of the forearc slope along the japan trench near the epicenter of the 2011 tohoku earthquake abstract to investigate the present day geological deformation occurring off the pacific coast of tohoku japan we obtained high resolution multichannel seismic reflection and bathymetric data in 2007 the study area is located along the japan trench near the epicenter of the 2011 off the pacific coast of tohoku earthquake the seismic profiles do not show active structures indicative of compressional stress on the forearc slope instead recent tectonic deformation is characterized by extensional subsidence and the occurrence of normal faults within a series of small basins on the slope to a water depth of 3000 m these isolated basins are thickest 525 m 0 7 s two way travel time in regions underlying areas of flat bathymetry the isolated basins range in width from several to 40 km and are covered by stratified sediments onlapping at the termination of concave down reflectors the seismic units below the basins show continuous subparallel internal reflectors suggesting that the subsidence related deformation started abruptly and recently the thickness of sediments overlying the unconformity at the top of the cretaceous is roughly constant in the upper slope area however lenticular internal reflection patterns occur locally the lenticular sedimentary units are similar to the isolated basins in terms of their widths and internal reflection patterns we infer that episodes of extensional deformation of the overriding plate in the form of isolated basins have occurred over geological time we suggest that the geological structures of the forearc slope along the japan trench are typical of those resulting from subduction erosion and propose that the episodic subsidence accompanied by normal faulting is the most recent deformation

a possible transoceanic tsunami directed toward the u s west coast from the semidi segment alaska convergent margin the semidi segment of the alaska convergent margin appears capable of generating a giant tsunami like the one produced along the nearby unimak segment in 1946 reprocessed legacy seismic reflection data and a compilation of multibeam bathymetric surveys reveal structures that could generate such a tsunami a 200 km long ridge or escarpment with crests 1 km high is the surface expression of an active out of sequence fault zone recently referred to as a splay fault such faults are potentially tsunamigenic this type of fault zone separates the relatively rigid rock of the margin framework from the anelastic accreted sediment prism seafloor relief of the ridge exceeds that of similar age accretionary prism ridges indicating preferential slip along the splay fault zone the greater slip may derive from quaternary subduction of the patton murray hot spot ridge that extends 200 km toward the east across the north pacific estimates of tsunami repeat times from paleotsunami studies indicate that the semidi segment could be near the end of its current inter seismic cycle gps records from chirikof island at the shelf edge indicate 90 locking of plate interface faults an earthquake in the shallow semidi subduction zone could generate a tsunami that will inundate the us west coast more than the 1946 and 1964 earthquakes because the semidi continental slope azimuth directs a tsunami southeastward this article is protected by copyright all rights reserved

interplate earthquakes as a driver of shallow subduction erosion basal erosion is a prevalent process at subduction zones and plays an important role in the mass balance of global plate tectonics in contradiction with the theoretical expectation that basal erosion requires high basal friction and hence compression in the upper plate extensional faulting is commonly observed in submarine wedges that undergo such erosion here we propose a model to explain this apparent paradox in terms of stress fl uctuations during earthquake cycles in this model basal erosion occurs during large earthquakes when the shallow rate strengthening part of the plate interface strengthens and its overlying wedge weakens but extension occurs during interseismic relaxation of wedge stress the mechanics of basal erosion provide important information on the nature of the updip limit of the megathrust seismogenic zone in margins dominated by basal erosion

hot spring and geyser sinters the integrated product of precipitation replacement and deposition complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world including those located in the taupo volcanic zone on the north island of new zealand those sinters are formed of opal a that replaced microbes opal a precipitated as cement accessory minerals e g kaolinite jarosite calcite biological detritus e g leaves wood pollen grains and lithic detritus the opal a is compositionally variable because of the amount of water oh and h2o and in some cases accessory elements e g au ag bound into its structure the composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement precipitation and deposition the microbes that inhabit these systems are of critical importance because they are commonly replaced by and or encrusted with opal a in many settings copious amounts of opal a are precipitated as cement around the frameworks of silicified filaments the cementation pro

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

spectral variability among rocks in visible and near infrared multispectral pancam data collected at gusev crater examinations using spectral mixture analysis and related techniques 1 visible and near infrared vnir multispectral observations of rocks made by the mars exploration rover spirit s panoramic camera pancam have been analyzed using a spectral mixture analysis sma methodology scenes have been examined from the gusev crater plains into the columbia hills most scenes on the plains and in the columbia hills could be modeled as three end member mixtures of a bright material rock and shade scenes of rocks disturbed by the rover s rock abrasion tool rat required additional end members in the columbia hills there were a number of scenes in which additional rock end members were required the sma methodology identified relatively dust free areas on undisturbed rock surfaces as well as spectrally unique areas on rat abraded rocks spectral parameters from these areas were examined and six spectral classes were identified these classes are named after a type rock or area and are adirondack lower west spur clovis wishstone peace and watchtower these classes are discriminable based primarily on near infrared nir spectral parameters clovis and watchtower class rocks appear more oxidized than wishstone class rocks and adirondack basalts based on their having higher 535 nm band depths comparison of the spectral parameters of these gusev crater rocks to parameters of glass dominated basaltic tuffs indicates correspondence between measurements of clovis and watchtower classes but divergence for the wishstone class rocks which appear to have a higher fraction of crystalline ferrous iron bearing phases despite a high sulfur content the rock peace has nir properties resembling plains basalts

tectonic structure across the accretionary and erosional parts of the japan trench margin structure sections across the japan trench from prestack depth migrated seismic data define the accretionary prism a wedge shaped seaward end of the continental framework and a tectonized middle slope between them the 10 km wide accretionary prism is underthrust by sediment remaining with the subducted oceanic crust structure beneath the steep middle slope more nearly resembles the adjacent continental margin than the accreted mass this deformed middle slope domain forms a buffer between the compliant accretionary wedge and a more rigid older continental framework along the plate boundary subducted strata thicken beneath the middle and upper slopes and where last imaged are four times the input thickness beneath the accretionary prism this interplate stratified layer appears to control interplate friction because the layer is imaged 45 km landward from the trench axis to 12 km depth and in that expanse few upper plate earthquakes are recorded erosion of the base of the upper plate beneath the middle continental slope is indicated by margin subsidence and material flux this erosion is concurrent with accretion at the front of the margin

eddy transport of heat and thermocline waters in the north pacific a key to interannual decadal climate variability abstract high resolution xbt transects in the north pacific ocean at an average latitude of 22 n are analyzed together with topex poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field based on anomalies in dynamic height 410 eddies are identified in 30 transects from 1991 to 1999 including eddies seen in multiple transects over a year or longer their wavelength is typically 500 km with peak to trough temperature difference of 2 2 c in the center of the thermocline the features slant westward with decreasing depth by 0 8 of longitude on average from 400 m up to the sea surface this tilt produces a depth varying velocity temperature correlation and hence a vertical meridional overturning circulation in the mean 3 9 sv sv 106 m3 s 1 of thermocline waters are carried southward by the eddy field over the width of the basin balanced mainly by northward flow in the surface layer corresponding northward heat transport is 0 086 0 012 pw

spirit rover localization and topographic mapping at the landing site of gusev crater mars 1 by sol 440 the spirit rover has traversed a distance of 3 76 km actual distance traveled instead of odometry localization of the lander and the rover along the traverse has been successfully performed at the gusev crater landing site we localized the lander in the gusev crater using two way doppler radio positioning and cartographic triangulations through landmarks visible in both orbital and ground images additional high resolution orbital images were used to verify the determined lander position visual odometry and bundle adjustment technologies were applied to compensate for wheel slippage azimuthal angle drift and other navigation errors which were as large as 10 5 in the husband hill area we generated topographic products including 72 ortho maps and three dimensional 3 d digital terrain models 11 horizontal and vertical traverse profiles and one 3 d crater model up to sol 440 also discussed in this paper are uses of the data for science operations planning geological traverse surveys surveys of wind related features and other science applications

coseismic strengthening of the shallow portion of the subduction fault and its effects on wedge taper 1 according to the dynamic coulomb wedge model coseismic strengthening of the shallowest part of the subduction interface can cause permanent deformation of the overlying outer wedge so that the cumulative effects of great interplate earthquakes control the geometry of the wedge in this work we use a numerical model which is a hybrid of the frictional contact model and the classical crack model to study how stress is coseismically transferred from the seismogenic zone to the strengthening updip zone to cause wedge deformation in this static model the critical strengthening required to prevent the rupture from breaking the trench depends on the force drop of the seismogenic zone defined as the product of the average shear stress drop and the area of the seismogenic zone in a simple model of uniform material properties with a few megapascals average stress drop over a seismogenic zone of 120 km downdip width the critical strengthening for a 30 km wide updip zone is an increase in the effective friction coefficient by about 0 05 using the coulomb wedge theory we demonstrate that this level of strengthening can readily push the overlying wedge into a critical state of failure with much greater strengthening the rupture is able to extend into the updip zone only slightly causing localized wedge compression in the area of slip termination we examined wedge geometry of 22 subduction zones in the light of the model results we found that the surface slope of these wedges is generally too high to be explained using the classical wedge theory but can be explained using the dynamic coulomb wedge model including coseismic strengthening of the shallow portion of the megathrust

mesoscale eddies in the south china sea observed with altimeter data 1 a composite time series 1993 2000 of sea surface height anomaly from several satellites is used to identify eddies in the south china sea scs the eddy lifetime radius strength and straight line travel distance are estimated altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period they are grouped into four geographical zones according to known eddy generation mechanisms and their statistics are discussed accordingly our geographical classification is a useful first step in gaining an overview of their generation

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

megathrust shear force controls mountain height at convergent plate margins the shear force along convergent plate boundary faults megathrusts determines the height of mountain ranges that can be mechanically sustained1 4 however whether the true height of mountain ranges corresponds to this tectonically supported elevation is debated4 7 in particular climate dependent erosional processes are often assumed to exert a first order control on mountain height5 12 although this assumption has remained difficult to validate12 here we constrain the shear force along active megathrusts using their rheological properties and then determine the tectonically supported elevation using a force balance model we show that the height of mountain ranges around the globe matches this elevation irrespective of climatic conditions and the rate of erosion this finding indicates that mountain ranges are close to force equilibrium and that their height is primarily controlled by the megathrust shear force we conclude that temporal variations in mountain height reflect long term changes in the force balance but are not indicative of a direct climate control on mountain elevation

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

sediment flow routing during formation of forearc basins constraints from integrated analysis of detrital pyroxenes and stratigraphy in the kumano basin japan the evolution of sediment flow routing during complete evolution of the kumano forearc basin is determined through integration of stratigraphic and sediment provenance analyses in the upper nankai forearc a new approach uses the compositional variability of detrital clinopyroxenes and orthopyroxenes collected at eight major rivers in japan and three drill sites in the basin and nearby slope environment including the first drill cuttings retrieved by the integrated ocean drilling program iodp joint interpretation of these datasets reveals that the sedimentation history of the basin is characterised by three main phases separated by newly recognised time transgressive boundaries we show that the kumano basin initiated as a trench slope basin in the early quaternary 1 93 ma and that it progressively evolved towards an upper slope environment with increased turbidite confinement and influence from climatic forcing basin initiation was broadly synchronous with development of the nankai megasplay fault suggesting a causal relationship with construction of the nankai accretionary prism unlike preceding studies documenting long distance longitudinal transport of clastic material along the lower nankai forearc only limited longitudinal transport is documented by detrital pyroxenes in the upper forearc these results suggest that transverse canyons are a major control on the sediment flow routing during maturation of forearc basins and that long distance longitudinal flows along convergent margins are principally restricted to near trench environments even in the presence of large forearc basins

mechanics of non critical fold thrust belts based on finite element models abstract the mechanics of fold thrust belts and accretionary wedges is investigated using a two dimensional plane strain elastic plastic cohesive mohr coulomb mechanical model solved with the finite element method results show that when a layer with an initially non critical geometry is compressed from the rear it does not form a wedge that is at failure throughout as assumed in critical wedge theory rather the wedge consists of narrow plastic shear zones that propagate sequentially outward with time loading rocks ahead while unloading rocks behind not only are stress states within the wedge not everywhere at failure but principal stress orientations vary strongly in time and space particularly across shear zones near the basal detachment and in the hanging wall of active structures where local surface extension may be observed the reason the investigated wedges are not stressed to compressive failure throughout is related to strength reduction associated with strain localisation that enables material outside shear zones to unload and return to an elastic stress state this mechanism is intrinsic to elastic plastic materials and occurs regardless of any material degradation such as loss of cohesion even though the stress state of the investigated wedges is generally non critical the overall geometry may still be consistent with cohesionless critical wedge theory since the local surface slope is created when a particular part of the wedge is at a limit state prowedge tapers display non self similar growth through time but eventually evolve to the minimum critical taper retrowedges on the other hand may get caught within this initial transient state and thus may have tapers anywhere between the minimum and maximum critical taper however if the basal detachment is such that lateral propagation is not kinematically inhibited retrowedges are shown to also eventually evolve towards minimum critical tapers resulting in a symmetrical doubly vergent orogen because all of these wedges have non critical stress states both pro and retrowedges are predicted to display stable non equilibrium taper angles in the presence of external perturbations for example related to erosion or sediment deposition

crustal structure of the peruvian continental margin from wide angle seismic studies keine zusammenfassung in englischer sprache vorhanden no summary in english language