geomechanics of hydraulic fracturing microseismicity part 1 shear hybrid and tensile events we investigate the geomechanical behavior of hydraulic fracturing induced microseismicity microseismic events are commonly used to discern stimulation patterns and hydraulic fracture evolution however techniques beyond fracture mapping are required to explain the mechanisms of microseismicity in this series we present an approach to combine seismological and geomechanical techniques to investigate how microseismicity relates to propagating hydrofractures as well as existing natural fractures and faults part 1 describes the first analysis step which is to characterize the microseismic events by their source parameters focal mechanisms and fault plane orientations these parameters are used to determine the mechanical conditions responsible for activation of discrete populations or subpopulations of microseismic events that then can be interpreted in their geological and operational context first we compare microseismic fault plane populations from a mississippian barnett shale texas data set that are determined using a traditional double couple model shear only with a tensile source model hybrid events which may be more suitable for hydraulic fracturing conditions second we employ a new method to distinguish fault planes from auxiliary planes using iterative stress inversion and critical stress instability selection criteria the result is an enhanced microseismic characterization that includes geomechanical parameters such as slip tendency and local activation stress state during the operation using this approach on the barnett shale data two microseismic fault sets are resolved an inclined northeast southwest set with dominant shear and a vertical north south set with more hybrid behavior the results are used in part 2 to further investigate the heterogeneity of the stimulations and to compare models for microseismic activation

chemically striking regions on mars and stealth revisited 1 the mars odyssey gamma ray spectrometer suite has yielded global chemical information for mars in this work we establish regions of unusual chemical composition relative to average mars primarily on the basis of ca cl fe h k si and th using data from mars odyssey the mars exploration rovers the mars reconnaissance orbiter imaging and 3 5 cm and 1 35 cm radar observations from earth we examine a chemically striking 2 e6 km2 region and find it to overlap significantly with a radar stealth region on mars it is remarkably enriched in cl and depleted in fe and si along with minor variations in h k and th relative to average mars surface dust observed at the two rover sites mixed with and indurated by ca mg bearing sulfate salts would be a reasonable chemical and physical analog to meter scale depths we describe potential scenarios that may have contributed to the unique properties of this region the bulk dust component may be an air fall deposit of compositionally uniform dust as observed in situ hydrothermal acid fog reactions on the flanks of nearby volcanoes may have generated sulfates with subsequent deflation and transport alternatively sulfates may have been produced by low temperature regional scale activity of ground ice driven brine and or regional scale deposition of acidified h2o snowfall

the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

overview of the microscopic imager investigation during spirit s first 450 sols in gusev crater the microscopic imager mi on the mars exploration rover spirit has returned images of mars with higher resolution than any previous camera system allowing detailed petrographic and sedimentological studies of the rocks and soils at the gusev landing site designed to simulate a geologist s hand lens the mi is mounted on spirit s instrument arm and can resolve objects 0 1 mm in size or larger this paper provides an overview of mi operations data calibration processing and analysis of mi data returned during the first 450 sols mars days of the spirit landed mission the primary goal of this paper is to facilitate further analyses of mi data by summarizing the methods used to acquire and process the data the radiometric and geometric accuracy of mi data products and the availability of archival products in addition scientific results of the mi investigation are summarized mi observations show that poorly sorted soils are common in gusev crater although aeolian bedforms have well sorted coarse sand grains on their surfaces abraded surfaces of plains rocks show igneous textures light toned veins or fracture filling minerals and discrete coatings the rocks in the columbia hills have a wide variety of granular textures consistent with volcaniclastic or impact origins case hardening and submillimeter veins observed in the rocks as well as soil crusts and cemented clods imply episodic subsurface aqueous fluid movement which has altered multiple geologic units in the columbia hills the mi also monitored spirit s solar panels and the magnets on the rover s deck

stress orientations obtained from earthquake focal mechanisms what are appropriate uncertainty estimates crustal stress orientations provide important information about the mechanics of regional deformation numerous methods exist for inverting earthquake focal mechanisms for stress orientation and the more widely used methods usually obtain similar results for similar data sets however error estimates are highly variable complicating the interpretation of results the southern california stress field for example contains much statistically significant spatial and temporal variability according to the error estimates of one method michael 1984 1987b but very little according to those of another gephart and forsyth 1984 to resolve whether the southern california stress field is generally homogeneous or heterogeneous we must determine which of the error estimates best reflects the true inversion uncertainty to do this we tested both methods on a suite of synthetic focal mechanism data sets containing random errors the method of gephart and forsyth 1984 usually provides more accurate estimates of stress orientation especially for high quality data sets but its confidence regions are in most cases too large the method of michael 1984 1987b is more accurate for very noisy data sets and provides a more appropriate estimate of uncertainty implying that the stress field in southern california is probably heterogeneous

karst on mars the thumbprint terrain abstract some instances of the so called thumbprint terrain of the northern plains of mars may be caused by differential solution of large carbonate deposits occupying low lying areas and may represent an analog to the arid karst of the nullarbor plain in australia based on the comparative morphology of the two regions

a methodology for unstructured damped stress inversion of microseismic focal mechanisms application to the vaca muerta formation argentina current methodologies for stress inversion from microseismic focal mechanisms require the assignment of events to a regular grid and then solving for the stress state at each grid node this approach can lead to irregularities in the solution because some nodes may contain few or even no events to address this issue we modified the algorithm to solve for stresses on an irregular unstructured grid we first use the k means algorithm to split the data into suitably sized groups the centroids of these groups are then considered as the nodes of an unstructured grid and we simultaneously solve for the stress state in each group using damped inversion to account for the irregularity of the unstructured grid we use the reciprocal square distance between nodes as weights as opposed to the existing method in which a weight of unity is assigned between adjacent nodes on a regular grid focal planes are selected from the auxiliary plane using the fault instability criterion the method is first applied to synthetic data sets in which we simulate and subsequently invert for the stress field around a mode i fracture at depth in a strike slip and in a normal faulting stress regime results indicate a stress orientation error of 10 and a stress ratio error between 1 and 10 we then consider focal mechanism data from an unconventional shale play in the vaca muerta formation in argentina and our results suggest the presence of a preexisting strike slip faulting stress regime we also find that the unambiguous focal plane picks suggest that the apparent dip slip focal mechanisms are indeed dip slip movement along subvertical natural fractures which correlate well with image log data we suggest that these dip slip events are caused by stress changes induced by the opening of the hydraulic fractures

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

geomechanics of hydraulic fracturing microseismicity part 2 stress state determination we investigate the hydraulic fracturing process by analysis of the associated microseismicity in part 1 we recognized double couple and hybrid microseismic events and their fault plane orientations critical stress instability and stress inversion techniques were used to assess fracture activation conditions in part 2 we apply results from the tensile source model to investigate how activated faults relate to the stress state and geologic setting we assess potential mechanisms for induced microseismicity including leakoff and diffuse pressurized fracture network flow stress shadowing adjacent to large parent hydraulic fractures and crack tip stress perturbations data are from the mississippian barnett shale texas and include microseismic events from sequential pumping stages in two adjacent horizontal wells that were recorded in two downhole monitor wells as well as operations wellbore derived stress and natural fracture data results point to activation of inclined faults whose orientation is dominantly northeast southwest and vertical north south faults the activation stress states for a range of modeling scenarios show stress rotation decreased mean stress and increased deviatoric stress this stress state cannot be explained by sidewall leakoff in the stress shadow region adjacent to hydrofractures but is consistent with hybrid and shear activation obliquely ahead of pressurized fractures information about hydrofracture evolution and operationally related dynamic stress change is obscured by geomechanical heterogeneity that is likely geologic in nature the most compelling observation is that the most highly misoriented microseismic faults occur in the same vicinity as a carbonate dominated submarine fan feature that was previously expected to act as a minor fracture barrier

spatial variations in heavy minerals and patterns of sediment sorting along the nile delta egypt abstract sand samples were collected along 34 beach profiles spanning the 240 km length of the nile delta in order to examine the sorting patterns of heavy minerals that develop during cross shore and alongshore sediment transport factor analysis of the heavy mineral contents shows that two mineral factors or groups result from sorting due to the contrasting densities and sizes of the grains one factor is dominated by augite hornblende and epidote while the second factor consists of opaques garnet zircon rutile and monazite minerals of factor 1 are of lower densities and coarser sizes and represent the grains that are selectively entrained by waves and currents in areas of beach erosion and preferentially transported to zones of beach accretion where they are deposited the higher density minerals of factor 2 tend to become concentrated in areas of beach erosion accounting for the formation of black sand placers where the erosion has been greatest the spatial distributions of these two factors reflect the grain sorting patterns of the heavy minerals which coincide with the general trends of shoreline erosion versus accretion that exist along the length of the delta there is also a distinctive pattern of cross shore sorting with factor 2 containing the denser minerals being best developed within the inner surf zone generally with a maximum at the shoreline its development corresponds to the formation of black sand concentrates on the beach face where erosion has been greatest implying that grain sorting has taken place mainly within the swash zone there is a general decrease in factor 2 relative to factor 1 toward the offshore often with oscillations that are congruent with the beach topography factor 1 with the lower density minerals is greatest over offshore bars where deposition has prevailed

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

microseismic moment tensors a path to understanding frac growth microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process with sufficient resolution the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

chemical composition of martian soil and rocks complex mixing and sedimentary transport chemical compositions of martian soil and rocks indicate complex mixing relationships mixing of rock and soil clearly takes place and explains some of the chemical variation because sulfur chlorine magnesium and perhaps iron are positively correlated due to their control from a secondary sedimentary mineralogy e g mg and possibly fesulfate fe oxides that is present within the soils certain deviations from simple soil rock mixing are consistent with mineralogical fractionation of detrital iron and titanium oxides during sedimentary transport

are there carbonate deposits in the valles marineris mars the thick sequences of layered deposits found in the valles marineris have recently been determined by s s nedell s w squyres and d w andersen 1987 icarus 70 409 441 to contain a minimum of 105 km3 of material we suggest that this material could be derived from the precipitation of 30 mbar of atmospheric co2 as carbonates in lakes as surface temperatures fell on mars the presence of an insulating ice cover would have allowed liquid water to exist fed by transitory surface melting atmospheric co2 would have accumulated in such lakes enhancing carbonate precipitation support for this hypothesis comes from processes that occur in the perennially frozen lakes in the dry valleys of antarctica where the mean temperature is 253 k and the lake water is supersaturated with atmospheric gases a search of the recently reissued mariner 6 7 infrared spectrometer data in the wavelength region between 2 and 6 m failed to confirm the presence of carbonates due to the fact that no spectral footprints appear to directly overlie the layered deposits and that deposits may be blanketed by an eolian mantle this negative result is inconclusive we feel that the canyon deposits are still a prime site for future searches for carbonates on mars

mossbauer spectroscopy on the surface of mars constraints and expectations abstract mossbauer spectrometers will be included on the upcoming mer athena and mars express beagle rovers these instruments have the exciting potential to characterize the surface mineralogy of mars but there are several complicating factors it is difficult to differentiate minerals with similar structures particularly if the rock or soil is multimineralic and the peaks overlap mineral modes cannot be determined from mossbauer spectra alone the temperature dependence of mossbauer parameters for common rock forming minerals and glasses is known for only a few minerals but it is strong no database of mars surface temperature mossbauer spectra of minerals or glasses currently exists with which martian data can be compared peak areas in mossbauer spectroscopy do not directly correspond to the abundances of the minerals that give rise to them and the calibration correction factors to compensate for this problem are currently known for only a few minerals we assess here the advantages and disadvantages of mossbauer spectroscopy for remote data acquisition and describe work currently under way in our laboratory to address these potential complications

a tensile shear crack model for the mechanism of volcanic earthquakes abstract temporary seismic observations were carried out for about 1 month at miyakejima island on the izu bonin arc after an eruption on october 3 1983 more than 3000 seismic events were observed and they are classified into 4 different categories short period earthquakes long period earthquakes isolated tremors and continuous tremors two active source regions of the short period earthquakes were located along the old caldera rim of the miyakejima volcano one region was very close to the eruptive fissures another was about 1 2 km northwest of the fissures almost all the earthquakes in the former region showed dilatant first motions of p waves at all the stations in the island on the other hand almost all events in the latter region showed compressive first motions of p waves at all the stations the first motions of p waves for these earthquakes cannot be explained by the quadrant type pattern due to a double couple force system nucleation of a tensile crack coupled with a shear crack a tensile shear crack model is proposed as a source mechanism of the short period earthquakes moment tensor elements of tensile and shear cracks have been determined by the least squares method using observed p and s wave data results suggest that tensile cracking opening or closing is dominant for generating those earthquakes in comparison with shear cracking the strikes of the tensile cracks for the earthquakes are shown to be nearly parallel to the strike of the fissures the earthquakes that occurred in the northwestern region of the fissures are considered to be generated by a sudden opening of tensile shear cracks due to the excess pressure of intrusive magma in contrast the earthquakes occurring beneath the fissures are probably generated by a sudden closing of tensile shear cracks and this suggests that the magmatic pressure under the fissures rapidly decreased after the eruption moment tensor analysis of the tensile shear crack model in this study demonstrates the non double couple source mechanism for volcanic earthquakes related to magmatic activity

soil grain analyses at meridiani planum mars 1 grain size analyses of the soils at meridiani planum have been used to identify rock sources for the grains and provide information about depositional processes under past and current conditions basaltic sand dust millimeter size hematite rich spherules interpreted as concretions spherule fragments coated partially buried spherules basalt fragments sedimentary outcrop fragments and centimeter size cobbles are concentrated on the upper surfaces of the soils as a lag deposit while finer basaltic sands and dust dominate the underlying soils there is a bimodal distribution of soil grain sizes with one population representing grains 125 m and the other falling between 1 4 5 mm soils within craters like eagle and endurance show a much greater diversity of grain morphologies compared to the plains the spherules found in the plains soils are approximately 1 2 mm smaller in size than those seen embedded in the outcrop rocks of eagle and endurance craters the average major axis for all unfractured spherules measured in the soils and outcrop rocks is 2 87 1 18 mm with a trend toward decreasing spherule sizes in both the soils and outcrop rocks as the rover drove southward wind ripples seen across the plains of meridiani are dominated by similar size 1 3 1 7 mm hematite rich grains and they match in size the larger grains on plains ripples at gusev crater larger clasts and centimeter size cobbles that are scattered on the soils have several spectral and compositional types reflecting multiple origins the cobbles tend to concentrate within ripple troughs along the plains and in association with outcrop exposures

an updated global review of solutional weathering processes and forms in quartz sandstones and quartzites abstract quartz is considered one of the less soluble minerals of the earth s crust and thus hardly affected by chemical weathering despite this for more than forty years it is clear that the formation of caves and peculiar solutional weathering dominated landforms in quartz rich lithologies is common and shares several similarities to the well known karstic ones in carbonate rocks in the last thirty years great strides have been made in furthering our knowledge of the distribution of these forms around the world and the geochemical processes involved these studies have clearly shown that solutional weathering is a fundamental process acting through intergranular dissolution of quartz increasing the rock porosity and decreasing the rock strength to erosion this process has been described in the concepts of arenization and phantomization and the widespread evidences of the fundamental role of quartz solution in landform genesis has even developed to the extent of several geomorphologists reassessing the definition of the term karst and its application to these peculiar lithologies nonetheless the process is complicated by several factors related both to environmental conditions water chemistry and availability as well as to the compositional and textural characters of the lithology presence of clays iron hydroxides carbonate cement etc all these aspects have to be taken carefully in consideration in order to understand if solution is a dominant or accessory process in the landscape evolution in this review the state of knowledge on the relevant chemical processes weathering mechanisms and speleogenesisk involved in the surface and underground karstification and clear examples of quartz solution and solutional landforms from different world locations are outlined and discussed

shear and tensile earthquakes caused by fluid injection 1 we apply rock mechanics concepts to the seismological observations in order to explain why during hydraulic injection some events display tensile and some shear deformation the presence of non shear components depends on the differential stress and the fracture orientation with respect to the 1 direction provided the slip vector is parallel to the traction we define four types of earthquakes according to the ratio of the shear and tensile components assuming a griffith failure envelope hybrid events containing both shear and tensile components can occur for fractures striking within 22 5 of 1 we argue that pure tensile fractures striking parallel to 1 are unlikely in the presence of natural fractures the low shear traction of tensile events also implies their small stress drops by applying the analysis to two different data sets soultz sous forets and cotton valley we show that different orientations of natural fractures and differential stress in the targeted formations made each region favorable for different non dc components in the injection induced seismicity

geochemistry of martian soil and bedrock in mantled and less mantled terrains with gamma ray data from mars odyssey 1 surficial materials including soil and dust are abundant in the upper tens of centimeters of the martian surface sensed by the mars odyssey gamma ray spectrometer grs seven large areas 14 of the martian surface that represent possible compositional end members were selected including three regions heavily mantled with surficial materials the selection process included mapping the ratio of exposed rocky terrain to surficial materials using high resolution imagery grs data for h cl fe si k and th were obtained for each area the areas are chemically homogeneous within each area given the spatial resolution and analytical uncertainty of the grs data however substantial chemical differences exist among the areas including the different mantled terrains contrary to earlier assumptions that surficial materials are globally homogeneous due to aeolian mixing the observed chemical differences among the areas may be due to variations in the protolith compositions extent of alteration of the protolith regions or post soil formation processes the abundances of cl k and th in rockier but still soil rich areas such as syrtis major planum can be explained by mixing between a soil with higher concentrations of cl k and th similar to the abundances in the mantled terrains and some of the landing sites and crustal rocks containing lower abundances of these elements similar to martian meteorites

inversion of seepage channels based on mining induced microseismic data abstract water inrush in mines has always been a major technical problem restricting the safe production of mines with abundant water seepage channels formed by fractures in rock masses provide the necessary conditions for water inrush to occur effectively controlling the formation of fractures in rock masses is essential for preventing water inrush disasters in response to the shortcomings of conventional water inrush monitoring methods a set of methods for the inversion of seepage channels in rock masses based on mining induced microseismic ms data was proposed in this paper a discrete fracture network dfn was built based on moment tensor mt theory and a method for extracting reasonable fractures associated with different failure mechanisms was proposed to enhance the applicability of the fractures derived from ms data ms derived fractures the ms derived fractures were transformed into a graph structure by graph theory subsequently the hydraulic properties of each node and edge in the graph structure were obtained based on darcy s law in addition the fluid flow time in the ms derived fractures was weighted to detect the shortest seepage channel finally the method was applied to a mine that experienced a water inrush disaster the seepage channel formation process water pressure distribution and main seepage channel in the study area of the mine were analyzed the results may provide references for decision makers regarding when and where to implement water shutoff measures in mines

geochemical evolution of the northern plains of mars early hydrosphere carbonate development and present morphology it is likely that early in mars history abundant liquid water was available under a thick several bars carbon dioxide atmosphere this water could have formed an ocean located primarily in the lowlands of the northern hemisphere an equilibrium geochemical model of this ocean and its interactions with the atmosphere and regolith of mars was developed and the results of this model were used to discuss the evolution of the volatile budget of mars including the deposition of large carbonate beds on the northern plains differential solutional weathering of these carbonate beds may have caused the formation of some of the enigmatic features seen on the northern plains of mars such as the thumbprint terrain and enclosed depressions

identification delineation and morphometric analysis of closed terrain depressions on mars abstract the purpose of this paper is to introduce an easy to use but powerful methodology that allows closed terrain depressions on the mars landscape to be correctly identified and delineated from digital elevation models closed terrain depressions have important implications for the geology and geomorphology of mars where they have been formed by the processes of impact subsidence collapse trickle down of unconsolidated material tensional tectonic forces dissolution and erosion the application of the procedure to six test sites covering a representative range of mars landscapes shows that closed depressions are ubiquitous on mars from the southern highlands where they cover 37 of the surface to the northern lowlands where they cover 26 of the surface the minimum coverage of 9 occurs on the tharsis dome around the three giant tharsis volcanoes a power law distribution which is directly related to the fractal dimension is shown to provide a very good fit to the size distribution of mars depressions in addition to the fractal dimension several other morphometric parameters are calculated to demonstrate the use of the methodology in planetary geology the work presented here uses digital elevation models provided by the mars orbiter laser altimeter mola the resolution of which limits the identification of terrain depressions to those that have diameters greater than around 460 m the methodology is however general and can be applied to smaller scale depressions that are available in detailed digital elevation models obtained from high resolution images such as the high resolution imaging science experiment hirise mounted on the mars reconnaissance orbiter this opens up a wide range of applications using the simple but powerful methodology described in this paper

geochemistry of 4 vesta based on hed meteorites prospective study for interpretation of gamma ray and neutron spectra for the dawn mission asteroid 4 vesta believed to be the parent body of the howardite eucrite and diogenite hed meteorites will be investigated by the dawn orbiting spacecraft dawn carries a gamma ray and neutron detector grand that will measure and map some major and trace element abundances drawing on hed geochemistry we propose a mixing model that uses element ratios appropriate for the interpretation of grand data because the spatial resolution of grand is relatively coarse the analyzed chemical compositions on the surface of vesta will likely reflect mixing of three endmember components diogenite cumulate eucrite and basaltic eucrite reliability of the mixing model is statistically investigated based on published whole rock data for hed meteorites we demonstrate that the mixing model can accurately estimate the abundances of all the grand analyzed major elements as well as of minor elements na cr and mn not analyzed by this instrument we also show how a similar mixing model can determine the modal abundance of olivine and we compare estimated and normative olivine data for olivine bearing diogenites by linking the compositions of well analyzed hed meteorites with elemental mapping data from grand this study may help constrain the geological context for hed meteorites and provide new insight into the magmatic evolution of vesta

discriminating induced seismicity from natural earthquakes using moment tensors and source spectra earthquake source mechanisms and spectra can provide important clues to aid in discriminating between natural and induced events in this study we calculate moment tensors and stress drop values for eight recent induced earthquakes in the western canadian sedimentary basin with magnitudes between 3 2 and 4 4 as well as a nearby magnitude 5 3 event that is interpreted as a natural earthquake we calculate full moment tensor solutions by performing a waveform fitting procedure based on a 1 d transversely isotropic velocity model in addition to a dominant double couple dc signature that is common to nearly all events most induced events exhibit significant non double couple components a parameter sensitivity analysis indicates that spurious non dc components are negligible if the signal to noise ratio snr exceeds 10 and if the 1 d model differs from the true velocity structure by less than 5 estimated focal depths of induced events are significantly shallower than the typical range of focal depths for intraplate earthquakes in the canadian shield stress drops of the eight induced events were estimated using a generalized spectral fitting method and fall within the typical range of 2 to 90 mpa for tectonic earthquakes elastic moduli changes due to the brittle damage production at the source presence of multiple intersecting fractures dilatant jogs created at the overlapping areas of multiple fractures or non planar pre existing faults may explain the non dc components for induced events

stress tensor inversion using detailed microearthquake information and stability constraints application to olfus in southwest iceland using detailed microearthquake data we present a stress tensor inversion scheme with new methods for selecting the fault planes and allowing for errors in the focal mechanisms the nonuniqueness of earthquake focal mechanisms is accounted for in our inversion scheme through the introduction into the inversion of a range of well fitting focal mechanisms for each event the range of focal mechanisms significantly improves the quality of the estimated stress tensor relative localization of clusters of microearthquakes is used to obtain information about which nodal plane could be correct fault plane the clusters frequently fall on a common fault plane and if there are acceptable focal mechanisms where one nodal plane has orientation similar to the common plane we assume this is the correct fault plane for the event if there is no predefined fault plane we utilize a simple mohr coloumb failure criterion to obtain a physical choice of fault plane between the two nodal planes in the focal mechanism the nodal plane with highest relative instability is chosen as the fault plane differences between the instability and the standard slip angle criterion are investigated the new inversion scheme has been applied to microearthquake data from the olfus area in the vicinity of the southwest iceland triple junction we estimate an oblique strike slip state of stress maximum horizontal stress at n30 e and minimum horizontal stress at n60 w with significant normal faulting influence the instability fault selection criterion predicts very well the orientation of faults mapped by relative localization

mars regolith versus snc meteorites possible evidence for abundant crustal carbonates abstract viking xrf analyses of the martian regolith are compared with typical igneous rocks of the earth the moon the eucrite parent asteroid and especially the shergottites nakhlites and chassigny snc meteorites which are suspected to be basalts and mafic cumulates from mars a striking feature of the martian regolith compared to igneous rocks with similar molar mg fe si ratios is its extraordinarily low ca si ratio the regolith s low ca si ratio is probably not a result of simple mixing isochemical weathering of snc like rocks with other igneous rocks unless the regolith contains a large component of rock with an improbable combination of extremely low ca si and mg fe si and yet low k 2 o and zr several other models might conceivably account for the low ca si ratio but i suggest that most of the missing ca was removed from the regolith as ca carbonate formation of a mass of carbonate equivalent to a global shell 20 m thick would suffice to remove 1000 mbar of co 2 from the martian atmosphere thus the peculiar ca si ratio of the martian regolith tends to support the hypothesis that the climate of mars was once far warmer and wetter than it is today

geochemical and mineralogical indicators for aqueous processes in the columbia hills of gusev crater mars 1 water played a major role in the formation and alteration of rocks and soils in the columbia hills the extent of alteration ranges from moderate to extensive five distinct rock compositional classes were identified the order for degree of alteration is watchtower clovis wishstone peace backstay the rover s wheels uncovered one unusual soil paso robles that is the most s rich material encountered clovis class rocks have compositions similar to gusev plains soil but with higher mg cl and br and lower ca and zn watchtower and wishstone classes have high al ti and p and low cr and ni peace has high mg and s and low al na and k backstay basalts have high na and k compared to plains adirondack basalts and paso robles soil has high s and p some rocks are corundum normative indicating that their primary compositions were changed by loss and or gain of rock forming elements clovis materials consist of magnetite nanophase ferric oxides npox hematite goethite ca phosphates ca and mg sulfates pyroxene and secondary aluminosilicates wishstone and watchtower rocks consist of fe oxides oxyhydroxides ilmenite ca phosphate pyroxene feldspar mg sulfates and secondary aluminosilicates peace consists of magnetite npox mg and ca sulfates pyroxene olivine feldspar apatite halides and secondary aluminosilicates paso robles consists of fe3 mg ca and other sulfates ca phosphates hematite halite allophane and amorphous silica columbia hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks volcaniclastic materials and or impact ejecta by solutions that were rich in acid volatile elements

chemical compositions at mars landing sites subject to mars odyssey gamma ray spectrometer constraints 1 the mars odyssey gamma ray spectrometer grs is the first instrument suite to return elemental abundances throughout the midlatitudes of mars concentrations of cl fe h k si and th have been determined to tens of centimeter depths as mass fractions with reasonable confidence comparing such data with or normalizing them to in situ compositional data is difficult due to issues such as dramatic differences in spatial resolution difficulties in convolving densities abundances and compositions of different regolith components and a limited number of elements observed in common we address these concerns in the context of the grs using si at pathfinder to normalize remote data in addition we determine representative in situ compositions for spirit both with and without columbia hills rocks opportunity and viking 1 landing sites using grs derived h content to hydrate the soil component our estimate of the si mass fraction at pathfinder with 13 areal fraction of rocks is 21 the composition of major elements such as si and fe is similar across the four landing sites while minor elements show significant variability areal dominance of soil at all four landing sites causes representative compositions to be driven by the soil component while proportionally large uncertainties of bulk densities dominate the net uncertainties grs compositional determinations compare favorably with the in situ estimates for cl and k and for si by virtue of the normalization however the grs determined fe content at each landing site is consistently higher than the in situ value

mixing relationships and the effects of secondary alteration in the wishstone and watchtower classes of husband hill gusev crater mars 1 the wishstone and watchtower class rocks on husband hill preserve evidence for a geochemical relationship consistent with two component mixing between a high al 2 o 3 tio 2 cao na 2 o p 2 o 5 end member and a second end member enriched in the elements mgo zn s br and cl the first end member appears to be reasonably well represented by rocks of the wishstone class while the second end member is consistent with a chemical component not represented by any lithology encountered by spirit the watchtower class appears to be an intermediate in the mixture the concentration of the redox sensitive elements fe and mn display no systematic variation between rock classes and the fe redox state of the watchtower class is elevated relative to the wishstone class combined with evidence for two component mixing these observations suggest that the mixture was generated by interaction between an initially wishstone like deposit and a fluid phase enriched in the elements mgo zn s br and cl the fluid phase may have been weakly acidic ph 4 to basic ph 9 resulting in oxidation and immobilization offe and mn a number of secondary rock surface alteration processes which obscure the mixing relationship are also identified these include 1 removal of cao and p 2 o 5 from rock surfaces by dissolution of ca phosphate minerals under acidic low water to rock ratio conditions 2 addition of so 3 to rock surfaces via aeolian deposition of high so 3 soil and or precipitation of sulfate salts from solution and 3 homogenization of rock surface chemistry by soil contamination

a refined methodology for stress inversions of earthquake focal mechanisms we develop an improved methodology for reliable high resolution inversions of focal mechanisms to background stress field orientation and stress ratio r in two or three dimensions the earthquake catalog is declustered to remove events likely affected strongly by local stress interactions rather than reflecting the large scale background stress field the declustered data are discretized with the k means algorithm into groups containing a number of focal mechanisms between a minimum number nmin and 2nmin synthetic tests indicate that nmin 30 provides stable inversion results under different stress regimes and noise conditions when r 0 5 while nmin 45 is needed for r near 0 or 1 additional synthetic tests compare the performance of selecting the fault plane of each focal mechanism using a the plane with lowest misfit angle between the slip vector from the focal mechanism and shear traction from the stress tensor and b the plane with highest instability coefficient representing proximity to the optimally oriented fault for given stress field and friction coefficient the instability criterion is found to provide more accurate inversion results under all tested stress regimes stress ratios and noise conditions the refined inversion methodology combines selecting fault planes using the instability criterion iteratively with a damped simultaneous inversion of different focal mechanism groups results characterizing neighborhoods of discretized domains merged during the damped inversion provide high resolution information independent of the discretization some aspects of the methodology are illustrated with focal mechanism data from the san jacinto fault zone in southern california

sedimentary deposits in the northern lowland plains mars the lowland plains on mars have surfaces marked by large polygonal fracture patterns it was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels we support this hypothesis because of the following observations 1 polygonal fracture patterns tend to occur in low areas on mars that apparently received influx of sediments the area of northern plains in which the fractures occur also forms a regional low 2 the fracture patterns are concentrated near reentrants of the plains projecting into the southern highlands not only are these reentrants associated with outflow channels but channels and polygonally fractured deposits have similar ages 3 sinuous ridges at the mouths of martian outflow channels resemble ridges in antarctic ice streams and ice shelves the similarity suggests that the martian material was transported from the southern highlands toward the northern plains as the antarctic material is transported from the continent toward the adjacent ocean overall it appears that a massive transfer of material took place midway in martian history either through the outflow channels or elsewhere along the northern highland scarp and that this material probably formed the deposits now characterized by polygonal fracture patterns

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

the matter of size on the moment magnitude of microseismic events abstractwe investigated the method of estimating seismic moment and moment magnitude for microseismic events we determined that the m0t defined by bowers and hudson is the proper scalar moment to be used in microseismic studies for characterizing the size of an event and calculating its moment magnitude for non double couple sources the proportional relationship between body wave amplitude and seismic moment in the brune model breaks down so under such situations the brune model is not an appropriate way to estimate the seismic moment and magnitude moreover the s wave alone is not sufficient for determining the total seismic moment instead the p wave must be analyzed an example barnett shale data set was studied and the results concluded that the magnitudes estimated with the brune model could be off by as much as 1 92 with an absolute average of 0 35 the moment magnitudes based on the scalar moment m0t also gave a significantly different event size distribution and b value estimation finall

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

geology and landscape evolution of the hellas region of mars hellas basin on mars has been the site of volcanism tectonism and modification by fluvial mass wasting and eolian processes over its more than 4 b y existence our detailed geologic mapping and related studies have resulted in the following new interpretations the asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low angle bolide having a trajectory heading s60 e during the late noachian the basin was infilled perhaps by lava flows that were sufficiently thick 1 km to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin at about the same time deposits buried northern malea planum which are interpreted to be pyroclastic flows from amphitrites and peneus paterae on the basis of their degraded morphology topography and the application of a previous model for pyroclastic volcanism on mars peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma whereas amphitrites is a less distinct circular feature surrounded by a broad low dissected shield that suggests generally smaller volume eruptions during the early hesperian a 1 to 2 km thick sequence of primarily fined grained eolian material was deposited on the floor of hellas basin subsequently the deposit was deeply eroded except where armored by crater ejecta and it retreated as much as 200 300 km along its western margin leaving behind pedestal craters and knobby outliers of the deposit local debris flows within the deposit attest to concentrations of groundwater perhaps in part brought in by outflow floods along the east rim of the basin these floods may have deposited 100 200 m of sediment subduing wrinkle ridges in the eastern part of the basin floor during the late hesperian and amazonian eolian mantles were emplaced on the basin rim and floor and surrounding highlands their subsequent erosion resulted in pitted and etched plains and crater fill irregular mesas and pedestal craters local evidence occurs for the possible former presence of ground ice or ice sheets 100 km across however we disagree with a hypothesis that suggests that the entire south rim and much of the floor of hellas have been glaciated orientations of dune fields and yardangs in lower parts of hellas basin follow directions of the strongest winds predicted by a recently published general circulation model gcm transient frost and dust splotches in the region are by contrast related to the gcm prediction for the season in which the images they appear in were taken

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

induced stresses and fault potential in eastern canada due to a realistic load a preliminary analysis summary in order to understand the causal relation between postglacial rebound and earthquakes a simple disc load model is used to 1 calculate stresses induced in the lithosphere and mantle by glacial loading melting and postglacial rebound and 2 evaluate the effect of glacial loading rebound on the failure potential for earthquakes in the upper crust the dependence of the failure potential and the actual mode of failure on the coefficient of friction the ambient tectonic stress magnitude direction the stress due to the overlying rocks and lithospheric thickness are investigated prominent features of this paper are the inclusion of 1 a viscoelastic mantle and thus the migration of stress and 2 the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field it is assumed that throughout the earth there are optimally oriented pre existing virtual faults that are initially close to but not at failure thus a time dependent quantity called dfsm related to the coulomb mohr failure criterion can be defined such that a negative value of dfsm would advocate faulting or earthquake activities whereas a positive value of dfsm would promote stability the results indicate that under all combinations of tectonic stress magnitude and overburden stress crustal loading promotes fault stability directly underneath the load upon the removal of the load thrust faulting is predicted within the ice margin if the horizontal stress s induced by the overburden is greater than or equal to the vertical component s of the overburden stress 121 where sjs under this condition theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation if the horizontal stress induced by the overburden is less than the vertical component of the overburden stress 1 l then theory predicts fault stability within the ice margin the theory predicts fault instability both north and south of the ice margin the mode of failure however is completely determined by the value of i the trade off between the tectonic stress magnitude and the overburden stress parameter 1 is also investigated it is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of 1 the results of this analysis show that variations in the coefficient of friction lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions

determination of the tectonic stress tensor from slip along faults that obey the coulomb yield condition a new method to calculate the stress tensor associated with slip along a population of faults is derived here the method incorporates two constraints first the stresses in the slip direction satisfy the coulomb yield criterion and second the slip occurs in the direction of maximum shear stress along the fault the computations provide the complete stress tensor normalized by the vertical stress and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting the present method is applied to three field cases dixie valley nevada wadi neqarot israel and yuli microearthquakes taiwan it is shown that the coefficieet of friction of the three cases varies between 0 1 to 0 8 further it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults

mixing relationships in the martian regolith and the composition of globally homogeneous dust abstract comparison of the chemical compositions of martian soils reveals distinct mixing trends resulting from admixture of variable amounts of sulfate chloride cement at viking landing sites and of the local andesitic rock fragments at the mars pathfinder site these trends most easily visualized in plots of oxides versus so 3 intersect approximately at a common composition thought to represent a global dust that has been homogenized by pervasive aeolian activity the source rocks that were weathered to produce the global dust are inferred to have been basalts rather than felsic rocks based on the observation that the dust lies along well established chemical weathering trends for terrestrial basalts the basaltic protolith was chemically similar e g high fe mg low al 2 o 3 to basaltic shergottite meteorites chemical changes during the weathering of martian basaltic rocks are apparently not as drastic as in terrestrial weathering perhaps because of evaporation of hydrous fluids that leave soluble components behind in the residue comparison with chemical trends for previously proposed martian soil formation mechanisms suggests that palagonitization of basalts more readily explains the dust composition than do hydrothermal alteration at higher temperatures or reactions of rocks with an acid fog produced by volcanic exhalations local or temporal processing of dust into soil involves not only cementation by salts and mixing with rock fragments but also chemical fractionations of fe 2 o 3 tio 2 presumably resulting from aeolian sorting by grain size and density if the global dust represents a broad average of the martian surficial or upper crustal composition the planet s surface geology is dominated by basaltic volcanic rocks and evaporitic salts

focal mechanisms in anisotropic media summary focal mechanisms of seismic sources in anisotropic media are more complicated than in isotropic media planar shear faulting produces pure double couple dc mechanism in isotropy but generally non double couple non dc mechanism in anisotropy the non dc mechanism can comprise both the isotropic iso and compensated linear vector dipole clvd components the amount of the iso and clvd components depends on strength and symmetry of anisotropy and on the orientation of faulting shear faulting in anisotropy generates a pure dc mechanism provided that faulting is situated in symmetry planes of orthorhombic or of higher anisotropy symmetries the fault plane solution i e the orientation of the fault normal and the slip direction can be retrieved from the seismic moment tensor and from elastic parameters describing anisotropy at the source numerical modelling shows that shear faulting in anisotropic rocks present in the earth crust the earth mantle or in the subduction zones can produce mostly mechanisms with the clvd up to 30 per cent and with the iso up to 15 per cent the fault plane solutions calculated under the assumption of isotropy typically deviate from the true solutions by an angle of 5 to 10

non double couple earthquakes of 1997 january in west bohemia czech republic evidence of tensile faulting summary a mixed family of double couple dc and non double couple non dc earthquakes was observed during the 1997 january earthquake swarm in west bohemia which is a geothermal region typical for the occurrence of earthquakes swarms the dc and non dc earthquakes occurred within a small area of less than 1 km 3 on faults of different orientations the stress in the area is determined from focal mechanisms and attains values plunge azimuth 1 33 156 2 48 20 3 23 262 with a shape ratio of r 0 69 0 15 the error in the stress directions plunge azimuth is up to 5 10 the absolute stress values were estimated to be 1 350 mpa 2 220 mpa and 3 162 mpa the lithostatic stress is 250 mpa the stress analysis shows that the dc earthquakes occurred on optimally oriented faults with high shear traction but the non dc earthquakes occurred on misoriented faults with low shear traction the percentage of the dc in earthquakes clearly correlates with the magnitude of shear traction high low dc is associated with high low shear traction this indicates that the type of faulting is probably controlled by tectonic stress and that the non dc earthquakes are not related to pure shear faulting but may combine shear and tensile faulting the tensile faulting is manifested by positive isotropic and compensated linear vector dipole components the tensile faulting is conditioned by high pore fluid pressure which was estimated to be approximately 244 mpa the fluid pressure is less than the lithostatic stress by 5 mpa the ratio of the fluid pressure to the maximum compressive stress is 0 7

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

soil sedimentology at gusev crater from columbia memorial station to winter haven 1 a total of 3140 individual particles were examined in 31 soils along spirit s traverse their size shape and texture were quantified and classified they represent a unique record of 3 years of sedimentologic exploration from landing to sol 1085 covering the plains unit to winter haven where spirit spent the martian winter of 2006 samples in the plains unit and columbia hills appear as reflecting contrasting textural domains one is heterogeneous with a continuum of angular to round particles of fine sand to pebble sizes that are generally dust covered and locally cemented in place the second shows the effect of a dominant and ongoing dynamic aeolian process that redistributes a uniform population of medium size sand the texture of particles observed in the samples at gusev crater results from volcanic aeolian impact and water related processes

a 3 5 ga record of water limited acidic weathering conditions on mars abstract the secondary mineral budget on earth is dominated by clay minerals al hydroxides and fe oxides which are formed under the moderate ph high water to rock ratio conditions typical of earth s near surface environment in contrast geochemical analyses of rocks and soils from landed missions to mars indicate that secondary mineralogy is dominated by mg fe ca sulfates and fe oxides this discrepancy can be explained as resulting from differences in the chemical weathering environment of earth and mars we suggest that chemical weathering processes on mars are dominated by 1 a low ph sulfuric acid rich environment in which the stoichiometric dissolution of labile mineral phases such as olivine and apatite fe ti oxides is promoted and 2 relatively low water to rock ratio such that other silicate phases with slower dissolution rates e g plagioclase pyroxene do not contribute substantially to the secondary mineral budget at the martian surface under these conditions al mobilization is limited and the formation of significant al bearing secondary phases e g clays al hydroxides al sulfates is inhibited the antiquity of rock samples analyzed in situ on mars suggest that water limited acidic weathering conditions have more than likely been the defining characteristic of the martian aqueous environment for billions of years

non double couple mechanisms of microearthquakes induced by hydraulic fracturing 1 we have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the carthage cotton valley east texas gas field with vertical arrays of four and eight three component geophones in two monitoring wells respectively we were able to reliably determine source mechanisms of the strongest events with the best signal to noise ratio our analysis indicates predominantly non double couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation our observations suggest the induced events are directly the result of opening cracks by fluid injection in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

a bayesian approach to estimating tectonic stress from seismological data summary earthquakes are conspicuous manifestations of tectonic stress but the non linear relationships between the stresses acting on a fault plane its frictional slip and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress moreover observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations however by assuming that each earthquake in a small volume of the crust represents a single uniform state of stress the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated here we outline a probabilistic bayesian technique for estimating tectonic stress directions from primary seismological observations the bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation we show our bayesian formulation to be equivalent to a well known analytical solution for a single errorless focal mechanism observation the new approach has the distinct advantage however of including 1 multiple earthquakes 2 fault plane ambiguities 3 observational errors and 4 any prior knowledge of the stress field our approach while computationally demanding in some cases is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters such as seismic anisotropy and geodetic strain rate observations and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations

constraints on the strength of the upper crust from stress inversion of fault slip data the coefficient of friction of small faults in the field are estimated here by stress inversion of fault slip data the small faults that were measured in israel and the grand canyon arizona are considered as representing natural friction experiments the stresses associated with the faulting are determined by a stress inversion method which incorporates the coulomb failure criterion reches 1987 the coefficients of friction determined for 27 fault clusters in limestone sandstone and basalt range from 0 0 to 1 3 with mean value of 0 58 0 37 these values are in general agreement with the friction of 0 6 0 85 determined from laboratory experiments the magnitudes of the calculated principal stresses are compared with in situ stress measurements in similar tectonic environments

the reliability of microseismic moment tensor solutions surface versus borehole monitoring abstractsource mechanisms of microseismic events resolved as moment tensor solutions usually are obtained using either surface monitoring arrays which appear to obtain mechanisms with high shear components or borehole arrays which tend to constrain more variable mechanisms with higher tensile components however the corresponding reliability of the solutions remains unclear synthetic tests are therefore conducted to compare the reliability of moment tensor solutions from surface and two and three well borehole arrays based purely on geometry moment tensor inversion is carried out for synthetically generated amplitudes with added random noise and the bias and variance in the solutions are calculated for the surface array all inversions are able to constrain reliable results with negligible bias and low variance whereas borehole geometries with two wells produce reliable results only when including p and s wave amplitudes recorded on three components in the inversion as is usual surface a

global spectral classification of martian low albedo regions with mars global surveyor thermal emission spectrometer mgs tes data 1 martian low albedo surfaces defined here as surfaces with mars global surveyor thermal emission spectrometer mgs tes albedo values 0 15 were reexamined for regional variations in spectral response low albedo regions exhibit spatially coherent variations in spectral character which in this work are grouped into 11 representative spectral shapes the use of these spectral shapes in modeling global surface emissivity results in refined distributions of previously determined global spectral unit types surface types 1 and 2 pure type 2 surfaces are less extensive than previously thought and are mostly confined to the northern lowlands regional scale spectral variations are present within areas previously mapped as surface type 1 or as a mixture of the two surface types suggesting variations in mineral abundance among basaltic units for example syrtis major which was the surface type 1 type locality is spectrally distinct from terrains that were also previously mapped as type 1 a spectral difference also exists between southern and northern acidalia planitia which may be due in part to a small amount of dust cover in southern acidalia groups of these spectral shapes can be averaged to produce spectra that are similar to surface types 1 and 2 indicating that the originally derived surface types are representative of the average of all low albedo regions

grid mapping the northern plains of mars geomorphological radar and water equivalent hydrogen results from arcadia plantia a project of mapping ice related landforms was undertaken to understand the role of sub surface ice in the northern plains this work is the first continuous regional mapping from ctx context camera 6 m pixel malin et al 2007 imagery in arcadia planitia along a strip 300 km across stretching from 30 n to 80 n centred on the 170 west line of longitude the distribution and morphotypes of these landforms were used to understand the permafrost cryolithology the mantled and textured signatures occur almost ubiquitously between 35 n and 78 n and have a positive spatial correlation with inferred ice stability based on thermal modelling neutron spectroscopy and radar data the degradational features into the ldm latitude dependent mantle include pits scallops and 100 m polygons and provide supporting evidence for sub surface ice and volatile loss between 35 70 n in arcadia with the mantle between 70 78 n appearing much more intact pitted terrain appears to be much more pervasive in arcadia than in acidalia and utopia suggesting that the arcadia study area had more wide spread near surface sub surface ice and thus was more susceptible to pitting or that the ice was less well buried by sediments correlations with ice stability models suggest that lack of pits north of 65 70 n could indicate a relatively young age 1ma however this could also be explained through regional variations in degradation rates the deposition of the ldm is consistent with an airfall hypothesis however there appears to be substantial evidence for fluvial processes in southern arcadia with older underlying processes being equally dominant with the ldm and degradation thereof in shaping the landscape

regional and grain size influences on the geochemistry of soil at gusev crater mars 1 congruous with earlier work martian soil along the spirit rover s traverse at gusev crater can be divided into three broad groups by size fines 150 m sand and a mix of various grain sizes the key chemical observation is greater homogeneity in fines relative to the other two consistent with regional and global scale sampling of chemical compositions by finer particle sizes the mix class is generally more heterogeneous as are samples from the columbia hills within each class variation in the trace element ni is consistent with a ci contribution not exceeding 3 while that of ti is compatible with fe ti oxide enrichment not exceeding 3 physical mixing models are poorly supported among many potential binary and three component mixing models only two show some consistency with the soil data typical fines with the opaline si end member identified at home plate and typical fines with sulfates bearing a variable mix of ca fe and mg cations we also infer that binary mixing transcends classes contrasting strongly with terrestrial sediments and that mixing trends are consistent with significant nonmixing contributions perhaps including localized chemical alteration the decoupling between chemistry and grain size classes also suggests that processes linking composition with grain size such as heavy mineral sorting may have been minimal or absent entirely the primary exception to this is the correlation between cl and si cl s and al si which is strongest in the fines class

geochemical properties of rocks and soils in gusev crater mars results of the alpha particle x ray spectrometer from cumberland ridge to home plate 1 geochemical diversity of rocks and soils has been discovered by the alpha particle x ray spectrometer apxs during spirit s journey over husband hill and down into the inner basin from sol 470 to 1368 the apxs continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission germanium has been added to the spirit apxs data set with the confirmation that it occurs at elevated levels in many rocks and soils around home plate twelve new rock classes and two new soil classes have been identified at the spirit landing site since sol 470 on the basis of the diversity in apxs geochemistry the new rock classes are irvine alkaline basalt independence low fe outcrop descartes outcrop similar to independence with higher fe and mn algonquin mafic ultramafic igneous sequence barnhill volcaniclastic sediments enriched in zn cl and ge fuzzy smith high si and ti rock elizabeth mahon high si ni and zn outcrop and rock halley hematite rich outcrop and rock montalva high k hematite rich rock everett high mg magnetite rich rock good question high si low mn rock and torquas high k zn and ni magnetite rich rock new soil classes are gertrude weise very high si soil and eileen dean high mg magnetite rich soil aqueous processes have played a major role in the formation and alteration of rocks and soils on husband hill and in the inner basin

mineralogy of volcanic rocks in gusev crater mars reconciling mossbauer alpha particle x ray spectrometer and miniature thermal emission spectrometer spectra 1 complete sets of mineral abundances for relatively unaltered volcanic or volcaniclastic rocks in gusev crater have been determined by modeling mossbauer subspectral areas as mineral weight percentages and combining those percentages with the proportions of iron free minerals not detected by mossbauer normative plagioclase apatite and chromite as calculated from alpha particle x ray spectrometer apxs chemical analyses comparisons of synthetic thermal emission spectra calculated for these mineral modes with measured miniature thermal emission spectrometer mini tes spectra for the same rock classes show either good agreements or discrepancies that we attribute to sodic plagioclase compositions or unmodeled sulfate glass or pigeonite the normative compositions of olivine pyroxene and feldspar calculated from apxs data are consistent with spectroscopic constraints on mineral compositions systematic variations between olivine abundances in apxs norms which sample tens of micrometers depth and olivine proportions measured by mossbauer which sample hundreds of micrometers depth support the hypothesis that dissolution of olivine by acidic fluids has occurred on weathered rock surfaces

non double couple earthquake mechanisms at the hengill grensdalur volcanic complex southwest iceland the hengill grensdalur area in iceland generates frequent small non double couple earthquakes with explosive volumetric components we collected high quality three component digital recordings of 4 000 earthquakes on a purpose designed 32 station network in 1991 and determined focal mechanisms for 100 of the best recorded earthquakes by inverting amplitude ratios many of the mechanisms are consistent within the errors with simultaneous shear and tensile faulting with tensile faults parallel to the local spreading ridge and shear faulting similar to that in the south iceland transform fault zone some events cannot be explained by this model however and require other processes such as crack closing and partial compensation of tensile cracks by fluid flow

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes