lower mantle inhomogeneities inferred from pcp precursors a search of phases arriving between p and pcp the reflection from the core mantle boundary cmb was performed in the bulletins of the international seismological center bisc the distribution of the turning reflection points of anomalous waves in the lowermost mantle indicates the areas which are possibly anomalous regions the regions exhibiting these anomalies cover only a small fraction of the lowermost mantle sampled the areas which can be associated with anomalous arrivals are the lowermost mantle under the north pole region northern siberia central siberia western mongolia afghanistan northeastern china korea and the north atlantic ridge these are the regions which should be studied in more detail by analyzing the seismograms i e the amplitude and waveform information at the corresponding stations in addition to the travel time information reported to the isc

the shear wave velocity gradient at the base of the mantle the relative amplitudes and travel have been directed toward obtaining global times of scs and s phases are utilized to place averages and the degree of lateral variation in constraints on the shear wave velocity gradient d properties remains an open question above the core mantle boundary a previously a conflicting result was found by mitchell and reported long period scsh sh amplitude ratio helmberger 1973 who utilized the relative minimum in the distance range 65 o to 70 o is shown amplitudes and timing of long period scs and s to be a localized feature apparently produced by phases to constrain the s wave velocity gradient an amplitude anomaly in the direct s phase and in d they found a minimum in the scsh sh therefore need not reflect the velocity gradient amplitude ratio near 68 o which was attributed to at the base of the mantle the amplitude ratios low amplitudes of the scs arrivals unable to that are free of this anomaly are consistent with explain this feature by models with negative or calculations for the jb model or models with mild near zero shear velocity gradients in d they positive or negative velocity gradients in the proposed models with positive s wave velocity lowermost 200 km of the mantle scsv arrivals gradients above the cmb these positive are particularly sensitive to the shear velocity gradients extended over 40 to 70 km above the structure just above the core mantle boundary core reaching velocities at the cmb as high as the apparent arrival time of the peak of scsv is 7 6 to 7 8 km s these models can explain the as much as 4 sreater than that of scsh in the observed amplitude ratio behavior as well as an distance range 75 v to 80 o for sea of okhotsk apparent difference observed in the arrival times events recorded in north america this can be of transversely and radially polarized scs explained by interference effects produced by a mitchell and helmberger also proposed a low q localized high velocity layer or strong positive zone in d or finite outer core rigidity to s wave velocity gradient in the lowermost 20 km explain the baseline of the scsh sh amplitude of the mantle a velocity increase of about 5 ratios while the majority of their data was for is required to explain the observed shift between deep south american events recorded in north scsv and scsh this thin high velocity layer america they did analyze one deep sea of okhotsk varies laterally as it is not observed in event for which the radial and transverse scs similar data from argentine events refined arrival times were not different which suggested estimates of the outermost core p velocity lateral variations in the d velocity structure structure are obtained by modeling sks signals in in this paper we extend the analysis of scs the distance range 75 o to 85 o s

analysis of asymmetric multipathing with a generalization of the double beam method abstract an array method integrating source and receiver array beamforming is presented the method is a generalization of previous work kruger et al 1993 to independent variation of slowness and azimuth in both the source and the receiver array compared to the analysis capabilities of a single array the resolution is enhanced and asymmetric scattering configurations and multipathing can be studied the generalized double beam method dbm is applied to a data set consisting of nuclear explosions detonated in eastern kazakhstan and recorded at the yellowknife array in northern canada the multipathing found for pcp and pdp is interpreted in terms of lateral inhomogeneity in the lowermost mantle below severnaya zemlya indications for rayleigh to p wave scattering observed for the shagan river and degelen subsites of the former main test site of the ussr in eastern kazakhstan can be related to the structure in the vicinity of the two subsites

absence of short period ulvz precursors to pcp and scp from two regions of the cmb we present results from a study of the core mantleboundary cmb underneathmexico centralamer ica and the northeast pacic using core reflected phases pcpand scp which provide a direct means of sampling the deep mantle precursor arrivals to these phases pro duced by reflection from the top of an ultra low velocity layer ulvz at the base of themantle would contain infor mation about the thickness of such a layer and the velocity reductions within it stacks of these phases from 17 earth quakes recorded by the northern and southern california seismographic networks do not exhibit coherent or inco herent precursor arrivals from a ulvz in precursor time windows ratios of stack amplitudes to those of the cmb reflected phases fall below predicted values from published ulvz models we conclude that ulvzs if present in these regions havevp andvs reductions less than 10 are less than ve km thick or have transitions greater thanve km wide at their upper boundaries

alternatives to core mantle boundary topography abstract nuclear explosions at the french test sites in the south pacific have been recorded at the regional seismic networks in the western united states a total of approximately 600 good quality short period seismograms were selected from an initial set of 900 the dense receiver spacing particularly in california allows the division of the networks into numerous subarrays and the data from each subarray can be analysed using conventional array techniques such as beam forming and frequency wave number analysis the seismic rays provide dense sampling of a small area of the core mantle boundary cmb beneath the eastern pacific from 5 to 13 n and 133 to 126 w pcp has a shallow incidence angle on the cmb at an epicentral distance of 65 and d is sampled over a large swathe from 2 s to 24 n and from 134 to 123 w beam traces have been formed for the p and pcp phases for each of the subarrays using slowness and azimuth values derived from array methods good quality beams have been selected for further analysis by applying a matched filter to the beamed traces an accurate set of pcp p differential travel times has been determined and compared with iasp91 the residuals show a smooth trend over the area sampled for the given epicentral distances p and pcp have similar paths through the crust and upper mantle so we make the assumption that near source and near receiver structures have negligible effect on the differential times we also assume that the midmantle is relatively homogenous many previous studies have interpreted pcp p residuals in terms of cmb topography by mapping the residuals directly to topography a range in elevation of 40 km over a lateral extent of about 700 km results alternatively we attempted to interpret the residuals in terms of velocity heterogeneity in d a range of d models have been tested including lateral velocity variation in a d layer with constant thickness the pcp p residuals may be explained by allowing the p wave velocity to vary laterally by a factor of 2 over the region sampled with most of the region being marginally fast this suggests that d heterogeneity has large spectral power at relatively short wavelengths in this scenario previous tomographic inversions for cmb topography will have large errors since in these inversions corrections for d structure are based on low order spherical harmonic models

sound velocity of mgsio3 post perovskite phase a constraint on the d discontinuity abstract the discovery of a post perovskite phase transition in mgsio 3 has significant implications for seismological observations in the d region at the bottom of earth s mantle the d discontinuity which is manifested as a sharp positive seismic wave velocity jump 200 300 km above the core mantle boundary at pressure of 119 125 gpa is one of the most enigmatic seismic features in this region whether this velocity increase may be due to the formation of a post perovskite phase at the d discontinuity has not however been directly addressed by experiments here we present the results of aggregate sound velocity measurements of the mgsio 3 post perovskite phase by brillouin spectroscopy in the diamond anvil cell dac up to a pressure of 172 gpa in combination with infrared laser annealing of the sample based on these results and our recent high pressure velocity measurements on perovskite the aggregate shear wave velocity contrast across the perovskite to post perovskite phase transition is at most 0 5 this contrast is much smaller than typically observed across the d discontinuity indicating that the formation of an isotropic aggregate of the post perovskite phase provides an insufficient velocity increase to explain the d discontinuity lattice preferred orientation lpo of post perovskite is likely to be crucial for explaining the d discontinuity

multiple phase analysis of the shear velocity structure in the d region beneath alaska a large data set more than 990 total waveforms comprised of north american station recordings of a variety of long period s phases s scs sdiff ss sscs sks skks from 36 earthquakes in western pacific subduction zones is analyzed to determine characteristics of the shear velocity structure in the d region beneath alaska three hypotheses that have been proposed to explain observed scs precursors and s waveform distortions for this region are appraised with the multiple phase data set and the radial and lateral variations of the shear velocity structure in the 1500 km broad portion of d sampled are also assessed the observed travel time and waveform variations may result from diffraction by near source slab structure scattering by low velocity heterogeneity in the lower mantle or interaction with complex velocity gradients in d associated with a deep mantle velocity discontinuity we utilize waveform modeling and differential time analysis to resolve greater detail of the structure than can presently be obtained by standard travel time tomography techniques and find that the discontinuity model is most consistent with the data subdivision of the data by source region and source to receiver azimuth establishes that the observations exhibit fairly stable behavior which is consistent with extensive local stratification of d the data show sufficient coherence over the 1500 km broad region that we find it useful to present a local average radial model the preferred model sylo has a 2 75 velocity increase 243 km above the core mantle boundary and a negative velocity gradient within the d layer analysis of sks s sks scs and sks skks differential times also indicates that the outermost 100 km of the core below the fast d region underlying alaska must be slower than the prem structure the observations exhibit significant scatter most of which can be attributed to unmodeled heterogeneity in the midmantle and near source regions as well as lateral variations in the d region the complex structure of d that we prefer may be associated with large scale downwelling in the lower mantle but it is not certain whether it is a purely thermal or a combined chemical and thermal effect

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

seismic evidence of partial melt within a possibly ubiquitous low velocity layer at the base of the mantle three source regions show evidence of a low velocity layer that is less than 15 kilometers thick on top of the core mantle boundary and require about a 3 1 ratio of shear to compressional velocity reduction which is consistent with partial melt layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity these observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core mantle boundary low viscosity accompanying partial melt can localize the upwelling of warmed mantle making the low velocity layer a plausible source of mantle plumes

imaging scattering structures in the lower mantle by migration of long period s waves a simplified wave field migration method is applied to long period tangential component recordings to image lower mantle heterogeneity beneath alaska observed wave field complexities are dominated by coherent arrivals between direct s or ss and the core reflected scs or sscs phases a relative waveform inversion method is used to objectively extract the time and amplitude of the three main spikes in each wavetrain removing the effects of source time function receiver and instrument responses the timing of the intermediate arrivals relative to s or scs is used to define the volumetric position of scattering ellipsoids in the lower mantle with intersections of ellipsoids illuminating possible regions of isotropic scattering while a complete waveform migration is not viable due to the very limited ray path coverage and the band limited data the kinematics and relative amplitudes of the scattered arrivals are still valuable for assessing the origin of the waveform complexity in this region which displays particularly uniform existence of an extra arrival in the data the simplest interpretation is that a scattering surface with lateral dimensions exceeding 1500 km at a depth near 2600 km in the mantle is responsible for the extra phase this is consistent with previous interpretations involving a one dimensional model with a rapid shear velocity increase or discontinuity 240 280 km above the core mantle boundary the proposed methodology can potentially image both heterogeneities or layering in the d region as well as scattering from midmantle structure although data limitations will continue to be a major obstacle

inhomogeneities near the core mantle boundary inferred from short period scattered pkp waves recorded at the global digital seismograph network we analyze short period pkp precursor wave trains recorded at global digital seismograph network stations in the distance range 120 140 to infer the nature of inhomogeneities near the core mantle boundary travel times and particle motions are consistent with predictions of single scattered waves near the cmb the dominant frequencies are around 1 hz the regions best sampled are beneath indonesia north america central africa and south america based on first order scattering theory the characteristics of the wave number spectrum of the structural inhomogeneities are obtained for two hypotheses volume inhomogeneities and topographic irregularities for the range of wavelengths sampled by these data between 10 and 70 km the spectrum of inhomogeneities is best represented by a power law of index 5 3 for volume inhomogeneities and 6 8 for topographic irregularities if the scattering is due only to volumetric inhomogeneities we estimate the strength of the structural variations to be about 0 5 in p wave velocity for a 200 km thick layer if the scattering is due only to topographic irregularities the topography has an rms height of 280 m at present we can not distinguish between these two types of inhomogeneities

probing the core mantle boundary beneath europe and western eurasia a detailed study using pcp summary we use pcp the core reflected p phase recordings of deep earthquakes and nuclear explosions from the grafenberg germany and norsar norway arrays to investigate the core mantle boundary region beneath europe and western eurasia we find evidence for a previously unknown ultra low velocity zone 600 km south east of moscow located at the edge of a middle size low shear velocity region imaged in seismic tomography that is located beneath the volga river region the observed amplitude variations of pcp can be modelled by velocity reductions of p and s waves of 5 and 15 respectively with a density increase of 15 travel time delays of pre and postcursors are indicating a thickness of about 13 km for this ultra low velocity region ulvz however our modelling also reveals highly ambiguous amplitude variations of pcp and a reflection off the top of the anomaly for various ulvzs and topography models accordingly large velocity contrasts of up to 10 in vp and 20 in vs cannot be excluded in general the whole volga river region shows a complex pattern of pcp amplitudes caused most likely by cmb undulations further pcp probes beneath paris kiev and northern italy indicate likely normal cmb conditions whereas the samples below finland and the hungary slovakia border yield strongly amplified pcp signals suggesting strong cmb topography effects we evaluate the amplitude behaviour of pcp as a function of distance and several ulvz models using the 1d reflectivity and the 2d gauss beam method the influence of the velocity and density perturbations is analysed as well as the anomaly thickness the dominant period of the source wavelet and interface topographies strong variation of the pcp amplitude are obtained as a function of distance and of the impedance contrast we also consider two types of topographies undulations atop the cmb in the presence of flat ulvzs and vice versa where a broad range of cmb topography dimensions lead to large pcp amplitude variations only large ulvz undulations generate significant amplitude scattering consequently this indicates that topography effects of anomalies may mask the true medium parameters as well as the ulvz thickness moreover there might be a possibility of misinterpreting the precursor as pcp in particular for thin ulvzs

seismology of the lower mantle and core mantle boundary the thermal and chemical processes operating near the core mantle boundary cmb play a major role in the planet s evolution influencing the magnetic field behavior chemical cycling in the mantle irregularities in the rotation and gravitation of the planet and the configuration of mantle convection the past decade has witnessed extensive investigation of the core mantle transition zone using seismological geodynamical geomagnetic and mineral physics experimental techniques the many multidisciplinary contributions on this region have been surveyed in several recent review articles e g loper and lay 1994 jeanloz and lay 1993 bloxham and jackson 1991 which provide a comprehensive survey of the recent literature i confine my attention here to recent seismological evidence for laterally heterogeneous structure in the d region the lowermost 200 km of the mantle while seismic models for d are still low resolution we have attained general constraints on the extent of heterogeneity which raise provocative questions as to the origins of the complex structures the idea that chemical and thermal heterogeneity in d is a manifestation of boundary layer processes is a long standing one bullen 1949 but we are far short of quantifying this notion in particular it is not known whether heterogeneities in d are relics of subducted slabs in situ accumulations of core mantle chemical reaction products primordial residuum from the core formation process or thermal heterogeneities within a hot unstable thermal boundary layer

textures of the soils and rocks at gusev crater from spirit s microscopic imager the microscopic imager on the spirit rover analyzed the textures of the soil and rocks at gusev crater on mars at a resolution of 100 micrometers weakly bound agglomerates of dust are present in the soil near the columbia memorial station some of the brushed or abraded rock surfaces show igneous textures and evidence for alteration rinds coatings and veins consistent with secondary mineralization the rock textures are consistent with a volcanic origin and subsequent alteration and or weathering by impact events wind and possibly water

pancam multispectral imaging results from the opportunity rover at meridiani planum panoramic camera pancam images from meridiani planum reveal a low albedo generally flat and relatively rock free surface within and around impact craters and fractures laminated outcrop rocks with higher albedo are observed fine grained materials include dark sand bright ferric iron rich dust angular rock clasts and millimeter size spheroidal granules that are eroding out of the laminated rocks spectra of sand clasts and one dark plains rock are consistent with mafic silicates such as pyroxene and olivine spectra of both the spherules and the laminated outcrop materials indicate the presence of crystalline ferric oxides or oxyhydroxides atmospheric observations show a steady decline in dust opacity during the mission astronomical observations captured solar transits by phobos and deimos and time lapse observations of sunsets

small scale changes of core mantle boundary reflectivity studied using core reflected pcp abstract short period pcp phases from earthquakes in the western aleutians recorded at the canadian yellowknife array yka sample the core mantle boundary cmb beneath the alaskan kenai peninsula and the cook inlet the pcp to p amplitude ratios for these events show large variability with some amplitude ratios more than an order of magnitude larger than predicted by radial earth models such as iasp91 or prem the amplitude ratios vary laterally with pcp core mantle boundary reflection points showing a 1 region with exceptionally large amplitude ratios it is likely that the variability in relative pcp amplitudes is due in large part to cmb topography other mechanisms such as radiation pattern mantle attenuation focusing and defocusing and core mantle boundary velocity and density perturbations could cause variations on scale lengths of less than a degree as found in this study but are unable to produce variations as large as those we observe

seismic discontinuity at the top of d a world wide feature considering the growing number of observations of a seismic discontinuity at the top of d some 300 km above the core mantle boundary we investigate the scenario of whether this feature could be global we show that the mean first arrivals of p waves as used to build global models can be fit by the two branches of a discontinuous model we argue that the intermittence of the detection of the reflector is due to lateral variations of a global discontinuity these observations put strong constraints on the type of chemical layering that could explain the discontinuity we speculate that the properties of the d discontinuity are better explained in terms of a new phase transition

athena microscopic imager investigation 1 the athena science payload on the mars exploration rovers mer includes the microscopic imager mi the mi is a fixed focus camera mounted on the end of an extendable instrument arm the instrument deployment device idd the mi was designed to acquire images at a spatial resolution of 30 microns pixel over a broad spectral range 400 700 nm the mi uses the same electronics design as the other mer cameras but has optics that yield a field of view of 31 31 mm across a 1024 1024 pixel ccd image the mi acquires images using only solar or skylight illumination of the target surface a contact sensor is used to place the mi slightly closer to the target surface than its best focus distance about 66 mm allowing concave surfaces to be imaged in good focus coarse focusing 2 mm precision is achieved by moving the idd away from a rock target after the contact sensor has been activated the mi optics are protected from the martian environment by a retractable dust cover the dust cover includes a kapton window that is tinted orange to restrict the spectral bandpass to 500 700 nm allowing color information to be obtained by taking images with the dust cover open and closed mi data will be used to place other mer instrument data in context and to aid in petrologic and geologic interpretations of rocks and soils on mars

concretion morphology classification and genesis abstract a discussion of the most relevant morphological features of concretionary bodies and the different classifications and the criteria involved in these classifications is presented together with suggestions for improvements to the various classification schemes the meaning of syngenetic diagenetic and epigenetic related to the relative timing and environment of growth of concretionary bodies is also reviewed and discussed the replacement of mixed morphogenetic classifications which lead to conflicting results by classification categories based on textural features is proposed because the identification of the genetic environment of a concretionary body tells little about its history i recommend defining growth patterns in which the successive steps associated with changes in composition and or texture and the development of new structures are recorded a new path is presented that accounts for the contradiction between textural and isotope features which suggests respectively syngenetic and diagenetic or even epigenetic signatures this new path is characterized by the preservation of large porosities over very long time spans and down to depths that are somewhat greater than expected due to the inhibition of normal compaction caused by early overpressuring this overpressuring is the result of the development of hydraulic seals since approximately the syngenetic phase times the concepts of force of crystallization and displacive growth are also reviewed it is being suggested to discard some controversial interpretations of their actual importance for true concretionary displacive growth under epigenetic conditions in accordance with other authors the conclusion is reached that displacive growth is only possible if the shear strength of the host is very low and the stress field within the host is almost hydrostatic a new model the symcompactional concretionary growth model is proposed which explains how a concretionary body generally a nodule can grow while its host thins down by compaction this overpressured undercompacted model will be useful for the interpretation of an assemblage of features such as injection dikes hydraulic breccias cone in cone structures among others that are thought to be representative of the former presence of overpressured horizons these overpressured horizons could serve as detachment planes in paleotectonically active basins seals that could have controlled the movement of brines and hydrocarbons during the diagenetic evolution of the basin can also be assessed this is relevant for the identification of maturation conditions the potential development of secondary fracture permeability due to hydraulic fracturing in buried areas of the basin can also be evaluated based on the identification of formerly overpressured horizons in outcrops the origin of concretions is generally a geological puzzle clifton 1957

scp a probe of ultralow velocity zones at the base of the mantle the core reflected phase scp is a sensitive probe of the properties of an ultralow velocity zone ulvz at the base of the mantle in synthetic experiments a ulvz with large depressions in p and s velocities results in scp having two diagnostic precursors and one later arrival whose timing depends on ulvz vp vs and thickness amplitudes of the additional arrivals can be large if ulvz shear velocity has extreme reductions such as 30 and greater some data examples are presented for southwest pacific events recorded at short period and broadband arrays in hawaii which show evidence for a ulvz resolving all three additional arrivals will help in addressing the strength and ratio of vs and vp reductions in ulvz and thus the issue of partial melt

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

bounce rock a shergottite like basalt encountered at meridiani planum mars additional co authors thanasis economou steven p gorevan brian c hahn gostar klingelhofer timothy j mccoy harry y mcsween jr douglas w ming richard v morris daniel s rodionov steven w squyres heinrich wanke shawn p wright michael b wyatt albert s yen

fine scale ultralow velocity zone structure from high frequency seismic array data 1 variability of core mantle boundary cmb structure is imaged at the kilometer to tens of kilometers scale by intensive waveform modeling of the scp phase recordings of earthquakes in the tonga fiji subduction zone from the small aperture 10 km high frequency 2 4 hz alice springs array in central australia are used to document anomalous scp waveform variations due to the presence of an ultralow velocity zone ulvz at the cmb these data expand coverage from previous results using the warramunga array which is located slightly to the north and indicate the existence of a geographically confined ulvz at the cmb roughly 100 km in lateral extent south of new caledonia and east of australia synthetic modeling indicates seismic velocity reductions of 8 and 24 for p wave and s waves respectively and a well constrained density increase of 10 in a 8 5 km thick layer above the cmb this ulvz patch is well explained by an elevated iron content of partially molten mantle material likely present as divalent oxidized iron in the low spin state the properties of such an iron enriched assemblage are consistent with both an elevated density and bulk modulus of this region as are dictated from our best fit seismic results furthermore a positive velocity gradient within the ulvz may be present which need not be associated with a decrease in melt content within this region but could rather be associated with a shift in the textural distribution of melt within the ulvz

the core mantle boundary the largest compositional discontinuity within the earth is the core mantle boundary cmb at a depth of 2889 km this boundary and the adjacent transition zones in the lowermost mantle and outermost core play a critical role in the earth s thermal and chemical evolution estimates of the heat flux out of the core indicate that the 200 km thick d region at the base of the mantle is a major thermal boundary layer the d region like its counterpart boundary layer in the lithosphere is laterally heterogeneous and possibly chemically stratified this complexity obscures the exact dynamic behavior of the d region however it is clear that the large density contrast 4 3 g em 3 across the cmb provides favorable con ditions for density stratification on both sides of the boundary the d region may be the refuse pile for heavy mantle heterogeneities while the outermost core may have a concentration of light components boundary layer instabilities in d have been invoked as sources of both localized mantle plumes and major upwelling currents in whole mantle convection systems dynamically supported topography on the cmb and lateral temperature gradients in d may produce coupling between the core and mantle influencing the excitation of the geodynamo the outer most core is generally believed to be radially and laterally homogeneous although chemical stratification has not been ruled out seismological geodynamical and geomagnetic investigations are unveiling the three dimensional complexity of the deep earth in the vicinity of the cmb

the core mantle boundary under the gulf of alaska no ulvz for shear waves the earth s core mantle boundary cmb marks the boundary between the hot molten iron core and the silicate mantle and is a thermal chemical and flow boundary previous observations of very slow compressional wavespeeds suggest that thin ultra low velocity zones ulvzs possibly composed of a mixture of molten iron and silicates exist at the base of the mantle a molten or partially molten layer would cause a large shear wavespeed decrease however this velocity drop has not been observed here we use core reflected scp phases to investigate the shear properties of ulvzs these phases reveal at least two distinct regions one region under central america which is distinctly average prem and iasp91 like and a second region under the entire gulf of alaska that produces large scp reflections with amplitudes of up to 30 times larger than calculated with average earth models the large amplitudes suggest a combination of focusing by cmb topography high shear wavespeeds at the bottom of the mantle and low attenuation high q along the scp path high shear wavespeeds and low attenuation are opposite from what would be expected from a shear wave ulvz a ulvz in compressional wavespeeds ultra low vp has previously been observed in this region however in addition to the large amplitudes the short period scp waveforms show no complexity that can be related to a ulvz thus either there is not a ulvz under the gulf of alaska or if it does exist it is restricted to compressional wavespeed changes precluding interpretation as partial melt but rather suggesting a chemical origin fl 2000 published by elsevier science b v all rights reserved

complex scattering within d observed on the very dense los angeles region seismic experiment passive array several seismic phases that scattered within a few hundred kilometers of the base of the mantle are observed in a very dense seismic section the los angeles region seismic experiment passive phase array was composed of 88 seismometers placed along a 175 km profile records from two deep earthquakes in tonga and one earthquake near honshu japan show a secondary arrival between clear p and pcp arrivals modeling with layered structures shows that the tonga and honshu seismic sections are consistent with an increase in seismic velocity 140 and 240 km above the core mantle boundary respectively and a 10 km thick low velocity zone at the base of the mantle beneath a region in the mid pacific several of these arrivals are not coherent enough to appear in higher resolution stacks from the much larger southern california seismic network this experiment illustrates that fine scale passive array data can reveal small scale deep earth structure invisible to larger scale seismic networks

crater gradation in gusev crater and meridiani planum mars 1 the mars exploration rovers investigated numerous craters in gusev crater and meridiani planum during the first 400 sols of their missions craters vary in size and preservation state but are mostly due to secondary impacts at gusev and primary impacts at meridiani craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes effects of gradation on crater form are dependent on size local lithology slopes and availability of mobile sediments at gusev impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks ejecta initially experience eolian stripping which becomes weathering limited as lags develop on ejecta surfaces and sediments are trapped within craters subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting at meridiani the sulfate rich bedrock is more susceptible to eolian erosion and exposed crater rims walls and ejecta are eroded while lower interiors and low relief surfaces are increasingly infilled and buried by mostly basaltic sediments eolian processes outpace early mass wasting often produce meters of erosion and mantle some surfaces some small craters were likely completely eroded buried craters 100 m in diameter on the hesperian aged floor of gusev are generally more pristine than on the amazonian aged meridiani plains this conclusion contradicts interpretations from orbital views which do not readily distinguish crater gradation state at meridiani and reveal apparently subdued crater forms at gusev that may suggest more gradation than has occurred

comment on reproducing earth s kernel uncertainty of the shape of the core mantle boundary from pkp and pcp travel times by p b stark and n w hengartner

influence of fissuring and karstification of the carbonate aquifer unsaturated zone on its vulnerability to contamination cracow upper jurassic region poland the carbonate fissure karstic aquifer of upper jurassic age is the main aquifer in the cracow upper jurassic region cujr the aquifer is recharged directly or indirectly by quaternary or quaternary cretaceous overburden of varying permeability which predominates diffused recharge concentrated recharge occurs locally and has a diverse nature field studies carried out in 20 quarries show moderate permeability of the unsaturated zone of carbonate massif karst funnels are filled with rubble and clay material and dominate filled fissures with an opening b 10 mm the average surface fissure porosity of massive with chalky limestones and bedded limestones reach 0 12 and 0 45 respectively while fissure permeability coefficient is respectively ks 6 60 10 5 and 1 27 10 3 m s the average karstification in quarries was determined as nk 2 5 tracer studies carried out in an unconfined carbonate zakrzowek horst in cracow krakow document vertical migration of infiltrating water through the systems with different hydraulic resistance with a flow rate from 8 1 10 6 to 4 9 10 5 m s and the lateral migration velocity between communicated caves from 6 94 10 6 to 1 06 10 4 m s the significant presence of poorly permeable overburden and moderate fissuring and karstification of rock in the unsaturated zone of cujr are reflected in the assessment of the upper jurassic aquifer vulnerability to contamination performed by a modified drastic method in the area of unconfined karst occupying 55 of the area vulnerability to contamination is high while as much as 45 of the area is characterized by medium and low vulnerability

a martian analog in kansas comparing martian strata with permian acid saline lake deposits an important result of the mars exploration rover s mer mission has been the images of sedimentary structures and diagenetic features in the burns formation at meridiani planum bedding cross bedding ripple marks mud cracks displacive evaporite crystal molds and hematite concretions are contained in these martian strata together these features are evidence of past saline groundwater and ephemeral shallow surface waters on mars geochemical analyses of these martian outcrops have established the presence of sulfates iron oxides and jarosite which strongly suggests that these waters were also acidic the same assemblage of sedimentary structures and diagenetic features is found in the salt bearing terrestrial red sandstones and shales of the middle permian ca 270 ma nippewalla group of kansas which were deposited in and around acid saline ephemeral lakes these striking sedimentological and mineralogical similarities make these permian red beds and evaporites the best known terrestrial analog for the martian sedimentary rocks at meridiani planum

athena mars rover science investigation 1 each mars exploration rover carries an integrated suite of scientific instruments and tools called the athena science payload the primary objective of the athena science investigation is to explore two sites on the martian surface where water may once have been present and to assess past environmental conditions at those sites and their suitability for life the remote sensing portion of the payload uses a mast called the pancam mast assembly pma that provides pointing for two instruments the panoramic camera pancam and the miniature thermal emission spectrometer mini tes pancam provides high resolution color stereo imaging while mini tes provides spectral cubes at mid infrared wavelengths for in situ study a five degree of freedom arm called the instrument deployment device idd carries four more tools a microscopic imager mi for close up imaging an alpha particle x ray spectrometer apxs for elemental chemistry a mossbauer spectrometer mb for the mineralogy of fe bearing materials and a rock abrasion tool rat for removing dusty and weathered surfaces and exposing fresh rock underneath the payload also includes magnets that allow the instruments to study the composition of magnetic martian materials all of the athena instruments have undergone extensive calibration both individually and using a set of geologic reference materials that are being measured with all the instruments using a mer like rover and payload in a number of field settings we have devised operations processes that will enable us to use the mer rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites

observations of high frequency scattered energy associated with the core phasepkkp stacks of global seismic network data reveal emergent high frequency 1 hz energy extending back from the pkkpc caustic at 72 to a distance of about 60 the arrival s emergent onset long duration 150 s apparent slowness and proximity to the core phase pkkp indicate a deep scattering origin however the amplitude and timing of the observations are difficult to explain with simple models of pkkp scattering

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

localized boundary layer below the mid pacific velocity anomaly identified from a pcp precursor dense record sections from deep earthquakes in fiji and argentina recorded on hundreds of short period stations in california at distances of 81 to 85 are used to investigate the detailed p wave velocity structure above the core mantle boundary cmb in the fiji data a secondary phase arriving 2 to 4 s after the direct p is identified as a precursor to pcp this phase provides good evidence for a reflection off the top of a thin low velocity layer above the cmb comparisons to synthetic seismograms indicate a layer thickness of 10 km and a velocity reduction of 5 10 compared to the overlying mantle a record section from an argentina event does not show the pcp precursor indicating that the low velocity layer is not a global feature this thin low velocity layer is in the same place as a much larger s wave velocity anomaly in the lower mantle and is probably indicative of a boundary layer just above the cmb under the mid pacific

simulation of long period 3 d elastic responses for whole earth models summary improvements in gdsn seismic data quality and advances in numerical algorithms for solution of the wave equation now make it useful and feasible to simulate long period elastic responses for 3 d whole earth models the algorithm used is eighth order finite differencing on a staggered grid this allows stable computation at boundaries with large contrasts in poisson s ratio such as the core mantle boundary as the solution automatically generates all wave types it may lead to prediction of previously unobserved or misinterpreted phases and allow more detailed analysis of all phases simulations of large e g nuclear explosions and double couple earthquake sources reveal the effects on relative amplitudes of their respective radiation patterns in both wavefield snapshots and seismogram profiles a large number of phases are affected even by a single smooth bump on the core mantle boundary a 3 d whole earth model implicitly contains the travaltimes for all source receiver positions and for any source configuration the corresponding amplitudes of all phases thus 3 d numerical modelling of whole earth responses is a potentially valuable diagnostic and interpretive tool and a basis for globalization in contrast to regionalization of traveltime tables

soils of eagle crater and meridiani planum at the opportunity rover landing site the soils at the opportunity site are fine grained basaltic sands mixed with dust and sulfate rich outcrop debris hematite is concentrated in spherules eroded from the strata ongoing saltation exhumes the spherules and their fragments concentrating them at the surface spherules emerge from soils coated perhaps from subsurface cementation by salts two types of vesicular clasts may represent basaltic sand sources eolian ripples armored by well sorted hematite rich grains pervade meridiani planum the thickness of the soil on the plain is estimated to be about a meter the flatness and thin cover suggest that the plain may represent the original sedimentary surface

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

constraints on small scale heterogeneity in the lowermost mantle from observations of near podal pcp precursors abstract volumetric heterogeneities on large 1000 km and intermediate scales 100 km in the lowermost mantle have been established with seismological approaches however there are controversies regarding the level of heterogeneity in the lowermost mantle at small scales a few kilometers to tens of kilometers with lower bound estimates ranging from 0 1 to a few percent we take advantage of the small amplitude pcp waves at near podal distances 0 12 to constrain the level of small scale heterogeneity within 250 km above the cmb first we compute short period synthetic seismograms with a finite difference code for a series of volumetric heterogeneity models in the lowermost mantle and find that pcp is not identifiable if the small scale heterogeneity in the lowermost mantle is above 2 5 we then use a functional form appropriate for coda decay to suppress p coda contamination by comparing the corrected envelope of pcp and its precursors with synthetic seismograms we find that perturbations of small scale 8 km heterogeneity in the lowermost mantle is 0 2 0 5 beneath regions of the china myanmar border area okhotsk sea and south america whereas strong perturbations 1 0 are found beneath central america in the regions studied we find that this particular type of small scale heterogeneity in the lowermost mantle is weak yet there are some regions requiring heterogeneity up to 1 0 where scattering is stronger such as under central america more chemically complex mineral assemblages may be present at the core mantle boundary

seismological constraints on the ultralow velocity zones in the lowermost mantle from core reflected waves abstract analyses of reflected seismic phases pcp and scp from the core mantle boundary cmb enable us to constrain the physical properties of the ultralow velocity zones ulvzs at the base of the mantle the cmb region beneath the western and southern pacific is investigated in detail by using a large amount of waveform data recorded by the short period array stations clear arrivals of postcursor to scp scsp are detected from several event receiver pairs which sample the cmb regions beneath philippine kalimantan and east of australia indicating the existence of ulvzs under the regions no scp precursors sdp and spcp are found in our data set except for a few events with a large epicentral distance over 45 no additional arrivals related to pcp are found in the region where scsp is observed in the scp wavelet elastic properties of the ulvz are precisely constrained by waveform modeling of both pcp and scp which sample the cmb region under philippine kalimantan different ulvz structures are found between the northeastern and southwestern parts of the philippine kalimantan the ratio of shear to compressional velocity reductions is 2 0 2 5 and the ratio of density to shear velocity changes is 0 5 to 0 33 in the northeastern part while minimal changes in compressional velocity and large shear velocity decrease in the southwestern part are found a certain degree of density increases and shear velocity decreases are also observed in the ulvz beneath east of australia increase in density and decrease in shear velocity throughout our observation imply that the iron incorporation into the lowermost mantle minerals may generate the ulvz anomaly however other mechanisms such as partial melting can explain the structural difference between the northeastern and southwestern parts of the ulvz beneath the philippine kalimantan region

extraction of weak pcp phases using the slant stacklet transform i method and examples summary in order to study fine scale structure of the earth s deep interior it is necessary to extract generally weak body wave phases from seismograms that interact with various discontinuities and heterogeneities the recent deployment of large scale dense arrays providing high quality data in combination with efficient seismic data processing techniques may provide important and accurate observations over large portions of the globe poorly sampled until now major challenges are low signal to noise ratios snr and interference with unwanted neighbouring phases we address these problems by introducing scale dependent slowness filters that preservetime spaceresolution wecombinecomplexwaveletandslant stacktransformstoobtain the slant stacklet transform this is a redundant high resolution directional wavelet transform with a direction here slowness resolution that can be adapted to the signal requirements to illustrate this approach we use this expansion to design coherence driven filters that allow us to obtain clean pcp observations a weak phase often hidden in the coda of the p wave for events with magnitude mw 5 4 and distances up to 80 in this context we then minimize a linear misfit between p and pcp waveforms to improve the quality of pcp p traveltime measurements as compared to a standard cross correlation method this significantly increases both the quantity and the quality of pcp p differential traveltime measurements available for the modelling of structure near the core mantle boundary the accuracy of our measurements is limited mainly by the highest frequencies of the signals used and the level of noise we apply this methodology to two examples of high quality data from dense arrays located in north america while focusing here on body wave separation the tools we propose are more general and may contribute to enhancing seismic signal observations in global seismology in situations of low snr and high signal interference

a sharp and flat section of the core mantle boundary the transition zone between the earth s core and mantle plays an important role as a boundary layer for mantle and core convection1 this zone conducts a large amount of heat from the core to the mantle and contains at least one thermal boundary layer2 3 the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4 here we investigate one region of the core mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary the use of this phase known as scp the large number of receiving stations and the large aperture of our array all provide higher resolution than has previously been possible5 7 for the 350 km long section of the core mantle boundary under the northeast pacific sampled by the reflections the local boundary topography has an amplitude of less than 500 m no sharp radial gradients exist in the 400 km above the boundary and the mantle to core transition occurs over less than 1 km the simplicity of the structure near and above the core mantle boundary argues against chemical heterogeneity at the base of the mantle in this location

aeolian features and processes at the mars pathfinder landing site the mars pathfinder landing site contains abundant features attributed to aeolian or wind processes these include wind tails drift deposits duneforms of various types ripplelike features and ventifacts the first clearly seen on mars many of these features are consistant with formation involving sand size particles although some features such as dunes could develop from saltating sand size aggregates of finer grains the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline rather than aggregates excluding the ventifacts the orientations of the wind related features correlate well with the orientations of bright wind steaks seen on viking orbiter images in the general area they also correlate with wind direction predictions from the nasa ames general circulation model gcm which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209

rock abrasion tool mars exploration rover mission 1 the rock abrasion tool rat is an integral part of the athena science payload serving primarily as the geologist s rock hammer the rat will expose fresh surfaces of martian rocks to other instruments on the payload the rat also brushes dust and debris from an excavated hole or unaltered rocks to accomplish these tasks autonomously the rat a sophisticated 3 axis precision controlled device was designed data products derived from rat telemetry enable the rat to also act as an important rock physical properties science instrument the returned rat grinding and penetration rate data will be inverted and compared to a rock library on the earth the design is also very compact and lightweight the rat is contained within a cylinder 128 mm long and 85 mm in diameter and has a mass of 687 g

a scattering region near the core mantle boundary under the north atlantic summary we analysed pcp precursors in seven events from central america recorded at the uk array of short period stations to determine the most likely source of this signal combinations of observations of slowness traveltime and backazimuth were used to investigate the properties of the phase with the result that its source is identified as p to p scattering from an anomalous region in the lower mantle within d using a joint likelihood method the best estimate of a point source for scattering is at 44 0 n 71 5 w under nova scotia and 2720 km depth analysis of the spectrum of the scattered signal indicates that the region contains small scale heterogeneities on the order of 0 6 to 0 7 km and is 700 km in size the velocity contrast between the scattering bodies and ambient mantle is as high as 0 4 to 0 7 per cent vp and 1 4 to 6 6 per cent vs on account of their small size positive velocity anomaly and association with the reconstructed position of ancient subducted material we conclude that they represent chemical heterogeneity in the lower mantle

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

hydrothermal synthesis of hematite spherules and jarosite implications for diagenesis and hematite spherule formation in sulfate outcrops at meridiani planum mars we synthesized hematite spherules whose mineralogic chemical and crystallographic properties are strikingly similar to those for the hematite rich spherules in lag deposits on the surface and embedded in outcrops at meridiani planum mars the spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from fe al mg s cl acid sulfate solutions under hydrothermal conditions the reaction sequence was 1 precipitation of hydronium jarosite 2 jarosite dissolution and precipitation of hematite spherules and 3 precipitation of hydronium alunite upon depletion of hydronium jarosite the spherules exhibit a radial growth texture with the crystallographic c axis aligned along the radial direction so that thermal emission spectra have no hematite emissivity minimum at 390 cm 1 our experiments show that hydrothermal acid sulfate solutions are a pathway for formation of jarosite and the hematite spherules at meridiani planum mars

evidence from opportunity s microscopic imager for water on meridiani planum the microscopic imager on the opportunity rover analyzed textures of soils and rocks at meridiani planum at a scale of 31 micrometers per pixel the uppermost millimeter of some soils is weakly cemented whereas other soils show little evidence of cohesion rock outcrops are laminated on a millimeter scale image mosaics of cross stratification suggest that some sediments were deposited by flowing water vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis microscopic images support the hypothesis that hematite rich spherules observed in outcrops and soils also formed diagenetically as concretions

lower mantle heterogeneity beneath eurasia imaged by parametric migration of shear waves abstract lower mantle structure beneath central eurasia is examined using a recently developed technique for migrating parametric representations of shear waves from teleseismic events the migration method of lay and young lay t young c j 1996 imaging scattering structures in the lower mantle by migration of long period shear waves j geophys res 101 20 023 20 040 assumes isotropic scattering from discrete heterogeneities to account for s wave coda arrivals and provides resolution at scale lengths of about 500 km the migration is applied to 15 s period shear wave data from 21 western pacific earthquakes recorded in europe and the middle east that exhibit extra arrivals between s and scs on the transverse components migrations are performed using prem as well as model sgle gaherty j b lay t 1992 investigation of laterally heterogeneous shear velocity structure in d beneath eurasia j geophys res 97 417 435 which has a discontinuity at 2605 km 286 km above the core mantle boundary the migration images for the most coherent coda arrival scd resemble those expected for a lower mantle discontinuity model and simulations are performed for models with discontinuities at various depths quantitative correlation of the images for the data and synthetic migrations show the optimal average depth of the discontinuity to be 2605 km migrations of subsets of the data suggest that the discontinuity depth varies from 2605 km in the northern end of the study area to 2620 km in the southern end an additional intermediate arrival scd2 is observed in a limited portion of the dataset and migrations indicate this phase is generated by localized discrete scatterers located at depths of 2750 to 2770 km under north central eurasia these results are generally consistent with previous forward modeling studies but the migration approach allows lateral variations to be modeled more systematically the heterogeneous structure near the base of the mantle appears to be a manifestation of a complex boundary layer

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

observations of pkkp precursors used to estimate small scale topography on the core mantle boundary stacks of global seismic data reveal the time and distance dependence of high frequency 1 hertz precursors to the seismic phasepkkp synthetic seismogram modeling shows that scattering from random small scale topography at the pkkpcore mantle boundary reflection point generates precursory arrivals similar to those seen in the data models with a root mean square core mantle boundary topography of 250 to 350 meters and correlation length of 7 to 10 kilometers explain the main features of the data however a systematic range dependent misfit between observed and predicted precursor power suggests that inner core scattering may contribute to the precursors

seismological mapping of fine structure near the base of the earth s mantle the earth s core mantle boundary cmb juxtaposes liquid iron and crystalline silicates and is a region of large vertical thermal gradients the d region which extends up to 200 300 km above the cmb often has elevated shear wave velocity and suggestions of lateral variations in structure1 recent improvements in our ability to assemble and analyse records from regional seismic networks have allowed us to examine long profiles of travel times amplitudes and waveforms from more than a thousand short period seismometers2 we observe across canada and the united states p waves that have grazed the cmb from the powerful nuclear test in lop nor china on 21 may 1992 first arrival travel times and large secondary arrivals are consistent with a 1 5 compressional velocity increase with depth 130 km above the cmb about half the thickness of d in this locality3 our observations together with evidence for the absence of such a thin fast layer in neighbouring regions suggest the presence of lateral heterogeneity in composition or phase at the base of the mantle

a new hematite formation mechanism for mars the origin of hematite detected in martian surface materials is commonly attributed to weathering processes or aqueous precipitation here we present a new hematite formation mechanism that requires neither water nor weathering glass rich basalts with martian meteorite like chemistry high feo low al2o3 oxidized at high 700 and 900 c temperatures in air and co2 respectively form thin 1 m hematite coatings on their outermost surfaces hematite is manifested macroscopically by development of magnetism and a gray metallic sheen on the glass surface and microscopically by fe enrichment at the glass surface observed in element maps visible and nearinfrared thermal infrared and raman spectroscopy confirm that the fe enrichment at the oxidized glass surfaces corresponds to hematite mineralization hematite formation on basaltic glass is enabled by a mechanism that induces migration of fe2 to the surface of an oxidizing glass and subsequent oxidation to form hematite a natural example of the hematite formation mechanism is provided by a hawaiian basalt hosting a gray metallic sheen that corresponds to a thin hematite coating hematite coating development on the hawaiian basalt demonstrates that martian meteorite like feo contents are not required for hematite coating formation on basalt glass and that such coatings form during initial extrusion of the glassy basalt flows if gray hematite originating as coatings on glassy basalt flows is an important source of martian hematite which is feasible given the predominance of igneous features on mars then the requirement of water as an agent of hematite formation is eliminated

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

localization and physical property experiments conducted by opportunity at meridiani planum the location of the opportunity landing site was determined to better than 10 m absolute accuracy from analyses of radio tracking data we determined rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images topographic profiles generated from rover data show that the plains are very smooth from meter to centimeter length scales consistent with analyses of orbital observations solar cell output decreased because of the deposition of airborne dust on the panels the lack of dust covered surfaces on meridiani planum indicates that high velocity winds must remove this material on a continuing basis the low mechanical strength of the evaporitic rocks as determined from grinding experiments and the abundance of coarse grained surface particles argue for differential erosion of meridiani planum

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

high resolution cmb imaging from migration of short period core reflected phases abstract the fine scale structure of the core mantle boundary cmb region beneath southern alaska is studied using core reflected p waves pcp recorded at the canadian yellowknife array seismic studies of the lowermost mantle have detected a multitude of structures at this contact zone between iron alloy liquid of the core and the silicates of the mantle these structures offer key constraints for the dynamics of mantle and core high quality waveform information and migrated array data have been used to infer the existence of thin layering at the cmb in the form of ultra low velocity zones the data clearly show the absence of an ultra low velocity zone thicker than about 7 km in this region while there is evidence for a weak p wave reflector about 110 km above the cmb beneath the kenai peninsula these observations are in good agreement with the hypothesis that ultra low velocity zones are related to areas with lower than average seismic velocities in tomographic images and absent in regions of fast seismic velocities likely related to subduction processes such as beneath alaska

few 2 50 km corrugations on the core mantle boundary short period pcp amplitudes have been observed to vary by a factor of about 20 in the epicentral range 40 85 this behavior is due to the reflection coefficient at the core mantle boundary which varies from a maximum of about 0 5 at an angle of incidence of about 65 to zero at an angle of incidence of about 85 corresponding to an epicentral ranges of about 60 90 we present physical model experiments in which we study the effect of corrugations of the core mantle boundary on pcp amplitudes we find that corrugations with 2 50 km scale lengths would radically alter the amplitude range behavior of short period pcp reducing its variation with range the observed pattern of short period pcp amplitudes indicates that the core mantle boundary is smooth on these scales with amplitudes less than a few hundred meters

layered mantle convection a model for geoid and topography the long wavelength geoid and topography are dynamic effects of a convecting mantle the long wavelength geoid of the earth is controlled by density variations in the mantle and has been explained by circulation models involving whole mantle flow however the relationship of long wavelength topography to mantle circulation has been a puzzling problem in geodynamics we show that the dynamic topography is mainly due to density variations in the upper mantle even after the effects of lithospheric cooling and crustal thickness variation are taken into account layered mantle convection with a shallow origin for surface dynamic topography is consistent with the spectrum small amplitude and pattern of the topography layered mantle convection with a barrier about 250 km deeper than the 670 km phase boundary provides a self consistent geodynamic model for the amplitude and pattern of both the long wavelength geoid and surface topography

an empirical search for short wavelength heterogeneities in d using isc p delays abstract the spectrum of the heterogeneities in the d layer at the base of the mantle is investigated using a comparison of p delays for rays bottoming respectively inside and above d data come from the international seismological centre isc bulletins they reveal a decoupling between d and the overlying structures and the presence in d of a short wavelength signal which may contaminate global tomographic models

small scale ultralow velocity zone structure imaged by scp 1 short period teleseismic scp phases from events in the tonga fiji region recorded at the short period small aperture warramunga array in australia are used to study structure at the core mantle boundary cmb we examine the data for evidence of precursors and postcursors to scp such additional arrivals are generated by the interaction of scp with structure at the reflection and conversion point at or near the cmb we show precursors and postcursors to scp indicating an ultralow velocity zone ulvz at the cmb in the region between tonga fiji and australia one dimensional forward modeling of the short period data leads to models of the ulvz with thickness varying between 5 and 20 km velocity reductions of 0 10 and 10 30 for p velocity and s velocity respectively and 0 50 density increase many events however show simple waveforms consistent with a locally simple cmb models for proximal events can vary greatly indicating very complex three dimensional structure with scale lengths of a few tens of kilometers these results point to complex chemical and physical processes in the lowermost mantle

spectrophotometric properties of materials observed by pancam on the mars exploration rovers 2 opportunity 1 the panoramic camera pancam on the mars exploration rover opportunity acquired visible near infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in meridiani planum nearly 25 000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles 0 150 at eagle crater in the surrounding plains in endurance crater and in the plains between endurance and erebus craters through sol 492 corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission disparity maps created from pancam stereo images allowed inclusion of local facet orientation estimates outcrop rocks overall exhibited the highest single scattering albedos 0 9 at 753 nm and most spherule rich soils exhibited the lowest 0 6 at 753 nm macroscopic roughness among outcrop rocks varied but was typically larger than spherule rich soils data sets with sufficient phase angle coverage resulting in well constrained hapke parameters suggested that models using single term and two term henyey greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule rich soils rover tracks and other compressed soils exhibited forward scattering while outcrop rocks were intermediate in their scattering behaviors some phase functions exhibited wavelength dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission

characterization and mapping of surface physical properties of mars from crism multi angular data application to gusev crater and meridiani planum the analysis of particle physical properties grain size shape and internal structure and its organization surface porosity roughness and grain size distribution provides information about the geological processes which formed and modified planetary surfaces crism compact reconnaissance imaging spectrometer for mars multi angular observations varied emission angles allow for the characterization of the surface scattering behavior which depends on the composition and on the material physical properties such as the grain size shape internal structure and the surface roughness after an atmospheric correction compensating mineral aerosol effects by the multi angle approach for retrieval of the surface reflectance from crism observations mars reco the surface reflectances at different geometries were analyzed by inverting the hapke photometric model depending on six parameters single scattering albedo 2 phase function terms macroscopic roughness and 2 opposition effects terms in this work surface photometric maps are created to observe the spatial variations of surface scattering properties as a function of geological units information regarding the single scattering albedo the particle phase function and the macroscopic roughness are provided at the crism spatial resolution 200 m pixel this article describes the application of this methodology to the data covering the mars exploration rover mer landing sites located at gusev crater and meridiani planum where orbital and in situ observations are available complementary orbital observations e g crism spectra thermal emission imaging system themis high resolution imaging science experiment hirise images were used for interpreting the modeled hapke photometric parameters in terms of physical properties which can be used to constrain the geological processes available mer in situ observations were used as ground truth to validate the interpretations of the hapke parameters varied scattering properties were observed within a crism observation 5 10 km suggesting that the surfaces are controlled by local geological processes e g volcanic resurfacing aeolian and impact processes rather than regional or global processes results are consistent with the in situ observations thus validating the approach and the use of photometry for the characterization of martian surface physical properties

reflection properties of the core mantle boundary from global stacks of pcp and scp 1 seismic phases that reflect off the core mantle boundary cmb are sensitive to the velocity and density contrasts between the base of the mantle and the core we measure the amplitudes of cmb reflections to seek effects of large velocity reductions and possible density increases in proposed thin basal layers ultralow velocity zones or ulvzs we construct globally averaged envelope stacks of pcp and scp in 3 wide epicentral distance bins correcting for propagation and source effects we measure the amplitude ratios pcp p and scp p and compare them with the predicted range dependence for preliminary reference earth model prem and several proposed ulvz models the amplitude ratios are not compatible with ulvzs containing 30 s wave velocity reductions or with a 3 km wide core mantle transition zone the pcp data cannot distinguish between prem and models with 10 reductions in both p wave velocity vp and s wave velocity vs and up to a 20 increase in density the scp data also match prem closely but contain greater uncertainty from the correction for mantle attenuation in well sampled regions lateral variations of reflection amplitudes mapped to bounce point locations are consistent with previous detections and nondetections of ulvzs these results suggest that extreme velocity reductions near the cmb are not global features and that regions with large velocity reductions do not result from global phenomena such as phase changes in an isochemical mantle but rather from local thermal or compositional anomalies index terms 7203 seismology body wave propagation 7207 seismology core and mantle 8124 tectonophysics earth s interior composition and state 1212 keywords core mantle boundary ultralow velocity zones pcp scp citation persh s e and j e vidale 2004 reflection properties of the core mantle boundary from global stacks of pcp and scp j geophys res 109 b04309 doi 10 1029 2003jb002768

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

lowermost mantle anisotropy beneath the pacific imaging the source of the hawaiian plume we utilized recordings of seismic shear phases provided by several north american broadband seismometer arrays to provide unique constraints on shear wave anisotropy beneath the northern and central pacific ocean using a new analysis method that reduces measurement errors and enables the analysis of a larger number of available waveforms we examined relative travel times of teleseismic s and sdiff that sample a large area of lowermost mantle structure the results of this study provide evidence for small scale lateral and depth variations in shear wave anisotropy for a broad region of the lowermost mantle beneath the pacific ocean in particular we image a localized zone of anomalously strong anisotropy whose strength increases toward the top of dq beneath hawaii our results combined with a previous study of vp vsh ratios indicate that ancient subducted slab material may be responsible for observations beneath the northern pacific while lenses or layers of core mantle boundary reaction products or partial melt oriented by horizontal inflow of mantle material to the hawaiian plume source can explain observations beneath the central pacific fl 2001 elsevier science b v all rights reserved

antarctic permafrost an analogue for water and diagenetic minerals on mars at high altitudes 1000 m throughout the dry valleys antarctica liquid water is rare yet ground ice which may be millions of years old is pervasive in glacial sediments and bedrock the origin of this ice is different from its arctic and alpine counterparts and may be similar to water on mars we present chemical and isotopic analyses of antarctic ground ice from cores of sirius group sediments at table mountain in the dry valleys these data together with the presence of diagenetic calcite and chabazite in the frozen sediments indicate that the ice and minerals accumulated over long periods of time from atmospheric water vapor and brine films formed on the surface of the ground this analogy indicates that ferric bearing minerals could precipitate under present conditions in the martian soil

mantle layering from scs reverberations 4 the lower mantle and core mantle boundary this is the final installment in a four part sequence that examines the nature of mantle layering required by the multiple scs phases and internal reflections observed within the reverberative interval of sh polarized seismograms in this paper long period sh polarized multiple scs phases reflected once from a mantle discontinuity first order reverberations are used to search for abrupt shear wave impedance contrasts in the lower mantle beneath the geographic regions sampled the depth interval of 1000 2600 km bullen s region d appears free of any distinct radial layering in agreement with the majority of recent seismic models and the notion of near adiabatic compression of a compositionally homogeneous lower mantle to pass undetected discontinuities in d must be either small sh polarized reflection coefficient r0 1 0 highly intermittent or subject to lateral depth variations well in excess of 50 km at greater depths corresponding to the d region of the lowermost mantle we find evidence for a reflector of long period seismic energy situated an average of 325 km above the core mantle boundary cmb similar to the discontinuity proposed by t lay and coworkers our results indicate a 4 4 increase in shear wave impedance and a 1 7 increase in density if the 2 75 increase in shear velocity proposed by lay and helmberger 1983 holds true for our study area the discontinuity is observed beneath less than one third of the 18 seismic corridors examined and does not appear to be a ubiquitous feature of the lower mantle this plus an observed correlation of discontinuity depth and lower mantle velocity heterogeneity and the lack of experimental evidence for deep mantle phase transformations strongly favor a compositional origin mantle side layering nearer the cmb perhaps associated with a thin chemical boundary layer would mimic the effects of the surface crust producing a complex wave train of first and higher order reverberations superposed upon all other reverberative interval arrivals if present and unaccounted for cmb structure would drive estimates of crustal structure and qscs obtained by multiple scs waveform inversion away from their true values compared to independent estimates our results admit little bias monte carlo tests are used to assess the sensitivity of this technique to cmb layering which decreases with decreasing boundary layer thickness nonetheless the results limit cmb transition zones in excess of 20 km to impedance contrasts less than 12 8 for a 40 km transition beneath much of the western pacific australia melanesia and indonesia

laboratory simulated acid sulfate weathering of basaltic materials implications for formation of sulfates at meridiani planum and gusev crater mars 1 acid sulfate weathering of basaltic materials is a candidate formation process for the sulfate rich outcrops and rocks at the mer rover opportunity and spirit landing sites to determine the style of acid sulfate weathering on mars we weathered basaltic materials olivine rich glassy basaltic sand and plagioclase feldspar rich basaltic tephra in the laboratory under different oxidative acid sulfate conditions and characterized the alteration products we investigated alteration by 1 sulfuric acid vapor acid fog 2 three step hydrothermal leaching treatment approximating an open system and 3 single step hydrothermal batch treatment approximating a closed system in acid fog experiments a1 fe and ca sulfates and amorphous silica formed from plagioclase rich tephra and mg and ca sulfates and amorphous silica formed from the olivine rich sands in three step leaching experiments only amorphous si formed from the plagioclase rich basaltic tephra and jarosite mg and ca sulfates and amorphous silica formed from olivine rich basaltic sand amorphous silica formed under single step experiments for both starting materials on the basis of our experiments jarosite formation in meridiani outcrop is potential evidence for an open system acid sulfate weathering regime waters rich in sulfuric acid percolated through basaltic sediment dissolving basaltic phases e g olivine and forming jarosite other sulfates and iron oxides aqueous alteration of outcrops and rocks on the west spur of the columbia hills may have occurred when vapors rich in so 2 from volcanic sources reacted with basaltic materials soluble ions from the host rock e g olivine reacted with s to form ca mg and other sulfates along with iron oxides and oxyhydroxides