working models for spatial distribution and level of mars seismicity 1 we present synthetic catalogs of mars quakes intended to be used for performance assessments of future seismic networks on the planet we have compiled a new inventory of compressional and extensional tectonic faults for the planet mars comprising 8500 faults with a total length of 680 000 km the faults were mapped on the basis of mars orbiting laser altimeter mola shaded relief hence we expect to have assembled a homogeneous data set not biased by illumination and viewing conditions of image data updated models of martian crater statistics and geological maps were used to assign new maximum ages to all faults on the basis of the fault catalog spatial distributions of seismicity were simulated using assumptions on the available annual seismic moment budget the moment frequency relationship and a relation between rupture length and released moment we have constructed five different models of martian seismicity predicting an annual moment release between 3 42 1016 nm and 4 78 1018 nm and up to 572 events with magnitudes greater than 4 per year as upper limit end member case most events are expected on the tharsis shield but minor seismic centers are expected south of hellas and north of utopia planitia

field experiments in a fractured clay till 2 solute and colloid transport a field tracer experiment was conducted in a lateral flow field in the weathered and highly fractured upper 6 m of a 40 m thick clay rich till plain in southwestern ontario in the upper 3 m where fractures are closely spaced 5 m d simulations with a discrete fracture porous matrix flow and transport model which used the cubic law for flow in fractures showed that diffusion of the solutes but not the much larger colloids into the matrix pore water between fractures is sufficient to cause the observed difference in solute and colloid transport rates transport derived and hydraulic conductivity derived fracture aperture values were similar within a factor of 3 and falling mainly within a range of 5 40 m in the upper 3 m the solute tracers were evenly distributed between pore water in the fractures and the matrix and as a result solute transport can be closely approximated with an equivalent porous medium epm approach below this depth fractures are more widely spaced 0 13 to 1 m with concentration peaks tending to occur near visible fractures and solute transport cannot be adequately described with an epm approach

possible long term decline in impact rates 1 martian geological data abstract quantin et al quantin c allemand p mangold n delacourt c 2004a icarus 172 555 572 tabulated crater count data for 56 landslides along the walls of valles marineris under the assumption of a constant cratering rate after about 3 gyr ago as used in the 1999 2005 iterations of the crater chronology isochron system of hartmann and in the hartmann and neukum system these data indicate a regularly increasing rate of landslides which would be difficult to explain we suggest that these data may support a decline in inner solar system cratering rates by about a factor of 3 since 3 gyr ago not unlike predictions based on asteroid belt collision models such a decline is also supported by our review of data on lunar impact melts and glass spherules in a companion paper hartmann w k quantin c mangold n 2007 icarus 186 11 23 such models produce not only a more uniform rate of landslides over the last 3 gyr but also a more uniform rate of resurfacing processes which also had an apparent increase under the assumption of a constant cratering rate

eastern boundary contribution to the residual and meridional overturning circulations a model of the thermocline linearized around a specified stratification and the barotropic linear winddriven stommel solution is constructed the forcings are both mechanical the surface wind stress and thermodynamical the surface buoyancy boundarycondition the effects of diapycnal diffusivity and of eddy fluxesofbuoyancy parameterizedintermsofthelarge scalebuoyancygradient areincluded theeddyfluxes of buoyancy are especially important near the boundaries where they mediate the transport in and out of the narrow ageostrophic down upwelling layers the dynamics of these narrow layers can be replaced by effective boundary conditions on the geostrophically balanced flow the effective boundary conditions state that the residual flow normal to the effective coast vanishes the separate eulerian and eddy induced components may be nonzero this formulation conserves the total mass and the total buoyancy while permitting an exchangebetweentheeulerianandeddytransportofbuoyancy withinthedown upwellinglayers inturn this exchange allows buoyancy gradients along all solid boundaries including the eastern one a special focus is on the buoyancy along the eastern and western walls since east west buoyancy difference determines the meridional overturning circulation the inclusion of advection of buoyancy by the barotropic flow allows a meaningful distinction between the meridional and the residual overturning circulations while retaining the simplicity of a linear model the residual flow in both meridional and zonal directions reveals how the subsurface buoyancy distribution is established and in particular how the meridional buoyancy gradient is reversed at depth in turn the horizontal buoyancy gradient maintains stacked counterrotating cells in the meridional and residual overturning circulations quantitative scaling arguments are given for each of these cells which show how the buoyancy forcing the wind stress and the diapycnal and eddy diffusivities as well as the other imposed parameters affect the strength of the overturn

identifying the water source for subsurface flow with deuterium and oxygen 18 isotopes of soil water collected from tension lysimeters and cores the conventional identification of soil water with pre event water limits deep insights into the involvement of stationary and mobile soil water in subsurface hydrological processes in three tilled sloping field plots at a hilly area of southwestern china dominated by entisols soil water collected with a suction lysimeter was distinguished from the total soil water through an analysis of the stable isotopes deuterium and oxygen 18 differences in the depth profile of soil water before and after storm events were observed and used to examine how rainwater mixes with soil water and to identify the source contribution of different fractions of soil water in subsurface flow generation only water in the 0 10 cm soil layer was significantly affected by evaporation and infiltration water in the top 5 cm layer of the soil exhibited the lowest residence time because a storm can replace a substantial proportion of the pre event water soil water at the 10 20 cm depth showed the longest residence time as indicated by its high proportion of pre event water the isotopic signatures demonstrated that piston flow and preferential flow coexisted in this soil high antecedent soil water content and high rain intensity favor the formation of piston flow the water collected with the suction lysimeter represented the mobile fraction of the pre event water in the soil which effectively participates in the generation of subsurface flow newly infiltrated rainwater did not well mix with stationary pre event water in the soil the use of recent rainfall to represent mobile soil water may provide a practical solution for overcoming the negative effect of the spatial heterogeneity of the isotopic composition of soil water on hydrograph separation results bulk soil water and lysimeter water showed significant differences in isotopic composition under low soil water content or in the top soil layer stable isotopes in bulk and lysimeter soil water should be monitored synchronously to reveal the sources and pathways of soil water and their contributions to the generation of subsurface flow in the vadose zone c 2013 elsevier b v all rights reserved

estimates of seismic activity in the cerberus fossae region of mars 1 the 2016 nasa insight lander is the first planetary mission designed to study the deep interior of mars insight s seismic experiment for interior structure seis package will quantify global and regional seismic activity and determine parameters like core properties mantle composition and martian lithospheric thickness an improved understanding of the location magnitude and frequency of potential seismic sources is essential for optimization of instrument design sampling strategy and interpretation of mission data we focus on forecasting seismic activity for the cerberus fossae of the elysium planitia chosen for their proximity to the proposed landing site and their recent formation and assuming these are active tectonic grabens the minimum age we determine for the units around the fossae using context camera and high resolution imaging science experiment imagery for crater density surveying is 10 ma placing them in the late amazonian we are able to determine the rate of motion from measurements of observed throw assuming that the faults remain active digital terrain models made from stereo image pairs from the high resolution stereo camera hrsc are used to determine the maximum throw on four graben systems using these measured throws to estimate a length averaged slip and assuming an inferred slip rate from surface age we estimate an annual moment release of 1 58 1 03 2 35 1017nm from this we calculate an annual size frequency distribution of events using the gutenberg richter relationship we estimate that between 1 5 100and 1 9 105events per year will have an amplitude greater than the peak band noise and so will be detectable at the insight landing site

the current martian cratering rate abstract the discovery of 248 dated impact sites known to have formed within the last few decades allows us to refine the current cratering rate and slope of the production function at mars we use a subset of 44 of these new craters that were imaged before and after impact by mars reconnaissance orbiter s context camera a thoroughly searched data set that minimizes biases from variable image resolutions we find the current impact rate is 1 65 10 6 craters with an effective diameter 3 9 m km2 yr with a differential slope power law exponent of 2 45 0 36 this results in model ages that are factors of three to five below the hartmann hartmann w k 2005 icarus 174 294 320 and neukum et al neukum g ivanov b a hartmann w k 2001 space sci rev 96 55 86 ivanov ivanov b a 2001 space sci rev 96 87 104 model production functions where they overlap in diameter the best fit production function we measure has a shallower slope than model functions at these sizes but model function slopes are within the statistical errors more than half of the impacts in this size range form clusters which is another reason to use caution when estimating surface ages using craters smaller than 50 m in diameter

analysis of a crater forming meteorite impact in peru 1 the fireball producing a crater forming meteorite fall near carancas peru on 15 september 2007 has been analyzed using eyewitness seismic and infrasound records the meteorite impact which produced a crater of 13 5 m diameter is found to have released of order 1010 j of energy equivalent to 2 3 tons of tnt high explosives based on infrasonic measurements our best fit trajectory solution places the fireball radiant at an azimuth of 82 relative to the crater with an entry angle from the horizontal of 63 from entry modeling and infrasonic energetics constraints we find an initial energy for the fireball to be in the 0 06 0 32 kton tnt equivalent the initial velocity for the meteoroid is restricted to be below 17 km s from orbit considerations alone while modeling suggests an even lower best fit velocity close to 12 km s the initial mass of the meteoroid is in the range of 3 9 tons at impact modeling suggests a final end mass of order a few metric tons and impact velocity in the 1 5 4 km s range we suggest that the formation of such a substantial crater from a chondritic mass was the result of the unusually high strength and corresponding low degree of fragmentation in the atmosphere of the meteoritic body additionally the high altitude of the impact site 3800 m a s l resulted in an almost one order of magnitude higher impact speed than would have been the case for the same body impacting close to sea level

fate and transport of pathogens in a fractured aquifer in the salento area italy 1 this study investigates the fate and transport of pathogens introduced by artificial groundwater recharge at the nardo fractured aquifer in the salento area italy wastewater effluents from a municipal treatment plant with known pathogen concentrations were injected into a sinkhole and the migration of pathogens in the fractured aquifer was monitored at six sampling wells the fate of pathogens was quantified by a mathematical model describing colloid transport in a set of three dimensional parallel fractures with spatially variable aperture the number of parallel fractures and their average fracture aperture were determined from appropriate field pumping and tracer tests the aperture spatial distribution was described by an experimental semivariogram developed from available field data obtained from two tracer tests and 34 pumping tests the experimental results suggest that for the municipal wastewater injected into the nardo aquifer the required most conservative set back distance for drinking wells should be over 8000 m

high precision location and yield of north korea s 2013 nuclear test 1 using north korea s 2009 nuclear test as reference and satellite imagery we show that the location and yield of north korea s 2013 nuclear test can be quickly and accurately determined based on seismic data north korea s 2013 nuclear test site is pinpointed by deriving relative location of north korea s 2009 and 2013 nuclear tests and using the previously determined location of the 2009 nuclear test while its yield is estimated based on the relative amplitude ratios of the lg waves recorded for both events the previously determined lg magnitude of 2009 nuclear test and burial depth inferred from satellite imagery north korea s 2013 test site is determined to be located at 41 17 26 88 n 129 4 34 68 e about 345 m south and 453 m west of its 2009 nuclear test site with a geographic precision of 94 m its yield is estimated to be 12 2 3 8 kt

evidence for a meteoritic origin of the september 15 2007 carancas crater on september 15th 2007 around 11 45 local time in peru near the bolivian border the atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations soon after a crater was discovered south of lake titicaca these events have been detected by the bolivian seismic network and two infrasound arrays operating for the comprehensive nuclear test ban treaty organization situated at about 80 and 1620 km from the crater the localization and origin time computed with the seismic records are consistent with the reported impact the entry elevation and azimuthal angles of the trajectory are estimated from the observed signal time sequences and backazimuths from the crater diameter and the airwave amplitudes the kinetic energy mass and explosive energy are calculated using the estimated velocity of the meteoroid and similarity criteria between orbital elements an association with possible parent asteroids is attempted the favorable setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of the object that generated the first actual terrestrial meteorite impact seismically recorded

a meteorite crater on earth formed on september 15 2007 the carancas hypervelocity impact on september 15 2007 a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of lake titicaca in the community of carancas peru a 13 5 m crater and several fragments of a stony meteorite were found close to the site of the impact the carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater forming meteorite impact on earth we present several lines of evidence that suggest that the carancas crater was a hypervelocity impact an event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the earths atmosphere therefore it challenges our present models of entry dynamics we discuss alternatives to explain this particular event this emphasizes the weakness in the pervasive use of average parameters such as tensile strength fragmentation behavior and ablation behavior in current modeling efforts this underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes

distinct meteoroid families identified on the lunar seismograms we reexamined the seismic events originating from impacts of meteoroids on the lunar surface as recorded by the apollo lunar seismic network in terms of 1 difference in temporal distribution between large and small impacts 2 clustering of impacts in a two dimensional space of the time of the year and the time of the month lunar day and 3 their relationship with terrestrial observations the study led us to identify several distinct families of meteoroids impacting the moon most meteoroids producing small impact seismic events appear to approach from retrograde heliocentric orbits including many that are associated with well known cometary showers in contrast most meteoroids associated with large impact seismic events appear to approach from prograde orbits although some of them may also be cometary the observation is consistent with a hypothesis that many of them represent stony asteroidal material a unique cluster of large amplitude impact events observed in june 1975 appears to be associated with the taurid cometary complex suggesting that the taurids contain more massive or even denser objects than other meteor showers the previously reported discrepancy between lunar and terrestrial meteoroid flux estimates may be due to the differences in lunar and terrestrial detection efficiency among various families of meteoroids

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

ventilation potential vorticity homogenization and the structure of the ocean circulation abstract a model for the vertical structure of the oceanic circulation is presented that combines elements of the theory of the ventilated thermocline given by luyten pedlosky and stommel with the theory of rhines and young for the wind driven circulation of an unventilated ocean our model consists of a ventilated thermocline region above an unventilated zone in which motion is limited to pools of constant potential vorticity the model is nonlinear and hence the presence of ventilation affects the dynamics of the unventilated motion and vice versa the planetary geostrophic equations are used and so the quasi geostrophic assumption of rhines and young is relaxed allowing large isopycnal excursions it is shown that the presence of ventilation generally shrinks and weakens the size and vigor of the subsurface pools of homogenized potential vorticity at the same time within those domains the strength of circulation in the ventilated zone is somewhat diminished as the subsurface layers carry a porti

seismic observations of meteors coupling theory and observations to date coupling of acoustic waves directly with the earth s surface represents the bulk of the observed meteor related seismic signals while precursory and impact related seismic waves remain an observational rarity with proliferation of infrasound and seismic monitoring systems new opportunities exist to explore the relationship between earth s atmosphere andsurface continued studyofmeteorseismologywillleadto new methods to constrain energies sizes and fluxes for moderately cm to m sized meteoroids on earth and potentially on mars

adjustment of the ventilated thermocline the time dependence of the ventilated thermocline is examined via analytical and numerical means the original henderschott model is modified such that the outcrops all occur on the same geopotential surface rather than at staggered geopotential surfaces this model has the advantage that the ocean interior can be ventilated directly by the sverdrup flow rather than by western boundary processes the propagation of disturbances governed by linearized forms of the three layer or four layer modified henderschott model nonlinear solutions of the full modified henderschott model and numerical solutions of the planetary geostrophic equations are considered low frequency disturbances are predicted by the linear models to move on characteristics jointly set by advection and wave dynamics it is shown that perturbations due to wind stress anomalies project strongly onto the first mode and propagate westward similarly to the classical first baroclinic rossby mode they do not experience much interaction with the mean flow the so called non doppler effect on the other hand perturbations generated by buoyancy anomalies have strong projections onto the second or third modes and propagate along pathways very close to the mean circulation their speed is somewhat slower than the current speed however these properties appear in the linearized and simplified nonlinear models and their occurrence in planetary geostrophic results argues the relevance of the henderschott model also these properties are consistent with results from other studies

seismic q of the lunar upper mantle we have determined the frequency dependence of anelastic attenuation for both p and s waves in the upper mantle of the moon in the frequency range of roughly 3 to 8 hz the method used is a combination of a single station method in which q 1 is obtained as an integral with an unknown constant and a multiple station method the result of which is used to determine the integration constant the q determined for p waves qp appears to decrease with increasing frequency though it is not significantly different from a constant q while the q for s waves qs increases with frequency becoming significantly greater than qp at high frequencies all q values remain greater than 4000 within this frequency range qs above 5 hz is approximately proportional to the 0 7th power of frequency the high q for shear waves at high frequencies suggests that compressional heat loss may be a dominant dissipation mechanism some uncertainties in the absolute q values remain because the detailed velocity structure of the lunar upper mantle is largely unknown

understanding the rapidity of subsurface storm flow response from a fracture oriented shallow vadose through a new perspective abstract velocity and celerity in hydrologic systems are controlled by different mechanisms efforts were made through joint sample collection and the use of hydrographs and tracers to understand the rapidity of the subsurface flow response to rainstorms on hourly time scales three deep subsurface flows during four natural rainstorm events were monitored the results show that 1 deeper discharge was observed early in responding rainfall events and yielded a high hydrograph amplitude 2 a ratio index k reflecting the dynamic change of the rainfall perturbation intensity in subsurface flow might reveal inner causal relationships between the flow index and the tracer signal index most values of k were larger than 1 at the perturbation stage but approximated 1 at the no perturbation stage and 3 for statistical analysis of tracer signals in subsurface flows the total standard deviation was 17 2 11 9 7 4 and 3 5 at perturbation stages and 4 4 2 5 1 1 and 0 95 at the non perturbation stage for observed events these events were 3 7 times higher in the former rather than the later reflecting that the variation of tracer signals primarily occurred under rainfall perturbation thus we affirmed that the dynamic features of rainfall have a key effect on rapid processes because besides the gravity mechanical waves originating from dynamic rainfall features are another driving factor for conversion between different types of rainfall mechanical energy a conceptual model for pressure wave propagation was proposed in which virtual subsurface flow processes in a heterogeneous vadose zone under rainfall are analogous to the water hammer phenomenon in complex conduit systems such an analogy can allow pressure in a shallow vadose to increase and decrease and directly influence the velocity and celerity of the flow reflecting a mechanism for rapid subsurface hydrologic response processes in the shallow vadose zone

geophysical constraints on the composition and structure of the martian interior 1 most recent martian interior structure models are based on the planet s polar moment of inertia c although the mean moment of inertia i is required for constructing spherically symmetric models of planetary interiors using the improved value of c mprp2 recently obtained from a combined reanalysis of the entire set of radio science data collected during the last three decades and accounting for the rotationally and topographically induced shape of the planet s gravitational field we find a mean moment of inertia factor of i mprp2 0 3635 0 0012 the new lower value suggests a core radius several tens of kilometers larger if other parameters like core density crust density and crust thickness are fixed it further implies that the martian crust is several tens of kilometers thicker than previously thought if crust and mantle densities and core size are given moreover the martian mantle may be less dense about several tens of kg m 3 with a smaller iron content than previously thought if crust thickness and core size are specified the mantle density of mars is relatively well determined by the planet s moment of inertia factor if crust thickness and density are specified

verifying single station seismic approaches using earth based data preparation for data return from the insight mission to mars abstract the planned insight mission will deliver a single seismic station containing 3 component broadband and short period sensors to the surface of mars in 2016 while much of the progress in understanding the earth and moon s interior has relied on the use of seismic networks for accurate location of sources single station approaches can be applied to data returned from mars in order to locate events and determine interior structure in preparation for the data return from insight we use a terrestrial dataset recorded at the global seismic network station bfo located at the black forest observatory in germany to verify an approach for event location and structure determination based on recordings of multiple orbit surface waves which will be more favorable to record on mars than earth due to smaller planetary radius and potentially lower background noise with this approach applied to events near the threshold of observability on earth we are able to determine epicentral distance within approximately 1 corresponding to 60 km on mars and origin time within 30 s with back azimuth determined from rayleigh wave polarization absolute locations are determined generally within an aperture of 10 allowing for localization within large tectonic regions on mars with these locations we are able to recover earth mantle structure within 5 the insight mission requirements for martian mantle structure using 1d travel time inversions of p and s travel times for datasets of only 7 events the location algorithm also allows for the measurement of great circle averaged group velocity dispersion which we measure between 40 and 200 s to scale the expected reliable frequency range of the insight data from earth to mars data using the terrestrial data we are able to resolve structure down to 200 km but synthetic tests demonstrate we should be able to resolve martian structure to 400 km with the same frequency content given the smaller planetary size

the production of small primary craters on mars and the moon abstract we model the primary crater production of small d d 10 20 cm well below the downturn observed in the distribution of fresh craters detected by the mars global surveyor mgs mars orbiter camera moc or the mars reconnaissance orbiter mro context camera ctx crater counts are conducted on the ejecta blanket of zunil crater and the interior of pangboche crater on mars and north ray and cone craters on the moon our model isochrons produce a similar slope and age estimate for the formation of zunil crater as the hartmann production function 1 ma we derive an age of 35 1 ma for pangboche when accounting for the higher elevation 20 km higher than zunil a factor 2 younger than estimated using the hartmann production function which assumes 6 mbar surface pressure we estimate ages of 52 3 ma and 23 9 ma for north ray and cone crater respectively consistent with cosmic ray exposure ages from apollo samples our results indicate that the average cratering rate has been constant on these bodies over these time periods since our monte carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the moon and mars we conclude that the signal from secondary craters in the isochrons must be relatively small at these locations as our monte carlo model only generates primary craters

predicted detection rates of regional scale meteorite impacts on mars with the insight short period seismometer abstract in 2016 nasa will launch the insight discovery class mission which aims to study the detailed internal structure of mars for the first time short and long period seismometers form a major component of insight s payload and have the potential to detect seismic waves generated by meteorite impacts large globally detectable impact events producing craters with diameters of 100 m have been investigated previously and are likely to be rare teanby n a wookey j 2011 phys earth planet int 186 70 80 but smaller impacts producing craters in the 0 5 20 m range are more numerous and potentially occur sufficiently often to be detectable on regional scales 1000 km at these distances seismic waves will have significant high frequency content and will be suited to detection with insight s short period seismometer seis sp in this paper i estimate the current martian crater production function from observations of new craters malin m c et al 2006 science 314 1573 1577 daubar i j et al 2013 icarus 225 506 516 model results williams j p pathare a v aharonson o 2014 icarus 235 23 36 and standard isochrons hartmann w k 2005 icarus 174 294 320 these impact rates are combined with an empirical relation between impact energy source receiver distance and peak seismogram amplitude derived from a compilation of seismic recordings of terrestrial and lunar impacts chemical explosions and nuclear tests the resulting peak seismogram amplitude scaling law contains significant uncertainty but can be used to predict impact detection rates i estimate that for a short period instrument with a noise spectral density of 10 8 ms 2 hz 1 2 in the 1 16 hz frequency band approximately 0 1 30 regional impacts per year should be detectable with a nominal value of 1 3 impacts per year therefore small regional impacts are likely to be a viable source of seismic energy for probing mars crustal and upper mantle structure this is particularly appealing as such impacts should be easily located with orbital imagery increasing their scientific value compared to other types of events with unknown origins finally comparison of the empirical results presented here with the modelling study of teanby and wookey teanby n a wookey j 2011 phys earth planet int 186 70 80 provides constraints on the seismic efficiency suggesting that values of 5 10 4 may be appropriate for impact generated seismic waves comparing explosion and impact datasets indicate that buried explosions are 10 times more efficient at generating seismic waves than impacts

apollo lunar seismic experiment final summary processing and initial analysis of the entire set of apollo lunar seismic data collected continuously from 1969 through 1977 have now been completed recent results include 1 better defined deep moonquake locations which appear to be bounded rather sharply between about 800 km and 1000 km depths with concentrations near both boundaries and 2 middle mantle 500 to 1000 km depth seismic velocities of vp 8 3 0 4 km sec and vs 4 6 0 2 km sec which are significantly higher than previous estimates and represent an increase of velocities from the upper mantle as opposed to a decrease in previous estimates

the global effects of impact induced seismic activity on fractured asteroid surface morphology abstract impact induced seismic vibrations have long been suspected of being an important surface modification process on small satellites and asteroids in this study we use a series of linked seismic and geomorphic models to investigate the process in detail we begin by developing a basic theory for the propagation of seismic energy in a highly fractured asteroid and we use this theory to model the global vibrations experienced on the surface of an asteroid following an impact these synthetic seismograms are then applied to a model of regolith resting on a slope and the resulting downslope motion is computed for a full range of impactor sizes next this computed downslope regolith flow is used in a morphological model of impact crater degradation and erasure showing how topographic erosion accumulates as a function of time and the number of impacts finally these results are applied in a stochastic cratering model for the surface of an eros like body same volume and surface area as the asteroid with craters formed by impacts and then erased by the effects of superposing craters ejecta coverage and seismic shakedown this simulation shows good agreement with the observed 433 eros cratering record at a main belt exposure age of 400 200 myr including the observed paucity of small craters the lowered equilibrium numbers loss rate production rate for craters less than 100 m in diameter is a direct result of seismic erasure which requires less than a meter of mobilized regolith to reproduce the near observations this study also points to an upper limit on asteroid size for experiencing global surface modifying seismic effects from individual impacts of about 70 100 km depending upon asteroid seismic properties larger asteroids will experience only localized regional seismic effects from individual impacts

empirical dependence of seismic ground velocity on the weight of explosives shotpoint site condition and recording distance for seismic refraction data in this study we have constructed an empirical least squares model for maximum seismic ground velocity vertical component as a function of source size and distance from explosions in drillholes and bodies of water this model is intended in part for use in designing explosion seismic experiments in order to produce acceptable signal to noise ratios at larger distances 10 km and to avoid damaging human structures at smaller distances 1 km data consist of velocities recorded by 120 portable seismographs from 159 shots fired by the u s geological survey in alaska and arizona results show that maximum ground velocity amplitude not necessarily first arrival amplitude decreases with distance and the functional dependence changes with distance for example at 3 km amplitudes decrease as r 2 but at 73 km they decrease as r 1 results also show a strong dependence on site conditions at the shotpoint for example a drillhole shot in wet alluvium produces amplitudes that are four times larger than a drillhole shot in dry alluvium ground velocities are proportional to the square root of the weight of explosives

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

lg attenuation near the north korean border with china part ii model development from the 2006 nuclear explosion in north korea an underground nuclear explosion was set off on 9 october 2006 in north korea the event was recorded at near regional to regional distances over purely continental paths by a network of broadband seismographs located along the northern edge of the korean peninsula the event provided the first window of opportunity to make a reliable measurement of lg wave attenuation in northernmost north korea where the regional phase propagation characteristics are poorly known the results of our analysis show q0 317 14 and 0 343 0 024 in close agreement with the corresponding values obtained of late using a completely different methodology and an independent set of seismic recordings in an adjacent region to the northwest in southern jilin and in liaoning provinces in china

large impacts detected by the apollo seismometers impactor mass and source cutoff frequency estimations abstract meteoroid impacts are important seismic sources on the moon as they continuously impact the moon they are a significant contribution to the lunar micro seismic background noise they also were associated with the most powerful seismic sources recorded by the apollo seismic network we study in this paper the largest impacts we show that their masses can be estimated with a rather simple modeling technique and that high frequency seismic signals have reduced amplitudes due to a relatively low about 1 s corner frequency resulting from the duration of the impact process and the crater formation if synthetic seismograms computed for a spherical model of the moon are unable to match the waveforms of the observations they nevertheless provide an approximate measure of the energy of seismic waves in the coda the latter can then be used for an estimation of the mass of the impactors when the velocity of the impactor is known this method for the artificial impacts of the lm and sivb apollo upper stages allows us to retrieve the mass within 20 of relative error the estimated mass of the largest impacts observed during the 7 years of activity of the apollo seismic network provides an explanation for the non detection of surface waves on the seismograms the specifications of future moon seismometers in order to provide the detection of surface waves are given in conclusion

three dimensional isoneutral potential vorticity structure in the indian ocean the three dimensional isoneutral potential vorticity structure of the indian ocean is examined using world ocean circulation experiment and national oceanic and atmospheric administration conductivity temperature depth data and historical bottle data the distribution of the potential vorticity is set by the indian ocean s source waters and their circulation inside the basin the lower thermocline has a high potential vorticity signal extending westward from northwest of australia and a low signal from the subantarctic mode water in the south the antarctic intermediate water inflow creates patches of high potential vorticity at intermediate depths in the southern indian ocean below which the field becomes dominated by planetary vorticity indicating a weaker meridional circulation and weaker potential vorticity sources wind driven gyre depths have lower potential vorticity gradients primarily due to same source waters homogenization and western shadow zones are not observed the effect dominates the effect of the somali current and the red sea water on the potential vorticity distribution isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the circumpolar deep water fills the basins in deep western boundary currents indicating a strong meridional circulation north of the antarctic circumpolar current the lower gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical indian ocean suggests that rossby waves will travel 1 3 times faster than standard theory predicts to the south several pools of homogenized potential vorticity appear in the upper 2000 m of the southern ocean where gyres previously have been identified south of australia the abyssal potential vorticity structure is set by a combination of the antarctic circumpolar current and the bathymetry

buoyancy and wind driven circulation in an extended model of potential vorticity homogenization an analytical model is proposed on the middepth water circulation between the surface wind driven circulation and the deep buoyancy driven circulation the model consists of three and a half layers with the second and third layers being the middepth layers the model includes thermohaline processes by allowing diapycnal flows at interfaces between layers in addition to the potential vorticity homogenization proposed by rhines and young the velocities of diapycnal flow are calculated from the density stratification which can be given solely by a wind driven model as a good approximation the divergence of diapycnal velocity causes a circulation in addition to the wind driven circulation although in pure wind driven theories motion was absent outside the region of homogenized potential vorticity the present model gives significant currents there in particular a prominent eastward flow appears in the third layer along the southern rim of the homogeneous potential vorticity region in the second layer the flow pattern in the present model is consistent with that estimated diagnostically from the climatological density distribution in the north pacific the diagnosed flow field is further supported by the oxygen distribution there

a prediction of mars seismicity from surface faulting the shallow seismicity of mars has been estimated by measurement of the total slip on faults visible on the surface of the planet throughout geologic time seismicity was calibrated with estimates based on surface structures on the moon and measured lunar seismicity that includes the entire seismogenic lithosphere results indicate that mars is seismically active today with a sufficient number of detectable marsquakes to allow seismic investigations of its interior

the interior structure of mars implications from snc meteorites two end member models of mars present interior structure are presented the first model is optimized to satisfy the geochemical data derived from the snc meteorites in terms of the bulk chondritic ratio fe si 1 71 while the second model is optimized to satisfy the most probable maximum value c 0 366 x m p r p 2 of the polar moment of inertia factor hydrostatic equilibrium and stationary heat transfer are assumed and the basic differential equations for the mechanical and thermal structure are solved numerically together with an isothermal murnaghan birch type equation of state truncated in eulerian strain at forth order we obtain the radial distribution of mass hydrostatic pressure gravity temperature and heat flow density along with the corresponding density stratification viscosity profiles and the global seismic velocity structure of model mars the first model being consistent with the geochemical requirement produces c 0 357 x m p r p 2 whereas the second model commensurate with the geophysical constraint gives fe si 1 35 the calculated central pressure is about 40 gpa in both models and the central temperature is in the 2000 to 2200 k range the model calculations suggest a fe ni fes core a little less than one half of the planetary radius in size surrounded by a silicate mantle subdivided into lower spinel and upper olivine layers and overlain by a 100 to 250 km thick basaltic crust and a surface heatflow density of 25 to 30 mw m 2 in both models the pressure in the mantle is not sufficient for the spinel to perovskite transition to occur the present thermal lithosphere is estimated to be about 500 km thick and to be subdivided into a 300 km thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection given the core sulfur content of 14 wt as derived from snc meteorites the martian core is found to be entirely molten implying the nonoperation of a self sustained dynamo due to the absence of sufficiently vigorous convection

the seismic signatures of recently formed impact craters on mars we investigated the seismic signatures of recent impact crater clusters on mars that would be recorded by the interior exploration using seismic investigations geodesy and heat transport insight seismometers we used a database of 77 measured and dated impact sites with craters with diameters between 2 1 and 33 8 m along with inferred impact angle bolide trajectory and varying target material properties to empirically scale for the momentum expected seismic source function and radiation pattern of impacts the impact source is simulated in a local 3 d finite difference wave propagation code and coupled to teleseismic distances by scaling the spectra of 1 d global synthetic seismograms we use the insight seismometer noise floors to estimate detectability of impact s across azimuth and distance our experiments reveal that impact clusters have a higher peak corner frequency resulting from energy contributed by smaller craters to the power spectrum we also find that the time separation between individual impacts in a cluster is small 100 hz to resolve individual impacts within the cluster two of the clusters in our database 20 m effective diameter would have been detectable by insight with the assumptions that the martian background noise and seismic attenuation are both low joint detection of surface changes from newly formed crater s in images and by insight will provide precise source locations that are crucial for constraining the internal structure of mars

a coupled field study of subsurface fracture flow and colloid transport field studies of subsurface transport of colloids which may act as carriers of contaminants are still rare this is particularly true for heterogeneous and fractured matrices to address this knowledge gap a 30 m long monitoring trench was constructed at the lower end of sloping farmland in central sichuan southwest china during the summer of 2013 high resolution dynamic and temporal fracture flow discharging from the interface between fractured mudrock and impermeable sandstone was obtained at intervals of 5 min for fast rising stages 30 60 min for slow falling stages or 15 min at all other times this discharge was analyzed to elucidate fracture flow and colloid transport in response to rainfall events colloid concentrations were observed to increase quickly once rainfall started 15 90 min and reached peak values of up to 188 mg l interestingly maximum colloid concentration occurred prior to the arrival of flow discharge peak i e maximum colloid concentration was observed before saturation of the soil layer rainfall intensity rather than its duration was noted to be the main factor controlling colloid response and transport dissolved organic carbon concentration and 6180 dynamics in combination with soil water potential were used to apportion water sources of fracture flow at different stages these approaches suggested the main source of the colloids discharged to be associated with the flushing of colloids from the soil mesopores and macropores beyond the scientific interest of colloid mobilization and transport at the field scale these results have important implications for a region of about 160 000 km 2 in southwest china that featured similar hydrogeologic settings as the experimental site in this agriculture dominated area application of pesticides and fertilizers to farmland is prevalent these results highlight the need to avoid such applications immediately before rainfall events in order to reduce rapid migration to groundwater via fracture flow in either dissolved form or in association with colloids c 2015 elsevier b v all rights reserved

seismic detection of meteorite impacts on mars abstract meteorite impacts provide a potentially important seismic source for probing mars interior it has recently been shown that new craters can be detected from orbit using high resolution imaging which means the location of any impact related seismic event could be accurately determined thus improving the constraints that could be placed on internal structure using a single seismic station this is not true of other seismic sources on mars such as sub surface faulting which require location using multiple seismic stations this study aims to determine the seismic detectability of meteorite impacts and assess whether they are a viable means of probing deep internal structure first we derive a relation between crater diameter and equivalent seismic moment based on observational data compiled from impact tests controlled explosions and earthquake seismology second this relation was combined with updated cratering rates based on newly observed craters to derive the impact induced seismicity on mars which we estimate to total 10 13 10 14 n m per year finally seismic waveform modelling was used to determine the detectability of these impacts based on reasonable assumptions about likely seismometer performance and background noise levels for our nominal noise instrument case we find that detectable impacts at teleseismic distances source receiver offsets greater than 60 are very rare and occur approximately once every 10 years for our most optimistic noise instrument case approximately one such event occurs each year this suggests that using solely meteorite impacts is not a reliable way of probing the martian interior although local impacts are more frequently detectable and could provide important constraints on near surface seismic properties

martian cratering vi crater count isochrons and evidence for recent volcanism from mars global surveyor this paper develops a methodology to establish absolute martian ages by deriving isochrons on a plot of martian impact crater density vs crater diameter calibrated by lunar crater age data the isochrons illustrated here are based on a mars moon cratering ratio of 1 6 at constant size but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages martian crater diameter distributions are determined in several areas down to diameter d 16 45 m the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by neukum the youngest areas studied here display the lunar like production function down to d 30 m where saturation equilibrium sets in model crater retention ages of several volcanic units are found to be a few hundred million years or less with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher the results are consistent with martian meteorite ages volcanism on mars has probably persisted into the last 10 to 15 of the planet s history and is likely ongoing because surfaces as young as a few hundred million years have reached crater saturation equilibrium at d 60 to 100 m mars is likely to have widespread impact produced regoliths at least a few meters deep and this may contribute to the widespread mobile dust and boulder fields of mars

colloid transport and remobilization in porous media during infiltration and drainage summary colloids are potential vectors of many contaminants in porous media understanding colloid transport is critical for assessing the migration of contaminants e g pathogens in the vadose zone in this study a series of column experiments were conducted to investigate the coupled effects of flow velocity water content and solution ionic strength on transport and remobilization of a model colloid montmorillonite clay in a model porous medium accusand during transient unsaturated flow and steady state saturated flow the unsaturated transport experiments included a series of infiltration and drainage pulses e g infiltration with colloids followed by drainage of colloid suspensions followed by infiltration with a colloid free solution and drainage of the solution saturated flow experiments included only the infiltration of the colloid and colloid free solutions tests were repeated for a variety of solution ionic strengths results showed that colloid transport was more sensitive to changes in solution ionic strength at low infiltration rates and the effect of infiltration rate was more significant at high ionic strength as a result increased flow velocities and water content resulting from high infiltration rates enhanced colloid transport and remobilization under ionic strength conditions e g 100 mm that would otherwise lead to strong colloid retention this observation conceptually suggests that chemical threshold values for preventing colloid movement in porous media might be larger for transient flow conditions than for uniform flow conditions in addition drainage was found to induce remobilization of the retained colloids suggesting transport of colloids even after termination of injection overall the study experimentally highlights the complicated interdependence of the effects of water content flow velocity and solution chemistry on colloid transport and remobilization