structure of the california coast ranges and san andreas fault at safod from seismic waveform inversion and reflection imaging 1 a seismic reflection and refraction survey across the san andreas fault saf near parkfield provides a detailed characterization of crustal structure across the location of the san andreas fault observatory at depth safod steep dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the saf the resulting velocity model constrains the top of the salinian granite with great detail steep dip reflection seismic images show several strong amplitude vertical reflectors in the uppermost crust near safod that define an 2 km wide zone comprising the main saf and two or more local faults another prominent subvertical reflector at 2 4 km depth 9 km to the northeast of the saf marks the boundary between the franciscan terrane and the great valley sequence a deep seismic section of low resolution shows several reflectors in the salinian crust west of the saf two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along strike of the saf they represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust the deepest reflections from 25 km depth are interpreted as crust mantle boundary

evidence for the episodic erosion of the medusae fossae formation preserved within the youngest volcanic province on mars we use orbital shallow radar sharad sounder data to three dimensionally visualize the subsurface structure of elysium planitia the youngest volcanic province on mars our results reveal an emplacement history consisting of multiple groups of overlapping lava flow units originating from different sources the uniquely complex radar stratigraphy of elysium planitia relative to other volcanic regions requires a distinct mechanism to generate the numerous reflectors observed in sharad data sedimentary deposits interbedded with successive batches of lava flows could account for the elaborate pattern of reflectors we infer that widespread rapidly emplaced material sourced from the enigmatic medusae fossae formation mff creates these sedimentary layers this implies that episodes of atmospheric activity perhaps linked with the obliquity of mars periodically erode and redeposit material from the mff across a large region

transience and persistence in the depositional record of continental margins 1 continental shelves and coastal plains are large persistent depositional landforms which are stationary nonmigrating at their proximal ends and characterized by relatively steady long term growth in detail however their surface form and stratigraphic record is built of transient freely migrating landscape elements we derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time based upon tens of thousands of empirical measurements a stochastic noisy diffusion model with drift predicts all the gross features of the empirical data it satisfies first order goals of describing both the surface morphology and stratigraphic completeness of depositional systems the model crossover from noise dominated to drift dominated behavior corresponds to the empirical crossover from transport dominated autogenic transient behavior to accommodation dominated subsidence persistent behavior which begins at timescales of 102 103 years and is complete by scales of 104 105 years because the same long term scaling behavior emerges for off shelf environments it is not entirely explicable by steady subsidence fluctuations in sediment supply and routing probably have significant influence at short term transient scales the exponents of the scaling relations vary with environment particularly the prevalence of channeled sediment transport at very small scales modeling sediment transport as a diffusive process is inappropriate our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging

stratigraphy of the north polar layered deposits of mars from high resolution topography nasa earth and space science fellowship nnx13ao55h nasa s mars reconnaissance orbiter project hirise

degradation of the organic molecules in the shallow subsurface of mars due to irradiation by cosmic rays 1 detection of the organic matter on mars is one of the main goals of the future martian landing missions yet the degradation of organic molecules by cosmic ray irradiation on mars is often ignored we calculate the radiation dose accumulation rates from solar and galactic cosmic rays at various depths in the shallow martian subsurface we demonstrate that a 1 billion year outcrop on mars accumulates the dosage of 500 mgy in the top 0 2 cm and 50 mgy at 5 10 cm depths we show that the preservation of ancient complex organic molecules in the shallow 10 cm depth subsurface of rocks could be highly problematic if the exposure age of a geologic outcrop would exceed 300 myr we demonstrate that more simple organic molecules with masses 100 amu should have a good chance to survive in the shallow subsurface of rocks implications to the sampling strategy for the oncoming martian missions are discussed

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

gypsum bassanite and anhydrite at gale crater mars analyses by the chemin x ray diffraction instrument on mars science laboratory show that gypsum bassanite and anhydrite are common minerals at gale crater warm conditions 6 to 30 c within chemin drive gypsum dehydration to bassanite measured surface temperatures and modeled temperature depth profiles indicate that near equatorial warm season surface heating can also cause gypsum dehydration to bassanite by accounting for instrumental dehydration effects we are able to quantify the in situ abundances of ca sulfate phases in sedimentary rocks and in eolian sands at gale crater all three ca sulfate minerals occur together in some sedimentary rocks and their abundances and associations vary stratigraphically several ca sulfate diagenetic events are indicated salinity driven anhydrite precipitation at temperatures below 50 c may be supported by co occurrence of more soluble salts an alternative pathway to anhydrite via dehydration might be possible but if so would likely be limited to warmer near equatorial dark eolian sands that presently contain only anhydrite the polyphase ca sulfate associations at gale crater reflect limited opportunities for equilibration and they presage mixed salt associations anticipated in higher strata that are more sulfate rich and may mark local or global environmental change mineral transformations within chemin also provide a better understanding of changes that might occur in samples returned from mars

possible closed system pingo and ice wedge thermokarst complexes at the mid latitudes of utopia planitia mars abstract on earth hydrostatic or closed system pingos csps are perennial ice cored mounds formed by the freeze thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation the mounds vary in shape from circular or sub circular to elongate are sub kilometre in their long axes and may reach decametres in height often the mounds show summit depressions radial fractures and single tiers or benches as the csps degrade small scale debris flows or slumps occur end stage degradation typically exhibits debris laden ramparts elevated metres above the surrounding terrain typically the csps originate and develop where deep and continuous permafrost is ice rich i e infused with excess ice as it is in the tuktoyaktuk coastlands of northern canada mid to northern alaska and northeast russia in these areas or regions the terrain often is populated by a thermokarst lakes and alases thermokarst lake basins absent of water b fields of small scale ice wedge polygons either low centred or high centred relative to the polygon margins and c melt water filled or emptied polygon margin troughs or corner pits individual troughs and pits connected by means of the local topographical gradient comprises beaded stream systems or networks here we report describe and discuss a suite of candidate csps at the mid latitudes of utopia planitia up 35 50 n 80 115 e the morphologies scale and height of the martian mounds as well as the surface textures and characteristics landscape features and spatially associated landforms are consistent with the csps observed in ice rich regions on earth the up mounds are nested in or reside adjacent to flat floored possibly thermokarstic depressions small scale polygons some of which exhibit low or high centres relative to their margins and connected polygon margin depressions or pits that mirror beaded stream systems in ice rich terrain on earth the size frequency distribution of craters in our study region precludes a surface younger than 100 ma thus the csp like mounds in up and the pre mound periglacial revisions of the landscape presented by us may be markers of freeze thaw cycling that occurred much earlier in the amazonian epoch than most of the current discussions about periglaciation in up suggest

estimating crustal seismic anisotropy with a joint analysis of radial and transverse receiver function data summary we developed an integrated technique for estimating crustal anisotropy with a horizontal axis using radial r and transverse t receiver functions the technique includes computing three individual and one joint objective function jof and a reliability analysis of the estimated anisotropy the individual objective functions iofs are designed to 1 maximize the peak energy of the stacked r receiver function after a cosine moveout correction in the ps arrival time 2 to maximize the correlation of the radial receiver functions after a full correction of anisotropy or 3 to minimize the total energy of transverse receiver functions stacked after a removal of crustal anisotropy the jof was computed by a weighted average of the three iofs and the reliability analysis uses the principle that stacking coherent signals can lead to an increase of signal to noise ratio we applied the technique to synthetic receiver functions generated with 30 60 per cent white noise from a variety of anisotropic and heterogeneous models the synthetic tests indicate that the proposed technique has good capability to recover the input models despite the presence of random and other coherent noises such as those caused by inhomogeneous structures in the data the technique can always provide accurate estimates of crustal anisotropy we applied the technique to two permanent seismic stations in western china and found significant crustal anisotropy beneath one station located at the northern edge of the tibetan plateau the observed fast polarization direction at this station follows the direction of the maximum horizontal tensile stress suggesting that the observed seismic anisotropy is likely caused by mineral alignment in the lower crust the station situated in the sichuan basin on the other hand shows little to no seismic anisotropy which may suggest that the crust beneath the basin is nearly rigid with very little deformation the developed technique can be applied to any broadband seismic stations that have a good backazimuthal coverage of teleseismic events

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

gusev crater wind related features and processes observed by the mars exploration rover spirit 1 wind related features observed by the rover spirit in gusev crater mars include patches of soil on the surface some of which are organized into bed forms windblown grains include dust inferred to be 2 mm in diameter microscopic imager data show the sands and granules to be rounded and relatively spherical typical of grains transported long distances by the wind the interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains indicating that these sands are not currently experiencing saltation orientations of 1520 features such as bed forms and ventifacts along spirit s traverse from the landing site the columbia memorial station to west spur in the columbia hills suggest primary formative winds from the north northwest which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models a secondary wind from the southeast is also suggested which correlates with predictions for nighttime early morning winds wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks the orientations of which also indicate prevailing winds from the north northwest orientations of many aeolian features in the west spur area however have more scatter than elsewhere along the traverse which is attributed to the influence of local topography on the patterns of wind active dust devils observed on the floor of gusev from the columbia hills demonstrate that dust is currently mobile sequential images of some dust devils show movement as rapid as 3 8 m s consistent with wind velocities predicted by atmospheric models for the afternoon when most of the dust devils were observed sands accumulated on the rover deck in the same period suggest that some sands in the columbia hills experience active saltation two toned rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure while perched rocks could represent materials lowered onto other rocks by deflation of supporting soils measurements of the heights of the light bands and the perched rocks range from 1 cm to 27 cm indicating local deflation by as much as 27 cm

wind as the primary driver of erosion in the qaidam basin china deserts are a major source of loess and may undergo substantial wind erosion as evidenced by yardang fields deflation pans and wind scoured bedrock landscapes however there are few quantitative estimates of bedrock removal by wind abrasion and deflation here we report wind erosion rates in the western qaidam basin in central china based on measurements of cosmogenic 10 be in exhumed miocene sedimentary bedrock sedimentary bedrock erosion rates range from 0 05 to 0 4 mm yr although the majority of measurements cluster at 0 12570 05 mm yr these results combined with previous work indicate that strong winds hyper aridity exposure of friable neogene strata and ongoing rock deformation and uplift in the western qaidam basin have created an environment where wind instead of water is the dominant agent of erosion and sediment transport its geographic location upwind combined with volumetric estimates suggest that the qaidam basin is a major source up to 50 of dust to the chinese loess plateau to the east the cosmogenically derived wind erosion rates are within the range of erosion rates determined from glacial and fluvial dominated landscapes worldwide exemplifying the effectiveness of wind to erode and transport significant quantities of bedrock

a global mars dust composition refined by the alpha particle x ray spectrometer in gale crater modern martian dust is similar in composition to the global soil unit and bulk basaltic mars crust but it is enriched in s and cl the alpha particle x ray spectrometer apxs on the mars science laboratory curiosity rover analyzed air fall dust on the science observation tray o tray in gale crater to determine dust oxide compositions the o tray dust has the highest concentrations of so3 and cl measured in mars dust so3 8 3 cl 1 1 wt the molar s cl in the dust 3 35 0 34 is consistent with previous studies of martian dust and soils s cl 3 7 0 7 fe is also elevated 25 over average mars soils and the bulk crust these enrichments link air fall dust with the s cl and fe rich x ray amorphous component of gale crater soil dust and soil have the same s cl constraining the surface concentrations of s and cl on a global scale

mars sedimentary rock erosion rates constrained using crater counts with applications to organic matter preservation and to the global dust cycle abstract small crater counts on mars light toned sedimentary rock are often inconsistent with any isochron these data are usually plotted then ignored we show using an 18 hirise image 104 crater dataset that these non isochron crater counts are often well fit by a model where crater production is balanced by crater obliteration via steady exhumation for these regions we fit erosion rates we infer that mars light toned sedimentary rocks typically erode at 102 nm yr when averaged over 10 km2 scales and 107 108 yr timescales crater based erosion rate determination is consistent with independent techniques but can be applied to nearly all light toned sedimentary rocks on mars erosion is swift enough that radiolysis cannot destroy complex organic matter at some locations e g paleolake deposits at sw melas but radiolysis is a severe problem at other locations e g oxia planum the data suggest that the relief of the valles marineris mounds is currently being reduced by wind erosion and that dust production on mars

carving intracrater layered deposits with wind on mars crater basins on mars host thick sedimentary sequences which record the environments of early mars these basin fills commonly exhibit mound morphologies thought to arise from aeolian erosion of initially crater filling strata this study presents transport based models explaining how mounds could be carved by wind wind tunnel experiments generated morphologies similar to those observed on mars and numerical modeling of flow over a crater using large eddy simulation les demonstrated a positive feedback between topographic focusing of flow and erosion potential observations of yardangs dunes and wind streaks all proxies for wind direction largely agree with model results where mound strata origins have been interpreted basal subaqueous deposits are overlain by aeolian deposits this stratigraphic progression culminating in wind driven excavation is consistent with a global desiccation event the occurrence of sedimentary mounds only on noachian terrain argues that this event was related to late noachian climatic change

small crater modification on meridiani planum and implications for erosion rates and climate change on mars a morphometric and morphologic catalog of 100 small craters imaged by the opportunity rover over the 33 5 km traverse between eagle and endeavour craters on meridiani planum shows craters in six stages of degradation that range from fresh and blocky to eroded and shallow depressions ringed by planed off rim blocks the age of each morphologic class from 50 200 ka to 20 ma has been determined from the size frequency distribution of craters in the catalog the retention age of small craters on meridiani planum and the age of the latest phase of ripple migration the rate of degradation of the craters has been determined from crater depth rim height and ejecta removal over the class age these rates show a rapid decrease from 1 m myr for craters 1 ma to 0 1 m myr for craters 10 20 ma which can be explained by topographic diffusion with modeled diffusivities of 10 6 m2 yr in contrast to these relatively fast short term erosion rates previously estimated average erosion rates on mars over 100 myr and 3 gyr timescales from the amazonian and hesperian are of order 0 01 m myr which is 3 4 orders of magnitude slower than typical terrestrial rates erosion rates during the middle late noachian averaged over 250 myr and 700 myr intervals are around 1 m myr comparable to slow terrestrial erosion rates calculated over similar timescales this argues for a wet climate before 3 ga in which liquid water was the erosional agent followed by a dry environment dominated by slow eolian erosion

occurrence and origin of rhythmic sedimentary rocks on mars sedimentary rocks preserved on the surface of mars represent a natural archive of past climate conditions although the details of their formation often remain poorly constrained the recent detection of rhythmic bedding patterns in the arabia terra region suggests the influence of orbital variations on sedimentary deposition here we detail a number of new sites which exhibit quasiperiodic stratigraphic variations demonstrating their occurrence throughout the equatorial region of the planet we characterize these recorded signals as well as the local geomorphic context and structural attributes two cyclic units are identified within gale crater the landing site of the mars science laboratory mission enabling estimation of possible formation timescales for the geologic units that may be studied in situ by the rover we find a general lack of fluvial features in connection with rhythmic geologic units contrasting these sites with the aperiodic deltaic stratigraphy found at eberswalde crater possible formation scenarios and their climatic implications are discussed for the diverse set of quasiperiodic sedimentary units we propose multiple depositional pathways for recording cyclic climate changes including repeated evaporitic precipitation from groundwater discharge in topographic lows as well as largely anhydrous accumulation of atmospheric dust for deposits outside of confined basins the preservation of orbital signals in sediments distributed across a wide range of geographic settings suggests a pervasive influence on martian climate conditions through time

sublacustrine depositional fans in southwest melas chasma two depositional fan complexes have been identified on the floor of southwest melas chasma the western fan complex is located near the center of an enclosed basin in southwest melas chasma and is composed of multiple lobes with dendritic finger like terminations these fans are very flat and have a morphology unlike any other fan that has been previously identified on mars on the basis of the morphologic similarity of the western fan complex to the mississippi submarine fan complex we suggest that it may be a deep subaqueous fan depositional system there are numerous channels on the surface of the western fan complex and measurements of channel length width and sinuosity are consistent with channels observed on terrestrial submarine fans the eastern melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin recognition of the fans supports earlier suggestions for the presence of a former lake in melas chasma and indicates that a significant body of water was present and stable at the surface of mars for at least 10 2 to 10 4 years

changes in blast zone albedo patterns around new martian impact craters abstract blast zones bzs around new martian craters comprise various albedo features caused by the initial impact including diffuse halos extended linear and arcuate rays secondary craters ejecta patterns and dust avalanches we examined these features for changes in repeat images separated by up to four mars years here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time such changes are most likely due to airfall of high albedo dust restoring darkened areas to their original albedo the albedo of adjacent non impacted surfaces although some sites show drastic changes over short timescales nearly half of the sites show no obvious changes over several mars years albedo changes are more likely to occur at higher latitude sites lower elevation sites and at sites with smaller central craters no correlation was seen between amount of change and dust cover index relative halo size or historical regional albedo changes quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features the average lifetime among sites with measurable fading is 15 mars years the median is 8 mars years for a linear brightening however at approximately half of sites with three or more repeat images a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior this would predict even longer lifetimes the predicted lifetimes of bzs are comparable to those of slope streaks and considered representative of fading by global atmospheric dust deposition they last significantly longer than dust devil or rover tracks albedo features that are erased by different processes these relatively long lifetimes indicate that the measurement of the current impact rate by daubar et al daubar i j et al 2013 icarus 225 506 516 http dx doi org 10 1016 j icarus 2013 04 009 does not suffer significantly from overall under sampling due to blast zones fading before new impact sites can be initially discovered however the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution

quantitative assessment of uncertainties in modeled crater retention ages on mars abstract with increasing high resolution coverage of mars surface crater count analysis is being used to estimate the formative ages of small depositional features 3 ga than nearby fans 1 3 ga this analysis provides a simple quantitative framework for assigning probable surface age ranges for small features on mars

the contribution of mountains to global denudation the hypothesis that mountains infl uence global climate through links among rock uplift physical and chemical denudation and the carbon cycle remains vigorously debated we address the contribution of mountains to global denudation with an empirical model that predicts that 50 of the total denudation and 40 of the chemical denudation occur on the steepest 10 of earth s terrestrial surface these fi ndings contrast with those from a recent study that suggested global scale denudation occurs primarily on gently sloping terrain but did not account for the infl uence of digital elevation model resolution on modeled denudation rates comparison of calculated denudation rates against the sum of measured sediment and solute yields from 265 watersheds indicates a positive correlation r 2 0 44 with order ofmagnitude variability refl ecting among other things the effects of dams and agriculture in addition ratios of measured river yield to modeled denudation rate decline as catchment area increases due to progressively greater sediment storage with increasing drainage area our results support the conclusion that the small mountainous fraction of earth s surface dominates global denudation and the fl ux of sediment and solutes to oceans

teleseismic waveform modelling with a one way wave equation summary it is now widely accepted that elastic properties of the continental lithosphere and the underlying sublithospheric mantle are both anisotropic and laterally heterogeneous at a range of scales to fully exploit modern three component broad band array data sets requires the use of comprehensive modelling tools in this work we investigate the use of a wide angle one way wave equation to model variations in teleseismic 3 d waveforms due to 2 d elastic heterogeneity and anisotropy the one way operators are derived based on a high frequency approximation of the square root operator and include the effects of wave propagation as well as multiple scattering computational cost is reduced through a number of physically motivated approximations we present synthetic results from simple 1 d layer over a half space and 2 d subduction zone models that are compared with reference solutions the algorithm is then used to model data from an array of broad band seismograph stations deployed in northwestern canada as part of the iris passcal lithoprobe canoe experiment in this region radial component receiver functions show a clear continental moho and the presence of crustal material dipping into the mantle at the suture of two palaeo proterozoic terranes the geometry of the suture is better defined on the transverse component where subduction is associated with a 10 km thick layer exhibiting strong elastic anisotropy the modelling reproduces the main features of the receiver functions including the effects of anisotropy heterogeneity and finite frequency scattering

a progression of induration in medusae fossae formation transverse aeolian ridges evidence for ancient aeolian bedforms and extensive reworking a progression of induration erosion and redeposition of transverse and networked transverse aeolian ridges tars has been documented in the medusae fossae formation mff mars cratered and eroded aeolian bedforms are rarely observed on mars indicating that those found in the mff have been inactive for much longer than those found elsewhere indurated tars are observed to grade into faceted mff terrain indicating a genetic relationship between the two we propose that tar deposition induration and erosion have played a larger role in the surface morphology and evolution of the mff than previously recognized the deposition induration and erosion of tars indicate that the mff has undergone multiple cycles of reworking and that much of its current surface morphology does not reflect the circumstances of its primary emplacement copyright 2011 john wiley sons ltd

the current martian cratering rate abstract the discovery of 248 dated impact sites known to have formed within the last few decades allows us to refine the current cratering rate and slope of the production function at mars we use a subset of 44 of these new craters that were imaged before and after impact by mars reconnaissance orbiter s context camera a thoroughly searched data set that minimizes biases from variable image resolutions we find the current impact rate is 1 65 10 6 craters with an effective diameter 3 9 m km2 yr with a differential slope power law exponent of 2 45 0 36 this results in model ages that are factors of three to five below the hartmann hartmann w k 2005 icarus 174 294 320 and neukum et al neukum g ivanov b a hartmann w k 2001 space sci rev 96 55 86 ivanov ivanov b a 2001 space sci rev 96 87 104 model production functions where they overlap in diameter the best fit production function we measure has a shallower slope than model functions at these sizes but model function slopes are within the statistical errors more than half of the impacts in this size range form clusters which is another reason to use caution when estimating surface ages using craters smaller than 50 m in diameter

constraints on ripple migration at meridiani planum from opportunity and hirise observations of fresh craters 1 observations of fresh impact craters by the opportunity rover and in high resolution orbital images constrain the latest phase of granule ripple migration at meridiani planum to have occurred between 50 ka and 200 ka opportunity explored the fresh resolution crater cluster and concepcion crater that are superposed on and thus younger than the ripples these fresh craters have small dark pebbles scattered across their surfaces which are most likely fragments of the impactor suggesting that the dark pebbles and cobbles observed by opportunity at meridiani planum are a lag of impactor derived material either meteoritic or secondary impactors from elsewhere on mars two larger fresh rayed craters in meridiani planum bracket ripple migration secondaries from ada crater are clearly superposed on and secondaries from an unnamed 0 84 km diameter crater have been modified and overprinted by the ripples three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred the inactivity of the ripples over the past 50 ka at meridiani is also consistent with other evidence for the stability of the ripples the lack of observed eolian bed forms in craters that formed in the past 20 years and little evidence for much dune motion in the past 30 yr on mars observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in meridiani planum over the past million years

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

variations of sulfur isotopes trace element compositions and cathodoluminescence of mississippi valley type pb zn ores from the drau range eastern alps slovenia austria implications for ore deposition on a regional versus microscale the sulfur isotope composition of sulfide ore minerals of the drau range varies considerably down to centimeter scale variations both on a regional and a local scale broadly scattering 34s values ranging between 2 and 25 per mil with a mean around 17 per mil are probably related to both local bacteriogenic and thermal reduction of late triassic marine sulfate the 34s is typically more depleted in ore deposited in subtidal carbonate rocks than in the economic zn and pb ore preferably deposited within intratidal carbonate host rock the 34s 32s ratio increases on the order of fes2 pbs zns which reflects disequilibrium and low temperature formation the strong depletion of 34s in botryoidal sphalerite ranging between 24 and 32 per mil appears to be correlated with the crystal mode wurtzite sphalerite fibers and the enrichment of the trace elements fe as tl and ge sphalerite generations of specific cathodoluminescense color and closely related trace element composition are correlated district wide a decrease of the trace elements fe as tl and ge in the sphalerite generations is coeval with a minor depletion of 34s in the range of 3 and 12 per mil for 34s values in several hand specimens variations in 34s values and trace element zonation on a regional to local scale indicates mixing of local sulfur sources with a regional metal rich brine however distinct peaks in some ore deposits and more positive 34s values of between 5 and 10 per mil are also compatible with derivation of the sulfur from basement rocks the enrichment of the trace element cu in orange luminescing sphalerite negatively correlated with fe as tl and ge and therefore strongly suggests leaching of copper from late permian to early triassic continental red beds frequent evaporites in this stratigraphic section might have supplied sulfur of relatively heavy isotopic composition to the brine hence some sulfur may also have been transported with a metal rich brine

martian fan deposits insights on depositional processes and origin from mass balance survey abstract fan deposits located at the mouths of martian valleys have been interpreted as indicators of wet conditions during mars history however the processes time and amount of water needed to carve the valleys and form the fans are still debated here we present a detailed morphometric and mass balance analysis of valleys and fan shaped deposits using high resolution topography which provides new insights into past depositional environments based on morphometric and volumetric measurements we found that several martian fans previously interpreted as deltas can be categorized into two main types type i fans are more numerous relatively well preserved are associated with smaller and less mature drainage networks and were deposited on steeper gradients the balance between eroded and deposited materials indicates that this set of fans might have been formed mainly in subaerial settings by depositional processes other than typical deltaic sedimentation e g alluvial glacial mass wasting in general since a significant loss of sediment during deposition did not occur we obtained a volume ratio of eroded vs deposited materials of approximately 1 therefore we propose that the identified type i fans were not deposited in prevailing subaqueous deltaic settings but mainly in subaerial conditions with perhaps sporadic presence of ephemeral bodies of standing water within the basins in contrast type ii fans are less abundant highly eroded were deposited on flatter areas and formed downstream of more mature drainage networks with longer deeper and wider valleys the mass balance for this set of fans clearly shows that considerable amounts of sediment were not retained in the fans implying large offshore transport of sediment during their formation eroded vs deposited volume ratios between 3 and 10 are probable this evidence supports a fluvio deltaic origin for this class of fans indicating the existence of paleolakes over substantial periods of time based on the collected morphometric measurements and mass balance modeling we conclude that only a small percentage of the fans type ii fans correspond to 1 3 of the sampled areas are consistent with the occurrence of favorable and durable conditions for life i e long lived integrated fluvial deltaic and lacustrine environments whereas the majority of fans might have been formed in subaerial settings with significant contributions of alternative processes besides fluvial transport and deposition thus not necessarily requiring the occurrence of extended epochs of clement climatic conditions

organic molecules in the sheepbed mudstone gale crater mars the sample analysis at mars sam instrument on board the mars science laboratory curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of mars at gale crater central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin diagenesis concentration and long term preservation this will guide the future search for biosignatures here we report the definitive identification of chlorobenzene 150 300 parts per billion by weight ppbw and c2 to c4 dichloroalkanes up to 70 ppbw with the sam gas chromatograph mass spectrometer gcms and detection of chlorobenzene in the direct evolved gas analysis ega mode in multiple portions of the fines from the cumberland drill hole in the sheepbed mudstone at yellowknife bay when combined with gcms and ega data from multiple scooped and drilled samples blank runs and supporting laboratory analog studies the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in sam we conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources e g igneous hydrothermal atmospheric or biological or exogenous sources such as meteorites comets or interplanetary dust particles

role of material properties in the cratering record of young platy ridged lava on mars 1 platy ridged surfaces in the elysium planitia region of mars exhibit different crater densities on rafted plates and polygonally patterned areas between them rather than being indicative of different ages these differences provide insight into the variable strength of different types of lava surface the sizes of small craters and the resulting size frequency distribution sfd depend on the material strength of target surfaces brecciated lava surfaces are likely to have higher crater densities than coherent lava

dating very young planetary surfaces from crater statistics a review of issues and challenges determining the ages of young planetary surfaces relies on using populations of small often sub km diameter impact craters due to the higher frequency at which they form smaller craters however can be less reliable for estimating ages as their size frequency distribution is more susceptible to alteration with debate as to whether they should be used at all with the current plethora of meter scale resolution images acquired of the lunar and martian surfaces small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events in this review paper we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation

morphometry of small recent impact craters on mars size and terrain dependence short term modification most recent studies of crater morphometry on mars have addressed large craters d 5 km using elevation models derived from laser altimetry in the present work we examine a global population of small 25 m d 5 km relatively well preserved simple impact craters using hirise stereo derived elevation models we find that scaling laws from prior studies of large simple craters generally overestimate the depth and volume at small diameters we show that crater rim curvature exhibits a strong diameter dependence that is well described by scaling laws for d 1 km above this diameter upper rim slopes begin to exceed typical repose angles and crater rims sharpen significantly this transition is likely the result of gravity driven collapse of the upper cavity walls during crater formation or short term modification in addition we identify a tendency for small craters d 500m to be more conical than large craters and we show that the average cavity cross section is well described by a power law with exponent 1 75 neither conical nor paraboloidal we also conduct a statistical comparison of crater subpopulations to illuminate trends with increasing modification and target strength these results have important implications for describing the initial condition of simple crater shape as a function of diameter and geological setting and for understanding how impact craters are modified on the martian surface over time

hypotheses for the origin of the hypanis fan shaped deposit at the edge of the chryse escarpment mars is it a delta abstract we investigated the origin of the fan shaped deposit at the end of hypanis valles that has previously been proposed as an exomars mars 2020 and human mission candidate landing site and found evidence that the landform is an ancient delta previous work suggests that the deposit originated from a time of fluvial activity both distinct from and prior to catastrophic outflow and crater counting placed the deposit s age at 3 6 ga we found over 30 thin sedimentary strata in the proposed delta wall and from our slope analysis conclude that the fluvial sequence is consistent with a lowering retreating shoreline we measured nearly horizontal bedding dip angles ranging from 0 to 2 over long stretches of cliff and bench exposures seen in hirise images and hirise stereo dtms from themis night ir images we determined that the fan shaped deposit has a low thermal inertia 150 240 jm 2k 1s 1 2 and the surrounding darker toned units correspond to thermal inertia values as high as 270 390 jm 2k 1s 1 2 we interpret these findings to indicate that the fan shaped deposit consists mostly of silt sized and possibly finer grains and that the extremely low grade and large lateral extent of these beds implies that the depositional environment was calm and relatively long lived our assessment of the geomorphology and composition seems to indicate that the alluvial fan and mudflow hypotheses are less compatible from our stratigraphic mapping we interpret the order of events which shaped the region after the chryse impact sediment filled the basin a confined lake or sea formed allowing a large delta to be deposited near its shoreline the water level receded to the north darker sedimentary volcanic units covered the region and capped the light toned deposit as hydro volcanic eruptions shaped the interior of lederberg crater freeze thaw cycles and desiccation induced local fracturing and finally wrinkle ridges associated with rounded cones warped the landscape following trends in degraded crater rims and existing tectonic features the ancient deltaic deposit we observe today was largely untouched by subsequent catastrophic outflows and its surface has been only moderately reshaped by over 3 billion years of aeolian erosion

equivalence of abrupt grain size transitions in alluvial rivers and eolian sand seas a hypothesis gravel bed rivers organize to a threshold state in which the fluid stress during dominant flow conditions slightly exceeds the critical value these channels change fairly abruptly to sand dominated beds facilitated by a paucity of sediment in the range of 1 10 mm eolian sediments are also bimodal sand seas often transition rapidly downwind to silty loess deposits in this paper we hypothesize that both transitions result from the same processes 1 production of fine sediment by spallation from saltation abrasion of coarse grains and 2 segregation of fine and coarse modes by suspension and saltation transport respectively we demonstrate that gravel rivers and eolian dune fields are dynamically equivalent in terms of threshold transport shields stress and collision dynamics stokes number while abrasion may not be the dominant cause of downstream fining of fluvial gravels the reduction of collision efficiency with grain diameter sets a lower limit on gravel size leading to a grain size gap the collision efficiency hypothesis potentially reconciles conflicting studies on the importance of sorting and lithology in downstream fining shields and stokes similitude in rivers and deserts may be used to design appropriately scaled experiments to test and refine our hypothesis

simulations of tremor related creep reveal a weak crustal root of the san andreas fault 1 deep aseismic roots of faults play a critical role in transferring tectonic loads to shallower brittle crustal faults that rupture in large earthquakes yet until the recent discovery of deep tremor and creep direct inference of the physical properties of lower crustal fault roots has remained elusive observations of tremor near parkfield ca provide the first evidence for present day localized slip on the deep extension of the san andreas fault and triggered transient creep events we develop numerical simulations of fault slip to show that the spatiotemporal evolution of triggered tremor near parkfield is consistent with triggered fault creep governed by laboratory derived friction laws between depths of 20 35 km on the fault simulated creep and observed tremor northwest of parkfield nearly ceased for 20 30 days in response to small coseismic stress changes of order 104 pa from the 2003 m6 5 san simeon earthquake simulated afterslip and observed tremor following the 2004 m6 0 parkfield earthquake show a coseismically induced pulse of rapid creep and tremor lasting for 1 day followed by a longer 30 day period of sustained accelerated rates due to propagation of shallow afterslip into the lower crust these creep responses require very low effective normal stress of 1 mpa on the deep san andreas fault and near neutral stability frictional properties expected for gabbroic lower crustal rock

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

layered crustal anisotropy around the san andreas fault near parkfield california the rheology of the earth s crust controls the long term and short term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials in this paper we examine the seismic structure and anisotropy of the crust around the san andreas fault saf near parkfield california using teleseismic receiver functions these data indicate that the crust is characterized by spatially variable and strongly anisotropic upper and middle crustal layers with a moho at 35 km depth the upper layer is 5 10 km thick and is characterized by strong 30 anisotropy with a slow axis of hexagonal symmetry where the plane of fast velocity has a strike parallel to that of the saf and a dip of 40 we interpret this layer as pervasive fluid filled microcracks within the brittle deformation regime the 10 15 km thick midcrustal layer is also characterized by a weak axis of hexagonal symmetry with 20 anisotropy but the dip direction of the plane of fast velocity is reversed the midcrustal anisotropic layer is more prominent to the northeast of the san andreas fault we interpret the mid crustal anisotropic layer as fossilized fabric within fluid rich foliated mica schists when combined with various other geophysical observations our results suggest that fault creep behavior around parkfield is favored by intrinsically weak and overpressured crustal fabric

from dust to dust quaternary wind erosion of the mu us desert and loess plateau china the ordos basin of china encompasses the mu us desert in the northwest and the chinese loess plateau to the south and east the boundary between the mostly internally drained mu us desert and fluvially incised loess plateau is an erosional escarpment up to 400 m in relief composed of quaternary loess linear ridges with lengths of 10 2 10 3 m are formed in cretaceous quaternary strata throughout the basin ridge orientations are generally parallel to near surface wind vectors in the ordos basin during modern winter and spring dust storms our observations suggest that the loess plateau previously extended farther to the north and west of its modern windward escarpment margin and has been partially reworked by eolian processes the linear topography mu us desert internal drainage and escarpment retreat are all attributed to wind erosion the aerial extent of which expanded southeastward in china in response to quaternary amplification of northern hemisphere glaciation

pacing early mars river activity embedded craters in the aeolis dorsa region imply river activity spanned 1 20 myr we find net sedimentation rate 13 200 m yr in the aeolis dorsa region mars using the frequency of crater river interactions this sets a lower bound of 1 20 myr on the total interval spanned by fluvial activity which we correlate to the noachian hesperian transition the main uncertainty is the impact flux at the time of deposition this result rules out basin filling by a single catastrophic episode such as a single impact induced water vapor greenhouse

aeolian bedforms yardangs and indurated surfaces in the tharsis montes as seen by the hirise camera evidence for dust aggregates abstract hirise images of mars with ground sampling down to 25 cm pixel show that the dust rich mantle covering the surfaces of the tharsis montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology the material composing these reticulate bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation suspension boundary both of which vary as a function of elevation atmospheric pressure particle size and particle composition considering all of these factors dust aggregates are the most likely material composing these bedforms we propose that airfall dust on and near the volcanoes aggregates in situ over time maybe due to electrostatic charging followed by cementation by salts the aggregates eventually reach a particle size at which saltation is possible aggregates on the flanks are transported downslope by katabatic winds and form linear and accordion morphologies materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds forming an interlinked honeycomb texture in many places on and near the volcanoes light toned low thermal inertia yardangs and indurated surfaces are present these may represent duststone formed when aggregates reach a particle size below the threshold curve such that they become stabilized and subsequently undergo cementation

light toned layered deposits in juventae chasma mars abstract we examine hypotheses for the formation of light toned layered deposits in juventae chasma using a combination of data from mars global surveyor s mars orbiter camera moc mars orbiter laser altimeter mola and thermal emission spectrometer tes as well as mars odyssey s thermal emission imaging system themis we divide juventae chasma into geomorphic units of i chasm wall rock ii heavily cratered hummocky terrain iii a mobile and largely crater free sand sheet on the chasm floor iv light toned layered outcrop llo material and v chaotic terrain using surface temperatures derived from themis infrared data and slopes from mola we derive maps of thermal inertia which are consistent with the geomorphic units that we identify llo thermal inertias range from 400 to 850 j m 2 k 1 s 1 2 light toned layered outcrops are distributed over a remarkably wide elevation range 5 8 km from the chasm floor to the adjacent plateau surface geomorphic features the absence of small craters and high thermal inertia show that the llos are composed of sedimentary rock that is eroding relatively rapidly in the present epoch we also present evidence for exhumation of llo material from the west wall of the chasm within chaotic and hummocky terrains and within a small depression in the adjacent plateau the data imply that at least some of the llo material was deposited long before the adjacent hesperian plateau basalts and that juventae chasma underwent and may still be undergoing enlargement along its west wall due to wall rock collapse chaotic terrain evolution and exposure and removal of llo material the new data allow us to reassess possible origins of the llos gypsum one of the minerals reported elsewhere as found in juventae chasma llo material forms only at low temperatures 60 c and thus excludes a volcanic origin instead the data are consistent with either multiple occurrences of lacustrine or airfall deposition over an extended period of time prior to emplacement of hesperian lava flows on the plateau above the chasm

quantification of the dry history of the martian soil inferred from in situ microscopy 1 the particle size distribution psd of a martian soil sample a useful indicator of the underlying soil formation processes has been determined using optical and atomic force microscopy data acquired by the phoenix mars lander in particular the presence and fraction of clay sized particles in the psd reflects the extent of aqueous interaction with the soil two size populations have been identified for the martian sample larger mostly rounded grains and small reddish fines notably with a very low mass proportion in the clay size range below 2 m these fines reflect the smallest scale formation processes and indicate a single method of production for the particles up to 11 m a much larger value than that expected for the aqueous interaction of clay formation this suggests the fines are predominantly the product of global aeolian weathering under very dry conditions the proportion of clay sized soils can be used to estimate that there has been much less than 5 000 years exposure to liquid water over the history of the soil from the perspective of the psd lunar regolith rather than terrestrial soil is the best analog to martian soil a globally homogenous soil with such a psd would be an unlikely habitat for the propagation of life on mars

structure controlled seismic anisotropy along the karadere duzce branch of the north anatolian fault revealed by shear wave splitting tomography abstract we use a three dimensional 3d shear wave splitting sws tomography method developed by zhang et al 2007 to map the spatial distribution of crustal anisotropy in the karadere duzce branch of the north anatolian fault naf in western turkey the input data consists of 20 751 measurements of the sws delay times from 7856 aftershocks of the 1999 mw 7 4 izmit and mw 7 1 duzce earthquakes the results show a continuous belt like highly anisotropic zone along the karadere duzce branch of naf generally 3 km wide and down to 5 km deep the observed asymmetric pattern of anisotropy along the karadere segment is qualitatively consistent with asymmetric damages from the unilateral eastward propagation of the izmit rupture another strong anisotropy region was found near the end of the izmit rupture zone close to the dipping direction of the fault segment that ruptured during the subsequent duzce earthquake these results are generally consistent with the shallow fault zone anisotropy inferred from previous studies while the anisotropy generally becomes weaker at depth and or outside the fault zone we also identify several highly anisotropic regions as deep as 10 km primarily within the almacik block these isolated anisotropy regions could be explained by individual intrusive igneous rock bodies with different mineral alignment overall seismic anisotropy in upper crust of the karadere duzce branch of the naf is structurally controlled

the production of small primary craters on mars and the moon abstract we model the primary crater production of small d d 10 20 cm well below the downturn observed in the distribution of fresh craters detected by the mars global surveyor mgs mars orbiter camera moc or the mars reconnaissance orbiter mro context camera ctx crater counts are conducted on the ejecta blanket of zunil crater and the interior of pangboche crater on mars and north ray and cone craters on the moon our model isochrons produce a similar slope and age estimate for the formation of zunil crater as the hartmann production function 1 ma we derive an age of 35 1 ma for pangboche when accounting for the higher elevation 20 km higher than zunil a factor 2 younger than estimated using the hartmann production function which assumes 6 mbar surface pressure we estimate ages of 52 3 ma and 23 9 ma for north ray and cone crater respectively consistent with cosmic ray exposure ages from apollo samples our results indicate that the average cratering rate has been constant on these bodies over these time periods since our monte carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the moon and mars we conclude that the signal from secondary craters in the isochrons must be relatively small at these locations as our monte carlo model only generates primary craters

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

effect of obliteration on crater count chronologies for martian surfaces 1 the density of impact craters calibrated against lunar data is currently the only quantitative measure of surface age for terrestrial planetary surfaces unlike the moon however mars has been weathered and eroded obliterating some small 10 km diameter craters a phenomenon addressed in the mariner viking days of mars exploration but commonly overlooked in recent studies we present a quantitative model that extends this earlier work to assess the effect of erosion and infilling on surface ages inferred from crater frequency distributions our work affirms that small cratersizedistributionscanbeinterpretedquantitatively in terms of effects of erosion and crater infilling at rates comparable to those reported for mars a reanalysis of prior studies indicates that low to moderate long term rates of erosion and crater infilling can mask an ancient age and result in small crater populations similar to those offered as evidence for young and geologically significant surface activity citation smith m r a r gillespie and d r montgomery 2008 effect of obliteration on crater count chronologies for martian surfaces geophys res lett 35 l10202 doi 10 1029 2008gl033538

crater based dating of geological units on mars methods and application for the new global geological map abstract the new post viking generation of mars orbital imaging and topographical data provide significant higher resolution details of surface morphologies which induced a new effort to photo geologically map the surface of mars at 1 20 000 000 scale although from unit superposition relations a relative stratigraphical framework can be compiled it was the ambition of this mapping project to provide absolute unit age constraints through crater statistics in this study the crater counting method is described in detail starting with the selection of image data type locations both from the mapper s and crater counter s perspectives and the identification of impact craters we describe the criteria used to validate and analyse measured crater populations and to derive and interpret crater model ages we provide examples of how geological information about the unit s resurfacing history can be retrieved from crater size frequency distributions three cases illustrate short intermediate and long term resurfacing histories in addition we introduce an interpretation independent visualisation of the crater resurfacing history that uses the reduction of the crater population in a given size range relative to the expected population given the observed crater density at larger sizes from a set of potential type locations 48 areas from 22 globally mapped units were deemed suitable for crater counting because resurfacing ages were derived from crater statistics these secondary ages were used to define the unit age rather than the base age using the methods described herein we modelled ages that are consistent with the interpreted stratigraphy our derived model ages allow age assignments to be included in unit names we discuss the limitations of using the crater dating technique for global scale geological mapping finally we present recommendations for the documentation and presentation of crater statistics in publications

strong tremor near parkfield ca excited by the 2002 denali fault earthquake 1 we show clear evidence of non volcanic tremor triggered by 2002 mw7 8 denali fault earthquake near parkfield triggered tremor is identified as bursts of high frequency 2 8 hz non impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves the tremor originates from at least three hypocenters near the san andreas fault with differing frictional regimes two in the creeping section and the other where the san andreas is transitional between creeping and locked all the sources originate below the seismogenic zone suggesting that transitional frictional properties are necessary conditions for tremor generation tremor is excited by the love waves when the san andreas is sheared in a right lateral sense encouraging slip and is absent when the san andreas is sheared in a left lateral sense consistent with a simple frictional response to the driving stress

decameter scale pedestal craters in the tropics of mars evidence for the recent presence of very young regional ice deposits in tharsis abstract global climate models predict that ice will be deposited in tropical regions during obliquity excursions from the current mean obliquity of 25 to 35 but no geological evidence for such deposits has been reported we document the presence of very small decameter scale pedestal craters in the tropics of mars the daedalia planum tharsis region that are superposed on an impact crater dated to 12 5 ma ago the characteristics abundance and distribution of these small pedestal craters provide geological evidence that meters thick ice accumulations existed in the tropical tharsis region of mars in the last few million years when mean obliquity was 35 5 15 ma before it transitioned to a mean of 25 0 3 ma a reconnaissance survey reveals similar small pedestal crater examples superposed on the older amazonian arsia mons tropical mountain glacier deposit suggesting that ice can accumulate in these tropical regions without initiating large scale glacial conditions these results support the predictions of general circulation models that ice can migrate to the equatorial regions during periods of moderate obliquity and then serve as a source for mid latitude deposits

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

wind driven erosion and exposure potential at mars 2020 rover candidate landing sites aeolian processes have likely been the predominant geomorphic agent for most of mars history and have the potential to produce relatively young exposure ages for geologic units thus identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions such as the mars 2020 rover mission that aims to explore astrobiologically relevant ancient environments here we investigate wind driven activity at eight mars 2020 candidate landing sites to constrain erosion potential at these locations to demonstrate our methods we found that contemporary dune derived abrasion rates were in agreement with rover derived exhumation rates at gale crater and could be employed elsewhere the holden crater candidate site was interpreted to have low contemporary erosion rates based on the presence of a thick sand coverage of static ripples active ripples at the eberswalde and southwest melas sites may account for local erosion and the dearth of small craters moderate flux regional dunes near mawrth vallis were deemed unrepresentative of the candidate site which is interpreted to currently be experiencing low levels of erosion the nili fossae site displayed the most unambiguous evidence for local sand transport and erosion likely yielding relatively young exposure ages the downselected jezero crater and northeast syrtis sites had high flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses both sites had relatively high estimated abrasion rates which would yield young exposure ages the downselected columbia hills site lacked evidence for sand movement and contemporary local erosion rates are estimated to be relatively low

physical abrasion of mafic minerals and basalt grains application to martian aeolian deposits abstract sediment maturity or the mineralogical and physical characterization of sedimentary deposits has been used to identify sediment sources transport medium and distance weathering processes and paleoenvironments on earth mature terrestrial sands are dominated by quartz which is abundant in source lithologies on earth and is physically and chemically stable under a wide range of conditions immature sands such as those rich in feldspars or mafic minerals are composed of grains that are easily physically weathered and highly susceptible to chemical weathering on mars which is predominately mafic in composition terrestrial standards of sediment maturity are not applicable in addition the martian climate today is cold and dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering due to these large differences in weathering processes and composition martian sediments require an alternate maturity index this paper reports the results of abrasion tests conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted well rounded spherical polycrystalline materials such as basalt volcanic glass is also likely to persist in a mechanical weathering environment while more fragile and chemically altered products are likely to be winnowed away a modified sediment maturity index is proposed that can be used in future studies to constrain sediment source paleoclimate mechanisms for sediment production and surface evolution this maturity index may also provide insights into erosional and sediment transport systems and preservation processes of layered deposits

erosion rate and previous extent of interior layered deposits on mars revealed by obstructed landslides we describe interior layered deposits on mars that have obstructed landslides before undergoing retreat by as much as 2 km these landslides differ from typical martian examples in that their toe height increases by as much as 500 m in a distinctive frontal scarp that mimics the shape of the layered deposits by using crater statistics to constrain the formation ages of the individual landslides to between ca 200 and 400 ma we conclude that the retreat of the interior layered deposits was rapid requiring erosion rates of between 1200 and 2300 nm yr 1 we suggest that the interior layered deposits are either extremely friable if eroded strictly by wind or composed of a material whose degradation has been enhanced by ice sublimation these erosion rates also confirm that the interior layered deposits have been in a state of net degradation over the past 400 m y suggesting that the process that caused net deposition in the past has ceased or slowed substantially on mars relative to erosion our results imply that interior layered deposits with a similar morphology across mars including the mound in gale crater have probably undergone similar rapid erosion and retreat suggesting that their total modern volume underrepresents the depositional record and thus sedimentary history of mars

the rock abrasion record at gale crater mars science laboratory results from bradbury landing to rocknest ventifacts rocks abraded by wind borne particles are found in gale crater mars in the eastward drive from bradbury landing to rocknest they account for about half of the float and outcrop seen by curiosity s cameras many are faceted and exhibit abrasion textures found at a range of scales from submillimeter lineations to centimeter scale facets scallops flutes and grooves the drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow this upwind direction is inconsistent with predictions based on models and the orientation of regional dunes suggesting that these ventifact features formed from very rare high speed winds the absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today

west margin of north america a synthesis of recent seismic transects abstract a comparison of the deep structure along nine recent transects of the west margin of north america shows many important similarities and differences common tectonic elements identified in the deep structure along these transects include actively subducting oceanic crust accreted oceanic arc or oceanic like lithosphere of mesozoic through cenozoic ages cenozoic accretionary prisms mesozoic accretionary prisms backstops to the mesozoic prisms and undivided lower crust not all of these elements are present along all transects in this study nine transects including four crossing subduction zones and five crossing transform faults are plotted at the same scale and vertical exaggeration v e 1 1 using the above scheme for identifying tectonic elements the four subduction zone transects contain actively subducting oceanic crust cenozoic accretionary prisms and bodies of basaltic rocks accreted in the cenozoic including remnants of a large oceanic plateau in the oregon and vancouver island transects rocks of age and composition eocene basalt similar to the oceanic plateau are currently subducting in southern alaska where they are doubled up on top of pacific oceanic crust and have apparently created a giant asperity or impediment to subduction most of the subduction zone transects also contain mesozoic accretionary prisms and two of them vancouver island and alaska also contain thick tectonically underplated bodies of late mesozoic early cenozoic oceanic lithosphere interpreted as fragments of the extinct kula plate in the upper crust most of the five transform fault transects all in california reflect 1 tectonic wedging of a mesozoic accretionary prism into a backstop which includes mesozoic early cenozoic forearc rocks and mesozoic ophiolitic arc basement rocks and 2 shuffling of the subduction margin of california by strike slip faulting in the lower crust they may reflect migration of the mendocino triple junction northward seen in rocks east of the san andreas fault and cessation of farallon plate subduction seen in rocks west of the san andreas fault in northern california lower crustal rocks east of the san andreas fault have oceanic crustal velocity and thickness and contain patches of high reflectivity they may represent basaltic rocks magmatically underplated in the wake of the migration of the mendocino triple junction or they may represent stalled subducted fragments of the farallon gorda plate the latter alternative does not fit the accepted slabless window model for the migration of the triple junction this lower crustal layer and the moho are offset at the san andreas and maacama faults in central california a similar lower crustal layer is observed west of the san andreas fault west of the continental slope it is pacific oceanic crust but beneath the continent it may represent either pacific oceanic crust stalled subducted fragments microplates of the farallon plate or basaltic rocks magmatically underplated during subduction of the pacific farallon ridge or during breakup of the subducted farallon plate the transect in southern california is only partly representative of regional structure as the structure here is 3 dimensional in the upper crust a mesozoic prism has been thrust beneath crystalline basement rocks of the san gabriel mountains and mojave desert in the mid crust a bright reflective zone is interpreted as a possible master decollement that can be traced from the fold and thrust belt of the los angeles basin northward to at least the san andreas fault a moho depression beneath the san gabriel mountains is consistent with downwelling of lithospheric mantle beneath the transverse ranges that appears to be driving the compression across the transverse ranges and los angeles basin

present day mass wasting in sulfate rich sediments in the equatorial regions of mars abstract present day topographic changes are observed on steep slopes in equatorial regions of mars that are associated with sulfate rich sediments hydrated sulfates are known to be present in many sedimentary deposits on mars we document volume changes in the form of mass movements and gullies over these regions we have estimated erosion rates of 12 mm yr or 1 2 120 mm yr with uncertainties over steep slopes on sulfate rich mounds in ganges chasma much higher than mars average erosion rate near a few m yr at this rate the mounds would have shrunk in diameter by 18 000 km over 3 b y which greatly exceeds the width of the canyon supporting suggestions that these sediments once filled the canyons due to the soft nature of typical sulfate rich sediment it is susceptible to mass wasting and active eolian processes may remove loose material to maintain steep slopes the water in hydrated sulfates could potentially be extracted and used as a resource for future humans on mars and our results suggest that such deposits would be mechanically weak

minimum effective area for high resolution crater counting of martian terrains the acquisition of high resolution imagery for the surface of mars has enabled mapping of spatially limited order of 200 m on four type terrains using mars reconnaissance orbiter mro context camera ctx imagery that span the noachian hesperian and amazonian epochs the counts from each location include a region covering 10 000 km2 ten 1000 km2 subsets of that larger area and approximately one hundred 100 km2 samples the data demonstrate significant variation in the crater size frequency and derived model ages across a single terrain type for the 100 km2 samples the crater size frequency at this area scale varies across a single uniform geologic unit by up to a factor of 2 3 on the four different terrains at 1000 km2 the local pattern variations that are relevant at the 100 km2 scale become less important and the age variations are tighter in all four terrain cases the 10 000 km2 and 1000 km2 samples capture distinct crater populations km sized craters that formed before and after resurfacing event s however due to the relatively high mean distance between km sized craters the 100 km2 size area samples more commonly than not exclude a statistically significant sample at the kilometer size range masking important information about the pre resurfacing history of the terrain we therefore suggest that due to the effect of pattern variability in cratering over 100 km2 and the susceptibility of smaller craters to resurfacing crater counts derived from small area samples are suspect to major uncertainties

the variability of crater identification among expert and community crater analysts abstract the identification of impact craters on planetary surfaces provides important information about their geological history most studies have relied on individual analysts who map and identify craters and interpret crater statistics however little work has been done to determine how the counts vary as a function of technique terrain or between researchers furthermore several novel internet based projects ask volunteers with little to no training to identify craters and it was unclear how their results compare against the typical professional researcher to better understand the variation among experts and to compare with volunteers eight professional researchers have identified impact features in two separate regions of the moon small craters diameters ranging from 10 m to 500 m were measured on a lunar mare region and larger craters 100s m to a few km in diameter were measured on both lunar highlands and maria volunteer data were collected for the small craters on the mare our comparison shows that the level of agreement among experts depends on crater diameter number of craters per diameter bin and terrain type with differences of up to 45 we also found artifacts near the minimum crater diameter that was studied these results indicate that caution must be used in most cases when interpreting small variations in crater size frequency distributions and for craters 10 pixels across because of the natural variability found projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

planetary surface dating from crater size frequency distribution measurements multiple resurfacing episodes and differential isochron fitting abstract the analysis of crater size frequency distributions and absolute densities forms the basis of current approaches for estimating the absolute and relative ages of planetary surfaces users of the neukum system of crater dating have conventionally used a cumulative presentation of the data but because of the recent proliferation of interest in identifying resurfacing ages it is worth emphasising the utility of the differential presentation of crater data in identifying resurfacing events and particularly in distinguishing the signature of short lived events such as volcanic flows from long acting processes such as aeolian erosion the work describes some additional considerations for making isochron fits to differentially plotted crater populations with respect to the removal of a binning bias for incrementally differentially plotted data the hartmann approach has not typically employed the fitting of isochrons but differential fitting would be a natural choice for this system and is implemented in the craterstats software a revised calculation of the martian epoch boundary times in both chronology systems is provided

low palaeopressure of the martian atmosphere estimated from the size distribution of ancient craters the decay of the martian atmosphere which is dominated by carbon dioxide is a component of the long term environmental change on mars from a climate that once allowed rivers to flow to the cold and dry conditions of today the minimum size of craters serves as a proxy for palaeopressure of planetary atmospheres because thinner atmospheres permit smaller objects to reach the surface at high velocities and form craters the aeolis dorsa region near gale crater on mars contains a high density of preserved ancient craters interbedded with river deposits and thus can provide constraints on atmospheric density at the time of fluvial activity here we use high resolution images and digital terrain models from the mars reconnaissance orbiter to identify ancient craters in deposits in aeolis dorsa that date to about 3 6 gyr ago and compare their size distribution with models of atmospheric filtering of impactors we obtain an upper limit of 0 9 0 1 bar for the martian atmospheric palaeopressure rising to 1 9 0 2 bar if rimmed circular mesas interpreted to be erosionally resistant fills or floors of impact craters are excluded we assume target properties appropriate for desert alluvium if sediment had rock mass strength similar to bedrock at the time of impact the paleopressure upper limit increases by a factor of up to two if mars did not have a stable multibar atmosphere at the time that the rivers were flowing as suggested by our results then a warm and wet co 2 h 2o greenhouse is ruled out and long term average temperatures were most likely below freezing

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event