how do submarines use gravity gradients to avoid collisions with underwater mountains abstract gravity gradiometers in use today have their origins in naval special warfare because they ensure safe navigation and accurate detection of underwater objects submarines rely on accurate detection of their surroundings and gravity gradiometry is a passive technique that does not compromise the submarine s position because it is a technique that does not emit energy however the way submarines achieve collision avoidance has never been addressed using gravity gradiometry data in real time warns of the existence of an underwater mountain in a submarine s trajectory the method does not require accurate positioning extensive measuring over large areas or a gravity gradient map of the ocean bottom the results of a study demonstrate how gravity gradiometry can be used effectively to detect anomalous mass in a trajectory quickly without involving sophisticated processing or interpretation algorithms for many years geophysicists have known the original use of the modern gravity gradiometry tec

liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

recognizing and dating prehistoric liquefaction features lessons learned in the new madrid seismic zone central united states the new madrid seismic zone nmsz which experienced severe liquefaction during the great new madrid missouri earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes is a superb laboratory for the study of world class earthquake induced liquefaction features and their use in paleoseismology in seismically active regions like the nmsz frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret lessons learned studying liquefaction features in the nmsz may help to unravel the paleoseismic record in other seismically active regions soil characteristics of liquefaction features as well as their structural and stratigraphic relations to native american occupation horizons and other cultural features can help to distinguish prehistoric liquefaction features from historic features in addition analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features also new methods for dating liquefaction features are needed

long lived deformation in the southern mississippi embayment revealed by high resolution seismic reflection and sub bottom profiler data three high resolution seismic reflection profiles and two sub bottom profiler sections acquired along the mississippi river in southern central u s image deformation in post paleozoic sediments the northernmost profile images two faults offsetting cretaceous through at least eocene cane river reflectors interpreted to strike northwest and to be part of the arkansas river fault zone the central profile shows a down to the north fault displacing cretaceous and paleocene midway group reflectors by 210 m and 160 m respectively the fault is interpreted as the northern edge fault of the monroe uplift a late cretaceous uplift associated with igneous intrusions the southernmost profile displays a down to the south fault offsetting cretaceous and paleocene eocene wilcox group reflectors by 125 m and 32 m respectively tilted reflectors in the first 80 m indicate eocene oligocene activity of the fault although quaternary activity cannot be ruled out quaternary tectonic activity is proposed for a series of faults that offset shallow 40 m depth eocene sequences and the base of the quaternary alluvium as imaged on two sub bottom profiler sections these shallow faults are imaged in the vicinity of holocene earthquake induced liquefaction fields corroborating the evidence for recent tectonic activity in the area the spatial coincidence of the imaged faults with the inferred location of the alabama oklahoma transform strongly argues toward a long lived influence of this precambrian continental margin in focusing tectonic activity in the southern u s by controlling the reactivation of triassic jurassic syn rift basement structures and guiding the emplacement of late cretaceous igneous intrusions and the location of cenozoic deformation

cosmic ray exposure history of two frontier mountain h chondrite showers from spallation and neutron capture products we measured the concentrations of iobe 26a1 36cl 41ca and 14c in the metal and or stone fractions of 27 antarctic chondrites from frontier mountain fro including two large h chondrite showers to estimate the pre atmospheric size of the two showers we determined the contribution of neutron capture produced 36cl half life 3 01 x 105 years and 41ca 1 04 x lo5 years in the stone fraction the measured activities of neutron capture 36cl and 41ca as well as spallation produced 1obe and 26a1 were compared with monte carlo based model calculations the largest shower fro 901 74 includes eight fragments with an average terrestrial age of 1 00 30 x 103 years the neutron capture saturation activities extend to 27 dpmkg stone for 36c1 and 19 dpmkg stone for 41ca the concentrations of spallation produced loge 26a1 and 36cl constrain the radius r to 80 100 cm while the neutron capture 4lca activities indicate that the samples originated from the outer 25 cm with a pre atmospheric radius of 80 1 00 cm fro 90 174 is among the largest of the antarctic stony meteorites the large pre atmospheric size supports our hypothesis that at least 50 of the 1 50 classified hs h6 chondrites from the frontier mountain stranding area belong to this single fall this hypothesis does not entirely account for the high h l ratio at frontier mountain the smaller shower fro 9000 1 includes four fragments with an average terrestrial age of 40 2 10 x 103 years they contain small contributions of neutron capture 36c1 but no excess 0f41ca fro 9000 1 experienced a complex exposure history with high shielding conditions in the first stage 1 50 r 300 cm and much lower shielding in the second stage r 30 cm the latter starting 1 o million years ma ago based on the measured 1obe 2lne and 26a1 21ne ratios the cosmic ray exposure ages of the two showers are 7 2 k 0 5 ma for fro 90174 and 8 1 ma for fro 90001 these ages coincide with the well established h chondrite peak and corroborate the observation that the exposure age distribution of fro h chondrites is similar to that of non antarctic falls in addition we found that corrections for neutron capture 36ar from decay of 36cl result in concordant 21ne and 38ar exposure ages

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

development of magnitude bound relations for paleoliquefaction analyses new zealand case study abstract magnitude bound relations are often used to estimate paleoearthquake magnitudes from paleoliquefaction data this study proposes new zealand based magnitude bound curves that are developed using a liquefaction field observations and b a newly proposed back calculation approach that combines the simplified liquefaction evaluation procedure with a regionally appropriate ground motion prediction equation for b both deterministic and probabilistic frameworks are proposed the magnitude bound curves back calculated using either the deterministic or probabilistic frameworks are advantageous in that they can be used to predict the spatial distribution of liquefaction in regions where historical liquefaction field observations are limited or poorly documented and because soil and site specific conditions can be incorporated into magnitude bound analyses moreover curves developed using the probabilistic framework allow for the range of possible causative earthquake magnitudes to be better understood and quantified to demonstrate the use of the proposed relations paleoliquefaction features discovered in eastern christchurch nz are analyzed the 1869 mw4 8 christchurch earthquake and or 1717 mw8 1 alpine fault earthquake are found to be the most likely candidates amongst known historical and paleoearthquakes for triggering liquefaction over the permissible time range ca 1660 to 1905 a d this study demonstrates the potential of the proposed magnitude bound curves to provide insight in to past present and future hazards proving their utility even in cases of limited evidence the approach of developing and applying magnitude bound curves proposed herein is not limited to parts of new zealand but rather can be applied worldwide

seismotectonic implications of sand blows in the southern mississippi embayment we explore seismically induced sand blows from the southern mississippi embayment and their implications in resolving the question of near or distal epicentral source region this was accomplished using aerial photography field excavations and cone penetration tests our analysis shows that three sand blow fields exhibit a distinct chronology of strong ground motion for the southern embayment 1 the ashley county arkansas sand blow field near the arkansas louisiana state border experienced four holocene sand venting episodes 2 to the north the desha county field experienced at least three episodes of liquefaction and 3 the lincoln jefferson counties field experienced at least one episode cone penetration tests cpt conducted in and between the sand blow fields suggest that the fields may not be distal liquefaction associated with new madrid seismic zone earthquakes but rather are likely associated with strong earthquakes on local faults this conclusion is consistent with the differences in timing of the southern embayment sand venting episodes and those in the new madrid seismic zone these results suggest that active tectonism and strong seismicity in intraplate north america may not be localized at isolated weak spots but rather widespread on fault systems that are favorably oriented for slip in the contemporary stress field

explosive craters and soil liquefaction curious dry craters formed in the aftermath of a disastrous earthquake are explained the bhuj earthquake in january 2001 with a moment magnitude of 7 7 was one of the most disastrous in india s recorded history although its fault plane did not rupture the surface the earthquake caused ground failure including the formation of sand blow craters and sand fissures indicative of liquefaction of subsurface sediment over an area of about 15 000 square kilometres1 here we investigate the two large dry craters that formed during the earthquake and estimate the likely subsurface pressure at the time from a trajectory analysis of the ejected clasts we conclude that the craters were created by explosive deformation of the ground that probably resulted from the delayed effects of soil liquefaction

activity along the osning thrust in central europe during the lateglacial ice sheet and lithosphere interactions abstract the osning thrust is one of the major fault systems in central europe with a length of approximately 115 km it underwent a polyphase tectonic evolution in the mesozoic that ranged from extensional movements in the jurassic to reverse faulting and thrusting during inversion in the late cretaceous a series of complex metre scale faults and related fold structures are developed within the upper pleistocene alluvial aeolian complex of the upper senne 1 km away from the thrust the faults dip towards the north and show offsets in a range of several decimetres growth strata indicate a two fold evolution of the structures the faults began as normal faults and were later transformed into reverse faults which resulted in the formation of small scale inversion structures with a typical harpoon shape glaciotectonics can be ruled out as the driving mechanism for these structures because new optically stimulated luminescence osl ages imply that the sedimentary succession was deposited during the late pleistocene between 29 3 2 9 ka and 13 1 1 5 ka at which time the ice margin was much further to the northeast we believe the inversion structures were caused by movement on the osning thrust due to generation of a forebulge of the late pleistocene weichselian ice sheet this led to normal faulting as a consequence of extension in the forebulge area during glaciation the osl ages for the normal fault related growth strata are in a range of 16 13 ka later reverse movements occurred during deglaciation due to the n s directed compressional stress field in northern germany numerical simulations of the deglaciation seismicity point to seismic events with a thrust mechanism in the study area between 15 5 and 12 3 ka bp although normal faulting is also possible in this time period numerous soft sediment deformation structures imply that movement on the osning thrust caused earthquakes with a significant magnitude in the autumn of 1612 an earthquake took place in this area it is very likely that this event is related to background seismicity on this fault although movement due to the influence of the ongoing glacial rebound in fennoscandia is also possible

erosion by tectonic carving in the concordia subglacial fault zone east antarctica abstract in this work we present the analysis of the footwall morphology of the concordia subglacial extensional fault in the east antarctic craton the concordia fault is a regional fault zone that extends for almost 200 km the displacement up to 1800 m and the listric geometry were recognized by numerical modeling of the resulting hangingwall bedrock morphology and is responsible for the marked asymmetry that characterizes the corresponding scarp in the concordia subglacial trench the portion of the footwall in the proximity of the master fault exhibits an excavated morphology about 500 m deep and up to 5 km wide showing strong correlation with the master fault displacement we excluded a predominant glacial and fluvial origin of this morphology considering i the sharp topography of the concordia fault suggesting that the fault activity started after the onset of the ice sheet ii the ice sheet bedrock contact is characterized by a general negligible erosion deposition rates still allowing clast removal iii the lack of significant deposits in the concordia trench we hence explored the possibility that this morphology may result from the combined action of fault induced fracturing and passive clast removal and scattering by flow and plastic deformation within the ice sheet we introduced the term tectonic carving for this process our modeling shows that tectonic carving relates to the relative fracture intensity in the concordia fracture zone that corresponds to the envelope of master and secondary fault damage zones fracture intensity depends on the frequency and the displacement of secondary faulting and can be approximated by a normal distribution using a monte carlo modeling approach we selected the set of parameters that best fits the data set with the carving theoretical curve the final results of the monte carlo analysis show a root mean square of about 50 meters comparable with the data resolution this analysis demonstrates a method to unravel the presence of fracture zones in similar weak erosional environments

higher order gravitational potential gradients for geoscientific applications abstract gravity data have been applied for modelling and interpretation studies in geosciences this contribution reviews currently observable and foreseen gravity data represented by gradients of the gravitational potential functional models linking 3 d mass density distribution functions to potential gradients of up to the third order are formulated using volume integrals of the newtonian type with unitless kernel functions expressed both analytically and using infinite series of associated legendre functions spatial and spectral properties of the kernel functions are analysed and sensitivity of the gradients to particular mass density distributions is studied two particular mass density distribution models are used in numerical experiments a local 3 d mass density model representing shallow mass density variations and a global mass model represented by earth s upper sediments with lateral mass density variations computed values of the gradients demonstrate their different sensitivities to particular mass density distributions which change with an increasing distance of the gradients from gravitating masses third order gradients are particularly useful for studying near subsurface or shallow density structures such as caves caverns salt domes sediment basement morphology continental margins or buried fault systems that could be identified spatially more closely thus higher order gradients would offer an interesting tool for mass density mapping once their observability with the sufficient accuracy and resolution is realized

relict nebkhas pimple mounds record prolonged late holocene drought in the forested region of south central united states the origin and significance of pimple mounds low elliptical to circular dune like features found across much of the south central united states have been debated for nearly two centuries we cored pimple mounds at four sites spanning the ozark plateau arkansas river valley and gulf of mexico coastal plain and found that these mounds have a regionally consistent textural asymmetry such that there is a significant excess of coarse grained sediment within their northwest flanks we interpret this asymmetry as evidence of an eolian depositional origin of these mounds and conclude they are relict nebkhas coppice dunes deposited during protracted middle to late holocene droughts these four mounds yield optically stimulated luminescence ages between 2400 and 700 yr that correlate with well documented periods of eolian activity and droughts on the southern great plains including the medieval climate anomaly we conclude vegetation loss during extended droughts led to local eolian deflation and pimple mound deposition these mounds reflect landscape response to multi decadal droughts for the south central u s the spatial extent of pimple mounds across this region further underscores the severity and duration of late holocene droughts which were significantly greater than historic droughts

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

a new reference model for 3d inversion of airborne magnetic data in hilly terrain a case study from northern sweden abstractthe inherent nonuniqueness in modeling magnetic data can be partly reduced by adding prior information either as mathematical constructs or simply as bounds on magnetization obtained from laboratory measurements if a good prior model can be used as a reference model then the quality of estimated models through an inverse approach can be greatly improved but even though data on magnetic properties of rocks might exist their distribution may often be quite irregular on local and regional scales so that it is difficult to define representative classes of rock types suitable for constraining geophysical models of magnetization we have developed a new way of constructing a reference model that varies only laterally and is confined to the part of the terrain that lies above the lowest topography in the area to obtain this model several estimated 2d magnetization distributions were constructed by data inversion as a function of the iteration number then a suitable 2d model of the magnetization

model for the tectonic evolution of the mississippi embayment and its contemporary seismicity aeromagnetic and gravity surveys of the northern mississippi embayment have delineated a northeast trending basement depression about 70 km wide and more than 300 km long the feature the mississippi valley graben is remarkably linear over its known length has nearly parallel sides and has estimated depths relative to surrounding basement of more than 2 km both gravity and magnetic anomalies show an alignment of dense magnetic plutons along the boundaries of the graben estimated magnetization directions for the plutons indicate a mesozoic age the graben of probable earliest paleozoic age underlies the northwest side of the embayment and contains the area of major seismicity in particular much of the instrumentally located contemporary seismicity and the estimated locations of the large magnitude 1811 1812 earthquakes are in the central part of the graben we interpret the early paleozoic graben the mesozoic plutonism and the sedimentation cycles as evidence of stretching events seismicity is attributed to strain in and below the central graben area which would appear to be a focal point of deformation in the stretching model we suggest that the sequence of events can be explained by the action of a rotating horizontal stress field on a crustal flaw that persisted well back in pre cambrian time the postulated rotating stress field is presumably controlled by the system that drives the global plates

mid continental earthquakes spatiotemporal occurrences causes and hazards abstract large earthquakes in north china australia northwestern europe central and eastern united states and other mid continents show complex spatiotemporal patterns that do not fit existing earthquake models individual faults or fault zones tend to fall into long term thousands of years or longer dormancy after a cluster of ruptures whereas large earthquakes seem to roam between widespread faults these behaviors are characteristic of complex dynamic systems of interacting faults in such systems widespread faults collectively accommodate slow tectonic loading and a major fault rupture both transfers stress to the neighboring faults and perturbs loading conditions on distant faults because of the slow tectonic loading local stress variations from fault interaction or nontectonic processes or changes of fault strength could trigger mid continental earthquakes the precise spatiotemporal occurrence of large mid continental earthquakes may be unknowable an intrinsic limitation of complex dynamic systems but their qualitative system behavior may be understood by a system approach this approach would render some commonly used concepts such as seismic cycles recurrence intervals characteristic earthquakes and seismic gaps inadequate or irrelevant in mid continents and calls for rethinking of the probability estimates based on these concepts it requires a better understanding of fault interactions on multiple spatial and temporal scales rather than focusing solely on the balance of tectonic loading and yield strength of individual faults or fault segments it also indicates the need for paleoseismic and geodetic studies extending beyond areas where recent large earthquakes occurred and for hazard assessments to reduce the biasing influence of the most recent large earthquakes that tend to dominate the short and incomplete earthquake records

jurassic earthquake sequence recorded by multiple generations of sand blows zion national park utah earthquakes along convergent plate boundaries commonly occur in sequences that are complete within 1 yr and may include 8 10 events strong enough to generate sand blows dune crossbeds within the jurassic navajo sandstone of utah western united states enclose intact and truncated sand blows and the intrusive structures that fed them we mapped the distribution of more than 800 soft sediment dikes and pipes at two small sites all water escape structures intersect a single paleo surface and are limited to the upper portion of the underlying set of cross strata and the lower portion of the overlying set a small portion of one set of crossbeds that represents 1 yr of dune migration encloses eight generations of eruptive events we interpret these superimposed depositional and deformational structures as the record of a single shock aftershock earthquake sequence the completeness and temporal detail of this paleoseismic record are unique and were made possible when sand blows repeatedly erupted onto lee slopes of migrating dunes similar records should be sought in modern dunefields with shallow water tables

the frontier mountain meteorite trap antarctica the frontier mountain blue ice field is an important antarctic meteorite trap which has yielded 472 meteorite specimens since its discovery in 1984 remote sensing analyses and field campaigns from 1993 to 1999 have furnished new glaciological data on ice flow ice thickness bedrock topography ice ablation and surface mass transport by wind along with detailed descriptions of the field situation at the trap this solid set of data combined with an updated meteorite distribution map and terrestrial ages available from literature allows us to better describe the nature of the concentration mechanism in particular we observe that the meteorite trap forms in a blue ice field 1 located upstream of an absolute and a shallow sub ice barriers 2 characterized by compressive ice flow with horizontal velocities decreasing from 100 to 10 cm year on approaching the obstacle 3 undergoing mean ablation rates of 6 5 cm year 4 nourished by a limited snow accumulation zone extending 20 km upstream of the blue ice area we also draw the following conclusions 1 the origin of the meteorite trap can be explained according to the present day glaciological situation 2 the meteorite concentration develops according to the general principles of the ice flow model 3 the accumulation model can be described as stagnant ice or slow moving ice against an absolute and submerged barriers according to the descriptive schemes present in literature 4 the frontier mountain ice field is an effective trap for meteorites weighing more than 200 g for smaller masses the combination of wind and glacial drift may remove meteorites in less than a few tens of thousands of years 5 although the activation age of the frontier mountain trap is not yet constrained we infer that one of the most important findsites may be as old as 50 ka predating the last glacial maximum

last interglacial vegetation and climate history from the portuguese coast we examine the atlantic maritime vegetation history from praia rei cortico portugal to understand natural vegetation patterns and infer climatic conditions during the transition from the last interglacial to early glacial periods optically stimulated luminescence dating of quartz grains from sediments surrounding the 1 3 m thick organic deposit date the section to within 120 89 ka pollen data were used to reconstruct the vegetation history and determine a range of possible past climates using an ensemble of seven modern analogue approaches a five part environmental sequence transitioned from heath pine dominated communities deciduous hardwood forests and pine forests to heathlands surrounded by steppe like environments mixed temperate and mediterranean forest elements existed during the last interglacial period at praia rei cortico suggesting a proximal limit to these floras abundant fagus pollen 6 suggests local beech populations existed within maritime forests of the iberian atlantic margin representing a greater distribution of this genus during interglacial periods than has previously been recognized climate reconstructions indicate that variations in moisture availability may have been a major driver of the observed environmental changes

liquefaction at oceano california during the 2003 san simeon earthquake the 2003 m 6 5 san simeon california earthquake caused liquefaction induced lateral spreading at oceano at an unexpectedly large distance from the seismogenic rupture we conclude that the liquefaction was caused by ground motion that was enhanced by both rupture directivity in the mainshock and local site amplification by unconsolidated fine grained deposits liquefaction occurred in sandy artificial fill and undisturbed eolian sand and fluvial deposits the largest and most damaging lateral spread was caused by liquefaction of artificial fill the head of this lateral spread coincided with the boundary between the artificial fill and undisturbed eolian sand deposits values of the liquefaction potential index in general were greater than 5 at liquefaction sites the threshold value that has been proposed for liquefaction hazard mapping although the mainshock ground motion at oceano was not recorded peak ground acceleration was estimated to range from 0 25 and 0 28 g on the basis of the liquefaction potential index and aftershock recordings the estimates fall within the range of peak ground acceleration values associated with the modified mercalli intensity vii reported at the u s geological survey usgs did you feel it web site

paleoseismic features as indicators of earthquake hazards in north coastal san diego county california usa abstract new road cut and mass grading excavations in the north coastal area of san diego county california expose heretofore generally unrecognized probable late holocene tsunami deposits and paleoseismically deformed sediments remnant tsunami deposits occur up to 100 m in elevation around the margins of modern coastal lagoons and estuaries and combined with local mima mounds of possible sand blow origin provide indirect but compelling evidence for the late quaternary activity of onshore and offshore faults in the immediate study area probable paleoliquefaction features are regionally widespread and range from fissures filled with sediments derived from overlying marine terrace sand and soil to the more traditional sand filled injection dikes and sills lateral spreads and filled craterlets the source of most liquefied sediment is underlying tertiary bedrock sand and local quaternary marine terrace deposits a paleoseismic liquefaction origin rather than soft sediment loading is deduced for these features based on morphology internal stratigraphy field setting and near proximity to known seismogenic sources some paleoseismic events impacted late holocene indian middens and burial sites the last seismic event probably occurred within the past 1 to 3 ka and possibly even records the historic earthquakes of either november 22 1800 or may 27 1862 the liquefaction features also affect marine terrace sediments tens of meters above modern regional water levels inferentially recording paleoseismic events in this mediterranean type climatic region during winter rains when high level perched water saturates the several meter thick source sediments based on their regional extent the paleoseismic features were likely caused by m 7 tectonic events inferentially generated by the nearby offshore newport inglewood rose canyon fault system or possibly by smaller recently exposed related and localized faults accordingly the seismic hazard of the north coastal area of san diego county may be substantially higher than previously assumed and hence of concern owing to the rapid ongoing and projected population increase

tectonic history and setting of a seismogenic intraplate fault system that lacks microseismicity the saline river fault system southern united states abstract although the northwest striking saline river fault system of southeastern arkansas is not defined by microseismicity it is associated with sand blows and shows evidence of pleistocene and holocene surface ruptures suggesting a significant seismogenic potential this fault system is within the northern gulf of mexico interior coastal plain a region only recently recognized as containing seismogenic faults to better characterize this active fault system we reconstructed its post paleozoic history using petroleum and coal industry wire line well log and seismic reflection subsurface data the saline river fault system initiated as a series of northwest striking grabens during triassic jurassic uplift and incipient gulf of mexico rifting along the basement alabama oklahoma transform margin of the north american proterozoic craton during post rift subsidence these grabens were buried by gulf sediments until mid cretaceous uplift and igneous activity resulted in minor extensional reactivation of graben faults faulting style changed from extension to transpression during the late cretaceous due to compression of eastern north america as the north atlantic rapidly widened and due to thermal weakening of the alabama oklahoma transform lithospheric discontinuity as it obliquely crossed a mantle hot spot in the late cretaceous graben faults experienced contractional reactivation and steep deeply rooted transpressional faults developed within and parallel to the graben system these transpressional faults locally displace eocene pleistocene and holocene sediments fault activity continues on the saline river fault system due to thin crust along the alabama oklahoma transform and to high heat flow which act together to weaken the crust and promote seismogenic tectonism the fault system may lack appreciable microseismicity because the aftershock sequence of the last large earthquake has had time to dissipate

quaternary faulting in the southern mississippi embayment and implications for tectonics and seismicity in an intraplate setting the recently recognized saline river fault zone in the southwestern mississippi embayment strike 135 is characterized by moderate historic seismicity we document paleoseismicity possibly strong on the saline river fault zone that is outside the known region of neotectonism in the northern embayment six surface faults were excavated within the saline river fault zone and all faults displace marine eocene units and fluvial pliocene pleistocene units five show post wisconsin loess movement thermoluminescence tl age 23 6 3 ka and three deform middle to late holocene eolian silt tl age 5 1 0 6 ka and 3 6 0 5 ka as fault tip flexures along the principal excavated fault fault plane braiding and plunging drag folding suggest a strong component of left slip and subsidiary faults show both normal and reverse displacement 1m of pliocene pleistocene wisconsin and holocene units we interpret these faults as components of a left slip flower structure a shallow seismic reflection profile acquired across the principal fault and a subsidiary fault shows eocene stratigraphy separated in a reverse sense below 120 m depth and separated in a normal sense above 120 m supporting a strike slip interpretation in addition the only focal plane mechanism available in the area indicates left slip with a small reverse component we conclude that the saline river fault zone is a paleozoic mesozoic basement fault zone reactivated as a left slip system in a quaternary east west compressive stress field field evidence suggests that earthquakes with several meters of strike slip may be characteristic and the width of a liquefaction field on the saline river fault zone suggests an event of magnitude 5 5 6 considering a similarity of strike and sense of holocene movements of the meers fault of southern oklahoma and of the saline river fault zone there may be additional active fault zones that pose seismic hazards concealed by sediments in southern north america

evidence of strong earthquake shaking in the lower wabash valley from prehistoric liquefaction features earthquake induced liquefaction features in holocene sediments provide evidence of strong prehistoric shaking magnitude m b 6 2 to 6 7 in the wabash valley bordering indiana and illinois the source of the one or more earthquakes responsible was almost certainly in or near the wabash valley the largest event is interpreted to have occurred between 7500 and 1500 years ago on the basis of archeological pedological and stratigraphic relations

liquefaction during the 1977 san juan province argentina earthquake ms 7 4 liquefaction effects generated by the 1977 san juan province argentina earthquake ms 7 4 are described the larger and more abundant effects were concentrated in the 60 km long band of the lowlands in the valle del bermejo and in an equally long band along the rio san juan in the valle de tulum fissures in the valle del bermejo were up to several hundred meters long and up to several meters wide sand deposits from boils that erupted through the fissures covered areas up to tens of square meters fissures generally parallelled nearby stream channels because the valle del bermejo is undeveloped these large features caused no damage liquefaction in the valle del tulum caused important or unusual damage at several localities including the following five sites 1 at the barrio justo p castro a subdivision of caucete liquefaction of subsurface sediments decoupled overlying unliquefied stiff sediments producing a form of ground failure called ground oscillation the associated differential ground movements pulled apart houses and pavements in extension while shearing curbs and buckling canal linings in compression at the same locality 2 at the escuela normal in caucete the roof of a 30 m long single story classroom building shifted westward relative to the foundation that displacement fractured and tilted columns supporting the roof the foundation was fractured at several places leaving open cracks as wide as 15 mm the cumulative width of the open cracks was 48 mm an amount roughly equivalent to the 63 mm of offset between the roof and foundation at the east end of the building the ground and foundation beneath the building extended or spread laterally opening cracks and lengthening the foundation while the roof remained in place 3 the most spectacular damage to structures at the community of san martin was the tilting of a 6 m high water tower and the toppling of a nearby pump house into a 1 m deep crater similarly a small crater developed beneath a hand pump in an open area and a large 6 m diameter crater formed nearby the following sequence of events created the craters and toppled the pump structures during the earthquake ground shaking generated excess pore pressures which were dissipated by upward flow of groundwater free drainage was restricted by an impermeable plastic silt layer water apparently accumulated below the plastic silt layer and then burst to the surface through several holes and cracks including holes around well casings 4 at the san isidro winery nine storage tanks tilted 2 to 5 five reinforced concrete tanks were dismantled but four steel tanks were repaired by placing new footings and jacking the structures into an upright position 5 at escuela j j pasos differential settlement beneath building fractured several columns and walls the largest settlements were about 60 mm and the maximum settlement of footings supporting columns was about 40 mm in spite of the damage the buildings were in no danger of collapse

hotspot origin of the mississippi embayment and its possible impact on contemporary seismicity abstract previous authors have related the late cretaceous early tertiary subsidence of the mississippi embayment to the opening of the gulf of mexico but the gulf opened earlier in triassic jurassic time we offer an alternative hypothesis that development of the embayment was coeval with the passage of the mississippi valley graben system over the bermuda hotspot about 90 ma several lines of evidence of significant uplift of the embayment axis accompanying mid cretaceous magmatism and prior to late cretaceous subsidence support this proposal first reactivation of the pascola arch in the northern embayment is recorded by flanking deposits of basal upper cretaceous gravel second beneath a regional mid cretaceous unconformity subcrops of jurassic and early cretaceous strata define a pronounced southwest plunging arch in the southern embayment this arch is collinear with an arch revealed in paleozoic rocks after restoration to mid cretaceous structural geometries third a deep weathering profile on mid cretaceous alkalic plutons along the western embayment margin is nonconformably overlain by paleocene sediments and rapid mid cretaceous cooling of these intrusions has been interpreted from apatite fission tracks moreover exploratory holes along the embayment axis encountered similar weathered alkalic intrusions nonconformably overlain by basal upper cretaceous strata fourth there was an anomalous influx of clastic sediment into the northern gulf of mexico during mid cretaceous time and subsequent clastic facies patterns suggest the mississippi river drainage began to enter the gulf in the late cretaceous passage of the mississippi valley graben over the bermuda hotspot during elevated hotspot activity of cretaceous time may have significantly weakened the previously rifted lithosphere rifted continental margin at charleston south carolina also passed over this hotspot in latest cretaceous time similarly the st lawrence rift system passed over the great meteor hotspot during the cretaceous it is important to note that these rift systems are the principal loci of strong seismicity in eastern north america and thus weakening by increased cretaceous hotspot activity may be an important common factor for these seismic rift zones

mapping blue ice areas in antarctica using etm and modis data blue ice areas bias and their geographical distribution in antarctica were mapped using landsat 7 etm images with 15 m spatial resolution obtained during the 1999 2003 austral summers and covering the area north of 82 58 s and a snow grain size image of the modis based mosaic of antarctica moa dataset with 125 m grid spacing acquired during the 2003 04 austral summer from 82 58 s to the south pole a map of bias was created with algorithms of thresholds based on band ratio and reflectance for etm data and thresholds based on snow grain size for the moa dataset the underlying principle is that blue ice can be separated from snow or rock by their spectral discrepancies and by different grain sizes of snow and ice we estimate the total area of bias in antarctica during the data acquisition period is 234 549 km 2 or 1 67 of the area of the continent blue ice is scattered widely over the continent but is generally located in coastal or mountainous regions the bia dataset presented in this study is the first map covering the entire antarctic continent sourced solely from etm and modis data this dataset can potentially benefit other studies in glaciology meteorology climatology and paleoclimate meteorite collection and airstrip site selection

geophysical survey at talos dome east antarctica the search for a new deep drilling site talos dome is an ice dome on the edge of the east antarctic plateau because accumulation is higher here than in other domes of east antarctica the ice preserves a good geochemical and palaeoclimatic record a new map of the talos dome area locates the dome summit using the global positioning system gps 72 47 14 s 159 04 2 e 2318 5 m elevation wgs84 a surface strain network of nine stakes was measured using gps data indicate that the stake closest to the summit moves south southeast at a few cm a 1 the other stakes located 8 km away move up to 0 33 m a 1 airborne radar measurements indicate that the bedrock at the talos dome summit is about 400 m in elevation and that it is covered by about 1900 m of ice snow radar and gps surveys show that internal layering is continuous and horizontal in the summit area 15 km radius the depth distribution analysis of snow radar layers reveals that accumulation decreases downwind of the dome north northeast and increases upwind south southwest the palaeomorphology of the dome has changed during the past 500 years probably due to variation in spatial distribution of snow accumulation driven by wind sublimation in order to calculate a preliminary age vs depth profile for talos dome a simple one dimensional steady state model was formulated this model predicts that the ice 100 m above the bedrock may cover one glacial interglacial period

rapid 3 d forward model of potential fields with application to the palinuro seamount magnetic anomaly southern tyrrhenian sea italy 1 we show a set of forward model equations in the fourier domain for calculating the 3 d gravity and magnetic anomalies of a given 3 d distribution of density or magnetization one property of the potential field equations is that they are given by convolution products providing a very simple analytic expression in the fourier domain under this assumption the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions a very fine spatial discretization can be obtained by using a large number of points within a unique 3 d grid where both the source distributions and field data are defined the main advantage of this formulation is that it dramatically reduces execution times providing a very fast forward model tool useful for modeling anomalies at different altitudes we use this method to evaluate an average magnetization of 8 a m for the palinuro seamount in the tyrrhenian sea southern italy thus performing a joint interpretation of morphological and newly acquired magnetic data

variations in water level for lake turkana in the past 8500 years near mt porr kenya and the transition from the african humid period to holocene aridity abstract a stratigraphic and geomorphic study of relict beaches up to 80 m above current water level of lake turkana reveal four major lake level fluctuations of 50 m between ca 8 5 and 4 5 ka during the transition from the african humid period to holocene aridity we hypothesize that high stands of lake turkana reflect complex hydrological processes with variability in atlantic and indian ocean derived moisture into east africa ultimately linked to changes in sea surface temperatures ssts lake level rise was also amplified regionally by increased precipitation causing overflow from the adjacent suguta and chew bahir basins particularly during high stands at ca 8 5 ka and at 6 4 ka the timing of transgressive and regressive events is constrained by 14c dating of carefully selected lacustrine mollusks incorporation of previous shell ages with sufficient elevational control and osl dating of quartz grains from littoral and sublittoral deposits by a multiple aliquot regeneration mar approach there was a high water level up to at least 70 m at 8 5 ka that probably reached the spillover limit 100 m a brief

optical ages on loess derived from outwash surfaces constrain the advance of the laurentide ice sheet out of the lake superior basin usa abstract we present textural and thickness data on loess from 125 upland sites in west central wisconsin which confirm that most of this loess was derived from the sandy outwash surfaces of the chippewa river and its tributaries which drained the chippewa lobe of the laurentide front during the wisconsin glaciation mis 2 on bedrock uplands southeast of the widest outwash surfaces in the chippewa river valley this loess attains thicknesses 5 m osl ages on this loess constrain the advance of the laurentide ice from the lake superior basin and into west central wisconsin at which time its meltwater started flowing down the chippewa drainage the oldest mar osl age 23 8 ka from basal loess on bedrock agrees with the established but otherwise weakly constrained regional glacial chronology basal ages from four other sites range from 13 2 to 18 5 ka pointing to the likelihood that these sites remained geomorphically unstable and did not accumulate loess until considerably later in the loess depositional interval other osl ages from this loess taken higher in the stratigraphic column but below the depth of pedoturbation range to nearly 13 ka suggesting that the chippewa river valley may have remained a loess source for several millennia

necessary conditions for intraplate seismic zones in north america the cause of intraplate seismic zones persists as an important scientific and societal question most intraplate earthquakes are concentrated in specific seismic zones along or adjacent to large scale basement structures e g rifts or sutures at ancient plate boundaries within continental crust the major intraplate seismic zones are limited to specific segments and are not distributed along the lengths of the ancient structures we present a new hypothesis that major intraplate seismic zones are restricted to places where concentrated crustal deformation ccd is overprinted on large scale basement structures examples where ccd affects the stability of specific parts of large scale structures in response to present day stress conditions include the most active seismic zones in central and eastern north america charlevoix eastern tennessee and new madrid our hypothesis has important implications for the assessment of seismic hazards

allan hills 88019 an antarctic h chondrite with a very long terrestrial age we have measured the concentrations of the cosmogenic radionuclides loge 26al and 36cl half lives 1 51 ma 716 ka and 300 ka respectively in two different laboratories by accelerator mass spec trometry ams techniques as well as concentrations and isotopic compositions of stable he ne and ar in the antarctic h chondrite allan hills alh 88019 in addition nuclear track densities were measured from these results it is concluded that the meteoroid alh 880 19 had a preatmospheric radius of 20 5 cm and a shielding depth for the analyzed samples of between 4 and 8 cm using calculated and experimentally deter mined production rates of cosmogenic nuclides an exposure age of 40 ma is obtained from cosmogenic 21ne and 38ar the extremely low concentrations of radionuclides are explained by a very long terrestrial age for this meteorite of 2 f 0 4 ma a similarly long terrestrial age was found so far only for the antarctic l chon drite lewis cliff lew 86360 such long ages establish one boundary condition for the history of mete orites in antarctica

what lies beneath geophysical mapping of a concealed precambrian intrusive complex along the iowa minnesota border large amplitude gravity and magnetic highs over northeast iowa are interpreted to reflect a buried intrusive complex composed of mafic ultramafic rocks the northeast iowa intrusive complex neiic intruding yavapai province 1 8 1 72 ga rocks the age of the complex is unproven although it has been considered to be keweenawan 1 1 ga because only four boreholes reach the complex which is covered by 200 700 m of paleozoic sedimentary rocks geophysical methods are critical to developing a better understanding of the nature and mineral resource potential of the neiic lithologic and cross cutting relations interpreted from high resolution aeromagnetic and airborne gravity gradient data are presented in the form of a preliminary geologic map of the basement precambrian rocks numerous magnetic anomalies are coincident with airborne gravity gradient agg highs indicating widespread strongly magnetized and dense rocks of likely mafic ultramafic composition a yavapai age metagabbro unit is interprete

a priori models and inversion of gravity gradient data in hilly terrain abstract the increased popularity of airborne measurements of the gravity gradient tensor for resource studies and geological mapping has resulted in a new awareness of the importance of terrain effects in these measurements the terrain effect often overwhelms that of the underlying crust and it becomes important to formulate a strategy for taking it into account when presenting the data and when inverting the data into density models using newly acquired data from northern sweden we first attempted to estimate a variable terrain density model by inverting the data using a terrain model with a laterally varying density using data weights related to the topography variations we find the best estimate of the lateral variation of the terrain density we translate this model into a full three dimensional model such that all columns have the same vertical centre of mass as estimated from inspecting the radially averaged power spectrum of the area this then defines a reference model for subsequent three dimensional inversion of the gravity gradient tensor dataset we tested this approach first on synthetic data calculated from the measured topography including two density anomalies before we applied it to the measured data the result is a model in which the surface density variations are propagated downwards in a systematic manner now in better agreement with measured densities of rock samples in the area

conforming falcon gravity and the global gravity anomaly gravity derived only from airborne gravity gradient measurements with a normal error distribution will have an error that increases with wavelength it is straightforward in principle to use sparsely sampled regional gravimeter data to provide the long wavelength information thereby conforming the derived gravity to the regional gravity regional surface or airborne gravimeter data are not always available and can be difficult and expensive to collect in many of the areas where an airborne gravity gradiometer survey is flown however the recent release by the danish national space centre of the dnsc08 global gravity anomaly data has provided regional gravity data for the entire earth of adequate quality for this purpose studies over three areas including comparisons with ground marine and airborne gravimetry demonstrate the validity of this approach future improvements in global gravity anomaly data are expected particularly as the product from the recently launched gravity field and steady state ocean circulation explorer goce satellite becomes available and these will lead directly to an improvement in the very wide bandwidth gravity available after conforming gravity derived from gravity gradiometry with the global gravity

gravity gradient and magnetic terrain effects for airborne applications a practical fast fourier transform technique we have implemented a practical fast fourier transform technique for fast and approximate calculation of terrain effects for airborne measurement of the gravity gradient tensor and the total magnetic field the calculations proceed in two steps starting from a digital terrain model dtm we first calculate the fields on a plane surface lying above the highest point of the terrain in the selected area this calculation can be made arbitrarily accurate by including a sufficiently large number of terms in parker s well known fourier transform technique the second step involves a downward continuation of the fields to a draped surface describing the positions of the airborne measurements the inherent instability of downward continuation through the level of the highest terrain is compensated for by low pass filtering the calculated fields on the plane surface prior to downward continuation we use a gaussian filter with cutoff wavenumbers well below the nyquist wavenumber corresponding to a wavelength equal to the distance between flight lines tests on synthetic data as well as on real data from a dtm from northern sweden demonstrated that the method works well and provides a low pass filtered version of the true terrain effect

quaternary deformation along the meeman shelby fault near memphis tennessee imaged by high resolution marine and land seismic reflection profiles 1 a series of high resolution seismic reflection surveys was carried out in 2008 2010 and 2011 providing a total of five new seismic profiles constraining the location and character of the meeman shelby fault msf about 9 km west of memphis tennessee in the central u s the msf is the best documented fault closest to memphis yet discovered and shows a recurrent fault history the fault as imaged by the reflection profiles is 45 km long strikes n25 e and dips west northwest 83 exhibiting an up to the west sense of motion with a possible right lateral strike slip component the data show that on average the msf offsets the paleozoic unit 77 m and folds the top of the cretaceous unit and the paleocene eocene wilcox group 44 and 25 m respectively one seismic profile acquired along the mississippi river images the bottom of the quaternary alluvium warped up 28 m indicating recent activity of the msf calculated vertical slip rates of the msf during the deposition of the upper cretaceous paleocene eocene and quaternary sediments are 0 0022 0 0010 0 0004 and 0 2154 mm yr respectively suggesting an increase in fault activity during the quaternary consistent with the present stress field and the deformation of the new madrid seismic zone fault system we interpret the msf as a p shear fault in the context of a left stepping right lateral constraining strike slip fault system under a nearly east west oriented compressional stress field source scaling estimates indicate that the msf is capable of generating a m6 9 earthquake if rupturing in one event

airborne gravity gradiometry terrain corrections and elevation error terrain corrections for airborne gravity gradiometry data are calculated from a digital elevation model dem grid the relative proximity of the terrain to the gravity gradiometer and the relative magnitude of the density contrast often result in a terrain correction that is larger than the geologic signal of interest in resource exploration residual errors in the terrain correction can lead to errors in data interpretation such errors may emerge from a dem that is too coarsely sampled errors in the density assumed in the calculations elevation errors in the dem or navigation errors in the aircraft position simple mathematical terrains lead to the heuristic proposition that terrain correction errors from elevation errors in the dem are linear in the elevation error but follow an inverse power law in the ground clearance of the aircraft simulations of the effect of elevation error on terrain correction error over four measured dems support this proposition this power law relation may be used in selecting an optimum survey flying height over a known terrain given a desired terrain correction error

neotectonics of the upper mississippi embayment abstract although the upper mississippi embayment is an area of low relief the region has been subjected to tectonic influence throughout its history and continues to be so today tectonic activity can be recognized through seismicity patterns and geological indicators of activity either those as a direct result of earthquakes or longer term geomorphic structural and sedimentological signatures the rate of seismic activity in the upper mississippi embayment is generally lower than at the margins of tectonic plates the embayment however is the most seismically active region east of the rocky mountains with activity concentrated in the new madrid seismic zone this zone produced the very large new madrid earthquakes of 1811 and 1812 geological and geophysical evidence of neotectonic activity in the upper mississippi embayment includes faulting in the benton hills and thebes gap in missouri paleoliquefaction in the western lowlands of missouri subsurface faulting beneath and tilting of crowley s ridge in northeastern arkansas and southeastern missouri subsurface faulting along the crittenden county fault zone near memphis tennessee faulting along the east flank of the tiptonville dome and numerous indicators of historic and prehistoric large earthquakes in the new madrid seismic zone paleoearthquake studies in the new madrid seismic zone have used trenching seismic reflection shallow coring pedology geomorphology archaeology and dendrochronology to identify and date faulting deposits of liquefied sand and areas of uplift and subsidence the cause of today s relatively high rate of tectonic activity in the mississippi embayment remains elusive it is also not clear whether this activity rate is a short term phenomenon or has been constant over millions of years ongoing geodetic and geological studies should provide more insight as to the precise manner in which crustal strain is accumulating and perhaps allow improved regional neotectonic models

ice flow dynamics and meteorite collection in antarctica abstract typical targets for meteorite searches in antarctica are blue ice fields in front of major bedrock obstacles where the meteorite bearing ice slows down is uplifted and exhumed by ablation however in some areas collection occurs in the lee of topographic barriers as documented in the downstream side of the frontier mountain a major emerged bedrock barrier in this study we present an analogue modelling study of ice flow at frontier mountain which has been chosen as example study area because an exceptionally complete set of glaciological data is available to investigate the causes leading to meteorite concentration results of modelling show how the boundary conditions mainly the bedrock topography control ice flow and how this flow coupled to high ablation may give rise to a stable meteorite trap downstream of major topographic obstacles modelling results support the contention that as erosion is not a mountain builder ablation does not represent a driving force in ice flow dynamics although it plays a significant role in shaving stranding surfaces and exhuming meteorites

terrestrial ages pairing and concentration mechanism of antarctic chondrites from frontier mountain northern victoria land we report concentrations of cosmogenic 10be 26al 36cl and 41ca in the metal phase of 26 ordinary chondrites from frontier mountain fro antarctica as well as cosmogenic 14c in eight and noble gases in four bulk samples thirteen out of 14 selected h chondrites belong to two previously identified pairing groups fro 90001 and fro 90174 with terrestrial ages of 40 and 100 kyr respectively the fro 90174 shower is a heterogeneous h3 6 chondrite breccia that probably includes more than 300 individual fragments explaining the high h l chondrite ratio 3 8 at frontier mountain the geographic distribution of 19 fragments of this shower constrains ice fluctuations over the past 50 100 kyr to less than 40 m supporting the stability of the meteorite trap over the last glacial cycle the second h chondrite pairing group fro 90001 is much smaller and its geographic distribution is mainly controlled by wind transport most l chondrites are younger than 50 kyr except for the fro 93009 01172 pair which has a terrestrial age of 500 kyr these two old l chondrites represent the only surviving members of a large shower with a similar preatmospheric radius 80 cm as the fro 90174 shower the find locations of these two paired l chondrite fragments on opposite sides of frontier mountain confirm the general glaciological model in which the two ice flows passing both ends of the mountain are derived from the same source area on the plateau the 50 fro meteorites analyzed so far represent 21 different falls the terrestrial ages range from 6 kyr to 500 kyr supporting the earlier proposed concentration mechanism

geologic evidence for recurrent moderate to large earthquakes near charleston south carolina multiple generations of earthquake induced sand blows in quaternary sediments and soils near charleston south carolina are evidence of recurrent moderate to large earthquakes in that area the large 1886 earthquake the only historic earthquake known to have produced sand blows at charleston probably caused the youngest observed blows older late quaternary sand blows in the charleston area indicate at least two prehistoric earthquakes with shaking severities comparable to the 1886 event

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

paleoliquefaction evidence for a strong holocene earthquake in south central indiana earthquake induced paleoliquefaction features in holocene sediments in south central indiana are evidence for strong shaking in the recent prehistoric past in an area where only infrequent low magnitude earthquakes have occurred during the 200 yr of the historic record distribution of liquefaction features and geotechnical analyses of liquefied sediments are the basis for estimating that an earthquake with a magnitude of 6 9 was centered near vallonia indiana radiometric archaeologic and stratigraphic relations bracket the event to between 3 7 ka and 4 2 ka b p evidence for a local source for strong shaking requires reassessment of earthquakes hazards in the southern indiana northern kentucky southwestern ohio area

physical modeling of the influence of bedrock topography and ablation on ice flow and meteorite concentration in antarctica 1 three dimensional laboratory physical experiments have been used to investigate the influence of bedrock topography and ablation on ice flow different models were tested in a plexiglas box where a transparent silicone simulating ice in nature was allowed to flow experimental results show how the flow field in terms of both flow lines and velocity and variations in the topography of the free surface and internal layers of the ice are strongly influenced by the presence and height of bedrock obstacles in particular the buttressing effect forces the ice to slow down rise up and avoid the obstacle the higher the bedrock barrier the more pronounced the process only limited uplift of internal layers is observed in these experiments in order to exhume deep material embedded in the ice ablation simulated by physically removing portions of silicone from the model surface to maintain a constant topographic depression must be included in the physical models in this case the analogue ice replenishes the area of material removal thereby allowing deep layers to move vertically to the surface and severely altering the local ice flow pattern this process is analogous to the ice flow model proposed in the literature for the origin of meteorite concentrations in blue ice areas of the antarctic plateau

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

alluvial river response to neotectonic deformation in louisiana and mississippi repeat geodetic surveys show uplift of the monroe and wiggins anticlines in louisiana and mississippi there are deformed quaternary terraces which indicate long term deformation in the valleys of the alluvial rivers that cross these structures and there are floodplain and channel convexities that provide evidence of modern deformation in addition the channels show significant variations of morphology sinuosity gradient and depth and behavior appropriate to reaches of increased and decreased valley slope these alluvial rivers are adjusting to modern deformation and their adjustment confirms two geodetic leveling anomalies

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

soft sediment deformation structures in nw germany caused by late pleistocene seismicity new data on seismically triggered soft sediment deformation structures in pleniglacial to late glacial alluvial fan and aeolian sand sheet deposits of the upper senne area link this soft sediment deformation directly to earthquakes generated along the osning thrust which is one of the major fault systems in central europe soft sediment deformation structures include a complex fault and fold pattern clastic dikes sand volcanoes sills irregular intrusive sedimentary bodies flame structures and ball and pillow structures the style of soft sediment deformation will be discussed with respect to brittle failure liquefaction and fluidization processes and was controlled by 1 the magnitude of the earthquake and 2 the permeability tensile strength and flexural resistance of the alluvial and aeolian sediments it is the first time in northern germany that fluidization and liquefaction features can be directly related to a fault the occurrence of seismicity in the late pleistocene and in the seventeenth century indicates ongoing crustal movements along the osning thrust and sheds new light on the seismic activity of northern germany the late pleistocene earthquake probably occurred between 15 9 1 6 and 13 1 1 5 ka the association of soft sediment deformation structures implies that it had a magnitude of at least 5 5

preliminary assessment of sand blows in the southern mississippi embayment trenching of sand blows in two liquefaction fields on late to mid holocene alluvium within the southern mississippi embayment was conducted to determine the origin of the sand blows and their possible relationship to new madrid seismic zone events trench stratigraphy and crosscutting relationships show evidence of multiple events of seismically induced sand venting these two fields of moderate to intense liquefaction are 175 km and 240 km southwest of the southern limit of similarly intense sand blows within the new madrid seismic zone nmsz liquefaction field the southernmost field ashley county arkansas is 25 km in diameter and sand blows are densely spaced sand blows are more sparsely spaced in the larger 30 km by 45 km northern field desha county arkansas various correlations of liquefaction events between these two fields and between each of these fields and the nmsz can be accommodated by our radiocarbon and infrared stimulated luminescence irsl ages of sediments predating and postdating vented sand deposits in our trenches these ages show a major liquefaction event at both the ashley and desha county fields between 4600 and 5500 years ago and a major event at the ashley county field approximately 700 years ago the early venting episode is older than the documented nmsz chronology and so a nmsz seismic source cannot be assessed the age of the later venting episode falls between two postulated nmsz events so it may reflect seismicity from a different source zone our trench logs show at least three other moderate to minor sand venting episodes at the ashley county field and two at the desha county field and one may be the same event at both fields about 2200 years ago if these sand blows formed during large nmsz events 175 km northeast the area of strong ground motion for this seismic source has been underestimated alternatively if these liquefaction fields formed due to local seismicity then additional significant seismic source zones are present in the mississippi embayment outside the nmsz each of the two fields sits astride seismicity alignments associated with the margins of a previously identified active fault block between the arkansas river fault zone that projects through the desha county field and the saline river fault zone that projects through the ashley county field

episodic eolian deposition in the past ca 50 000years in the alto ilo dune field southern peru abstract the alto ilo dune field in the coastal desert of southern peru is located at the edge of the atacama desert and is one of the driest landscapes on earth a stratigraphic sequence of eolian sands paleosols and debris flow deposits are identified in this dune field spanning the past 55 ka we infer that eolian deposition is preceded by an increase in sediment supply from local alluvial fans that are upwind of the alto ilo dune field and thus reflects periods of relative hydrologic excess eolian sediment supply may increase also with the concomitant fall in sea level providing an additional foreland source area for eolian particles the presence of paleosols indicate millennial scale periods of locally wetter conditions possibly associated with spread of lomas vegetation fed from coastal fog sources debris flows reflect significant rainfall events possibly associated with enso variability the chronology is provided by optically stimulated luminescence using multiple aliquot regeneration protocols which reveal four major eolian depositional episodes at ca 55 to 45 ka 38 to 27 ka 22 to 16 ka and 12 ka eolian deposition in the late pleistocene dominates the record and is generally coincident with metrics of hydrologic excess from the peruvian andes and the altiplano which appears to translate into enhanced sediment availability on the coast a significant period of soil development between 18 and 13 ka is consistent with timing of central andean pluvial event and indicates widespread wet conditions the holocene record of eolian deposition is sparse reflecting limited alluvial fan sources and decreasing particle availability upwind with the rise in postglacial sea level

heli borne gravity gradiometry in rugged terrain abstract for airborne gravity gradiometry in rugged terrain helicopters offer a significant advantage over fixed wing aircraft their ability to maintain much lower ground clearances crucially this provides both better signal to noise and better spatial resolution than is possible with a fixed wing survey in the same terrain comparing surveys over gentle terrain at margaret lake canada and over rugged terrain at mount aso japan demonstrates that there is some loss of spatial resolution in the more rugged terrain the slightly higher altitudes forced by rugged terrain make the requirements for terrain correction easier than for gentle terrain transforming the curvature gradients measured by the falcon gravity gradiometer into gravity and the complete set of tensor components is done by a fourier method over gentle terrain and an equivalent source method for rugged terrain the fourier method is perfectly stable and uses iterative padding to improve the accuracy of the longer wavelengths the equivalent source method relies on a smooth model inversion and the source distribution must be designed to suit the survey design

ouachita appalachian juncture a paleozoic transpressional zone in the southeastern u s a the northern margin of gondwana collided with the southern margin of the north american craton in the late paleozoic 330 265 ma near normal compressional stresses generated where the trend of the north american margin was nearly perpendicular to gondwana s plate motion vector closure direction caused extensive crustal shortening and decollement thrusting within the sedimentary section the appalachian and ouachita fold belts are the erosional remnants of this collision on the north american margin transecting the ouachita fold belt are several zones of late paleozoic transcurrent faulting the val verde ardmore anadarko and reelfoot zones they occur where the precollision margin of the north american craton was oriented oblique or parallel to the closure direct on with gondwana stresses generated within these zones during the collision were transpressional rather than simply compressional and gave rise to high angle faulting high amplitude vertical displacements and the emplacement of positive flower structures in the val verde and ardmore anadarko basins these features have proven to be major structural traps for oil and gas on the basis of seismic and well data this study identifies a zone of complex structures including positive flower structures in the subsurface paleozoic section of kemper county in east central mississippi the region is considered to be another transpressional zone analogous to the val verde ardmore anadarko and reelfoot zones the kemper county zone separates and truncates the appalachian valley and ridge fo d belt in the subsurface from the mississippi ouachita deformed belt to the west and is therefore also identified as the juncture between the ouachita and appalachian fold belt systems in the southeastern u s a

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

dating antarctic blue ice areas using a novel ice flow model 1 we present a new type of flow model suitable for antarctic blue ice areas with application to dating ice for paleoclimate purposes the volume conserving model uses field data for surface velocities mass balance and ice thickness along a flow line with parameterized variation of ice rheology with depth to produce particle trajectories and isochrones the model is tested on the contrasting allan hills near western ice field and the scharffenbergbotnen blue ice fields in antarctica by comparing predicted ages with ages inferred from meteorites and 14c data during the glacial periods ice surface velocities at the allan hills must have been 25 less and accumulation rates 50 less than present day values in order to match meteorite ages in contrast scharffenbergbotnen velocities have probably been fairly constant over time due to the atypical valley where it resides

field occurrences of liquefaction induced features a primer for engineering geologic analysis of paleoseismic shaking discussed in this paper are the factors that control the typical manifestations of liquefaction that are found in continental field settings the factors are given mainly in terms of the local geologic field situation and the geotechnical properties there a meaningful interpretation of liquefaction based data for quantitative analysis of paleoseismic shaking requires understanding of both geologic and geotechnical roles in the mode of ground failure at a specific site recommendations are made for the size of the field area that must be searched for liquefaction effects in order to develop adequate data for engineering geologic geotechnical analyses of paleoseismicity the areal extent must be based on an appreciation that the tectonic situation can cause seismically induced liquefaction effects to form in some locales but not in others nearby even for a strong earthquake in the region our guidelines for the conduct of the field search and preliminary analysis of the data relate to three issues for which liquefaction features are especially useful in answering has there been strong holocene latest pleistocene shaking in the region where was the tectonic source and what was the strength of shaking understanding of the various factors that control the manifestations of liquefaction effects which we present in this paper is essential for developing credible answers to these questions

paleoseismology of the southeastern reelfoot rift in western tennessee and implications for intraplate fault zone evolution 1 the southeastern reelfoot rift margin is expressed as a series of collinear scarps across western tennessee and shallow s wave reflection profiles coring and trenches show late quaternary faulting along this lineament at the north end our seismic profile and coring suggest 1 5 m of wisconsin down to the nw faulting coring and trenches across the central lineament show 3 m of up to the nw and 8 15 m of right lateral late wisconsin holocene faulting averaged late quaternary right lateral slip has been 0 85 0 37 mm yr on one fault plane at this locality suggesting that total slip across all southeast rift margin fault planes may accommodate much of the regional strain our seismic profile at this site shows up to the west faulting of eocene strata folded down to the west indicating structural inversion seismic profiles electrical surveys coring and a trench across the southern lineament segment show holocene faulting trenching exposed a vertical fault with 0 5 m of late holocene down to the nw displacement nearby coring and electrical surveys show 0 5 m of late holocene up to the nw faulting we conclude the southeastern reelfoot rift margin is a right lateral system with high angle faults showing both up to the nw and down to the nw separations age constraints permit an earthquake circa 2500 to 2000 years b p on the southwestern central segment of this fault system that ruptured 80 km we suggest the northeastern segment of the southeastern rift margin turned off in holocene when the reelfoot step over thrust turned on

unravelling the high altitude nansen blue ice field meteorite trap east antarctica and implications for regional palaeo conditions abstract antarctic blue ice zones the most productive locations for meteorite recovery on earth contain old ice that is easily accessible and available in large quantities however the mechanisms behind these meteorite traps remain a topic of ongoing debate here we propose an interdisciplinary approach to improve our understanding of a meteorite trap in dronning maud land east antarctica on the nansen blue ice field meteorite trap 2600 3100 m above sea level where more than half of the asuka meteorites have been collected based on 185 surface blue ice samples one of the largest observed spatial patterns in oxygen isotopic variation to date is found relying on meteorites for which the terrestrial ages are determined using 14c and 36cl this surface ice is interpreted to date from the last interglacial up to the present day by combining state of the art satellite derived surface velocities surface mass balance modelling and ice flow modelling we estimate that about 75 85 of the meteorites found on the ice field were supplied by ice flow after entering the ice sheet in an accumulation area of a few hundred square kilometres located south upstream of the ice field less than 0 4 new meteorites per year are supplied to the ice field through ice flow suggesting that the hundreds of meteorites found 25 years after the first visit to this ice field mostly represent meteorites that were previously not found rather than newly supplied meteorites by combining these findings the infall rate of meteorites from space is estimated which is in line with values from the literature but situated at the higher end of the range a comparison of the oxygen isotopic variation of the surface blue ice to that of the european project for ice coring in antarctica epica dronning maud land edml ice core located 750 km to the west at the same elevation suggests that the regional changes in topography have been relatively limited since the last interglacial supporting theories of an overall stable east antarctic ice sheet eais over this time period

meteorites constrain the age of antarctic ice at the frontier mountain blue ice field northern victoria land abstract we show that meteorites can provide chronological constraints upon the age of the ice cropping out at the frontier mountain meteorite trap antarctica when their terrestrial age is placed in a glaciological context amongst the over 700 meteorites found so far frontier mountain fro 84001 99028 93005 and 93054 were most likely not wind drifted across the ice field since their masses 772 1665 g are much heavier than the local 200 g wind transport threshold the four meteorites were found along a stretch of ice where a representative section of the frontier mountain blue ice crops out based on the bedding of englacial tephra layers the structure of the ice along the section appears to be essentially an up glacier dipping monocline the 14 c terrestrial age of fro 8401 99028 and 93005 are 13 2 21 3 and 27 2 ky respectively the 41 ca 36 cl age of fro 93054 is 40 10 ky the terrestrial ages of the four meteorites increase from the top to the bottom layers of the monocline this geographic distribution is best explained by delivery of meteorites at the ice surface through the ice flow model i e englacial transport from the snow accumulation zone and exhumation in the blue ice area through ablation rather than direct fall since the effect of ablation in decoupling terrestrial ages of meteorites and the age of the ice on which they sit must have been minor most likely 7 ky based on the local ice dynamics we conclude that the age of the bulk of the ice body currently under ablation at frontier mountain is up to 50 ky old this result has implications on both the meteorite concentrations mechanism at frontier mountain and the regional ice dynamics

liquefaction potential index field assessment cone penetration test cpt soundings at historic liquefaction sites in california were used to evaluate the predictive capability of the liquefaction potential index lpi which was defined by iwasaki et al in 1978 lpi combines depth thickness and factor of safety of liquefiable material inferred from a cpt sounding into a single parameter lpi data from the monterey bay region indicate that the probability of surface manifestations of liquefaction is 58 and 93 respectively when lpi equals or exceeds 5 and 15 lpi values also generally correlate with surface effects of liquefaction decreasing from a median of 12 for soundings in lateral spreads to 0 for soundings where no surface effects were reported the index is particularly promising for probabilistic liquefaction hazard mapping where it may be a useful parameter for characterizing the liquefaction potential of geologic units

lewis cliff 86360 an antarctic l chondrite with a terrestrial age of 2 35 million years we measured the concentrations of the cosmogenic radionuclides 10be half life 1 51 106 a 26al 7 05 105 a and 36cl 3 01 105 a in lewis cliff lew 86360 an l chondrite from the lewis cliff stranding area east antarctica in addition the concentrations and isotopic compositions of he ne and ar were measured the combined results yield a terrestrial age of 2 35 0 15 ma only one other stony meteorite with a similar terrestrial age 2 ma is known from the allan hills stranding area alh 88019 whereas all previously dated stony meteorites from antarctica are younger than 1 ma we argue that lew 86360 spent most of its terrestrial residence time deep inside the ice near the base of the glacier where ice flow rates are much lower than at the surface the terrestrial ages of lew 86360 and alh 88019 are consistent with existing hypotheses concerning the stability and persistence of the east antarctic ice sheet

the 410 000 year terrestrial age of eucrite rio cuarto 001 we have measured a surprisingly long terrestrial age of 410 000 20 000 45 000 years 410 20 45 ka for basaltic eucrite ro cuarto 001 using accelerator mass spectrometry of 26al 36cl and 41ca though many meteorites are known to have survived for tens or hundreds of ka in antarctica or hot deserts the mean annual precipitation of 815 mm in ro cuarto cordoba province argentina makes the long survival of this meteorite remarkable we propose two explanations for the exceptional preservation of ro cuarto 001 first the meteorite contains only trace amounts of metal so the weathering and oxidation of metallic fe which commonly destroys chondrites is ineffective in this case second the meteorite was found in a relatively young deflation basin and may have been exhumed only recently from beneath a protective layer of soil insofar as the survival on earth of ro cuarto 001 is due to environmental factors there may be other meteorites with comparably long terrestrial ages still to be discovered in the vicinity

meteoritic and bedrock constraints on the glacial history of frontier mountain in northern victoria land antarctica abstract in 2001 a small h4 chondrite frontier mountain fro 01149 was found on a glacially eroded surface near the top of frontier mountain antarctica about 600 m above the present ice level the metal and sulphides are almost completely oxidized due to terrestrial weathering we used a chemical leaching procedure to remove weathering products which contained atmospheric 10 be and 36 cl in a ratio similar to that found in antarctic ice the fro 01149 meteorite has a terrestrial age of 3 0 0 3 myr based on the concentrations of the cosmogenic radionuclides 10 be 26 al and 36 cl this age implies that fro 01149 is the oldest stony meteorite fossil meteorites excluded discovered on earth the noble gas cosmic ray exposure age of fro 01149 is 30 myr the meteorite thus belongs to the 33 myr exposure age peak of h chondrites the bedrock surface on which fro 01149 was found has wet based glacial erosional features recording a former high stand of the east antarctic ice sheet this ice sheet evidently overrode the highest peaks 2800 m a s l of the inland sector of the transantarctic mountains in northern victoria land we argue that fro 01149 was a local fall and that its survival on a glacially eroded bedrock surface constrains the age of the last overriding event to be older than 3 myr the concentrations of in situ produced cosmogenic 10 be 26 al and 21 ne in a glacially eroded bedrock sample taken from near the summit of frontier mountain yield a surface exposure age of 4 4 myr and indicate that the bedrock was covered by several meters of snow the exposure age is also consistent with bedrock exposure ages of other summit plateaus in northern victoria land

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

interpretation of magnetic and gravity gradient tensor data using normalized source strength a case study from mcfaulds lake northern ontario canada in this paper we present a case study on the use of the normalized source strength nss for interpretation of magnetic and gravity gradient tensors data this application arises in exploration of nickel copper and platinum group element ni cu pge deposits in the mcfaulds lake area northern ontario canada in this study we have used the normalized source strength function derived from recent high resolution aeromagnetic and gravity gradiometry data for locating geological bodies in our algorithm we use maxima of the normalized source strength for estimating the horizontal location of the causative body then we estimate depth to the source and structural index at that point using the ratio between the normalized source strength and its vertical derivative calculated at two levels the measurement level and a height h above the measurement level to discriminate more reliable solutions from spurious ones we reject solutions with unreasonable estimated structural indices this method uses an upward continuation filter which reduces the effect of high frequency noise in the magnetic case the advantage is that in general the normalized magnetic source strength is relatively insensitive to magnetization direction thus it provides more reliable information than standard techniques when geologic bodies carry remanent magnetization for dipping gravity sources the calculated normalized source strength yields a reliable estimate of the source location by peaking right above the top surface application of the method on aeromagnetic and gravity gradient tensor data sets from mcfaulds lake area indicates that most of the gravity and magnetic sources are located just beneath a 20 m thick on average overburden and delineated magnetic and gravity sources which can be probably approximated by geological contacts and thin dikes come up to the overburden

performance of airborne gravity gradiometers airborne gravity gradiometry agg is becoming a widely accepted tool in exploration it provides rapid acquisition of accurate gravity data at high spatial resolution with complete coverage over large areas the data are of significant value to explorers for a wide range of commodities throughout the world with the advent of airborne gravity gradiometer technology it is now possible to collect high resolution gravity with all the attendant advantages