present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

fossil strain from the 1811 1812 new madrid earthquakes observations of postseismic deformation generally suggest that the effects of postseismic viscoelastic relaxation may persist for many decades after an earthquake in particular strain effects from the three great earthquakes that occurred in the new madrid seismic zone in 1811 1812 may influence present day measurements of ground deformation in this active seismic region of the central united states forward calculations using an earth rheology that may be appropriate for a continental intraplate region and a simple fault model for the 1811 1812 sequence suggest that postseismic relaxation may be an important factor in driving the unexpectedly high rate of shear deformation recently observed in the southern new madrid seismic zone

slip along the sultanhani fault in central anatolia from deformed pleistocene shorelines of palaeo lake konya and implications for seismic hazards in low strain regions

northeast oriented transpression structure in the northern new madrid seismic zone extension of a shear zone across the reelfoot fault stepover arm high resolution seismic reflection profiles recently acquired 12 km northeast of the new madrid seismic zone s reelfoot thrust and along the central axis of the reelfoot rift imaged steeply dipping n30 e striking faults that have uplifted and arched post paleozoic sediments in a manner consistent with a dextral strike slip component of displacement the subparallel fault strands have been traced 1 4 km between reflection profiles in order to evaluate the structure s potential regional scale the strike was projected northeast 22 km to its intersection with a nearby industry profile at the intersection this lower resolution profile exhibits a discrete 0 75 km wide structure with style and offset similar to the high resolution lines the high resolution images indicate the deformation extends above paleozoic bedrock affecting the late cretaceous and eocene mississippi embayment sediments as well as the base of the quaternary the paleozoic and cretaceous horizons show as much as 75 and 50 m of relief respectively with the middle eocene and basal quaternary disrupted 25 and 15 m respectively geologic and geophysical logs from a borehole adjacent to the seismic lines constrain the depth velocity and stratigraphic interpretations we interpret the faults as a minimum 34 km northeast extension of the axial fault zone from a throughgoing intersection with the left stepover reelfoot thrust

brittle tectonics and pore fluid conditions in the evolution of the great boundary fault around chittaurgarh northwestern india abstract this paper aims at reconstructing paleostress history and deciphering the pore fluid pressure conditions during the reactivation of a regional scale fault paleostress analyses of the mesoscopic structures suggest that three successive events of reactivation on the great boundary fault occurred in thrust type strike slip type and thrust type tectonic settings respectively whereas the pore fluid pressure was supralithostatic during the first and third events of reactivation it was sublithostatic during the second event each event of reactivation induced a fluid pressure gradient which resulted in the focused and enhanced flow of syntectonic fluids within the high permeability locales primarily fractures and faults fluid inclusion study on strike slip veins reveals that the syntectonic fluids were highly dense na ca cl brines of formational water origin stratigraphic evidence in favour of a 2 km thick column of overburden above kaimur sandstone beds implies that the strike slip faulting occurred at 160 202 c temperature and 53 mpa pressure variation in homogenization temperature reflects fluctuation in pore fluid pressure during entrapment of syntectonic fluids and points to seismic pumping as a possible mechanism of fluid flow during faulting high paleogeothermal gradient obtained by fluid inclusion data is ascribed to the high heat flow due to crustal stretching during the proterozoic rifting the basal and intermittent volcanism in the basin and occurrence of berach granite as the basement

interannual observations and quantification of summertime h2o ice deposition on the martian co2 ice south polar cap abstract the spectral signature of water ice was observed on martian south polar cap in 2004 by the observatoire pour l mineralogie l eau les glaces et l activite omega bibring et al 2004 three years later the omega instrument was used to discover water ice deposited during southern summer on the polar cap langevin et al 2007 however temporal and spatial variations of these water ice signatures have remained unexplored and the origins of these water deposits remains an important scientific question to investigate this question we have used observations from the compact reconnaissance imaging spectrometer for mars crism instrument on the mars reconnaissance orbiter mro spacecraft of the southern cap during austral summer over four martian years to search for variations in the amount of water ice we report below that for each year we have observed the cap the magnitude of the h2o ice signature on the southern cap has risen steadily throughout summer particularly on the west end of the cap the spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap montmessin et al 2007 this increase in water ice signatures is most likely caused by deposition of atmospheric h2o ice and a set of unusual conditions makes the quantification of this transport flux using crism close to ideal we calculate a minimum apparent amount of deposition corresponding to a thin h2o ice layer of 0 2 mm with 70 porosity this amount of h2o ice deposition is 0 6 6 of the total martian atmospheric water budget we compare our minimum apparent quantification with previous estimates this deposition process may also have implications for the formation and stability of the southern co2 ice cap and therefore play a significant role in the climate budget of modern day mars

strain accumulation in the new madrid and wabash valley seismic zones from 14 years of continuous gps observation the mechanical behavior and hence earthquake potential of faults in continental interiors is an issue of critical importance for the resultant seismic hazard but no consensus has yet been reached on this controversial topic the debate has focused on the central and eastern united states in particular the new madrid seismic zone struck by four magnitude 7 or greater earthquakes in 1811 1812 and to a lesser extent the wabash valley seismic zone just to the north a key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults a quantity that remains debated here we address this issue with an analysis of up to 14 6 years of continuous gps data from a network of 200 sites in the central united states centered on the new madrid and wabash valley seismic zones we find that the high quality sites in these regions show motions that are consistently within the 95 confidence limit of zero deformation these results place an upper bound on strain accrual on faults of 0 2 mm yr and 0 6 mm yr in the new madrid and wabash valley seismic zones respectively for the new madrid region where a paleoseismic record is available for the past 5000 years we argue that strain accrual if any does not permit the 500 900 year repeat time of paleo earthquakes observed in the upper mississippi embayment these results together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicate that either tectonic loading rates or fault properties vary with time in the new madrid seismic zone and possibly plate wide

slow deformation and lower seismic hazard at the new madrid seismic zone global positioning system gps measurements across the new madrid seismic zone nmsz in the central united states show little if any motion these data are consistent with platewide continuous gps data away from the nmsz which show no motion within uncertainties both these data and the frequency magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8 their recurrence interval should well exceed 2500 years longer than has been assumed alternatively the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed hence the hazard posed by great earthquakes in the nmsz appears to be overestimated

observations of the south seasonal cap of mars during recession in 2004 2006 by the omega visible near infrared imaging spectrometer on board mars express 1 the omega visible near infrared imaging spectrometer on board mars express has observed the southern seasonal cap in late 2004 and 2005 and then in the summer of 2006 these observations extended from the period of maximum extension close to the southern winter solstice to the end of the recession at ls 325 the spectral range and spectral resolution of omega make it possible to monitor the extent and effective grain size of co2 ice and h2o ice on the ground the level of contamination of co2 ice and h2o ice by dust and the column density of m sized ice grains in the atmosphere the co2 seasonal cap is very clean and clear in early southern winter contamination by h2o ice spreads eastward from the hellas basin until the southern spring equinox during southern spring and summer there is a very complex evolution in terms of effective grain size of co2 ice and contamination by dust or h2o ice h2o ice does not play a significant role close to the southern summer solstice contamination of co2 ice by h2o ice is only observed close to the end of the recession as well as the few h2o ice patches already reported by bibring et al 2004a these observations have been compared to the results of a general circulation model with good qualitative agreement on the distribution of h2o ice on the surface and in the atmosphere resolving the remaining discrepancies will improve our understanding of the water cycle on mars

mars south polar spring and summer behavior observed by tes seasonal cap evolution controlled by frost grain size thermal emission spectrometer tes observations of the recession phase of mars south polar cap are used to quantitatively map this recession in both thermal and visual appearance geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior for most of the cap while temperatures remain near the co2 frost point albedos slowly increase with the seasonal rise of the sun then drop rapidly as frost patches disappear over a period of 20 days a cryptic region remains dark and mottled throughout its cold period tes observations are compared with first order theoretical spectra of solid co2 frost with admixtures of dust and h2o the tes spectra indicate that the cryptic region has much larger grained solid co2 than the rest of the cap and that the solid co2 here may be in the form of a slab the mountains of mitchel remain cold and bright well after other areas at comparable latitude apparently as a result of unusually small size of the co2 frost grains we found little evidence for a significant presence of h2o although co2 grain size may be the major difference between these regions incorporated dust is also required to match the observations a self cleaning process carries away the smaller dust grains comparisons with viking observations indicate little difference in the seasonal cycle 12 martian years later the observed radiation balance indicates co2 sublimation budgets of up to 1250 kg m 2 regional atmospheric dust is common localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm

fluid composition and thermal regime during zn pb mineralization in the lower windsor group nova scotia canada the zn pb ba cu ag f deposits hosted by lower windsor group early carboniferous carbonates in nova scotia are located along the southern margin of the maritimes basin various geochemical studies indicate that the deposits were formed by fluids expelled from the basin but it remains unclear whether the ore forming fluids for different deposits were derived from a common source region in the central part of the basin as proposed previously or from separate source regions it is also unknown how the ore fluids were conveyed from the source regions to the sites of mineralization and whether or not the mineralizing systems of different deposits were hydrologically related this paper addresses these problems through a compilation of regional fluid composition and temperature data and thermal comparisons between the ore forming fluids and their host rocks the compositions and temperatures of the fluids were evaluated from fluid inclusion data whereas host rock temperatures were estimated from vitrinite reflectance measurements the ore forming fluids are characterized by 1 variable but generally high salinities mainly between 15 and 30 wt nacl equiv 2 variable but generally detectable amounts of bivalent cations mainly ca super 2 3 significant concentrations of hydrocarbon species and 4 high temperatures mainly between 150 degrees and 250 degrees c nacl nacl cacl 2 wt ratios in fluid inclusions show a broad district scale variation mainly 0 4 for the gays river and walton deposits in mainland nova scotia ch 4 higher hydrocarbons ratios of the gas components are greater for the gays river deposit 3 8 9 7 than the jubilee deposit 0 7 1 3 fluid inclusion homogenization temperatures do not show a negative correlation with the distance between the deposits and the central part of the maritimes basin as might be expected if the fluids for different deposits were derived from the same source region the background temperatures prior to mineralization were estimated from mean vitrinite reflectance r o in host rocks which were relatively far from the deposit and were probably least affected by the mineralizing events and from homogenization temperatures of fluid inclusions in preore minerals these temperatures are in the range of 70 degrees to 155 degrees c which are significantly lower than those of the ore forming fluids the paleogeothermal gradients estimated from the background temperatures and burial depths are ca 65 degrees c km vitrinite reflectance values in host rocks adjacent to the deposits indicate that these rocks were heated by the mineralizing fluids to variable degrees but thermal equilibrium between the fluids and rocks was not attained in most eases this thermal relationship suggests focused and short lived rather than pervasive and long lived fluid flow the regional variation of fluid composition and thermal patterns supports a model in which the ore forming fluids of individual deposits were derived from separate sources fluid flow was focused along confined conduits and individual mineralizing systems were unconnected hydrologically under paleogeothermal gradients of ca 65 degrees c km fluids with temperatures of ca 250 degrees c could have been generated in sub basins proximal to the deposits sudden release of overpressured fluids from the basal part of the proximal sub basins characterized by high flow rate and short duration is proposed as the mechanism of ore forming fluid flow

spatiotemporal complexity of continental intraplate seismicity insights from geodynamic modeling and implications for seismic hazard estimation continental intraplate seismicity seems often episodic clustered and mi grating the observed seismicity shows both spatial clustering in seismic zones and scattering across large plate interiors temporal clustering followed by long periods of quiescence and migration of seismicity from one seismic zone to another here we explore the complex spatiotemporal patterns of intraplate seismicity using a 3d visco elasto plastic finite element model the model simulates tectonic loading crustal failure in earthquakes and coseismic and postseismic stress evolution for a later ally homogeneous lithosphere with randomly prespecified perturbations of crustal strength the model predicts various spatiotemporal patterns of seismicity at different timescales spatial clustering in narrow belts and scattering across large regions over hundreds of years connected seismic belts over thousands of years and widely scat tered seismicity over tens of thousands of years the orientation of seismic belts coincides with the optimal failure directions associated with the assumed tectonic loading stress triggering and migration cause spatiotemporal clustering of earth quakes when weak zones are included in the model the predicted seismicity initiates within the weak zones but then extends far beyond them if a fault zone is weakened following a large earthquake repeated large earthquakes can occur on the same fault zone even in the absence of strong tectonic loading these complex spatiotemporal patterns of intraplate seismicity predicted in this simple model suggest that assessment of earthquake hazard based on the limited historic record may be biased toward over estimating the hazard in regions of recent large earthquakes and underestimating the hazard where seismicity has been low during the historic record

compact reconnaissance imaging spectrometer for mars crism south polar mapping first mars year of observations 1 we report on mapping of the south polar region of mars using data from the compact reconnaissance imaging spectrometer for mars crism instrument our observations have led to the following discoveries 1 water ice is present in the form of pole circling clouds originating from the circum hellas region beginning prior to ls 162 and diminishing markedly at ls 200 204 2 it has previously been inferred by thermal infrared observations by titus et al 2003 and co2 h2o mixture spectral models by langevin et al 2007 that surface water ice was present in the cryptic region in the final stages of sublimation the high resolution of crism has revealed regions where only water ice is present not a co2 h2o ice mixture this water ice disappears completely by ls 252 and may be the source of water vapor observed by crism in southern latitudes between ls 240 260 by m smith et al 2009 3 we have estimated surface co2 ice grain size distributions for the south pole residual cap sprc and the seasonal co2 ice cap that covers it throughout summer spring and summer our analysis suggests that grain sizes peak at ls 191 199 with an apparent grain size of 7 1 cm by the end of the summer period our analysis demonstrates minimum apparent grain sizes of 5 1 mm predominate in the sprc 4 fine grained co2 ice condenses from ls 0 40 and extends symmetrically away from the geographic pole extending beyond 80 s by ls 4 10 no evidence for unusual co2 depositional processes in the cryptic region is observed up to ls 16

thermal infrared and visual observations of a water ice lag in the mars southern summer 1 we present thermal infrared and visual evidence for the existence of water ice lags in the early southern summer the observed h2o ice lags lay in and near a chasma and appears to survive between 6 8 sols past the sublimation of the co2 possible sources of the h2o that compose the lag are 1 atmospheric h2o that is incorporated into the seasonal cap during condensation 2 cold trapping of atmospheric water vapor onto the surface of the cap in the spring or 3 a combination of the 2 processes where water is released from the sublimating cap only to be transported back over the cap edge and cold trapped we refer to this later process as the houben effect which may enrich the amount of water contained in the seasonal cap at 85 s by as much as a factor of 15 this phenomenon which has already been identified for the northern retreating cap may present an important water transport mechanism in the southern hemisphere

recent rheologic processes on dark polar dunes of mars driven by interfacial water abstract in springtime on hirise images of the southern polar terrain of mars flow like or rheologic features were observed their dark color is interpreted as partly defrosted surface where the temperature is too high for co2 but low enough for h2o ice to be present there these branching streaks grow in size and can move by an average velocity of up to about 1 m day and could terminate in pond like accumulation features the phenomenon may be the result of interfacial water driven rheologic processes liquid interfacial water can in the presence of water ice exist well below the melting point of bulk water by melting in course of interfacial attractive pressure by intermolecular forces van der waals forces e g curvature of water film surfaces and e g by macroscopic weight acting upon ice this melting phenomenon can be described in terms of premelting of ice it is a challenging consequence that liquid interfacial water unavoidably must in form of nanometric layers be present in water ice containing soil in the subsurface of mars it is the aim of this paper to study possible rheologic consequences in relation to observations which seem to happen at sites of dark polar dunes on mars at present the model in this work assumes that interfacial water accumulates at the bottom of a translucent water ice layer above a dark and insolated ground this is warmed up towards the melting point of water the evolving layer of liquid interfacial water between the covering ice sheet and the heated ground is assumed to drive downward directed flow like features on slopes and it can at least partially infiltrate seep into a porous ground there in at least temporarily cooler subsurface layers the infiltrated liquid water refreezes and forms ice the related stress built up is shown to be sufficient to cause destructive erosive processes the above mentioned processes may cause change in the structure and thickness of the covering ice and or may cause the movement of dune grains all these processes may explain the observed springtime growing and downward extension of the slope streaks analyzed here

space geodetic evidence for rapid strain rates in the new madrid seismic zone of central usa a series of large earthquakes centred on the town of new madrid in the mississippi valley in the winter of 1811 12 still reverberates in the world of seismology the controversy relates to their origin over 2 000 km from the nearest plate boundary and their relevance to earthquake hazard today the population of new madrid in the early nineteenth century was tiny a similar event today would have much more serious consequences new evidence based on gps data points to the existence of rapid strain rates in the area comparable in magnitude to those across active plate boundaries and consistent with known active faults in the region in the winter of 1811 1812 near the town of new madrid in the central united states and more than 2 000 km from the nearest plate boundary three earthquakes within three months shook the entire eastern half of the country and liquefied the ground over distances far greater than any historic earthquake in north america1 2 the origin and modern significance of these earthquakes however is highly contentious3 geological evidence demonstrates that liquefaction due to strong ground shaking similar in scale to that generated by the new madrid earthquakes has occurred at least three and possibly four times in the past 2 000 years refs 4 6 consistent with recurrence statistics derived from regional seismicity7 here we show direct evidence for rapid strain rates in the area determined from a continuously operated global positioning system gps network rates of strain are of the order of 10 7 per year comparable in magnitude to those across active plate boundaries and are consistent with known active faults within the region these results have significant implications for the definition of seismic hazard and for processes that drive intraplate seismicity

reconciling different observations of the co2 ice mass loading of the martian north polar cap 1 the grs measurements of the peak mass loading of the north polar co2 ice cap on mars are about 60 lower than those calculated from mgs tes radiation data and those inferred from the mola cap thicknesses however the grs data provide the most accurate measurement of the mass loading we show that the tes and mola data can be reconciled with the grs data if 1 subsurface heat conduction and atmospheric heat transport are included in the tes mass budget calculations and 2 the density of the polar deposits is 600 kg m 3 the latter is much less than that expected for slab ice 1600 kg m 3 and suggests that processes unique to the north polar region are responsible for the low cap density

geodetic constraints on glacial isostatic adjustment in europe 1 direct measurements of surface deformation due to glacial isostatic adjustment gia in europe have been so far mostly limited to the present day uplift area here we use permanent gps networks results to investigate the significance of gia effects in europe south of fennoscandia we show that uplift in fennoscandia is surrounded by subsidence reaching as far south as the alps with a maximum vertical rate of 1 5 mm yr between 50 5 53 n horizontal velocity gradients show shortening between fennoscandia and north central europe with strain rates of 10 9 yr 1 and principal compressional strain axis pointing to the gulf of bothnia in a radial pattern we find a very good quantitative agreement with the 3d surface displacement predicted by milne et al 2001 although the increase of misfit in far field of fennoscandia suggests that geodetic data outside of the uplift area may bring additional constraints to the rheological parameters used in gia models

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

formation of a giant zn pb deposit from hot brines injecting into a shallow oil gas reservoir in sandstones jinding southwestern china the association between mineralization and hydrocarbons in sedimentary basins is widely recognized but the nature and significance of their relationships are not fully understood this paper provides an example of metalliferous brines injecting into a palaeo oil gas reservoir to form a world class zn pb deposit jinding china petrographic and microthermometric studies of oil inclusions and pvt simulations suggest that oil and gas were charged in a shallow 1300 m environment before mineralization this environment favoured bacterial sulfate reduction bsr which produced large amounts of h2s that accumulated in the gas cap forceful injection of hot brines penetrated the oil zone to reach the h2s rich gas cap and precipitated sulfide ores individual fluid injection events were short lived and the reservoir was only partly and briefly heated to beyond the bacterial survival temperature episodic injection of metalliferous brines and sustained supply of h2s through bsr resulted in the formation of a large zn pb deposit this article is protected by copyright all rights reserved

the polar deposits of mars the tantalizing prospect of a readable record of martian climatic variations has driven decades of work toward deciphering the stratigraphy of the martian polar layered deposits and understanding the role of the residual ice caps that cover them spacecraft over the past decade have provided a massive infusion of new data into mars science polar science has benefited immensely due to the near polar orbits of most of the orbiting missions and the successful landing of the phoenix spacecraft in the northern high latitudes topographic thermal radar hyperspectral and high resolution imaging data are among the datasets that have allowed characterization of the stratigraphy of the polar layered deposits in unprecedented detail additionally change within the residual ice caps has been monitored with spacecraft instruments for several years these new data have provided a golden opportunity to understand the interplay between the martian orbit climate and polar ice

time variable deformation in the new madrid seismic zone new geodetic measurements show that the new madrid is currently deforming too slowly if at all to account for large earthquakes in the region over the past 5000 years this result together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicates that either tectonic loading rates or fault properties vary over a few thousand years

cation study of fluid inclusion decrepitates in the jubilee and gays river canada zn pb deposits characterization of ore forming brines an sem eds instrument sensitive to c and o is used to measure cation ratios in individual fluid inclusion decrepitates of main paragenetic phases from two nova scotian mississippi valley type deposits the technique confirms that the analyses obtained for the carbonate hosts are not contaminated by substrate and permits measurements of small amounts of decrepitates the technique has been used to investigate fluid compositions in inclusions of presulfide stage dolomite and calcite sulfide stage sphalerite and calcites and postsulfide calcite at the gays river and jubilee zn pb deposits in nova scotia the results indicate that na and ca are the two major cations minor amounts of k and mg are also detected nacl and cacl 2 ranges for decrepitates from the two deposits are as broad as for modem mixed brines and thereby suggest that solution mixing partly controlled the paleobrine compositions when compared to other mississippi valley type deposits the gays river and jubilee deposits are similar in nacl cacl 2 kcl composition to a group of mississippi valley type districts including deposits from the ozark region that are associated with large volume clastic sequences or paleoaquifers higher proportions of kcl at gays river and higher proportions of cacl 2 at jubilee indicate that the mineralizing brines interacted with horton group clastic aquifers of different mineral compositions the brines in the two areas might have originated from evaporation of seawater but they were later modified by interaction with clastic rocks of different compositions

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

lithospheric velocity structure of the new madrid seismic zone a joint teleseismic and local p tomographic study 1 the enigmatic seismicity in the new madrid seismic zone nmsz has been attributed to some abnormal lithospheric structure including the presence of dense mafic intrusions and a low viscosity lower crust however the area s detailed lithospheric structure remains unclear here we invert 2 056 teleseismic p and 12 226 local p first arrival times from a recent nine year dataset to infer the lithospheric velocity structure beneath the nmsz our results show that the seismically active zone is associated with a local ne sw trending low velocity anomaly in the lower crust and upper mantle instead of high velocity intrusive bodies proposed in previous studies the low velocity anomaly is on the edge of a high velocity lithospheric block consistent with the notion of stress concentration near rheological boundaries this lithospheric weak zone may shift stress to the upper crust when loaded thus leading to repeated shallow earthquakes

seismology tectonic strain in plate interiors arising from r smalley jr m a ellis j paul r b van arsdale nature 435 1088 1090 2005 r smalley et al reply it is not fully understood how or why the inner areas of tectonic plates deform leading to large although infrequent earthquakes smalley et al 1 offer a potential breakthrough by suggesting that surface deformation in the central united states accumulates at rates comparable to those across plate boundaries however we find no statistically significant deformation in three independent analyses of the data set used by smalley et al and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

structural inheritance control on intraplate present day deformation gps strain rate variations in the saint lawrence valley eastern canada structural inheritance is one of the key factors commonly proposed to control the localization of strain and seismicity in continental intraplate regions primarily on the basis of a first order spatial correlation between seismicity and inherited tectonic structures in this paper we present new gps global positioning system velocity and strain rate analyses that provide strong constraints on the magnitude and style of present day strain localization associated with the inherited tectonic structures of the saint lawrence valley eastern canada we analyze 143 continuous and campaign gps stations to calculate velocity and strain rate patterns with specific emphases on the combination of continuous and campaign velocity uncertainties and on the definition of robustness categories for the strain rate estimations within the structural inheritance area strain rates are on average 2 11 times higher than surrounding regions and display strong lateral variations of the style of deformation these gps velocity and strain rate fields primarily reflect ongoing glacial isostatic adjustment gia their comparison with gia model predictions allows us to quantify the impact of the structural inheritance and the associated lithosphere rheology weakening outside of the major tectonic inheritance area gps and gia model strain rates agree to first order both in style and magnitude in contrast the saint lawrence valley displays strong strain amplification with gps strain rates 6 28 times higher than model predicted gia strain rates our results provide the first quantitative constraints on the impact of lithospheric scale structural inheritance on strain localization in intraplate domains

distribution of the ices exposed near the south pole of mars using thermal emission imaging system themis temperature measurements 1 understanding the present and past water cycle on mars requires an accurate knowledge of the distribution and amount of h2o available near the surface in this article we present a map of the distribution of the surface material exposed between 87 s and 70 s in the summer e g co2 and h2o ices dust based on temperature measurements made by thermal emission imaging system themis our compositional map 100 m per pixel is in good agreement with spectral mapping returned by observatoire pour la mineralogie l eau la glace et l activite omega and compact reconnaissance imaging spectrometer for mars crism exposed water ice covers a total surface area of approximately 40 000 km2 a large fraction of the water ice is exposed at the periphery of the co2 cap an approximately 25 000 km2 large patch centered at 83 5 s and 345 e is discovered and represents the largest exposure of water ice in the southern hemisphere it is not located on the south polar layered deposits but on the surrounding mantled terrains themis vis moc and hirise images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust polygonal patterns are observed on the water ice but not exclusively there is a strong correlation between the surface albedo the composition of the exposed material and the timing of the initial seasonal co2 frost deposition and final removal these exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere the spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal co2 frost indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere as water ice is not stable it may indicate the past location of part of the co2 perennial cap that has been eroded

crustal stress and strain patterns in the indian plate interior implications for the deformation behaviour of a stable continent and its seismicity terra nova 23 407 415 2011 abstract the present analyses indicate that the maximum principal stress axis of the indian plate interior does not coincide with the plate motion vector the strain rate curves for the indian plate indicate interference of two different orders of deformation the magnitudes of the first order maximum strain rates are lower than local extreme strain rates of the second order deformation it has been shown herein that the oblique motion of the indian plate with respect to a state of dominant strike slip deformation in the indian plate interior is partitioned into a principal deformation zone synthetic shear and antithetic shear the strain rates along these regional shear zones show complex association of second order high shortening rate coinciding with high extension rate the earthquakes of the indian plate interior are interpreted to be results of periodic accumulation of stress strain due to shortening and release of strain along the same directions during the extension

quaternary deformation and fault structure in the northern mississippi embayment as imaged by near surface seismic reflection data seismicity in the new madrid seismic zone nmsz in the central united states constrains the location of present deformation at depth along four main distinct arms while the surface expression of the ongoing deformation is still unclear to better constrain the surface deformation in the nmsz we integrate existing seismic reflection data with a new 300 km long high resolution seismic reflection profile acquired along the mississippi river from cape girardeau mo to caruthersville mo based on the data we interpret the reelfoot thrust and the new markham fault as upward splays of a blind master fault defined by the seismicity and extending at depth farther north to the south two faults the axial fault and the cottonwood grove fault are imaged above the southern arm of the nmsz both fault display deformation of the paleozoic through the tertiary sediments and a relief of 20 25 m at the base of the quaternary alluvium which we interpret as the result of strike slip motion along a complex fault plane geometry we propose two alternative interpretations for the relationship between the shallow faults and the seismicity in this area 1 the faults merge at depth and are presently both active and 2 the faults are distinct at depth and were active during the quaternary and only the axial fault is presently deforming geological structures mapped at the surface as part of this study show that quaternary deformation is accommodated along a fault network that is more complex than the simple four arm system illuminated by the seismicity a behavior predicted by analog and computer models

graviquakes in italy abstract we discuss the mechanics of crustal normal fault related earthquakes and show that they represent dissipation of gravitational potential energy graviquakes and their magnitude increases with the involved volume delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall and the fault dip the magnitude increases with the deepening of the brittle ductile transition bdt which in turn enlarges the involved volume the fault dip seems rather controlled by the static friction of the involved crustal layers we apply the model to the extensional area of the italian peninsula whose geodynamics is controlled by the alpine and apennines subduction zones the latter has a well developed backarc basin and a large part of the accretionary prism is affected by on going extensional tectonics which is responsible for most of peninsular italy seismicity analyzing the seismic record of the apennines the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth we compile a map of the brittle ductile transition depth and assuming a fixed 45 or 60 fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane we compute the maximum volume of the hangingwall collapsing at the coseismic stage and estimate the maximum expected magnitude lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow moreover lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values

descent of the ancient farallon slab drives localized mantle flow below the new madrid seismic zone 1 the great earthquake sequence that occurred in the central mississippi river valley during the winter of 1811 1812 is unprecedented in the historical record of seismicity within stable continental plate interiors we show using viscous flow models based on high resolution seismic tomography that the descent of the ancient farallon slab into the deep mantle beneath central north america induces a highly localized flow directly below the new madrid seismic zone nmsz this localization arises because of structural variability in the farallon slab and the low viscosity of the sub lithospheric upper mantle and it represents a heretofore unrecognized and possibly significant driving mechanism for the enigmatic intraplate seismicity

seismology tectonic strain in plate interiors reply the independent analyses of gama global positioning system gps array in mid america data by calais 1 demonstrate the difficulties in determining patterns of rational deformation within otherwise rigid plates we are a long way from incorporating this type of information into seismic hazard analysis and we agree that longer time spans and improved spatial coverage with geodetic quality data are required in order to gather the observations necessary to start modelling and understanding this enigmatic region

modeling the martian seasonal water cycle ever since the observations of percival lowell the annual cycle of martian water has been a fascinating topic in planetary exploration observations by the viking orbiter supplemented by earth based microwave and infrared observations have given us a reasonable picture of this cycle we are now also able to model the cycle using our mars climate model a simplified atmospheric general circulation model designed specifically for this purpose we find that a thin adsorbing layer of the martian regolith plays a fundamental role in the water cycle limiting the lower atmospheric relative humidity and preventing the formation of widespread ice deposits at low latitudes we are thus able to estimate a large scale average value of the specific soil surface area of this regolith water which evaporates from the permanent north polar ice cap during summer is returned by a process of repeated evaporation and precipitation on the retreating seasonal cap the following spring so that the global inventory of water outside the polar caps ranges within narrow limits there is a small net annual deposition of water ice at the south polar cap which is always at dry ice temperatures if ice on the residual south polar cap is exposed during the summer it rapidly sublimes generating vapor amounts similar to those observed in northern summer recovery to normal dry conditions in the southern atmosphere occurs very rapidly in the next year such an event could explain the otherwise anomalous earth based pre viking observations of a wet southern summer if southern ice deposits at lower latitudes are exposed the vapor can be transferred irreversibly through the strong hadley cell to the north polar cap we therefore speculate that the asymmetry of mars current orbit is responsible for the asymmetry of the present water distribution with extensive permanent water ice deposits located only in the colder aphelion summer northern hemisphere