martian stepped delta formation by rapid water release deltas and alluvial fans preserved on the surface of mars provide an important record of surface water flow understanding how surface water flow could have produced the observed morphology is fundamental to understanding the history of water on mars to date morphological studies have provided only minimum time estimates for the longevity of martian hydrologic events which range from decades to millions of years here we use sand flume studies to show that the distinct morphology of martian stepped terraced deltas could only have originated from a single basin filling event on a timescale of tens of years stepped deltas therefore provide a minimum and maximum constraint on the duration and magnitude of some surface flows on mars we estimate that the amount of water required to fill the basin and deposit the delta is comparable to the amount of water discharged by large terrestrial rivers such as the mississippi the massive discharge short timescale and the associated short canyon lengths favour the hypothesis that stepped fans are terraced delta deposits draped over an alluvial fan and formed by water released suddenly from subsurface storage

elastic full waveform inversion of multi component obc seismic data elastic full waveform inversion of seismic reflection data represents a data driven form of analysis leading to quantification of sub surface parameters in depth in previous studies attention has been given to p wave data recorded in the marine environment using either acoustic or elastic inversion schemes in this paper we exploit both p waves and mode converted s waves in the marine environment in the inversion for both p and s wave velocities by using wide angle multi component ocean bottom cable seismic data an elastic waveform inversion scheme operating in the time domain was used allowing accurate modelling of the full wavefield including the elastic amplitude variation with offset response of reflected arrivals and mode converted events a series of one and two dimensional synthetic examples are presented demonstrating the ability to invert for and thereby to quantify both p and s wave velocities for different velocity models in particular for more realistic low velocity models including a typically soft seabed an effective strategy for inversion is proposed to exploit both p and mode converted ps waves whilst p wave events are exploited for inversion for p wave velocity examples show the contribution of both p and ps waves to the successful recovery of s wave velocity

monte carlo estimation and resolution analysis of seismic background velocities the complete solution to an inverse problem including information on accuracy and resolution is given by the a posteriori probability density in the model space by running a modified simulated annealing samples from the model space can be drawn in such a way that their frequencies of occurrence approximate their a posteriori likelihoods using this method maximum likelihood estimation and uncertainty analysis of seismic background velocity models are performed on multioffset seismic data the misfit between observed and synthetic waveforms within the time windows along computed multioffset travel times is used as an objective function for the simulated annealing approach the real medium is modeled as a series of layers separated by curved interfaces lateral velocity variations within the layers are determined by interpolation from specified values at a number of sampling points the input data consists of multioffset seismic data additionally zero offset times are used to migrate the reflectors in time to the depth domain the multioffset times are calculated by an efficient ray tracing algorithm which allows inversion of a large number of seismograms the a posteriori probability density for this problem is highly multidimensional and highly multimodal therefore the information contained in this distribution cannot be adequately represented by standard deviations and covariances however by sequentially displaying a large number of images computed from the a posteriori background velocity samples and the data it is possible to convey to the spectator a better understanding of what information we really have on the subsurface

watershed modeling in the tyrrhena terra region of mars 1 watershed analyses from high resolution image viking mars orbiter camera and thermal emission imaging system and topographic mars orbiter laser altimeter mola data are used to qualitatively and quantitatively characterize highland fluvial systems and analyze the role of water in the evolution of tyrrhena terra 13 s 30 s 265 w 280 w mars in this study geographical information system software is used in conjunction with mola digital elevation models to delineate drainage basin divides extract valley networks and derive basin and network morphometric parameters e g drainage density stream order bifurcation ratio and relief morphometry useful in characterizing the geologic and climatic conditions of watershed formation as well as for evaluating basin maturity and processes of watershed development model predicted valley networks and watershed boundaries which are dependent on the degree to which pixel sinks are filled in the topographic data set and a channelization threshold are evaluated against image and topographic data slope maps and detailed maps of valley segments from photogeologic analyses valley morphologies crater valley relationships and impact crater distributions show that valleys in tyrrhena terra are ancient based on geologic properties of the incised materials valley and network morphologies morphometric parameters and the presence of many gullies heading at or near crater rim crests surface runoff derived from rainfall or snowmelt was the dominant erosional process sapping may have only played a secondary role in valley formation in tyrrhena terra furthermore spatial and temporal relationships of dissected highland materials and impact craters suggests widespread but relatively short lived erosion by runoff with most activity in the noachian period

pre stack full waveform inversion of ultra high frequency marine seismic reflection data the full waveform inversion fwi of seismic reflection data aims to reconstruct a detailed physical properties model of the subsurface fitting both the amplitude and the traveltime of the reflections generated at physical discontinuities in the propagation medium unlike reservoir scale seismic exploration where seismic inversion is a widely adopted remote characterization tool ultrahigh frequency uhf 0 2 4 0 khz multichannel marine reflection seismology is still most often limited to a qualitative interpretation of the reflections architecture here we propose an elastic fwi methodology custom tailored for pre stack uhf marine data in vertically heterogeneous media to obtain a decimetric scale distribution of p impedance density and poisson s ratio within the shallow subseabed sediments we address the deterministic multiparameter inversion in a sequential fashion the complex trace instantaneous phase is first inverted for the p wave velocity to make up for the lack of low frequency in the data and reduce the nonlinearity of the problem this is followed by a short offset p impedance optimization and a further step of full offset range poisson s ratio inversion provided that the seismogram contains wide reflection angles 40 we show that it is possible to invert for density and decompose a posteriori the relative contribution of p wave velocity and density to the p impedance a broad range of synthetic tests is used to prove the potential of the methodology and highlights sensitivity issues specific to uhf seismic an example application to real data is also presented in the real case trace normalization is applied to minimize the systematic error deriving from an inaccurate source wavelet estimation the inverted model for the top 15 m of the subseabed agrees with the local lithological information and core log data thus we can obtain a detailed remote characterization of the shallow sediments using a multichannel sub bottom profiler within a reasonable computing cost and with minimal pre processing this has the potential to reduce the need of extensive geotechnical coring campaigns

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

an alternative strategy for non linear inversion of seismic waveforms1 a common example of a large scale non linear inverse problem is the inversion of seismic waveforms techniques used to solve this type of problem usually involve finding the minimum of some misfit function between observations and theoretical predictions as the size of the problem increases techniques requiring the inversion of large matrices become very cumbersome considerable storage and computational effort are required to perform the inversion and to avoid stability problems consequently methods which do not require any large scale matrix inversion have proved to be very popular currently descent type algorithms are in widespread use usually at each iteration a descent direction is derived from the gradient of the misfit function and an improvement is made to an existing model based on this and perhaps previous descent directions a common feature in nearly all geophysically relevant problems is the existence of separate parameter types in the inversion i e unknowns of different dimension and character however this fundamental difference in parameter types is not reflected in the inversion algorithms used usually gradient methods either mix parameter types together and take little notice of the individual character or assume some knowledge of their relative importance within the inversion process we propose a new strategy for the non linear inversion of multi offset reflection data the paper is entirely theoretical and its aim is to show how a technique which has been applied in reflection tomography and to the inversion of arrival times for 3d structure may be used in the waveform case specifically we show how to extend the algorithm presented by tarantola to incorporate the subspace scheme the proposed strategy involves no large scale matrix inversion but pays particular attention to different parameter types in the inversion we use the formulae of tarantola to state the problem as one of optimization and derive the same descent vectors the new technique splits the descent vector so that each part depends on a different parameter type and proceeds to minimize the misfit function within the sub space defined by these individual descent vectors in this way optimal use is made of the descent vector components i e one finds the combination which produces the greatest reduction in the misfit function based on a local linearization of the problem within the subspace this is not the case with other gradient methods by solving a linearized problem in the chosen subspace at each iteration one need only invert a small well conditioned matrix the projection of the full hessian on to the subspace the method is a hybrid between gradient and matrix inversion methods the proposed algorithm requires the same gradient vectors to be determined as in the algorithm of tarantola although its primary aim is to make better use of those calculations in minimizing the objective function

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

drainage network development in the keanakāko i tephra kīlauea volcano hawai i implications for fluvial erosion and valley network formation on early mars 1 a number of studies have attempted to characterize martian valley and channel networks to date however little attention has been paid to the role of lithology which could influence the rate of incision morphology and hydrology as well as the characteristics of transported materials here we present an analysis of the physical and hydrologic characteristics of drainage networks gullies and channels that have incised the keanak ko i tephra a basaltic pyroclastic deposit that occurs mainly in the summit area of k lauea volcano and in the adjoining ka desert hawai i the keanak ko i tephra is up to 10 m meters thick and largely devoid of vegetation making it a good analog for the martian surface although the scales are different the keanak ko i drainage networks suggest that several typical morphologic characteristics of martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics many gully headwalls and knickpoints within the drainage networks are amphitheater shaped which results from strong over weak stratigraphy beds of fine ash commonly bearing accretionary lapilli pisolites are more resistant to erosion than the interbedded coarser weakly consolidated and friable tephra layers because the banks of the gullies and channels are easily eroded widths vary downslope similar to martian valley networks that have been characterized as degraded the floors of the gullies and channels tend to be low relief with few prominent bed forms reflecting the large proportion of sediment transported as bed load in high energy but short lived flood events we calculate that the average flow velocities within the drainage networks are typically 1 m 24 h given some recent modeling of the early martian climate our observations imply that rainfall on early mars could also be associated with large intense events and that martian valley network formation may be related to similar cyclonic storms

erosional valleys in the thaumasia region of mars hydrothermal and seismic origins analysis of erosional valleys geologic materials and features and topography through time in the thaumasia region of mars using co registered digital spatial data sets reveals significant associations that relate to valley origin valleys tend to originate 1 on noachian to early hesperian stages 1 and 2 large volcanoes 2 within 50 100 km of stages 1 and 2 rift systems and 3 within 100 km of noachian stage 1 impact craters 50 km in diameter these geologic preferences explain observations of higher valley source densities vsds in areas of higher elevations and regional slopes 1 because the volcanoes rifts and craters form high steep topography or occur in terrain of high relief other stage 1 and stage 2 high steep terrains however do not show high vsds the tendency for valleys to concentrate near geologic features and the overall low drainage densities in thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation as is proposed in wann wet climate scenarios except perhaps during the early noachian for which much of the geologic record has been obliterated instead volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation melting of ground ice and snow and groundwater sapping however impact crater melt would provide a heat source at the surface that might drive away water fonning valleys in the process post stage 1 craters mostly have low nearby vsds which for valleys incised in older rocks suggests burial by ejecta and for younger valleys may indicate desiccation of near surface water and deepening of the cryosphere later hesperian and amazonian stages 3 and 4 valleys originate within 100 200 km of three young large impact craters and near rifts systems at warrego valles and the southern part of coprates rise these valleys likely developed when the cryosphere was a couple kilometers or more thick inhibiting valley development by hydrothermal circulation however eruption of groundwater may have occurred from impact induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping the two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau in the case of the larger crater lowell 200 km in diameter potential aquifers would likely be at depths of kilometers below the cryosphere seismic energy generated by the lowell impactor would have been much greater pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit along the margin of thaumasia tectonic pressurization of groundwater also may have contributed to valley formation dissection of rim materials of the argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta

inversion migration tomography seismic inversion broadly enough defined is equivalent to doing migration and reflection tomography simultaneously diffraction tomography and inversion work best when sources and receivers surround the region of interest as in medical imaging applications theoretical studies have shown that high vertical wavenumber velocity perturbations are resolved by inverting surface seismic reflection data but the low vertical wavenumbers must be obtained using a separate step such as velocity analysis or reflection tomography i propose that a nonlinear iterative inversion that updates a varying background velocity obtains all wavenumbers that are resolvable separately by migration and tomography the background velocity must contain reflectors to provide data on both upward and downward transmission paths through the earth and hence the low wavenumbers by considering the downward transmission paths to be between surface sources and buried image geophones and the upward transmission paths to be between surfa

stratigraphic analysis of the distributary fan in eberswalde crater using stereo imagery the eroded remains of a fluvial distributary network in eberswalde crater are uniquely well preserved among similar structures on mars a quantitative analysis of the exposed stratigraphy has been performed to investigate the internal structure of the deposit using topographic information derived from stereo pairs of high resolution mars orbiter camera images we have for the first time quantified the orientation of individual layers exposed along the distal end of the distributary network in combination with topographic data from the mars orbiter laser altimeter we have examined plausible scenarios for the formation of this structure we find that the evidence is inconsistent with formation both as an alluvial fan and as a progradational delta instead we find that an aggradational delta best fits the observed characteristics of the channel network and the eberswalde basin as a whole we conclude that the delta likely formed not in a stable long lived lake but over the course of a small number of shorter lacustrine episodes which were not sustained at equilibrium conditions

borehole guided avo analysis of p p and p s reflections quantifying uncertainty on density estimates seismic properties of isotropic elastic formations are characterized by the three parameters acoustic impedance poisson s ratio and density whilst the first two are usually well estimated by analysing the amplitude variation with angle ava of reflected p p waves density is known to be poorly resolved however density estimates would be useful in many situations encountered in oil and gas exploration in particular for minimizing risks in looking ahead while drilling we design a borehole seismic experiment to investigate the reliability of ava extracted density receivers are located downhole near the targeted reflectors and record reflected p p and converted p s waves a non linear wide angle based bayesian inversion is then used to access the a posteriori probability distributions associated with the estimation of the three isotropic elastic parameters the analysis of these distributions suggests that the angular variation of reflected p s amplitudes provides additional substantial information for estimating density thus reducing the estimate uncertainty variance by more than one order of magnitude compared to using only reflected p waves

pyroclastic activity at home plate in gusev crater mars home plate is a layered plateau in gusev crater on mars it is composed of clastic rocks of moderately altered alkali basalt composition enriched in some highly volatile elements a coarse grained lower unit lies under a finer grained upper unit textural observations indicate that the lower strata were emplaced in an explosive event and geochemical considerations favor an explosive volcanic origin over an impact origin the lower unit likely represents accumulation of pyroclastic materials whereas the upper unit may represent eolian reworking of the same pyroclastic materials

the formation of martian river valleys by impacts we explore the role of large impacts in creating the martian valley networks recent dating shows that some large impact basins are contemporaneous with the valley networks the mass deposited and volatiles released by impacts is large and comparable with the mass from the tharsis volcanic construct steam atmospheres formed after large impacts can produce more than 600 m of rainfall followed by rainfall from water vapor greenhouse atmospheres and snowmelt the erosion rates from impacts that created the currently visible craters are somewhat less than the erosion rates suggested for the noachian 4 2 to 3 82 gya there are several possible explanations for this difference and it is possible that erosion rates are overestimated because the burial of small craters by global debris layers from impacts has not been considered rainfall after the noachian was low because the impact rate and co2 pressure declined we suggest tests of the hypothesis that impacts caused the river valleys

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

seismic identification of a karstified reservoir in the adriatic sea in this study an elastic prestack migration inversion m i scheme was applied to a 2 d seismic line collected in the adriatic sea the objective was to use m i images to describe a hydrocarbon reservoir consisting of karstified brine saturated limestones the m i technique offers the benefit of extracting maximum information from seismic reflection data to describe and in some cases characterize the reservoir target m i images are calibrated with well data and represent approximate changes in p and s wave impedances across the reservoir combining these two images yields a poisson s ratio image

characterization of fluvial activity in parana valles using different age dating techniques martian valley networks provide the best evidence that the climate on mars was different in the past although these features are located primarily in heavily cratered terrain of noachian age 3 7 ga the ages of the features and the time when they were active is not well understood from superposed craters several recent global studies determined that most valley networks formed during the late noachian to early hesperian however there were some disparities between the techniques in this study our principal objective was to test the reliability of the different age dating techniques to better understand their accuracy and limitations we applied these techniques to parana valles using a variety of high resolution images taken from different instruments that allow us to identify smaller craters d 125 m while providing sufficient coverage to support a statistically reliable sampling of crater populations which is necessary to reduce the uncertainties in age determination our results indicate that parana valles formed during the early hesperian period but that the crater density d 353 m is heterogeneous inside the parana valles basin the crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub basins the terrain near the source area is late noachian to early hesperian in age while terrains closer to the outlet are early to late hesperian in age crater densities d 125 m inside the valley are also heterogeneous and record several resurfacing events on the valley floor where the width of the valley network narrows to 2 km we found evidence of an amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences our results validate the reliability of several proposed age dating techniques but we also determined the accuracy and applicability of these techniques our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

late alluvial fan formation in southern margaritifer terra mars 1 crater statistics indicate alluvial fans crater floor and fill mantling deposits within impact craters 50 km in diameter in southern margaritifer terra were likely emplaced during multiple epochs fans formed during the amazonian or near the amazonian hesperian boundary crater floor deposits are likely hesperian in age and most fill mantling deposits are amazonian the regional distribution of fans points to a late period of widespread water driven degradation two of the final candidate landing sites for the 2011 mars science laboratory mission would land on or near some of these fans which appear younger than previously considered

supraglacial and proglacial valleys on amazonian mars abundant evidence exists for glaciation being an important geomorphic process in the mid latitude regions of both hemispheres of mars as well as in specific environments at near equatorial latitudes such as along the western flanks of the major tharsis volcanoes detailed analyses of glacial landforms lobate debris aprons lineated valley fill concentric crater fill viscous flow features have suggested that this glaciation was predominantly cold based this is consistent with the view that the amazonian has been continuously cold and dry similar to conditions today we present new data based on a survey of images from the context camera ctx on the mars reconnaissance orbiter that some of these glaciers experienced limited surface melting leading to the formation of small glaciofluvial valleys some of these valleys show evidence for proglacial erosion eroding the region immediately in front of or adjacent to a glacier while others are supraglacial eroding a glacier s surface these valleys formed during the amazonian consistent with the inferred timing of glacial features based on both crater counts and stratigraphic constraints the small scale of the features interpreted to be of glaciofluvial origin hindered earlier recognition although their scale is similar to glaciofluvial counterparts on earth these valleys appear qualitatively different from valley networks formed in the noachian which can be much longer and often formed integrated networks and large lakes the valleys we describe here are also morphologically distinct from gullies which are very recent fluvial landforms formed during the last several million years and on much steeper slopes 20 30 for gullies versus 10 for the valleys we describe these small valleys represent a distinct class of fluvial features on the surface of mars glaciofluvial their presence shows that the hydrology of amazonian mars is more diverse than previously thought

a sedimentary origin for intercrater plains north of the hellas basin implications for climate conditions and erosion rates on early mars understanding the origin volcanic or sedimentary and timing of intercrater plains is crucial for deciphering the geological evolution of mars we have produced a detailed geological map of the intercrater plains north of the hellas basin based on images from the mars express high resolution stereo camera the mars reconnaissance high resolution imaging science experiment and context erosional windows and fresh impact craters provide a way of studying the lithology of intercrater plain units they are composed predominantly of light toned sedimentary rocks with subhorizontal bedding over a broad extent greater than tens of kilometers showing cross bedding stratifications locally the broad extent geometry and flat topography of these sediments favor a formation by aqueous processes alluvial and lacustrine rather than airfall eolian and volcaniclastic the late noachian 3 7 ga sedimentary plains are locally covered by dark toned rough textured lava flows of late hesperian age 3 3 ga fe mg phyllosilicates were detected within sedimentary rocks whereas volcanic rocks contain pyroxene and lack signatures of alteration in agreement with interpretations made from texture and morphology in erosional windows the superimposition of sedimentary rocks by younger volcanic flows enables the estimation of an erosion rate of 1000 nm yr 1 during the hesperian period 3 3 3 7 ga thus our study shows that an intense sedimentary cycle occurred on the northern rim of the hellas basin before and during the late noachian leading to the formation of widespread sedimentary plains which were then eroded in agreement with a gradual change in the climatic conditions in this period and later covered by volcanic flows

noachian hesperian geologic history of the echus chasma and kasei valles system on mars new data and interpretations abstract new high resolution datasets have prompted a mapping based study of the 2500 km long echus chasma and kasei valles system that utilizes geomorphic details stratigraphic relations and cratering statistics derived from the new datasets our results suggest that between the hesperian and amazonian epochs on mars 3 7 ga to recent the study area was affected by at least 4 episodes of widespread volcanic activity and 4 periods of episodic fluvio glacial activity this paper discusses the noachian to hesperian 2 6 ga history of the study area during which time in the hesperian three of the volcanic episodes took place along with the first two episodes of fluvio glacial activity highlights of our new findings and refinements from this time period include 1 two ancient western floods sourced from tharsis that occurred around 3 61 and 3 4 ga and carved the east trending path of north kasei valles 2 uranius dorsum with 58 aligned cones along its length that was emplaced in north kasei around 3 6 ga between these periods of early flooding 3 possible ash deposits surrounding echus chasma one of which contains narrow dendritic valley systems that may have been carved over a period of about 10 000 yr and 4 evidence that suggests glaciers and near surface ice may have contributed to erosion of local units

anisotropic elastic full waveform inversion of walkaway vertical seismic profiling data from the arabian gulf abstract borehole seismic addresses the need for high resolution images and elastic parameters of the subsurface full waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium full waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data multi component measurements anisotropic effects compressional and shear waves and transmitted converted and reflected waves and multiples full waveform inversion therefore has the potential to provide a more accurate result compared with conventional processing methods we present a feasibility study with results of the application of high frequency up to 60 hz anisotropic elastic full waveform inversion to a walkaway vertical seismic profile data from the arabian gulf full waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium

interior channels in martian valleys constraints on fluvial erosion by measurements of the mars express high resolution stereo camera 1 in high resolution stereo camera hrsc images of the mars express mission a 130 km long interior channel is identified within a 400 km long valley network system located in the lybia montes ages of the valley floor and the surroundings as derived from crater counts define a period of 350 myrs during which the valley might have been formed based on hrsc stereo measurements the discharge of the interior channel is estimated at 4800 m3 s corresponding to a runoff production rate of 1 cm day mass balances indicate erosion rates of a few cm year implying the erosion activity in the valley to a few thousand years for continuous flow or one or more orders of magnitude longer time spans for more intermittent flows therefore during the hesperian relatively brief but recurring episodes of erosion intervals are more likely than sustained flow

fluvial and lacustrine activity on layered deposits in melas chasma valles marineris mars 1 valley networks on mars are the most obvious features attesting that different geologic processes and possibly climatic conditions existed in the past themis images reveal valley networks within melas chasma in valles marineris a hesperian age canyon system the valley networks in melas chasma are dense and highly organized and the heads of the valleys are scattered at different elevations all these features suggest that the networks were fed by precipitation the morphological details reveal inner channels on some valley floors attesting that water flowed within these valleys on the dem the valleys flow into a completely enclosed depression the edge of this feature follows a mola contour line and the depression shows many sedimentary morphologies suggesting lacustrine environment these landforms are located on remnants of layered deposits possibly composed of sulfate layers suggesting that fluvial activity could have contributed to the erosion of the layered terrains in valles marineris collectively the features in melas chasma are a maximum of hesperian in age these results suggest that warm wet environmental conditions on mars persisted through the hesperian and were present during the formation of valles marineris the evidence for a paleolake in melas chasma attests to adequate environmental conditions for life development through the hesperian period

extraction of martian valley networks from digital topography 1 we have developed a novel method for delineating valley networks on mars the valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks instead of being manually mapped from images individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters drainage networks are extracted from their underlying basins using the contributing area threshold method we demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency we have applied this method to 28 noachian locations on mars exhibiting prominent valley networks all extracted networks have a planar morphology similar to that of terrestrial river networks they are characterized by a drainage density of 0 1 km 1 low in comparison to the drainage density of terrestrial river networks slopes of streams in martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks this analysis based on a sizable data set of valley networks reveals that although valley networks have some features pointing to their origin by precipitation fed runoff erosion their quantitative characteristics suggest that precipitation intensity and or longevity of past pluvial climate were inadequate to develop mature drainage basins on mars

elastic full waveform inversion of multicomponent ocean bottom cable seismic data application to alba field u k north sea elastic full waveform inversion of multichannel seismic data represents a data driven form of analysis leading to direct quantification of the subsurface elastic parameters in the depth domain previous studies have focused on marine streamer data using acoustic or elastic inversion schemes for the inversion of p wave data in this paper p and s wave velocities are inverted for using wide angle multicomponent ocean bottom cable obc seismic data inversion is undertaken using a two dimensional elastic algorithm operating in the time domain which allows accurate modeling and inversion of the full elastic wavefield including p and mode converted ps waves and their respective amplitude variation with offset avo responses results are presented from the application of this technique to an obc seismic data set from the alba field north sea after building an initial velocity model and extracting a seismic wavelet the data are inverted instages in the first stage the intermediate wavelength p wave v

multiparameter full waveform inversion of multicomponent ocean bottom cable data from the valhall field part 2 imaging compressive wave and shear wave velocities

stratigraphy and paleohydrology of delta channel deposits jezero crater mars abstract the jezero crater open basin lake contains two well exposed fluvial sedimentary deposits formed early in martian history here we examine the geometry and architecture of the jezero western delta fluvial stratigraphy using high resolution orbital images and digital elevation models dems the goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position the delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret from oldest to youngest as 1 point bar strata deposited by repeated flood events in meandering channels 2 inverted channel filling deposits formed by avulsive distributary channels and 3 a valley that incises the deposit we use dems to quantify the geometry of the channel deposits and estimate flow depths of 7 m for the meandering channels and 2 m for the avulsive distributary channels using these estimates we employ a novel approach for assessing paleohydrology of the formative channels in relative terms this analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four fold decrease in the water to sediment discharge ratio we use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the jezero western delta the delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin followed by outlet breaching and eventual erosion of the delta our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the jezero basin without major drops in lake level but also with discrete flooding events at non orbital e g annual to decadal timescales

geomorphic study of fluvial landforms on the northern valles marineris plateau mars 1 fluvial landforms are observed on the plateau near echus chasma and other locations on the valles marineris plateau using high resolution 10 to 50 m pixel mars express images and topography branching valleys have a 20 to 100 m deep v shape profile typical of fluvial processes their incision occurred in a thin 150 m and weak dark unit that overlies the plateau basement the valleys are distributed close to watershed boundaries as expected for overland flows and different from pure glacial or hydrothermal processes the 2d geometry of valley networks show drainage densities reaching 1 3 km 1 that indicate a strong 2d extension stage that usually requires a minimum of thousands of years as established from terrestrial examples however the 3d valley geometry shows a limited incision and a lack of concavity suggesting a limited development in time millions of years of evolution are unlikely many outlets connect to the heads of canyons of echus chasma that might involve sapping processes these canyons might have formed coevally with shallow valleys their difference in geometry is a consequence of the difference in lithology which induced a difference in the erosion capacity and an enhanced infiltration conducing to sapping valleys are submitted to modification by aeolian processes sometimes leading to the formation of inverted channels as observed more broadly through the region these landforms formed late in the early mars history and might be considered as examples of episodic fluvial events due to short term climate changes and or regional fluvial activity after the noachian

information on elastic parameters obtained from the amplitudes of reflected waves seismic amplitude variation with offset data contain information on the elastic parameters of geological layers as the general solution of the inverse problem consists of a probability over the space of all possible earth models we look at the probabilities obtained using amplitude variation with offset avo data for different choices of elastic parameters a proper analysis of the information in the data requires a nontrivial definition of the probability defining the state of total ignorance on different elastic parameters seismic velocities lame s parameters etc we conclude that mass density seismic impedance and poisson s ratio constitute the best resolved parameter set when inverting seismic amplitude variation with offset data

amazonian aged fluvial valley systems in a climatic microenvironment on mars melting of ice deposits on the interior of lyot crater valley networks regional drainage patterns suggesting liquid water stability at the surface are confined to early in the history of mars the noachian hesperian boundary and before prior to a major climate transition to the hyperarid cold conditions of the amazonian several later fluvial valley systems have been documented in specific hesperian and early amazonian environments and are thought to have formed due to local conditions here we describe fluvial valley systems within lyot crater that have the youngest well constrained age reported to date middle or late amazonian for systems of this size tens of km these valleys are linked to melting of near surface ice rich units extend up to 50 km in length follow topographic gradients and deposit fans the interior of lyot crater is an optimal micro environment since its low elevation leads to high surface pressure and temperature conditions at its location in the northern mid latitudes are sufficient for melting during periods of high obliquity this micro environment in lyot apparently allowed melting of surface ice and the formation of the youngest fluvial valley systems of this scale yet observed on mars

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

hack s relation and optimal channel networks the elongation of river basins as a consequence of energy minimization as pointed by hack 1957 river basins tend to become longer and narrower as their size increases this work shows that this property may be partially regarded as the consequence of competition and minimization of energy expenditure in river basins

composition of the drainage network on early mars abstract among the 2208 martian fluvial features plotted in a previous study z geomorphol 37 1 1993 57 the hydrological characteristics of 71 pristine fluvial valley networks located between 18 0 n and 55 0 s were surveyed using viking orbiter photomosaic bases at 1 2 million scale the surveyed networks display 1 systems organized mainly as first order streams 85 of which have lengths not exceeding 1000 km with a large amount of the statistical sample having lengths between 200 and 500 km generally shorter than the degraded valleys studied by baker and partridge j geophys res 91 1986 3561 2 drainage basins with average areas of about 5000 km2 3 a random distribution and 4 headwater tributary drainage densities kd ranging systematically between 0 03 and 0 2 km 1 which are comparable to terrestrial drainage densities in arid climates the compositions of the surveyed pristine valley networks are comparable to the degraded fluvial systems that dissect older martian surface materials thus it appears that no dramatic changes occurred in martian hydrology since the earlier period of formation of the degraded valleys such as described by baker and partridge j geophys res 91 1986 3561 subsurface aquifer drainage may have been a large contributor to drainage basin formation since early in mars history

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

topography of valley networks on mars from mars express high resolution stereo camera digital elevation models 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands the geometry of valley networks can be studied using mars orbiter laser altimeter mola altimetry which is sufficient to map large valleys without a detailed 3 d shape of valley networks imaging from the mars express high resolution stereo camera hrsc is used to generate digital elevation models dems with resolution 50 m and vertical accuracy 60 m we studied valleys near huygens crater and in the aeolis region both in the noachian bedrock and on the west echus plateau in hesperian bedrock hrsc dems in these areas show that 1 drainage density is 3 times higher than is observed in mola data 2 degree of ramification is 1 order more than with mola 3 transverse valley profiles show a v shape more accurately and a minimum depth of 20 m and 4 higher drainage density shows greater headward extension that is not correlated to greater valley depth the deepest valleys 400 m are found in the huygens region where the density in the dem is 0 1 km 1 compared to shallow valleys 100 m of the echus region where the density is higher 0 3 km 1 these regional differences are due to spatially variable preservation and bedrock lithology longitudinal profiles suggest variations in duration of activity profile concavity is only developed in some noachian terrains valleys visible in hrsc images correspond to topographic features in dems showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

multiparameter l 1 norm waveform fitting interpretation of gulf of mexico reflection seismograms estimation of the elastic properties of the crust from surface seismic recordings is of great importance for the understanding of lithology and for the detection of mineral resources although in marine reflection experiments only p waves are recorded information on shear properties of the medium is contained in multioffset reflection seismograms being able to retrieve both dilatational and shear properties gives stronger constraints on the lithology it is therefore desirable to recover isotropic elastic parameters from multioffset seismograms unfortunately most classical waveform fitting methods used for extracting shear properties of the subsurface are based on a 1 d earth model assumption and on linear approximations of the wave equations in this paper a 2 5 d elastic waveform inversion method is used to extract the variations of acoustic impedance and poisson s ratio from marine multioffset reflection seismograms collected in the gulf of mexico area a complete seismic profile is interpreted i

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

scaling relations for large martian valleys 1 the dendritic morphology of martian valley networks particularly in the noachian highlands has long been argued to imply a warmer wetter early martian climate but the character and extent of this period remains controversial we analyzed scaling relations for the 10 large valley systems incised in terrain of various ages resolvable using the mars orbiter laser altimeter mola and the thermal emission imaging system themis four of the valleys originate in point sources with negligible contributions from tributaries three are very poorly dissected with a few large tributaries separated by long uninterrupted trunks and three exhibit the dendritic branching morphology typical of terrestrial channel networks we generated width area and slope area relationships for each because these relations are identified as either theoretically predicted or robust terrestrial empiricisms for graded precipitation fed perennial channels we also generated distance area relationships hack s law because they similarly represent robust characteristics of terrestrial channels whether perennial or ephemeral we find that the studied martian valleys even the dendritic ones do not satisfy those empiricisms on mars the width area scaling exponent b of 0 7 4 7 contrasts with values of 0 3 0 6 typical of terrestrial channels the slope area scaling exponent ranges from 25 6 5 5 whereas values of 0 3 0 5 are typical on earth the length area or hack s exponent n ranges from 0 47 to 19 2 while values of 0 5 0 6 are found on earth none of the valleys analyzed satisfy all three relations typical of terrestrial perennial channels as such our analysis supports the hypotheses that ephemeral and or immature channel morphologies provide the closest terrestrial analogs to the dendritic networks on mars and point source discharges provide terrestrial analogs best suited to describe the other large martian valleys

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

sequence and relative timing of large lakes in gale crater mars after the formation of mount sharp the quantification of lake levels in gale crater is important to define the hydrologic and climatic history experienced by the sedimentary deposits found by curiosity we propose that there were at least three major lake stands within gale each persisted 1000 years and all occurred after mount sharp reached close to its current topographic form deltaic deposits off the southern rim of gale derived from incision of farah vallis and corresponding deposits off the southern flank of mount sharp define the highest lake level which had a mean depth of 700 m canyons similar in form to farah vallis enter into craters and or the crustal dichotomy near gale from the south suggesting that the highest lake was supplied by a large scale flow system the next lake level established after a period of drying and rewetting is defined by four deltaic features three sourced from mount sharp and one from the western rim of gale as well as the termination of gullies around the northern rim of gale this second lake level had a mean depth of 300 m the presence of the gullies suggests more locally sourced water lake levels then rose another 100 m as evidenced by two deltaic deposits derived from the rim of gale and the termination of a second set of gullies post lake reduced hydrologic activity continued evidenced by a time of fan building including peace vallis the sequence of events suggests an episodic shift through time from relatively wet regional conditions to a drier environment with local runoff

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

3d morphometry of valley networks on mars from hrsc mex dems implications for climatic evolution through time 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands eight dense branching valley networks were studied in noachian terrains of huygens newcomb and kepler craters south tyrrhena terra and thaumasia in hesperian terrains of echus plateau and west eberswalde craters and in amazonian terrains of alba patera using images and digital elevation models from the mars express high resolution stereo camera to determine 2d and 3d morphometric parameters extracted geomorphic parameters show similar geometry to terrestrial valleys drainage densities organization from bifurcation ratios and lengths ratios hack exponent consistent with terrestrial values of 0 6 and progressive deepening of valleys with increasing strahler order in addition statistics on valley depths indicate a deeper incision of noachian valleys compared to younger post noachian valleys 100 m for noachian ones showing a strong difference in fluvial erosion these characteristics show that dense martian valley networks formed by overland flows in relation to a global atmospheric water cycle in noachian epoch and confirm that the later stages of activity may be related to shorter duration of activity distinct climatic conditions and or regional processes or conditions

alba patera mars topography structure and evolution of a unique late hesperian early amazonian shield volcano 1 new spacecraft data especially mola topography reveal important characteristics of alba patera that were either unknown or poorly resolved in previous data sets the major and consistent breaks of slope and the specific pattern of lava flows within a broad region around alba patera permit division of this area into two major parts that appear to be related to different episodes of volcanism at alba patera a low lying apron of lava flows that broadly surrounds the edifice a high standing main construct consisting of a central edifice western and eastern flanking lobes and a summit area characterized by a summit plateau and a summit dome topped by a caldera complex volcanic activity apparently began as massive effusive eruptions that formed the broad apron of lava flows followed by more focused effusive eruptions that built the central construct the construct spread gravitationally in a northerly direction to favor e w dike propagation leading to the formation of tharsis montes like flanking lobes the final stages of volcanic activity at alba patera were concentrated in the summit area forming a summit dome 400 km in diameter a caldera complex and two small shields near and inside the caldera which underwent late stage tilting and deformation the load of the newly documented summit dome may have led to the development of alba fossae reactivation of graben within tantalus fossae and tilting of the summit dome to the east a clear sequence in eruptive style is observed early massive sheet flows later tube fed flows and late shorter length and lower volume sheet flows dendritic valley networks on the northern flanks of alba patera have been interpreted to be evidence of easily erodable material of pyroclastic origin but new data suggest that these friable deposits and the valley networks may have formed instead during amazonian climate excursion periods the extensive apron of lava flows combined with the flanking lava lobes and the tharsis montes scale summit dome make alba patera much more similar to the tharsis montes than to the hesperian aged paterae the alba patera lava apron was emplaced on early hesperian ridged plains largely during the middle to late hesperian stratigraphic relationships suggest that effusive eruptions from alba patera interacted with ice rich deposits in the northern lowlands alba patera flanking lobes and the summit dome were emplaced in the earliest amazonian accompanied by late stage loading graben formation and edifice tilting

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

silicate microspherules intercepted in the plume of etna volcano a possible volcanic origin has been suggested for the micrometre sized spherules that have been discovered in polar snows or ice cores1 5 and in the stratosphere6 7 however although such particles especially when black and magnetic have been identified among the tephra deposits of some volcanoes3 8 12 their volcanic emission has never been directly observed here we describe micro spherules intercepted in the plume of mount etna sicily during moderate recurring volcanic activity their study using analytical transmission and scanning electron microscopy atem and asem demonstrates the simultaneous presence in the plume of glassy silicate microspherules of various chemical compositions 47 98 sio2

waveform inversion of marine reflection seismograms for p impedance and poisson s ratio summary the estimation of the elastic properties o the crust from surface seismic recordings is of great importance for an understanding of the lithology and the detection of mineral resources although in marine reflection experiments only p waves are recorded information on shear properties o the medium si contained in the reflection amplitudes recorded at different distances from the source being able to estimate both dialatational and shear properties gives stronger constraints on the lithology it is therefore desirable to recover both types of elastic parameters from multi offset seismograms in the real data example presented here the amplitude of the reflections cannot be explained by one parameter related to the dilatational properties p impedance only when trying to minimize the least squares fit between synthetic and real multi offset seismograms when adding an additional parameter related to the shear properties poisson s ratio the fit between synthetic and real seismograms improves synthetic wavefrom fitting experiments underline the possibility of recovering poisson s ration when the p impedance model is well known from fitting waeveforms recorded at small offsetts in the real data example the resulting models for p impedance and poisson s ratio are anticorrelated in most depth regions but are correlated in particular depth region indicating a sudden change in lithology

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s

lava tubes on earth moon and mars a review on their size and morphology revealed by comparative planetology abstract sinuous collapse chains and skylights in lunar and martian volcanic regions have often been interpreted as collapsed lava tubes also known as pyroducts this hypothesis has fostered a forty years debate among planetary geologists trying to define if analogue volcano speleogenetic processes acting on earth could have created similar subsurface linear voids in extra terrestrial volcanoes on earth lava tubes are well known thanks to speleological exploration and mapping in several shield volcanoes with examples showing different genetic processes inflation and overcrusting and morphometric characters on the moon subsurface cavities have been inferred from several skylights in maria smooth plains and corroborated using gravimetry and radar sounder while on mars several deep skylights have been identified on lava flows with striking similarities with terrestrial cases nonetheless the literature on this topic is scattered and often presents inaccuracies in terminology and interpretation a clear understanding of the potential morphologies and dimensions of martian and lunar lava tubes remains elusive although it is still impossible to gather direct information on the interior of martian and lunar lava tube candidates scientists have the possibility to investigate their surface expression through the analysis of collapses and skylight morphology morphometry and their arrangement and compare these findings with terrestrial analogues in this review the state of the art on terrestrial lava tubes is outlined in order to perform a morphological and morphometric comparison with lava tube candidate collapse chains on mars and the moon by comparing literature and speleological data from terrestrial analogues and measuring lunar and martian collapse chains on satellite images and digital terrain models dtms this review sheds light on tube size depth from surface eccentricity and several other morphometric parameters among the three different planetary bodies the dataset here presented indicates that martian and lunar tubes are 1 to 3 orders of magnitude more voluminous than on earth and suggests that the same processes of inflation and overcrusting were active on mars while deep inflation and thermal entrenchment was the predominant mechanism of emplacement on the moon even with these outstanding dimensions with total volumes exceeding 1 billion of m3 lunar tubes remain well within the roof stability threshold the analysis shows that aside of collapses triggered by impacts tectonics most of the lunar tubes could be intact making the moon an extraordinary target for subsurface exploration and potential settlement in the wide protected and stable environments of lava tubes

quasi cylindrical 2 5d wave modeling for large scale seismic surveys 1 the most common form of seismic exploration remains a nearly linear survey with data acquisition lines including the source and receivers the interpretation of amplitude and waveform information for such linear acquisition requires consideration of 3d seismic wavefields in many scenarios the structure is approximately 2d but still modeling is needed for point sources in recent years 2 5d modeling methods have been developed for the simulation of 3d seismic wavefields in media varying in two dimensions although the computer memory requirements are only slightly larger than those for 2d computations the computation times are too long for ready application to actual surveys to overcome this problem we propose a new approach for modeling 2 5d seismic wavefields using a quasi cylindrical representation we show an implementation of this approach using the finite difference method and demonstrate the validity and efficiency of the technique with numerical examples including a profile across a realistic model of subduction zone structure

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

mars reconnaissance orbiter observations of light toned layered deposits and associated fluvial landforms on the plateaus adjacent to valles marineris abstract we have used data from the mars reconnaissance orbiter to study 30 80 m thick light toned layered deposits on the plateaus adjacent to valles marineris at five locations 1 south of ius chasma 2 south of western melas chasma 3 south of western candor chasma 4 west of juventae chasma and 5 west of ganges chasma the beds within these deposits have unique variations in brightness color mineralogy and erosional properties that are not typically observed in light toned layered deposits within valles marineris or many other equatorial areas on mars reflectance spectra indicate these deposits contain opaline silica and fe sulfates consistent with low temperature acidic aqueous alteration of basaltic materials we have found valley or channel systems associated with the layered deposits at all five locations and the volcanic plains adjacent to juventae ius and ganges exhibit inverted channels composed of light toned beds valleys channels and light toned layering along the walls of juventae and melas chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata although the source of water and sediment remains uncertain the strong correlation between fluvial landforms and light toned layered deposits argues for sustained precipitation surface runoff and fluvial deposition occurring during the hesperian on the plateaus adjacent to valles marineris and along portions of chasmata walls

theoretical background for continental and global scale full waveform inversion in the time frequency domain summary we propose a new approach to full seismic waveform inversion on continental and global scales this is based on the time frequency transform of both data and synthetic seismograms with the use of time and frequency dependent phase and envelope misfits these misfits allow us to provide a complete quantification of the differences between data and synthetics while separating phase and amplitude information the result is an efficient exploitation of waveform information that is robust and quasi linearly related to earth s structure thus the phase and envelope misfits are usable for continental and global scale tomography that is in a scenario where the seismic wavefield is spatially undersampled and where a 3 d reference model is usually unavailable body waves surface waves and interfering phases are naturally included in the analysis we discuss and illustrate technical details of phase measurements such as the treatment of phase jumps and instability in the case of small amplitudes the frechet kernels for phase and envelope misfits can be expressed in terms of their corresponding adjoint wavefields and the forward wavefield the adjoint wavefields are uniquely determined by their respective adjoint source time functions we derive the adjoint source time functions for phase and envelope misfits the adjoint sources can be expressed as inverse time frequency transforms of a weighted phase difference or a weighted envelope difference in a comparative study we establish connections between the phase and envelope misfits and the following widely used measures of seismic waveform differences 1 cross correlation time shifts 2 relative rms amplitude differences 3 generalized seismological data functionals and 4 the l2 distance between data and synthetics used in time domain full waveform inversion we illustrate the computation of frechet kernels for phase and envelope misfits with data from an event in the west irian region of indonesia recorded on the australian continent the synthetic seismograms are computed for a heterogeneous 3 d velocity model of the australian upper mantle with a spectral element method the examples include p body waves rayleigh waves and s waves interfering with higher mode surface waves all the kernels differ from the more familar kernels for cross correlation time shifts or relative rms amplitude differences the differences arise from interference effects 3 d earth s structure and waveform dissimilarities that are due to waveform dispersion in the heterogeneous earth

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

decimetric resolution stochastic inversion of shallow marine seismic reflection data dedicated strategy and application to a geohazard case study characterisation of the top 10 50 m of the subseabed is key for landslide hazard assessment offshore structure engineering design and underground gas storage monitoring in this paper we present a methodology for the stochastic inversion of ultra high frequency uhf 0 2 4 0 khz pre stack seismic reflection waveforms designed to obtain a decimetric resolution re mote elastic characterisation of the shallow sediments with minimal pre processing and lit tle a priori information we use a genetic algorithm in which the space of possible solutions is sampled by explicitly decoupling the short and long wavelengths of the p wave velocity model this approach combined with an objective function robust to cycle skipping outperforms a conventional model parametrisation when the ground truth is offset from the centre of the search domain the robust p wave velocity model is used to precondition the width of the search range of the multi parameter elastic inversion thereby improving the efficiency in high dimensional parametrizations multiple independent runs provide a set of independent results from which the reproducibility of the solution can be estimated in a real dataset acquired in finneidfjord norway we also demonstrate the sensitivity of uhf seismic inversion to shallow subseabed anomalies that play a role in submarine slope stability thus the methodology has the potential to become an important practical tool for marine ground model building in spatially heterogeneous areas reducing the reliance on expensive and time consuming coring campaigns for geohazard mitigation in marine areas

hypsometric analysis of margaritifer sinus and origin of valley networks 1 the formation of martian valley networks has been debated since their discovery the relative roles of groundwater sapping and fluvial runoff processes have different implications on martian paleoclimate this paper uses a hypsometric analysis technique that has been tested on terrestrial landforms to analyze the hypsometric attributes of watershed basins in the margaritifer sinus region on mars using mars orbiter laser altimeter mola gridded topographic data on the basis of quantitative characteristics of their hypsometric attributes the majority of the basins covering 3 5 of the study area look more like terrestrial basins of sapping origin and a significant number of basins covering 1 5 of the study area are more fluvial like the classification of the rest of the basin is less certain at the presently available resolution of the digital elevation model dem overlay with viking photomosaic indicates that the classification is generally consistent with the morphology shown in viking images although this analysis alone cannot make a sure determination of valley network origin combined with other morphometric analysis the results from this study are consistent with a valley network formation by precipitation recharged groundwater sapping suggesting a warm and wet climate for early mars

early mars climate near the noachian hesperian boundary independent evidence for cold conditions from basal melting of the south polar ice sheet dorsa argentea formation and implications for valley network formation currently and throughout much of the amazonian the mean annual surface temperatures of mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold based the documented evidence for extensive and well developed eskers sediment filled former sub glacial meltwater channels in the south circumpolar dorsa argentea formation is an indication that basal melting and wet based glaciation occurred at the south pole near the noachian hesperian boundary we employ glacial accumulation and ice flow models to distinguish between basal melting from bottom up heat sources elevated geothermal fluxes and top down induced basal melting elevated atmospheric temperatures warming the ice we show that under mean annual south polar atmospheric temperatures 100 c simulated in typical amazonian climate experiments and typical noachian hesperian geothermal heat fluxes 45 65mw m 2 south polar ice accumulations remain cold based in order to produce significant basal melting with these typical geothermal heat fluxes the mean annual south polar atmospheric temperatures must be raised from today s temperature at the surface 100 c to the range of 50 to 75 c this mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water and thus does not favor a warm and wet early mars seasonal temperatures at lower latitudes however could range above the melting point of water perhaps explaining the concurrent development of valley networks and open basin lakes in these areas this treatment provides an independent estimate of the polar and non polar surface temperatures near the noachian hesperian boundary of mars history and implies a cold and relatively dry mars climate similar to the antarctic dry valleys where seasonal melting forms transient streams and permanent ice covered lakes in an otherwise hyperarid hypothermal climate 2012 elsevier inc

wave propagation effects on amplitude variation with offset measurements a modeling study wave propagation effects can significantly affect amplitude variation with offset avo measurements these effects include spreading losses transmission losses interbed multiples surface multiple reflections p sv mode converted waves and inelastic attenuation examination of prestack elastic synthetic seismograms suggests that spreading losses and the transmission losses plus compressional interbed multiples are manifest mainly as a time and offset effect on the primary reflections the surface related multiples and the p sv mode converted waves interfere with prestack amplitudes inducing distortions in the avo pattern such distortions cause large variances in avo model fitting prestack viscoelastic synthetic seismograms also suggest that inelastic attenuation further complicates the avo response because of the offset and time variant amplitude decay effects and the phase change due to dispersion together all these effects severely alter avo behavior and result in serious errors in avo parameter

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

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

combined traveltime and frequency domain seismic waveform inversion a case study on multi offset ultrasonic data we present the acquisition and processing of a multi offset ultrasonic tomography experiment in which we aim to precisely reconstruct the image and kinematic properties of two scatterers that contrast strongly with the water background the resultant non linearity causes the failure of a frequency domain waveform fitting strategy for retrieving the whole range of experimentally covered wavenumbers a mixed tomographic approach is instead adopted in which traveltime and waveform inversion are combined iteratively this strategy helps in overcoming the waveform inverse problem non linearity and the data computed in our final tomographic model match most of the observed features in the experimental seismograms this model is in good agreement with what is known concerning the properties of the scatterers and it is characterized by both the high focusing of waveform tomography and the accurate kinematics of traveltime tomography these achievements are reached in spite of a limited but nevertheless uniform geometric coverage our strategy of using two different tomographic tools sequentially therefore appears to be a possible solution to addressing the issue of highly non linear seismic inverse problems

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

arecibo radar imagery of mars ii chryse xanthe polar caps and other regions abstract we conclude our radar imaging survey of mars which maps spatial variations in depolarized radar reflectivity using arecibo s band 12 6 cm observations from 2005 2012 whereas our earlier paper harmon et al 2012 arecibo radar imagery of mars the major volcanic provinces icarus 220 990 1030 covered the volcanic regions of tharsis elysium and amazonis this paper includes non volcanic regions where hydrologic and impact processes can be the dominant resurfacing agents affecting radar backscatter many of the more prominent and interesting radar bright features outside the major volcanic provinces are located in and around chryse planitia and xanthe terra these features are identified with a basin in northeast lunae planum containing the combined deposits from maja vallis and ganges catena outflows channel outwash plains in western and southern chryse basin plateaus bordering chasma chaos zones where surface modification may have resulted from hydrologic action associated with incipient chaos formation and some bright ejecta craters in chryse basin of a type otherwise rare on mars dark halo craters have also been identified in chryse and elsewhere that are similar to those seen in the volcanic provinces although the cratered highlands are relatively radar bland they do exhibit some bright depolarized features these include eroded crater rims several unusual ejecta flows and impact melts and terrain softened plains the rims of large impact basins hellas argyre isidis show a variety of radar bright features provisionally identified with massif slopes erosion sediments eroded pyroclastics impact melts and glacial deposits the interiors of these basins are largely radar dark which is consistent with coverage by rock free sediments tempe terra and acheron fossae show bright features possibly associated with rift volcanism or eroded tectonic structures and northwest tempe terra shows one very bright feature associated with glacial or other ice processes in the dichotomy boundary region the first delay doppler images of the radar bright features from the north and south polar icecaps are presented both poles show the circular polarization inversion and high reflectivity characteristic of coherent volume backscatter from relatively clean ice the south polar feature is primarily backscatter from the residual co 2 icecap with a lesser contribution from the polar layered deposits whose finite optical depth probably accounts for the feature s strong s x band wavelength dependence conversely the north polar radar feature appears to be mostly backscatter from the h 2 o ice rich polar layered deposits rather than from the thin residual h 2 o cap the north polar region shows additional radar bright features from korolev crater and a few other outlying circumpolar ice deposits

phyllosilicates in the mawrth vallis region of mars 1 omega mars express has discovered large outcrops rich in phyllosilicates in the region of mawrth vallis mars around 20 w 25 n the region is located in noachian highly cratered terrains close to the limit of the martian dichotomy where the outflow channel mawrth vallis cuts the highlands we have examined this region using omega spectra of the surface from 0 9 m to 2 6 m with spatial sampling from 500 m to 3 km offering a full coverage of the region omega spectra show two broad bands centered at 1 m and 2 2 m revealing the presence of clinopyroxene on dark surfaces phyllosilicates have been identified by absorption bands at 1 4 m 1 9 m and 2 2 or 2 3 m comparison with laboratory spectra reveals similarities with al oh smectites such as montmorillonites or fe or mg oh smectites such as nontronite a precise location of the phyllosilicate rich areas on visible hrsc images indicates that they are placed exclusively on bright outcrops mostly on the plateaus dated to the noachian period on hrsc and moc images the phyllosilicate rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick the phyllosilicate rich unit corresponds to a geological unit more than 100 m thick over a horizontal extension approximately of 300 km 400 km this unit implies a large volume of altered rocks either in situ or after transport and deposition in noachian terrains revealing a different climatic and geologic environment from the present one

rock magnetic signature of the cretaceous tertiary boundary black magnetic microspherules commonly found in cretaceous tertiary k t boundary sediments and believed to be of an impact melt origin were found to be responsible for a strong magnetic anomaly at the k t boundary in petriccio italy and in almost all deep sea drilling project dsdp sediment cores investigated in which the k t boundary was present the enriched concentrations of magnetic minerals have been detected by measurements of the magnetic susceptibility which is in a good approximation proportional to the magnetic microspherule content a rock magnetic characterization of extracted microspherules by hysteresis isothermal remanent magnetization acquisition demagnetization and thermomagnetic measurements describes the magnetic minerals in the microspherules as ferrites with a near magnetite composition and soft i e multidomain magnetic behavior in agreement with earlier nonmagnetic studies on the contrary volcanic ash from hawaii has distinctively harder magnetic properties an important finding with regard to the proposed alternative a volcanic origin of the well known ir anomaly at the k t boundary it is suggested here that from magnetic susceptibility scanning of numerous cross sections of the k t boundary a distinct worldwide pattern might evolve that can potentially reveal the impact volcano site because of a presumed higher microspherule concentration near the source the advantage of mapping the microspherule distribution over the previous unsuccessful attempt using ir concentrations lies in the large size hundreds of microns of the microspherules with relatively short airborn life times while the iridium might have adhered to small dust particles that circled the globe several times before settling

automated large scale full seismic waveform inversion for north america and the north atlantic we present a new anisotropic seismic tomography model based on a multiscale full seismic waveform inversion for crustal and upper mantle structure from the western edge of north america across the north atlantic and into europe the gradient based inversion strategy utilizes the adjoint state method coupled with an l bfgs quasi newton optimization scheme to improve the handling of large data quantities in the context of full seismic waveform inversions we developed a workflow framework automating the procedure across all stages enabling us to confidently invert for waveforms from 72 events recorded at 7 737 unique stations resulting in a total of 144 693 raypaths most of them with three component recordings the final model after 20 iterations is able to explain complete waveforms including body as well as surface waves of earthquakes that were not used in the inversion down to periods of around 30s the model is complemented by a detailed resolution analysis in the form of 3 d distributions of direction dependent resolution lengths

some effects of velocity variation on avo and its interpretation in recent years interest has increased in the interpretation of the amplitude variation of reflected signals as a function of offset avo a more meaningful relationship for interpreting reflection coefficients at the target horizon is amplitude variation with incident angle ava the challenge is to convert from avo to ava the effects of velocity variation in the overburden on amplitude variation with offset avo and on the final inversion of avo data into velocity density and poisson s ratio can be significant examples are given here for subsurface medium with a vertical velocity gradient range of 0 2s 1 to 0 8s 1 when the medium is treated as homogeneous in the conversion from avo to ava this velocity variation causes significant errors about 10 percent in both the gradient of ava and in the normal incident reflection coefficient such errors produce errors of similar magnitude in the inversion of ava data into the elastic parameters of velocity poisson s ratio and density the errors dep