nonlinear waveform and delay time analysis of triplicated core phases 1 we introduce a new method to measure differential travel times and attenuation of seismic body waves the problem is formulated as a nonlinear inverse problem which is solved by simulated annealing using this technique we have analyzed triplicated pkp waves recorded by the temporary eifel array in central europe these examples demonstrate the potential of the technique which is able to determine differential travel times and waveforms of the core phases even when they interfere on the seismograms or when additional depth phases are present the pkp differential travel times reveal the presence of large amplitude and small scale heterogeneities along the pkp ab ray paths and favor a local radial inner core model with 0 9 velocity perturbation in its top 150 km and small velocity perturbations below the quality factor in the top 300 km of this inner core region is estimated from pkp differential attenuation its preferred value is 330 with a lower bound of 75

late quaternary environmental changes in the pearl river mouth region china abstract this study presents findings concerning late quaternary environmental changes in the pearl river mouth region china based on the study of over 300 boreholes out of these 35 boreholes are selected for the reconstruction of transects across the deltaic plain and estuary 39 radiocarbon dates obtained from these boreholes are used to help define the chronology of stratigraphic units present including two terrestrial units t1 and t2 and two marine units m1 and m2 diatom assemblages are studied in 6 boreholes revealing similarities and differences between the two marine units before the area was inundated by the last interglacial sea mis 5 an older terrestrial unit of sand and gravel t2 was laid down in a number of palaeo valleys during the last interglacial period an older marine unit of silt and clay m2 was laid down which was subsequently subaerially exposed when sea level regressed during the last glacial period mis 4 2 causing the uppermost section to be weathered during the same period a younger terrestrial unit of sand and gravel t1 was deposited along palaeo river channels around the early holocene before 8 2 cal ka bp the postglacial rise in sea level initiated a new phase of sedimentation in the outer part of the estuary characterised by the high percentages of marine diatoms in the sediments in the early holocene strong monsoon freshwater discharge resulted in sedimentation of a fine sand layer in the inner part of the estuary after 8 2 cal ka bp rapid rises in sea level caused widespread marine inundation and sedimentation the diatom data suggest that the relative sea level associated with the m2 and m1 units were both at similar levels because the m2 unit is typically recorded at altitudes of 15 m and 20 m below the present sea level this is likely to be a result of long term subsidence although numerical dating of the pre m1 units has not been made in the present study the chronology of these units can be inferred from uranium series ages and optically stimulated luminescence dating obtained from the adjacent coastal waters of hong kong the t1 unit has yielded ages of about 30 0 cal ka bp while the m2 unit has yielded ages about 130 0 cal ka bp confirming their mis 4 2 and mis 5 ages respectively

imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

measurement of the settling rate of atmospheric dust on mars by the mae instrument on mars pathfinder the materials adherence experiment mae on pathfinder was designed to measure the rate of dust settling from the martian atmosphere onto the solar array of the mars pathfinder sojourner rover the mae measurements indicate steady dust accumulation at a rate of about 0 28 per day this value is consistent with the performance of the lander solar arrays which decreased in power at an estimated rate of 0 29 per day over the same period

support for differential inner core superrotation from earthquakes in alaska recorded at south pole station observational evidence for differential inner core rotation has recently been reported the most convincing evidence has been restricted to one ray path from earthquakes in the south sandwich islands to stations in alaska here we show that the differential travel times between pkp df and pkp bc for a new ray path from earthquakes in southern alaska to the station at the south pole have increased by about 0 6 s over 37 years providing support for a differential inner core rotation we apply a newly developed technique to invert simultaneously for the inner core structure and the rotation rate the rotation rate determined from the new pathway is about 0 6 yr faster than the mantle compatible with the estimates of the rate from earthquakes in the south sandwich islands to stations in alaska we also address some criticisms concerning the reported detection of the differential inner core rotation including biases from event mislocations biases from mantle heterogeneity and uncertainty in the tilt of the inner core anisotropy axis we show that although these potential biases would affect the determination of the rotation rate they are unlikely to account for the observed time dependence in the bc df times we found no evidence for a correlation between bc df residuals and event magnitudes as suggested previously

normal mode coupling due to hemispherical anisotropic structure in earth s inner core summary we present illustrative calculations of the effect of hemispherical variation in inner core anisotropy on earth s normal modes of oscillation body wave studies show that the anisotropy in the inner core is not simple cylindrical anisotropy which is often portrayed in models derived from normal mode data but varies with longitude hemispherical or odd degree structure has to be studied by cross coupling normal modes as the self coupling technique is sensitive only to even degree earth structure a completely general definition of inner core anisotropy would require a prohibitive number of degrees of freedom however we show that any existing cylindrical anisotropy model can be confined to only one part of the inner core using our new theory we find that hemispherical anisotropy causes significant changes in the frequency and quality factor of several inner core sensitive normal modes the effect of hemispherical inner core anisotropy can also be seen in synthetic seismograms radial pkikp and pkjkp modes all respond to the presence of hemispherical variation in inner core anisotropy if the variations in inner core anisotropy seen in body wave data are part of a gross large scale pattern then this structure should also affect normal mode data on an observable scale

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

dust devil track survey at elysium planitia mars implications for the insight landing sites abstract the insight interior exploration using seismic investigations geodesy and heat transport robotic lander is scheduled to land in elysium planitia on mars in september 2016 insight will perform the first comprehensive surface based geophysical investigation including seismic measurements knowledge about encounter rates of dust devils with the insight lander are important for two main reasons 1 dust devils will affect the scientific measurements i e wind induced seismic noise and 2 the power supply of the insight lander and instruments is provided by solar arrays and previous landers and rovers on mars were affected by a steady decline in electrical power output due to atmospheric dust deposition on the solar panels long term science operations were only made possible by dust clearing events of the solar arrays caused by wind gusts and dust devils in this study we analyzed dust devil tracks ddts at the final insight landing site region in elysium planitia formation of ddts is caused by the removal of a layer of dust by passing dust devils hence in principle the same process as clearing of dust from solar panels we mapped the number size width and length and orientation of ddts in repeat observations using high resolution imaging science experiment hirise images covering the exact same surface area acquired within a relatively short time span l s 200 consistent with the seasonal reversal in direction of the hadley circulation ddt formation rates vary between 0 002 and 0 08 ddt km 2 sol 1 ddt area formation rates using the measured ddt widths lengths and formation rates are in the range of 0 0003 0 00006 km 2 km 2 sol 1 implying that a given spot on the surface may be cleared of dust only once between 3000 and 16 000 sols i e every 5 24 mars years measured ddt formation rates were used to find a scaling factor to the seasonal dda index and then integrated over the year to estimate a mean annual ddt formation rate of 0 046 ddt km 2 sol 1 this translates into a solar panel clearing recurrence interval estimate of 11 mars years using the mean annual ddt formation rate and the mean ddt width and length from all measured ddts due to several uncertainties this solar panel clearing recurrence interval for the insight landing should be seen as an upper limit estimate

stratigraphy of quaternary offshore sand and gravel deposits in the hong kong sar china abstract the mining of quaternary offshore sand and gravel deposits in the hong kong special administrative region sar down to a depth of about 60 m below the present sea level has yielded an estimated 350 million m3 to date three main types of deposits have been identified 1 intertidal and near shore subtidal deposits at the mouth of major streams formed by the reworking of pre holocene colluvial alluvial fans 2 alluvial deposits of last glacial and or earlier glacial periods buried by holocene and or earlier interglacial marine deposits and 3 last interglacial marine deposits reworked during the holocene transgression the first two types of deposits commonly occur in areas with or adjacent to granitic bedrock these deposits were formed by the selective transport of deeply weathered granitic residual soils by fluvial processes the third type of deposit includes calcareous shell remains often showing signs of dissolution eustatic sea level changes dating back to approximately 440 000 yr bp were responsible for the quaternary succession palaeo desiccated crusts formed by acid sulphate soil development of the exposed interglacial marine deposits during glacial low sea level stand s are found to be useful stratigraphic markers in assisting interpretation

offshore quaternary sediments and their engineering significance in hong kong yim w w s 1994 offshore quaternary sediments and their engineering significance in hong kong in e f j de mulder editor engineering geology of quaternary deposits eng geol 37 31 50 investigation works undertaken for coastal engineering projects in hong kong has provided abundant information on the quaternary sedimentary sequence beneath the sea floor although the significance of such information may not have been realized at the time of these projects valuable lessons have often been learnt afterwards some examples of the important engineering applications concerning offshore quaternary sediments include 1 the provision of information on water movement sediment transport and sedimentation rates during the holocene period 2 the identification of exploitable offshore sand and gravel resources 3 the interpretation of marine geophysical data through the availability of reliable borehole descriptions 4 the enhancement of engineering soil testing results and their interpretation 5 the prediction of rates of long term ground settlement in coastal land reclaimations 6 the selection of offshore sites for waste disposal 7 the reduction in cost of coastal engineering projects through choosing the most cost effective site 8 the provision of baseline data to assist environmental impact assessment a new geological model is proposed for the offshore quaternary sedimentary sequence of hong kong the engineering properties of the sediments are found to be closely related to the palaco environmental changes

distribution of moisture contents and thermoluminescence ages in an inner shelf borehole from the new hong kong international airport site china abstract offshore boreholes and excavations available through coastal engineering projects in the siliciclastics dominated inner shelf of the northern south china sea off hong kong have permitted the reconstruction of quaternary sea level history dating back to almost 0 5 ma in this study moisture content and thermoluminescence tl dating are utilized to help verify ages for marine and terrestrial sediments in a 39 52 m offshore borehole from the new hong kong international airport site the distribution of moisture contents in borehole samples indicated the presence of three palaeo desiccated crusts formed by soil development when the marine deposits of oxygen isotope oi stage 5 oi stage 7 and oi stage 9 were sub aerially exposed during the low sea level stand s of oi stages 2 4 oi stage 6 and oi stage 8 respectively out of the six tl dated borehole samples three from a terrestrial deposit horizon have yielded finite ages of about 250 000 yr bp suggestive of oi stage 8 in these samples the tl signal of quartz grains was found to increase well beyond the 250 gy saturation level with the relatively high radiation fluxes allowing for age determination for only three samples the three remaining samples of pre holocene marine deposits yielded minimum ages each having reached tl saturation the importance of the moisture content upon the final determination of these sediment ages and the collection and storage of samples for tl dating is clearly demonstrated

magnetic susceptibility study of late quaternary inner continental shelf sediments in the hong kong sar china abstract four cores of inner continental shelf sediment from the hong kong special administrative region sar have been measured for magnetic susceptibility in all the cores the upper part of marine isotope stage mis 1 down to about 3 m below seabed show abruptly elevated but highly variable levels of magnetic susceptibility attributable mainly to shipping contamination over the past 160 years the uncontaminated lower mis 1 deposits show a consistently low magnetic susceptibility above a sharp increase at the holocene pleistocene boundary this increase is accounted for by the presence of eroded palaeosol fragments enriched in iron oxides and hydroxides acid sulphate soil development during mis 2 4 on the sub aerially exposed inner continental shelf covered by mis 5 deposits is responsible for the formation of palaeosols the timing is therefore the opposite of palaeosols within terrestrial loess sequences in that they were formed during the last glacial period seventeen uncorrected conventional and accelerator mass spectrometry ams radiocarbon dates of mud and shell samples from the cores indicated that the palaeosols were formed before about 9130 yr bp to 19 430 yr bp

physical properties and localization investigations associated with the 2003 mars exploration rovers 1 a number of physical properties experiments will be conducted during the nasa 2003 mars exploration rover mission as the two vehicles explore meridiani planum and the floor of gusev crater the investigations will include quantifying dust accumulation and dispersal dynamics by periodically monitoring the rover decks with the athena pancam and mini tes instruments properties of soil like materials will be inferred from analyses of wheel track patterns depths and wheel slippage dynamics during traverses the rovers will be modeled as dynamic mechanical systems to extract along track terrain topography and physical properties from times series of rover tilt vectors wheel encoder counts azimuths motor currents and rocker and bogie angles trenches will be excavated using rover wheels to characterize mechanical properties of soil like materials with depth and to expose subsurface materials for remote and in situ observations using the athena payload the rock abrasion tools will be used to expose rock subsurfaces for detailed analyses motor currents and penetration magnitudes will be compared to a database of rocks excavated by an engineering model of the rock abrasion tool to understand martian rock mechanical properties image based localization analyses will be pursued to better understand rover traverse directions and magnitudes and thus rover locations as a function of time the physical properties and localization investigations when combined with analyses of the full ensemble of athena observations will greatly improve our understanding of martian surface properties and provide significant technology lessons for future landed missions

global seismic body wave observations of temporal variations in the earth s inner core and implications for its differential rotation differential rotation of the earth s inner core has been predicted in some geodynamo models and seismic studies over the past 15 yr have resolved rotation rates up to 1 yr 1 most previous seismic body wave studies have focussed on south sandwich islands events recorded at station col in alaska here we present a globally extended study into temporal variations in the inner core over some 25 yr using pkpbc pkpdf traveltime residuals to test for differential rotation of the inner core displacement of inner core heterogeneities over time is sought we introduce a new method of space flattening to remove the effect of spatial variations on the time variations this allows for the use of both polar semi equatorial and equatorial geometries first we reanalyse polar paths from south sandwich islands events to stations col and ink in north america these stations yield a differential rotation of the inner core at a rate of 0 12 0 38 yr 1 in an eastward direction in agreement with previous studies however station dawy which has a very similar path through the inner core as col yields at best a westward differential rotation of the inner core thus dawy results are incompatible with the col ink inferred rotation secondly earthquakes in the aleutian islands region observed at bosa and lbtb in southern africa exhibit temporal variations that are incompatible with the south sandwich islands col ink inferred rotation rate thirdly kuril islands events recorded in south america at station bdf yield inconclusive results finally our final piece of evidence for the irreconcilability of differential inner core rotation with global data comes from using earthquakes in the vanuatu region recorded at bcao bgca in central africa an equatorial geometry these residuals resolve a westward inner core rotation at a rate of 0 14 yr 1 over the same time period that south sandwich islands events indicate an eastward rotation as any rigid body rotation should yield the same direction and rate independent of where the inner core is sampled our results allow us to reject previously reported inner core differential rotation rates of up to 0 1 0 5 yr 1 instead our results suggest that structure in either the inner or the outer core is varying with time over relatively short timescales and in ways that cannot be explained by and do not support a differentially rotating inner core

clastic patterned ground in lomonosov crater mars examining fracture controlled formation mechanisms the area surrounding lomonosov crater on mars has a high density of seemingly organised boulder patterns these form seemingly sorted polygons and stripes within kilometre scale blockfields patches of boulder strewn ground which are common across the martian high latitudes several hypotheses have been suggested to explain the formation of clastic patterned ground on mars it has been proposed that these structures could have formed through freeze thaw sorting or conversely by the interaction of boulders with underlying fracture polygons in this investigation a series of sites were examined to evaluate whether boulder patterns appear to be controlled by the distribution of underlying fractures and test the fracture control hypotheses for their formation it was decided to focus on this suite of mechanisms as they are characterised by a clear morphological relationship namely the presence of an underlying fracture network which can easily be evaluated over a large area it was found that in the majority of examples at these sites did not exhibit fracture control although fractures were present at many sites there were very few sites where the fracture network appeared to be controlling the boulder distribution in general these were not the sites with the best examples of organization suggesting that the fracture control mechanisms are not the dominant geomorphic process organising the boulders in this area

geology of the gusev cratered plains from the spirit rover transverse 1 the cratered plains of gusev traversed by spirit are generally low relief rocky plains dominated by impact and eolian processes ubiquitous shallow soil filled circular depressions called hollows are modified impact craters rocks are dark fine grained basalts and the upper 10 m of the cratered plains appears to be an impact generated regolith developed over intact basalt flows systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops consistent with an upper inflated surface of lava flows with adjacent collapse depressions crater and hollow morphometry are consistent with most being secondaries the size frequency distribution of rocks 0 1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5 35 systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced similar to a desert pavement or lag eolian bed forms ripples and wind tails have coarse surface lags and many are dust covered and thus likely inactive deflation of the surface 5 25 cm likely exposed two toned rocks and elevated ventifacts and transported fines into craters creating the hollows this observed redistribution yields extremely slow average erosion rates of 0 03 nm yr and argues for very little long term net change of the surface and a dry and desiccating environment similar to today s since the hesperian or 3 ga

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se

dust coatings on basaltic rocks and implications for thermal infrared spectroscopy of mars 1 thin coatings of atmospherically deposited dust can mask the spectral characteristics of underlying surfaces on mars from the visible to thermal infrared wavelengths making identification of substrate and coating mineralogy difficult from lander and orbiter spectrometer data to study the spectral effects of dust coatings we acquired thermal emission and hemispherical reflectance spectra 5 25 m 2000 400 cm 1 of basaltic andesite coated with different thicknesses of air fall deposited palagonitic soils fine grained ceramic clay powders and terrestrial loess the results show that thin coatings 10 20 m reduce the spectral contrast of the rock substrate substantially consistent with previous work this contrast reduction continues linearly with increasing coating thickness until a saturation thickness is reached after which little further change is observed the saturation thickness of the spectrally flat palagonite coatings is 100 120 m whereas that for coatings with higher spectral contrast is only 50 75 m spectral differences among coated and uncoated samples correlate with measured coating thicknesses in a quadratic manner whereas correlations with estimated surface area coverage are better fit by linear functions linear mixture modeling of coated samples using the rock substrate and coating materials as end members is also consistent with their measured coating thicknesses and areal coverage a comparison of ratios of thermal emission spectrometer tes spectra of dark and bright intracrater and windstreak deposits associated with radau crater suggests that the dark windstreak material may be coated with as much as 90 areal coverage of palagonitic dust the data presented here also will help improve interpretations of upcoming mini tes and thermal emission imaging system themis observations of coated mars surface materials

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

velocity constraints for the inner core inferred from long period pkp amplitudes abstract long period pkp amplitudes from 16 earthquakes in the distance range 110 170 are compared with theoretical amplitudes which are derived from synthetic seismograms calculated for 56 systematic modifications of earth model 1066b in the inner core a suitable normalization procedure allows for the common representation of all observed amplitudes as a function of epicentral distance using the theoretical amplitude distributions it can be shown that the parameters of a regression line through the logarithmic and normalized amplitudes between 110 and 134 are related to the velocity and density jump at the inner core boundary icb the analysis shows that the dominant influence on the pkp amplitudes is the p velocity jump which can be restricted to 0 64 0 05 km s 1 there exists a trade off between the s velocity jump and the density jump restricting the latter to the reasonable range 0 1 2 g cm 3 the s velocity jump at the icb can be inferred to be 2 5 3 0 km s 1 a rather strong s velocity gradient below the icb follows from the condition that the s wave travel time through the inner core agrees with that implied by free oscillation observations this leads to central s velocities between 3 81 and 4 15 km s 1 assuming a parabolic velocity law

depth dependence of anisotropy of earth s inner core both body wave pkp travel times creager 1992 song and helmberger 1993a mcsweeney and creager 1993 shearer 1994 and fits to the splitting of core modes tromp 1993 show general agreement that the top 300 km of inner core is very anisotropic the anisotropy displays axial symmetry around the earth s spin axis with the polar direction 3 faster than the equatorial direction one key problem now is the depth dependence of the inner core anisotropy here we extend our polar path studies to include both long period and short period modeling for the pkp phases at ranges 120 to 173 arrivals from the top of the inner core pkikp and reflections from the inner core boundary pkikp can be observed distinctly in short period records at ranges 130 to 140 and as waveform distortions in the long period records at ranges 130 to 146 these waveforms provide a new set of data for examining the topmost 150 km of the inner core which is not well sampled by the previous body wave travel times record sections of waves traversing the inner core nearly parallel to the earth s spin axis polar paths from three events two beneath the south sandwich islands and one along the macquarie ridge recorded at world wide standardized seismograph network canadian network and long range seismic measurements stations are analyzed our results suggest that the top 150 km of the inner core is only weakly anisotropic less than 1 with strong evidence indicating that the top 60 km is not anisotropic at all

diatom preservation in an inner continental shelf borehole from the south china sea abstract diatom distribution in a 60 m long borehole from a siliciclastics dominated stable inner continental shelf in the south china sea off hong kong was investigated the quaternary sediments contained evidence for five interglacial marine transgressions dating back to oxygen isotope stage 12 and yielded 53 genera and 186 taxa of diatoms intertidal species and nearshore shallow water species including both planktonic and benthonic tropical and subtropical varieties were dominant four diatom zones reflecting the shallow water environment have been recognized in the top 13 8 m of the borehole diatoms are missing in stage 11 while stage 7 and stage 9 are very low in diversity and abundance compared to stage 1 and stage 5 the distribution pattern found is accounted for by the duration of time available for frustule dissolution through acid sulphate soil development during stages 2 6 8 and 10 when the shelf was subaerially exposed preservation of diatoms is best in stage 1 because the deposits have never been subaerially exposed followed closely by stage 5 aging mainly through post depositional dissolution is identified as the important controlling factor in determining diatom distribution in pre holocene deposits

velocity structure near the inner core boundary from waveform modeling a velocity model of the inner core boundary icb region is developed from broadband wave form modeling the data consist of long period and short period record sections gathered from the u s arrays wwssn and lrsm deep events beneath indonesia were used these sampled the icb structure beneath the north pacific the cagniard de hoop technique was used to generate the synthetics which allowed considerable flexibility in forward modeling these individual pkp phases our preferred model was developed from modifications of the preliminary reference earth model prem it contains a relatively low velocity gradient above the icb a sharp jump at the icb of about 0 78 km s and a relatively large gradient underneath these features are constrained largely by the differential travel times and amplitude ratios of pkikp and pkikp of the short period section further modification of prem in the fluid core was required to explain the long period observations associated with pkp waveforms our modeling results suggest a low velocity gradient at the bottom roughly 400 km of the fluid core a low q zone at the top of the inner core is required to fit the relative amplitudes of pkikp phases similar to earlier studies this model indicates possible inhomogeneity above the icb as suggested by other authors

results from the mars pathfinder camera images of the martian surface returned by the imager for mars pathfinder imp show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial aeolian and impact processes analysis of the spectral signatures in the scene at 440 to 1000 nanometer wavelength reveal three types of rock and four classes of soil upward looking imp images of the predawn sky show thin bluish clouds that probably represent water ice forming on local atmospheric haze opacity 0 5 haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers

solar panel clearing events dust devil tracks and in situ vortex detections on mars abstract spirit rover solar array data which if publicly archived would provide a useful window on mars meteorology shows dust clearing events coinciding with the onset of dust devil season in three mars years the recurrence interval of 100 700 days is consistent with the extrapolation of pathfinder and phoenix vortex encounters indicated by pressure drops of 6 40 pa similar to laboratory measurements of dust lifting threshold and with observed areas and rates of generation of dust devil tracks on mars

characteristics of the pathfinder apxs sites implications for the composition of martian rocks and soils an integrated study of spectral elemental abundance and image data from the pathfinder alpha proton x ray spectrometer apxs measurement sites has led to a better understanding of the nature of martian surface materials this rigorous analysis provides a new level of detail that forms the basis for the results reported here and that can be used by future scientists trying to understand rocks and soils on mars each apxs site has been precisely located by analyzing stereo imager for mars pathfinder imp and rover camera images to determine the position of the apxs during deployment rover and imp images are used to assess local geology namely the presence of pebbles clods and aeolian features in soils and surface textures and dust concentrations on rocks imp spectra using the latest calibrations for radiance and reflectance are analyzed at a number of different illumination geometries for each apxs site the three dimensional orientation of the sites has been determined and then used to compute the true sunlight incidence and viewing emission angles where suitable photometric coverage is available reflectances are fit to the hapke irvine function this is then used to adjust spectral reflectances to a normalized illumination geometry common to all rocks and soils comparing all the data sets shows a positive correlation among red blue reflectance ratio so3 content and dust abundance on rocks indicating that rocks are coated with varying amounts of sulfur rich red dust other elements such as silicon and iron are poor tracers for dust because their abundances within soil are similar to those within rock rock apxs targets that are bluer poorer in sulfur and have minimal dust coverage face toward the northeast the direction in which winds may be capable of efficiently removing loose material under current martian conditions the imp spectral properties of the soils show poor correlations with apxs elemental abundances on the basis of currently released apxs data bulk soils at the pathfinder landing site are richer in silica and sulfur than the viking landing sites suggesting a different composition the apxs soils with the most apparent pebbles are the poorest in sio2 indicating that either the pebbles are more mafic than the apxs rocks or the pebble free soil component is inherently enriched in sio2 compared to viking soils the mixture of materials at the apxs sites is a reflection of the overall complexity of martian surface materials a detailed understanding of which should drive the choice of future instruments and missions

regionally heterogeneous uppermost inner core observed with hi net array studies of velocity structure in the earth s inner core and its volumetric variations illuminate our understanding of inner core dynamics and composition here we use an extensive number of seismograms recorded by the hi net array to construct complete empirical curves of pkpbc pkpdf differential traveltimes the nature of these curves implies that significant variations in traveltimes are accumulated during the passage of pkpdf waves through the uppermost inner core and rules out outer core structure effects uniform cylindrical anisotropy of a plausible strength in the uppermost inner core can also be ruled out as a cause of the observed traveltime variations because the range of sampled ray angles is too narrow the configuration and strength of inhomogeneities from a recent tomographic model of the lowermost mantle cannot account for the observed traveltime variations therefore we infer that either variations of p wave isotropic velocity on the scale of about hundred km and less are present in the uppermost inner core or the material may be organized in distinctive anisotropic domains and both of these features may be superimposed on long wavelength hemispherical structure if the former holds true the absolute magnitude of required p wave velocity perturbations from referent values is 0 60 0 10 in the quasi eastern and 1 55 0 15 in the quasi western hemisphere 0 85 0 05 and 1 10 0 10 respectively with the lowermost mantle correction the existence of these variations is a plausible physical outcome given that vigorous compositional convection in the outer core and variations in heat exchange across the inner core boundary may control the process of solidification

rift zone volcanism and associated cinder cone field in utopia planitia mars 1 we analyzed a small cone field in sw utopia planitia that shows striking similarities to volcanic rift zones on earth this is of particular interest as the study area lies off any of the volcanic centers of mars in the northern hemisphere lowlands and is surrounded by material of the amazonian aged vastitas borealis formation vbf we believe that the study area could be the first direct evidence for volcanic activity in utopia planitia prior to the resurfacing by vbf material the most striking characteristics that we observed are 1 a set of broad eruptive fissures showing signs of ongoing extension during cone formation 2 parallel dike swarms 3 magmatic intrusions and 4 a number of lava flows that have erupted from the fissures and pitted cones that surround a larger cone in the center of the study area and that are often associated with or aligned along the fissures and dikes cratering model ages indicate that the study area is of late noachian to early hesperian age and is thus distinctly older than the surrounding vbf falling into the time frame of the main phases of activity in the volcanic centers of syrtis major elysium planitia and the southern highlands

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

characterization of the martian surface deposits by the mars pathfinder rover sojourner sojourner the mars pathfinder rover discovered pebbles on the surface and in rocks that may be sedimentary not volcanic in origin surface pebbles may have been rounded by ares flood waters or liberated by weathering of sedimentary rocks called conglomerates conglomerates imply that water existed elsewhere and earlier than the ares flood most soil like deposits are similar to moderately dense soils on earth small amounts of dust are currently settling from the atmosphere

planet within a planet rotation of the inner core of earth the time dependence of the orientation of earth9s inner core relative to the mantle was determined using a recently discovered 10 degree tilt in the axis of symmetry of the inner core9s seismic velocity anisotropy two methods of analyzing travel time variations for rays traversing the inner core on the basis of 29 years of data from the international seismological centre 1964 1992 reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle an anomalous variation in inner core orientation from 1969 to 1973 coincides in time with a sudden change jerk in the geomagnetic field

modern fine grained sedimentation spatial variability and environmental controls on an inner pericontinental shelf hong kong abstract fine grained sediments in hong kong form part of an extensive cover that extends from nearshore locations to the mid continental shelf this featureless mud blanket is associated with sediment inputs from the pearl river and has generally been considered to be homogeneous in its characteristics however detailed sedimentological and geochemical analyses have revealed that the superficial deposits show systematic spatial variations that reflect contrasts in deposition between the pearl river estuary to the west and fully marine conditions to the east results indicate significant differences in particle size accumulation rates biogenic silica organic carbon content c n ratios and stable carbon and nitrogen isotopes that reflect location with respect to the pearl river delta calcium carbonate content varies widely tending to be higher close to land major controls over spatial variability include rainfall patterns and the supply of estuarine suspended particulate matter the effects of palaeotopography and modern water depth resuspension induced by monsoon winds and typhoons and human impacts on the sea floor

a diatom record of mid to late holocene palaeoenvironmental changes in the southern okinawa trough palaeoceanographic changes over the last 6800 years are documented in a diatom record from core md05 2908 from the southern okinawa trough changes in diatom components are used to reflect variations in the strength of the kuroshio current and the influence of coastal waters and these changes are compared with records of the east asian summer monsoon which exerts an important influence on regional climate and oceanography a decreasing trend in the contribution of coastal diatoms during the last 6800 years is related to the weakening of the east asian summer monsoon during the holocene in response to diminishing insolation and a southward shift in the intertropical convergence zone relatively high abundances of the kuroshio current indicator species during the intervals 2600 2200 and 4800 3600 cal a bp and lower abundances during the intervals 3200 2800 and 2200 1300 cal a bp imply that there is no consistent weakening of the kuroshio current during the interval 4500 3000 cal a bp the pulleniatina minimum event which is a widespread feature in the east china sea and the south china sea a major reduction in coastal diatoms at 3200cal a bp and a slight decrease in the kuroshio current indicator species during the interval 3200 2800 cal a bp indicate that a palaeoceanographic shift occurred in the southern okinawa trough which coincided with a northern hemisphere climatic cooling denoted the neoglaciation in europe in addition changes in the freshwater species component of the record are suggested mainly to result from variations in flood frequency in north eastern taiwan caused by typhoons a dramatic increase in the frequency of flood events during the last millennium may have been caused by relatively strong el nino southern oscillation activity compared with the more stable period between 6800 and 1000 cal a bp which experienced a low frequency of flood events

joint inversion for inner core rotation inner core anisotropy and mantle heterogeneity observational evidence for differential rotation of the inner core has recently been reported from time dependent travel times of the seismic inner core phase pkp df these analyses are hindered by potential biases from the mantle heterogeneity and systematic earthquake location errors which have raised doubts about the reality of the inferred differential rotation here we report time dependent pkp df pkp bc differential travel times of a total of 611 measurements obtained from 92 earthquakes in the south sandwich islands ssi over the past nearly half a century recorded at the college alaska station col and alaska seismic network asn the events are relocated using the joint hypercenter determination jhd technique dewey 1971 travel time residuals at col from ssi earthquakes over a period of 45 years and at three additional stations from ssi earthquakes over periods of about 22 years show steady increases with time the temporal trends are demonstrated to be statistically very significant with dense samples of the pathway at different time periods we use a joint inversion technique that allows us to separate the time dependent inner core structure from the time independent mantle biases surprisingly the inner core rotation seems resolvable even from digital data observed at asn in the 1990s spanning over 8 years alone in such a joint inversion the results provide strong support for a differential inner core rotation the inferred rotation rate ranges from 0 3 to 1 1 per year faster than the mantle when we take into account the uncertainty in the tilt of the anisotropy axis of the patch of the inner core that was sampled a westward inner core rotation can be ruled out

seismic structure near the inner core boundary in the south polar region 1 it is crucial to obtain good spatial coverage of seismic data points for better understanding the earth s core but the core beneath the polar regions remains largely unexplored we analyzed differential traveltimes and amplitude ratios of core phases whose raypaths run beneath antarctica for determining the vp and qp structure near the inner core boundary in the south polar region the model we obtained south polar region model spr is described relative to the preliminary reference earth model prem as follows a 0 05 km s lower vp value at the top of the inner core a 1 5 times steeper vp gradient in the upper 300 km of the inner core a smaller qp 300 in the upper 300 km of the inner core and a 0 04 km s lower vp at the bottom of the outer core the vp values of spr in the lowermost outer core lie between those of prem and ak135 being closer to those of ak135 the lowermost outer core vp inside the tangent cylinder is thus close to the global average in the upper inner core spr has lower vp than ak135 and prem the spr vp profile is close to that of previous models for the western hemisphere although most of our data sample the eastern hemisphere of the inner core our results indicate that the inner core does not have a simple hemispherical variation as usually supposed our data support an eyeball shaped high vp anomaly with compressional velocity higher than in 1 d reference earth models concentrated to a smaller region beneath eastern asia

late quaternary environmental changes in hong kong abstract the offshore quaternary deposits of hong kong include a wide range of clastic sediments that accumulated in a variety of settings including lacustrine channel overbank coastal and marine environments detailed studies of the sedimentology and diatoms of several long continuously sampled cores combined with seismic reflection profiles has enabled the reconstruction of late pleistocene and holocene palaeoenvironments in hong kong the quaternary sediments comprise several informal seismic units that are separated by marine planation tidal scour and fluvial erosion surfaces seismic unit 1 represents pre quaternary bedrock and weathered bedrock which is separated from a complex assemblage of pleistocene channel floodplain backswamp and lacustrine deposits seismic unit 2 by a major erosion surface u1 sediments that represent the basal part of unit 2 have been dated at about 248 000 yr b p well preserved laminations at several horizons suggest periodic deposition and probably seasonal flooding the presence of kaolin indicates strong chemical weathering and warm humid conditions at the time of deposition seismic unit 3 consists of marine mud that unconformably overlies a fluvial erosion surface fe1 cut into deposits represented by seismic unit 2 the sediments comprising unit 3 are tentatively correlated with oxygen isotope stage 5e and high sea levels at about 128 000 105 000 yr b p a marine planation surface r1 terminates unit 3 and is overlain by coastal and nearshore deposits comprising seismic unit 4 at about 95 000 to 80 000 yr b p this phase of marine deposition was terminated by a major fall in sea level that caused widespread fluvial incision across hong kong and produced surface fe2 a subsequent rise in sea level after about 18 000 yr b p led to deposition of a complex succession of marine sediments and erosion surfaces initially homogeneous mud seismic unit 5a was laid down tidal currents perhaps related to base level changes then caused incision and the formation of surface ts1 at several localities further shallow marine mud comprising unit 5b was laid down between about 9500 and 8000 yr b p a planar erosion surface r2 with local palaeosols and minor incision cuts across earlier deposits the overlying seismic unit 5c represents diatomaceous marine mud and a basal sand at one coring site these sediments have been divided into five major diatom zones that reflect changes in salinity and sea level modern sea level was attained by about 6000 yr b p in broad terms the late quaternary record is one of two periods of marine flooding separated by a major regressive episode with no evidence of older quaternary marine sediments being present

reconstruction of holocene monsoon history from the pearl river estuary southern china using diatoms and carbon isotope ratios this study employs a multiproxy approach in the reconstruction of holocene monsoon history from sedimentary sequences obtained from the pearl river estuary southern china a set of modern surface sediment samples were collected within and outside the estuary and a sediment core was obtained from the mouth of the estuary a range of modern environmental variables were recorded including water salinity summer winter and annual average and water depth the diatom results show a good relationship with water salinity with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux this pattern is matched by the bulk organic carbon isotopes the isotope values vary between 21 1 0 3 0 for samples from the fully marine environment between 23 2 0 8 and 23 7 0 8 for samples from the mid to outer estuary brackish water environment and less than 24 7 1 3 for samples from the inner estuary close to the freshwater sources similarly the c n ratios vary from below 7 0 6 in the marine end members to over 14 8 3 0 in the freshwater end members both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal yr bp resulting from the enhanced summer monsoon regime in early holocene the strength of freshwater flux reached its highest between 7500 and 6000 cal yr bp in the last 6000 years freshwater flux decreased towards present reflecting a gradual weakening of the summer monsoon

inner core anisotropy beneath australia and differential rotation summary the inner core anisotropy of p wave velocity has been suggested since 1986 the detail of the anisotropic structure is now under discussion we have studied a regional structure in the inner core beneath australia to reveal the detail of the anisotropy using the residuals of the differential traveltimes of pkp bc minus pkp df we have collected the rays not only nearly parallel to the earth s rotation axis but also nearly parallel to the equatorial plane to distinguish the anisotropy from the isotropic heterogeneity in the inner core the collected rays cross each other with different angles in the inner core beneath australia we have studied inner core anisotropy assuming locally uniform transverse isotropy the velocity anomalies decrease with the angles between the ray directions in the inner core and the earth s rotation axis which supports inner core anisotropy beneath this region the top 190 km of the inner core is isotropic with a velocity anomaly of 0 11 per cent and the deeper part shows the anisotropy with an amplitude of 3 1 per cent the symmetry axis of the anisotropy crosses the earth s surface at 80 n and 103 e this result suggests that previous studies underestimated the size of the anisotropy in the inner core beneath this region because the symmetry axis is inclined from the earth s rotation axis we can observe the temporal variation of the velocity anomalies caused by the anisotropy in the inner core if it rotates at a different rate from the crust and the mantle the possibility of differential rotation is studied by considering the regional structure of the inner core anisotropy beneath australia we use seismograms recorded at syowa station in antarctica over the past 27 yr we have found no evidence for significant differential rotation though we cannot rule out a small rate of about 0 2 deg yr 1 or less even if the inner core rotates faster than the crust and mantle the difference is fairly small and we need not consider the influence of the differential rotation on the study of anisotropy in the inner core

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

hemispherical structure in inner core velocity anisotropy 1 we investigate the hemispherical pattern in inner core velocity anisotropy using a new and independent high quality data set of pkpbc pkpdf and pkpab pkpdf body wave observations our data show no evidence for a tilted anisotropy axis with respect to the earth s rotation axis and is significantly better fit by a model with 4 4 anisotropy in the western hemisphere and only 1 0 in the eastern hemisphere than by a model of uniform anisotropy we carry out variance minimization and find the boundaries between the hemispheres at lines of constant longitude at 14 e and 151 w variance minimization enables us to extract the imprint of hemispherical structure from all of the data and not just polar paths resulting in boundaries which are nearly 30 from the results of previous studies the high quality of the data allows us to provide robust evidence that the isotropic velocity in the eastern hemisphere is 0 2 lower than in the western hemisphere in the top 660 km of the inner core our data set also suggests an increase in inner core anisotropy in the eastern hemisphere from 1 to around 6 at depths deeper than 660 km indicating that the hemispherical pattern in anisotropy may disappear at greater depths the presence of hemispherical structure rules out mechanisms for creating anisotropy which are unable to sustain longitudinal variations in the inner core furthermore steady inner core superrotation of the order of 0 1 year would eradicate the hemispherical differences though inner core oscillation would still be permissible

new seismological constraints on differential rotation of the inner core from novaya zemlya events recorded at drv antarctica summary novaya zemlya nuclear test records at the seismic station drv antarctica are analysed in order to obtain further constraints on a possible diverential rotation of the inner core with respect to the mantle these data allow the sampling of the inner core along a nearly polar path in very stable conditions over more than two decades from 1966 to 1990 the pkp bc pkp df traveltime residuals which reflect the innercore anisotropy and or heterogeneities sampled along the path exhibit a great stability through time a computation of the residuals that are expected for various diverential rotation rates and the same rotation axis as the mantle has been performed using the worldwide residual catalogue of engdahl et al 1997 for summary rays that include the time as an additional parameter in data stacking comparison of data and predictions shows that an eastward diverential rotation with a rate as large as 3 yr 1 as suggested by some authors is not possible but an eastward rotation at 1 yr 1 or lower cannot be rejected

stratigraphy and optically stimulated luminescence dating of subaerially exposed quaternary deposits from two shallow bays in hong kong china episodes of subaerial exposure recorded in quaternary sedimentary sequences on continental shelves are indicators of sea level change in this study the quaternary superficial deposits from two shallow bays in hong kong are examined in order to identify the timing of such episodes two rotary boreholes in tai o bay penetrated a succession of marine and terrestrial deposits formed during the last four interglacial glacial cycles the interglacial periods and the glacial periods are found to be represented by siliciclastic dominated shallow marine estuarine deposits and colluvial alluvial fan deposits respectively an excavation of a coastal land reclamation in deep bay revealed holocene intertidal subtidal estuarine deposits overlying aeolian deposits of the last glacial age optically stimulated luminescence dating carried out has confirmed the last glacial age of the terrestrial unit unconformably overlain by the holocene marine unit but only minimum ages can be obtained from the pre last glacial terrestrial units in one of the tai o boreholes studied the density and moisture content distribution is found to reflect the episodes of subaerial exposure of the pre holocene interglacial marine units in the palaeo desiccated crusts of these units density increases through iron cementation resulting from acid sulphate soil development while moisture content decreases as a consequence of desiccation quaternary terrestrial deposits occurring on continental shelves are therefore datable to a greater degree of certainty than their subaerial counterparts

pkp bc versus pkp df differential travel times and aspherical structure in the earth s inner core pkp bc versus pkp df differential travel times show coherent patterns of residuals indicating aspherical structure within the earth s inner core using a waveform correlation method we measure 318 differential pkp bc versus pkp df travel times from 5 years of global digital seismograph network gdsn short period data at ranges between 145 and 155 in addition we obtain 19 470 probable bc versus df travel times at these ranges by searching through 23 years of the international seismological centre isc catalog plots of residuals versus turning point location and residuals versus ray direction show clear patterns which indicate that the differential travel times are highly correlated along similar ray paths this pattern is robust with respect to range and source depth these anomalies are almost certainly due to aspherical inner core structure since pkp bc and pkp df have nearly coincident ray paths in the mantle and outer core the gdsn and isc residual patterns are in general agreement but the isc residuals underpredict the gdsn residuals by about a factor of 2 the isc data have better spatial coverage particularly for n s ray paths within the inner core these n s ray paths show positive residuals of about 0 5 s indicating faster inner core p velocities in this direction a result consistent with previous studies of absolute pkp df travel times but derived from an independent data set due to the sparse ray coverage of our data either heterogeneity or anisotropy within the inner core with about 1 velocity variations could explain these residual patterns however inversions of the isc data for heterogeneity require many more free parameters to achieve the same variance reduction as a simple two parameter anisotropy model

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

reconciling the hemispherical structure of earth s inner core with its super rotation earth s solid inner core grows through solidification of material from the fluid outer core onto its surface at rates of about 1 mm per year1 freezing in core properties over time and generating an age depth relation for the inner core a hemispherical structure of the inner core is well documented an isotropic eastern hemisphere with fast seismic velocities contrasts with a slower anisotropic western hemisphere2 3 4 independently the inner core is reported to super rotate at rates of up to 1 per year5 6 7 considering the slow growth steady rotation rates of this magnitude would erase frozen in regional variation and cannot coexist with hemispherical structure here we exploit the age depth relation using the largest available pkikp pkikp seismic travel time data set to confirm hemispherical structure in the uppermost inner core and to constrain the locations of the hemisphere boundaries we find consistent eastward displacement of these boundaries with depth from which we infer extremely slow steady inner core super rotation of 0 1 1 per million years our estimate of long term super rotation reconciles inner core rotation with hemispherical structure two properties previously thought incompatible it is in excellent agreement with geodynamo simulations8 9 while not excluding the possibility that the much larger rotation rates inferred earlier5 6 7 correspond to fluctuations in inner core rotation on shorter timescales10

seismic structures in the earth s inner core below southeastern asia documenting seismic heterogeneities in the earth s inner core ic is important in terms of getting an insight into its history and dynamics a valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary icb here we investigate eastern hemisphere of the solid core by means of pkpbc pkpdf differential travel times that sample depths from 140 to 360 km below its boundary we study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the ic in both planes equatorial residuals show slight spatial variations in the sampled ic volume mostly below the level of 0 5 whereas polar residuals are up to three times as big direction dependent and can exhibit higher local variations the measurements reveal fast changes in seismic velocity within a restricted volume of the ic we interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter we particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the ic from its anisotropic body whereas the depth of isotropy anisotropy transition increases in southeast direction from 190 km below southeastern asia off the coast of china to 350 km beneath australia another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below southeastern asia and the rest of polar data are treated separately this model envisages almost isotropic eastern hemisphere of the ic at least down to the depth of 360 km below the icb and constrains the anisotropic volume only to the ranges of north latitudes from 18 to 23 east longitudes from 125 to 135 and depths exceeding 170 km the anisotropy strength in either model is about 2 further effective pursuit of the models presents challenges in terms of resolution and coverage and basically requires a significant dataset extension

localization and physical properties experiments conducted by spirit at gusev crater the precise location and relative elevation of spirit during its traverses from the columbia memorial station to bonneville crater were determined with bundle adjusted retrievals from rover wheel turns suspension and tilt angles and overlapping images physical properties experiments show a decrease of 0 2 per mars solar day in solar cell output resulting from deposition of airborne dust cohesive soil like deposits in plains and hollows bright and dark rock coatings and relatively weak volcanic rocks of basaltic composition volcanic impact aeolian and water related processes produced the encountered landforms and materials

seismic evidence for an inner core transition zone seismic waves that traverse earth s inner core along north south paths produce unusually broad pulse shapes at long periods compared with waves along east west paths and reflections from below the inner core boundary at short periods the observations provide compelling evidence for a seismic velocity discontinuity along north south paths about 200 kilometers below the inner core boundary separating an isotropic upper inner core from an anisotropic lower inner core the triplication associated with such a structure might be responsible for reported waveform complexity of short period inner core arrivals along north south paths and if the depth of the boundary is laterally variable their large travel time variation

visible near infrared spectra and two layer modeling of palagonite coated basalts fine grained dust coatings on martian rocks and soils obscure underlying surfaces and hinder mineralogic interpretations of both remote sensing and in situ observations we investigate laboratory visible near infrared spectra of various thicknesses of palagonite coatings on basalt substrates we develop a two layer hapke scattering model incorporating porosity grain size and derived absorption coefficients of palagonite and basalt that reproduces the observed spectra only when the single scattering particle phase function is varied with wavelength

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate