crustal architecture of central australia based on deep seismic reflection profiling abstract the crustal architecture of central australia is interpreted from deep seismic reflection profiling conducted by the australian geological survey organisation in two surveys in 1985 and 1993 the seismic traverses oriented normal to the main surface structures ran north south in central australia and crossed parts of the arunta block amadeus basin musgrave block and officer basin the present crustal fabric was set in place by the end of the mesoproterozoic by about 1100 ma reactivation of the structures took place in a continental intraplate setting mainly during the middle late palaeozoic alice springs orogeny but also during other orogenic events in the arunta block the crust is dominated by major north dipping planar structures interpreted as thick skinned thrusts many of these thrusts cut deep into the crust and at least one the redbank thrust zone appears to cut and offset the moho in contrast in the northern musgrave block limited field mapping and teleseismic data suggest that the major crustal scale planar structures are south dipping in the central to southern amadeus basin deformation is essentially thin skinned with north directed thrusting confined to the sedimentary succession thus the deep seismic profiles in central australia show a present day crustal architecture that is the response of the crust to mesoproterozoic terrane amalgamation and to later reactivation by intraplate deformational events therefore central australia is a model for intraplate cratonic deformation that occurs in continental crust that is cold thick and strong

modal analysis of the range evolution of broadband wavefields in the north pacific ocean low mode numbers the results of mode processing measurements of broadband acoustic wavefields made in the fall of 2004 as part of the long range ocean acoustic propagation experiment loapex in the eastern north pacific ocean are reported here transient wavefields in the 50 90 hz band that were recorded on a 1400 m long 40 element vertical array centered near the sound channel axis are analyzed this array was designed to resolve low order modes the wavefields were excited by a ship suspended source at seven ranges between approximately 50 and 3200 km from the receiving array the range evolution of broadband modal arrival patterns corresponding to fixed mode numbers modal group arrivals is analyzed with an emphasis on the second variance and third skewness moments a theory of modal group time spreads is described emphasizing complexities associated with energy scattering among low order modes the temporal structure of measured modal group arrivals is compared to theoretical predictions and numerical simulations theory simulations and observations generally agree in cases where disagreement is observed the reasons for the disagreement are discussed in terms of the underlying physical processes and data limitations

windy mars a dynamic planet as seen by the hirise camera 1 with a dynamic atmosphere and a large supply of particulate material the surface of mars is heavily influenced by wind driven or aeolian processes the high resolution imaging science experiment hirise camera on the mars reconnaissance orbiter mro provides a new view of martian geology with the ability to see decimeter size features current sand movement and evidence for recent bedform development is observed dunes and ripples generally exhibit complex surfaces down to the limits of resolution yardangs have diverse textures with some being massive at hirise scale others having horizontal and cross cutting layers of variable character and some exhibiting blocky and polygonal morphologies reticulate fine polygonal texture bedforms are ubiquitous in the thick mantle at the highest elevations

the geology of the viking lander 2 site revisited abstract reevaluating the geologic history of the prior mars landing sites provides important ground truth for recent and ongoing orbital missions at the viking 2 lander vl2 site topographic measurements of relict landforms indicate that at least 100 m of sedimentary mantle material has been stripped away the observed paucity of impact craters

imaging crust and upper mantle seismic structure in the southwestern united states using teleseismic receiver functions rio grande rift seismic transect ristra is designed to image and interpret crust and mantle structures beneath the southwestern united states including the nature of the colorado plateau and rio grande rift figure 1 key questions include the nature of crustal and mantle structures and thermal conditions beneath one of the more dramatic continental rifts on earth and clues to understanding the anomalously unextended colorado plateau which is currently surrounded by the predominantly extensional deformation of the western united states figure 1 regional tectonic map with ristra station locations stars indicate the 54 main transect stations the diamond locates global seismic network borehole station anmo stations tx01 tx06 lie in texas nm07 nm44 in new mexico az45 az50 in arizona and ut51 ut54 in utah the data collecting stage of ristra provided an exceptional 18 months 1999 2001 of broadband streckheisen sts 2 120 s seismometers teleseismic iris passcal data along a 950 km great circle transect of 54 sites with 18 3 6 km station spacing with endpoints near lake powell utah and pecos texas the northwest southeast trending transect was oriented parallel to the azimuth of the very active western pacific seismogenic zones analysis applied to this seismic data set includes surface wave dispersion inversion for crustal and mantle structure teleseismic body wave tomography and teleseismic mantle anisotropy here we discuss the use of ristra data to examine lithospheric structure using p to s mantle and crustal forward scattering observed in the s phases immediately following several tens of seconds the teleseismic p arrival figure 2 we migrate these signals to produce p to s converted mode images of the structure along the ristra array figure 2 global distribution of the 285 earthquakes red points with body wave magnitude 5 6 recorded during the ristra network deployment which have suitable offsets for calculating the 8361 receiver functions used in this study we use teleseisms from epicentral distances of

wave field continuation and decomposition for passive seismic imaging under deep unconsolidated sediments abstract the coastal plains of the central and eastern united states contain deep sections of unconsolidated to poorly consolidated sediments these sediments mask deeper crustal and upper mantle converted phases in teleseismic receiver functions through large amplitude near surface reverberations thick sediments also amplify ambient noise levels to generally reduce data signal to noise ratios removing shallow sediment wave propagation effects is critical for imaging deep lithospheric structures a propagator matrix formalism is used to downward continue the wave field for teleseismic p waves into the midcrust and then to separate the upgoing s wave field from the total teleseismic response of the p wave to expose deep sp conversions this method requires that the earth model from the surface to the reference depth be known teleseismic p wave data for the memphis tennessee station mph are analyzed using a reference station deconvolution technique to produce vertical and radial p wave transfer functions these transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion the inverted earth model is incorporated into the wave field continuation and decomposition technique to estimate the upgoing s wave field at 10 km depth in the crust moho and possible deeper ps conversions are identified with this process

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

deep seafloor arrivals an unexplained set of arrivals in long range ocean acoustic propagation receptions from a ship suspended source in the band 50 100 hz to an ocean bottom seismometer about 5000 m depth and the deepest element on a vertical hydrophone array about 750 m above the seafloor that were acquired on the 2004 long range ocean acoustic propagation experiment in the north pacific ocean are described the ranges varied from 50 to 3200 km in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals leaking below turning points deep seafloor arrivals that are dominant on the seafloor geophone but are absent or very weak on the hydrophone array are observed these deep seafloor arrivals are an unexplained set of arrivals in ocean acoustics possibly associated with seafloor interface waves

stratigraphy of the archean western superior province from p and s wave receiver functions further evidence for tectonic accretion the archean western superior province in canada represents the nucleus of the north american continent whose origin has been speculated to be the result of widespread crustal accretion some 2 7 ga ago in this paper crustal and upper mantle seismic discontinuities beneath the western superior province of the canadian shield are imaged with teleseismic p to s and s to p converted phases using the receiver function method three crustal discontinuities are observed the moho ranging in depth between 38 and 47 km and dipping to the south and two intra crustal discontinuities having depths of approximately 15 and 30 km the crustal discontinuities undulate laterally and often lose continuity possibly indicating an imbricated structure and or regions of velocity gradients in the shallow lithosphere a positive discontinuity is imaged at approximately 65 km depth and is consistent with earlier refraction and wide angle reflection results additionally two zones of negative receiver function amplitudes at 55 km depth are observed and are coincident with a region of anomalous tomographic low p and s wave velocities as well as a zone of high electrical conductivity the images for the crust and shallow upper mantle when integrated with previous geophysical studies are consistent with ideas of continental root formation due to imbrication of archean subducted material and accretion of island arcs observed in surface geology

global duricrust on mars analysis of remote sensing data global remote sensing data for mars are analyzed to obtain a simple self consistent model for the surface layer the data sets discussed include radar cross section measurements at several wavelengths radio whole disk thermal emission observations at two wavelengths the global distribution of thermal inertia deviations of diurnal temperatures from those of a homogeneous model and thermal spectral estimates of surface rock abundance and of the thermal inertia of the nonrocky component of the surface the data sets which most constrain the interpretation are the rock abundance map and the correlation of thermal inertia with radar cross section these require the rock abundance to not vary significantly from place to place and simultaneously require the density and thermal inertia of the fines to vary in a consistent manner the simplest model which can explain all of the data involves a global case hardened crust duricrust which varies spatially in its degree of formation in general low thermal inertia regions have a poorly developed crust and highinertia regions have a well developed crust there are however regions that consist of coarse particles and which do not fit this model e g chryse this model is consistent with the ages of low inertia regions and with aeolian mechanisms for their development the duricrust is thought to form via the mobilization of salt ions within a layer of water adsorbed within the regolith and its formation may be associated with the exchange of water between the regolith and atmosphere which occurs on the 105 and 106 year time scale

turning point filters analysis of sound propagation on a gyre scale acoustic transmissions from pioneer seamount off california to a vertical array near hawaii are analyzed using a technique which we call a turning point filter the observables travel time and axial inclination are interpreted in terms of the ocean sound speed field the method permits a uniform treatment of the arrival pattern from the early ray like arrivals to the late mode like arrivals including peak arrivals which cannot be identified as either rays or modes an adiabatic range dependence is assumed and wentzel kramers brillouin jeffreys formalism is applied

temporal and vertical scales of acoustic fluctuations for 75 hz broadband transmissions to 87 km range in the eastern north pacific ocean observations of scattering of low frequency sound in the ocean have focused largely on effects at long ranges involving multiple scattering events fluctuations due to one and two scattering events are analyzed here using 75 hz broadband signals transmitted in the eastern north pacific ocean the experimental geometry gives two purely refracted arrivals the temporal and vertical scales of phase and intensity fluctuations for these two ray paths are compared with predictions based on the weak fluctuation theory of munk and zachariasen which assumes internal wave induced sound speed perturbations j acoust soc am 59 818 838 1976 the comparisons show that weak fluctuation theory describes the frequency and vertical wave number spectra of phase and intensity for the two paths reasonably well the comparisons also show that a resonance condition exists between the local acoustic ray and the internal wave field as predicted by munk and zachariasen such that only internal waves whose crests are pa

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

depth extent of cratons as inferred from tomographic studies we address the question of the depth extent of mantle high velocity zones under ancient cratons by using seismic velocity maps from recent mantle tomographic studies we divided old continents into two age provinces 800 1700 ma middle proterozoic and older than 1700 ma archean and early proterozoic the areas included in these age provinces are cross correlated with the tomography at different depths to quantify the global occurrence of high velocity anomaly hva extensions beneath cratons statistically significant hvas underlie the oldest cratons to a depth of 250 km there is no significant consistent correlation between tomography and younger cratons the older cratons have correlated hvas extending to depths varying from 100 to 450 km there is no significant difference in the average velocity anomaly beneath the early proterozoic part and the archean part of the canadian shield whereas the middle proterozoic part does not contain any hva the mantle under early precambrian crust is distinctly different from mantle elsewhere we propose two different hypotheses to explain these results 1 cratons of early proterozoic age or older contain ancient and deep physically attached roots or 2 these cratons contain a small permanent physical root that induces cold downwellings beneath it a root thickness of 200 km can be explained by an feo poor olivine rich mineralogy whereas a requirement of high strength probably demands in addition a volatile poor composition different root depths for cratons of similar age may be related to their location in the various supercontinents in which they were involved and to their subsequent deformational history or they may represent different snapshots in time of transient roots such as thermal boundary layers

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

major crustal boundaries of australia and their significance in mineral systems targeting abstract for over 35 years deep seismic reflection profiles have been acquired routinely across australia to better understand the crustal architecture and geodynamic evolution of key geological provinces and basins major crustal scale breaks have been interpreted in some of the profiles and are often inferred to be relict sutures between different crustal blocks as well as sometimes being important conduits for mineralising fluids to reach the upper crust the widespread coverage of the seismic profiles now allows the construction of a new map of major crustal boundaries across australia which will better define the architecture of the crustal blocks in three dimensions it also enables a better understanding of how the australian continent was constructed from the mesoarchean through to the phanerozoic and how this evolution and these boundaries have controlled metallogenesis starting with the locations in 3d of the crustal breaks identified in the seismic profiles geological e g outcrop mapping drill hole geochronology isotope and geophysical e g gravity aeromagnetic magnetotelluric data are used to map the crustal boundaries in plan view away from the seismic profiles some of the boundaries mapped are subsurface boundaries and in many cases occur several kilometres below the surface hence they will not match directly with structures mapped at the surface for some of these boundaries a high level of confidence can be placed on the location whereas the location of other boundaries can only be considered to have medium or low confidence in other areas especially in regions covered by thick sedimentary successions the locations of some crustal boundaries are essentially unconstrained unless they have been imaged by a seismic profile from the mesoarchean to the phanerozoic the continent formed by the amalgamation of many smaller crustal blocks over a period of nearly 3 billion years the identification of crustal boundaries in australia and the construction of an australia wide gis dataset and map will help to constrain tectonic models and plate reconstructions for the geological evolution of australia and will provide constraints on the three dimensional architecture of australia deep crustal penetrating structures particularly major crustal boundaries are important conduits to transport mineralising fluids from the mantle and lower crust into the upper crust there are several greenfields regions across australia where deep crustal penetrating structures have been imaged in seismic sections and have potential as possible areas for future mineral systems exploration

effects of variability associated with the antarctic circumpolar current on sound propagation in the ocean a series of small depth charges was detonated along a transect from new zealand to antarctica over a period of three days in late december of 2006 signals were recorded by hydrophones deployed near the source and at a sparse network of permanent hydrophone stations operated by the international monitoring system ims at distances up to 9 600 km our purpose was to determine how well signal characteristics could be predicted by the world ocean atlas 2005 woa05 climatological database for sources within the antarctic circumpolar current acc where recorded signal to noise ratios are high travel times and signal dispersion are predicted to within two seconds under the assumption that propagation is adiabatic and follows a geodesic path the deflection of the transmission path by abrupt spatial variations in sound speed at the northern acc boundary is predicted to decrease travel times to the ims stations by several seconds depending on the path the accuracy of source locations estimates based only on travel times depends on the monthly or seasonal database used to predict velocities and on whether we account for path deflection the configuration of the ims hydrophones limits source location accuracy within the acc comparison of signal spectra for recordings near the source and at distance show that transmission loss is nearly uniform as a function of frequency

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

mgs tes thermal inertia study of the arsia mons caldera 1 temperatures of the arsia mons caldera floor and two nearby control areas were obtained by the mars global surveyor mgs thermal emission spectrometer tes these observations revealed that the arsia mons caldera floor exhibits thermal behavior different from the surrounding tharsis region when compared with thermal models our technique compares modeled and observed data to determine best fit values of thermal inertia layer depth and albedo best fit modeled values are accurate in the two control regions but those in the arsia mons caldera are consistently either up to 15 k warmer than afternoon observations or have albedo values that are more than two standard deviations higher than the observed mean models of both homogeneous and layered such as dust over bedrock cases were compared with layered cases indicating a surface layer at least thick enough to insulate itself from diurnal effects of an underlying substrate material because best fit models of the caldera floor poorly match observations it is likely that the caldera floor experiences some physical process not incorporated into our thermal model even on mars arsia mons is an extreme environment where co2 condenses upon the caldera floor every night diurnal temperatures range each day by a factor of nearly 2 and annual average atmospheric pressure is only around one millibar here we explore several possibilities that may explain the poor modeled fits to caldera floor and conclude that temperature dependent thermal conductivity may cause thermal inertia to vary diurnally and this effect may be exaggerated by presence of water ice clouds which occur frequently above arsia mons

dark material in the polar layered deposits and dunes on mars viking infrared thermal mapping and bistatic radar data suggest that the bulk density of the north polar erg material is much lower than that of the average martian surface or of dark dunes at lower latitudes we have derived a thermal inertia of 245 280 j m 2 s 1 2 k 1 5 9 6 7 10 3 cal cm 2 s 1 2 k 1 for the proctor dune field and 25 150 j m 2 s 1 2 k 1 0 6 3 6 10 3 cal cm 2 s 1 2 k 1 for the north polar erg the uniqueness of the thermophysical properties of the north polar erg material may be due to a unique polar process that has created them the visible and near infrared spectral reflectance of the erg suggests that the dark material may be composed of basalt or ferrous clays these data are consistent with the dark material being composed of basaltic ash or filamentary sublimate residue fsr particles derived from erosion of the layered deposits dark dust may be preferentially concentrated at the surface of the layered deposits by the formation of fsr particles upon sublimation of water ice further weathering and erosion of these areas of exposed layered deposits may form the dark saltating material that is found in both polar regions dark fsr particles may saltate for great distances before eventually breaking down into dust grains re mixing with the global dust reservoir and being recycled into the polar layered deposits via atmospheric suspension

contrasts in lithospheric structure within the australian craton insights from surface wave tomography abstract contrasts in the seismic structure of the lithosphere within and between elements of the australian craton are imaged using surface wave tomography new data from the wacraton and tigger experiments are integrated with re processed data from previous temporary deployments of broad band seismometers and permanent seismic stations the much improved path coverage in critical regions allows an interpretation of structures in the west of australia and a detailed comparison between different cratonic regions improvements to the waveform inversion procedure and a new multi scale tomographic method increase the reliability of the tomographic images in the shallowest part of the model 75 km a region of lowered velocity is imaged beneath central australia and confirmed by the delayed arrival times of body waves for short paths within the cratonic lithosphere there is clearly structure at scale lengths of a few hundred kilometres resolution tests indicate that path coverage within the continent is sufficient to reveal features of this size in the upper part of our model in western australia differences are seen beneath and within the archaean cratons at depths greater than 150 km faster velocities are imaged beneath the yilgarn craton than beneath the pilbara craton in the complex north australian craton a fast wavespeed anomaly continuing to at least 250 km is observed below parts of the craton suggesting the possibility of archaean lithosphere underlying areas of dominantly proterozoic surface geology

elevation corrected thermal inertia and derived particle size on mars and implications for the tharsis montes one persistent difficulty associated with the interpretation of martian thermal inertia and the derivation of particle size from it has been the degree to which atmospheric properties affect both the energy balance at the surface and the gas conductivity because both these factors vary with atmospheric pressure derivation of thermal inertias and particle sizes must incorporate a correction for elevation here by utilizing currently available thermal models and laboratory data fine component thermal inertia has been combined with topography to compute particle size corrected for these elevation dependent effects the corrected particle sizes at high elevations are as much as 2 orders of magnitude larger than the uncorrected values with the tharsis shield volcanoes generally having inferred sizes larger than dust in contrast to previous interpretations of a thick dust cover this large effective particle size may be a manifestation of the average conductivity produced by a mixture of dust and intervening bedrock outcrops smaller in size than those computed by christensen 1986b in addition the time variable albedo in the upper regions of these volcanoes argues against the presence of large dust deposits

another look at the 1960 perth to bermuda long range acoustic propagation experiment 1 during a 1960 experiment on long range ocean acoustic propagation the signals of explosive shots made near perth australia were recorded by a hydrophone array at bermuda the acoustic paths followed by those pulses are recalculated using a modern atlas for global ocean sound speed the blocking or refractive effects of topographic features besides continents are ignored in this simple calculation no direct path to the hydrophone array is obtained and the array is found to be in the acoustic shadow by 300 400 km the large energy of the 300 lb explosive sound sources required for adequate snr at the receiver also points to a shadowed reception given nominal estimates for temperature warming on the sound channel axis due to climate change the experiment repeated today would give signals that arrive 12 s earlier but this signal could not be reliably measured because of intra annual variability

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

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

stripping of keanakakoi tephra on kilauea volcano hawaii morphological characteristics erosional processes and effects of burial and exhumation by debris mantles on basaltic volcanic landforms have been evaluated through field study of the keanakakoi formation a basaltic tephra formed in 1790 by phreato magmatic eruptions from kilauea caldera hawaii the upper coarse lithic intermediate fine vitric and lower mixed members of this formation play different roles in the creation of micro terrain elements during stripping of tephra from the underlying bedrock of the seven micro terrain elements defined bedrock scabby upland surfaces and lag gravels are the most distinctive and widely distributed different proportions and combinations of micro terrain elements define five zones of progressive deterioration of the keanakakoi tephra blanket southwestward from kilauea caldera into the kau desert fluvial and eolian processes operate on different time scales and at different locations governed by blanket thickness debris caliber and the formation of case hardened crusts stripping of an entire mantle is probably not possible however materials trapped within depressions form the only clearly discernible morphological expression of previously more extensive debris blankets

a test of basin scale acoustic thermometry using a large aperture vertical array at 3250 km range in the eastern north pacific ocean broadband acoustic signals were transmitted during november 1994 from a 75 hz source suspended near the depth of the sound channel axis to a 700 m long vertical receiving array approximately 3250 km distant in the eastern north pacific ocean the early part of the arrival pattern consists of raylike wave fronts that are resolvable identifiable and stable the later part of the arrival pattern does not contain identifiable raylike arrivals due to scattering from internal wave induced sound speed fluctuations the observed ray travel times differ from ray predictions based on the sound speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates suggesting that the equation used to compute sound speed requires refinement the range averaged ocean sound speed can be determined with an uncertainty of about 0 05 m s from the observed ray travel times together with the time at which the near axial acoustic reception ends used as a surroga

the role of porosity in thermal inertia variations on basaltic lavas abstract thermal inertia is inversely proportional to porosity for hawaiian basalts extreme porosities 80 are required if the observed low thermal inertias on the martian shield volcanoes are the result of pristine lava flow surface properties such volcanic surfaces are anticipated to have a short lifetime in the martian environment and an aeolian origin appears to be the most likely interpretation of the thermal measurements on mars

the nature of the crust beneath the afar triple junction evidence from receiver functions the afar depression is an ideal locale to study the role of extension and magmatism as rifting progresses to seafloor spreading here we present receiver function results from new and legacy experiments crustal thickness ranges from 45 km beneath the highlands to 16 km beneath an incipient oceanic spreading center in northern afar the crust beneath afar has a thickness of 20 26 km outside the currently active rift segments and thins northward it is bounded by thick crust beneath the highlands of the western plateau 40 km and southeastern plateau 35 km the western plateau shows vp vs ranging between 1 7 1 9 suggesting a mafic altered crust likely associated with cenozoic flood basalts or current magmatism the southeastern plateau shows vp vs more typical of silicic continental crust 1 78 for crustal thicknesses 2 0 can only be explained by significant amounts of magmatic intrusions in the lower crust this suggests that melt emplacement plays an important role in late stage rifting and melt in the lower crust likely feeds magmatic activity the crust between the location of the miocene red sea rift axis and the current rift axis is thinner 2 0 than beneath the eastern part of afar 26 km vp vs 1 9 this suggests that the eastern region contains less partial melt has undergone less stretching extension and has preserved a more continental crustal signature than west of the current rift axis the red sea rift axis appears to have migrated eastward through time to accommodate the migration of the afar triple junction

testing the limits of virtual deep seismic sounding via new crustal thickness estimates of the australian continent we apply virtual deep seismic sounding vdss to data collected from both permanent and temporary seismic stations in australia with the goal of examining i the resilience of the method to the presence of complex lithospheric structure and ii the effectiveness of different approaches for estimating bulk crustal properties namely thickness and vp data from the permanent wrab in the northern territory station is ideal for benchmarking vdss large number and favourable distribution of recorded earthquakes with the results from several approaches agreeing on a thickness of 40 42 km application of vdss to data from the temporary bilby array a linear distribution of broadband stations that traverses central australia shows that strong moho reflections can be retrieved with as few as two earthquakes even at the transition between crustal blocks of different character and in the presence of thick sedimentary basins crustal thickness varies between 36 54 km and compare well with the reflectivity character of nearby deep seismic reflection lines furthermore we find that off line estimates of crustal thickness calculated by binning the source regions according to back azimuth produce estimates of crustal thickness that are consistent with the regional geology overall we find that vdss is a powerful technique for estimating crustal thickness and velocity due to its insensitivity to complex short wavelength structure and requirement of a small number earthquakes to produce a stable result however not all schemes tested for extracting bulk crustal properties appear to be robust and stringent data quality checking is still required during implementation

multi genetic origin of the continental moho insights from lithoprobe this paper reviews four hypotheses for the origin of the continental crust mantle boundary and discusses seismic parameters with which these hypotheses might be tested the relict moho hypothesis posits that the oceanic moho is preserved during continental assembly the magmatic underplating hypothesis posits formation of a new moho by episodic emplacement of sill like intrusive bodies the metamorphic or metasomatic front hypothesis posits that the moho is overprinted by a phase transformation and the regional decollement hypothesis posits that the moho behaves as a structural detachment these hypotheses are not mutually exclusive and examples from the canadian lithoprobe program suggest that all four may be applicable in different regions of north america comparison of seismic images from a fossil subduction zone with modern subduction at cascadia suggests that serpentinization of the forearc mantle a previously unrecognized mechanism for overprinting and erasing the reflection moho may have occurred in the proterozoic

assessing the horizontal refraction of ocean acoustic tomography signals using high resolution ocean state estimates the analysis of signals for acoustic tomography sent between a source and a receiver most often uses the unrefracted geodesic path an approximation that is justified from theoretical considerations relying on estimates of horizontal gradients of sound speed or on simple theoretical models to quantify the effects of horizontal refraction caused by a realistic ocean environment horizontal refractions of long range signals were computed using global ocean state estimates for 2004 from the estimating the circulation and climate of the ocean ecco2 project basin scale paths in the eastern north pacific ocean and regional scale paths in the philippine sea were used as examples at o 5 mm basin scales refracted geodesic and geodesic paths differed by only about 5 km gyre scale features had the greatest refractive influence but the precise refractive effects depended on the path geometry with respect to oceanographic features refraction decreased travel times by 5 10 ms and changed azimuthal angles by about 0 2 at o 500 km regional scales paths deviated from the geodesic by only 250 m and travel times deviated by less than 0 5 ms such effects are of little consequence in the analysis of tomographic data refraction details depend only slightly on mode number and frequency

on the time mean state of ocean models and the properties of long range acoustic propagation 1 receptions on three vertical hydrophone arrays from basin scale acoustic transmissions in the north pacific during 1996 and 1998 are used to test the time mean sound speed properties of the world ocean atlas 2005 woa05 of an eddying unconstrained simulation of the parallel ocean program pop and of three data constrained solutions provided by the estimating the circulation and climate of the ocean ecco project a solution based on an approximate kalman filter from the jet propulsion laboratory ecco jpl a solution based on the adjoint method from the massachusetts institute of technology ecco mit and an eddying solution based on a green s function approach from ecco phase ii ecco2 predictions for arrival patterns using annual average woa05 fields match observations to within small travel time offsets 0 3 1 0 s predictions for arrival patterns from the models differ substantially from the measured arrival patterns from the woa05 climatology and from each other both in terms of travel time and in the structure of the arrival patterns the acoustic arrival patterns are sensitive to the vertical gradients of sound speed that govern acoustic propagation basin scale acoustic transmissions therefore provide stringent tests of the vertical temperature structure of ocean state estimates this structure ultimately influences the mixing between the surface waters and the ocean interior the relatively good agreement of the acoustic data with the more recent ecco solutions indicates that numerical ocean models have reached a level of accuracy where the acoustic data can provide useful additional constraints for ocean state estimation

wind streaks in tharsis and elysium implications for sediment transport by slope winds detailed maps of wind streaks in tharsis and elysium have been compiled from viking orbiter observations spanning one complete martian year the streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the tharsis bulge while the global circulation dominates in elysium dust erosion by downslope winds occurs over much of tharsis and in the vicinity of elysium mons this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes erosional streaks are largely absent in elysium planitia net deposition of dust might have occurred during the period of our observations surface properties such as slope thermal inertia and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions

thick crust beneath the ordos plateau implications for instability of the north china craton abstract surrounded by seismicity and other manifestations of active deformation the ordos plateau or the western portion of the north china craton ncc is a uniquely stable terrane in asia results from virtual deep seismic sounding and crustal receiver functions suggests that the crust under the eastern ordos is thicker at least 60 km than expected from previous studies and from its modest elevation 1500 m above sea level receiver functions also reveal a pronounced elastic impedance contrast within the crust at 40 km depth which we interpret as the conrad discontinuity the presence of a 20 km thick layer of mafic lower crust between the conrad and moho discontinuities would maintain crustal isostasy the 1000 km long seismic profile from the ordos plateau in the west to the north china basin in the east reveals that crustal thickness changes by almost a factor of two across the active shanxi rift in central ncc over a distance of only about 100 km insofar the current configuration of the lithosphere under the ordos plateau might serve as a proxy for the initial condition prior to reactivation of the eastern part of ncc where a cratonic keel no longer seems to exist our results support the hypothesis that lower crust foundering was due to transformation of a thick mafic lower crust to a garnet rich assemblage possibly caused by hydration associated with subduction during and or before mid mesozoic times

atmospheric effects on the mapping of martian thermal inertia and thermally derived albedo we examine the effects of a dusty co2 atmosphere on the thermal inertia and thermally derived albedo of mars and we present a new map of thermal inertias this new map was produced using a coupled surface atmosphere csa model dust opacities from viking infrared thermal mapper irtm data and co2 columns based on topography the csa model thermal inertias are smaller than the 2 model thermal inertias with the difference largest at large thermal inertia although the difference between the thermal inertias obtained with the two models is moderate for much of the region studied it is largest in regions of either high dust opacity or of topographic lows including the viking lander 1 site and some geologically interesting regions the csa model thermally derived albedos do not accurately predict the irtm measured albedos and are very similar to the thermally derived albedos obtained with models making the 2 assumption

mode coherence at megameter ranges in the north pacific ocean this article analyzes the coherence of low mode signals at ranges of 3515 and 5171 km using data from the acoustic thermometry of ocean climate atoc and alternate source test ast experiments vertical line arrays at hawaii and kiritimati received m sequences transmitted from two sources the 75 hz bottom mounted atoc source on pioneer seamount and the near axial dual frequency 28 84 hz ast source deployed nearby this study demonstrates that the characteristics of the mode signals at 5171 km range are quite similar to those at 3515 km range at 75 hz the mode time spreads are on the order of 1 5 s implying a coherence bandwidth of 0 67 hz the time spread of the 28 hz signals is somewhat lower but these signals show significantly less frequency selective fading than the 75 hz signals suggesting that at the lower frequency the multipaths are temporally resolvable coherence times for mode 1 at 75 hz are on the order of 8 min for the 3515 km range and 6 min for 5171 km range at 28 hz mode 1 is much more stable with a magnitude squared coherence of greater than 0 6 for the 20 min transmission period

the burning heart the proterozoic geology and geological evolution of the west musgrave region central australia the musgrave province is one of the most geodynamically significant of australia s proterozoic orogenic belts lying at the intersection of the continent s three cratonic elements the west north and south australian cratons while remoteness and cultural sensitivity have slowed geological research into this region recent collaborative programs in western australia the west musgrave province have done much to address this this focus review provides a synthesis of this and previous work investigating the mesoproterozoic to neoproterozoic geological evolution of the province the musgrave province is a mesoproterozoic to neoproterozoic belt dominated by granites formed and deformed during several major events a cryptic juvenile basement is exposed mainly in the east musgrave province as c 1600 1550 ma orthogneiss and in the west musgrave province as isolated outcrops of granulite facies metagranites of the c 1575 ma warlawurru supersuite zircon hf isotopic data suggest an earlier major juvenile crust forming event at c 1950 1900 ma there is however no evidence that the province evolved over archean crust the c 1600 1550 ma period probably involved evolution within a primitive arc setting perhaps developed on c 1950 1900 ma oceanic or oceanic arc crust voluminous calc alkaline plutonism was accompanied by clastic and volcaniclastic basin formation during the 1345 1293 ma mount west orogeny this stage traced the evolution of a continental arc reflecting the final amalgamation of the combined north and west australian craton with the south australian craton the intervening c 1400 ma primitive crust the madura province on which the proto musgrave province had evolved was consumed during amalgamation the thickened crust resulting from this accretion was drastically thinned at the beginning of the c 1220 1150 ma musgrave orogeny as this central part of the new combined craton entered an extraordinary period of high heat flow characterised by c 100 m y of ultrahigh temperature metamorphism and high temperature anhydrous alkali calcic magmatism sourced from mash chambers developed at the base of the thinned crust the ridged cratonic architecture and a massive accumulation of high radiogenic heat producing granites within the mid crust perpetuated a thin crustal regime voluminous magmatism was again triggered during the c 1090 1040 ma giles event with the evolution of the magmatism dominated ngaanyatjarra rift this event was likely initiated through renewed movement along translithospheric faults that intersected the thermally perturbed musgrave province pinned at a cratonic junction mantle derived bimodal magmatism extended more or less continuously for 50 m y producing one of the world s largest layered mafic intrusions and supervolcano sized additions of juvenile felsic crust in the form of alkali calcic to alkali a type rhyolite deposits together the albany fraser orogen which developed over the southern margin of the west australian craton and the musgrave province mark the preserved edge of the north and west australian craton these two belts show remarkable chronological links between c 1345 and 1150 ma but contrasting histories before and after that period their period of shared evolution reflects collision and accretion of the south australian craton but their tectonic setting and basement geology throughout that event were very different