microseismic signatures of non linear pore fluid pressure diffusion summary most fractured porous rocks show a strong dependence of their fluid transport properties on the effective pressure and thus on the pore fluid pressure we investigate the case where the hydraulic transport properties are exponentially dependent on pore fluid pressure as a consequence the process of pore fluid pressure diffusion is governed by a non linear diffusion equation solutions of this equation that describe fluid injection experiments are analysed and the associated microseismic signatures are explored in particular it is shown that this process of non linear pore fluid pressure diffusion allows us to define two signatures one which is the triggering front corresponding to the triggering of microseismic events without changing the fluid transport properties significantly the other signature is the so called fracturing domain it triggers the majority of microseismic events and alters the fluid transport properties significantly evidence for the microseismic signature of a fracturing domain at the fenton hill hydrofrac experiment is given

optical scattering properties of terrestrial varnished basalts compared with rocks and soils at the viking lander sites basalt flows at the pisgah volcanic field california are mantled by aeolian silt sized deposits the bright mantle is overlain by a dense pavement of basalt cobbles smoothed by aeolian abrasion and coated with glossy dark gray and red desert varnishes in contrast the two viking landing sites on mars lack desert pavements and rocks have glossy surfaces that in some cases are brighter than soils to pursue further the scattering characteristics of varnished basalt cobbles for comparison to mars rocks laboratory measurements of bidirectional reflectance 0 69 m center wavelength were made as a function of incidence and emission angle along the principal plane for varnished and fresh basalt surfaces the reflectance data fit with a scattering model that includes specular reflections from rough surfaces and volume penetration and reflection show that the red varnished surfaces have higher single scattering albedoes and higher surface roughness values than the dark gray varnished surfaces 0 56 and 0 42 21 and 17 respectively fresh cut surfaces have lowest values 0 40 and 6 results are consistent with observations made from thin sections for these surfaces and with field observations that show dark gray varnished surfaces are smoothed by exposure to wind abrasion dark red varnished surfaces tend to be rougher because they are embedded in the aeolian mantle and develop in a protected environment application of the model to atmospherically corrected radiometrically calibrated viking lander images 0 60 to 0 74 m shows that many rocks are smoother and have single scattering albedoes higher than soils 9 versus 27 0 71 versus 0 63 respectively results are consistent with a model in which rocks at the surface of mars become smoothed by aeolian abrasion and coated with atmospheric dust lack of desert pavement on mars is probably associated with a scarcity of cobbles and a lack of soil forming processes similar bright smooth coatings are expected at other locations on mars including the pathfinder ares vallis site

hubble space telescope observations of the martian aphelion cloud belt prior to the pathfinder mission seasonal and interannual variations the presence of a globally extant equatorial belt of water ice clouds on mars is quantitatively investigated using data from three seasons of our hubble space telescope synoptic monitoring program 1993 1997 a subset of the 1996 1997 images covers the landing site of the mars pathfinder including a set of images taken after touchdown using multicolor imaging from the wide field planetary camera and the wide field planetary camera 2 we characterize both water ice cloud and dust optical depths as a function of latitude at several local times for each observing epoch the analysis technique models calibrated data using a multiple scattering radiative transfer code our results support the initial results of clancy et al 1996a regarding changes between the aphelion and perihelion climate of mars and provide a more detailed look at the development and decay of the cloud belt comparing our dust optical depths to those of the viking landers for the same seasons we note a trend toward lower dust loading in late northern winter and in spring our observations of the pathfinder site in july 1997 reveal a dust opacity in good agreement with that reported by pathfinder smith et al 1997b in addition the serendipitous occurrence of a dust storm in valles marineris in late june 1997 allows us to derive a set of dust single scattering albedos for use in more accurately modeling the dust s radiative properties and effects

martian surface properties indicated by the opposition effect abstract opposition measurements made by the viking orbiter television cameras in the arabia syrtis major and elysium planitia regions have been combined with observations previously reported to provide a photometric comparison of these areas and several generic features radiative transfer expressions were used to derive average surface particle single scattering albedos phase functions and porosities best functional fit to the data includes consideration of atmospheric scattering two particle populations and surface roughness several findings include the ubiquitous presence of high albedo high porosity surface particles the absence of an opposition surge in the syrtis major region and the largest surface roughness in the chryse areas

submillimeter scale topography of the lunar regolith we have applied computer stereophotogrammetry to apollo lunar surface closeup camera alscc pictures of the lunar surface to construct the first ever digital topographic relief maps of undisturbed lunar soil over spatial scales from 85 m to 8 5 cm using elevation histograms fractal analysis and hapke s photometric roughness model we show that apollo 14 fra mauro imbrium ejecta is rougher than average apollo 11 mare tranquilitatis and apollo 12 oceanus procellarum mare surfaces at submillimeter to decimeter size scales we confirm the early result of k lumme et al 1985 earth moon planets33 19 29 that the cumulative distribution of elevations for lunar soil is typically well described by gaussian statistics however cumulative distributions are insensitive to asymmetries in the shapes of elevation histograms of 11 discrete elevation histograms we measured about half exhibit significant deviations from gaussian behavior we also confirm lumme et al s finding that the roughnesses of all lunar surfaces increase with decreasing size scale we further show that the scale dependence of roughness is well represented by fractal statistics the rates of change of roughness with size scale represented by fractal dimension d are remarkably similar among terrians after correcting for the contribution of large scale roughness our average value of d 2 31 0 06 falls within the range 2 0 d 2 4 reported from lunar radar studies the amplitude of roughness which we characterize with the rms slope angle at 1 mm scale varies significantly among terrains for lunar mare the average rms slope angle is 16 4 3 and that for fra mauro regolith is 25 1 by comparison to radar data we suggest that the roughness of fra mauro imbrium ejecta regolith is similar to that of lunar highland terrains we find that the gaussian slope distribution assumed in b w hapke s model 1984 icarus59 41 59 adequately describes typical lunar regolith surfaces a revised form of hapke s equation that models realistic particle phase functions and the coherent backscatter opposition effect was fitted to disk resolved lunar photometric observations and yields estimates of 27 1 for highland and 24 1 for mare regolith these values of as well as the implied relative highland mare photometric roughness ratio are best matched in our elevation data by the cummulative contributions of surface topography covering all scales greater than 0 1 mm less than 5 of the photometrically detected roughness of lunar regolith is contributed by surface relief at scales larger than 8 cm this conclusion implies that values of derived from whole disk and disk resolved photometry respectively may be taken to represent the same physical quantity in addition particulate samples used in goniophotometric measurements should not be assumed to be photometrically smooth i e 0 as is often done in laboratory applications of hapke s photometric model the predicted photometric roughness at size scales of 0 1 mm and less significantly exceed photometric estimates and suggests that there exists a measurable size scale below which topographic relief either is not photometrically detectable or is not represented in the hapke model as macroscopic roughness

near infrared imaging of mars from hst surface reflectance photometric properties and implications for mola data abstract we report initial results from hubble space telescope hst images of mars obtained at a near ir wavelength of 1042 nm between february 1995 and june 1997 the images provide the highest spatial resolution global near ir measurements of mars obtained to date the data have been calibrated to radiance factor i f to an absolute accuracy of 2 to 5 including new refinements to several hst calibration parameters and now exist as a set of coregistered map projected images spanning a range of phase angles between 10 and 41 the relatively high spatial resolution 20 30 km pixel global maps when compared with viking era global albedo maps reveal that substantial variations in mars surface albedo patterns have occurred in the past 20 years the most obvious changes include several classical dark regions that have become substantially brighter and a few formerly bright regions that have darkened the normal albedo of typical surface regions in the near ir is derived from the multiple phase angle observations and is found to be bimodal with typical bright and dark values of 0 36 and 0 18 respectively the surface near ir phase coefficient ranges from 0 0 to 0 013 mag deg and there is no systematic correlation between phase coefficient and normal albedo this observation is consistent with the diffusely scattering nature of the martian atmosphere even during times of low dust opacity the data presented here may facilitate the planning and optimization of measurements to be obtained by the mars global surveyor mgs mars orbiter laser altimeter mola which will begin mapping the planet in 1999 these hst data also provide a basis for comparison with future mola and mars orbiter camera moc data in searches for seasonal and interannual variations in surface and polar cap albedo

mars aerosol studies with the mgs tes emission phase function observations optical depths particle sizes and ice cloud types versus latitude and solar longitude 1 emission phase function epf observations taken in 1999 2001 by mars global surveyor thermal emission spectrometer mgs tes support the broadest study of martian aerosol properties to date tes solar band and infrared ir spectral epf sequences are analyzed to obtain first time seasonal latitudinal distributions of visible optical depths particle sizes and single scattering phase functions this combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45 s 45 n type 1 ice clouds exhibit small particle sizes reff 1 2 m and a distinctive backscattering increase they are most prevalent in the southern hemisphere during aphelion but also appear more widely distributed in season and latitude as topographic and high altitude 20 km ice hazes type 2 ice clouds exhibit larger particle sizes reff 3 4 m a distinct side scattering minimum at 90 100 phase angles characteristic of a change in particle shape relative to the type 1 and appear most prominently in the northern subtropical aphelion cloud belt the majority of retrieved dust visible to ir optical depth ratios are indicative of reff 1 5 0 1 m consistent with pathfinder and viking mariner 9 reanalyses however increased ratios 2 7 versus 1 7 appear frequently in the northern hemisphere over ls 50 200 indicating substantially smaller dust particles sizes reff 1 0 0 2 m at this time in addition larger reff 1 8 2 5 m dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm detailed spectral modeling of the tes visible band pass indicates agreement of epf derived dust single scattering albedos 0 92 0 94 with the spectrally resolved results from pathfinder observations

global color variations on io abstract visible and near infrared images of io from the galileo spacecraft reveal a surface more colorful than previously thought red yellow green white and black hues decorate the satellite presumably caused by a varied composition of sulfur compounds and silicates almost a third of io is covered by red and orange materials particularly at polar latitudes above 30 these red regions were scarcely distinguishable in the shorter wavelength voyager observations bright red pyroclastic deposits mark the locations of many hot spots plumes and visible surface changes providing a prominent flag of recent volcanic activity io s equatorial regions are dominated by yellow materials which occupy about 40 of the satellite s surface white and gray materials cover about 27 of io primarily in equatorial areas and in localized deposits at high latitudes these are identified with moderate to coarse grained so2 as mapped by the nims instrument on galileo r w carlson et al 1997 geophys res lett 24 2479 2482 greenish yellow materials in small isolated spots on io s anti jupiter hemisphere were recently discovered in 3 km pixel color imaging from orbit 14 unlike other ionian terrains these regions have a negative near infrared spectral slope suggesting contamination by a nonsulfur component only about 1 4 of io s surface is occupied by dark materials which display a variety of visible colors ranging from black to red and green most dark spots have a shallow spectral absorption feature at 0 9 m suggesting magnesium rich silicates rather than black sulfur little large scale alteration in the global color and albedo pattern has occurred between the voyager and galileo eras 90 of the surface appears unchanged despite the vigorous volcanic activity which must have taken place in the intervening 17 years this suggests that over a time scale of decades the bulk of io s resurfacing is restricted to a few small but persistently active areas

consistent trends in the true triaxial strength and deformability of cores extracted from icdp deep scientific holes on three continents abstract an extensive true triaxial testing program was carried out on core samples from three icdp sponsored deep scientific boreholes ktb germany safod united states and tcdp taiwan the three rocks differ in the processes that formed them and in many of their mechanical properties however all three rocks exhibited similar failure mechanism in which induced or reopened microcracks are primarily aligned with the 1 2 plane and the developed fault is steeply inclined in the 3 direction rock strength in all tested rocks increases with 2 when 3 is kept constant thus the common mohr type criteria which ignore the effect of 2 typically underestimate rock strength rather a 3d criterion that involves all three principal stresses represents well experimental results fracture plane slope for the same 3 steepens as 2 rises contrary to mohr type criteria with respect to deformation the onset of dilatancy increases with 2 in conclusion true triaxial tests conducted on cores from three scientific boreholes revealed important details of mechanical behavior not otherwise observed in conventional triaxial tests in addition they show mechanical behavior similarities as related to 2 effect regardless of rock type

voyager photometry of europa abstract ninety voyager images ranging in phase angle from 3 to 143 and covering the spectral range from 0 34 to 0 58 m were analyzed to derive the photometric properties of europa at small phase angles the disk integrated phase curve is remarkable in that it shows little or no evidence of an opposition effect in agreement with earlier earth based observations by millis and thompson icarus 26 408 1975 the phase integral determined in the voyager clear filter centered near 0 47 m is 1 09 0 11 in good agreement with previous estimates based on radiometry the bolometric bond albedo is 0 62 0 14 the scattering properties of europa in general and of the two major terrain types bright plains and darker mottled terrain in particular cannot be represented by a lunar like photometric law however an equation which is a linear superposition of a lunar like scattering law and a lambert component provides an adequate simple representation of the scattering properties the plains are photometrically more homogeneous than the darker mottled terrain in the voyager clear filter the average normal reflectance is 0 71 for the plains on both the leading and trailing hemispheres for the darker mottled terrain the values are 0 60 on the leading hemisphere and 0 48 on the trailing one

galileo photometry of asteroid 243 ida galileo imaging observations over phase angles 19 5 to 109 8 are combined with near opposition earth based data to derive the photometric properties of ida to first order these properties are uniform over the surface and well modeled at 0 55 m by hapke parameters 0 0 22 h 0 020 b0 1 5 g 0 33 and 18 with corresponding geometric albedop 0 21 0 030 01and bond albedoab 0 081 0 0170 008 ida s photometric properties are more similar to those of average s asteroids p helfenstein and j veverka 1989 asteroids ii univ of arizona press tucson than are those of 951 gaspra two primary color units are identified on ida terrain a exhibits a spectrum with relatively shallower 1 m absorption and a relatively steeper red spectral slope than average ida while terrain b has a deeper 1 m absorption and a less steep red slope the average photometric properties of ida and terrain a are similar while those of terrain b differ mostly in having a slightly higher value of 0 0 22 versus 0 21 suggesting that terrain b consists of slightly brighter more transparent regolith particles galileo observations of ida s satellite dactyl over phase angles 19 5 to 47 6 suggest photometric characteristics similar to those of ida the major difference being dactyl s slightly lower albedo 0 20 compared to 0 21

preliminary results on photometric properties of materials at the sagan memorial station mars reflectance measurements of selected rocks and soils over a wide range of illumination geometries obtained by the imager for mars pathfinder imp camera provide constraints on interpretations of the physical and mineralogical nature of geologic materials at the landing site the data sets consist of 1 three small photometric spot subframed scenes covering phase angles from 20 to 150 2 two image strips composed of three subframed images each located along the antisunrise and antisunset lines photometric equator covering phase angles from 0 to 155 and 3 full image scenes of the rock yogi covering phase angles from 48 to 100 phase functions extracted from calibrated data exhibit a dominantly backscattering photometric function consistent with the results from the viking lander cameras however forward scattering behavior does appear at phase angles 140 particularly for the darker gray rock surfaces preliminary efforts using a hapke scattering model are useful in comparing surface properties of different rock and soil types but are not well constrained possibly due to the incomplete phase angle availability uncertainties related to the photometric function of the calibration targets and or the competing effects of diffuse and direct lighting preliminary interpretations of the derived hapke parameters suggest that 1 red rocks can be modeled as a mixture of gray rocks with a coating of bright and dark soil or dust and 2 gray rocks have macroscopically smoother surfaces composed of microscopically homogeneous clear materials with little internal scattering which may imply a glass like or varnished surface

effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock implication on mechanism of borehole breakouts abstract we conducted laboratory true triaxial experiments in the nearly impermeable pohang rhyolite to investigate failure mechanisms under dry and wet rock conditions under dry conditions prismatic specimens were jacketed all around to prevent confining fluid penetration under wet conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid kerosene applying the least principal stress in an attempt to simulate the case of an unlined borehole wall in both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises the unjacketed rhyolite strength is however only 60 to 85 of the strength under dry conditions depending on the magnitude of the intermediate principal stress in dry rhyolite the failure process begins upon dilatancy onset followed by microcrack localization and ending in a steeply dipping shear fracture on the other hand brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through going extensile fractures subparallel and adjacent to one of the unjacketed faces resembling the extensile cracks leading to borehole breakouts in crystalline rocks we infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress induced microcracks subparallel to the unjacketed faces leading to early failure

characteristics of surface ruptures associated with the chi chi earthquake of september 21 1999 abstract the chi chi earthquake which reactivated the chelungpu fault in central taiwan generated surface ruptures over 100 km long surface ruptures of the chi chi earthquake can be divided into the north south and the east west sections the north south section extends for about 84 km and the northern e w section 16 km the north south section consists of a continuous main rupture and some branches these are characterized by thrust motion with some strike slip components topographic surveys indicate that the ground commonly uplifted as a single continuous ramp step surface and deformation is mainly concentrated on the hanging wall fault slip data and gps measurements show that the hanging wall along the northern segment of the chelungpu fault moved northwest but that along the southern segment of the fault the hanging wall shifted to the southwest sandbox models suggest that the above dissimilarity in hanging wall movement direction is mainly due to the presence of the peikang basement high in the east west section the ruptures comprise a series of en echelon steep faults with right step or left step geometry and trend ene wsw to e w near the ta an river the surface rupture orientation shifts from ne sw to nw se and terminates at the shuangtung fault here the ruptures appear to be controlled by the 10 15 km wide nw trending sanyi puli shear zone clay modeling displays the development of e w trending ruptures when a n s trending fault meets a n30 w trending weak zone

the scattering properties of natural terrestrial snows versus icy satellite surfaces abstract a j verbiscer and j veverka 1990 icarus 88 418 428 demonstrated that the single scattering properties of terrestrial snows are highly forward scattering in contrast to the single scattering properties of icy satellite surfaces which all have a backscattering component to their single scattering functions as modeled with b hapke s equations 1981 j geophys res 86 3039 3054 1984 icarus 59 41 59 1986 icarus 67 264 280 this study demonstrates to first order that the differences between the scattering properties of icy satellite regoliths and their terrestrial counterparts are due to differences in particle structure and textures we find that the particles of the regoliths of the icy satellites are composed of a complex mixture of grain textures and structures

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

true triaxial strength and deformability of the siltstone overlying the chelungpu fault chi chi earthquake taiwan 1 we conducted true triaxial compression tests to examine the effect of the intermediate principal stress 2 on brittle failure and deformability of the siltstone overlying the chelungpu fault taiwan for constant minimum stress 3 a pattern of increased strength 1 as a function of 2 unpredicted by common strength criteria was observed strength data are well fitted by a mogi modified nadai criterion relating the octahedral shear stress at failure to the mean normal stress on the induced shear fracture or fault the induced fault strikes subparallel to 2 and dips steeply in the direction of 3 significantly fault dip angle steadily increases as 2 rises for unchanged 3 sem inspection of tested specimens reveals only sporadic localized intergranular microcracks associated with the creation of the fault the modulus of elasticity and the onset of dilatancy exhibit a similar behavior to that of 1 as they increase with 2 when subjected to a constant 3

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

mars surface mineralogy from hubble space telescope imaging during 1994 1995 observations calibration and initial results visible to near infrared observations of mars were made with the hubble space telescope hst during 1994 1995 with the goals of monitoring seasonal variability of the surface and atmosphere and mapping specific spectral units to constrain the planet s surface mineralogy this paper presents the details of the collection and calibration of the data concentrating specifically on the near ir data that were obtained exclusively for the surface mineralogy aspect of our hst mars observing program we also present some initial results from the calibrated data set our calibration procedures included the standard pipeline processing steps supplemented by special procedures required for use with the linear ramp filters on the wide field planetary camera 2 instrument and an additional point spread function deconvolution procedure applied in order to realize the full potential spatial resolution of the images 23 to 64 km pixel between august 1994 and august 1995 the calibration results in a set of images projected onto a standard map grid and presented in radiance factor i f units having an estimated 5 photometric accuracy based on the performance of hst and comparisons with previous ground based and spacecraft mars spectra initial scientific analyses of these data reveal 1 distinct red blue color units within the classical bright regions similar to those seen in viking orbiter images and possibly related to variations in nanophase and or crystalline ferric mineral abundance 2 near ir spectral slope variations correlated with albedo on a large scale darker is bluer near ir slope but exhibiting wider variations among many of the small scale features visible in the data 3 an absorption at 860 nm that occurs in all regions but which is 3 to 5 stronger in many of the classical dark regions than in the bright regions possibly because of a greater abundance of a well crystalline ferric phase like hematite or a very low ca pyroxene or opx cpx mixture and 4 an absorption from pyroxene at 953 nm with a band depth that is inversely correlated with albedo bright regions 0 to 5 deep dark regions 7 to 15 deep and which shows the highest band depth values in individual craters calderas and other small geologic units that are resolved in the images

application of multiple photometric models to disk resolved measurements of mercury s surface insights into mercury s regolith characteristics abstract photometric analyses are used to standardize images obtained at a variety of illumination and viewing conditions to a common geometry for the construction of maps or mosaics and for comparison with spectral measurements acquired in the laboratory many models exist that can be used to model photometric behavior two of the most commonly use models those of hapke and kaasalainen shkuratov are compared for their ability to standardize messenger images of mercury analysis of the modeling results shows that photometric corrections using the kaasalainen shkuratov model provides significantly less contrast between images acquired at large differences in emission angle the contrast seen between images acquired at large differences in either incidence and phase angle is smaller with the hapke model based corrections but not significantly better than that provided by the kaasalainen shkuratov model photometric studies are also used to infer scattering properties of the surface regolith the quantitative correlation between photometric model parameters and surface properties is questionable but laboratory studies do indicate general correlations and trends between parameters and sample properties that allow for comparisons between surfaces based on photometric modeling based on comparisons with the moon and several asteroids that have been observed by spacecraft the photometric analyses presented here are interpreted to indicate that mercury s regolith is smoother on micrometer scales and has a narrower particle size distribution with a lower mean particle size than lunar regolith grain structures of regolith particles from mercury are inferred to be different than those of the moon or those asteroids observed to date mercury s regolith may contain a component compositionally distinct from lunar regolith

high resolution topography and albedo of the south polar layered deposits on mars using a new photoclinometric technique with high resolution mariner 9 images maximum slopes of 10 20 are found to occur on an exposure of layered deposits within the south polar residual cap of mars stereophotogrammetry is used to constrain the photoclinometric solutions which resolve layer thicknesses of 100 300 m albedo variations are correlated with slope indicating that frost is present on level areas there is evidence for temporal changes in frost distribution in the 7 days 4 of l s between the two images used in this study the magnitude of the slopes derived here and consideration of the stability of water ice at the surface of the layered deposits strongly suggest the presence of a competent weathering rind the weathered surface may be composed of dark filamentary sublimation residue particles that protect the underlying ice from solar heating this hypothesis is consistent with previous studies of the regional color and albedo of the layered deposits which indicate that the deposits are slightly darker and less red than the bright dust that mantles much of the south polar region furthermore the proposed weathering mechanism provides a plausible source of dark saltating material for the martian polar dune fields

the effect of the intermediate principal stress on fault formation and fault angle in siltstone abstract we conducted true triaxial compression tests on specimens prepared from two siltstone core sections one above and one below the chelungpu fault taiwan for different constant 2 and 3 magnitudes the maximum principal stress 1 was raised until a post failure stage was reached and a through going fault had developed despite differences between the properties of the two cores in all tests peak 1 increased as 2 was set at higher levels than 3 in contrast to mohr coulomb condition predictions the fault normal vector was aligned with the 3 direction and made an angle with 1 direction the angle which corresponds to fault dip in case of normal faulting increased monotonically with 2 for fixed 3 a variation that is also inconsistent with mohr coulomb theory the results of shear band localization theory are used with fault angles observed for axisymmetric compression and deviatoric pure shear to infer properties of the inelastic constitutive behavior these properties are significantly different for the two cores using them to predict for other deviatoric stress states yields good agreement with the observations for core ii and acceptable agreement for core i the results are used to predict the angle variation for constant mean normal stress decreases as the deviatoric stress state varies from axisymmetric extension to axisymmetric compression and at fixed deviatoric stress state decreases monotonically with increasing mean normal stress

martian phase function modeling the visible to near infrared surface photometric function using hst wfpc2 data abstract images of mars in the visible to near infrared acquired from 1996 to 2005 using the hubble space telescope wfpc2 have been used to model the martian surface photometric function at 502 673 953 and 1042 nm these data range in spatial resolution from 12 to 70 km pixel at the sub earth point and in phase angle coverage from 0 34 to 40 5 the wfpc2 images have been calibrated to radiance factor or i f and projected to a cylindrical map for coregistration and comparison to similarly mapped spacecraft data sets of albedo topography thermal inertia composition and geology we modeled the observed i f as a function of phase angle using minnaert lambert lunar lambert and hapke photometric functions for numerous regions of interest binned into albedo units defined by viking and tes albedo maps and thermal inertia units defined by tes thermal inertia maps visibly opaque water ice clouds and data acquired under high dust opacity conditions were excluded from the analysis our modeling suggests that under average to low atmospheric dust opacity conditions and over this range of phase angles the photometric properties of the martian surface at 502 673 953 and 1042 nm are best modeled by lunar lambert functions with parameters derived for three surface units defined by low moderate and high tes bolometric albedos

shear strengths of sandstone fractures under true triaxial stresses abstract true triaxial shear tests have been performed to determine the peak shear strengths of tension induced fractures in three thai sandstones a polyaxial load frame is used to apply mutually perpendicular lateral stresses p and o to the 76 76 126 mm rectangular block specimens the normal to the fracture plane makes an angle of 59 1 with the axial major principal stress results indicate that the lateral stress that is parallel to the fracture plane p can significantly reduce the peak shear strength of the fractures under the same normal stress n the fractures under high p dilate more than those under low p according to the coulomb criterion the friction angle decreases exponentially with increasing p o ratio and the cohesion decreases with increasing p the lateral stress p has insignificant effect on the basic friction angle of the smooth saw cut surfaces the fracture shear strengths under p 0 correlate well with those obtained from the direct shear tests it is postulated that when the fractures are confined laterally by p their asperities are strained into the aperture and are sheared off more easily compared to those under unconfined condition

paul mohr coulomb failure criterion for geomaterials abstractpaul mohr coulomb pmc failure criterion provides enhanced representations of pyramidal failure surfaces with recognizable material parameters by considering all three principal stresses

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

exogenic and endogenic albedo and color patterns on europa new global and high resolution multispectral mosaics of europa have been produced from the voyager imaging data photometric normalizations are based on multiple image techniques that explicitly account for intrinsic albedo variations through pixel by pixel solutions the exogenic color and albedo pattern on europa is described by a second order function of the cosine of the angular distance from the apex of orbital motion on the basis of this second order function and of color trends that are different on the leading and trailing hemispheres the exogenic pattern is interpreted as being due to equilibrium between two dominant processes 1 impact gardening and 2 magnetospheric interactions including sulfur ion implantation and sputtering redistribution removal of the model exogenic pattern in the mosaics reveals the endogenic variations consisting of only two major units darker redder and bright materials therefore europa s visual spectral reflectivity is simple having one continuous exogenic pattern and two discrete endogenic units

the application of a matsuoka nakai lade duncan failure criterion to two porous sandstones abstract we summarize two suites of recent true triaxial tests in two porous sandstones coconino and bentheim one suite of tests conducted under constant 2 and 3 which revealed the effect of 2 and 3 on rock failure the other suite of tests performed under constant lode angle determined the failure dependencies on mean stress and lode angle building and modifying failure descriptions by matsuoka nakai mn and lade duncan ld an explicit failure criterion modified mnld that generalizes a class of failure forms is used to fit the novel loading path data of both sandstones the determined failure descriptions fit both rocks well over a wide range of failure conditions then the generated failure descriptions were further used to predict failure conditions under the constant 2 and 3 loading path the predictions by the modified mnld are generally consistent with these data the predictions also successfully replicated the variation of 1 peak with 2 under constant 3 suggesting the potential of the modified mnld to clarify the effect of 2 on rock failure

photometric diversity of terrains on triton voyager disk resolved images of triton in the violet 0 41 m and green 0 56 m wavelengths have been analyzed to derive the photometric characteristics of terrains on triton similar conclusions are found using two distinct but related definitions of photometric units one based on color ratio and albedo properties a s mcewen 1990 geophys res lett 17 1765 1768 the other on albedo and brightness ratios at different phase angles cf p lee et al 1992 icarus 99 82 97 a significant diversity of photometric behavior much broader than that discovered so far on any other icy satellite occurs among triton s terrains remarkably differences in photometric behavior do not correlate well with geologic terrain boundaries defined on the basis of surface morphology this suggests that in most cases photometric properties on triton are controlled by thin deposits superposed on underlying geologic units single scattering albedus are 0 98 or higher and asymmetry factors range from 0 35 to 0 45 for most units the most distinct scattering behavior is exhibited by the reddish northern units already identified as the anomalously scattering region asr by lee et al which scatters light almost isotropically with g 0 04 in part due to the effects of triton s clouds and haze it is difficult to constrain the value of hapke s macroscopic roughness parameter precisely for triton or to map differences in among the different photometric terrains however our study shows that triton must be relatively smooth with less than 15 20 and suggests that a value of 14 is appropriate the differences in photometric characteristics lead to significantly different phase angle behavior for the various terrains for example a terrain e g the asr that appears dark relative to another at low phase angles will reverse its contrast become relatively brighter at larger phase angles the photometric parameters have been used to calculate hemispherical albedos for the units and to infer likely surface temperatures based on these results we determine that all but the most southerly regions south of the equator of the reddish northern terrains are likely to have been covered with deposits of nitrogen frost at the time of the voyager flyby in agreement with the suggestion from the photometry that these units are overlain by a thin veneer of material

calcite twinning strains from syn faulting calcite gouge small offset strike slip normal and thrust faults we have evaluated the stress strain behavior of calcite precipitated and mechanically twinned in small offset strike slip normal and thrust faults of a variety of ages and from a variety of tectonic settings n 3001 twin measurements 63 strain analyses from 18 field sites five strike slip faults with syn faulting horizontally striated calcite rake 0 were studied and we report the orientations of the contemporaneous stress strain field associated with each fault intrusion of the marathon large igneous province mafic dikes 2 1 ga in archean crust minnesota usa post keweenaw rift 1 1 ga faulting island lake fault central ontario canada subduction associated with metamorphic core complex formation cretaceous china subduction cretaceous to miocene italy and continental extension recently active furnace creek fault death valley california usa seven normal faults with synfaulting dip slip striated calcite were studied and are from the following tectonic settings a normal fault slip surface in an ordovician piedmont fold appalachian s paleo subduction associated with cretaceous metamorphic core complex formation china 3 sites the paleo extensional atlantic margin 55 ma ireland 1 site with a u pb calcite age continental extension 1 active site mojave desert a transcurrent margin jamaica 1 active fault site and subduction 2 active faults along the eur african margin in italy with calcite u th disequilibria ages and crete respectively six thrust fault examples are all from convergent orogenic settings the basal thrust of the penokean 1850 ma fold and thrust belt the penokean orogen foreland in mesabi range banded iron formation folds an offset breccia body in the permian gondwanide belt ellsworth mountains antarctica the frontal thrust of the gondwanide cape belt south africa the paleocene frontal prospect thrust sevier belt wyoming and an alpine foreland back thrust lulworth cove u k for each strike slip fault system the twinning shortening strain is horizontal and at an angle of 0 60 to the respective fault plane dextral or sinistral although in the majority of cases the shortening axis is parallel to fault strike 13 of 23 results in each normal fault example dip slip kinematic striations dominate the faulted surface yet the orientation of the maximum principal compressive stress 1 and shortening strain axis e1 are not 45 to the fault plane as predicted but are sub horizontal and either strike parallel 25 of 35 results or strike normal 10 of 35 results thrust faults preserve shortening strain axes parallel to the dip slip kinematic direction within the fault plane plane strain and not at 45 to the principal plane 5 of 5 results none of the fault stress strain field results reported here support the andersonian or mohr coulomb criteria for stress strain relations predicted along faults

nature and distribution of surficial deposits in chryse planitia and vicinity mars color images of bright red dust deposits at the mutch memorial station were acquired at variable incidence angles during sol 611 subsolar longitude 70 northern spring season after removing effects due to atmospheric scattering and absorption the data were used to estimate the independent variables in the hapke 1986 photometric function in blue green and red coordinates the vector representing the space radiance factor of the landing site extracted from viking orbiter images acquired on sol 609 is separated by a euclidean distance of only 0 022 units and an angle of only 1 5 from the vector estimated from the station data for the orbiter lighting and viewing geometries this result implies that light reflected from dust exposures dominates the orbiter signal multiplicative and additive atmospheric terms cancel one another and surface roughness is a second order effect in the orbiter data dust radiance factors computed from station data are most like laboratory spectra for fine grained hawaiian palagonite and are indistinguishable from earth based spectra of classical bright areas color composites of orbiter images show that the dust is found immediately south of acidalia planitia and in association with topographic barriers such as craters and cliffs examination of viking infrared thermal mapper data shows that the dust deposits typically do not have distinctive thermal inertia signatures implying that the deposits are optically thick hundreds of micrometers but thinner than the diurnal thermal skin depth centimeters dark gray material with thermal inertia values 8 12 10 3 cal cm 2 s 1 2 k 1 indicative of sand grain sizes 0 5 1 5 mm dominates the acidalia planitia lowlands and parts of kasei vallis this material also occurs as dark streaks extending from craters in xanthe terra and oxia palus space radiance factors of dark gray material are similar to spectra of mafic rock mixed with a minor amount of palagonitelike material material that is darker than but just as red as the dust deposits occurs in lunae planum xanthe terra and oxia palus areas of intermediate elevation multiple phase angle orbiter images suggest that the dark red exposures are a mixture of bright red and dark gray materials with the dark red exposures being relatively rough at a subpixel scale as compared to exposures of the other two materials thus only two types of materials can be detected in the data covering the study area palagonitelike dust and mafic rock fragments thermal inertia values 4 8 10 3 cal cm 2 s 1 2 k 1 for the dark red material are consistent with the presence of fine to medium sand size particles 0 10 0 5 mm such material should be easily moved by winds the lack of aeolian features implies that the dark red deposits are not composed of loose material rather they are probably more eroded versions of blocky soil or duricrust cemented dust and rock fragments exposed at the station both bright red dust aeolian suspension load and dark gray materials saltation traction loads migrate over the dark red substrate the overall distribution of the surficial units is controlled by topography at a variety of length scales lower wind threshold friction velocities associated with higher atmospheric densities in lowlands keep dust from accumulating and duricrust from forming while higher threshold velocities in highlands lead to net accumulation of dust local topographic obstacles craters walls ridges perturb wind flow and lead to local accumulation or erosion at a variety of elevations in addition the bright red dust ubiquitously found between exposures of dark gray and dark red materials may accumulate as the wind velocity gradient decreases at the transition from smoother dark gray exposures to rougher dark red exposures the distribution of the materials must also be modulated by climatic variations induced by quasi periodic oscillations in obliquity eccentricity and spin axis direction constraining these surficial deposits to be 1 ma

disk resolved photometric analysis of european terrains abstract using hapke s photometric model we examined the photometric textures of a representative subset of the geologic units on europa defined by lucchitta and soderblom 1982 satellites of jupiter pp 521 555 university of arizona press tucson the individual units studied possess the same small mean photometric slope angle as that found by domingue et al 1991 icarus 90 30 42 for the entire disk with one major exception the particles composing the surfaces of most of the units have similar scattering properties however the single particle scattering functions of the two bright plains regions examined are very different from each other and from the other units if the bright plains units are geologically younger than the other units an aging process that affects the single particle phase functions and albedos is inferred in our previous study we concluded that the disk integrated photometric properties of europa could not be explained adequately by ion bombardment however a new study on the effects of ion irradiation on the optical properties of materials sack et al 1991 j geophys res e 96 2 17535 17539 renders this conclusion invalid

non dilatant deformation and failure mechanism in two long valley caldera rocks under true triaxial compression abstract we conducted laboratory rock strength experiments in two ultra fine grained brittle rocks hornfels and metapelite which together are the major constituent of the long valley caldera california usa basement in the 2025 2996 m depth range both rocks are banded and have very low porosity uniaxial compression tests at different orientations with respect to banding planes reveal that while the hornfels compressive strength is nearly isotropic the metapelite possesses distinct anisotropy conventional triaxial tests in these rocks reveal that their respective strengths in a specific orientation increase approximately linearly with confining pressure true triaxial compression experiments in specimens oriented at a consistent angle to banding in which the magnitudes of the least 3 and the intermediate 2 principal stresses are different but kept constant during testing while the maximum principal stress is increased until failure exhibit a behavior unlike that previously observed in other rocks under similar testing conditions for a given magnitude of 3 compressive strength 1 does not vary significantly in both long valley rock types regardless of the applied 2 suggesting little or no intermediate principal stress effect strains measured in all three principal directions during loading were used to obtain plots of 1 versus volumetric strain these are consistently linear almost to the point of rock failure suggesting no dilatancy the phenomenon was corroborated by sem inspection of failed specimens that showed no microcrack development prior to the emergence of one through going shear failure plane steeply dipping in the 3 direction the strong dependency of compressive strength on the intermediate principal stress in other crystalline rocks was found to be related to microcrack initiation upon dilatancy onset which rises with increased 2 and retards the failure process we infer that strength independence of 2 in the long valley rocks derives directly from their non dilatant deformation

reexamination of fault angles predicted by shear localization theory this paper reexamines orientations of shear bands fault angles predicted by a theory of shear localization as a bifurcation from homogeneous deformation in contrast to the coulomb prediction which does not depend on deviatoric stress state the angle between the band normal and the least most compressive principal stress increases as the deviatoric stress state varies from axisymmetric compression to axisymmetric extension this variation is consistent with the data of mogi 1967 on dunham dolomite for axisymmetric compression extension and biaxial compression but the predicted angles are generally less than observed this discrepancy may be due to anisotropy that develops due to crack growth in preferred orientations results from specialized constitutive relations for axisymmetric compression and plane strain that include this anisotropy indicate that it tends to increase the predicted angles measurements for a weak porous sandstone castlegate indicate that the band angle decreases with increasing inelastic compaction that accompanies increasing mean stress this trend is consistent with the predictions of the theory but for this rock the observed angles are less than predicted