two mars years of surface changes seen at the viking landing sites color and brightness changes have occurred at both viking landing sites during the first two mars years of the lander mission the contrast between adjacent soil units decreased and the surface generally became brighter and redder these changes are attributed to the deposition of a layer of bright red dust that is most likely only several micrometers in thickness analysis of the spectrophotometric properties of the new dust deposited at the viking lander 1 site suggests that the new deposits are the same as the bright red material that only partially covered the site at the beginning of the mission certain areas of the viking 1 site also exhibited an increase in contrast during the second year the contrast increase is interpreted to be due to the partial removal of the recently deposited dust cover by high velocity winds in addition a small soil slump occurred near the base of a boulder located about 25 m from viking lander 1 no obvious erosion has been detected at the viking 2 site however periodic removal of the dust cover at the viking 2 site is implied by the abundance of rocks at the site

hydrothermal venting at hinepuia submarine volcano kermadec arc understanding magmatic hydrothermal fluid chemistry the hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast with an active cone complex in the se hinepuia is one of several active volcanoes in the northern segment of the kermadec arc regional magnetic data shows no evidence for large scale hydrothermal alteration at hinepuia yet plume data confirm present day hydrothermal discharge suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal gravity data are consistent with crustal thinning and shallow mantle under the volcanic center following the discovery of hydrothermal plumes over hinepuia the submersible shinkai 6500 was used to explore the se cone and sample hydrothermal fluids the chemistry of hydrothermal fluids from submarine arc and backarc volcanoes are typically dominated by water rock interactions and or magmatic degassing chemical analyses of vent fluids show that hinepuia does not quite fit either traditional model moreover the hinepuia samples fall between those typically ascribed to both end member fluid types when plotted on a k mg so4 ternary diagram due to evidence of strong degassing abundant native sulfur deposition and h2s presence the vent sampled at hinepuia is ultimately classified as a magmatic hydrothermal system with a water rock influence this vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation magmatic hydrothermal fluid chemistry appears to be controlled by a combination of gas flux phase separation processes and volcano evolution and or distance from the magma source

crustal features along a w e tyrrhenian transect from sardinia to campania margins central mediterranean abstract the tyrrhenian sea is a neogene back arc basin formed by continental extension at the rear of the eastward migrating apennine subduction system its central part generated from tortonian to pliocene includes the sardinia rifted margin to the west an area with large volcanoes in the deep central sector and the campania rifted margin to the east a reprocessing of some 2000 km of mcs lines a new swath bathymetric map and a review of previous geological and geophysical data allow to analyse the nature and distribution of continental vs oceanic crust in this area which evolved in a short time span the central portion of the southern tyrrhenian sea is characterized by moho at about 10 km depth north of magnghi and vavilov smts this thinned crustal domain include a wide continent ocean transition with the occurrence of extensional allochthons and of serpenitinzed sub continental mantle recalling other well known rifted margins as the iberia one sectors floored by oceanic crust should occur mainly in the southern part of the study area but they do not appear related to discrete spreading ridges the continent ocean boundary cannot be drawn unequivocally in the area due also to the occurrence of widespread and huge magmatic manifestations not related to oceanic spreading these portions of the southern tyrrhenian sea represents therefore a complex oceanic back arc basin surrounded by magma rich rifted continental margins the abundant igneous manifestations and the very high stretching rates observed in the area may be related to the fact that the present tyrrhenian area was occupied by an orogenic domain affected by shortening until middle miocene times which is just before the late miocene onset of back arc extension the lithosphere in the region had then to be rheologically weak abundant generation and ascent of magmas mostly of ocean island basalt type was favoured by the large lithospheric permeability induced by strong extensional deformations

interpretation of gravity and magnetic anomalies at lake rotomahana geological and hydrothermal implications abstract we investigate the geological and hydrothermal setting at lake rotomahana using recently collected potential field data integrated with pre existing regional gravity and aeromagnetic compilations the lake is located on the southwest margin of the okataina volcanic center haroharo caldera and had well known pre 1886 tarawera eruption hydrothermal manifestations the famous pink and white terraces its present physiography was set by the caldera collapse during the 1886 eruption together with the appearance of surface activities at the waimangu valley gravity models suggest that subsidence associated with the haroharo caldera is wider than the previously mapped extent of the caldera margins magnetic anomalies closely correlate with heat flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of lake rotomahana are characterized by a large well developed hydrothermal field the field extends beyond the lake area with deep connections to the waimangu area to the south on the south the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat flux and bubble plumes which suggest hydrothermal activity occurring west of patiti island the absence of a well defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 tarawera eruption locally confined intense magnetic anomalies on the north shore of lake rotomahana are interpreted as basalt dikes with high magnetization some appear to have been emplaced before the 1886 tarawera eruption a dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the patiti geothermal system and could have been originated from the 1886 tarawera eruption

upper mantle structure below the european continent constraints from surface wave tomography and grace satellite gravity data 1 we here exploit fundamental mode rayleigh and love seismic wave information and the high resolution satellite global gravity model ggm02c to obtain a 1 1 3 d image of a upper mantle isotropic shear wave speeds b densities and c density vscoupling below the european plate 20 n 90 n 40 w 70 e the 3 d image of the density vscoupling provides unprecedented detail of information on the compositional and thermal contributions to density structures the accurate and high resolution crustal model allows us to compute a reliable residual topography to understand the dynamic implications of our models the correlation between residual topography and mantle residual gravity anomalies defines three large scale regions where upper mantle dynamics produce surface expression the east european craton the eastern side of the arabian plate and the mediterranean basin the effects of mantle convection are also clearly visible at 1 the eastern sirt embayment 2 the west african craton northern margins 3 the volcanically active region of the canarian archipelago 4 the northern edge of the central european volcanic province and 5 the northeastern part of the atlantic ocean between greenland and iceland strong connections are observed among areas of weak radial anisotropy and areas where the mantle dynamics show surface expression although both thermal and additional dependencies have been incorporated into the density model convective down welling in the mantle below the east european craton is required to explain the strong correlation between the estimated negative mantle residual anomalies and the negative residual topography

geophysical modeling of collapse prone zones at rumble iii seamount southern pacific ocean new zealand 1 catastrophic collapses of submarine volcanoes have the potential to generate major tsunami threatening many coastal populations recognizing the difficulties surrounding anticipations of these events quantitative assessment of collapse prone regions based on detailed morphological geological and geophysical mapping can still provide important information about the hazards associated with these collapses rumble iii is one of the shallowest and largest submarine volcanoes found along the kermadec arc and is both volcanically and hydrothermally active previous surveys have delineated major collapse features at rumble iii based on time lapse bathymetry dramatic changes in the volcano morphology have been shown to have occurred over the interval 2007 2009 furthermore this volcano is located just 300 km from the east coast of the north island of new zealand here we present a geophysical model for rumble iii that provides the locations and sizes of potential weak regions of this volcano shipborne and near seafloor geological and geophysical data collected by the auv sentry are used to determine the subsurface distribution of weak and unstable volcanic rocks the resulting model provides evidence for potentially unstable areas located in the southeastern flank of this volcano which should be included in future hazard predictions

martian surface properties indicated by the opposition effect abstract opposition measurements made by the viking orbiter television cameras in the arabia syrtis major and elysium planitia regions have been combined with observations previously reported to provide a photometric comparison of these areas and several generic features radiative transfer expressions were used to derive average surface particle single scattering albedos phase functions and porosities best functional fit to the data includes consideration of atmospheric scattering two particle populations and surface roughness several findings include the ubiquitous presence of high albedo high porosity surface particles the absence of an opposition surge in the syrtis major region and the largest surface roughness in the chryse areas

the two stage opening of the western central mediterranean basins a forward modeling test to a new evolutionary model abstract the algero provencal and the tyrrhenian extensional basins developed in two stages in a geodynamic setting characterized by the nearly n s convergence between africa and eurasia the spreading of the provencal basin occurred in the early miocene following a long period of rifting in the western mediterranean area a dramatic eastward shift of the active extensional deformation resulted in the tortonian to quaternary opening of the tyrrhenian basin in a companion paper carminati et al propose that a trench retreat process in a geodynamic setting locked by the continental collisions in the alps and in the betic chain is a viable mechanism for the late oligocene early langhian opening of the western mediterranean a langhian slab detachment episode along the north african margin is likely to have caused the end of the trench retreat along this part of the boundary determining the end of active expansion in the western mediterranean and the beginning of active extension in the tyrrhenian basin the objective of the present paper is to quantitatively test this proposed scenario we calculate by means of a thin shell model the effects of these plate boundary reorganizations on the european stress and strain field we show that the two stage opening of the western and central mediterranean can be explained by the evolution proposed by carminati et al and that in particular the eastward shift of the active extension which produced the termination of the first opening stage and the beginning of the second is likely to have been triggered by the slab detachment episode along the north african margin

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

joint inversion methods with relative density offset correction for muon tomography and gravity data with application to volcano imaging muography is a relatively new geophysical imaging method that uses muons to provide estimates of average densities along particular lines of sight muography can only see above the horizontal elevation of the detector and it is therefore attractive to attempt a joint inversion of muography data with gravity data which is also responsive to density but generally requires combination with another geophysical data set to overcome issues related to non uniqueness and poor depth resolution some previous work has investigated this joint inverse problem and demonstrated the potential improvements to be gained by jointly inverting muography and gravity data however there has yet to be a thorough investigation of different numerical approaches for formulating the joint inverse problem particularly important is how to account for the fact that even though the two data types are sensitive to the same physical quantity density they respond through different response functions moreover the two measurements are affected by different systematic uncertainties that are difficult to model in this work we considered an approximation where the two density quantities inferred from the two data types can be related by an unknown scalar offset we considered various existing and new joint inversion methods that might solve this problem and we applied them to a synthetic volcano imaging scenario based on the puy de dome volcano in the central massif region of france we used unstructured meshes in our modelling to adequately honour the significant topography in that scenario our experiments indicated that the most successful joint inversion method for this type of geological scenario was one in which the data misfit function is reformulated to automatically determine the best fitting offset following a least squares minimization argument however other approaches showed merit and we suggest several of the investigated methods be applied and compared for any specific joint inversion scenario

crustal model for the middle east and north africa region implications for the isostatic compensation mechanism summary we present a new 3 d crustal model for the middle east and north africa region that includes detailed topography sediment thickness and moho depth values the model is obtained by collecting integrating and interpolating reliable published sedimentary rock thickness and moho depth measurements in the middle east and north africa region to evaluate the accuracy of the model the 3 d gravity response of the model is calculated and compared with available observed bouguer gravity anomalies in the region the gravity modelling shows that the new crustal model predicts large portions of the observed bouguer anomalies however in some regions such as the red sea and caspian sea regions where crustal structure is relatively well determined the residual anomalies are of the order of a few hundred milligals since the new crustal model results in large residual anomalies in regions where reasonably good constraints exist for the model these large residuals cannot simply be explained by inaccuracies in the model to analyse the cause of these residuals further we developed an isostatically compensated airy type moho depth model and calculated its gravity response isostatic gravity anomalies are in nearly perfect agreement with the observed gravity values however the isostatic model differs significantly from the new 3 d crustal model if isostasy is to be maintained crustal and or upper mantle lateral density variations are needed to explain the large observed gravity residuals

bouguer density determination by fractal analysis density values for the bouguer reduction of two gravity data sets from iceland are determined using a new method based on minimization of the roughness of the bouguer anomaly surface the fractal dimension of the surface is used as a gauge of the roughness the analysis shows the size of topographic features supported by crust without isostatic compensation to be 25 to 30 km in southwest iceland and 9 to 10 km inside the active rifting zone the densities selected for these areas are 2490 and 2730kg m3 respectively

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

daily temperature variations on mars the viking infrared thermal mapper irtm has measured the infrared brightness temperature of mars for more than a full martian year the daily variation of the 20 m brightness temperature can be predicted to within 5 k for most of the martian surface during any season if the radiometric albedo and the thermal inertia of the model are allowed to increase with increasing atmospheric dust opacity however for approximately 32 of the martian surface area no values of thermal inertia or albedo can fit the thermal observations these temperature anomalies isolate one large region on mars which connects the low thermal inertia regions of arabia tharsis and elysium the anomalies do not correlate with elevation geologic units morphology or atmospheric dust content all regions with lambert albedo less than 0 18 can be well fit with the standard thermal model but all areas with albedo greater than 0 28 are anomalous there is a strong inverse correlation between the magnitude of the anomaly and the thermal inertia this correlation indicates that some surface property is responsible for the anomaly in the anomalous region the observed temperatures are warmer in the morning cooler late in the afternoon and decrease more slowly during the night than the viking model temperatures of all the physical processes likely to occur on mars but not included in the viking thermal model only a layered soil can explain the observations a low thermal inertia layer covering a high thermal inertia material will heat up quickly in the morning and cool down quickly in the afternoon at night the high thermal inertia material will moderate the temperature a possible interpretation for the layering deduced from the irtm observations is a layer of aeolian deposited dust about one thermal skin depth thick 1 to 4 cm covering a duricrust because dust accumulates in some areas after every global dust storm the duricrust must be actively forming a one thermal skin depth dust layer covering a duricrust is compatible with viking lander observations irtm spectral observations and viking orbiter imaging

crustal thickness beneath libya and the origin of partial melt beneath as sawda volcanic province from receiver function constraints this study investigates crustal thickness and properties within the libyan region results obtained from 15 seismic stations belonging to the libyan center for remote sensing and space science are reported in addition to 3 seismic stations publically available using receiver functions the results show crustal thicknesses ranging from 24 km to 36 km with uncertainties ranging between 0 10 km to 0 90 km more specifically crustal thickness ranges from 32 km to 36 km in the southern portion of the libyan territory then becomes thinner between 24 km and 30 km in the coastal areas of libya and thinnest between 24 km and 28 km in the sirt basin the observed high vp vs value of 1 91 at one station located at the as sawda volcanic province in central libya indicates the presence of either partial melt or an abnormally warm area this finding suggests that magma reservoirs beneath the libyan territory may still be partially molten and active thereby posing significant earthquake and volcanic risks the hypothesis of an active magma source is further demonstrated though the presence of asthenospheric upwelling and extension of the sirt basin this study provides a new calculation of unconsolidated sediment layers by using the arrival time of the p to s converted phases the results show sediments thicknesses of 0 4 km to 3 7 km with the vp vs values ranging from 2 2 to 4 8 the variations in crustal thickness throughout the region are correlated with surface elevation and bouguer gravity anomalies which suggest that they are isostatically compensated

transfer zones in an oblique back arc basin setting insights from the latium campania segmented margin tyrrhenian sea new multichannel seismic reflection profiles were acquired to unravel the structure of a portion of the eastern margin of the tyrrhenian basin this extensional feature is part of an oligocene to present back arc basin in the hangingwall of the west directed apennines subduction system the basin provides excellent conditions to investigate the early stage processes leading to the development of rifted passive margins and to the emplacement of oceanic crust in an oblique setting the interpreted post stack migrated seismic profiles highlight the geometry and kinematics of the pontine escarpment that connects the latium campania continental margin to the vavilov basin the latter is the main feature of the area related to the early pliocene extension of the tyrrhenian sea several morphological variations are pointed out along strike mirroring different structural settings of the margin itself a steeper margin to the north corresponds to high angle possibly transtensional faults whereas a smooth slope in the southern portion corresponds to several more distributed listric faults this work contributes to the understanding of the interplay between extensional and transtensional tectonics along the margins of an oblique back arc basin

present wind activity on mars relation to large latitudinally zoned sediment deposits the relation of present martian winds to large latitudinally zoned sediment deposits has been investigated using global wind streak data and mapping of large sand and dust deposits dune sand deposits occur primarily in three latitude belts north polar 74 85 degrees north low latitude 5 degrees north 20 degrees south and south polar 40 80 degrees south comparison with wind streak data shows the high latitude dunes to be in areas of seasonally reversing winds the present winds can form latitudinal dune belts from a variety of initial dune distributions including uniform distribution and a polar source the presence of dune sand within the polar layered deposits the erosional state of the deposits and the present surface wind flow away from the poles indicate that both polar dune concentrations have been derived from erosion of the layered deposits the low latitude dunes are topographically confined in canyons and craters they are probably subject to long term reversal of orientations with climate cycles

integrated crustal model beneath the po plain northern italy from surface wave tomography and bouguer gravity data abstract to obtain a 3 d crustal density and shear wave velocity structure beneath the po plain we exploit seismic records gathered from 2006 to 2014 and bouguer gravity data assembled for the last estimation of the italian geoid 2 d maps for both love and rayleigh fundamental mode at periods between 4 and 20 s are obtained applying a tomographic inversion the defined local dispersion curves are then jointly inverted using a linearized scheme to obtain a 3 d isotropic shear wave velocity model across the po plain region the model transformed into density through a priori velocity density relationships is then the input of the sequential integrated inversion algorithm which enables us to recover a new 3 d density shear wave velocity coupling and inferences on the lithology and tectonics low and fast s wave velocities are highlighted for the shallow pliocene quaternary sediments along the foredeep in front of the northern apennines and for the presence of limestone units in the upper crust respectively whereas sediment trends seem to be consistent with the results obtained the mesozoic carbonates which are inherently characterized by high variability are less resolved a major result is the recovery of a high speed 3 3 km s density 2 2 kg m3 structure in the upper crust 6 10 km localized beneath the arcuate po plain thrust front expanding from the external margin of the ferrara arc toward the alps and the adriatic sea at the boundaries of this brittle body we locate earthquakes of the emilia 2012 seismic sequence and the historical seismicity mapping lateral discontinuities in density and shear wave velocity could provide insights in defining strengthening and weakening zones and in focusing on transition zones often prone to earthquakes

a deterministic approach toward isostatic gravity residuals a case study from south america a new deterministic method for correcting isostatic effects in gravity data sets overcomes the deficiencies of empirically based methods this technique produces a superior gravity image for south america and has application to other continental scale gravity data sets the basis for the correction is the airy heiskanen isostatic model which assumes that surface topography is supported by crustal thickening the three key parameters 1 the crustal thickness at sea level 2 the surface reduction density and 3 the density contrast between the crust and the mantle are determined directly from the elevation free air gravity and bouguer gravity data sets the surface density parameter of 2 60 g cc is determined using a new fractal technique this technique assumes that the topography is fractal the best value for density is that which minimizes the fractal component caused by topographic effects the new value is substantially different than the 2 67 g cc density assumed by many previous workers for most continental scale data sets the crust mantle density contrast parameter of 0 45 g cc is determined by comparison between the densities determined from crossplots of the bouguer values versus elevation the crustal thickness parameter of 30 km is determined using a spectral method applied to the free air gravity the results of this work are not only an isostatic residual map but a methodology that cross checks the data for quality control the final isostatic residual map can be used with confidence for basin evaluation throughout the continent of south america basins at high elevations like the eastern foreland basins of the andes and the altiplano basin are imaged better by using this method

determining the optimal bouguer density for a gravity data set implications for the isostatic setting of the mediterranean sea summary we have used free air gravity satellite data from geosat and ers 1 missions to compile a bouguer gravity map of the mediterranean sea the complete bouguer correction has been applied by using the method of parker that acts in the fourier domain and permits the exact evaluation of the gravity contribution from an highly sampled topographic model of the land the density used for the bouguer reduction has been obtained from the gravity data set itself by using two different optimization methods that have given the same optimal result of 2400 kg m 3 we have studied the radial power spectrum of the data choosing the optimal bouguer density from its slope as the one which minimizes the fractal dimension of the resulting gravity map the second approach consists of studying the correlation between topography and bouguer anomaly by spatial cross plots for a significant subset of the data both these approaches are aimed at reducing the short wavelength effects of topography in the gravity map but in the past they have been traditionally used alternatively since they gave different optimization values especially the second method that seems to ignore large wavelength isostatic effects actually we have revisited both the methodologies proposing slight modifications to make their efforts compatible their coincident results confirm their validity of application and give reliability to the recovered value of the bouguer optimal density moreover modifying the second approach allows us to compile a sort of normalized correlation map which we propose in this paper defining the 2 d isostatic setting of the investigated region without introducing any further lithospheric model the final result is a revised bouguer map compiled using a grid with a resolution of 2 min that is useful for large scale geological studies and gives important information about the compensation mechanism of the mediterranean sea in a direct way we have found that the overall region seems to be in a complete isostatic equilibrium apart from the young basins of tyrrhenian sea and aegean sea confirming previous similar results

formation and erosion of layered materials geologic and dust cycle history of eastern arabia terra mars 1 eastern arabia terra is mantled in a layer of dust a few centimeters to a meter thick yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine grained material and a significant amount of erosion early in martian history this region was affected by volcanic and fluvial activity but has since been dominated by aeolian processes five craters in this region contain interior mound material that ranges in height from 1600 to 2100 m above the crater floor the fluted erosional pattern and the thermal inertia are suggestive of a weakly indurated material and the extensive layering implies that these mounds were formed by a repeated process or processes although these materials primarily occur within craters there are materials outside craters that have similar erosional features and fine laminations suggesting a more extensive deposit the most likely process to form this material is the deposition and cementation of air fall dust and is potentially related to martian obliquity changes the significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past 106 108 years currently dust is accumulating in this region in years with planet encircling dust events but global circulation model results indicate that dust devils may be removing slight amounts of dust from arabia terra these observations suggest that the thickness of the dust mantle may not be currently increasing and may instead be in equilibrium

gravity data inversion for moho depth modeling in the hellenic area the main objective of this study is the determination of the moho discontinuity in the hellenic area based on gravity data inversion high resolution 2 arcmin and accuracy 2 to 3 mgal gravity data were used in the computations following the parker oldenburg iterative method and a low pass filter was applied to gravity information towards the convergence of the final solution to determine the cut off wavenumber of the filter we tested different mean depths and density contrasts of the crust and the mantle mohorovicic discontinuity the selected density contrast and mean depth of the mohorovicic discontinuity are those which agree with the moho depth interpreted from deep seismic imaging data by comparing the moho depth estimated covering both land and marine areas and including the ionian and aegean sea with those interpreted from previous studies it is shown that our solution is consistent with the available seismic data interpretation moreover the resolution of the gravity data and the appropriate filtering used in this study contributed to the representation of local features of the moho discontinuity finally area dependent discrepancies detected between the moho depths of the current solution and those derived from previous studies are extensively discussed

isostatic response of the australian lithosphere estimation of effective elastic thickness and anisotropy using multitaper spectral analysis gravity and topography provide important insights regarding the degree and mechanisms of isostatic compensation the azimuthally isotropic coherence function be tween the bouguer gravity anomaly and topography evolves from high to low for increasing wavenumber a diagnostic that can be predicted for a variety of lithospheric loading models and used in inversions for flexural rigidity thereof in this study we investigate the isostatic response of continental australia we consider the effects of directionally anisotropic plate strength on the coherelce the anisotropic coherence function is calculated for regions of australia that have distinctive geological and geophysical properties the coherence estimation is performed by the thomson multiple slepian taper spectral analysis method extended to two dimensional fields our analysis reveals the existence of flexural anisotropy in central australia indicative of a weaker n s direction of lower te this observation is consistent with the suggestion that the parallel faults in that area act to make the lithosphere weaker in the direction perpendicular to them it can also be related to the n s direction of maximum stress and possibly the presence of e w running zones weakened due to differential sediment burial rates we also demonstrate that the multitaper method has distinct advantages for computing the isotropic coherence function the ability to make many independent estimates of the isostatic response that are minimally affected by spectral leakage results in a coherence that is more robust than with modified periodogram methods particularly at low wavenumbers our analysis elucidates the reasons for discrepancies in previous estimates of effective elastic thickness te of the australian lithosphere in isotropic inversions for te we obtain values that are as much as a factor of 2 less than those obtained in standard inversions of the periodogram coherence using bouguer gravity and topography but greater than those obtained by inversions that utilize free air rather than bouguer gravity and ignore the presence of subsurface loads however owing to the low spectral power of the australian topography the uncertainty on any estimate of te is substantial

confocal laser scanning microscopy and raman imagery of ancient microscopic fossils abstract among all problems confronting the study of ancient permineralized petrified microscopic fossils two stand out the need for 1 accurate documentation of their three dimensional morphology and 2 direct analysis of their chemical composition and that of their surrounding mineral matrices to address these problems we demonstrate the use of two techniques that we have recently introduced to precambrian paleobiology confocal laser scanning microscopy and raman imagery these techniques both of which are non intrusive and non destructive can provide data by which to characterize in situ and at micron scale resolution the cellular and organismal morphology of thin section embedded organic walled fossils in addition raman imagery provides direct analyses of the molecular structural composition of the kerogenous components of such fossils and of their surrounding matrices and a means to assess quantitatively the geochemical maturity of the preserved organics use of these techniques for studies of ancient microscopic fossils can provide information in three dimensions at high spatial resolution about their morphology and cellular anatomy taphonomy and fidelity of preservation composition and mode of preservation and their biogenicity and syngenetic origin with the rocks in which they occur

eolian intracrater deposits on mars physical properties and global distribution abstract an investigation of martian intracrater materials has been made using their thermophysical properties as derived from viking irtm observations over one fourth of all craters larger than 25 km in diameter between 50 s and 50 n have localized deposits of coarse material on the floor which are associated with dark splotches seen visually assuming homogeneous unconsolidated materials the measured thermal inertias of these deposits i 0 003 10 3 to 0 026 10 3 cal cm 2 sec 1 2 k 1 imply effective grain sizes ranging from 0 1 mm to 1 cm with a modal value of 0 9 mm these deposits are coarser and darker than the surrounding terrains and the majority of the martian surface but are not compositionally distinct from materials with similar albedos they occur more frequently in the south in regions of relatively coarse material 0 2 to 2 mm and in relatively dark areas these features most likely formed by entrapment of marginally mobile material which can be transported into but not out of crater depressions by the wind very few have recognizable dune forms those that do have effective grain sizes less than 0 5 mm the majority of the splotch deposits are coarser than the dune forming materials found in the north polar region and inside extreme southern latitude craters and probably form low broad zibar dunes or lag deposits intracrater deposits are noticeably lacking from the interior of the large northern hemisphere low inertia region of arabia 10 s to 30 n 300 to 360 w interpreted to be a sink for suspended dust but do occur around the perimeter of this region this distribution suggests that the intracrater features have been buried in the interior of arabia and that the dust deposit is less extensive at the margins and may currently be expanding the occurrence of regional dust deposits in the north may be related to the maximum wind activity currently occurring in the southern hemisphere and suggests that the location of regional sinks may migrate with time as the solar insolation maximum migrates

advances in gravity survey resolution major technological advances have been made in the last few years in gravity resolution for many acquisition systems currently available for exploration these advances have resulted from better instrumentation better use of dgps and better processing methods this in turn led to a renaissance in the use of gravity in modern multidisciplined cost effective oil and mineral exploration the aim of this article is to show how gravity resolution has improved with time rather than how improved resolution is being used to investigate and map subsurface density structures

north south asymmetry of eolian features in martian polar regions analysis based on crater related wind markers abstract a comparison of crater related wind markers in the north and south polar 40 90 latitude regions of mars has been made on the basis of comprehensive mapping from viking orbiter and mariner 9 images wind streaks show that present wind activity is most effective in both north and south in the southern spring and summer this asymmetry is consistent with the present asymmetry of climate the more massive intracrater dune fields are also oriented with the presently strongest winds this alignment may reflect a long term asymmetry in the effectiveness of northern and southern spring flow because reorientation times far exceed the period of cycles of hemispherical climate asymmetry 51 000 years streaks originating from dark crater splotches indicate that windflow away from the south pole is effective over a larger latitude range than it is in the north this difference may be partly responsible for the contrasting distribution of dune sand in the north and south polar regions

global marine gravity field from the ers 1 and geosat geodetic mission altimetry satellite altimetry from the geosat and the ers i geodetic missions provide altimeter data with very dense spatial coverage therefore the gravity field may be recovered in great detail as neighboring ground tracks are very closely distributed cross track variations in the sea surface heights are extremely sensitive to sea surface variability to avoid errors in the gravity field caused by such effects sea surface variability needs to be carefully eliminated from the observations initially a careful removal of gross errors and outliers was performed and the tracks were fitted individually to a geoid model and crossover adjusted using bias and tilt subsequently sea surface heights were gridded using local collocation in which residual ocean variability was considered the conversion of the heights into gravity anomalies was carried out using the fast fourier transform fft in this process filtering was done in the spectral domain to avoid the so called orange skin characteristics comparison with marine gravity was finally carried out in three different regions of the earth to evaluate the accuracy of the global marine gravity field from ers 1 and geosat

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

bouguer reduction density why 2 67 one of the most widely recognized parameters in solid earth geophysics is the assumed density of the surface rocks of the continental crust 2 67 g cm 3 or 2670 kg m 3 in today9s preferred si units in the calculation of bouguer and isostatic gravity anomalies which are widely used for geological studies the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite flat slab of a specified density that approximates the mass the datum for most surveys is sea level or in the case of surveys of limited areas it may be the elevation of the lowest station in the survey although the choice of datum is arbitrary commonly sea level is used in an attempt to standardize anomalies from different surveys similarly a density of 2 67 g cm 3 is generally assumed for the density of the included mass in regional gravity surveys

sensitivity of gravity and topography regressions to earth and planetary structures abstract the availability of global gravity fields and topography through calculation services like the international centre for global earth models allows easy access to gravity data greatly enlarging the spectrum of users the applications extend much farther than the classic modeling through the gravity specialist we investigate the sensitivity of the joint analysis of topography and gravity data based on linear regression analysis and clustering of the response to particular characteristics of the lithosphere structure the parameters of the regression analysis are predicted to have characteristic values which allow to distinguish continental crust from oceanic crust and signalize the presence of crustal inhomogeneity predictions are made through theoretical considerations and on synthetic models we use the south atlantic ocean and the confining south american and african continents for illustration where the regression parameters distinguish oceanic crust from the ridge up to the bathymetric inflection point from the transitional crust and the continental crust allowing to map these units the general properties of the parameters are statistically relevant since the errors on the parameters are

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

effect of the lateral topographic density distribution on interpretational properties of bouguer gravity maps until recently the information about the topographic density distribution has been limited to only certain regions and some countries while missing in the global context the unb topodens is the first model that provides the information about a lateral topographic density globally the analysis of this model also reveals that the average topographic density for the entire continental landmass excluding polar glaciers is 2247 kg m 3 this density differs significantly from the value of 2670 kg m 3 that is typically adopted to represent the continental upper crustal density in this study we use the unb topodens density model to inspect how the topographic density variations affect interpretational properties of bouguer gravity maps since this model provides also the information about density uncertainties of individual lithologies main rock types we estimate the corresponding errors in the bouguer gravity data despite a new estimate of the average topographic density corresponds to relative changes of 16 per cent in values of the topographic gravity correction these changes do not affect interpretational properties of bouguer gravity maps the anomalous topographic density distribution taken with respect to the average density of 2247 kg m 3 however modifies the bouguer gravity pattern we demonstrate that the gravitational contribution of anomalous topographic density is globally mostly within 25 mgal but much large values are detected in himalaya tibet central andes and along the east african rift system our estimates also indicate that errors in the bouguer gravity data attributed to topographic density uncertainties are mostly less than 15 mgal but in mountainous regions could reach large values exceeding even 50 mgal unarguably the unb topodens model provides an improved information about the global topographic density variations and their uncertainties nevertheless much more in situ measurements of rock density samples together with detailed 3 d geological models are still necessary to understand better the actual density distribution within the whole topography particularly to mention a density change with depth

what are the limitations of satellite altimetry radar altimeter measurements of the marine geoid collected during the seasat altimeter mission gave geophysicists hope of uncovering the gravity field over all the ocean basins however because of insufficient track density it has taken 16 years for the full potential of the satellite altimeter to be realized the high density coverage obtained by ers 1 during its geodetic mapping phase april 1994 march 1995 prompted the u s navy to declassify all of the geosat altimeter data in june 1995 the combination of these two high density data sets provided the first global view of all the ocean basins at a wavelength resolution of 20 30 km

visual and infrared observations of wind streaks on mars abstract estimation of surface properties and physical setting of three common martian wind streak types bright dark and splotch related provides constraints on models of the formation and variability of streaks bright streaks form independently of surface properties other than local topography this is consistent with their formation being due to deposition of atmospheric dust in the lee of topographic features although they are widespread on mars dark streaks are noted as variable only in regions near 30 s latitude and elevations between 3 and 7 km and are associated with dark surfaces that have relatively high thermal inertias splotch related streaks occur at elevations between 0 and 6 km and in regions of relatively high thermal inertia splotch related streaks occur near the boundaries of thermally defined regions such as the south polar cap and other areas of either low or high thermal inertia these thermal conditions are responsible for the production of surface winds which form and modify these streaks the source of sidements which form splotch related streaks varies from dunes to well indurated stratified deposits regional studies of the various types in syrtis major syria planum claritas fossae oxia palus mesogea and pettit craters and noachis confirm that the correlations found at the global level occur at regional scales

architecture and neogene to recent evolution of the western calabrian continental margin an upper plate perspective to the ionian subduction system central mediterranean the western calabria continental margin forms the transition between the pliocene to recent marsili spreading center and continental calabria all parts of the upper plate of the ionian subduction zone integrating high resolution and crustal seismic images constrained by gravity modeling we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its miocene to present evolution this time span encompasses the continent continent collision between africa and eurasia subsequent orogenic collapse and rifting apart between the two continental masses and the pliocene to recent emplacement of oceanic crust in the vavilov and marsili basins the crust of the margin thins from the calabria coast 25 km to the marsili continent ocean transition 12 km on the whole upper and lower crusts thin proportionally with pure shear geometry the continental margin is covered by an oligocene to present sedimentary succession reaching a maximum thickness of 6 0 km in the paola basin during the miocene the continental margin experienced regional shortening accommodated by a large number of mainly west vergent thrusts possibly associated with the late stages of the kabilo calabrian chain shortening continued through pliocene to recent but was accommodated by a limited number of west vergent thrust faults located in the western part of the margin and by a few tens of kilometers wide syncline located in the eastern part of the profile the accommodation space created in the syncline core hosted a 4 5 km thick plio quaternary sedimentary succession the paola basin no significant extensional fault is observed along the profile miocene to recent subsidence was controlled by 1 a short wavelength component related to shortening and responsible for the formation of the paola basin syncline and possibly contributing to the uplift of onshore calabria and 2 a long wavelength component responsible for the regional subsidence and oceanward tilting of the calabria margin short wavelength subsidence ended in the late pliocene but long wavelength downward movements persisted and even accelerated during late pliocene to quaternary times when the present day bathymetry was achieved both horizontal deformations and vertical movements are difficult to explain in the context of a normal back arc basin without taking into consideration patterns of secondary mantle flow generated by the retreat of the subducting slab

gravity constraints on the dynamics of the crust mantle system during calabrian subduction summary the thermomechanic evolution of the lithosphere upper mantle system during calabrian subduction is analysed using a 2 d finite element approach in which the lithosphere is compositionally stratified into crust and mantle gravity and topography predictions are cross checked with observed gravity and topography patterns of the calabrian region modelling results indicate that the gravity pattern in the arc trench region is shaped by the sinking of light material belonging to both the overriding and subduction plates the sinking of light crustal material up to depths of the order of 100 150 km is the ultimate responsible for the peculiar gravity signature of subduction characterized by a minimum of gravity anomaly located at the trench bounded by two highs located on the overriding and subducting plates with a variation in magnitude of the order of 200 mgal along a wavelength of 200 km in agreement with the isostatically compensated component of gravity anomaly observed along a transect crossing the calabrian arc from the tyrrhenian to the ionian seas the striking agreement between the geodetic retrieved profiles and the modelled ones in the trench region confirms the crucial role of compositional stratification of the lithosphere in the subduction process and the correctness of the kinematic hypotheses considered in our modelling that the present day configuration of crust mantle system below the calabrian arc results from trench s retreat at a rate of about 3 cm yr 1 followed by gravitational sinking of the subducted slab in the last 5 myr

the graham and terrible volcanic province nw sicilian channel gravimetric constraints for the magmatic manifestations a few kilometres off the sw coast of sicily lie the shallow banks of graham terrible and nerita these morphological reliefs are affected by two lithospheric scale n s trending tectonic lineaments known as capo granitola to the west and sciacca to the east within the graham and terrible banks several volcanic edifices have been documented and mapped using high resolution bathymetry and seismic profiles three groups of volcanic features can be distinguished i a cluster of n s aligned volcanic cones in the graham bank generally developed along the capo granitola fault ii a series of poorly developed volcanic constructs roughly positioned along the northern edge of the terrible bank and iii a few isolated volcanic centres located north of the terrible bank within an undeformed zone here we present a 2 d gravimetric model constrained at shallow levels by an integrated seismic dataset which we use to interpret the distribution of magmatic manifestations in this sector of the sicilian channel at the graham bank where there are no significant positive gravity anomalies the magmatic material seem to migrate to the surface along the capo granitola lithospheric fault without the presence of a shallow magma source in the terrible bank where there is a well defined positive gravity anomaly the model implies the presence of a shallow magma chamber from which sea floor volcanic constructs are fed upwards along cracks the origin for the volcanic cones located between the two fault systems is more problematic as no significant structural discontinuities were identified in this area from the available seismic data however the presence of a potential wide sill complex suggests that it facilitated lateral magma flow from source to surface over lateral distances of tens of kilometres

the combined inversion of seismological and goce gravity data new insights into the current state of the pacific lithosphere and upper mantle abstract in this study we combine seismological and goce satellite gravity information by using a bayesian like technique with the aim of inferring the density structure of the pacific 90 n 90 s 121 e 60 w lithosphere and upper mantle we recover a 1 1 3 d density model down to 300 km depth which explains gravity observations with a variance reduction of 67 41 the model with an associated a posteriori standard deviation provides a significant contribution to understanding the evolution of the pacific lithosphere and answers to some debated geodynamic questions our methodology enables us to combine the recovery of density parameters with the optimum density v sv scalings the latter account for both seismological and gravity observations in order to identify the regions characterized by chemically induced density heterogeneities which add to the thermally induced anomalies chemically modified structures are found west of the east pacific rise epr and are of relevant amplitude both below the north western side of the pacific plate at the base of the lithosphere and up to 100 km depth beneath the hawaiian and super swell regions thus explaining the anomalous shallow regions without invoking the thermal buoyancy as the sole justification coherently with the chemically modified structures our results a support a lighter and more buoyant lithosphere than that predicted by the cooling models and b are in favor of the hypothesized crustal underplating beneath the hawaiian chain and beneath the volcanic units in the southern branch of the super swell region the comparison between calculated mantle gravity residuals and residual topography a suggests a lateral viscosity growth associated with the increasing thickness and density of the plate and b correlates well with sub lithospheric mantle flow from the epr towards west up to the kermadec and tonga trench in the south and the kuril kamchatka trench in the north

global patterns in cloud forms on mars abstract mariner 9 images and all viking orbiter images through july 1979 were searched for cloud forms a computer accessible catalog was assembled consisting of a classification of cloud type lee wav wave for example and properties directionality wavelength for example lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor lee waves are rare at equatorial latitudes plumes probably dust occur preferentially at locations where strong boundary layer convection is expected