region specific key seismic parameters for earthquakes in northern iran strong motion accelerograms recorded within northern iran are used to examine the propagation characteristics of shear wave including geometric spreading behavior q value j 0 and horizontal to vertical h v ratio these region specific key seismic parameters are estimated from 259 three component records of 22 earth quakes with magnitude ranging from m 4 9 to m 7 4 in northern iran the geometric spreading follows a trilinear behavior with a strong postcritical reflection from the moho the first and second hinges of the trilinear behavior are at 75 and 150 km respectively the associated q value based on the vertical component is q 87 f 1 46 j0 value for vertical and horizontal components are 0 03 and 0 05 respec tively because of lack of station specific site information the h v ratio is considered to be a rough estimation of generic site amplification the obtained region specific parameters are used to estimate the average stress drop based on three stochastic modeling approaches stochastic point source modeling suggests a brune stress drop of 125 bars whereas stochastic finite fault modeling based on static and dynamic corner frequency approaches suggests a stress drop of 68 bars

effects of soil heterogeneity on martian ground ice stability and orbital estimates of ice table depth abstract data from the mars odyssey gamma ray spectrometer grs instrument suite and results from numerical simulations of subsurface ground ice stability have been used to estimate the depth of martian ground ice geographic correlation between these estimates is remarkable the relative ice table depth distributions also agree well however grs based estimates of ice table depth are generally deeper than predictions based on ground ice stability simulations this discrepancy may be related to heterogeneities in the martian surface such as rocks dust and albedo variations we develop a multi dimensional numerical model of ground ice stability in a heterogeneous martian subsurface and use it to place the first quantitative constraints on the response of the ice table to meter scale heterogeneities we find that heterogeneities produce significant undulations topography in the ice table at horizontal length scales of a few meters decimeter scale rocks create localized areas of deep ice producing a vertical depression of 10 60 cm in the ice table over a horizontal range of 1 2 rock radii decimeter scale dust lenses produce locally shallow ice however the magnitude of the vertical deflection of the ice table is small 1 4 cm the effects of decimeter scale albedo variations on the ice table are nearly negligible although albedo very weakly enhances the effects of dark rocks and bright dust on the ice table additionally we investigate the role played by rocks in estimates of ice table depth based on orbital data surface rocks can account for more than half of the discrepancy between ice table depths inferred from grs data and those predicted by theoretical ice stability simulations that utilize thermophysical observations our results have considerable relevance to the up coming mars scout mission phoenix because they indicate that the uncertainty in the ice table depth of a given region is greater than differences between current depth estimates likewise small scale depth variability due to heterogeneities at the eventual landing site is potentially greater than differences between current depth estimates

hydrogen content of sand dunes within olympia undae neutron currents measured using the mars odyssey neutron spectrometer seasonally varying temperatures measured using the thermal emission spectrometer and visible images measured using the high resolution imaging science experiment hirise are studied to determine the water content and stratigraphy of olympia undae both the neutron and thermal infrared data are best represented by a two layered model having a water ice equivalent hydrogen content of 30 5 in a lower semi infinite layer buried beneath a relatively desiccated upper layer that is 9 6g cm 2 thick about 6 cm depth at a density of 1 5 g cm 3 a model that is consistent with all three data sets is that the dunes contain a top layer that is relatively mobile which overlays a niveo aeolian lower layer the geomorphology shown by the hirise images suggests that the bottom layer may be cemented in place and therefore relatively immobile

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

boulder movement at high northern latitudes of mars 1 we examine a narrow latitudinal band 60 n 70 n on mars to place constraints on the seasonally averaged velocity q of boulder movements over patterned ground these latitudes comprise a region of the northern lowlands where patterned ground covers nearly every surface here boulders meters in diameter are consistently found to be concentrated at or near the cracks that define the polygonal networks indicating a mobilization process because impact craters are the source for many boulders we can use craters and their degradation to estimate the time scales for boulder movement we study and catalog 1018 degraded impact craters 100 m d 1 km in 55 high resolution imaging science experiment hirise images we find that crater degradation occurs on a time scale 1 ma which is too recent for melting related mechanisms in a past warmer epoch clustering of boulders occurs at a time scale of a few ma or shorter which means that boulders on 5 20 m diameter polygons move at seasonal velocities q 1 10 m yr or faster

sea99 a revised ground motion prediction relation for use in extensional tectonic regimes we present sea99 a revised predictive relation for geometric mean horizontal peak ground acceleration and 5 damped pseudovelocity response spec trum appropriate for estimating earthquake ground motions in extensional tectonic regimes which we demonstrate to have lower ground motions than other tectonic regimes sea99 replaces sea96 a relation originally derived by spudich et al 1996 1997 the data set used to develop sea99 is larger than that for sea96 and minor errors in the sea96 data set have been corrected in addition a one step regression method described by joyner and boore 1993 1994 was used rather than the two step method of joyner and boore 1981 sea99 has motions that are as much as 20 higher than those of sea96 at short distances 5 30 km and sea99 s motions are about 20 lower than sea96 at longer periods 1 0 2 0 sec and larger distance 40 100 km sea99 dispersions are significantly less than those of sea96 sea99 rock motions are on the average 20 lower than motions predicted by boore et al 1994 except for short distances at periods around 1 0 sec where sea99 motions exceed those predicted by boore et al 1994 by as much as 10 com parison of ground motions from normal faulting and strike slip events in our data set indicates that normal faulting horizontal ground motions are not significantly different from extensional regime strike slip ground motions

study of weak and strong ground motion including nonlinearity from the northridge california earthquake sequence abstract this article presents a new method to estimate s wave site response relative to a regional layered crustal model the method is useful for site specific strong motion prediction because the estimated site response functions are referenced to an idealized regional layered model for which we know the ground response exactly we applied this method to the northridge earthquake sequence we determined the site amplifications from aftershocks with magnitudes 2 6 to 4 3 at 21 stations that were colocated with strong motion stations these site response functions were then used to modify synthetic seismogram calculated for the northridge mainshock in the same regional layered crustal model and thus obtain site specific ground motion estimates these site specific synthetic seismograms have higher correlation to observations in comparison to the synthetic seismograms without weak motion site correction they have similar amplitude and frequency content to the observations especially at sites with recorded peak ground accelerations below 0 3 g at sites with larger ground motions however this approach overestimates the strong motion the differences are made clear when we estimate site response functions from the strong motion records and compare them with those from weak motion records we express the differences as the average ratio of the weak to strong motion site response aws ratio when the ground motion is low the aws ratio is near unity indicating that the weak and strong motion site responses agree with each other within the uncertainty however the aws ratio increases as the ground motion amplitude increses the difference in weak and strong motion site responses becomes significant at stations where peak acceleration was above 0 3 g peak velocity was above 20 cm sec or peak strain was above 0 06 during the mainshock this result demonstrates directly from the ground motion observations the relationship between nonlinear site response and peak ground motion parameters the nonlinearity is present on soft rock sites as well as on sediment sites

the 1 october 1995 dinar earthquake sw turkey the dinar earthquake ms 6 1 usgs pde of 1 october 1995 occurred on the nwse trending dinar fault the earthquake is associated with a 10 km long surface rupture with predominantly normal faulting the mainshock was preceded by a series of foreshocks that started 6 days before the mainshock and included two md 4 5 events the mainshock source mechanism derived from the inversion of broad band p waves revealed that two sub events occurred on a nw se trending normal fault with a small strike slip component according to the source model estimated in this study the first rupture started at a depth of about 8 km and reached to a depth of about 12 km propagating north west the total seismic moment found from the inversion of p waveforms is 2 0 times 10 18 nm the seismic moment of the second sub event was about four times larger than the first one field observations gps measurements and slip vector obtained from the inversion of broad band p waveforms suggest that the nw se trending dinar fault is due to the internal deformation of sw anatolia moving south westwards

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

size frequency distributions of rocks on the northern plains of mars with special reference to phoenix landing surfaces 1 the size frequency distributions of rocks 1 5 m diameter fully resolvable in high resolution imaging science experiment hirise images of the northern plains follow exponential models developed from lander measurements of smaller rocks and are continuous with rock distributions measured at the landing sites dark pixels at the resolution limit of mars orbiter camera thought to be boulders are shown to be mostly dark shadows of clustered smaller rocks in hirise images an automated rock detector algorithm that fits ellipses to shadows and cylinders to the rocks accurately measured within 1 2 pixels rock diameter and height by comparison to spacecraft of known size of 10 million rocks over 1500 km2 of the northern plains rock distributions in these counts parallel models for cumulative fractional area covered by 30 90 rocks in dense rock fields around craters 10 30 rock coverage in less dense rock fields and 0 10 rock coverage in background terrain away from craters above 1 5 m diameter hirise resolves the same population of rocks seen in lander images and thus size frequency distributions can be extrapolated along model curves to estimate the number of rocks at smaller diameters extrapolating sparse rock distributions in the phoenix landing ellipse indicate 1 chance of encountering a potentially hazardous rock during landing or that could impede the opening of the solar arrays extrapolations further suggest rocks large enough to depress the ground ice table and small enough to be picked up or pushed by the robotic arm should be present within reach for study after landing

martian high latitude permafrost depth and surface cover thermal inertia distributions 1 martian high latitudes have thermal properties consistent with an extensive high thermal inertia permafrost layer near the surface surface cover thermal inertias and permafrost depths at martian high latitudes 50 80 n s are derived from thermal emission spectrometer tes data and compared with previously published water ice depths determined from the mars odyssey neutron spectrometer mons the depth to the permafrost layer is correlated with surface cover thermal inertia albedo and latitude in general agreement with predicted trends of water ice stability comparison of permafrost depths with water ice rich layer depths derived from mons data displays good qualitative agreement although a divergence is present at greater burial depths this disparity may be due to the presence of hydrated minerals at shallow depths or a lower than expected permafrost thermal inertia corresponding with low water ice concentrations at greater depths surface cover thermal inertias are greater in the northern high latitudes than in the south and differences between these and previous results will have significant effects on the predicted depth of martian water ice stability several regions in the northern hemisphere display high surface cover thermal inertia associated with possible receding water ice deposits that are shallow enough to influence diurnal surface temperatures significant lateral and vertical heterogeneity in water ice distributions are present and the martian regolith is likely more complicated than can be described by simple two layered models and a single mode of water ice emplacement

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

ice sublimation as a geomorphic process a planetary perspective abstract sublimation plays a role in the shaping of landforms of planetary surfaces where ice is present as frost as polar caps or in the subsurface this review is focused primarily on the geomorphologic consequences of sublimation a summary of the suite of landforms that have been observed on the surface of various planetary bodies and whose formation is attributed to sublimation is presented this includes the sublimation of a range of different ices that are found on planetary bodies water ice carbonic ice etc at least four groups of landforms are distinguishable independent of the planetary body i residual lags that are depleted in ice which form after sublimation loss such residual lags isolate deeper ice from sublimation and thus can have an important impact on planetary volatile cycles ii landforms due to differential sublimation resulting from enhanced sublimation in low albedo warmer areas of the planet and preservation of ice in the high albedo regions iii landforms due to differential sublimation initiated by fractures or ground heterogeneities for example sublimation enhanced polygonal cracks iv pitted terrains that occur in a relatively homogeneous ice bearing subsurface or as an effect of local ice enrichment or segregation in the ground

seasonal h2o and co2 ice cycles at the mars phoenix landing site 1 prelanding crism and hirise observations 1 the condensation evolution and sublimation of seasonal water and carbon dioxide ices were characterized at the mars phoenix landing site from martian northern midsummer to midspring ls 142 ls 60 for the year prior to the phoenix landing on 25 may 2008 ice relative abundances and grain sizes were estimated using data from the compact reconnaissance imaging spectrometer for mars and high resolution imaging science experiment aboard mars reconnaissance orbiter and a nonlinear mixing model water ice first appeared at the phoenix landing site during the afternoon in late summer ls 167 as an optically thin layer on top of soil co2 ice appeared after the fall equinox by late winter ls 344 the site was covered by relatively pure co2 ice 30 cm thick with a small amount of 100 m diameter water ice and soil as spring progressed co2 ice grain sizes gradually decreased a change interpreted to result from granulation during sublimation losses the combined effect of co2 sublimation and decreasing h2o ice grain sizes allowed h2o ice to dominate spectra during the spring and significantly brightened the surface co2 ice disappeared by early spring ls 34 and h2o ice by midspring ls 59 spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values

high resolution subsurface water ice distributions on mars theoretical models predict that the depth at which water ice is stable in the subsurface of mars will vary due to local surface features such as rocks and slopes and the thermal inertia of the ground above the water so far measurements have been limited to overviews of the several hundred kilometre footprint covered by the ray spectrometer on board the mars odyssey spacecraft but joshua bandfield has now used the seasonal temperature response of the martian surface from odyssey s themis package to map water ice distribution at the sub kilometre scale the observations reveal significant regional and local water ice depth variability at potential landing sites for the mars phoenix mission due for launch later this year the phoenix lander s robotic arm will be able to dig up to half a metre or so into the soil to search for water ice and these results suggest that it may encounter considerable variation in the depth to the ice layer the seasonal temperature response of the martian surface is used to map local surface heterogeneities such as rocks slopes and thermal inertia of ground cover at subkilometre scale these observations show significant regional and local water ice depth variability and indicate that the depth to the water ice table is highly variable in the potential phoenix spacecraft landing ellipses theoretical models indicate that water ice is stable in the shallow subsurface depths of 1 2 m of mars at high latitudes1 2 3 4 5 6 7 these models have been mainly supported by the observed presence of large concentrations of hydrogen detected by the gamma ray spectrometer suite of instruments on the mars odyssey spacecraft8 9 10 the models and measurements are consistent with a water ice table that steadily increases in depth with decreasing latitude more detailed modelling has predicted that the depth at which water ice is stable can be highly variable owing to local surface heterogeneities such as rocks and slopes and the thermal inertia of the ground cover11 12 13 measurements have however been limited to the footprint several hundred kilometres of the gamma ray spectrometer suite preventing the observations from documenting more detailed water ice distributions here i show that by observing the seasonal temperature response of the martian surface with the thermal emission imaging system on the mars odyssey spacecraft14 it is possible to observe such heterogeneities at subkilometre scale these observations show significant regional and local water ice depth variability and in some cases support distributions in the subsurface predicted by atmospheric exchange and vapour diffusion models the presence of water ice where it follows the depth of stability under current climatic conditions implies an active martian water cycle that responds to orbit driven climate cycles15 16 17 several regions also have apparent deviations from the theoretical stability level indicating that additional factors influence the ice table depth the high resolution measurements show that the depth to the water ice table is highly variable within the potential phoenix spacecraft landing ellipses and is likely to be variable at scales that may be sampled by the spacecraft

in situ analysis of ice table depth variations in the vicinity of small rocks at the phoenix landing site 1 prior to the phoenix mission ice stability simulations predicted that surface rocks at the landing site would produce depressions in the ice table the boundary between dry and ice cemented soil if ground ice at the site were in diffusive equilibrium with atmospheric water vapor we use stereo images and digital elevation models to investigate variations in the depth of the ice table near two decimeter scale rocks at the phoenix landing site and compare the observed depth variations to ice stability simulations we find that ice table depth variations observed near rocks at the landing site are consistent with our theoretical predictions based on our results we conclude that 1 water transport in the near surface regolith occurs primarily via vapor diffusion 2 environmental conditions in which water transport is dominated by diffusion have been persistent at the landing site for 100s to 1000s of years or longer that is ground ice is in diffusive equilibrium with atmospheric water vapor and 3 in diffusive equilibrium thermal stability dictates the depth of the ice table on horizontal length scales as small as centimeters

ice table depth variability near small rocks at the phoenix landing site mars a pre landing assessment abstract we combine thermal simulations of ground ice stability near small rocks with extrapolations of the abundance of rocks at the phoenix landing site based on hirise rock counts to estimate the degree of ice table depth variability within the 3 8 m 2 workspace that can be excavated during the mission detailed predictions of this kind are important both to test current ground ice theory and to optimize soil investigations after landing we find that phoenix will very likely have access to at least one rock in the diameter range 5 cm to 1 m our simulations which assume the ice to be in diffusive equilibrium with atmospheric water vapor indicate that all rocks in this size range are associated with an annulus of deep ice free soil ice table depth variability of 1 5 cm is very likely at the landing site due to the presence of small rocks further there are scenarios in which phoenix might exploit the presence of individual large rocks and or the arrangement of small rocks to sample soils at depths 10 cm below the average depth predicted from orbit 4 cm scale analysis to constrain uncertainties in simulation results indicates that estimates of maximum depths may be somewhat conservative and that ice table depressions associated with individual rocks could be deeper and laterally more extended than indicated by formal predictions by mm to cm

results from the mars phoenix lander robotic arm experiment 1 the mars phoenix lander was equipped with a 2 4 m robotic arm ra with an icy soil acquisition device capable of excavating trenches in soil deposits grooming hard icy soil surfaces with a scraper blade and acquiring icy soil samples using a rasp tool a camera capable of imaging the scoop interior and a thermal and electrical conductivity probe were also included on the ra a dozen trench complexes were excavated at the northern plains landing site and 31 samples including water ice bearing soils were acquired for delivery to instruments on the lander during the 152 sol mission deliveries included sprinkling material from several centimeters height to break up cloddy soils on impact with instrument portals excavations were done on the side of the humpty dumpty and the top of the wonderland polygons and in nearby troughs resistive forces encountered during backhoe operations show that soils above the 3 5 cm deep icy soil interfaces are stronger with increasing depth further soils are similar in appearance and properties to the weakly cohesive crusty and cloddy soils imaged and excavated by the viking lander 2 which also landed on the northern plains adsorbed h2o is inferred to be responsible for the variable nature and cohesive strength of the soils backhoe blade chatter marks on excavated icy soil surfaces combined with rasp motor currents are consistent with laboratory experiments using grain supported icy soil deposits as is the relatively rapid decrease in icy soil strength over time as the ice sublimated on mars

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

initiation and growth of martian ice lenses abstract water ice in the upper meters of the martian regolith is a major volatile reservoir although the geographic extent burial depth and thermal stability of this shallow ice are well understood its origin history and stratigraphy are not over the past decade a growing body of observational evidence has indicated that shallow ground ice exceeds the pore volume of its host soil over large regions of both martian hemispheres this is confounding given that 1 the physical theory that accurately predicts the location of ground ice also assumes that ice should be pore filling in the upper meter of regolith and 2 the phoenix spacecraft uncovered far more pore filling ice than excess ice at its landing site in the northern hemisphere the development of ice lenses by low temperature in situ segregation analogous to the processes that generate frost heave on earth has been hypothesized to explain shallow excess ice on mars we have developed a numerical model of ice lens initiation and growth in the martian environment and used it to test this hypothesis for the first time we carried out a large suite of numerical simulations in order to place quantitative constraints on the timing and location of ice lens initiation and on the magnitude of ice lens growth in a variety of host soils we find that ice lens initiation is a ubiquitous process in the martian high latitudes but the ultimate magnitude of lens growth or frost heave is sensitive to the properties of the host soil depending on the specific properties of martian soils in situ segregation may be a very slow process sufficient to explain the excess ice observed in the dodo goldilocks trench at the phoenix landing site but without regionally significant effects alternatively if clay sized particles or perchlorate salts are present in situ segregation may be a vigorous process that has significantly affected the stratigraphy of ground ice in the upper meter of regolith throughout the high latitudes

vesicular komatiites 3 5 ga komati formation barberton greenstone belt south africa inflation of submarine lavas and origin of spinifex zones komatiites of the 3 5 ga komati formation are ultramafic lavas 23 mgo erupted in a submarine lava plain environment newly discovered vesicular komatiites have vesicular upper crusts disrupted by synvolcanic structures that are similar to inflation related structures of modern lava flows detailed outcrop maps reveal flows with upper vesicular zones 2 15 m thick which were 1 rotated by differential inflation 2 intruded by dikes from the interior of the flow 3 extended forming a flooded graben and or 4 entirely engulfed the largest inflated structure is a tumulus with 20 m of surface relief which was covered by a compound flow unit of spinifex flow lobes the lava that inflated and rotated the upper vesicular crust did not vesiculate but crystallized as a thick spinifex zone with fist size skeletal olivine instead of representing rapidly cooled lava the spinifex zone cooled slowly beneath an insulating upper crust during inflation overpressure of the inflating lava may have inhibited vesiculation this work describes the oldest vesicular komatiites known illustrates the first field evidence for inflated structures in komatiite flows proposes a new factor in the development of spinifex zones and concludes that the inflation model is useful for understanding the evolution of komatiite submarine flow fields

spinifex and swirling olivines in a komatiite lava lake munro township canada abstract spinifex veins and veins filled with swirling tabular olivine grains intrude the upper part of a 120 m thick lava lake in munro township ontario canada these veins are 20 200 cm wide tens of metres long and are oriented roughly parallel to the upper surface of the lava lake the spinifex texture differs from that found in simple layered komatiite flows rather than increasing downwards the size of skeletal olivine grains is greatest in the centres of the veins or varies irregularly upper contacts meander and veinlets penetrate overlying rock lower contacts are transitional the other type of vein contains 50 70 of 5 mm long hopper olivine grains whose orientation varies widely to produce a swirling contorted fabric both types of vein are believed to have formed when lava from the centre of the lake flowed into fractures in the solidified crust the lava lake has a dunitic lower portion and an olivine porphyry upper portion the composition of chill samples the compositions of olivine phenocrysts and variations in major element abundances throughout the unit are used to show that the lava originally was komatiite with about 22 mgo the lava lake is overlain by mafic scorias and breccias with moderate vesicularity and welding structures suggesting eruption in shallow water

vesicles in thick komatiite lava flows kambalda western australia traditionally vesicles have been considered to be rare in komatiites however field studies at kambalda western australia and critical literature examination suggest that vesicle presence and content in komatiites are grossly underestimated at kambalda vesicles are observed in significant amounts up to 30 in internal horizons within komatiite lavas the vesicular horizons are inferred to represent bubbles frozen in place below the upper crust during multiple episodes of flow through of bubble rich lava we conclude that vesicle and crystal distribution are compatible with many komatiites being emplaced under laminar flow conditions analogous to models for basalt lava emplacement

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

the behaviour of the fronts of komatiite lavas in medial to distal settings abstract field characteristics of komatiites and observations of flow behaviour and propagation processes for subaerial basalt lavas are used to reconsider the flow behaviour of archean komatiite lavas planar conformable bases at contacts with pelitic sedimentary strata the existence of coherent to quench fragmented tops but the absence of autobreccias indicate that many komatiite lavas were emplaced passively under laminar flow conditions to determine how widely this may apply to active komatiite lavas we model flow front thicknesses noting that the preserved flow thickness is thus significantly greater than the thickness of the propagating flow front we apply the concept of inflation of basalt lava flows to komatiites application of the jeffreys equation allows lava thickness to be determined as a function of flow velocity viscosity density and slope of the terrain using the results together with estimates of flow front velocities and viscosity in the reynolds number equation indicates that at expected low flow front velocities in medial to distal settings most komatiites would have propagated in a laminar flow state we therefore envisage that komatiites were turbulent in near vent settings and capable of physical erosion and at times as previously proposed channel forming thermal erosion as flow area increased downstream and magma supply rate to the flow front and the flow front velocity decreased significantly the flow state would have transformed to laminar flow preserved flow thicknesses are often considerably greater than the calculated flow front thicknesses for such low viscosity lavas indicating that the final preserved thicknesses are either due to flow inflation ponding in topography or that some komatiites were intrusions

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

the thermal stability of near surface ground ice on mars the existence of subsurface water ice on mars has been predicted in several theoretical studies1 5 but there are no definitive observations of its present distribution geomorphic features on the surface of mars have been widely interpreted as evidence for the presence of ground ice6 12 but many of these features are found at near equatorial latitudes where thermal models have predicted that near surface water ice should not be stable under present climate conditions3 13 14 here i present the results of thermal calculations which show that observed geographic variations in the thermal and reflectance properties of martian soils significantly affect subsurface temperatures my results indicate that in certain regions ground ice deposits could exist much closer to the surface and much closer to the equator than previously thought in the future these deposits could be a valuable resource for human exploration15

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

small scale trench in the north polar region of mars evolution of surface frost and ground ice concentration in this paper we attempt to answer the question how formation of a small scale trench in the martian regolith affects local distribution of the subsurface ice we are especially interested in the consequences of digging a trench to search for buried ice as has been done during the phoenix mars lander mission however the results may be also applicable for natural troughs or cracks we present results of simulations of diurnal exchange of water between the regolith and the atmosphere our model includes the heat and vapor migration in the regolith surrounding the trench as well as formation of diurnal frost we take into account scattering of light in the atmosphere and on the trench facets as well as changes of atmospheric humidity on diurnal and seasonal time scales our calculations show that the measurements of ice content in a sample obtained within one or two days from the beginning of digging should not be affected however on somewhat longer time scale at the south facing site of the trench the regolith can be significantly depleted from ice this effect should be taken into account if the excavation and taking samples from different depths will be performed in stages separated in time by a month or more

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

pulsed inflation of pahoehoe lava flows implications for flood basalt emplacement abstract dilated fractures in hawaiian pahoehoe lava flows contain three zones that show the kinematics of inflation the upper columnar zone forms through thermal contraction prior to inflation the middle planar zone reflects inflation induced tension and the lower banded zone contains evidence of brittle and ductile deformation the formation of the lower banded zone requires varying strain rates during fracture propagation and is best explained by a model where small pulses of lava inject beneath the cooled flow crust through a network of preferred pathways we demonstrate via simple models of pipe flow that this inflation mechanism is incapable of producing areally extensive continental flood basalts on earth although it may explain related features on large martian volcanoes

introduction to the 4th mars polar science and exploration conference special issue five top questions in mars polar science abstract as an introduction to this icarus special issue for the 4th mars polar science and exploration conference we discuss five key questions in mars polar science gleaned from plenary discussions and presentations held at the conference these questions highlight major unknowns in the field 1 what are the physical characteristics of the polar layered deposits pld and how are the different geologic units within beneath and surrounding the pld related 2 how old are the pld and what are their glacial fluvial depositional and erosional histories 3 what are the mass and energy budgets of the pld and what processes control these budgets on seasonal and longer timescales 4 what chronology compositional variability and record of climatic change is expressed in the stratigraphy of the pld 5 how have volatiles and dust been exchanged between polar and non polar reservoirs and how has this exchange affected the past and present distribution of surface and subsurface ice

new observations of martian southern mid latitude recurring slope lineae rsl imply formation by freshwater subsurface flows abstract southern mid latitude sml recurring slope lineae rsl are narrow 0 5 5 m dark albedo features that emanate from bedrock and incrementally lengthen down steep slopes that preferentially face the equator we observe that sml rsl begin lengthening prior to southern summer at a solar longitude ls of 245 11 when mars global surveyor thermal emission spectrometer tes derived near maximum surface temperatures are 296 5 k and mars reconnaissance orbiter mars climate sounder mcs and mars odyssey thermal emission imaging system themis derived mid afternoon surface temperatures are 273 k sml rsl continue to lengthen for 104 38 sols with an average near maximum surface temperature of 298 5 k the sml rsl then stop lengthening at ls 314 12 when mid afternoon surface temperatures drop below 273 k they remain dark for another 116 41 sols until ls 16 14 as surface temperatures continue to fall although the rsl recharge mechanism remains unknown our observation that the vast majority of rsl lengthen only when mid afternoon surface temperatures are 273 k supports the hypothesis that they are formed by shallow subsurface liquid water flows without significant freezing point depression the number and length of rsl at multiple sites increased dramatically following the mars year 28 globe encircling dust storm we interpret this increase to be due to warmer subsurface temperatures created by a dust laden greenhouse effect that may be unique to the southern mid latitudes near ls 270 therefore sml rsl flow is quite sensitive to ground temperature and may only occur under favorable orbital parameters when mean insolation during the rsl lengthening season is above that of the current southern mid latitude mean insolation value this value is currently at a peak that has not been attained for the last 100 ka meanwhile the rsl poor northern mid latitude mean insolation is near a minimum and has a value 27 lower than the southern value if sml rsl are indeed formed by shallow subsurface freshwater flows then they may be some of the best locations on mars to explore for extant life

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

the volcanology of komatiites as deduced from field relationships in the norseman wiluna greenstone belt western australia abstract komatiites in the western part of the norseman wiluna greenstone belt in the yilgarn block of western australia display a wide variety of volcanic facies ranging from very thin differentiated munro township type flow units through to very thick olivine rich cumulate flow units containing high proportions of adcumulate dunite cumulate flow units have been mapped in detail in the agnew wiluna segment of the norseman wiluna greenstone belt in the yakabindie and mt keith areas thick lenticular bodies of olivine adcumulate are flanked and overlain by thinner sheet like sequences of finer grained olivine orthocumulates they show fine scale internal layering broad scale cryptic layering and upper fractionated sequences containing harrisites pyroxene bearing cumulates and in some cases gabbroic derivatives low grade disseminated sulphide mineralisation occurs within the dunite lenses in the stratigraphically equivalent kathleen east area adcumulate dunite grades laterally into olivine orthocumulates and spinifex textured flows a similar relationship is also seen further south where the perseverance ultramafic complex consists of a thick central dunite lens flanked on one side by thin fine grained orthocumulate sequences and on the other by intercalated orthocumulates and spinifex textured flows these field relationships indicate an extrusive origin for the adcumulate dunite bodies the walter williams formation in the west central part of the norseman wiluna belt is a very large cumulate flow unit 150 km long and 30 km wide in presently exposed extent it consists of a central sheet like body of adcumulate dunite underlain and overlain by olivine orthocumulates the adcumulate sheet is everywhere capped by a distinctive thin layer of olivine harrisite at its northernmost extent the flow unit consists of cyclically layered olivine and pyroxene bearing cumulates capped by gabbros dolerites and pyroxene spinifex textured material interpreted as a periodically replenished lava lake sequence both the lenticular dunite bodies of the agnew wiluna belt and the sheet like dunite body of the walter williams formation are interpreted as crystallisation products of very large submarine komatiite lava flows which erupted and flowed at very high rates the adcumulate dunites are interpreted as the products of in situ crystallisation at low degrees of supercooling at the top of upward and inward accreting crystal piles at the bases of the flows flanking and overlying olivine orthocumulates reflect higher rates of heat loss at the site of crystallisation due to lower lava flow rates field evidence from perseverance and the general geometry of the dunite lenses suggest that the lenses formed within large thermal erosion channels developed by turbulent lava rivers flowing over low melting felsic volcanic substrates the textural range exhibited by komatiites can be integrated into a comprehensive model for the geometry of large komatiite flow fields formed by rapid extrusion dunite sheets form close to the eruption sites and dunite lenses as a result of channellisation further away from the vent or close to the vent in the situation where the substrate is non refractory and thermal erosion can take place readily kambalda type volcanic facies develop in more distal environments where lava emplacement is channellised and episodic and munro type flow units represent small scale lava tubes formed at low flow rates on the distal flanks of major eruptions or close to the vent of very small ones waning eruption rates leads to proximal facies being overridden by distal ones a common observation in komatiite sequences the size of thermal erosion channels requires very rapid eruption rates comparable to those in phanerozoic flood basalt terrains

dynamics of earthquake normal faulting two dimensional lattice particle model a 2d lattice particle model is used to simulate the dynamic rupture process of a normal fault the system equations for the particle motions are solved numerically by the finite difference method under a given block boundary condition the flexibility of the implementation of a 2d lattice particle model to simulate an earthquake dynamic process was demonstrated in previous modeling of a shallow angle thrust fault shi et al 1998 numerical results indicate that the particle motions displacement velocity and acceleration along the fault are discontinuous both in the fault parallel and fault normal directions with a localized slip rupture and localized fault separation in the vicinity of the fault outcrop the position at which the fault intersects with the free surface the particle velocity and acceleration increase rapidly both on the hanging wall and the footwall the particle motions on the hanging wall are larger than those on the footwall these motions are amplified as the fault scarp develops rupture breaks out at the surface with strong asymmetry between the hanging wall and the footwall along the free surface as the distance from the fault outcrop increases the particle velocity and acceleration decrease rapidly on the footwall and less rapidly on the hanging wall the asymmetrical particle motion results from the geometrical effect of the dip of the fault the free surface and the dynamic source rupture the combination of all of these effects causes a strong asymmetry in stress when the rupture pulse approaches the free surface the dynamically propagating rupture is characterized by a ramp slip time function accompanied with fault opening the slip pulse becomes sharper when the rupture approaches the free surface consequentially the hanging wall in the vicinity of the fault exhibits a large vibration which generates a strong surface wave propagating along the free surface away from the fault scarp on the hanging wall side this result is similar but significantly different from the numerical simulation of a normal fault with a moving double couple dislocation source benz and smith 1988 in addition the numerical result is qualitatively in agreement with recent foam rubber experiments brune and anooshehpoor 1999 and similar to results from a finite element simulation oglesby et al 1998 oglesby 1999 comparing with a 2d strike slip fault and thrust fault the particle motions in the vicinity of the normal fault on the free surface are smaller for a same size rupture pulse

stochastic strong ground motion simulation of the 12 november 1999 duzce turkey earthquake using a dynamic corner frequency approach on 12 november 1999 only three months after the 17 august 1999 kocaeli earthquake mw 7 4 an earthquake of mw 7 1 occurred immediately to the east of the kocaeli rupture in northwestern turkey resulting in extensive structural damage in the city of duzce and its surrounding area it was reported to be a right lateral strike slip event on the previously unbroken segment of the north anatolian fault zone with a north dipping fault plane this paper presents stochastic finite fault simulation of near field ground motions from this earthquake at selected near fault stations based on a dynamic corner frequency approach using the computer program exsim motazedian and atkinson 2005 the method requires region specific source path and site characterizations as input model parameters the source mech anism of the 1999 duzce event and regional path effects are well constrained from previous studies of the earthquake the local site effects at the selected stations are studied as a combination of the kappa operator and frequency dependent soil ampli fication the model parameters are validated against recordings and a stress drop value of 100 bars is estimated for the 1999 duzce earthquake the validated model is then used to compute synthetic records around the fault distribution of peak ground motion parameters is observed to be consistent with the building damage dis tribution in the near fault region most affected by the seismic shaking the attenuation of synthetic ground motion parameters is compared with recent ground motion pre diction equations proposed for the region by gulkan and kalkan 2002 ulusay et al 2004 and akkar and bommer 2007 as well as two next generation attenuation models by boore and atkinson 2007 and campbell and bozorgnia 2007 despite discrepancies at several stations stochastic finite fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

komatiitic sills and multigenerational peperite at dundonald beach abitibi greenstone belt ontario volcanic architecture and nickel sulfide distribution the density and the tectonic stresses in the deep crust and the physical properties of komatiitic magmas determine the level to which they will rise but once in the near surface environment the density and rheology of the near surface rocks consolidated and dense lava flows and sedimentary rocks versus unconsolidated sedimentary or volcaniclastic deposits govern whether they will be emplaced as lava flows invasive flows or sills where near surface strata are competent i e flow dominated or consolidated sedimentary and or volcaniclastic successions komatiitic magma erupts as flows that form extensive lava shields e g kambalda however where near surface strata are not competent i e unconsolidated volcaniclastic and or sediment dominated successions komatiitic magmas typically are emplaced as high level sills that increase the bulk density of the volcano sedimentary pile and eventually allow the eruption of lava and the construction of complex sub volcanic volcanic lava shields e g dundonald and shaw dome abitibi belt raglan cape smith belt pechenga kola peninsula thompson ni belt manitoba the latter environment is illustrated in the volcano sedimentary succession in dundonald township which is only weakly metamorphosed and deformed and superbly exposed in glacially polished outcrops the volcano sedimentary succession in this area comprises from base to top 1 the mcintosh formation composed of a succession of pillowed and massive intermediate volcanic flows 2 the dundonald formation composed of a lower section of komatiite sills argillites and felsic volcaniclastic deposits and an upper section of komatiite flows komatiitic sills and pillowed intermediate volcanic flows and 3 the frederick house lake formation composed of massive and pillowed mafic flows the distribution and thickness of argillites and felsic volcaniclastic rocks define a synvolcanic graben in which the dundonald south and alexo ni cu pge deposits occur within the center and the margin respectively sills and peperites in the lower komatiitic succession at dundonald beach exhibit a multigenerational emplacement history recording progressive lithification and increases in the bulk density and rheological strength of the unconsolidated argillites which ultimately permitted the eruption of lavas at alexo importantly the nature of the near surface rocks also influences the localization of ni cu pge deposits in lava shields e g kambalda the initial eruptions are typically most voluminous and if erupted at sufficient flow rates form channelized flows conducive to thermomechanical erosion of sulfur rich footwall rocks in sub volcanic volcanic lava shields however channelized units may occur within the subvolcanic plumbing system and or within overlying lavas where only sills are channelized e g thompson mineralization will occur only within the subvolcanic environment where only the flows are channelized e g damba silwane zimbabwe mineralization will occur only within the volcanic environment where both sills and lava flows are channelized e g dundonald shaw dome raglan the distribution of the mineralization is more diverse and may occur as subsea or sea floor ni cu pge deposits

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

possible mechanism of boulder clustering on mars whatever causes small scale polygonal patterned ground diameter 20 m to form pervasively in the northern plains of mars appears to also cause boulders to cluster at polygon margins assuming that these polygons are caused by the seasonal thermal contraction and expansion of ice in the near surface to meters of depth we propose a mechanism that ratchets boulders towards the edges in seasonal cycles on present day mars during the contraction cooling phase a co2 frost layer embeds the boulders buffered by condensation and sublimation the solid co2 is isothermal and does not contract we propose that it locks the boulders in place while the h2o ice in the near surface continues cooling and contracts beneath them in spring summer seasons when the frost sublimates and heating of the surface begins the boulders freely move with the expanding near surface ice we show that over many seasons this process would lead to progressive boulder movement towards polygon edges with an estimated rate of boulder migration 0 1 mm yr under present mars conditions

endogenous growth in channelized komatiite lava flows evidence from spinifex textured sills at pyke hill and serpentine mountain western abitibi greenstone belt northeastern ontario canada spinifex textured sills i e veins characterized by komatiitic magmas that have intruded their own volcanic piles have long been recognized for instance in the early 1970s pyke and coworkers in their classic work at pyke hill in munro township noted that not all spinifex bearing ultramafic rocks formed as lava flows rather some were clearly emplaced as small dikes and sills several hypotheses have been proposed to explain spinifex textured sills intrusion into a cold host filter pressing or drainage of residual liquid however these do not satisfactorily explain the phenomenon field and petrographic observations at pyke hill and serpentine mountain demonstrate that spinifex bearing komatiite sills and dikes were emplaced during channel inflation processes when new magma was intruded into a cooler semi consolidated but permeable cumulate material komatiitic liquids were intruded into the olivine cumulate rocks near the boundary between the spinifex and the cumulate zones of well organized to organized komatiite flows spinifex textured sills are generally tabular in morphology stacked one above another with curviplanar contacts sub parallel to stratigraphy some sills exhibit complex digitated apophyses thinner sills typically have a random olivine spinifex texture similar though generally composed of coarser crystals to that of komatiite lava flows thicker sills exhibit more complex organization of their constituent crystals characterized by zones of random olivine spinifex overlying zones of organized coarse spinifex crystals similar to those found in lava flows they have striking coarse dendritic spinifex zones composed of very large olivine crystals up to several centimetres long and up to 1 cm wide that are not observed in lava flows typically at the sill margins the cumulate material of the host flow is composed of euhedral to subhedral olivine crystals that are larger than those distal to the contact many of these margin crystals have either concentric overgrowth shells or dendritic olivine overgrowths that grew from the cumulate sill contact toward the sill interior the dendrites grew on pre existing olivine cumulate at the contact in response to a sharp temperature gradient imposed by the intrusion of hot material whereas the concentric overgrowths formed as new melt percolated into the unconsolidated groundmass of the host flow cumulate material spinifex textured sills and dikes occur in well organized to organized flows that are interpreted to have formed by breakouts above and peripheral to lava pathways channels conduits as a result of inflation that accompanied voluminous komatiitic eruptions responsible for the construction and channelization of komatiitic flow fields the spinifex textured dikes and sills represent komatiitic lava that was originally emplaced into the channel roof during periods of episodic inflation that resulted in lava breakouts and was subsequently trapped in the roof rocks during periods of channel deflation accordingly the occurrence of spinifex textured sills and dikes may indicate proximity to and aid in the identification and delineation of lava channel ways that could potentially host ni cu pge mineralization within komatiitic lava flow fields

predicting intensity and damage distribution during the 1995 dinar turkey earthquake with generated strong motion accelerograms a source model for the 1995 dinar earthquake that is capable of reproducing reasonably well the statistical characteristics of observed strong motion records is used to generate synthetic ground motion accelerograms at 29 different sites along five east west cross sections in the city each section crosses a distribution of topographical geotechnical and damage characteristics all synthetic stations are located within a circle of approximately 4 km diameter and a segment of the ruptured fault extends into the city four parameters are identified to represent the intensity of strong motion accelerograms two of them are the simplest kinematical parameters namely peak ground acceleration and peak ground velocity and the other two are spectral parameters namely the average over a period range of spectral acceleration and of spectral input energy the distribution of each intensity parameter is compared with the observed damage distribution in the city along the five sections spectral intensity parameters predict the damage distribution better than the two kinematical parameters with spectral input energy slightly outperforming spectral acceleration the results suggest that synthetic seismograms generated by using a realistic source model are capable of producing useful estimates of ground motion intensity and consequent structural damage even within the boundaries of a modestsized city in the near field of the earthquake source

source parameters of the 1 october 1995 dinar turkey earthquake from sar interferometry and seismic bodywave modelling abstract the 1 october 1995 m s 6 1 dinar earthquake ruptured a 10 km section of the nw se dinar civril fault there are discrepancies between the published source parameters from seismic data with seismic moments in disagreement by over a factor of two we use both sar interferometry and seismic bodywave modelling to determine earthquake source parameters an interferogram generated from ers 1 2 sar imagery spanning the event and separated by 5 months is used to derive source parameters by a downhill simplex inversion with multiple monte carlo restarts we model the displacements in the satellite line of sight initially using uniform slip on a rectangular dislocation in an elastic half space the resultant model fault plane agrees in strike and location with the observed surface break but systematic residuals exist in the line of sight deformation field resulting in a r m s residual of 20 mm in the interferogram the residuals are reduced if the depth distribution of slip is allowed to vary spatially in four segments along a continuous fault plane our best fitting solution with a r m s misfit of 8 mm reveals two distinct areas of slip on the fault plane strike 145 dip 49 rake 270 a main rupture slipping by 1 44 m between depths of 1 and 8 km becoming deeper to the se and matching the observed surface rupture and an along strike continuation to the nw of the same fault plane but between depths of 8 and 13 km and not associated with a surface break the total geodetic moment 4 5 0 1 10 18 nm is more than twice as large as published seismic moments based on the inversion of p waveforms alone but close to the harvard cmt moment 4 7 10 18 nm we use sh waveforms in addition to the p waves used previously to determine an alternative seismic source mechanism sh waves constrain the depth to be shallower than solutions based on p waves alone agreeing with the depths from the interferometric inversion and resulting in a larger moment 3 1 0 4 10 18 nm than the previous bodywave estimates 2 2 1 10 18 nm the cmt moment reduces in magnitude to a similar size 3 3 10 18 nm if the centroid depth and fault dip are constrained to the values determined from bodywave modelling and interferometry thus the geodetic moment is 40 bigger than the moment determined from seismology

a prelanding assessment of the ice table depth and ground ice characteristics in martian permafrost at the phoenix landing site 1 we review multiple estimates of the ice table depth at potential phoenix landing sites and consider the possible state and distribution of subsurface ice a two layer model of ice rich material overlain by ice free material is consistent with both the observational and theoretical lines of evidence results indicate ground ice to be shallow and ubiquitous 2 6 cm below the surface undulations in the ice table depth are expected because of the thermodynamic effects of rocks slopes and soil variations on the scale of the phoenix lander and within the digging area which can be advantageous for analysis of both dry surficial soils and buried ice rich materials the ground ice at the ice table to be sampled by the phoenix lander is expected to be geologically young because of recent climate oscillations however estimates of the ratio of soil to ice in the ice rich subsurface layer suggest that that the ice content exceeds the available pore space which is difficult to reconcile with existing ground ice stability and dynamics models these high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity initially high porosity soils or the migration of water along thin films measurement of the d h ratio within the ice at the ice table and of the soil to ice ratio as well as imaging ice soil textures will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

development of the 1990 kalapana flow field kilauea volcano hawaii the 1990 kalapana flow field is a complex patchwork of tube fed pahoehoe flows erupted from the kupaianaha vent at a low effusion rate approximately 3 5 m3 s these flows accumulated over an 11 month period on the coastal plain of kilauea volcano where the pre eruption slope angle was less than 2 the composite field thickened by the addition of new flows to its surface as well as by inflation of these flows and flows emplaced earlier two major flow types were identified during the development of the flow field large primary flows and smaller breakouts that extruded from inflated primary flows primary flows advanced more quickly and covered new land at a much higher rate than breakouts the cumulative area covered by breakouts exceeded that of primary flows although breakouts frequently covered areas already buried by recent flows lava tubes established within primary flows were longer lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply tubes within breakouts were never reoccupied once the supply was interrupted during intervals of steady supply from the vent the daily areal coverage by lava in kalapana was constant whereas the forward advance of the flows was sporadic this implies that planimetric area rather than flow length provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

active boulder movement at high martian latitudes lobate stony landforms occur on steep slopes at high latitudes on mars we demonstrate active boulder movement at seven such sites submeter scale boulders frequently move distances of a few meters the movement is concentrated in the vicinity of the lobate landforms but also occurs on other slopes this provides evidence for a newly discovered common style of activity on mars which may play an important role in slope degradation it also opens the possibility that the lobate features are currently forming in the absence of significant volumes of liquid water

a composite source model of the 1994 northridge earthquake using genetic algorithms abstract the 17 january 1994 northridge earthquake m w 6 7 occurred on a buried thrust fault in the northwest los angeles metropolitan area we investigate the source process of this earthquake using the csmip strong motion records and a composite source model developed by zeng et al 1994a for realistic earthquake strong ground motion prediction our previous studies demonstrated the realism of the synthetic strong motions generated from the composite source model by comparing them with observed records from earthquakes in many areas of the world this article addresses an inverse study of the problem to find a specific composite source model for the northridge earthquake this is done by adjusting the location of a suite of composite subevents using genetic algorithms holland 1975 to best match the observed waveforms a test run of the genetic algorithm on synthetic data sets finds a very good convergence of the approach we reduce largely the intensive computation time by identifying subevents with major contribution to the waveform fit our result for the 1994 northridge earthquake indicates a complex earthquake rupture process with three large slip zones one at the hypocenter and the other two to the west of the hypocenter we then use this model to compute the high frequency strong motion velocity and acceleration the results show that the composite source model provides a very realistic broadband source description for the northridge earthquake

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

analysis of accelerations from the 1 october 1995 dinar turkey earthquake the dinar earthquake 1 october 1995 occurred in southwestern turkey and had a moment magnitude of 6 4 and a normal faulting mechanism the earthquake caused 90 deaths over 200 injuries and a large amount of damage it was recorded by seven strong motion accelerographs the strong motion accelerograph at dinar is on the edge of the surface projection of the fault the record from dinar is possibly unique in its proximity to the causative fault for this type of mechanism the dinar strong motion station is in a small stiff building on soft sediments with a shallow water table the peak acceleration was 0 32 g on the horizontal component perpendicular to the fault trace the earthquake was caused by rupture on the dinar fault which is a normal fault trending generally toward the south southeast with the hanging wall on the west there was surface rupture along about a 12 km segment of this fault the dinar strong motion station is at the south end of the fault under 1 km from the nearest surface trace the hypocenter was at the south end beneath dinar with rupture propagating toward the north and away from the strong motion site a specific composite source model was found that reproduces the statistical characteristics of the ground motions and also approximately reproduces the low frequency waveform in the strong motion in this model the fault length l is 12 5 km the width w is 17 3 km and the moment m 0 is 4 72 10 25 dyne cm the fault strikes 130 and dips 45 toward the southwest from the surface to 12 km for the composite parameters the largest subevent r max is 4 0 km the rupture velocity is 1 5 km sec and the subevent stress drop is 60 bars after anderson 1997 the composite source model parameters imply that the static stress drop was 36 bars the radiated seismic energy in this event was 4 3 10 21 ergs the apparent stress was 18 bars and the savage wood ratio was 1 0 most of the seismic energy is released at depths greater than 2 km the major asperity is beneath the location where synthetic aperture radar interferometry found the maximum surface deformation

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh