crustal subsidence observed by grace after the 2013 okhotsk deep focus earthquake coseismic gravity changes stem from 1 vertical deformation of layer boundaries with density contrast i e surface and moho and 2 density changes of rocks at depth they have been observed in earthquakes with mw exceeding 8 5 by gravity recovery and climate experiment grace satellites but those of m8 class earthquakes have never been detected clearly here we report coseismic gravity change of the 24 may 2013 okhotsk deep earthquake mw8 3 smaller than the detection threshold in shallow thrust faulting factor 2 is dominant while factor 1 remains secondary due to poor spatial resolution of grace in the 2013 okhotsk earthquake however factor 2 is insignificant because they occur at depth exceeding 600 km on the other hand factor 1 becomes dominant because the centers of uplift and subsidence are well separated and grace can resolve them this enables grace to map vertical ground movements of deep earthquakes over both land and ocean

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

morphology of transverse aeolian ridges tars on mars from a large sample further evidence of a megaripple origin abstract using hirise digital terrain models dtms we developed a large morphological dataset to examine the three dimensional shape size and scaling of martian transverse aeolian ridges tars considerable debate exists on the characteristic morphology of tars and the origins of these enigmatic bedforms some researchers suggest polygenesis or multiple classes of similar bedforms reliably characterizing the morphology of tars is an essential prerequisite to developing and evaluating process based models of tar genesis and unraveling aeolian processes on the surface of mars we present measurements of tar morphology from a large dtm derived dataset n 2295 we focused on tars with simple morphologies in order enable more defensible discretization histograms and cumulative log frequency plots of morphometric parameters length width height elongation ratio and wavelength indicate the sample represents a continuum of bedforms from a single population a typical tar from our dataset is 88 5 m long longest planview axis 17 3 m wide shortest planview axis 1 3 m tall and has a wavelength of 25 8 m combined with these data the bulk of evidence presented to date suggests that interpreting tars as megaripples is the most viable working hypothesis

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 moore g f taira a klaus a becker l boeckel b cragg b a dean a fergusson c l henry p hirano s hisamitsu t et al 2001 new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 geochemistry geophysics geosystems 2 article no 2001gc000166

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

longevity of aeolian megaripples abstract megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain size distributions the interplay between wind grain size and ripple morphology height and wavelength controls their development two main mechanisms limit megaripple height the first megaripple flattening due to winds that are above the fluid threshold of the coarse grains destroys the armoring layer of the megaripple the second is megaripple erosion by the impacts of fast moving fine saltating grains that propel the coarse grains constituting the armoring layer for any given wind regime and grain size distribution the potential megaripple dimensions are limited by these two mechanisms here we study the first mechanism and estimate the duration of strong winds sustained above the fluid threshold needed to flatten megaripples strong gusts of wind in contrast cannot destroy the megaripples but can cause ripple migration based on data from previous works on megaripples we find a scaling law between the ripple morphology and the coarse mode of grains at the crest using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening in general the coarser the particles at the megaripple crest the stronger the wind needed to flatten the megaripples moreover the greater the strength of the wind required to flatten the megaripples the lower the recurrence probability taken together these findings increase the longevity of megaripples we apply the results for a megaripple field in the southern arava valley israel

latitude dependent nature and physical characteristics of transverse aeolian ridges on mars 1 narrow angle images from the mars orbiter camera moc have revealed the common occurrence of small scale 100 m wavelength bright transverse aeolian ridges tars on the surface of mars moc images were used to assess the broad distribution of tars from 90 n to 90 s between 180 e and 240 e to investigate their relationship to latitude elevation thermal inertia geologic units local slopes and surface roughness out of 5112 examined images from the primary mission 520 10 contain evidence of tars 92 of the images with tars are located between 50 latitude and very few occur in the middle to upper latitudes or polar regions of either hemisphere tars are observed at elevations from 5 km to 3 km with the highest frequency 26 between 1 and 0 km there is no systematic relationship between the distribution of tars and global thermal inertia measurements most tars occur in geologic units associated with the channel system materials 39 and the olympus mons aureole 33 at a length scale of 1 85 km pixel the average local slopes for images with and without tars are 1 92 and 1 36 respectively of the parameters investigated the latitudinal trend of tars in both hemispheres appears to be predominantly related to surface roughness with a positive linear correlation between the surface roughness of geologic units and frequency of tars r2 0 87 factors affecting the semiglobal distribution of tars are likely related to the climate and wind regimes in which they formed but do not provide definitive evidence for either saltation or reptation formation mechanisms

gypsum gravel devils in chile movement of largest natural grains by wind whirlwinds dry convective helical vortices move large gypsum crystals in the andes mountains of northern chile the crystals are entrained from a saline pan surface where they grew in shallow surface brines they are transported as much as 5 km and deposited in large dune like mounds the dune gravel is cemented relatively quickly by gypsum cement precipitating from near surface saline groundwater resulting in gypsum breccia this marks the first occurrence of gravel sized grains moved efficiently in air by suspension provides a new possible interpretation for some ancient breccias and conglomerates and improves understanding of limits of extremity of earth surface environments

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

coseismic gravity changes of the 2010 earthquake in central chile from satellite gravimetry 1 the first map of coseismic changes in gravity and geoid height has been drawn using the data from the gravity recovery and climate experiment grace satellites for the 2004 sumatra andaman earthquake here we present the second case of coseismic gravity change observation by satellite gravimetry i e the change caused by an interplate thrust earthquake that occurred on 27 february 2010 in central chile mw 8 8 gravity showed a negative jump with the largest drop of 5 gal on the back arc side the observed changes agree with those calculated assuming the realistic earth and fault parameters inferred from coseismic displacements of global positioning system gps stations gravity in this area shows large seasonal and inter annual variability and postseismic gravity changes could be isolated only by carefully removing hydrological signals

seismic velocities from the barbados ridge complex indicators of high pore fluid pressures in an accretionary complex three wide aperture 0 5 km offset seismic profiles were shot perpendicular to the strike of the barbados ridge accretionary complex at 16 12 n line 465 14 23 n line 480 and 13 20 n line 484 to image the deep structure of the accretionary complex and obtain seismic velocity data velocity analyses on full fold common depth point cdp gathers were used to provide velocity depth functions at 1 km separation along each line to map the variation in velocity with depth and distance across the accretionary complex the sediments within the complex show consolidation increasing laterally with greater age of the complex as indicated by the increase in seismic velocity and the inferred decrease in porosity the velocity at the base of the wedge along line 480 is 2 4 km s at the toe the velocity at the wedge base at 60 km from the toe where the wedge thickness has increased from 1 8 km to 5 0 km has increased to greater than 3 0 km s however the velocities within the leading margins and within undeithrust sequences in each of the three sections are low as much as 1 0 km s less than velocities found in undeformed sedimentary sequences of equivalent thickness the low velocity regions are interpreted as sediments with high porosity where porosity is inferred to be high pore fluid pressures are also inferred to exceed hydrostatic and pore fluids actually support the increased lithostatic load produced by recent thrusting and thickening of the complex the correlation between the most rapidly thickened regions and the velocity anomalies suggests that a rapid rate of loading relative to the rate of pore fluid expulsion produced these overpressured sediments velocities in the underthrust sequences where the differences between loading histories of wedge sediments and the underthrust sequences are largest are sufficiently low to produce velocity inversions low velocities also occur in regions adjacent to the complex where the pore fluid pressures may be elevated by the pressure produced in the adjacent wedge west of the wedge in the forearc basin along line 480 and near a seismically imaged mud diapir velocities at a depth of 3 5 km below the seafloor are 0 5 km s less than what is expected in a more normal sedimentary section immediately seaward of the complex the deepest undeformed sequences have a velocity anomaly of 0 5 km s velocities remain low for at least 12 km seaward of the complex but they become closer to a more normal sediment section farther from the wedge

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

megaripple flattening due to strong winds abstract megaripples in nahal kasuy in the southern negev desert of israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes the latter property being a pre requisite for their formation in our three year project megaripple development was monitored using a digital elevation model dem constructed from above ground stereo digital photographs temporal dynamics of wind power drift potential dp were measured and grain size analyses were performed on samples taken from different parts of the megaripple the coarse grains that protect the crest enable the ripple to grow but when ripple height becomes too high the bed shear stress increases thus allowing the wind to move the armoring layer when this happens during strong wind storms the megaripple will flatten and even disappear as was observed in our field study we present measurements that for the first time directly show the megaripple to normal ripple transition and we suggest two possible physical processes as potential causes of this phenomenon megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction

wind regime sediment transport and landscape dynamics at a mars analogue site in the andes mountains of northwestern argentina abstract the puna plateau of northwestern argentina is a promising region for analogue investigations of martian aeolian processes owing to its high altitude low atmospheric pressure aridity geology and widespread granular and bedrock aeolian landforms despite a growing body of research about the region s enigmatic aeolian landforms little is known about the contemporary aeolian environment processes and landscape dynamics to address this gap we used a combination of modelled weather data satellite imagery and field measurements to characterize the wind regime aeolian sediment transport and allied surface changes the study focused on the campo de piedra pomez cpp a volcanic landscape with a variety of mars analogue landforms gravel mantled megaripples yardangs ventifacts periodic bedrock ridges and aeolian rat tails modelled weather data from the european center for medium range forecasting s era interim reanalysis dataset confirm the contemporary dominance of northwesterly winds in this region consistent with the primary orientation of yardangs these data also indicate the presence of less frequent southeasterly winds which may explain why re entrant profiles are observed on the southeast flanks of a small portion of the yardang population and why some aeolian rat tails point to the northwest observations from multi temporal satellite imagery indicate that deposition and displacement of small sediment patches overlying ignimbrite bedrock is relatively common across the region samples retrieved from sediment traps deployed over one year in the region suggest a broad range of particle densities are mobilized by wind which implies a wide range of wind speed for fluid entrainment conventional aeolian transport models do not consider the effects of particle density variations on transport processes however in areas with multiple density sediment present our results point towards a need for aeolian models to consider density when quantifying and qualifying sediment transport

gravity and potential changes due to shear and tensile faults in a half space analytic expressions derived from a simplified model are invaluable because they often provide deep insight into geophysical phenomena such is the case with potential and gravity changes here we present expressions of potential and gravity changes caused by faulting on a finite rectangular plane buried in a homogeneous half space the expressions can be used to evaluate coseismic changes in surface gravity and geoid height observed gravimetric data combined with our formulae thus provide constraints on the fault geometry and magnitudes of dislocation

elasticity of marine sediments rock physics modeling we offer an effective medium model for the elastic moduli of high porosity ocean bottom sediments the elastic constants of the dry sediment frame depend on porosity elastic moduli of the solid phase and effective pressure the model connects two end points in the elastic modulus porosity plane the hertz mindlin modulus of a dense elastic sphere pack at critical porosity and zero at 100 porosity the elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation unlike the suspension model our model assigns non zero elastic constants to the dry sediment frame and can predict the shear wave velocity unlike various modifications of the travel time average equation it is first principle based and contains only physical parameters we justify this model by matching sonic data in shallow marine sediments and in an odp well

wind formed gravel bed forms wright valley antarctica 1 bed forms composed of gravel size particles 50 of particles 4 mm are observed in the wright valley of the mcmurdo dry valley system in antarctica these bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0 025 standard deviation 0 005 mean wavelength of 2 7 m 0 49 m and a mean height of 0 06 m 0 01 m particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0 5 mm and 0 25 mm time integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles 4 mm during the two year monitoring period was extremely low measurements of the horizontal displacement of tracer particles 14 mm 12 mm 10 mm 8 mm and 6 mm diameter placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles the bed forms share form and grain size characteristics with both ripples and mega ripples showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples but their sinuosity suggest that transverse instabilities affect their formation similar to mega ripples based on the data for the prevailing environmental conditions it can be argued that the wright valley form is an expression of gravel particles moved solely by highly intermittent creep processes this also argues for the need for a very long period of time for their evolution on the order of centuries

large scale cenozoic wind erosion in the puna plateau the salina del fraile depression wind erosion is integral to the evolution of arid landscapes on earth and mars but the nature of long term wind erosion of bedrock is poorly understood here we describe the salina del fraile sdf

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

aeolian granule ripple deposits namibia granule ripples are a common feature of most dunefields yet they have seldom been recognized in ancient deposits although granule ripples are common in erosional settings such as windward slopes of dunes or scour surfaces in interdunes they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks these deposits have characteristics of type b sand sheet deposits including poured in texture curving ripple trough tangential coarse grained foresets irregular silty layers well sorted coarse and fine layers either horizontal or within foresets and fine layers in ripple troughs wind tunnel experiments suggest that under low velocity wind conditions granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple although the depositional surface of granule ripples is commonly coated with a layer of coarse grains this is in most places only a few grains thick underlying deposits commonly have a poorly sorted or poured in texture this texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition

characterization of excess pore pressures at the toe of the nankai accretionary complex ocean drilling program sites 1173 1174 and 808 results of one dimensional modeling 1 elevated fluid pore pressures play a critical role in the development of accretionary complexes including the development of the decollement zone in this study we used measured permeabilities of core samples from ocean drilling program odp leg 190 to develop a permeability porosity relationship for hemipelagic sediments at the toe of the nankai accretionary complex this permeability porosity relationship was used in a one dimensional loading and fluid flow model to simulate excess pore pressures and porosities simulated excess pore pressure ratios as a fraction of lithostatic pressure hydrostatic pressure using the best fit permeability porosity relationship were lower than predicted from previous studies we then tested sensitivity of excess pore pressure ratios in the underthrust sediments to bulk permeability lateral stress in the prism and a hypothetical low permeability barrier at the decollement our results demonstrated significant increase in pore pressures below the decollement with lower bulk permeability such as obtained by using the lower boundary of permeability porosity data or when a low permeability barrier is added at the decollement in contrast pore pressures in the underthrust sediments demonstrated less sensitivity to added lateral stresses in the prism although the profile of the excess pore pressure ratio is affected both simulations with lateral stress and a low permeability barrier at the decollement resulted in sharp increases in porosity at the decollement similar to that observed in measured porosities furthermore in both scenarios maximum excess pore pressure ratios were found at the decollement suggesting that either of these factors would contribute to stable sliding along the decollement

coexisting active travertines and tufas in the southeastern border of the puna plateau abstract the terma los hornos is an active hydrothermal system located in the southeastern border of the andean puna plateau in catamarca province northwest argentina it exhibits a complete range from high to low temperature quaternary carbonate products still actively forming travertines and tufas can be considered lithological end members within the depositional system but the lack of clear boundaries has generated confusion when trying to distinguish them in the fossil record in the terma los hornos a continuum between both extremes is recorded through a transition of different morphologies and dominant but non diagnostic fabrics among which we recognize a variety of crystalline crusts shrubs spheroidal particles encrusted bubbles and reeds lithoclastic grumulous micritic and silty sandy carbonates these were grouped in the following depositional subsystems 1 vents and pinnacles 2 mound apron 3 terraced slope 4 steep slopes and 5 flooding areas and palustrine hydrochemistry results show substantial variabilities ranging from 65 c ph 6 41 1029 ppm alkalinity and 37 ppm calcium concentrations at the vents site to 21 c ph 8 13 and 800 ppm alkalinity and 14 ppm calcium concentrations at 1 km downstream were carbonate precipitation is no longer visible the set of linked subenvironments tend to merge into a larger scale geobody that defines the travertine system with a proximal area dominated by physicochemical processes and a distal extent with pervasive microbial and common macrophyte features the travertine system should not be understood as a fixed model and its limits as well as the existing subenvironments their extents and degree of overlapping will depend mainly on three factors 1 hydrothermal input 2 climate and 3 landscape perched past travertine deposits together with internal architectures and extent of the presently active travertine system allows thinking about constructive and destructive stages respectively thought as dominantly expanding and erosional periods alternation of these two evolutionary stages and their balance will dictate the volume of primary facies and potential reworking products a better understanding of these stages and their litho stratigraphic products will allow developing predictive stratigraphic and correlation models based on a sequence stratigraphic approach

aeolian processes and features in cool climates this review concentrates on the characteristics of wind processes and products in cold lowland deserts its main aims are to show how difficult it can be to separate wind generated from water generated processes and features without detailed study of lamination types to suggest cold aeolian interpretations for some ancient pre quaternary rocks and to encourage students to revisit many ancient deposits with such interpretations in mind although upper quaternary and recent cold climate aeolian deposits have been studied for many years there are very few older examples described martian features are included since mars is now one of the most exciting areas of study

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

glacial interglacial changes of southern hemisphere wind circulation from the geochemistry of south american dust abstract the latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of southern hemisphere atmospheric circulation during the late quaternary period to increase understanding of past atmospheric circulation and of the paleo environmental conditions associated with continental dust sources we dig deeper into dust provenance in paleo archives of the southern hemisphere we present here a sr nd isotopic and rare earth element study of surface sediments collected along a 4000 km latitudinal band from arid and semi arid terrains in southern south america findings from terrains that served as paleo dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band which affords a test on how actual present day aeolian compositions compare to those of the past potential source areas moreover the comparison between past and present day datasets is useful for understanding present day atmospheric circulation armed with a new comprehensive dataset we revise previous interpretations of the provenance of dust trapped in the antarctic ice and sediments deposited in the south atlantic sector of the southern ocean these comparisons support multiple source regions in southern south america that changed with climates the findings reveal that although patagonia plays an important role in contributing dust to the higher latitudes central western argentina and to a lesser extent the southern puna region also emerge as potentially important dust sources during glacial times the southern altiplano appears to be a major contributor during interglacial periods as well we rely in part on an understanding of modern wind dust activities to conclude that the possible presence of southern south america source regions other than patagonia in east antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid latitude westerlies and the subtropical jet stream

the largest wind ripples on earth reply we thank de silva 2010 1 for the opportunity to discuss the origin of the unique megaripples mr found on the puna plateau forman and krohling were invited as co authors of this reply because we produced new data supplied here de silva suggests that the genetic relationship inferred by

effective stress and pore pressure in the nankai accretionary prism off the muroto peninsula southwestern japan 1 we developed a theoretical method for predicting effective stress and pore pressure based on rock physics model we applied the method to reveal the pore pressure distribution within the nankai accretionary prism off southwestern japan and to investigate variations in pore pressure associated with evolution of the plate boundary decollement from the crack aspect ratio spectrum estimated from laboratory and well log data we calculated a theoretical relationship between acoustic velocity and mean effective stress by using differential effective medium theory by iteratively fitting the theoretically calculated velocity to the seismic velocities derived from 3d tomographic inversion we estimated in situ mean effective stress within the accretionary prism pore pressure is then the difference between the effective stress and the confining stress when we calculated pore pressure we considered compressive state of stress in the accretionary prism our results confirm that pore fluid pressure is high within the subducting sedimentary sequence below the decollement we determined a normalized pore pressure ratio of 0 4 0 7 abnormal pore pressures develop in the under thrust sequence as a result of the increase in overburden load because of the thickened overlying prism and a low permeability barrier across the decollement overpressuring within the accreted sequence is initiated at the deformation front and proceeds landward the increase in horizontal compaction within the accreted sequence may raise pore pressures within the accreted sequence and the pore pressure mean effective stress contrast at the decollement becomes smaller landward of the deformation front

porosity corrections for smectite rich sediments impact on studies of compaction fluid generation and tectonic history porosity is a fundamental parameter that must be correctly determined in order to relate physical property hydrologic and chemical flux studies to natural systems traditional porosity determinations generated from physical property or seismic data can greatly overestimate the true porosity of sediments in which hydrated minerals such as smectite are abundant to produce a true porosity distribution such data must be corrected to account for the h 2 o residing in smectite interlayers which can make up to 25 of the total hydrated mineral mass such h 2 o is easily removed from the mineral by oven drying and or exposure to low humidities standard physical property measurements can be corrected provided the weight percent smectite in the sediment is known and the interlayer h 2 o content of the mineral can be estimated we illustrate the significant consequences of this correction by comparing profiles of reported and corrected porosities for smectite rich barbados abyssal plain and accretionary wedge sediments from ocean drilling program leg 110 sites 671 and 672

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes

general formulations of global co seismic deformations caused by an arbitrary dislocation in a spherically symmetric earth model applicable to deformed earth surface and space fixed point summary based on the authors previous work co seismic deformations for a spherical symmetric earth model are summarized and reformulated unified expressions presented herein accommodate physical deformations displacement potential gravity geoid and strain changes the corresponding green s functions are derived by combining spheroidal and toroidal deformations sign errors in previous publications are corrected in these new formulas these expressions are developed basically for a deformed earth surface because most traditional geodetic measurements are performed on the terrain surface however through development of space geodetic techniques such as the satellite gravity missions co seismic gravity changes can be detected from space in this case the above dislocation theory e g the co seismic gravity change cannot be applied directly to the observed data because the data do not include surface crustal deformation the free air gravity change correspondingly the contribution by the vertical displacement part must be removed from the traditional expressions for this purpose we present the corresponding expressions applicable to space observations some numerical technical problems are discussed in addition a smoothing technique is necessary to damp the high frequency contribution so that the theory can be applied reasonably global co seismic deformations caused by the 2004 sumatra andaman earthquake m9 3 are studied as an application of the new green s function that earthquake caused a global deformation detected by gps strain metres and even a satellite gravity mission these global deformations are calculated based on the derived green s functions and the seismic wave derived earth model a segment summation scheme is used considering the slip distribution on a limited fault plane the results are useful for interpreting observed deformations especially those in the far field the earthquake reveals global co seismic deformations and effects of spherical curvature and the earth s layered structure comparisons between results for a spherical earth mode and a half space model show a large discrepancy at an epicentral distance of about 1000 km implying that effects of spherical curvature and layer structure are considerably large in addition the theoretical results are compared with the real observed strain steps horizontal displacements and gravity changes caused by that earthquake good agreement validates the results of the current theoretical work finally we discuss the application the above theory to the grace data through several case studies

pulsating flow dynamics of sustained forced pyroclastic density currents insights from a facies analysis of the campo de la piedra pomez ignimbrite southern puna argentina the quaternary campo de la piedra pomez ignimbrite cppi is a superbly exposed partially indurated rhyolitic ignimbrite emplaced on the southern puna of argentina it is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents pdcs detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that cppi was formed by sustained pdcs generated from a low fountain eruptive style boiling over the pdcs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles the mobility of the pdcs was largely controlled by high pore pressure and the continuous supply at the source sustained forced convection dominated pdcs the successive forestepping backstepping stacking patterns identified in the cppi reflect a marked unsteadiness of its parent pdcs due to a pulsating discharge rate at the source the lateral facies variations in the cppi record the non uniform character of its parent pdcs as they flowed outward from the base of the collapsing fountain proximal medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates to frontal edges characterized by the step aggradations of secondary decoupled pumice rich lobes collectively the facies variations in the cppi record the complex dynamics of sustained pdcs that include pulsating discharge rate at the source progressive modification of the original topography and lateral flow transformations

a discrete episode of seismic and aseismic deformation of the nankai trough subduction zone accretionary prism and incoming philippine sea plate new insights into episodic deformation at the nankai trough subduction zone are provided by data from two ocean drilling program borehole hydrologic observatories drilled into the philippine sea plate site 1173 and the seaward part of the nankai accretionary prism off southwestern japan site 808 and from an array of high sensitivity borehole accelerometer and velocity seismometers on shikoku island hi net fluid pressures monitored at multiple levels in each of the offshore boreholes document steady secular trends that indicate contraction of the crust and sedimentary section at the incoming plate site and relaxation of the accretionary prism toe the rate of strain ca 10 6 yr 1 inferred from the rates of pressure rise at site 1173 up to 5 kpa yr 1 is similar to that which would be produced by plate convergence if convergent elastic strain were distributed over a region a few tens of km wide opposing these trends are transient pressure anomalies observed in late june early july 2003 that indicate an episode of rapid relaxation of the incoming plate and contraction of the outer prism concurrent with these transients a swarm of very low frequency earthquakes occurred farther landward in the prism above the estimated seaward limit of the currently locked seismogenic portion of the subduction thrust reverse fault mechanisms determined for one event of this swarm and several of another also indicate transient contraction of the prism we suggest that both the earthquakes and the pressure transients are the consequences of an aseismic slip dislocation that initiated on about june 26 2003 at or near the up dip limit of the locked portion of the subduction thrust and propagated seaward over the course of about 10 days to the accretionary prism toe along the decollement separating the prism and underthrust section deformational events like this may serve incrementally to relieve stress locally along the subduction thrust and to load neighboring areas in addition to demonstrating that the prism is far from inactive during interseismic intervals the observations may also provide a small amplitude analog for strain and hydrologic response at the time of great subduction earthquakes

paleo eolian dynamics in the andean plateau inferences from sedimentology of fossil and modern dunes fil lopez steinmetz romina lucrecia universidad nacional de jujuy instituto de ecorregiones andinas consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de ecorregiones andinas argentina universidad nacional de jujuy argentina consejo nacional de investigaciones cientificas y tecnicas argentina

a wind tunnel investigation of particle segregation ripple formation and armouring within sand beds of systematically varied texture this paper reports on a wind tunnel investigation of particle segregation ripple formation and surface armoring within sand beds of systematically varied particle size distribution from coarsely skewed to bimodal by design the system was closed with no external inputs of mass from an external particle feed particles too coarse to travel in saltation for the given range in wind speed were dyed red in order to distinguish them in optical images from finer sand particles which could be entrained into the unidirectional airflow a 3d laser scanner measured the changing bed topography at regular time intervals during 18 experiments involving varied combinations of wind speed and bed texture image classification techniques were used to investigate the coincident self organization of the two populations of particles as distinguished by their colour as soon as saltation commenced some of the red particles segregated into thin discontinuous patches particle trapping and sheltering on these rough patches was strongly favoured causing them to grow preferentially during the earliest stages of formation bedform growth coincided with i rapid coarsening of the surface texture and ii the merging of proto ripple crests to generate larger rhythmic bedforms of lower frequency consistent with previous work ripple size was observed to increase under stronger winds when not exceeding the threshold for entrainment of the coarse mode or red particles from the crest with declining rates of mass transport and particle segregation as the bed surface armoured and the consequent deceleration of ripple propagation through to the end of each experiment all surfaces eventually attained a steady state morphometry at saturation the largest ripples developed upon beds having the lowest initial concentration of red particles this article is protected by copyright all rights reserved

aerodynamic roughness height for gravel mantled megaripples with implications for wind profiles near tars on mars abstract aerodynamic roughness heights of 1 3 cm were obtained from measured wind profiles collected among fields of gravel mantled megaripples in the high desert of the puna region of northwestern argentina roughness height appears to be relatively insensitive to the angle at which the wind was incident upon the bedforms throughout the study sites the results represent the first wind profiling measurements for large megaripples but they also demonstrate the importance of a careful evaluation of many potential effects that can influence the utility of wind profiling data the same effects that influence collection of fieldwork data must also be considered in any prediction of wind profiles anticipated to occur near transverse aeolian ridges and other aeolian features on mars that are intermediate in scale between wind ripples and small sand dunes

critical porosity a key to relating physical properties to porosity in rocks discovering accurate relations between porosity and seismic wave velocities in porous rocks has been an important topic of rock physics for decades such relations if they actually exist are critical when seismic and or sonic data are to be used to infer porosity and porosity related properties e g permeability strength saturation in situ these inferences became especially important in recent years with the rapid development of seismic and sonic methods which are applied to the characterization of heterogeneous reservoirs and recovery monitoring

dust provenance in antarctic ice during glacial periods from where in southern south america 1 the origin of dust deposited in east antarctica is not fully understood yet this study demonstrates that contrary to nd sr isotopes are strongly fractionated in the finest sized material representing potential dust sources in south america analysis of nd isotopes suggests that argentine loess southern ocean sediments and antarctic dust may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition this analysis also concludes that the patagonian signature can explain a high proportion of the isotopic composition of dust trapped in antarctic ice during glacial periods the puna altiplano plateau emerges as the second possible important sediment contributor explaining the crustal like signature found in east antarctic dust and should be considered as a potential source area when quaternary paleoclimate is reconstructed from argentine loess antarctic dust and south atlantic sediment records

mechanisms limiting the growth of aeolian megaripples megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution the interplay between wind grain size and morphology controls their development but the exact mechanisms that limit the size of megaripples have been unclear using wind tunnel experiments we found two main mechanisms that limit the height of megaripples the first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation the second mechanism is megaripple deflation by impacts of faster saltation grains in this latter mechanism the coarse grains are propelled by the impacts of fine saltating grains the occurrence of both these mechanisms depends on the grain size distribution and increases with both megaripple height and wind speed thus for a given wind environment and grain size distribution there exists a limit on the size of megaripples which is determined by these two mechanisms

pore pressure estimation from mudrock porosities in tertiary basins southeast asia porosity reduction during mechanical compaction of a sediment generally has been assumed to be controlled by the increase in vertical effective stress which is convenient because vertical stress profiles may be readily calculated from density logs poroelasticity theory shows however that mean effective stress controls porosity reduction according to published data horizontal stresses increase with overpressure as well as with depth so mean stress and vertical stress profiles are poorly correlated in overpressured sections we have used wireline logs to compare the pore pressures estimated in mudrocks by relating porosity to mean effective stress and to vertical effective stress for overpressured tertiary sections in southeast asia wells from three different basins were studied mudrock porosities were estimated from the sonic log response and sorted by lithology according to the natural gamma log response two sets of normal compaction curves relating porosity to mean effective stress and to vertical effective stress were determined empirically by fitting data points where the pore pressure was thought to be hydrostatic these curves were then used to estimate the minimum pore pressure corresponding to mudrock porosity values in the overpressured sections the pore pressures inferred using the mean effective stress are consistent with direct measurements of pore pressure in the adjacent sands in contrast pore pressures inferred in mudrocks using the vertical effective stress are significantly lower for the overpressured sections implying discontinuities in the pore pressure profiles at lithological boundaries which cannot readily be explained we conclude that the pore pressures estimated using the vertical effective stress are wrong and that empirical relationships between porosity and vertical effective stress should not be used for estimating pore pressures porosity should be empirically related to mean effective stress instead

frictional melting during the rupture of the 1994 bolivian earthquake the source parameters of the 1994 bolivian earthquake magnitude m w 8 3 suggest that the maximum seismic efficiency was 0 036 and the minimum frictional stress was 550 bars thus the source process was dissipative which is consistent with the observed slow rupture speed only 20 of the locals wave velocity the amount of nonradiated energy produced during the bolivian rupture was comparable to or larger than the thermal energy of the 1980 mount st helens eruption and was sufficient to have melted a layer as thick as 31 centimeters once rupture was initiated melting could occur which reduces friction and promotes fault slip

barbados ridge hydrogeologic tests implications for fluid migration along an active decollement hydrogeologic tests were conducted at a sealed borehole penetrating the decollement of the barbados ridge accretionary complex at low excess pore pressures p p p h p l p h 0 0 to 0 36 where p p pore pressure p h hydrostatic pressure and p l lithostatic pressure estimated permeabilities were comparable to those of similar unfractured sediment these tests complement shipboard packer tests completed at higher fluid pressures 0 5 to 1 0 during ocean drilling program odp leg 156 together the test results suggest a 4 to 5 order of magnitude permeability increase as fluid pressure varied from hydrostatic 0 to lithostatic 1 however unlike the results of the shipboard packer tests the test results presented here exhibit no evidence of a relationship between permeability and pore pressure the combined findings from the two sets of hydrogeologic tests indicate that significant permeability increases can occur within the decollement at pore pressures below lithostatic pressure

first geodetic observations of a deep earthquake the 2013 sea of okhotsk mw 8 3 611 km deep event we analyze the first ever gps observations of static surface deformation from a deep earthquake the 24 may 2013 mw 8 3 sea of okhotsk 611 km deep event previous studies of deep earthquake sources relied on seismology and might have missed evidence for slow slip in the rupture we observed coseismic static offsets on a gps network of 20 stations over the sea of okhotsk region the offsets were inverted for the best fitting double couple source model assuming a layered spherical earth the seismic moment calculated from static offsets is only 7 larger than the seismological estimate from global centroid moment tensor gcmt thus gps observations confirm shear faulting as the source model with no significant slow slip component the relative locations of the u s geological survey hypocenter gcmt centroid and the fault from gps indicate slip extending for tens of kilometers across most of the slab thickness

overpressure detection from compressional and shear wave data by analyzing experimental data we show that in many room dry rocks the poisson s ratio pr decreases with decreasing differential pressure confining minus pore pressure this means that in gas saturated rocks pr decreases with increasing pore pressure we confirm the generality of the observed effect by theoretically reproducing it via effective medium modeling this effect can be used as a new tool for overpressure detection from surface seismic cross well sonic logs and measurements ahead of the drill bit

megaripple migration on mars aeolian megaripples with 5 to 50 m spacing are abundant on the surface of mars these features were repeatedly targeted by high resolution orbital images but they have never been observed to move thus aeolian megaripples especially the bright toned ones often referred as transverse aeolian ridges tars have been interpreted as relict features of a past climate in this report we show evidence for the migration of bright toned megaripples spaced 1 to 35 m 5 m on average in two equatorial areas on mars indicating that megaripples and small tars can be active today the moving megaripples display sand fluxes that are 2 orders of magnitudes lower than the surrounding dunes on average and unlike similar bedforms on earth can migrate obliquely and longitudinally in addition the active megaripples in the two study areas of syrtis major and mawrth vallis show very similar flux distributions echoing the similarities between dune crest fluxes in the two study areas and suggesting the existence of a relationship between dune and megaripple fluxes that can be explored elsewhere active megaripples together with high sand flux dunes represent a key indicator of strong winds at the surface of mars a past climate with a denser atmosphere is not necessary to explain their accumulation and migration

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

a terrestrial analog for transverse aeolian ridges tars environment morphometry and recent dynamics abstract transverse aeolian ridges tars are a distinct aeolian bedform found on mars the formative processes evolution and geological significance of tars is poorly understood fundamentally it is unknown whether tars are dunes mega ripples or another bedform type we examined aeolian bedforms in the lut desert of iran as a terrestrial analog for martian tars from an objective sampling strategy with high resolution satellite imagery we developed a large morphometric dataset for comparison with existing martian tars we also examined the dynamics of the lut bedforms between 2004 and 2012 to determine if they were static or migrating results indicate that the range in the dimensions length width height and wavelength of the lut bedforms and martian tars overlap suggesting lut bedforms are a viable terrestrial tar analog our sample yielded median values of 55 18 m 9 80 1 02 m and 20 m for length longest planview axis width shortest planview axis height and wavelength respectively cumulative log frequency plots of morphometric parameters suggest the sample is from a single population and process mechanism although the vast majority of lut bedforms examined were static between 2004 and 2012 some migrated up to 0 09 myr 1 on average this is much slower than nearby dunes 4 12 myr 1 but is explained by the existence of a surface lag of coarse particles on the tar like bedforms the combination of morphometry surface sedimentology and slow migration rate indicate the lut bedforms are mega ripples which provides evidence supporting interpretation of martian tars as mega ripples testing the mega ripple hypothesis for martian tars requires measurements of their sedimentology which may be possible with the mars science laboratory rover curiosity as well as expanded measurements of tar morphometry to constrain their size shape and scaling

zebra stripes in the atacama desert revisited granular fingering as a mechanism for zebra stripe formation abstract although a number of studies have pointed out the remarkable slowness of earth surface processes in the atacama desert process mechanisms under such extremely limited water availability are poorly understood and process rates remain unknown this paper revisits the discussion on the formation of the prominent atacama specific hillslope zebra stone stripes previously interpreted to result from palaeo overland flow owen et al 2013 compared to this study our data document different stripe characteristics with regard to stripe form and orientation as well as sorting and bedding patterns of stripe confining surface gravel units we found a remarkable form concordance between zebra stripes and deposits from experiments on segregation induced granular fingering hence we propose a combination of seismic shaking and instantaneous dry granular free surface flows as the key mechanism for zebra stripe formation our findings underline the potential significance of seismicity in shaping atacama landscapes which bear important analogies to extra terrestrial surfaces

first data on volume and type of deflated sediment from southern puna plateau and its role as source of the chaco pampean loess abstract this paper presents the first attempt at qualitatively and quantitatively evaluating the sedimentary contribution of the puna plateau to the loess and soils of the argentinean pampas the origin of the pampean sediment has been traditionally ascribed to northern patagonia but new evidence supports a dual supply western central andes north patagonia and puna altiplano plateau three different lines of evidence show here that puna dust supply is active and produces significant sedimentary deposition up to places like buenos aires city the first evidence is meteorological and we show here one event related to an abnormal rainfall that deposited large quantities of a reddish brownish silt eroded out from the puna calling the attention of the environmental agency of buenos aires city the second evidence is the sampling of active wind transport collecting extremely coarse material carried out in the saltation layer suggesting the fine grained material escapes the area as fugitive dust this also demonstrates that observed gravel bearing bedforms of the puna are active and that the transport system seems to be activated by polar fronts only results show that the saltation curtain is abnormally thick and coarse suggesting that the kinetic energy peaks ca 7 10 times higher than for normal saltation while the transported grain size coincides with the lagged sediment in this basin composing different bedforms varying between sandy gravel and gravelly sand the third evidence is the quantification of the exported material by defining a reference surface as the initial time of evolution and the present day surface the initial surface is an alluvial surface of an estimated age of 11 12 ka bp volume balance was achieved by a detailed topographic stratigraphic and geophysical survey reconstructing old alluvial and present surfaces two gridding methods were used and more conservative results of the volume balance indicate a total erosion of ca 3 386 hm 3 of sediment in 72 ha spliced in 0 963 hm 3 of sediment that was left within the place forming gravel dunes while the remaining volume of ca 2 423 hm 3 is sediment truly exported from the surveyed area results imply a continuous blanket of ca 4 m thick of sediment exported out of this basin in the holocene these findings prove that the puna contribution to the chaco pampean plain is significant although not unique thus true proportions of sediment contribution to soils and loess from these multiple sources should be better evaluated in future studies

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

geodetic observations detecting coseismic displacements and gravity changes caused by the mw 9 0 tohoku oki earthquake 1 this paper reports coseismic displacements and gravity changes caused by the tohoku oki earthquake mw 9 0 as observed respectively using gps in japan and china and its surrounding area and as observed by grace to interpret geodetic observation data we must choose a reasonable model among the slip models presented for the event for this purpose we first calculated the displacements using three slip models from usgs ucsb and aria respectively with different dislocation theories then we compared the results with the displacements observed in japan and china results show that the modeled coseismic displacements calculated using the slip model of wei et al aria and the spherically layered dislocation theory under the prem model agree well with the observed ones indicating that the earth s layer structural and curvature effects should be considered then we computed the coseismic geoid and gravity changes on the earth surface and at a space fixed point using the three slip models and the spherically layered dislocation theory results show that the maximum coseismic geoid change reaches 2 5 cm and that the coseismic gravity changes are about 1000 600 gal for a solid earth furthermore we processed grace data to extract coseismic changes with decorrelation and a gaussian filter of 350 km the gravity changes observed by grace were dominated by a decrease over the back arc region with 5 gal reflecting coseismic crustal dilatation of the landward plate which agrees well with the theoretically modeled values from the three finite fault models after the 2004 sumatra andaman and 2010 central chile maule earthquakes this study presents the third case of clear detection of coseismic gravity changes by grace

the mechanism of the deep bolivia earthquake of june 9 1994 we analyzed the iris broad band seismograms for the june 9 1994 bolivia earthquake the largest deep focus earthquake ever recorded we inverted the record sections with a duration of 330 sec which include p pp and sp phases and obtained a dip slip mechanism dip rake strike 13 4 1 or 89 103 95 with a scalar moment of mo 2 9 10 21 nm mw 8 2 this mechanism is similar to that obtained from long period 175 to 250 sec rayleigh and love waves 83 100 90 mo 3 0 10 21 nm mw 8 3 the main rupture was preceded by about 10 sec by a cluster of smaller events with a total moment of 1 2 10 20 nm mw 7 3 the main rupture starts at about 20 km east or northeast of the initial break and propagates horizontally in the east to northeast direction the source duration is 40 sec and the rupture dimension is about 40km if a fault area of 40 40km is assumed the stress drop is 110 mpa an inversion of body waves p pp and sp with 6 basis moment tensors yielded a best fit solution with a 10 implosive component this result is of marginal significance and its confirmation would require more detailed information on the structures near the source region pp bounce points and stations the observed amplitude of the radial mode 0s 0 1226 sec is consistent with a double couple model with less than 2 isotropic component

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

abnormal formation pressure and shale porosity an abnormally pressured jurassic shale from the north sea viking graben has a fluid pressure over burden ration close to 0 8 at a depth of more than 4 000 m and is associated with low porosity and high density the porosity and fluid pressure history of the shale involves three successive stages 1 normal gravitational compaction prevailed during the first few hundred meters of burial 2 the shale porosity was severely reduced by carbonate cementation in conjunction with a major break in sedimentation but the fluid pressure remained hydrostatic and finally 3 the porosity was further reduced by compaction and possibly cementation and the fluid pressure increased to above hydrostatic in response to renewed subsidence and the cretaceous and tertiary overburden lo d

the largest wind ripples on earth comment the dominance of aeolian features on the surface of mars requires a better understanding of potential terrestrial analogs to provide constraints on models of origin in his timely article milana 2009 1 describes the largest wind ripples on earth from the puna plateau of argentina inverting

the ability of rock physics models to infer marine in situ pore pressure pore fluid pressure is an important parameter defining the mechanical strength of marine sediments obtaining high spatial resolution in situ pore pressure measurements in marine sediments however is a challenge and as a result only a handful of in situ pore pressure measurements exist at scientific drill sites integrating rock physics models with standard iodp odp measurements provides a potentially widely applicable approach for calculating in situ pore pressure here we use a rock physics approach to estimate in situ pore pressure at two scientific ocean drill sites where in situ pressure is well constrained odp site 1173 used as reference for normal hydrostatic fluid pressures and odp site 948 where previous studies infer high fluid pressures 0 45 0 95 where the pore pressure ratio is defined as the pore pressure above hydrostatic divided by the difference between the largest principal stress and hydrostatic stress our analysis indicates that the rock physics method provides an accurate low precision method for estimating in situ pore pressure at these drill sites and sensitivity analysis indicates this method can detect modestly high 0 6 pore pressure at the 95 confidence level this approach has broad applicability because it provides an inexpensive high resolution meter scale method for retrospectively detecting and quantifying high pore pressure at any drill site where quality wireline logs and ocean drilling data exist

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

wind blown sandstones cemented by sulfate and clay minerals in gale crater mars gale crater contains mount sharp a 5km thick stratigraphic record of mars early environmental history the strata comprising mount sharp are believed to be sedimentary in origin but the specific depositional environments recorded by the rocks remain speculative we present orbital evidence for the occurrence of eolian sandstones within gale crater and the lower reaches of mount sharp including preservation of wind blown sand dune topography in sedimentary strata a phenomenon that is rare on earth and typically associated with stabilization rapid sedimentation transgression and submergence of the land surface the preserved bedforms in gale are associated with clay minerals and elsewhere accompanied by typical dune cross stratification marked by bounding surfaces whose lateral equivalents contain sulfate salts these observations extend the range of possible habitable environments that may be recorded within gale crater and provide hypotheses that can be tested in situ by the curiosity rover payload

largest wind ripples on earth unique wind ripples attaining heights to 2 3 m wavelengths to 43 m and a crest maximum grain size of 19 mm occur on the argentine puna plateau at 4000 m altitude these are the largest ripples reported on earth comparable only to mars counterparts they form in the presence of high proportions of low density pumice clasts 0 91 g cm 3 although crests are exclusively composed of varnished normal density clasts 2 43 g cm 3 mature ripple profiles are partly excavated on bedrock so they form by a combination of deflation winnowing of finer grains minor wind drift of fine gravel and lagging of clasts 4 cm the large ripple size appears to be related to strong winds dense saltation layers and a long time for evolution ripple sizes are smaller on obstacles as compared to flat terrain there is a lack of correlation between clast size wavelength and the extreme ripple size in spite of the thin atmosphere all of which suggest that while small scale gravel ripples may form according to a reptation model their evolution into large scale types may relate to aerodynamic instabilities originating at the saltation curtain air interface

the size and duration of the sumatra andaman earthquake from far field static offsets the 26 december 2004 sumatra earthquake produced static offsets at continuously operating gps stations at distances of up to 4500 kilometers from the epicenter we used these displacements to model the earthquake and include consideration of the earth s shape and depth varying rigidity the results imply that the average slip was 5 meters along the full length of the rupture including the approximately 650 kilometer long andaman segment comparison of the source derived from the far field static offsets with seismically derived estimates suggests that 25 to 35 of the total moment release occurred at periods greater than 1 hour taking into consideration the strong dip dependence of moment estimates the magnitude of the earthquake did not exceed mw 9 2

grace gravity data help constraining seismic models of the 2004 sumatran earthquake 1 the analysis of gravity recovery and climate experiment grace level 2 data time series from the center for space research csr and geoforschungszentrum gfz allows us to extract a new estimate of the co seismic gravity signal due to the 2004 sumatran earthquake owing to compressible self gravitating earth models including sea level feedback in a new self consistent way and designed to compute gravitational perturbations due to volume changes separately we are able to prove that the asymmetry in the co seismic gravity pattern in which the north eastern negative anomaly is twice as large as the south western positive anomaly is not due to the previously overestimated dilatation in the crust the overestimate was due to a large dilatation localized at the fault discontinuity the gravitational effect of which is compensated by an opposite contribution from topography due to the uplifted crust after this localized dilatation is removed we instead predict compression in the footwall and dilatation in the hanging wall the overall anomaly is then mainly due to the additional gravitational effects of the ocean after water is displaced away from the uplifted crust as first indicated by de linage et al 2009 we also detail the differences between compressible and incompressible material properties by focusing on the most robust estimates from grace data consisting of the peak to peak gravity anomaly and an asymmetry coefficient that is given by the ratio of the negative gravity anomaly over the positive anomaly we show that they are quite sensitive to seismic source depths and dip angles this allows us to exploit space gravity data for the first time to help constraining centroid momentum tensor cmt source analyses of the 2004 sumatran earthquake and to conclude that the seismic moment has been released mainly in the lower crust rather than the lithospheric mantle thus grace data and cmt source analyses as well as geodetic slip distributions aided by gps complement each other for a robust inference of the seismic source of large earthquakes particular care is devoted to the spatial filtering of the gravity anomalies estimated both from observations and models to make their comparison significant

ground satellite observations and atmospheric modeling of dust storms originating in the high puna altiplano deserts south america implications for the interpretation of paleo climatic archives 1 this study provides a detailed description of the sources transport dispersion and deposition of two major dust events originating from the high altitude subtropical puna altiplano plateau 15 26 s 65 69 w in south america a long and severe drought provided the right conditions for the onset of both events in july 2009 and 2010 dust was transported se and deposited over the pampas region and was observed to continue to the atlantic ocean dust monitoring stations located downwind recorded both events and samples were characterized through chemical and textural analysis through a combination of meteorological data and satellite observations calipso and modis detectors we estimate the emission flux for the 2010 event this estimate was used to constrain the hybrid single particle lagrangian integrated trajectory hysplit transport model and simulate the dust event both satellite imagery and model results agree in the location and extension of the dust cloud calipso detected dust between 6000 and 8500 m a s l which remained at this height during most of its trajectory the dust cloud mixed with a strong convective system in the region and the associated precipitation brought down significant amounts of dust to the ground dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12 4 14 1 m similar to modes observed 1300 km away chemical composition of sediments from potential dust sources shows distinct signatures within the puna altiplano plateau the puna sector being clearly different from the altiplano area in addition both sources are markedly different from the patagonian chemical fingerprint these results have important implications to improve the interpretation of paleo environmental archives preserved on the argentine loess antarctic ice cores and southern ocean marine sediments

rupture complexity of the mw 8 3 sea of okhotsk earthquake rapid triggering of complementary earthquakes we derive a finite slip model for the 2013 m w 8 3 sea of okhotsk earthquake z 610 km by inverting calibrated teleseismic p waveforms the inversion shows that the earthquake ruptured on a 10 dipping rectangular fault zone 140 km 50 km and evolved into a sequence of four large sub events e1 e4 with an average rupture speed of 4 0 km s the rupture process can be divided into two main stages the first propagated south rupturing sub events e1 e2 and e4 the second stage e3 originated near e2 with a delay of 12 s and ruptured northward filling the slip gap between e1 and e2 this kinematic process produces an overall slip pattern similar to that observed in shallow swarms except it occurs over a compressed time span of about 30 s and without many aftershocks suggesting that sub event triggering for deep events is significantly more efficient than for shallow events

rupture complexity of the 1994 bolivia and 2013 sea of okhotsk deep earthquakes the physical mechanism of deep earthquakes depth 300 km remains enigmatic partly because their rupture dimensions are difficult to estimate due to their low aftershock productivity and absence of geodetic or surface rupture observations the two largest deep earthquakes the recent great 2013 sea of okhotsk earthquake m 8 3 depth 607 km and the great 1994 bolivia earthquake m 8 3 depth 637 km together provide a unique opportunity to compare their rupture patterns in detail here we extend a travel time sub event location method to perform full teleseismic p waveform inversion this new method allows us to explain the observed broadband records with a set of sub events whose model parameters are robustly constrained without smoothing we find that while the okhotsk event is mostly unilateral rupturing 90 km along strike with a velocity over 4 km s the bolivia earthquake ruptured about half this distance at a slow velocity about 1 5 km s and displayed a major change in rupture direction we explain the observed differences between the two earthquakes as resulting from two fundamentally different faulting mechanisms in slabs with different thermal states phase transformational faulting is inferred to occur inside the metastable olivine wedge within cold slab cores whereas shear melting occurs inside warm slabs once triggered

wind ripples in an active drift sand area in the netherlands a preliminary report two types of wind ripples are distinguished in an active drift sand area near hulshorst in the veluwe central netherlands the common type has amplitudes of about 0 5 cm and wavelengths of some 11 cm the atypical ripple has amplitudes of about 1 cm and wavelengths of some 16 cm in both cases the sand grains in the crests are coarser than those in the troughs however the coarseness of the grains in the crests of the higher ripples is much more pronounced than that of the lower it is tentatively suggested that wind ripples are initiated by a regular downwind alternation in the impact energy of the descending grains in saltation possibly due to fixed gravity waves in the sheared flows of air with grains which have strong density gradients with height

consolidation state and strength of underthrust sediments and evolution of the decollement at the nankai accretionary margin results of uniaxial reconsolidation experiments 1 uniaxial reconsolidation experiments conducted on ocean drilling program drill cores along the muroto transect of the nankai accretionary margin demonstrate complex yield and postyield behavior and provide evidence for enhanced strengths within sediments beneath the decollement zone tests were conducted on samples collected from similar stratigraphic levels below the decollement and its seaward projection consolidation state of the samples increased landward and with depth and was tracked closely by sediment yield stress for all but one of the samples the sediments however exhibited substantial postyield strength up to 2 8 times the predicted in situ effective vertical stress beneath the protothrust zone this enhanced strength results from diagenesis that leads to matrix cementation during stable effective stress conditions within the underthrust section the close correspondence between yield stress and predicted in situ effective stress suggests that despite the cemented state the sediment matrix remains sensitive to in situ stress conditions the low yield stress of one sample collected within 40 m of the decollement fault at site 808 may reflect diagenesis under reduced effective stress conditions due to postconsolidation increases in pore pressure along the decollement due to their cemented state the strong underthrust sediments resist decollement downcutting beneath the toe of the prism leading to preferential incorporation of weaker continuously deforming accreted sediments during shear seismogenic slip along the decollement at depth may create stresses in excess of sediment strength causing shear failure and rapid release of trapped pore fluids feeding high pore fluid pressures along the decollement zone