application of pair analysis statistics to aftershocks of the 1984 morgan hill california earthquake we apply statistical analysis based on pairs of earthquakes to study spatial and temporal patterns of earthquake distribution in the aftershock zone of the 1984 morgan hill california earthquake m 6 2 we examine 6 years of preshock and 23 months of aftershock data using frequency distributions of earthquake pairs the nonrandomness in the observed spatial and temporal distribution of pairs is studied by comparison with simulated expected distributions the significance of departures from the expected distributions is appraised by using tolerance limits that account for the scatter of the single trial expected frequencies we find that the eathquake spatial distribution is nonuniform in two major ways 1 short distance clustering distances less than 7 km occurs in both the preshock and aftershock period it is more pronounced and covers larger zones during the aftershock sequence 2 a long distance nonuniformity is also observed distances greater than 11 km caused by concentration of events in two areas separated by a gap in earthquake activity this feature is present in the preshock and early aftershock period but disappears in the late aftershock sequence the distribution of time intervals between preshocks does not indicate any substantial nonrandom features in contrast the temporal distribution of aftershocks although dominated by the classic power law decay in time suggests the possible existence of characteristic time intervals that increase with magnitude and time after the mainshock

an observational search for carbonates on mars a search for carbonates and other salts exposed on the surface of mars was undertaken by observing areas of the surface in the 2 6 m to 4 2 m spectral region using the university of hawaii 2 2 m telescope at the mauna kea observatory hawaii observations of four mars areas syrtis major hellas arabia and an area northeast of hellas were made on the night of september 19 1986 the reflectance spectra for two partially overlapping areas show a weak absorption band in the 3 8 m to 3 9 m region which is in the spectral region where carbonate absorptions appear 3 8 m to 4 0 m the mars area of overlap contains syrtis planum the spectral feature from about 3 76 m to 3 95 m is clearly shortward of and broader than the calcium carbonate band about 3 9 m to 4 0 m and is at a slightly shorter wavelength position than magnesium carbonate magnesite bands about 3 8 m to 3 96 m as measured in this study positive identification of this band cannot be made by us at this time measurements for two other mars areas show no evidence of carbonate or other bands if the band is due to absorptions in the mars surface material spectrum and if it is due to carbonates then the results imply about 3 to 5 wt of a carbonate such as magnesite on average in the upper few millimeters of the mars surface material over the two areas where the weak spectral feature appears we can place an upper limit of 3 to 5 wt calcium carbonate and about 5 wt magnesite for all areas observed the interpretations are based on laboratory measurements of the reflectance spectra of calcite and magnesite and their mixtures with palagonite effects of thermal emission on the detection of carbonates were also explored for a wide range of temperatures thermal effects are not sufficient to mask the presence of calcite in the 3 to 5 wt range theoretical reasoning strongly supporting the presence of carbonates as a component of the mars surface is reviewed these and earlier observations do not rule out carbonates below the surface in other locations as small outcrops or in concentrations of less than 3 to 5 of the areas observed

hyperspectral imaging of convective co2 ice clouds in the equatorial mesosphere of mars 1 a unique feature of the martian climate is the possibility for carbon dioxide the main atmospheric constituent to condense as ice co2 ice is usually detected as frost but is also known to exist as clouds this paper presents the first unambiguous observation of co2 ice clouds on mars these images were obtained by the visible and near infrared imaging spectrometer omega on board mars express the data set encompasses 19 different occurrences compositional identification is based on the detection of a diagnostic spectral feature around 4 26 m which is produced by resonant scattering of solar photons by mesospheric co2 ice particles in a spectral interval otherwise dominated by saturated gaseous absorption observed clouds exhibit a strong seasonal and geographic dependence concentrating in the near equatorial regions during two periods before and after northern summer solstice ls 45 and 135 radiative transfer modeling indicates that the 4 26 m feature is very sensitive to cloud altitude opacity and particle size thereby explaining the variety of spectra associated with the cloud images on two orbits the simultaneous detection of clouds with their shadow provides straightforward and robust estimates of cloud properties these images confirm the conclusions established from modeling clouds are thick with normal opacities greater than 0 2 in the near infrared and are lofted in the mesosphere above 80 km the mean radius of co2 ice crystals is found to exceed 1 m an unexpected value considering this altitude range this finding implies the existence of high altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles this statement is consistent with the cumuliform morphology of the clouds which may be linked to a moist convective origin generated by the latent heat released during co2 condensation

monitoring mars with the hubble space telescope 1990 1991 observations images of mars obtained using the planetary camera on the hubble space telescope during 1990 and 1991 are described and analyzed multispectral images of mars record the martian season between ls 348 and 60 corresponding to late winter and spring in the northern hemisphere the wavelengths of these observations varied between 230 nm in the ultraviolet and 890 nm in the near infrared we use these images to discuss atmospheric and polar phenomena to constrain the aerosols and ozone in the martian atmosphere and to compare surface albedo features within this data set as well as with previous observations two methods are used to constrain the opacity of the martian atmosphere comparisons of ultraviolet images with atmospheric scattering models and examination of contrast changes of surface features observed at visible wavelengths our observations are consistent with a mars which was quite different from the planet when it was viewed by viking we estimate an upper limit of 0 1 for equatorial dust opacity near vernal equinox compared to values of 0 4 to 0 5 measured in chryse by viking lander 1 later at ls 60 an upper limit of 0 2 was found for dust in the southern hemisphere except for suggestions of local dust activity near the north polar cap in late spring there was no visual evidence of dust storms on the planet the hartley band of ozone is within the f230w filter bandpass and the 230w 336w ratio is therefore sensitive to ozone high latitude ozone is observed at a concentration similar to that observed by mariner 9 a seasonal dependence in ozone concentration was observed with concentration decreasing at northern arctic latitudes and increasing at southern midlatitudes as ls increases from 350 to 60 despite the difference in dust loading the behavior of condensate clouds and the recession of the north polar cap are consistent with those observed during viking years late winter images of the north polar region reveal an active north polar hood with a maximum uv opacity of about 0 25 near 50 latitude the hood seems to have an annular form with the central polar regions having smaller opacity clouds observed in the northern hemisphere to the south of the hood boundary are suggestive of fronts similar to those observed during the mariner 9 mission a diurnal variation in the hood clouds which is anti correlated with the amount of water vapor in the atmosphere is noted spring images show significant clouds in the tharsis elysium and arabia regions the most optically thick components of these clouds are those near elysium alba patera and tithonius in the afternoon although these regions also are bright on the morning limb the cloud associated with elysium had the largest optical depth for a cloud in the uv 0 4 most of the hst monitoring sequences were targeted on the syrtis major region an area which was intensively studied during the viking mission during viking there were major changes in the region which were attributed to the two major 1977 global dust storms on mars our series of images was projected onto map grids and photometrically corrected in order to study changes in the syrtis albedo features to first order syrtis does not change over the time period of these observations as would have been expected if they followed major global dust storms during the preceding season images were deconvolved using the richardson lucy iterative algorithm to remove the defocussing effects of the spherical aberration of the hst primary even when mars subtended less than 5 arcsec in may 1991 the images were scientifically useful and comparable to photographic images obtained at opposition although the data are subject to the solar pointing constraint for hst the relatively slow movement of the allowed observation window which is more than one half martian year with respect to the martian seasons will permit us to address the question of major variations in the martian atmosphere

separation of a component of tectonic deformation from a complex magnetic fabric abstract a method has been developed for separation of the deformational component from a complex rock fabric for the separation data on the final measured fabric and the primary pre deformational fabric are necessary as input the primary fabric data are obtained either from measurements in terrains where gradual transitions from primary to deformational fabrics occur or in the case of magnetic anisotropy this may be obtained from data in the literature on individual rock types examples of the use of the method are presented for rocks from the nizk jesenik mountains of the ne bohemian massif

spectral imaging of martian water ice clouds and their diurnal behavior during the 1999 aphelion season ls 130 abstract we report high spectral resolution 800 2300 near infrared mapping observations of mars at ls 130 april 1999 which were obtained by drift scanning the cryogenic long slit spectrometer at the kpno 2 2 m telescope across the disk data were reformatted into calibrated spectral image cubes x y spanning 2 19 to 4 12 m which distinguish atmospheric co2 features solar lines and surface and aerosol features maps of relative band depth between 3 0 and 3 5 m trace water ice clouds and show the diurnal evolution of features in the persistent northern summer aphelion cloud belt which was mapped contemporaneously but at fixed local time by the mars global surveyor thermal emission spectrometer mgs tes cloud optical depth particle sizes and ice aerosol content were estimated using a two stream single layer scattering model with mie coefficients derived from recently published ice optical constants followed by a linear spectral deconvolution process a comparison of data and model spectra shows evaporating nighttime clouds in the morning followed by afternoon growth of a prominent orographic cloud feature on the west flank of elysium mons cloud optical depth at 3 2 m evolved to 0 28 0 13 and ice aerosol column abundance to 0 9 0 3 pr m in the afternoon column abundances as large as 0 17 pr m were retrieved in nonorographic clouds within the aphelion cloud band around midday these clouds exhibit a modest decline in optical depth during the afternoon results show that ice particle radii from 4 m exist in both cloud types however large particles dominate the spectra consistent with recent mgs tes emission phase function measurements of aphelion cloud aerosol properties

dust haze in valles marineris observed by hrsc and omega on board mars express 1 we present analysis of a bright haze observed inside valles marineris which formed in mid northern spring the data were collected by the high resolution stereo camera hrsc and the imaging spectrometer observatoire pour la mineralogie l eau les glaces et l activite omega aboard mars express this study provides a case example of the power of simultaneous multiple emission angle and hyperspectral imaging for study of aerosols and clouds in the martian atmosphere the haze appeared thinner after three days and disappeared in nine days it was limited to a 2 km layer at the bottom of the canyon the color was redder than the underlying surface the analysis of the omega spectra indicates that this haze was composed of dust particles the dust layer appeared brighter with the hrsc stereo channels than the nadir channel due to longer scattering paths we have estimated the optical depth of the haze by fitting both hrsc and omega data with radiative transfer calculations the retrieval of the optical depth is very sensitive to the aerosol scattering model used and the reflectance of the surface applying an aerosol scattering model derived from sky surveys at a constant elevation by the imager for mars pathfinder the optical depth of the haze is estimated from hrsc data to be within 1 7 to 2 3 at the wavelength of 0 675 m the wavelength dependence is obtained from omega spectrum it increases to 2 2 2 6 at 1 35 m and moderately decreases to 1 2 1 8 at 2 4 m

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

infrared spectral imaging of martian clouds and ices abstract multispectral images of mars taken at the nasa infrared telescope facility irtf near and at the 1995 opposition are used to identify and track its atmospheric clouds and ground ices band depth mapping is used to help distinguish between the composition of volatiles and provide a check for the techniques of principal components analysis pca and linear mixture modeling lmm pca lmm are used to create maps that track clouds and volatiles a technique that requires no a priori spectral information in order to create these maps band depth maps at 3 33 m which have been shown to trace co 2 frosts show some transient features which could indicate polar co 2 clouds at the time of these observations we show that band depth maps at 2 25 m are good tracers of h 2 o frosts and that band depth maps at 3 69 m can distinguish between coarse and fine grained water frosts these maps have allowed the detection of fine grained water frosts in the north polar region and along the morning and evening limb regions from the pca technique we find that just two principal components can account for over 99 of the data variance the first of these is an infrared albedo unit and the second is an ice thermal unit plotting the spectral data cubes in this new vector space we find that most of the martian disk can be modeled by spectrally mixing three endmember spectra having extreme values of these principal components the morning and evening regions of mars are composed of 40 60 of the north polar ice thermal component endmember indicating a frost component there consistent with the band depth mapping results with a combination of these techniques it is possible to not only identify the extensive martian clouds but to also determine composition these new results are particularly relevant in light of recent mars pathfinder descent temperature profile data that indicated upper atmosphere temperatures below the co 2 frost condensation point implying that co 2 ice clouds may be an important radiative component of the current martian climate

a martian general circulation experiment with large topography abstract a three layer general circulation model used to simulate the martian atmosphere is described and results are presented the model assumes a dust free pure c02 atmosphere and allows for a diurnally varying convective boundary layer smoothed martian topography and albedo variations are incorporated the simulation described is for the period near southern winter solstice season of the viking landings the zonally averaged circulation mass heat and momentum balances and properties of stationary and transient waves are described in some detail and are compared with results of previous simulations of the martian general circulation with related features of the earth s general circulation and with observed characteristics of the martian atmosphere the principal conclusions are the following 1 the simulated zonally averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of leovy and mintz 1969 and compares reasonably well wi

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

the state and future of mars polar science and exploration as the planet s principal cold traps the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of 10 6 km 2 and total as much as 3 4 km thick from the scarcity of superposed craters on their surface these layered deposits are thought to be comparatively young preserving a record of the seasonal and climatic cycling of atmospheric co 2 h 2o and dust over the past 10 5 10 8 years for this reason the martian polar deposits may serve as a rosetta stone for understanding the geologic and climatic history of the planet documenting variations in insolation due to quasiperiodic oscillations in the planet s obliquity and orbital elements volatile mass balance atmospheric composition dust storm activity volcanic eruptions large impacts catastrophic floods solar luminosity supernovae and perhaps even a record of microbial life beyond their scientific value the polar regions may soon prove important for another reason providing a valuable and accessible reservoir of water to support the long term human exploration of mars in this paper we assess the current state of mars polar research identify the key questions that motivate the exploration of the polar regions discuss the extent to which current missions will address these questions and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding

dynamic response of deep soft soil deposits under multidirectional earthquake loading the analysis of site response to earthquake is of great importance for seismic design of structure although it has long been recognized that the ground is simultaneously subjected to both horizontal and vertical motions during a real earthquake the effect of vertical motion is usually ignored in most site response analyses moreover some studies show that there are significant differences in site responses for saturated and unsaturated soil deposits and site response is influenced by variation of groundwater table therefore these factors should be considerably considered in the dynamic site response analysis based on the results of geological investigation as well as laboratory and field tests conducted in shanghai a deep geotechnical profile with a depth of 280 m is analyzed in this paper by using a verified fully coupled and inelastic finite element procedure a series of numerical analyses is carried out for a deep soft soil profile subjected to multidirectional earthquake loadings parameters of the model in the procedure are calibrated by field and laboratory tests numerical results demonstrate that the behavior of vertical amplification is quite different from the horizontal counterpart furthermore the use of a single horizontal component as seismic input in site response analysis neglecting the other horizontal component and the vertical one may result in considerable underestimation of site response variation of groundwater table brings about a profound effect on both vertical and horizontal motions its ratio the response spectra at ground surface and excess pore water pressure ratio the analysis can capture a more complete and fundamental aspects of ground response for preliminary seismic assessment

the influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks abstract magnetic fabrics of weakly deformed rocks are not simply correlated with the principal finite strain directions depositional magnetic fabrics persist at 30 shortening where the rocks are deformed by particulate flow grain boundary sliding rocks with a spaced stylolitic cleavage believed to be formed by pressure solution and shortened by 20 50 have maximum susceptibility parallel to the intersection of cleavage and bedding this type of magnetic fabric is attributed to the interference of a depositional magnetic fabric between cleavage surfaces with a tectonic magnetic fabric in the cleavage surfaces

interpretation of seismic vertical amplification observed at an array site strong ground motions were recorded at port island kobe by a borehole array during the 1995 hyogo ken nanbu kobe earthquake these records indicate that while the horizontal peak accelerations were reduced as seismic waves traveling from the bottom to the surface motions in the vertical direction were significantly amplified at the surface with peak value of 1 5 to 2 times larger than the horizontal components some studies have discussed local site effects on the horizontal motions whereas the available study on the vertical amplification is limited in this article we present a possible mechanism to explain the observed vertical amplification in detail we consider that the observed large vertical amplification is mainly associated with incomplete saturation of near surface soils which causes substantial amplification of p waves but does not affect the propagation of s waves based on the concept of homogeneous pore fluid and biot s theory of two phase media we discuss the characteristics of p wave velocity poisson s ratio and degree of saturation in shallow soil layers and show evidence of incomplete saturation of near surface soils at the array site we analyze a simple model to theoretically investigate the effects of saturation on vertical motion amplification the results show that the degree of saturation may produce substantial influence on the amplification both amplitude and frequency content using a solid fluid coupled finite element procedure we perform a simulation of the observed vertical motions at the array site by including the effects of saturation the results demonstrate the mechanism of large amplification caused by incomplete saturation of near surface layers the present study indicates that vertical component motions may significantly be affected by pore water saturation of soils suggesting that we may need to carefully examine the condition of saturation in the study of vertical site amplification manuscript received 24 may 1999

inverse magnetic fabric in carbonate bearing rocks abstract the observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric pole of bedding or schistosity is referred to as an inverse magnetic fabric the investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates that c axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones a mineralogical model based on the property of single domain grains to have a zero susceptibility parallel to their long axis is proposed however more complex cases are also encountered

horizontal and vertical motion at surface of a gassy ocean sediment layer induced by obliquely incident sv waves free gas is ubiquitous at shallow sediment depths of the continental margins of the worldwide oceans however theoretical study of the dynamic behavior of gassy seafloor under the action of earthquake has been rare in this paper a theoretical model for the analysis of the horizontal and vertical motion at the surface of a gassy ocean sediment layer induced by sv waves is developed based on the multiphase poroelasticity theory the marine sediment layer with finite thickness is assumed to between seawater and underlying elastic solid seabed the pores of sediment are filled by two compressible and viscous fluids i e liquid and gas the theoretical formulation is derived for the computation of horizontal and vertical motion in forms of displacement amplitudes displacement ratios and amplification coefficients which are defined as a function of incident angle wave frequency thickness of porous layer and saturation degree of sediment numerical results show that even a slight decrease of full saturation of the porous sediment may lead to significant influence on sediment s displacement amplitudes displacement ratios as well as the amplification coefficients apart from saturation degree this influence also depends on the incident angle wave frequency and thickness of sediment layer

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

chlorite control of correlations between strain and anisotropy of magnetic susceptibility abstract anisotropy of magnetic susceptibility ams has in the past been used as an indicator of finite strain mathematical relationships between the measured ams ellipsoid and the finite strain ellipsoid in slates are numerous the ordovician martinsburg formation at lehigh gap pennsylvania provides a unique opportunity to test this correlation as a complete shale to slate transition is preserved magnitudes of the principal susceptibility axes appear to reflect a strain gradient at this location apparent strain values derived from ams using equations from rathore and hrouda have x y z ratios from 2 79 1 87 0 19 shale to 2 92 0 82 0 42 slate the orientations of the susceptibility axes characterize two fabrics i k int k max planes at 20 to bedding and ii k int k max planes parallel to cleavage anisotropy of magnetic susceptibility fails to show any intermediate orientations of the principal susceptibility axes in the zone in which cleavage is developed comparison with phyllosilicate crystallographic orientations indicates that the ams intermediate and maximum susceptibility axes are parallel to chlorite basal planes because chlorite reoriented via dissolution and new growth as cleavage developed in this location and because models correlating ams and strain instead assume that strain is reflected by the rotation of the magnetic susceptibility carriers the apparent strain values calculated from ams reflect only the degree of dissolution and neocrystallization in these rocks and not the finite strain

synthetic magnetic fabrics in a plasticene medium mixtures of ferrimagnetic grains with a supporting medium of paramagnetic plasticene permit hypotheses concerning the interpretation of assemblages of different minerals to be confirmed the deformation of such plasticene mixtures in pure shear transpression and simple shear emphasize the dominance of the initial anisotropy over the end result for low strains 25 shortening in pure shear for minor amounts of multidomainal ferrimagnetic grains the deformation experiments indicate that the magnetic lineation rotates rapidly into the maximum extension direction for the three strain histories tested although the magnetic fabric directions are reliable kinematic indicators after modest strain in simple shear the symmetry of the fabric is not a plane strain fabric great discrepancies occur in the case of assemblages single domain femmagnetic grains in plasticene in pure shear these produce inverse fabrics in which the magnetic lineation spins towards parallelism with the maximum shortening direction

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

new near ir observations of mesospheric co2 and h2o clouds on mars 1 carbon dioxide clouds which are speculated by models on solar and extra solar planets have been recently observed near the equator of mars the most comprehensive identification of martian co2 ice clouds has been obtained by the near ir imaging spectrometer omega crism a similar instrument with a higher spatial resolution cannot detect these clouds with the same method due to its shorter wavelength range here we present a new method to detect co2 clouds using near ir data based on the comparison of h2o and co2 ice spectral properties the spatial and seasonal distributions of 54 crism observations containing co2 clouds are reported in addition to 17 new omega observations crism co2 clouds are characterized by grain size in the 0 5 2 m range and optical depths lower than 0 3 the distributions of co2 clouds inferred from omega and crism are consistent with each other and match at first order the distribution of high altitude 60 km clouds derived from previous studies at second order discrepancies are observed we report the identification of h2o clouds extending up to 80 km altitude which could explain part of these discrepancies both co2 and h2o clouds can exist at high mesospheric altitudes crism observations of afternoon co2 clouds display morphologies resembling terrestrial cirrus which generalizes a previous result to the whole equatorial clouds season finally we show that morning omega observations have been previously misinterpreted as evidence for cumuliform and hence potentially convective co2 clouds

factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments abstract the effect of magnetic interactions has been commonly neglected in the interpretation of the anisotropy of magnetic susceptibility ams of igneous rocks despite the likely occurrence of magnetic interactions due to their relatively high content of ferromagnetic minerals current models of magnetic interactions apply to highly simplified systems and are not directly applicable to natural rocks on this work a model that includes variables previously neglected is used to assess the relative importance of magnetically interactive and non interactive fractions in a rock results of the model show that a variable proportion of magnetically interactive grains the relative values of the bulk susceptibility degree of anisotropy and orientation of the anisotropies characteristic for each fraction all play an important role in controlling the rock ams experimental evidence illustrating the importance of the distribution of the ferromagnetic grains within a specimen is also reported and supports the model predictions both theory and experiments indicate that if a rock has unequant magnetic grains and clusters of magnetic grains the contribution to the ams of the rock will depend on the relative values of all the model variables and not only on the occurrence of magnetic interactions as previously presumed

effects of magnetic interactions in anisotropy of magnetic susceptibility models experiments and implications for igneous rock fabrics quantification besides granites of the ilmenite series in which the anisotropy of magnetic susceptibility ams is mainly controlled by paramagnetic minerals the ams of igneous rocks is commonly interpreted as the result of the shape preferred orientation of unequant ferromagnetic grains in a few instances the anisotropy due to the distribution of ferromagnetic grains irrespective of their shape has also been proposed as an important ams source former analytical models that consider infinite geometry of identical and uniformly magnetized and coaxial particles confirm that shape fabric may be overcome by dipolar contributions if neighboring grains are close enough to each other to magnetically interact on these bases we present and experimentally validate a two grain macroscopic numerical model in which each grain carries its own magnetic anisotropy volume orientation and location in space compared with analytical predictions and available experiments our results allow to list and quantify the factors that affect the effects of magnetic interactions in particular we discuss the effects of i the infinite geometry used in the analytical models ii the intrinsic shape anisotropy of the grains iii the relative orientation in space of the grains and iv the spatial distribution of grains with a particular focus on the inter grain distance distribution using documented case studies these findings are summarized and discussed in the framework of the generalized total ams tensor recently introduced by canon tapia canon tapia e 2001 factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments tectonophysics 340 117 131 the most important result of our work is that analytical models far overestimate the role of magnetic interaction in rock fabric quantification considering natural rocks as an assemblage of interacting and non interacting grains and that the effects of interaction are reduced by i the finite geometry of the interacting clusters ii the relative orientation between interacting grains iii their heterogeneity in orientation shape and bulk susceptibility and iv their inter distance distribution we reconcile analytical models and experiments with real case studies that minimize the role of magnetic interaction onto the measured ams limitations of our results are discussed and guidelines are provided for the use of ams in geological interpretation of igneous rock fabrics where magnetic interactions are likely to occur

magnetic fabric methods and applications fabric is a ubiquitous and significant feature of geological materials the processes involved in the formation and deformation of rocks and sediments leave their mark on the orientations of the constituent mineral grains petrofabrics thus provide essential keys to understanding the history of geological materials magnetic anisotropy is directly related to petrofabric and has become one of the most rapid sensitive and widely used tools for its characterization the relationship between magnetic fabric and petrofabric is complex and depends on various factors including the composition concentration and grain size of mineral grains ongoing research in geological applications is paralleled by studies of the fundamental mineral magnetic phenomena involved the papers in this book represent the current state of investigations in magnetic anisotropy studies as a discipline that integrates geological interpretations mineral fabric development technical advances and rock magnetic properties

formation of convective carbon dioxide clouds near the south pole of mars 1 observations from the mars orbiter laser altimeter mola indicate a distinct difference in the nature of north and south polar clouds the majority of north polar clouds are diffuse with relatively low optical extinction channel 4 clouds in contrast a significant number of south polar clouds provide very strong laser echoes suggesting optical extinction as high as 300 km 1 channel 1 clouds these high extinction clouds were almost exclusively observed in the polar night between 70 and 85 s we have previously shown that the low extinction clouds are composed of a small number of large carbon dioxide particles which form in relatively gentle updrafts or lee waves a possible explanation for the high extinction clouds is that they are composed of more but somewhat smaller carbon dioxide particles forming in high velocity convective updrafts numerical simulations using a microphysical cloud model show that the cloud extinction depends most strongly on the availability of ice nuclei in assumed to be dust and the updraft velocity radiative cooling by the co2 clouds can further destabilize the air column cloud extinction consistent with mola observations is produced for in concentrations greater than 5 cm 3 and updraft core velocities of 2 m s 1 the discrepancy in north and south cloud extinction may be the result of differing in concentrations and stability regimes between the north and south polar regions many channel 4 clouds may also be convective but formed in air with either low updraft velocities or low abundances of ice nuclei

detection and monitoring of h2o and co2 ice clouds on mars we have developed an observational scheme for the detection and discrimination of mars atmospheric h2o and co2 clouds using ground based instruments in the near infrared we report the results of our cloud detection and characterization study using mars near ir images obtained during the 1990 and 1993 oppositions we focused on specific wavelengths that have the potential based on previous laboratory studies of h2o and co2 ices of yielding the greatest degree of cloud detectability and compositional discriminability we have detected and mapped absorption features at some of these wavelengths in both the northern and southern polar regions of mars compositional information on the nature of these absorption features was derived from comparisons with laboratory ice spectra and with a simplified radiative transfer model of a co2 ice cloud overlying a bright surface our results indicate that both h2o and co2 ices can be detected and distinguished in the polar hood clouds the region near 3 00 m is most useful for the detection of water ice clouds because there is a strong h2o ice absorption at this wavelength but only a weak co2 ice band the region near 3 33 m is most useful for the detection of co2 ice clouds because there is a strong relatively narrow co2 ice band at this wavelength but only broad continuum h2o ice absorption weaker features near 2 30 m could arise from co2 ice at coarse grain sizes or surface dust minerals narrow features near 2 00 m which could potentially be very diagnostic of co2 ice clouds suffer from contamination by mars atmospheric co2 absorptions and are difficult to interpret because of the rather poor knowledge of surface elevation at high latitudes these results indicate that future ground based earth orbital and spacecraft studies over a more extended span of the seasonal cycle should yield substantial information on the style and timing of volatile transport on mars as well as a more detailed understanding of the role of co2 condensation in the polar heat budget

spatial variability in the seasonal south polar cap of mars we present the first comprehensive discussion of the south seasonal polar cap spectra obtained by the mariner 7 infrared spectrometer in the short wavelength region 2 4 m in addition we correlate the infrared spectra with images acquired by the wide angle camera significant spectral variation is noted in the cap interior and regions of varying water frost abundance co2 ice frost cover and co2 ice path length can be distinguished many of these spectral variations correlate with heterogeneity noted in the camera images but certain significant infrared spectral variations are not discernible in the visible we use simple reflectance models to classify the observed spectral variations into four regions region i is at the cap edge where there is enhanced absorption beyond 3 m inferred to be caused by an increased abundance of water frost the increase in water abundance over that in the interior is on the level of a few parts per thousand or less region ii is the typical cap interior characterized by spectral features of co2 ice at grain sizes of several millimeters to centimeters these spectra also indicate the presence of water frost at the parts per thousand level a third unusual region iii is defined by three spectra in which weak co2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the co2 such large paths are inconsistent with the high reflectance in the visible and at 2 2 m and suggest layered structures or deposition conditions that are not accounted for in current reflectance models the final region iv is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap these spectra are a combination of co2 and ground signatures

high resolution reflectance spectra of mars in the 2 3 μm region evidence for the mineral scapolite spatially resolved reflectance spectra of mars in the 2 2 to 2 4 m spectral region were obtained in august 1988 using the nasa 3 m infrared telescope facility the spectra show weak absorption features due to martian atmospheric carbon monoxide and a surface mineral both co and the mineral absorptions are composed of overlapping narrow features but in many locations such as hellas chryse eden and moab the mineral absorptions are quite strong at least 3 times stronger than at the most absorbing wavelengths of co near 2 33 m therefore co complicates the analysis of the surface mineral but does not always overwhelm its signature model removal of the martian atmospheric co has been performed and the remaining absorption bands are identified as scapolite relatively strong absorptions that match bands in the spectrum of scapolite and have little or no co absorption interference are seen near 2 41 2 39 and 2 29 m absorption also occurs at the scapolite bands at 2 36 and 2 33 m but the analysis is complicated by uncertainty in the atmospheric co removal at these wavelengths weaker scapolite bands are seen at 2 44 and 2 23 m where there is virtually no atmospheric interference the scapolite bands observed on mars are due to hco3 and hso4 ions in the scapolite structure the bicarbonate and bisulfate contents appear to vary with location the scapolite in hellas is more bisulfate rich relative to that in the chryse moab eden area other locations contain little arabia syrtis major hellespontica and isidis or no scapolite e g margaritifer ausonia and erythraeum the calculated abundances are unconstrained because the amounts of hco3 and hso4 in the martian scapolites as well as their grain sizes are not known if the scapolites contain about 3 wt of each near the maximum possible the scapolite abundances probably range from about 5 wt scapolite at eden and hellas 3 5 at chryse moab and oxia palus 2 3 at arabia syrtis major and isidis to less than 2 at hellespontica syrtis minor and margaritifer assuming a relatively large grain size of 50 100 m if the characteristic grain sizes are smaller or the hco3 and hso4 contents are lower the scapolite abundances required to match the observed band depths would be higher the mineral bands are apparent in many of the mars spectra measured so it appears to be widely but not uniformly distributed the newly observed fine structure also varies greatly in both depth and spectral detail with location on mars thus there appears to be regional variations in composition the mineral phases appear to reflect local or regional geology and are not primarily contained in the homogeneous globally redistributed aeolian dust higher spectral resolution martian spectra in the 2 3 m region as well as at 3 9 m are needed to confirm the scapolite identification and to constrain its abundance

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

anisotropy of magnetic susceptibility measurement schemes the precision of ams determination is enhanced by measuring susceptibility in directions with a uniform orientation distribution that include the four body diagonals some standard 10 5 cm samples with mean susceptibility 100 si possess too few magnetic grains for reliable petrofabric interpretation whatever the measurement strategy we should only interpret their ams if they pass fabric homogeneity tests

anisotropy of magnetic susceptibility in welded tuffs application to a welded tuff dyke in the tertiary trans pecos texas volcanic province usa consideration of published anisotropy of magnetic susceptibility ams studies on welded ignimbrites suggests that ams fabrics are controlled by groundmass microlites distributed within the existing tuff fabric the sum result of directional fabrics imposed by primary flow lineation welding and if relevant rheomorphism ams is a more sensitive indicator of fabric elements within welded tuffs than conventional methods and usually yields primary flow azimuth estimates detailed study of a single densely welded tuff sample demonstrates that the overall ams fabric is insensitive to the relative abundances of fiamme matrix and lithics within individual drilled cores ams determinations on a welded tuff dyke occurring in a choked vent in the trans pecos texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width the dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit followed by residual squeezing between the failed block and in situ wallrock irrespective of the precise mechanism widespread occurrence of both welded tuff dykes and point welded aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process

thermal emission spectra of mars 5 4 10 5 μm evidence for sulfates carbonates and hydrates we have obtained spectra of the thermal emission from mars in the 5 4 10 5 m wavelength domain at a resolving power of about 60 from the kuiper airborne observatory spectra were obtained for several large spots on mars whose ground temperatures and air masses through the martian atmosphere differed significantly these data were taken at two times during the flight by taking the ratio of the spectral flux from one spot to that of a second spot we obtained results that were independent of uncertainties in the instrument s spectral response and the transmission of the earth s atmosphere these data as well as spectral fluxes of single spots based using the star tau as a calibration standard show a number of emission and absorption features they are present in sets of spectra taken at two different times some of the absorption features are due to gaseous co2 in the martian atmosphere the remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface comparison of the strength of features seen at similar times but with three different air masses and ground temperatures suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere based on comparisons of the observed features with laboratory data for a broad ensemble of minerals spectra of other solar system bodies and relevant compositional information about mars we have made the following tentative identifications of the observed features emission features at 7 8 and 9 7 m are attributed to surface silicates an emission feature at 6 1 m is attributed to a molecular water component of the surface material an absorption band at 8 7 m as well as possibly one at 9 8 m is ascribed to sulfate or bisulfate anions probably located in a distorted crystalline site and an absorption band at 6 7 m is attributed to carbonate or bicarbonate anions located in a distorted crystalline site although we cannot totally rule out a nitrate origin for this feature we have simulated these spectra with radiative transfer programs for the atmosphere and surface these simulations indicate that the sulfate and carbonate bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals that the dust optical depth was about 0 6 at a reference wavelength of 0 3 m over the area of the observed spots and that sulfates and carbonates constitute about 10 15 and 1 3 by volume of the airborne dust respectively these results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current mars

observation of the biot slow wave in water saturated nivelsteiner sandstone acoustic signals are used extensively in the oil industry to determine the physical properties of reservoir rock in the interpretation of these signals empirical laws play a major role to obtain a more fundamental interpretation of the recorded wavetrains the need for a comprehensive theory for acoustic wave propagation and damping in rocks is obvious in this respect biot s 1956a b theory is a straightforward and effective two phase theory in contrast to biot who derived the macroscopic equations for wave propagation in saturated poro elastic material by postulating definite positive energy density functions burridge and keller 1981 whitaker 1986a b c and pride et al 1992 applied rigorous averaging techniques to derive the poro elastic equations from a microscale de vries 1989 and geerits 1996 used the averaging techniques to derive macroscopic poro elastic equations for the nonviscous case the fundamental feature of all these theoretical descriptions is the existence of both a fa

principal components analysis of mars in the near infrared abstract principal components analysis and target transformation are applied to near infrared image cubes of mars in a study to disentangle the spectra into a small number of spectral endmembers and characterize the spectral information the image cubes are ground based telescopic data from the nasa infrared telescope facility during the 1995 and 1999 near aphelion oppositions when ice clouds were plentiful clancy et al 1996 wolff et al 1999b and the 2003 near perihelion opposition when ice clouds are generally limited to topographically high regions volcano cap clouds but airborne dust is more common martin l j zurek r w 1993 j geophys res 98 e2 3221 3246 the heart of the technique is to transform the data into a vector space along the dimensions of greatest spectral variance and then choose endmembers based on these new trait dimensions this is done through a target transformation technique comparing linear combinations of the principal components to a mineral spectral library in general mars can be modeled on the whole with only three spectral endmembers which account for almost 99 of the data variance this is similar to results in the thermal infrared with mars global surveyor thermal emission spectrometer data bandfield j l hamilton v e christensen p r 2000 science 287 1626 1630 the globally recovered surface endmembers can be used as inputs to radiative transfer modeling in order to measure ice abundance in martian clouds klassen d r bell iii j f 2002 bull am astron soc 34 865 and a preliminary test of this technique is also presented

stress dilatancy behaviour of bubbled fine grained sediments abstract although the strength and stiffness of fine grained gassy soil have been relatively well characterised its dilatancy remains poorly understood this study aimed to understand and formulate the stress dilatancy behaviour of fine grained gassy soil through a series of triaxial tests 19 in total conducted on fine grained gassy specimens where different initial gas volume fractions 0 and initial pore water pressures uw0 were considered compared to the stress dilatancy relation of saturated fine grained soil the addition of gas bubbles was found to result in more contractive or dilative soil behaviour depending on the combination of 0 and uw0 these distinct features cannot be captured by the existing stress dilatancy functions for fine grained saturated soils which solely depend on the stress ratio therefore a new stress dilatancy function is proposed within the framework of critical state soil mechanics to quantify the distinct modification effects of bubbles which either suppress or enhance dilatancy on the dilatancy of gassy soils with different 0 and uw0 values in a unified manner this new function has been validated and can be readily implemented in critical state based constitutive models for predicting the shear behaviour of fine grained gassy soil and therefore the response of various offshore structures i e foundations and pipelines founded on a gas bearing seabed

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km