are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

physical links between crustal deformation seismic moment and seismic hazard for regions of varying seismicity summary seismic moment release rates m0 inferred from a weibull frequency magnitude distribution and its extreme value equivalent are compared with observation the seismotectonically diverse regions studied all exhibit the curvature of a log linear frequency magnitude plot associated with applying a maximum magnitude to earthquake recurrence statistics the inferred seismic moment release rates are consistent with available crustal deformation data within uncertainties resulting from the line fit and in magnitude determination the uncertainties for the regions studied southern california the new madrid seismic zone the central and eastern mediterranean and mainland uk vary from at worst an order of magnitude down to a factor of 2 or 3 this agreement can be used to justify the extrapolation of frequency magnitude statistics beyond the historical and instrumental era in seismic hazard studies as a test of the stationarity of short term statistics against long term effects a striking example of a bimodal seismicity distribution is observed in the new madrid zone this can be interpreted as being due to the superposition of two distinct seismogenic source types observed in the area a quantitative analysis of the separate orders of seismicity observed in the frequency magnitude statistics comparing the different maximum magnitudes and inferred seismic moment release rates with those observed supports this hypothesis superposition of many such seismogenic sources can explain the linearity observed in global frequency versus seismic moment magnitude statistics

mars near infrared spectral reflectance of surface regions and compositional implications reflectance spectra 0 65 2 50 m are presented for 11 martian areas the spectral resolution is 1 and the spatial resolution is 1000 2000 km these are the first high quality spectrophotometric data at these wavelengths for regions on the surface spectral features previously observed are confirmed and better defined and a number of important spectral properties are characterized for the first time the spectra show water ice absorptions in the 1 5 and 2 0 m regions which if due to surface frost would imply the presence of 1 to 2 mg cm2 h2o however other studies have shown that the presence of an unprotected surface frost in late morning is unlikely water ice is stable at night even at the equator and might persist until late morning when the air is well undersaturated if it is intimately dispersed in weathering products especially if clays are present the dark region spectra indicate about 4 times less water ice than seen in bright regions since some bright material is present in dark regions there may be no water ice associated with the dark materials themselves this tends to confirm that weathering products thought to be more abundant in bright regions are involved in the mechanism that allows temporary persistance of unstable water ice the presence of weak 2 3 m features in many of the spectra are consistent with the presence of hydroxylated magnesium rich minerals such as sheet silicates serpentine talc and magnesian smectites or amphiboles anthophyllite the apparent absence of a 2 2 m absorption implies that montmorillonite may not be a major component of the martian regolith many of the spectra also show an apparent absorption at 1 9 m in the wing of the 2 0 m martian atmospheric co2 absorption which would indicate bound molecular water observed dark regions have distinctive near infrared spectral shapes previously not well determined which are characteristic of thin semi transparent alteration coatings overlying dark unaltered rock previously observed ferrous and ferric iron absorptions in the 1 m region are better defined by these new data clinopyroxene augite is definitely present but olivine is not spectrally apparent

the geology of the terrestrial planets during the last four years our knowledge of the geology of the terrestrial planets has advanced rapidly the advances are particularly noticeable for venus and mars improved understanding of venus has come largely from the pioneer venus mission colin 1980 which has given us our first global view of the planet albeit at fairly low resolution the period was also one of almost continuous data gathering for mars as the viking orbiters and landers emplaced at the planet in 1976 continued to function

mars definition and characterization of global surface units with emphasis on composition units of similar optical properties have been defined for a large part of the surface of mars using primarily viking 2 approach maps of red 0 59 m and violet 0 45 m normal albedo of available global data sets spectral albedo most closely relates to surface mineralogy the resultant unit map represents mars at the time the viking images were acquired ls 103 105 morning northern hemisphere summer in 1976 computer processing of these data reveals clusters of albedo values which relate to specific contiguous regions on the planet final unit definitions were determined by an interactive iterative process which included scientific judgment on the part of the researchers the results therefore are not the product of an unsupervised statistical classification some unit boundaries are of a gradational nature while others are more discrete certain of the units are temporal and relate to the presence of condensates at the time of observation other units by virtue of their redness and low albedo are almost certainly not affected by condensates a study of the albedo properties of analog materials measured in the laboratory and of telescopic spectrophotometry of mars indicates that both hydroxylated low temperature or secondary and hematitic high temperature or primary oxidized materials exist on the surface the most likely surface expression of global dust and or high albedo soils is in the classical bright region arabia this material is probably a low temperature hydrated oxidation product of mafic volcanic glass such as a palagonite or amorphous iron silica gel most low albedo features in the region studied have red and violet albedos consistent with a dark substrate such as basalt coated by or mixed with the fine grained alteration product mentioned above there may be no genetic relationship between these two components in this majority of low albedo surface materials certain of the other low albedo regions are also the most red highest r v areas observed on the planet these areas are consistent with a nonhydroxylated more hematitic material such as that produced by high temperature hydrothermal alteration of basalt some of these dark very red regions correlate with exposures of very ancient terrain at this spatial resolution 10 20 km pixel there is no evidence of surface exposures of uncoated or unweathered basaltic rock or glass comparisons of the unit map with other data sets available to us revealed no striking detailed correlations larger scale correlations certainly do exist however among the various albedo data sets and with thermal inertia data

mars express high resolution stereo camera spectrophotometric data characteristics and science analysis 1 the high resolution stereo camera hrsc on the mars express mex spacecraft in orbit about mars is delivering images of the mars surface and atmosphere from its high inclination elliptical orbit that are intended to cover most of the mars surface by the end of the mission these are acquired in four specific spectral passbands that sample the scene at different parts of the extended visual spectrum from near 0 4 m to about 1 m and in five additional channels four used for stereo and one nadir that use the same fifth spectral passband these channels view from different angles and can be used for photometric and spectral analysis the data allow a variety of studies of the surface and atmosphere of mars but these require detailed understanding of the data characteristics as there are several effects including of the observation geometry and the atmosphere that need to be treated this article is a report to the science community on the current understanding of the hrsc color data after an initial analysis and also a demonstration of their capabilities for study of mars which from this study appear to be considerable we first discuss the characteristics and calibration of the hrsc spectral data the atmospheric influence on the photometric appearance of the surface materials is explored and methods of compensating are considered reflectances are calculated for surface units by assuming the dark material is basalt and scaling the entire hrsc scene using a laboratory basalt spectrum for the selected dark material area the results and the correction factors for different orbits are compared we present several examples of what could become a large volume of future science results utilizing the hrsc spectrophotometric data in conjunction with photo interpretation for example we find relatively few but very important distinct spectral components at the hrsc resolution including what we interpret as iron oxide rich material unoxidized basalt and polar ice consistent with past works the major spectral components are distributed in ways that suggest compositional mixing and the need to revise the current geologic understanding of major regions

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

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

a comparison of seismic and structural measurements of scaling exponents during tensile subcritical crack growth abstract the observed fractal nature of both fault length distributions and earthquake magnitude frequency distributions suggests that there may be a relationship between the structure of active fault systems and the resulting seismicity in previous theoretical work a positive correlation between the exponent d from the fracture length distribution and the seismic or acoustic emission ae b value has been inferred from a simple dislocation model of the seismic source here we present the first experimental evidence for a correlation between d and b from a series of tensile fracture mechanics tests on crystalline rock carried out in different environmental conditions both air dry and water saturated and at ambient temperature and pressure the microseismic acoustic emissions were monitored during subcritical crack growth under controlled conditions of constant stress intensity k i and quantitative analyses of the resulting fracture patterns were carried out on the same specimens it is found that ae b values ranging from 1 0 to 2 3 correlate negatively with the normalized stress intensity k i k ic where k ic is the fracture toughness of the specimen the microcrack length distribution exponent d ranges from 1 0 to 1 7 fluid presence has a first order influence on both the ae and structure produced in these experiments for experiments at low stress intensity or high fluid content the activation of the stress corrosion mechanism for k i k ic leads to a greater relative proportion both of small cracks and of low amplitude acoustic emissions reflected in higher values of d and b the exponent d is found to correlate positively with the ae b value

mapping of spectral variations on the surface of mars from high spectral resolution telescopic images abstract we analyze a high spectral resolution r 200 visible and near infrared 0 44 1 02 m telescopic spectral image of mars to explore surface material variations across the observed face of the planet which is centered on sinus meridiani two independent analysis methods are employed linear mixture modeling and supervised spectral pattern classification with an artificial neural network four endmember type regions are identified with linear mixing further refinement is achieved with the nonlinear neural network classification algorithm separating eight units of geological significance differences in spectral features among the mapped units are characterized among the medium to high albedo units northern lowlands typified by chryse planitia show far less evidence of bulk crystalline hematite than western arabia or any other highland regions the relationship of these bright units to the globally distributed aeolian dust is not yet clear within our image low albedo regions with the most pronounced crystalline hematite signature primarily correlate with the classic dark regions with the exception of acidalia planitia spectral evidence for pyroxenes also correlates well with most of the classic low albedo regions but again acidalia planitia is the major exception significant spectral anomaly is also found in an equatorial region deucalionis regio a companion paper in this issue discusses the soil properties of deucalionis our data and analysis support a compositional trend that is consistent with the global geologic crustal dichotomy of mars namely that the younger northern lowlands contain less bulk crystalline hematite than southern highlands

mars near infrared comparative spectroscopy during the 1986 opposition abstract near infrared 0 7 2 5 m spectral observations of mars during the 1986 opposition were carried out at the mauna kea observatory utilizing the university of hawaii 2 2 m telescope spectra were obtained of several martian locations using a continuously variable filter cvf spectrometer with a resolution of 1 25 during two separate runs in june and august approximately 60 distinct spots between 354 w and 163 w and 32 n and 53 s were observed at an angular resolution of 0 5 to 1 5 arcsec corresponding to a spatial resolution on mars of 200 to 460 km varying with nightly seeing conditions these different spots fall roughly into a set of eight distinct geologic regions volcanic regions ridged plains ridged volcanic plains scoured plains impact basins channels and canyons densely cratered regions and layered terrain and ice the spectra exhibit typical noise related or weather induced errors of less than 4 of the full scale signal to analyze these spectral data spot to spot ratios or relative reflectance spectra were produced between spectra taken in different geologic regions spectral features observed in these ratios can act as indicators of mineralogic differences between areas under consideration perhaps the most striking result obtained from the many ratios taken close in time and under similar viewing geometries was the consistent lack of noticeable differences between spectra taken of areas which in geologic maps and viking orbiter images appear to have very different morphologies this observation leads to several possible conclusions a the spectral feature differences are below the detection limit of these measurements b the spatial resolution of spots observed on mars was not high enough to merit comparison with medium to high resolution viking orbiter images and geologic maps i e the local morphology varies significantly within the aperture region and a mixing or averaging effect operates to reduce the spectral feature differences c all of these regions are the same spectrally in the near infrared it is likely that all three of these effects operate to some degree to prevent spectral features from being observed among the areas measured possibility c may best explain these results as it is consistent with several previous studies indicating a grossly uniform mantle of global dust over much of the observed surface the message to mars orbiting spectroscopy experiments such as mars observer vims is that the spectral differences are small only a few percent of the continuum or nonexistent among many areas on mars on the scale of several hundred kilometers

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

seismotectonics and the earthquake frequency magnitude distribution in the aegean area summary a study of aegean seismotectonics and the resulting frequency magnitude distribution on a broad scale is undertaken using the tectonic model of le pichon angelier this implies a tectonic moment release rate due to the spreading of the aegean of 17 8 times 1018 n m 1 yr 1 over the past 13 ma if stretching is due mainly to a series of normal faults dipping at about 45 in a seismogenic crust 10 20 km deep the moment magnitude relation from an instrumental magnitude catalogue is log m0 a bm with a 10 970 0 294 b 1 206 in si units this is established from 50 events of magnitude ms 5 3 whose scalar seismic moments m0 have been evaluated in a homogeneous manner for the region by spectral analysis of surface waves at 30 60 s period by contrast published body wave analyses from waveform modelling at 20 s period and moment tensor analyses seem to produce seismic moments which are lower by a factor of two or so on average this moment magnitude relation implies a seismogenic moment release rate due to stretching in the aegean of 14 times 1018 n m 1 yr 1 during the time period 1918 81 and 17 times 1018 n m 1 yr 1 for the period 1964 81 within a factor of two or so uncertainty this implies that the energy release in the brittle crust due to aegean spreading is substantially seismic within the stated accuracy and is also relatively stationary even when compared with the tectonic moment release rates a similar comparison using the same tectonic model shows that the subducting slab is sinking beneath the hellenic arc almost completely aseismically and that processes such as near vertical slab pull and confined thermal expansion could explain most of the observed seismic energy release by internal deformation of the slab the frequency magnitude statistics for the area of active extension has a characteristic earthquake of magnitude 7ms corresponding approximately to fault depths of 10 14 km for an aspect ratio of 2 and a strain drop of 10 4 this is close to the observed seismogenic depth 10 20 km for well determined earthquakes in the aegean area

statistics of small earthquakes and frequency of occurrence of large earthquakes along the mexican subduction zone abstract the validity of the gutenberg richter g r frequency magnitude relation over a wide range of magnitudes is usually accepted and the statistics of small earthquakes is often extrapolated to predict the frequency of occurrence of large earthquakes we take noaa and pde data from 1963 to 1981 related to the mexican subduction zone h 65 km and convert m b to m s in the range of 3 3 m b 5 7 for this conversion we use regression of m s on m b for mexican and central american events as well as an m s m b regression based on worldwide data wyss and habermann 1982 we also take into account the standard error in m s this may be important since the number of events decreases as m b increases the m s data of 18 5 yr is normalized to 75 5 yr and is compared to the statistics of observed large earthquakes m s 6 4 for the period 1906 to 1981 it is found that the g r relation in the range 4 5 m s 6 0 when extrapolated grossly underestimates the observed frequency of large earthquakes m s 6 5 for the oaxaca and jalisco regions there is strong evidence that the plate interface in the oaxaca region consists of a few 3 or 4 large fault zones each of which cyclically ruptures over its entire dimension without giving rise to smaller events in the manner implied by the g r relation the result is of profound importance in seismic risk analysis and in the understanding of fault mechanics this phenomenon has been reported for only a few regions e g turkey bath 1981 japan wesnousky et al 1983 it may have escaped detection in other regions due to a variety of causes the most important being the long recurrence periods of large earthquakes

on the spectral reflectance properties of materials exposed at the viking landing sites bidirectional reflectances calibrated to within 10 uncertainties for blue 0 40 0 52 m green 0 50 0 59 m and red 0 60 0 74 m channels were determined for 31 block and soil exposures imaged by the viking lander cameras reflectances were corrected for atmospheric attenuation by using optical depth measurements obtained by the lander cameras and for skylight illumination by subtracting the brightness values of adjacent shadowed areas reflectances for two facets on each of two large blocks were computed for a common geometry by determining facet orientations from high resolution lander stereo images and by fitting the hapke irvine photometric function to reflectances estimated for several geometries results indicate that individual facets on the same block have different optical properties the darkest grayest block facets have properties similar to laboratory reflectance spectra of mafic rocks that are thinly coated with ferric iron rich palagonite most block surfaces have reflectances consistent with thin to optically thick covers of palagonitic material limited exposures of soil have spectra that are also similar to palagonitic material the majority of the soils sampled and a few block surfaces have spectra with steeper slopes and greater spectral curvatures than the palagonite analog consistent with greater degree of ferric iron crystallinity the soils could be an intimate mixture of palagonitic material and other materials not seen in end member form but if so these other materials would need an even greater slope and curvature than observed soils the differences in reflectance properties for common block surfaces compared to common soils imply that local weathering of blocks has not contributed significantly to the soil exposed at the landing sites

global color and albedo variations on io abstract three multispectral mosaics of io have been produced from voyager imaging data a global mosaic from each of the voyager 1 and voyager 2 data sets and a high resolution mosaic of the region surrounding the volcano ra patera the mosaics are maps of normal albedo and color in accurate geometric map formats io s photometric behavior mapped with a two image technique is spatially variable especially in the bright white areas the disk integrated color and albedo of the satellite have been remarkably constant over recent decades despite the volcanic activity and the many differences between voyager 1 and 2 images acquired just 4 months apart this constancy is most likely due to the consistent occurrence of large pele type plumes with relatively dark red deposits in the region from long 240 to 360 a transient brightening southeast of pele during the voyager 1 encounter was probably due to real changes in surface and or atmospheric materials rather than to photometric behavior the intrinsic spectral variability of io as seen in a series of two dimensional histograms of the multispectral mosaics consists of continuous variation among three major spectral end members the data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur and it is closely associated with the peletype plume deposits unit 2 is strongly confined to the polar caps above about latitude 50 but its composition is unknown unit 5 is probably so 2 with relatively minor contamination it is concentrated in the equatorial region and near the long lived prometheus type plumes units 3 and 4 are gradational between units 1 and 5 in addition to so 2 and elemental sulfur other plausible components of the surface are polysulfur oxides fecl 2 na 2 s and nahs

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

global imaging of mars by hubble space telescope during the 1995 opposition hubble space telescope hst imaging of mars near the 1995 opposition resulted in excellent synoptic scale images of the planet during the spring season in the northern hemisphere because this season coincides with the aphelion position of mars in its orbit it is therefore the most difficult for ground based observation because of the relatively small angular size of mars this is the first sequence of images fully utilizing the capability of the new planetary camera to produce global synoptic images of the planet the images reveal bright discrete clouds associated with topographic features superimposed on a zonal band of condensate clouds between latitudes 10 and 30 the maximum violet optical depth of the cloud band is about 0 3 in a few instances the appearance of clouds beyond the morning terminator can be used to infer cloud heights of roughly 8 km a large dark albedo feature in the cerberus region observed for many years by ground based observers has almost disappeared in the 1995 hst images other aspects of mars such as the north polar cap appear much as they did during previous oppositions although cloudy regions were observed by spacecraft during this season the hst images uniquely reveal the global extent of significant optical depth clouds

revision of magnitudes of large shallow earthquakes 1897 1912 abstract in previous research trace amplitudes of surface wave maxima recorded by undamped milne seismographs were used to determine the surface wave magnitudes ms of large shallow earthquakes which occurred prior to 1912 for this purpose the effective gain of these instruments was calibrated by using the surface wave magnitudes ms gr which were calculated from the unpublished worksheets for seismicity of the earth of gutenberg and richter in this paper the real quality of ms gr is critically re evaluated by using independent sets of data it is found that ms gr for the period 1904 1909 is considerably overestimated the average excess from the real ms is 0 5 units for 1904 1906 0 4 for 1907 0 3 for 1908 1909 and 0 0 for 1910 1912 this overestimation is so systematic and large that the previous results are all redetermined the average effective gain of milne instruments is revised to be 21 9 previously the gain depended on ms this revision results in systematic reduction in the previously assigned magnitudes the revised values of ms for 264 shallow earthquakes with ms 6 8 and over in the period 1897 1912 inclusive are listed the present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century the present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909

spectral evidence for the mineralogy of high albedo soils and dust on mars because of the lack of direct mineralogic data available for mars spectral remote sensing techniques and in particular earth based reflectance spectroscopy remain the primary source of this information presented here are laboratory observations which further constrain the mineralogy and origin of the high albedo soils and dust earth based observations show the reflectance spectra of classical bright regions to be fairly uniform with a strong fe3 o2 charge transfer absorption edge extending from the near uv through the visible this absorption is relatively smooth unlike those observed for crystalline ferric oxides which have superimposed fe3 crystal field bands dilution of ferric oxide with a spectrally more neutral medium montmorillonite weakens the charge transfer and crystal field absorptions together and does not serve to make the ferric oxide spectrum more mars like smoother nontronite ferric iron bearing smectite clay was also investigated for spectral agreement with telescopic observations pure nontronite has fe3 absorptions analogous to but different from ferric oxides as in the previous case the absorptions are very distinct and inappropriate for mars admixture of neither montmorillonite nor ferric oxide serves to improve the nontronite spectrum the conclusion is that nontronite is not a major component of martian soils although the presence of other iron poor clays cannot be totally excluded based on currently available observational data the best spectral analogs known for high albedo soil and dust are a specific type of palagonite from hawaii x ray amorphous weathering products of mafic volcanic glass the indication is therefore that ferric iron on mars is likely to occur in poorly defined crystallo graphic sites such as found in these amorphous materials these materials form slowly under semiarid conditions at ambient temperature even low temperature hydrothermal alteration of glass might provide enough ion mobility to favor some formation of crystalline clays over amorphous gels and may therefore not be the primary mechanism responsible for soil formation on mars the amorphous hawaiian soils exist metastably for thousands of years on earth similar materials on mars would be expected to survive considerably longer under the present cold and dry climatic conditions

surface compositional properties of the malea planum region of the circum hellas volcanic province mars abstract we used thermal emission spectrometer tes thermal emission imaging system themis high resolution stereo camera hrsc and observatoire pour la mineralogie l eau les glaces et l activite omega data to assess the physical and compositional properties of the malea planum portion of the circum hellas volcanic province chvp our analysis of surface materials shows that the thermal inertia decreases from north to south and that there is greater dust cover on the flanks of the chvp volcanoes than in their putative calderas local variations in thermal inertia in malea planum are likely due to variations in surface material caused by aeolian and periglacial permafrost processes whereas regional variations are likely due to seasonal deposition and sublimation of ice at higher latitudes spectral analysis of omega data indicates the widespread presence of pyroxenes and or olivine particularly in the rims of craters that likely excavated volcanic materials dark materials occur throughout the chvp but are concentrated in topographic lows such as crater and caldera floors derivation of modal mineralogies from omega data show a variation in composition of dark materials across malea planum eastern dark deposits have higher olivine and low calcium pyroxene contents lower high calcium pyroxene contents and higher ratios of low calcium to total pyroxene relative to western dark deposits correlation with cratering model age estimates suggests that the western deposits are associated with older features 3 8 ga than the eastern deposits 3 6 ga but these age differences are within uncertainties nevertheless these results suggest a potential change in composition of volcanic materials in the malea planum portion of the chvp with space and possibly time

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

earthquake recurrence of a particular type the recurrence relation for turkish earthquakes expressed as the single frequency versus magnitude dependence exhibits significant maxima and minima reflecting true physical conditions various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity the results may be applicable to regions with high seismicity

earthquake frequency and energy in greece abstract on the basis of a newly published revised earthquake catalogue for the greek area a study is made of its seismicity in terms of earthquake frequency and energy as functions of space time and magnitude in addition attempts are made to estimate the maximum possible magnitudes as functions of space the study is essentially a methodological experiment with tectonophysical and engineering results

impact melts and glasses on mars 1 dark mobile materials on mars are widely considered to be volcanically derived windblown particulates such a conclusion is consistent with the large volcanic edifices on mars and the assumption that a volatile rich crust would not favor significant impact melt generation several post viking discoveries however provide new perspectives for reconsidering alternative origins not only for some of the mobile dark veneers but also certain materials at the pathfinder and viking landing sites first certain dark materials on mars do not exhibit the expected mafic absorption features in their reflectance spectra second the pathfinder mission revealed unexpected feldspathic compositions of vesicular blocks that lead to a preliminary conclusion that they represent andesites or basaltic andesites rather than basalts third recent discoveries of holocene to miocene impacts in argentine loessoid deposits provide new insights for the nature of melts generated from eolian sediments fourth global dispersal of impact melt products are now recognized in the terrestrial record throughout the cenozoic consequently the generation and preservation of impact glass on mars should be reconsidered possible occurrences include possible tektite like strewnfields downrange from recent oblique impacts dark avalanches emerging from backwasting cliffs of easily eroded unconformable deposits global dispersal of glassy ejecta from hesperian and amazonian craters of chicxulub scale and dark mobile veneers emerging from noachian craters we propose that the mobile dark materials comprising many of the named features of mars as well as some blocks at the pathfinder viking landing sites may represent impact melt products

constraints on the frequency magnitude relation and maximum magnitudes in the uk from observed seismicity and glacio isostatic recovery rates summary earthquake populations have recently been shown to have many similarities with critical point phenomena with fractal scaling of source sizes energy or seismic moment corresponding to the observed gutenberg richter g r frequency magnitude law holding at low magnitudes at high magnitudes the form of the distribution depends on the seismic moment release rate mand the maximum magnitude m max the g r law requires a sharp truncation at an absolute maximum magnitude for finite m i n contrast the gamma distribution has an exponential tail which allows a soft or credible maximum to be determined by negligible contribution to the total seismic moment release here we apply both distributions to seismic hazard in the mainland uk and its immediate continental shelf constrained by a mixture of instrumental historical and neotectonic data tectonic moment release rates for the seismogenic part of the lithosphere are calculated from a flexural plate model for glacio isostatic recovery constrained by vertical deformation rates from tide gauge and geomorphological data earthquake focal mechanisms in the uk show near vertical strike slip faulting with implied directions of maximum compressive stress approximately in the nnw sse direction consistent with the tectonic model maximum magnitudes are found to be in the range 6 3 7 5 for the g r law or 7 0 8 2 m l for the gamma distribution which compare with a maximum observed in the time period of interest of 6 1 m l the upper bounds are conservative estimates based on 100 per cent seismic release of the observed vertical neotectonic deformation glacio isostatic recovery is predominantly an elastic rather than a seismic process so the true value of m max is likely to be nearer the lower end of the quoted range

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

red violet contrast reversal on mars significance for eolian sediments abstract albedo markings on mars can exhibit reversed contrast with their surroudings when imaged in red and violet light a complete search of viking orbiter images shows this phenomenon on scales less than 300 km is restricted to specific eolian features intracrater deposits and wind streaks originating from the deposits contrast reversal is not found between features such as lava flows of different ages that might expose different materials without a largely eolian influence laboratory simulations suggest that iron oxides are the most likely materials involved in contrast reversal on the martian surface red violet contrast reversal is achieved easily but not exclusively between samples from which very fine particles m in diameter have been removed and corresponding samples in which larger grains are coated by such fine particles substantial particle size dependent albedo and color viriations exist for material which can be carried in suspension on mars m thus all fine grained eolian deposits on mars need not be the same as the brighter parts of arabia which have colors and albedos similar to the fine m component of martian dust storms the observed contrast reversal characteristics and colors of the intracrater dunes and related sediments can be explained readily if they are essentially free of adhering dust as would be the case if such eolian features were subject toactive saltation

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

determining the modal mineralogy of martian soils 1 a method for identifying the major and minor minerals and quantifying their proportions by weight in soils at the mars exploration rovers landing sites is presented the procedure utilizes modeled mossbauer data for iron bearing minerals chemical calculations of alpha particle x ray spectrometer data for iron absent minerals and modeling of minites thermal infrared spectra for silica and clays two models are formulated using different assumptions about the mineralogy of sulfur and chlorine sulfate chloride or incorporated in or adsorbed onto schwertmannite akaganeite the actual soil mineralogy may be bracketed by these results using either model average dark soils on the gusev crater plains and on meridiani planum are shown to be composed of a mixture of igneous olivine pyroxene plagioclase fe ti cr spinels phosphate and alteration amorphous silica hematite nanophase oxides clays plus sulfate chloride or oxysulfate oxychloride minerals this assemblage suggests that soil alteration did not occur in situ and that the igneous and alteration components were likely derived from different sources the model dependent mixing ratio of igneous and alteration components is identical at the two sites on opposite sides of the planet implying that martian soils may provide a representative mineralogical sampling of the exposed crust

observational evidence of crystalline iron oxides on mars visible to near ir 0 4 1 0 mu m spectral reflectance observations of mars during the 1988 opposition were performed at mauna kea observatory using a circular variable filter spectrometer at a spectral resolution r lambda delta lambda approx 80 on august 13 and 14 1988 ut 41 regions 500 600 km in diameter were observed on mars the data have been reduced both to reflectance relative to solar analog mars 16 cyg b and to relative reflectance spot spot the spectra show the strong near uv reflectance dropoff characteristic of mars as well as absorptions at 0 62 0 72 mu m and 0 81 0 94 mu m both seen here clearly for the first time these absorption features are interpreted as fe sup 3 electronic transition bands that indicate the presence of crystalline ferric oxide or hydroxide minerals on the martian surface comparison of these data with laboratory spectra obtained by other workers supports the conclusion that a single iron oxide phase most likely hematite could account for all of the observed spectral behavior of the martian surface soils and airborne dust in the 0 4 1 0 mu m region this possibility must be reconciled with data from other possible spectral analogs and other wavelength regions as well as geochemical and mineral stability considerations to arrive at amore more complete understanding of the role of ferric minerals in martian surface mineralogy and weathering less

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

moment magnitude scaling in the aegean area abstract sixteen new determinations of scalar seismic moment from spectral modelling of rayleigh waves at 30 60 s period in the aegean area are presented when combined with earlier results obtained by a similar method the moment magnitude relationship from 50 events in the magnitude range 5 3 m s log m o 1 5 m s 9 198 0 317 for a constant stress drop dislocation model and m o in n m in contrast 15 published moments from body wave modelling at 20 s period and moment tensor inversion at periods greater than 45 s give log m o 1 5 m s 8 823 0 248 the surface wave results imply stress drops of 25 12 25 bar for the dislocation model and the body wave results imply systematically higher stress drops of 55 27 55 bar compared to 24 bar from field observation of the gulf of corinth sequence and 7 12 bar from inversion of body wave spectra and aftershock studies the latter are likely to be underestimates however the factor two scatter in the stress drops determined from the moment magnitude relation is much less than the factor four error in the estimated stress drop which might be introduced by model dependent systematics effects and these discrepancies may not be significant if the stress drop is free to vary then log m o 1 206 0 105 m s 10 970 0 632 surface waves log m o 1 160 0 181 m s 11 027 0 338 body waves this shows that the discrepancy between the two sets of results in negligible at m o 5 5 and thereafter increases slightly with earthquake size indicating that the underlying cause of the systematic difference in seismic moment for a given magnitude may be related to source size

dust streaks on mars global mapping and photometry of selected areas on mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia data on the colors albedos and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter redder dust less than 20 of the ground need be covered by the optically thick dust in the brightest parts of the streaks the amount of dust in optically thick layers could be as little as 10 3 g cm2 dark streaks can be interpreted as erosional windows in a patchy dust cover our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous optically thin layers it has the advantage that large amounts of dust can be deposited without affecting regional albedos

the circum hellas volcanic province mars assessment of wrinkle ridged plains abstract wrinkle ridged plains common on the terrestrial planets are inferred to form by tectonic deformation of volcanic or sedimentary surfaces if wrinkle ridged plains adjacent to volcanic features originated from volcanic activity associated with the features then the plains should have similar ages to the volcanic features as well as other morphological or compositional indicators of volcanism we test this hypothesis on several regions of wrinkle ridged plains bounding the circum hellas volcanic province chvp we constructed themis daytime ir mosaics spatial resolution 100 m pixel and performed crater counts to determined cratering model formation ages of these regions we found ages of 3 4 3 7 ga for se malea planum 3 6 3 7 ga for w promethei terra 3 5 3 7 ga for hesperia planum and 3 6 3 8 ga for the eastern hellas basin floor all of which are contemporaneous with the formation of the major volcanic edifices 3 6 3 8 ga in the chvp although examination of available moc ctx hirise themis and hrsc data shows few examples of features definitive of a volcanic origin of these wrinkle ridged plains hrsc true color images 50 100 m pixel show that large areas of these plains have a dark blue black color consistent with previous viking and mars express hrsc and omega color spectral studies indicative of basaltic compositions however in some areas this color may be due to aeolian mantles rather than underlying bedrock thus we cannot demonstrate unequivocally that these wrinkle ridged plains are volcanic beyond the synchronicity of their formation ages with those of the chvp volcanoes nevertheless if these wrinkle ridged plains were originally formed by volcanic activity or other processes induced by volcanic activity then the inclusion of these regions brings the size of the chvp to 4 86 106 km 2 comparable in size to the elysium volcanic province thus the chvp may have been a dominant source of volcanism early in martian history

low albedo surfaces and eolian sediment mars orbiter camera views of western arabia terra craters and wind streaks 1 high spatial resolution 1 5 to 6 m pixel mars global surveyor mars orbiter camera images obtained september 1997 to june 2001 show that each of the large dark wind streaks of western arabia terra originate at a barchan dune field on a crater floor the streaks consist of a relatively thin 1 m coating of sediment deflated from the dune fields and their vicinity in most cases this sediment drapes over a previous mantle that more thickly covers nearly all of western arabia terra no concurrent eolian bedforms are found within the dark streaks nor do any dunes climb up crater walls to deliver sand via saltation to the streaks the relations between dunes wind streak and subjacent terrain imply that dark toned grains finer than those that comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain previous eolian physics and thermal inertia studies suggest that under modern martian conditions such grains likely include silt 3 9 62 5 m very fine sand 62 5 125 m and possibly fine sand to 210 m the streaks change in terms of extent relative albedo and surface pattern over periods measured in years however through june 2001 very little evidence for recent eolian activity dust plumes storms dune movement was observed

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

deep borehole log evidence for fractal distribution of fractures in crystalline rock summary sonic velocity and electrical resistivity logs run to a depth of 3 5 km in crystalline rock near the san andreas fault at cajon pass in southern california correlate over scale lengths both small sub metre and large tens to hundreds of metres no such correlations are seen with the more lithologically sensitive natural gamma intensity log the correlation between the sonic velocity and electrical resistivity logs suggests that a non lithologic property of the crystalline rock controls fluctuations in situ fracture intensity is a logical candidate for the controlling rock property the fluctuations of the individual sonic velocity and electrical resistivity logs are examined with the hurst rescaled range parameter over borehole log intervals 1 5 m l 1500 m for log fluctuations arising from a scale invariant physical process the hurst rescaled range scales with data interval as lh 0 h 1 a purely random sequence of in situ fractures produces a scaling exponent h 0 50 fluctuations in the cajon pass sonic velocity and electrical resistivity logs yield h 0 70 evidence that in situ fracture sets tend to occur in clusters rather than at purely random intervals the tendency for fracture clustering over log intervals 1 5 m l 1500 m suggests that fracture formation is a fractal process independent of length scale in which larger fracture intervals form from clustering of numerous smaller fracture intervals seismic reflectivity derived from the borehole sonic velocity log is also scale independent over the range of data intervals 1 5m l 1500 m with a hurst exponent h 0 21 if we associate fracture clustering with crustal fault formation the cajon pass borehole sonic velocity and electrical resistivity logs predict that crustal faults scale fractally with fractal dimension d 2 30 the equivalent b value for earthquake size distribution is b d 2 1 15 on this hypothesis observed b values 1 15 indicate a tendency for earthquakes to cluster on existing weak faults a scale independent mechanics for crystalline rock fracture formation in which larger scale fractures form as clusters of smaller scale fractures provides a mechanical link between the small pervasive stress aligned flaws cracks and microfractures which can impart anisotropy to crystalline rock and the larger scale fractures associated with finite strain and faulting thus in crustal regions of active but low strain fracture anisotropy is observed to be aligned with the inferred maximum principal stress while in actively faulted crust fracture anisotropy is observed to be more nearly fault parallel as if the fractures are aligned by the finite strain faulting process

numerical simulation of the earthquake generation process a numerical algorithm is proposed for the simulation of the earthquake process during a seismic cycle the algorithm is based on a heterogeneous discrete model of the fault plane and assumes there are two kinds of seismicity background crack like earthquakes and asperity like events an active zone of the fault contains an asperity distribution with a characteristic elementary area the background seismicity randomly develops shear stress free surfaces which tend to surround the asperities as in a 2d percolation process the model parameters are taken from observations on the vrancea romania intermediate depth seismic region the results emphasize the significant role of the geometry in the mechanism of the seismic failure the algorithm predicts the nonlinear behavior in the frequency magnitude distribution the decrease of theb slope associated with the asperity like events the magnitude range of major earthquakes and their recurrence times

estimates of long term probabilities for future great earthquakes in the aleutians we compute probabilities for future great earthquakes in the aleutian arc probability distributions are fitted to recurrence periods of great aleutian evens m sub w or 7 8 since 1788 given a probability distribution and data of the last grat earthquake in each arc segment time dependent conditional probabilities are determined for future periods of interest we obtain for the next two decades high probabilities 99 to 30 for great earthquakes in the shumagin yakataga unalaska and kommandorski seismic gaps these probabilities are higher than for any other assessed region of the u s believed to be capable of great earthquakes low probabilities 17 to 9 are found for segments that ruptured most recently in 1965 1964 and 1957 recurrence periods for great earthquakes measure on average about 80 years but vary substantially whether recurrence periods for great aleutian earthquakes follow a normal log normal or any other probability distribution is not resolved because in most arc segments the known seismic record embraces at best one or two recurrences the resulting uncertainty affects the magnitude of estimated probabilities especially in seismic gaps that have not ruptured for a long time in some instances a normal distribution yields a three times higher probability than the correspondingmore log normal distribution less

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

a fractal approach to probabilistic seismic hazard assessment abstract the definition of a fractal distribution is that the number of objects events n with a characteristic size greater than r satisfies the relation n r d where d is the fractal dimension the applicability of a fractal relation implies that the underlying physical process is scale invariant over the range of applicability of the relation the empirical frequency magnitude relation for earthquakes defining a b value is a fractal relation with d 2b accepting the fractal distribution the level of regional seismicity can be related to the rate of regional strain and the magnitude of the largest characteristic earthquake high levels of seismic activity indicate either a large regional strain or a low magnitude maximum characteristic earthquake or both if the regional seismicity has a weak time dependence the approach can be used to make probabilistic seismic hazard assessments as in many fractal applications the basic approach has been used in the past however the association of a fractal behavior with scale invariance provides a rational basis for the extrapolation of frequency magnitude statistics in order to make predictions of seismic hazards

spectral identification of geological units on the surface of mars related to the presence of silicates from earth based near infrared telescopic charge coupled device imaging during the september 1988 mars opposition the authors obtained new high spatial 100 150 km and spectral delta lambda lambda 1 resolution near ir telescopic charge coupled device images of mars from pic du midi observatory these images allow the association of spectral units with morphologic surface units on mars especially within the dark regions which exhibit much greater variability than the bright regions mineralogical interpretation of the data leads to a global description of the surface state of alteration consistent with the spatial distribution of bright and dark regions with the bright regions being more altered than the dark within the less altered regions fe sup 2 crystal field absorption bands are detected indicative of the presence of mafic minerals opx cpx o1 in agreement with a likely crustal basaltic composition the most conspicuous fe sup 2 absorption features are clearly related to the volcanic regions of the syrtis major shield and hesperia planum unit the strongest observed absorptions due to olivine and clinopyroxene are spatially associated with the restricted central caldera complex of nili meroe paterae within syrtis major and the tyrrhena patera unit within hesperia planum and indicate an ultramafic composition

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

dark materials in valles marineris indications of the style of volcanism and magmatism on mars rifting on the equatorial canyon system of valles marineris provides a unique view of the interior of the martian crust to depths reaching 7 km exposing several in situ bedrock units which testify to past volcanic and magmatic processes on mars a thick regionally extensive deposit observed in coprates and juventae chasmata is interpreted on the basis of spectral reflectance erosional morphology and tendency for eolian mobilization to be composed of mafic glass possibly an ancient martian analogue of the lunar terra mantling deposits spectral mapping suggests that the dark floor covering materials in the lower canyons are derived from this unit a series of cliffs in the ophir chasma wall rock is interpreted to be exposures of resistant bedrock the spectral signature of this massive and uniform unit most closely resembles that of terrestrial mafic rocks altered to or coated by crystalline hematite application of computer mapping techniques to probable young volcanic materials in the central troughs yields an inferred distribution of volcanic activity consistent with the interpretation of extrusion along faults near the margins of the canyon floors this result supports the hypothesis that the valles originated through tectonic extension

anisotropy of magnetic susceptibility in a palaeozoic flysch basin the windermere supergroup northern england abstract the windermere basin of northern england was initiated in late ordovician times and developed into a foreland basin by collision of the laurentian and eastern avalonian plates during silurian times it was largely filled by axial turbidite input in mid to late silurian times rock magnetic studies suggest that paramagnetic minerals probably mostly chlorite dominate the magnetic susceptibility studies of anisotropy of susceptibility ams identify a bedding related fabric which has survived later acadian deformation in all but the oldest u ordovician units the magnitude of the fabric becomes amplified in the higher more argillaceous parts of individual beds but the direction of maximum susceptibility k1 remains aligned with palaeoflow direction throughout the massive and parallel laminated divisions ams is best defined in those units with well developed planar and cross bedding the mechanism responsible for rippling the upper parts of the beds involves rolling of detrital grains along the bed during traction and alignment of the long axis the grain s rotation axis normal to the current consequently the intermediate axis of ams k2 is in the direction of the secondary current responsible for rippling some beds which are rippled throughout show the same feature hemipelagic facies comprising laminated silty mudstones have highly uniform fabrics to which detrital hematite is an important contributor the k1 directions in the bedding planes show cyclic swings in declination which may be related to some long period perhaps orbitally forced secular oceanographic variation since these sediments were deposited in optimum conditions for preserving grain alignment with the geomagnetic field ams and amr anisotropy of magnetic remanence study of such facies may provide methods for recovering secular variation in the remote geological past and for estimating rates of deposition

a cellular automata slider block model for earthquakes ii demonstration of self organized criticality for a 2 d system summary it has been suggested that distributed seismicity is an example of self organized criticality if this is the case the earth s crust in an active tectonic zone is in a near critical state and faults can interact over large distances observed seismicity and earthquake statistics are consequences of the dynamical interaction of seismic faulting over a wide range of scales we address this problem by considering a two dimensional array of slider blocks with static dynamic friction the twodimensional system is treated as a cellular automaton such that only one slider block is allowed to slip at a given time and interacts only with its nearest neighbours through connecting springs because of this treatment the amount of slip for each failed block can be obtained analytically and the system is deterministic with no stochastic inputs or spatial heterogeneities in many cases the slip of one block induces the slip of adjacent blocks the size of an event is specified by the number of blocks that participate in the event the number of small events with a specified size has a power law dependence on the size with a power close to 1 36 the distributions of normalized recurrence times for most events are close to a poisson process and gradually deviate towards periodicity for large events the recurrence time statistics are generally insensitive to parameter variations large events may occur at stress levels considerably lower than the failure strength of an individual block and the stress drops associated with large events are generally small this may provide an explanation for observed low stress levels in tectonically active

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

a characteristic earthquake model of the seismicity preceding the eruption of mount st helens on 18 may 1980 abstract the two classes of earthquakes which preceded the explosive eruption of mount st helens washington on 18 may 1980 can be related to two different forms of energy release this is manifest both in the predominant periods of the two classes of seismic energy release at 1 0 and 0 55 s and in the ratio of their source dimensions in the range 2 1 to 6 1 inferred from characteristic magnitudes of the two possible classes of earthquakes apparent in the discrete frequency magnitude distribution the observed increase in the ratio of long to short period amplitudes of surface waves recorded on mso a local wwssn station can be numerically related to the growth of a magma chamber or conduit within which are generated the transient oscillations thought to be responsible for volcanic tremor these calculations predict an increase in the chamber s diameter at a rate of 2 7 m day 1 at depth in the 2 months preceding the eruption and this is consistent with an observed growth rate of 2 m day 1 of the precursory bulge which appeared at the surface on the mountain s north flank at the time the frequency magnitude distribution is analysed in two parts corresponding to a power law at low magnitudes and a gaussian distribution of typical fault lengths at high magnitudes an extension of the characteristic earthquake model first developed for individual fault zones the power law can in general have a non integer exponent which can be equated to a fractal self similarity dimension d temporal changes in d which is proportional to the seismic b value are proposed as an alternative and complementary description of the way seismic energy is released to the more commonly used viewpoints of changes in stress and heterogeneity despite a reassessment of the completeness of the magnitude catalogue no clear seismic precursor to the explosive eruption is observed in the b value although an earlier phase of phreatic eruptions was strongly associated with a b value anomaly

scaling of intraplate earthquake recurrence interval with fault length and implications for seismic hazard assessment consensus indicates that faults follow power law scaling although significant uncertainty remains about the values of important parameters combining these scaling relationships with power law scaling relationships for earthquakes suggests that intraplate earthquake recurrence interval scales with fault length regional scaling data may be locally calibrated to yield a site specific seismic hazard assessment tool scaling data from small faults those that do not span the seismogenic layer suggest that recurrence interval varies as a negative power of fault length due to uncertainties regarding the recently recognized changes in scaling for large earthquakes it is unclear whether recurrence interval varies as a negative or positive power of fault length for large faults those that span the seismogenic layer this question is of critical importance for seismic hazard assessment

new radar derived topography for the northern hemisphere of mars earth based radar altimetry data for the northern equatorial belt of mars 6 s 23 n have recently been reduced to a common basis corresponding to the 6 1 mbar reference surface a first look at these data indicates that the elevations of tharsis elysium and lunae planum are lower by 2 5 km than has been suggested by previous estimates these differences show that the required amount of tectonic uplift or constructional volcanism for each area is less than has been previously envisioned atmospheric or surficial conditions are suggested which may explain the discrepancies between the radar topography and elevations measured by other techniques the topographies of chryse planitia syrtis major and valles marineris are also described

surficial geologic surveys of gale crater and melas chasma mars integration of remote sensing data abstract remote sensing observations of gale crater and melas chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions data sets analyzed include geologic maps mars orbiter laser altimeter mola elevation thermal emission spectrometer tes albedo tes thermal inertia mola residual pulse width tes rock abundance and viking and mars orbiter camera images using these data sets we constrain the properties of and processes acting on the present surface and create self consistent models for the surface layer surface properties within gale crater are variable and complex and interpreting the surface layer is not straightforward observations indicate that aeolian processes have shaped some of the intracrater surface but other areas do not comply with this model and have counterintuitive surface characteristics in contrast aeolian activity appears to have played a large role in shaping the present day physical structure of all surfaces in melas chasma and is reflected in the remote sensing data sets here we summarize our analysis and discuss the surface attributes as determined from these data sets

the nanophase iron mineral s in mars soil a series of surface modified clays containing nanophase np iron oxide oxyhydroxides of extremely small particle sizes with total iron contents as high as found in mars soil were prepared by iron deposition on the clay surface from ferrous chloride solution comprehensive studies of the iron mineralogy in these mars soil analogs were conducted using chemical extractions solubility analyses ph and redox x ray and electron diffractometry electron microscopic imaging specific surface area and particle size determinations differential thermal analyses magnetic properties characterization spectral reflectance and viking biology simulation experiments the clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron which slowly converts to more stable fully oxidized iron minerals the clay acted as an effective matrix both chemically and sterically preventing the major part of the synthesized iron oxides from ripening i e growing and developing larger crystals the precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1 10 nm having large specific surface area the noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate lepidocrocite gamma feooh was detected by selected area electron diffraction it is formed from a double iron fe ii fe iii hydroxy mineral such as green rust or ferrosic hydroxide magnetic measurements suggested that lepidocrocite converted to the more stable maghemite gamma fe2o3 by mild heat treatment and then to nanophase hematite alpha fe2o3 by extensive heat treatment after mild heating the iron enriched clay became slightly magnetic to the extent that it adheres to a hand held magnet as was observed with mars soil the chemical reactivity of the iron enriched clays strongly resembles and offers a plausible mechanism for the somewhat puzzling observations of the viking biology experiments their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide oxyhydroxides and silicate phase surfaces the reflectance spectrum of the clay iron preparations in the visible range is generally similar to the reflectance curves of bright regions on mars this strengthens the evidence for the predominance of nanophase iron oxides oxyhydroxides in mars soil the mode of formation of these nanophase iron oxides on mars is still unknown it is puzzling that despite the long period of time since aqueous weathering took place on mars they have not developed from their transitory stage to well crystallized end members the possibility is suggested that these phases represent a continuously on going extremely slow weathering process

frequency magnitude distribution of earthquakes in vrancea relevance for a discrete model a high resolution analysis of a homogeneous and complete data set of intermediate depth microearthquakes h 60 km extending over an interval of 9 3 years emphasizes a significant deviation at low magnitudes ml 4 in a linear frequency magnitude distribution it appears as a distinct change in the slope of the cumulative distribution and as a seismicity deficit followed by a relative enhancement in the corresponding noncumulative curve this is in agreement with the presence of two characteristic mechanisms and allows the identification of both the magnitude threshold of asperity like earthquakes and the transition zone ml 3 3 3 9 from crack like earthquakes background seismicity to asperity like events these features are better pointed out on well individualized active zones the background seismicity shows a tremendeous decrease in its b slope from 1 03 to 0 57 during a 6 year interval before the occurrence of a major earthquake in 1986 mw 7 3 followed by a fast recovery to 1 03 in 2 years after this event such a behavior could be correlated to the continuous growth of the shear stress free surface on the fault as in a percolation process followed by its sudden diminution due to the locking of the fault the above results provide relevance for the discrete character of faulting and enable a coherent modeling of the earthquake generation process from microearthquake to major event scale lengths

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

young volcanic deposits in the valles marineris mars abstract a study of the interior deposits of the central valles marineris has led to the discovery of a sequence of deposits that cover the chasma floors and range in thickness from that of thin dust to several kilometers the emplacement of the deposits was the last major event in the history of the valles marineris following deposition of older layered interior beds warping faulting erosion and landslide emplacement the young deposits are of three major types 1 dark patches typically occurring along faults 2 light colored deposits locally associated with craters and 3 rugged mottled deposits with in places light colored lobate fronts these young materials may be of volcanic origin as suggested by the low albedo and spectrally gray colors of some their association with faults and possible volcanic craters and calderas and their embayment relations and lobate margins no other mechanism explains all the observed features and relations as well as volcanism if these deposits are volcanic implications are that 1 volcanism was associated with rifting in the valles marineris 2 the volcanism was explosive in places and 3 the volcanism may be as young as the late tharsis volcanism and locally may well be recent

paleocurrent patterns of the sedimentary sequence of the taitao ophiolite constrained by anisotropy of magnetic susceptibility and paleomagnetic analyses abstract determination of paleocurrent directions is a robust approach to establish the mechanism of sediment transport and of deposition however in tectonically controlled or affected basins where rotations are suspected it is of critical importance to correct previously calculated paleocurrent directions to establish the original pre tectonic transport and deposition patterns in order to illustrate this we determined the orientations of the anisotropy of magnetic susceptibility ams fabrics from 14 sites distributed along the sedimentary deposits interbedded within the late miocene main volcanic unit mvu of the taitao ophiolite southern chile data were used to estimate characteristics directions and relative velocities of the sediment transporting paleocurrents and orientations of the depositional slope sedimentary deposits consist of a rhythmic sequence of conglomerate base sandstone and mudstone top beds that present a systematic decrease in grain size up sequence as a whole and within individual beds sedimentary deposits of the mvu as well as overlaying effusive volcanic products are disrupted by small and discrete dextral normal brittle faults the distribution of fault planes and their kinematic characteristics suggest the development of a dextral negative flower like fault zone in the area previously reported nw ward paleocurrent directions obtained from the orientations of sedimentary structures roughly agree with our calculations based on the orientations of ams fabrics calculated paleocurrent directions are sub parallel to the nw se trend of estero cono channel the main lineament in the area the spatial distribution of ams axes between and within sites suggest that coarse grain deposits were transported by relatively high velocity flows whereas fine grained deposits were by low to nearly null velocity flows previously reported paleomagnetic analyses indicate that counterclockwise rotations affected the whole taitao ophiolite including the mvu by applying the necessary corrections we obtained paleocurrent directions yielding mostly nnw ward directions restoration of the orientations of beddings indicates that the depositional surface dipped steeply at its easternmost edge and shallowly at the westernmost end we propose here that sediments were transported by turbidite flows generated by slope instabilities in the innermost part of the estero cono these turbidites followed the estero cono lineament while they filled the channel and transported sedimentary material eroded from the upper portions of the ophiolite and nearby units towards the pacific ocean sediments were deposited on a nw to w facing slope and sorted in decreasing grain size along the channel the instability of the slope was most probably triggered by the activity of a transtensional fault zone developed along the mid axis of the estero cono channel

frequency of occurrence of moderate to great earthquakes in intracontinental regions implications for changes in stress earthquake prediction and hazards assessments we investigate the departure of shallow intracontinental earthquakes from the frequency magnitude relationship log n m a bm we consider seven large continental regions but exclude subduction zones in each active and stable areas are differentiated within active areas we separately categorize earthquakes on faults with high slip rates we use data sets from 1978 1994 and 1900 1994 which are complete for moment magnitudes mw 5 3 and 7 0 to calculate changes in b value with mw for all active intracontinental regions combined except asia b changes at 98 confidence from 0 90 to 2 1 at a corner magnitude mc of 6 9 to 7 0 the distribution for stable regions indicates a similar change values of mc are associated with downdip widths of rupture of about 23 to 27 km which are smaller than those for subduction zones in each case mc marks a transition from unbounded to bounded earthquakes in asia events from 1958 to 1994 also delineate a similar change near mc 7 0 earthquakes in asia of 7 0 mw 8 1 from 1900 to 1957 however define a b value of 1 0 and a moment release rate 5 6 times higher than that from 1958 to 1994 those anomalous values indicate that a large region of asia was close to failure i e near a self organized critical state during the earlier period we associate those changes with the giant himalayan earthquake in 1950 of mw 8 6 regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries extrapolating rates of activity of the past 95 years to mw 8 0 indicates that such events should be very rare in stable areas

seismic risk of circum pacific earthquakes i strain energy release commonly used earthquake whole process frequency magnitude and strain energy magnitude laws are merged to obtain an analytic expression for an upper bound magnitude to regional earthquake occurrencem3 which is expressed primarily in terms of the annual maximum magnitudem1 and the magnitude equivalent of the annual average total strain energy releasem2 values ofm3 are also estimated graphically from cumulative strain energy release diagrams both methods are illustrated by application to the high seismicity of the circum pacific belt using duda s 1965 data and regionalisation values ofm3 obtained analytically with their uncertainties are in agreement with those obtained graphically empirical relations are then obtained betweenm1 m2 andm3 which could be of general assistance in regional seismic risk considerations if they are found to be of a universal nature for instance m3 andm2 differ by one magnitude unit in subregions of the circum pacific

maximum earthquake magnitudes in the aegean area constrained by tectonic moment release rates summary seismic moment release is usually dominated by the largest but rarest events making the estimation of seismic hazard inherently uncertain this uncertainty can be reduced by combining long term tectonic deformation rates with short term recurrence rates here we adopt this strategy to estimate recurrence rates and maximum magnitudes for tectonic zones in the aegean area we first form a merged catalogue for historical and instrumentally recorded earthquakes in the aegean based on a recently published catalogue for greece and surrounding areas covering the time period 550 bc 2000 ad at varying degrees of completeness the historical data are recalibrated to allow for changes in damping in seismic instruments around 1911 we divide the area up into zones that correspond to recent determinations of deformation rate from satellite data in all zones we find that the gutenberg richter gr law holds at low magnitudes we use akaike s information criterion to determine the best fitting distribution at high magnitudes and classify the resulting frequency magnitude distributions of the zones as critical gr law subcritical gamma density distribution or supercritical characteristic earthquake model where appropriate we determine the ratio of seismic to tectonic moment release rate low values of 1 0 the seismic and tectonic moment release rates are then combined to constrain recurrence rates and maximum credible magnitudes in the range 6 7 7 6 m w where the results are well constrained based on extrapolating the short term seismic data with current earthquake data many of the tectonic zones show a characteristic distribution that leads to an elevated probability of magnitudes around 7 but a reduced probability of larger magnitudes above this value when compared with the gr trend a modification of the generalized gamma distribution is suggested to account for this based on a finite statistical second moment for the seismic moment distribution

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and

earthquakes of the holocene geologic studies of earthquakes involve mapping of coseismic surface faulting and secondary deformation from historical events trenching and geomorphic analysis to define the timing and size of past earthquakes and investigations of fault zone structure and geometry in both unconsolidated sediments and bedrock this research is now being referred to as paleoseismology seismic geology and earthquake geology since the mid 1970s it has led to some of the most exciting and important contributions to the understanding of earthquake behavior in space and time hanks 1985 allen 1986 the present report is the first of what is hoped will become a regularly contributed summary of the geologic aspects of the study of earthquakes

nature and origin of materials exposed in the oxia palus western arabia sinus meridiani region mars abstract mars observer will map physical elemental and mineralogical properties of surface materials a key to understanding the regional variations in crustal composition will be the extent to which in situ debris produced from bedrock can be separated from laterally mixed eolian sediments viking orbiter image and thermal data covering equatorial cratered terrain in western arabia eastern oxia and sinuses sabaeus and meridiani were evaluated to test whether local materials related to bedrock could be identified characterized and mapped crater obliteration models imply that kilometers of debris have been produced locally although obliteration rates for the past few billion years have been less than 8 10 3 m year fluvial and eolian landforms clearly indicate lateral transport and mixing of tens of meters of debris six sets of calibrated violet green and red viking images covering the study area were mosaicked and examined in combination with block abundance and fine component inertias from irtm data three major color thermal units can be discerned bright red dust storm deposits brown materials that are probably indurated and dark less red materials that are probably composed of lithic fragments in the medium sand size range the unit boundaries are independent of bedrock geology and erosional landforms the brightest red material apparently mixes with each of the darker units the presence of dark splotches streaks and dunes associated with large craters in oxia indicates that the dark less red material is also mobile the surficial units exposed over the 6 10 6 km 2 study area are therefore likely to represent mixed eolian deposits predominantly decoupled from the underlying bedrock unraveling the mixtures and assignment of components to local bedrock origins will be a major challenge for mars observer