impact shock behavior of mg and ca sulfates and their hydrates abstract shock recovery experiments on mgso4 caso4 and their hydrates kieserite epsomite and bassanite were performed to investigate shock induced dehydration and decomposition at shock pressures up to 36 gpa the recovered solid samples indicated dehydration at pressures below 24 gpa but no clear evidence was found for possible decomposition of mgso4 and caso4 to produce mgo or cao as final products these sulfates and hydrates have been observed on the surface of mars and the present experimental results can be applied towards understanding the presence of surface water on mars and the recycling of water by impacts this finding that the sulfate hydrates undergo dehydration upon impact as well as the fact that the sulfates caso4 and mgso4 absorb moisture suggests the total amount of water on mars has remained almost unchanged since the time of formation of the planet

a nonlinear theory for el nino bursting abstract a new mechanism is proposed that explains two key features of the observed el nino southern oscillation enso phenomenon its irregularity and decadal amplitude changes using a low order enso model the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong el nino events la nina events are not affected a feature that is also seen in enso observations one key result of this analysis is that decadal variability in the tropics can be generated without invoking extratropical processes or stochastic forcing the el nino bursting behavior simulated by the low order enso model can be understood in terms of the concept of homoclinic and heteroclinic connections it is shown that this new model for enso amplitude modulations and irregularity although difficult to prove might explain some features of enso dynamics seen in more complex climate models and the observations

source of low frequency modulation of enso amplitude in a cgcm we study the relationship between changes in equatorial stratification and low frequency el nino southern oscillation enso amplitude modulation in a coupled general circulation model cgcm that uses an anomaly coupling strategy to prevent climate drifts in the mean state the stratification is intensified at upper levels in the western and central equatorial pacific during periods of high enso amplitude furthermore changes in equatorial stratification are connected with subsurface temperature anomalies originating from the central south tropical pacific the correlation analysis of ocean temperature anomalies against an index for the enso modulation supports the hypothesis of the existence of an oceanic tunnel that connects the south tropical pacific to the equatorial wave guide further analysis of the wind stress projection coefficient onto the oceanic baroclinic modes suggests that the low frequency modulation of enso amplitude is associated with a significant contribution of higher order modes in the western and central equatorial pacific in the light of these results we suggest that in the cgcm change in the baroclinic mode energy distribution associated with low frequency enso amplitude modulation have its source in the central south tropical pacific

robust rock properties through pp ps processing and interpretation marcellus shale the estimation of reservoir properties from seismic amplitude is generally an underdetermined problem which can result in ambiguous estimation of the sought for properties although seismic reflectivity is dependent upon formation p and s wave velocities and density it is common practice to estimate only two attributes from prestack p wave data because of data limitations at far offsets and instabilities of inversion on the other hand the number of petrophysical properties that determine reservoir storability and production are four in the simplest of cases porosity lithology pore fluids type and amount and permeability ambiguity and risk reduction require the inclusion of additional robust information into the estimation of reservoir properties this is particularly true in formations where reservoir storability and production depend on additional petrophysical properties as would be the case of unconventional plays where brittleness and vertical fracture density and orientation are fact

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

influence of recent stratification changes on enso stability in a conceptual model of the equatorial pacific abstractchanges in the mean circulation of the equatorial pacific ocean partly control the strong decadal modulation of el nino southern oscillation enso this relationship is considered from the linear stability of a conceptual recharge discharge model with parameters tuned from the observed mean state whereas decadal changes in the mean thermocline depth alone are usually considered in conceptual enso models here focus is given to decadal changes in the mean stratification of the entire upper ocean e g the mean thermocline depth intensity and thickness those stratification changes modify the projection of wind stress forcing momentum onto the gravest ocean baroclinic modes their influence on the simulated frequency and growth rate is comparable in intensity to the one of usual thermodynamic and atmospheric feedbacks while they have here a secondary effect on the spatial structure and propagation of sst anomalies this sensitivity is evidenced in particular for the climate shift of the 1970s

rectification of enso variability by interdecadal changes in the equatorial background mean state in a cgcm simulation the link between the changes in equatorial background stratification and el nino southern oscillation enso modulation is investigated using a simulation from a 260 yr long coupled general circulation model cgcm the work focuses on the role of nonlinearities associated with equatorial wave dynamics as a first step the low frequency change in mean stratification is diagnosed and documented from the shallow water parameters derived from a vertical mode decomposition of the cgcm the parameters vary differently according to the baroclinic mode order which may explain why a flattening thermocline does not necessarily lead to reduced enso activity estimations of baroclinic mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the baroclinic modes as compared to the interannual variability in particular the high order modes associated with decadal variability have a more pronounced signature in the western pacific whereas that associated with interannual variability i e enso shows more energy in the eastern pacific in the light of the results of the cgcm vertical mode decomposition an intermediate coupled model icm is used to test whether the nonlinearities associated with the changes in the baroclinic mode energy distribution can lead to coherent enso modulation the results indicate that rectification of the interannual variability enso time scales by the interdecadal variability associated with changes in the oceanic mean states takes place in the icm the rectified effect results mostly in an increased variability and skewness of the zonal advection which tends to produce a zonal seesaw of the sea surface temperature anomaly a tropical mechanism for producing enso modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal mode of thermocline depth arising from ekman pumping anomalies located in the central south pacific

long term el nino southern oscillation enso like variation with special emphasis on the south pacific mechanisms for el nino southern oscillation enso like decadal 7 35 years variability are analyzed using observational data when a decadal positive temperature anomaly occurs in the eastern tropical pacific the atmospheric response excites negative wind stress curl in the western tropical south pacific which causes the thermocline to shoal and induce a negative temperature anomaly there the cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east the eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly the cold anomaly in the east grows through tropical air sea interaction and induces a positive wind stress curl in the western tropical south pacific associated with the atmospheric teleconnection in the southern hemisphere subsequent evolution of the negative phase is similar to that of the positive phase the complete scenario for this enso like decadal variability due to the air sea interaction processes within the tropics has a period of 14 years we also discuss enso like variation on the interdecadal 35 years timescale with possible relationship to the 1976 1977 climate regime shift

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

physical properties of shocked and thermally altered nontronite implications for the martian surface both shock recovery and thermal annealing experiments have been carried out on riverside nontronite an iron rich smectite clay that closely matches the composition but neither the color nor magnetic properties of the martian fines nontronite was recovered from peak shock pressures between 7 and 32 gpa with calculated peak mean bulk temperatures ranging from 125 to 1100 c other nontronite samples were heated in air for one hour at temperatures ranging from 400 to 1000 c at 100 c increments both shocked and heat treated samples were analyzed by magnetic measurements x ray diffraction and mossbauer spectroscopy nontronite powders shock loaded to peak calculated temperatures of 650 c to 750 c show a dramatic increase in ferromagnetic saturation magnetization ms a similar increase in magnetization in the same temperature range is observed in isothermally annealed powders at atmospheric pressure the x ray diffraction and mossbauer studies show however that for samples that experienced temperatures of 600 c or more the shocked material has little structural similarity to the isothermally annealed nontronite this suggests that the ferromagnetic properties may be due to a minor phase there is evidence from mossbauer spectra for metallic iron in the shocked samples and for superparamagnetic fe2o3 in the annealed samples in addition to magnetic and structural changes the shock and heating experiments altered the color of the nontronite from olive yellow toward reddish brown yielding material that matches the observed properties of the martian fines much more closely than the starting material does if nontronite is the major component of the martian fines as some workers suggest some mechanism for altering its properties is necessary the most likely being repeated impacts onto the surface of mars

relationship of p wave seismic attributes azimuthal anisotropy and commercial gas pay in 3 d p wave multiazimuth data rulison field piceance basin colorado this case history is one of three field projects funded by the us department of energy as part of its ongoing research effort aimed to expand current levels of drilling and production efficiency in naturally fractured tight gas reservoirs the original stated goal for the 3 d p wave seismic survey was to evaluate and map fracture azimuth and relative fracture density throughout a naturally fractured gas reservoir interval at rulison field this interval is the cretaceous mesaverde approximately 2500 ft 760 m of lenticular sands silts and shales three dimensional full azimuth p wave data were acquired for the evaluation of azimuthal anisotropy and the relationship of the anisotropy to commercial pay in the target interval the methodology is based on the evaluation of two restricted azimuth orthogonal source receiver azimuth 3 d p wave volumes aligned with the natural principal axes of the azimuthal anisotropy as estimated from velocity analysis of multiazimuth prestack gathers the dix interval

seismic characterization of multiple fracture sets does orthotropy suffice as geophysicists rely increasingly on effective media theories to characterize naturally fractured reservoirs they become more and more interested in evaluating the accuracy of different theories estimating their limits of applicability and assessing their usefulness for practice with this in mind we compare two popular seismological theories of hudson and schoenberg with the theory of kachanov developed in the context of mechanics of materials by performing finite element simulations of effective media for models that contain several sets of nonintersecting circular vertical fractures embedded in otherwise isotropic host rock we examine the accuracy of these theories our numeric study reveals that predictions of both the first and second order hudson s theories are typically inferior to those of others especially when the fractures are dry while on average the theories of schoenberg and kachanov fit finite element computations with comparable accuracy the latter appears to be more useful

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

estimation of fracture parameters from reflection seismic data part iii fractured models with monoclinic symmetry existing geophysical and geological data indicate that orthorhombic media with a horizontal symmetry plane should be rather common for naturally fractured reservoirs here we consider two orthorhombic models one that contains parallel vertical fractures embedded in a transversely isotropic background with a vertical symmetry axis vti medium and the other formed by two orthogonal sets of rotationally invariant vertical fractures in a purely isotropic host rock using the linear slip theory we obtain simple analytic expressions for the anisotropic coefficients of effective orthorhombic media under the assumptions of weak anisotropy of the background medium for the first model and small compliances of the fractures all effective anisotropic parameters reduce to the sum of the background values and the parameters associated with each fracture set for the model with a single fracture system this result allows us to eliminate the influence of the vti background by evaluating the differences between t

quasi decadal and inter decadal climate fluctuations in the pacific ocean from a cgcm diagnostic analyses in the pacific have revealed distinct quasi decadal qd and inter decadal id climate fluctuations with coherent varying patterns of sea surface temperature sst and sea level pressure slp anomalies from a 200 year cgcm simulation distinct low frequency fluctuations are also obtained qd i e 8 12 years period band and id i e 18 25 years period band traced modeled qd evolution reveals equatorial sst anomalies resembling enso while tropical recharge discharge mechanisms seem to be operating the traced modeled id evolution reveals high latitudes spatially coherent patterns with maximum sst anomalies in the vicinity of the subarctic frontal zone safz and subtropical gyres through advection contrary to qd sst anomalies the modeled id sst anomalies peak away from the equator as observed qd fluctuations may then be viewed as low frequency enso phenomena while id fluctuations may set up thermal background modulating frequency and intensity of enso

the characteristic oscillation induced by coupled processes between oceanic vertical modes and atmospheric modes in the tropical pacific an intermediate coupled model icm based on an ocean model with three vertical modes and a statistical atmosphere model was used to investigate the relationship between the dominant modes of variability in the ocean and the atmosphere in the tropical pacific tests on sensitivity to the oceanic vertical structure of the ocean show that the time scale of variability in the sea surface temperature anomaly ssta mainly depends on the relative contribution of the baroclinic modes the first two atmospheric modes i e the central and off equatorial modes play different roles in modulating the impact of oceanic baroclinic modes on sst changes through coupled processes in the model the central mode excites the second oceanic mode which drives the observations like interannual variability in the model the atmospheric off equatorial mode on the other hand favors the gravest baroclinic mode through the forcing of rossby waves and consequently shortens the frequency of ssta variability in the tropical pacific this suggests a possible mechanism governing time modulation of the el nino events characteristics in the tropical pacific

low frequency modulation of intraseasonal equatorial kelvin wave activity in the pacific from soda 1958 2001 intraseasonal equatorial kelvin wave activity iekw at a low frequency in the pacific is investigated using the simple ocean data assimilation soda oceanic reanalyses a vertical and horizontal mode decomposition of soda variability allows estimation of the kelvin wave amplitude according to the most energetic baroclinic modes a wavenumber frequency analysis is then performed on the time series to derive indices of modulation of the iekw at various frequency bands the results indicate that the iekw activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low frequency climate variability in the pacific linear model experiments corroborate that part of the modulation of the iekw is tightly linked to change in oceanic mean state rather than to the low frequency change of atmospheric equatorial variability

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

are open fractures necessarily aligned with maximum horizontal stress abstract fluid flow in fractured rock is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy in predicting flow of pollutants underground in engineering structures and in understanding large scale crustal behaviour conventional wisdom assumes that fluids prefer to flow along fractures oriented parallel or nearly parallel to modern day maximum horizontal compressive stress or s hmax the reasoning is that these fractures have the lowest normal stresses across them and therefore provide the least resistance to flow for example this view governs how geophysicists design and interpret seismic experiments to probe fracture fluid pathways in the deep subsurface contrary to these widely held views here we use core stress measurement and fluid flow data to show that s hmax does not necessarily coincide with the direction of open natural fractures in the subsurface 3 km depth consequently in situ stress direction cannot be considered to predict or control the direction of maximum permeability in rock where effective stress is compressive and fractures are expected to be closed chemical alteration dictates location of open conduits either preserving or destroying fracture flow pathways no matter their orientation

3 d moveout inversion in azimuthally anisotropic media with lateral velocity variation theory and a case study reflection moveout recorded over an azimuthally anisotropic medium e g caused by vertical or dipping fractures varies with the azimuth of the source receiver line normal moveout nmo velocity responsible for the reflection traveltimes on conventional length spreads forms an elliptical curve in the horizontal plane while this result remains valid in the presence of arbitrary anisotropy and heterogeneity the inversion of the nmo ellipse for the medium parameters has been discussed so far only for horizontally homogeneous models above a horizontal or dipping reflector here we develop an analytic moveout correction for weak lateral velocity variation in horizontally layered azimuthally anisotropic media the correction term is proportional to the curvature of the zero offset traveltime surface at the common midpoint and therefore can be estimated from surface seismic data after the influence of lateral velocity variation on the effective nmo ellipses has been stripped the generalized dix equat

feasibility of seismic characterization of multiple fracture sets estimation of parameters of multiple fracture sets is often required for successful exploration and development of naturally fractured reservoirs the goal of this paper is to determine the maximum number of fracture sets of a certain rheological type which in principle can be resolved from seismic data the main underlying assumption is that an estimate of the complete effective stiffness tensor has been obtained for example from multiazimuth multicomponent surface seismic and vertical seismic profiling vsp data although typically only a subset of the stiffness elements or some of their combinations may be available this study helps to establish the limits of seismic fracture detection algorithms the number of uniquely resolvable fracture systems depends on the anisotropy of the host rock and the rheology and orientation of the fractures somewhat surprisingly it is possible to characterize fewer vertical fracture sets than dipping ones even though in the latter case the fracture dip has to be found from the data for the simplest rotationally invariant fractures embedded in either isotropic or transversely isotropic with a vertical symmetry axis vti host rock the stiffness tensor can be inverted for up to two vertical or four dipping fracture sets in contrast only one fracture set of the most general microcorrugated type regardless of its orientation is constrained by the effective stiffnesses these results can be used to guide the development of seismic fracture characterization algorithms that should address important practical issues of data acquisition processing and inversion for particular fracture models

experimental investigation into the effects of meteoritic impacts on the spectral properties of phyllosilicates on mars 1 phyllosilicates have been identified in some of the most highly cratered noachian terrains on mars to study the effects of such impacts on the properties of phyllosilicates we experimentally shocked six phyllosilicate minerals relevant to the martian surface montmorillonite nontronite kaolinite prehnite chlorite and serpentine the shock treated samples were analyzed with x ray diffraction xrd near and mid infrared nir and mir spectroscopy raman spectroscopy cathodoluminescence cl and the shock pressures and temperatures in some were modeled using autodyn modeling software xrd data show that the structure of each mineral except prehnite underwent partial structural deformation or amorphization we also found that while the nir spectra of shocked samples were very similar to that of the original sample the mir spectra changed significantly this may explain some of the discrepancies between crism omega data nir and tes themis mir observations of phyllosilicates on mars quartz was identified as a secondary phase in the xrd of shocked chlorite

thermal infrared spectroscopy of experimentally shocked anorthosite and pyroxenite implications for remote sensing of mars 1 the feldspar and pyroxene mineralogies on mars revealed by the thermal emission spectrometer tes on mars global surveyor likely record a variety of shock effects as suggested by petrologic analyses of the martian meteorites and the abundance of impact craters on the planet s surface to study the effects of shock pressures on thermal infrared spectra of these minerals we performed shock recovery experiments on orthopyroxenite and anorthosite samples from the stillwater complex montana over peak pressures from 17 to 63 gpa we acquired emissivity and hemispherical reflectance spectra 350 1400 cm 1 7 29 mm of both coherent chips and fine grained powders of shocked and unshocked samples these spectra are more directly comparable to remotely sensed data of mars e g tes than previously acquired absorption or transmission spectra of shocked minerals the spectra of experimentally shocked feldspar show systematic changes with increasing pressure due to depolymerization of the silica tetrahedra for the spectra of chips this includes the disappearance of small bands in the 500 650 cm 1 region and a strong band at 1115 cm 1 and changes in positions of a strong band near 940 cm 1 and the christiansen feature near 1250 cm 1 spectra of the shocked powders show the gradual disappearance of a transparency feature near 830 cm 1 fewer changes are observed in the pyroxene spectra at pressures as high as 63 gpa spectra of experimentally shocked minerals will help identify more precisely the mineralogy of rocks and soils not only from tes but also from future mars instruments such as minites and themis index terms 3944 mineral physics shock wave experiments 3934 mineral physics optical infrared and raman spectroscopy 5420 planetology solid surface planets impact phenomena includes cratering 5460 planetology solid surface planets physical properties of materials keywords anorthosite pyroxenite shock spectra thermal infrared remote sensing mars

south pacific origin of the decadal enso like variation as simulated by a coupled gcm 1 the hypothesis of the south pacific origin of the decadal 7 35 years enso like variation is investigated based on 200 year outputs of the echam4 opa oasis coupled gcm associated with the decadal warm cold sst anomalies in the tropical pacific an anomalous cyclonic anticyclonic circulation which is tilted in a southeast northwest direction appears in the south pacific this results in anomalous upward downward ekman pumping along the northeastern edge of the anomalous circulation and hence shallowing deepening the oceanic thermocline there such an external source of heat content tends to slowly discharge recharge the tropical ocean on the decadal timescale the above result is consistent with the observational study of luo and yamagata 2001 besides the model reproduces amazingly a high lagged correlation between the global land surface temperature and the decadal nino3 sst despite the model biases this suggests a potential prediction skill of the global warming based on the enso like decadal variation

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

mineralogical characterization of mars science laboratory candidate landing sites from themis and tes data abstract data from the mars global surveyor thermal emission spectrometer tes and the mars odyssey thermal emission imaging system themis instruments are used to assess the mineralogic and dust cover characteristics of landing regions proposed for the mars science laboratory msl mission candidate regions examined in this study are eberswalde crater gale crater holden crater mawrth vallis miyamoto crater nili fossae trough and south meridiani planum compositional units identified in each region from tes and themis data are distinguished by variations in hematite olivine pyroxene and high silica phase abundance whereas no units are distinguished by elevated phyllosilicate or sulfate abundance though phyllosilicate minerals have been identified in all sites using near infrared observations these minerals are not unambiguously detected using either tes spectral index or deconvolution analysis methods for some of the sites small phyllosilicate outcrop sizes relative to the tes field of view likely hinder phyllosilicate mineral detection porous texture and or small particle size 15 possibly up to 40 of a high silica phase such as amorphous silica or zeolite high silica phase abundance over phyllosilicate bearing surfaces in mawrth vallis is higher than that of surrounding surfaces by 10 15 with the exception of these high silica surfaces in mawrth vallis regions examined in this study exhibit similar bulk mineralogical compositions to that of most low albedo regions on mars the msl scientific payload will thus be able to provide important information on surface materials typical of low albedo regions in addition to investigating the origin of phyllosilicate and or sulfate deposits with the exception of gale crater all of the landing sites have relatively low dust cover compared to classic high albedo regions tharsis arabia and elysium and to previous landing sites in gusev crater utopia planitia and chryse planitia

halloysite as a kinetically controlled end product of arid zone basalt weathering abstract mineralogical and isotope results paired with field observations suggest that halloysite is the favored albeit metastable aluminosilicate end product of arid zone basalt weathering on kohala hawai i and that the formation of smectite has been inhibited by kinetic factors soils sampled on constructional lava flows having ages ranging from 4 to 350 ka provide a chronosequence that has had minimal physical disturbance thus allowing us to interpret chemical and mineralogical changes as the result of a time dependent process the halloysite content of the soil increases with increasing soil age its growth is at the expense of allophane which in turn forms at the expense of primary minerals these mineral relationships suggest that halloysite has been forming continuously throughout the lifetime of the soil smectite the thermodynamically stable phyllosilicate phase predicted by soil solution composition is not found in these arid soils we determined that our soil system is controlled by kinetic factors and that therefore thermodynamic predictions do not reflect reality the main factors favoring kinetic control of halloysite formation are intense but short wet periods followed by prolonged extremely dry seasons and microenvironmental conditions leading to immediate uptake of released al by the halloysite precursor mineral allophane the 18o relationship between present day soil water and halloysite formed over the last 170 ka was used as a tracer of past soil conditions results from a reconstruction of paleo climate and soil conditions combined with 18o data observed mineral relationships along the 350 ka chronosequence and field evidence for long term aridity rule out the possibility that the arid side of kohala was affected by prolonged periods of higher rainfall that could have produced more dilute soil waters and therefore altered mineralogical stabilities we conclude that pedogenic halloysite has been continually forming from the early stage of soil formation and that it has consistently formed under isotopic equilibrium conditions indicating that halloysite 18o compositions imply paleoclimatic conditions over the time of its formation that are similar to today s

seismic anisotropy of fractured rock a simple method for including the effects of geologically realistic fractures on the seismic propagation through fractured rocks can be obtained by writing the effective compliance tensor of the fractured rock as the sum of the compliance tensor of the unfractured background rock and the compliance tensors for each set of parallel fractures or aligned fractures the compliance tensor of each fracture set is derivable from a second rank fracture compliance tensor for a rotationally symmetric set of fractures the fracture compliance tensor depends on only two fracture compliances one controlling fracture compliance normal the other tangential to the plane of the fractures the stiffness tensor which is more useful in the consideration of elastic wave propagation through rocks can then be obtained by inversion the components of the excess fracture compliance tensor represent the maximum amount of information that can be obtained from seismic data if the background rock is isotropic and the normal a

k ar evidence from illitic clays of a late devonian age for the 120 km diameter woodleigh impact structure southern carnarvon basin western australia abstract woodleigh is a recently discovered impact structure with a diameter of 120 km and thereby represents the third largest proven phanerozoic impact structure known after morocweng and chicxulub k ar isotopic studies of fine grained authigenic illitic clay minerals

cathodoluminescence electron microscopy and raman spectroscopy of experimentally shock metamorphosed zircon thorough understanding of the shock metamorphic signatures of zircon could be the basis for the use of this mineral as a powerful tool for the study of old deeply eroded and metamorphically overprinted impact structures and formations this study of the cathodoluminescence cl and raman spectroscopic signatures of experimentally 20 60 gpa shock metamorphosed zircon single crystals contributes to the understanding of high pressure microdeformation in zircon for all samples an inverse relationship between the brightness of the backscattered electron bse signal and the corresponding cathodoluminescence intensity was observed the unshocked sample shows crosscutting irregular fractures the 20 gpa sample displays some kind of mosaic texture of cl brighter and darker domains but does not exhibit any shock metamorphic features in bse or cl images the 40 gpa sample shows a high density of lamellar features which might be explained by the phase transformation between zircon and scheelite structure phases of zircon and resulting differences in the energy levels of the activator elements the cl spectra of unshocked and shocked 20 40 and 60 gpa zircon samples are dominated by narrow emission lines and broad bands in the region of visible light and in the near uv range the emission lines result from rare earth element activators and the broad bands might be associated with lattice defects raman spectra revealed that the unshocked and 20 gpa samples represent zircon structure material whereas the 40 gpa sample yielded additional peaks with relatively high peak intensities which are indicative of the presence of the scheelite type high pressure phase the 60 gpa sample has a raman signature that is similar to that of an amorphous phase in contrast to the observations of an earlier tem study that the crystalline scheelite structure phase is stable at this shock pressure the 60 gpa raman signature cannot be explained at this stage the results show a clear dependence of the cl and raman properties of zircon on shock pressure which confirm the possible usage of these methods as shock indicators

structural and spectroscopic changes to natural nontronite induced by experimental impacts between 10 and 40 gpa many phyllosilicate deposits remotely detected on mars occur within bombarded terrains shock metamorphism from meteor impacts alters mineral structures producing changed mineral spectra thus impacts have likely affected the spectra of remotely sensed martian phyllosilicates we present spectral analysis results for a natural nontronite sample before and after laboratory generated impacts over five peak pressures between 10 and 40 gpa we conducted a suite of spectroscopic analyses to characterize the sample s impact induced structural and spectral changes nontronite becomes increasingly disordered with increasing peak impact pressure every infrared spectroscopic technique used showed evidence of structural changes at shock pressures above 25 gpa reflectance spectroscopy in the visible near infrared region is primarily sensitive to the vibrations of metal oh and interlayer h2o groups in the nontronite octahedral sheet midinfrared mir spectroscopic techniques are sensitive to the vibrations of silicon and oxygen in the nontronite tetrahedral sheet because the tetrahedral and octahedral sheets of nontronite deform differently impact driven structural deformation may contribute to differences in phyllosilicate detection between remote sensing techniques sensitive to different parts of the nontronite structure observed spectroscopic changes also indicated that the sample s octahedral and tetrahedral sheets were structurally deformed but not completely dehydroxylated this finding is an important distinction from previous studies of thermally altered phyllosilicates in which dehydroxylation follows dehydration in a stepwise progression preceding structural deformation impact alteration may thus complicate mineral specific identifications based on the location of oh group bands in remotely detected spectra this is a key implication for martian remote sensing arising from our results

non hyperbolic moveout inversion of wide azimuth p wave data for orthorhombic media the azimuthally varying non hyperbolic moveout of p waves in orthorhombic media can provide valuable information for characterization of fractured reservoirs and seismic processing here we present a technique to invert long spread wide azimuth p wave data for the orientation of the vertical symmetry planes and five key moveout parameters the symmetry plane nmo velocities v 1 nmo and v 2 nmo and the anellipticity parameters 1 2 and 3 the inversion algorithm is based on a coherence operator that computes the semblance for the full range of offsets and azimuths using a generalized version of the alkhalifah tsvankin non hyperbolic moveout equation the moveout equation provides a close approximation to the reflection traveltimes in layered anisotropic media with a uniform orientation of the vertical symmetry planes numerical tests on noise contaminated data for a single orthorhombic layer show that the best constrained parameters are the azimuth of one of the symmetry planes and the velocities v 1 nmo and v 2 nmo while the resolution in 1 and 2 is somewhat compromised by the trade off between the quadratic and quartic moveout terms the largest uncertainty is observed in the parameter 3 which influences only long spread moveout in off symmetry directions for stratified orthorhombic models with depth dependent symmetry plane azimuths the moveout equation has to be modified by allowing the orientation of the effective nmo ellipse to differ from the principal azimuthal direction of the effective quartic moveout term the algorithm was successfully tested on wide azimuth p wave reflections recorded at the weyburn field in canada taking azimuthal anisotropy into account increased the semblance values for most long offset reflection events in the overburden which indicates that fracturing is not limited to the reservoir level the inverted symmetry plane directions are close to the azimuths of the off trend fracture sets determined from borehole data and shear wave splitting analysis the effective moveout parameters estimated by our algorithm provide input for p wave time imaging and geometrical spreading correction in layered orthorhombic media

the eleventh international workshop on seismic anisotropy 11iwsa the 11th international workshop on seismic anisotropy 11iwsa hosted by memorial university of newfoundland and chaired by michael slawinski was held july 25 30 2004 at st john s newfoundland canada attendees presented more than 40 papers covering recent developments of the theory of seismic wave propagation in anisotropic media and its various applications to seismic exploration

applications for vector coordinate systems of 3 d converted wave data recently 3 d four component marine ocean bottom cable obc data has come into broad use for a variety of applications however understanding how these new components and their associated acquisition and processing coordinate systems are related to the vector wavefield has become a challenging task for the exploration industry the compressional wavefield p wave is obtained from the pressure response of the hydrophone plus the particle motion response from the vertical geophone a converted p wave to shear wavefield ps wave is obtained from two horizontal geophone components oriented in an acquisition coordinate system of in line and cross line particle motion

vertical structure variability and equatorial waves during central pacific and eastern pacific el ninos in a coupled general circulation model recent studies report that two types of el nino events have been observed one is the cold tongue el nino or eastern pacific el nino ep el nino which is characterized by relatively large sea surface temperature sst anomalies in the eastern pacific and the other is the warm pool el nino a k a central pacific el nino cp el nino or el nino modoki in which sst anomalies are confined to the central pacific here the vertical structure variability of the periods during ep and cp is investigated based on the gfdl cm2 1 model in order to explain the difference in equatorial wave dynamics and associated negative feedback mechanisms it is shown that the mean stratification in the vicinity of the thermocline of the central pacific is reduced during cp el nino which favours the contribution of the gravest baroclinic mode relatively to the higher order slower baroclinic mode energetic kelvin and first meridional rossby wave are evidenced during the cp el nino with distinctive amplitude and propagating characteristics according to their vertical structure mostly first and second baroclinic modes in particular the first baroclinic mode during cp el nino is associated to the ocean basin mode and participates to the recharge process during the whole el nino cycle whereas the second baroclinic mode is mostly driving the discharge process through the delayed oscillator mechanism this may explain that the phase transition from warm to neutral cold conditions during the cp el nino is delayed and or disrupted compared to the ep el nino our results have implications for the interpretation of the variability during periods of high cp el nino occurrence like the last decade

mechanisms of tropical pacific interannual to decadal variability in the arpege orca global coupled model spatial and temporal structures of interannual to decadal variability in the tropical pacific ocean are investigated using results from a global atmosphere ocean coupled general circulation model the model produces quite realistic mean state characteristics despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western pacific the periodicity and spatial patterns of the modelled el nino southern oscillations enso compare well with those observed over the last 100 years although the quasi biennial timescale is dominant lag regression analysis between the mean zonal wind stress and the 20 c isotherm depth suggests that the recently proposed recharge oscillator paradigm is operating in the model decadal thermocline variability is characterized by enhanced variance over the western tropical south pacific 7 s the associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole arising from ekman pumping anomalies located in the central pacific south of the equator related wind anomalies appear to be caused by sst anomalies in the eastern equatorial pacific this quasi decadal variability has a timescale between 8 years and 20 years the relationship between this decadal tropical mode and the low frequency modulation of enso variance is also discussed results question the commonly accepted hypothesis that the low frequency modulation of enso is due to decadal changes of the mean state characteristics

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

low frequency variability of temperature in the vicinity of the equatorial pacific thermocline in soda role of equatorial wave dynamics and enso asymmetry the simple ocean data assimilation soda reanalysis 1958 2001 is used to investigate the decadal variability in the equatorial thermocline in the pacific whereas the thermocline depth exhibits weak variation at decadal time scales the temperature change in the vicinity of the thermocline in the western pacific is significant and has a vertical scale of 150 m based on a modal decomposition of the model variability it is shown that such temperature change can be interpreted to a large extent as vertical displacements of the isotherms associated with the kelvin and first meridional rossby waves of the first three baroclinic modes this indicates that decadal change at the subsurface in the warm pool region may be forced by the winds consistent with the results of a multimode linear model simulation the decadal mode of vertical temperature can be described by the first two dominant statistical modes eofs the first mode is associated with changes in the slope of the thermocline swallowing in the western central pacific and deepening in the eastern pacific representative of the 1976 77 climate shift and ahead of the enso modulation and the second mode corresponds to a basinwide uplift of the thermocline and behind the enso modulation it is further shown that the subsurface temperature in the warm pool region is negatively skewed which results from the enso asymmetry the results are consistent with the hypothesis of change in mean state resulting from the residual effect of the asymmetric enso variability

shock metamorphism of clay minerals on mars by meteor impact a large fraction of clay minerals detected on mars by infrared remote sensing represent materials exhumed from the subsurface by meteor impact begging the question of whether the infrared features used to detect the clays are affected by shock associated with the impacts we used x ray diffraction and infrared and mossbauer spectroscopy to evaluate the mineralogy of five clay minerals after experimentally shocking them to six shock pressures from 10 40 gpa the shocked clays exhibit three main relevant shock effects 1 an overall decrease in infrared spectral contrast in the impact fragmented materials 2 oxidation of fe in ferrous clays and 3 loss of some spectral structure in relatively well ordered clays such as kaolinite other than the widespread oxidation of ferrous clays shock metamorphism likely has little effect on the accurate interpretation of clay mineralogy on mars from remote sensing data however we are able to identify rare cases of extreme shock in some martian clay deposits

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

hornblende alteration and fluid inclusions in kardla impact crater estonia evidence for impact induced hydrothermal activity the well preserved krdla impact crater on hiiumaa island estonia is a 4 km diameter structure formed in a shallow ordovician sea about 455 ma ago into a target composed of thin 150 m unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites amphibolites and gneisses the fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals the most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater chloritic mineral associations suggest formation temperatures of 100 300 c in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150 300 c in allochthonous breccia the rather low salinity of fluids in krdla crater 13 wt nacleq suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the cater rim walls raised above sea level after the impact or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement the well developed hydrothermal system in krdla crater shows that the thermal history of the shock heated and uplifted rocks in the central crater area rather than cooling of impact melt or suevite sheets controlled the distribution and intensity of the impact induced hydrothermal processes

mineralogical characterization of acid weathered phyllosilicates with implications for secondary martian deposits abstract the detection of phyllosilicates and sulfates on mars has revealed a complex aqueous history which suggests distinct geochemical environments separated temporally and spatially recent observations by mro crism in mawrth vallis have shown that phyllosilicate deposits exhibit a specific stratigraphy which remains incompletely understood moreover mer spirit has evidenced association between phyllosilicates amorphous silica and sulfates we investigated the hypothesis that these parageneses resulted from the acidic weathering of older phyllosilicate deposits we exposed nontronite fe rich smectite montmorillonite al rich smectite and kaolinite to h 2 so 4 solutions at ph 0 2 and 4 and at a temperature of 60 c after the acid treatment a combination of mineralogical techniques was used to assess the degree of alteration of the three phyllosilicate minerals xrf xrd and esem measurements show that nontronite was the most unstable when acid leached followed by montmorillonite and then kaolinite progressive acidic leaching of nontronite leads to alteration of the phyllosilicate to amorphous silica along with fe sulfate and anatase and the formation of an acidic al fe rich solution alteration of montmorillonite resulted in the formation of fe al ca and mg sulfates and a al rich leaching solution comparatively leaching of kaolinite resulted in the formation of al sulfates and a al rich solution as well with only slight alteration of the primary mineralogical features the effects of acid leaching of the phyllosilicates were also observed in nir reflectance spectra allowing a comparison with crism spectra from mawrth vallis based on our results we propose a new model where acid leaching of mixed phyllosilicate deposits leads to kaolinite overlaying montmorillonite which in turn caps fe mg smectites leaching of cations and subsequent evaporation leads to sulfate deposits as supported by geochemical modeling while amorphous silica remains as a residue depending on the intensity ph and length of exposure of acidic leaching our model can explain the stratigraphic distribution of phyllosilicates and the association of sulfates silica and smectites

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

abrupt shift in subsurface temperatures in the tropical pacific associated with changes in el nino radiocarbon 14c content of surface waters inferred from a coral record from the galapagos islands increased abruptly during the upwelling season july through september after the el nino event of 1976 sea surface temperatures ssts associated with the upwelling season also shifted after 1976 the synchroneity of the shift in both 14c and sst implies that the vertical thermal structure of the eastern tropical pacific changed in 1976 this change may be responsible for the increase in frequency and intensity of el nino events since 1976

vertical structure variability in the equatorial pacific before and after the pacific climate shift of the 1970s 1 oceanic baroclinic modes in the equatorial pacific are estimated using results from the soda system our result suggests that the vertical stratification increases at the upper levels after the late 1970s due to changes in the vertical temperature structure after the late 1970s the variability of the higher order baroclinic mode contributions to current anomalies and surface pressure significantly increases in the central equatorial pacific this is associated with an increase of the dominant period of the enso variability simple coupled model experiments indicate that when atmospheric forcing projects more onto the higher baroclinic modes according to the results of the soda decomposition the amplitude and dominant period of enso increase similarly to what is observed at the pacific decadal shift our results support that the changes in the behavior of enso after the late 1970s are associated with oceanic vertical structural changes in temperature that tend to increase the contribution of higher order baroclinic modes

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

a mechanism for decadal changes of enso behavior roles of background wind changes this study explains why a number of el nino properties period amplitude structure and propagation have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the pacific decadal climate shift evidence is presented to show that from the pre shift 1961 1975 to the post shift 1981 1995 epoch significant changes in the tropical pacific are found in the surface winds and temperature whereas changes in the thermocline are uncertain numerical experiments with the cane and zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in el nino properties the fundamental factor that altered the model s el nino is the decadal changes of the background equatorial winds and associated upwelling the annual cycle is also necessary for the mean state to modulate el nino from the pre to post shift epoch the changes in the background winds and upwelling modify the structure of the coupled mode eastward displacement of the equatorial westerly anomalies by reallocating anomalous atmospheric heating and sst gradient along the equator this structural change amplifies the enso cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa the changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection thus the prevailing westward propagation is replaced by eastward propagation or standing oscillation our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics and the possibility that the pacific climate shift might have affected el nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

emission spectroscopy of clay minerals and evidence for poorly crystalline aluminosilicates on mars from thermal emission spectrometer data 1 to understand the aqueous history of mars it is critical to constrain the alteration mineralogy of the martian surface previously published analyses of thermal infrared 6 25 m remote sensing data of mars suggest that dark regions have 15 20 clay minerals however near infrared 1 3 m spectral results generally do not identify widespread clay minerals thermal infrared detections of clays on mars are difficult to interpret owing in part to the relative paucity of published spectral analyses of clay minerals and clay bearing materials using similar spectra thermal infrared emission spectra in this study we present an analysis of the thermal emission spectral features 6 25 m or 400 1650 cm 1 of a suite of clay mineral reference materials and clay bearing rocks linking their spectral features to the crystal chemical properties of the clays on the basis of this context provided by the emission spectral analysis of clay minerals and clay bearing rocks we reconsider the evidence for clay minerals on mars from thermal emission spectrometer tes results we propose that global scale clay abundances determined from tes probably represent a geologically significant surface component though they may actually correspond to poorly crystalline aluminosilicates with similar si o ratios to clay minerals 0 3 0 4 rather than well crystalline clays if clay minerals or clay like materials on mars are poorly crystalline and or dessicated they may be detectable in the thermal infrared but not easily detected with near infrared data sets

evidence for a sedimentary origin of clay minerals in the mawrth vallis region mars clay minerals detected spectroscopically in the mawrth vallis region of mars correspond to a complex layered thick 600 m stratigraphic section of ancient bedrock because the light toned clay bearing rocks are lithologically diverse over a broad area 80 000 km2 have significant internal layering and complexity and contain buried impact craters within the section demonstrating that they were deposited over a geologically significant duration of time we interpret the host rocks as sedimentary or possibly pyroclastic crater counts date the clay bearing rocks to early middle noachian time estimated as 3 8 4 1 ga geomorphic observations suggest that the rocks were lithified early and deeply eroded during the late noachian early hesperian the combination of a probable ancient sedimentary context of the clays and a moderate ph formation environment implied by the occurrence of smectites clearly places these rocks among the most important targets for future astrobiological exploration

elastic wavefield interferometry using p wave source vsps at the wamsutter field wyoming in this study elastic wavefield interferometry was used to recover p and s waves from the 3d p wave vibrator vsp data at wamsutter field in wyoming s wave velocity and birefringence is of particular interest for the geophysical objectives of lithology discrimination and fracture characterization in naturally fractured tight gas sand reservoirs because we rely on deconvolution interferometry for retrieving interreceiver p and s waves in the subsurface the output fields are suitable for high resolution local reservoir characterization in 1d media where the borehole is nearly vertical data at the stationary phase point is not conducive to conventional interferometry strong tube wave noise generated by physical sources near the borehole interfere with s wave splitting analyses also converted p to s wave ps wave polarity reversals occur at zero offset and cancel their recovery we developed methods to eliminate tube wave noise by removing physical sources at the stationary phase point and pertur

the central pacific el nino intraseasonal kelvin wave in this study we document and interpret the characteristics of the intraseasonal kelvin wave iskw in the pacific over the 1989 2011 period based on observations a linear model and the outputs of an ocean general circulation model ogcm we focus on the wave activity during the central pacific cp el nino events contrasting with the extraordinary el nino of 1997 1998 we find that the iskw activity is enhanced in austral summer spring in the central pacific west of 120 w during cp el nino events the linear model experiment indicates that the austral summer peak is wind forced while the austral spring peak is not and consequently results from nonlinear processes in addition a strong dissipation of the iskws is observed east of 120 w which cannot be accounted for by a linear model using a rayleigh friction a vertical and horizontal mode decomposition of the ogcm simulation further confirms the sharp changes in characteristics of the iskws as well as the reflection of the latter into first meridional rossby wave at the longitude where the maximum zonal gradient of the thermocline is found 120 w our analysis suggests that the confinement of cp el nino warming in the central pacific may result from the reinforcement of the zonal gradient in stratification associated with the la nina like conditions since the late of the 1990s leading to scattering of the energy of the iskws in the eastern pacific

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

interdecadal variability of the pacific ocean model response to observed heat flux and wind stress anomalies variability of the pacific ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux wind stress and turbulent kinetic energy tke over the period 1970 88 the model captures the 1976 77 winter time climate shift in sea surface temperature as well as its monthly seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses examination of the surface mixed layer heat budget reveals that the 1976 77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi month period preceding the shift in both the central pacific region where cooling occurred and the california coastal region where warming occurred in the central pacific the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux tke input into the mixed layer which deepens in the model after the shift from the early 1970s to the late 1970s and 1980s since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976 77 shift it appears that the midlatitude part of the shift was driven by the atmosphere although effects of midlatitude ocean atmosphere feedback are still possible the surface mixed layer heat budget also reveals that in the central pacific the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size in the california coastal region in contrast where wind variability is much weaker than in the central pacific horizontal advection and vertical mixing effects on the mixed layer heat budget are only one quarter the size of typical heat flux input anomalies

review of characteristics of low permeability gas reservoirs in western united states tight gas reservoirs generally are defined as gas bearing rocks with an in situ permeability to gas of less than 0 1 md in 1980 the national petroleum council estimated that undiscovered recoverable gas resources in low permeability tight rht reservoirs in the united states excluding eastern gas shales are about 574 tcf 16 1012 m3 the possible recovery of this volume of gas was based on 9 mcf 1979 dollars and a level of recovery technology presently unknown advanced technology most of this resource is in the western united states the two main types of tight rocks are shallow high porosity reservoirs and deep low porosity reservoirs the high porosity rocks are tight because of their fine grain size the low porosity rocks are tight because diagenetic alteration has resulted in them having small microvugs porosity poorly connected by sheet or cracklike very thin capillaries the low porosity rocks are very stress sensitive and may be overpressured and all tight rocks are susceptible to formation damage to varying degrees during drilling and treatment the western tight gas reservoirs can be placed in two major geologic and engineering categories blanket and lenticular blanket reservoirs generally respond to artificial stimulation in a predictable manner whereas the response of lenticular reservoirs is mostly unpredictable many obstacles complicate the identification and recovery of gas from these unconventional reservoirs accurate borehole geophysical log analysis is generally difficult and economic stimulation commonly artificial fracturing of the tightest rocks is difficult or impossible with present technology geologists and engineers must better understand the characteristics of these reservoirs work together to improve present recovery technology and develop new innovative drilling and stimulation techniques

a heterogeneous solar nebula as sampled by cm hibonite grains abstract the magnesium isotopic compositions of 43 hibonite bearing inclusions extracted from cm2 meteorites murchion and paris were measured with a cameca 1280 hr2 ion microprobe the results are broadly consistent with the literature data most spinel hibonite spherules shibs bear evidence for in situ decay of 26 al at the canonical level whereas platy hibonite crystals placs either lack resolvable 26 mg excesses or are characterized by apparent 26 mg deficits by up to 5 relative to the terrestrial composition with higher precisions achieved in this study the 26 al 27 al scatter ranging from 6 10 6 to 6 10 5 previously seen in lower precision shib data can be clearly resolved a statistical treatment to all the data reveals three distinctive peaks at 26 al 27 al 4 9 10 5 3 5 10 5 and 6 5 10 6 and two minor barely resolved components at 26 al 27 al 6 10 5 and 2 5 10 5 possible explanations for the observed 26 al 27 al scatter in shibs include 1 isotopic disturbance 2 protracted shib formation 3 early formation before complete homogenization of 26 al in the solar nebula and 4 initial mg isotopic heterogeneity during shib formation we argue that the early formation of shibs was the most plausible scenario the placs could have formed in a reservoir characterized by 26 al 27 al similar to the average galactic background value or in an 26 al free environment in either case it is almost certain that the mg isotope distribution in the plac forming region was heterogeneous combining the hydrodynamic timescales of isotope mixing in the solar nebula one could infer that the duration for plac and shib formation should only be around tens of thousands of years

reinterpreting the thermocline feedback in the western central equatorial pacific and its relationship with the enso modulation vertical stratification changes at low frequency over the last decades are the largest in the western central pacific and have the potential to modify the balance between enso feedback processes here we show evidence of an increase in thermocline feedback in the western central equatorial pacific over the last 50 years and in particular after the climate shift of 1976 it is demonstrated that the thermocline feedback becomes more effective due to the increased stratification in the vicinity of the mean thermocline this leads to an increase in vertical advection variability twice as large as the increase resulting from the stronger enso amplitude positive asymmetry in the eastern pacific that connects to the thermocline in the western central pacific through the basin scale tilt mode although the zonal advective feedback is dominant over the western central equatorial pacific the more effective thermocline feedback allows for counteracting its warming cooling effect during warm cold events leading to the reduced covariability between sst and thermocline depth anomalies in the nino4 160 e 150 w 5 s 5 n region after the 1976 climate shift this counter intuitive relationship between thermocline feedback strength as derived from the linear relationship between sst and thermocline fluctuations and stratification changes is also investigated in a long term general circulation coupled model simulation it is suggested that an increase in enso amplitude may lead to the decoupling between eastern and central equatorial pacific sea surface temperature anomalies through its effect on stratification and thermocline feedback in the central western pacific

seismic characterization of multiple fracture sets at rulison field colorado conventional fracture characterization methods assume the presence of a single set of aligned vertical cracks in the subsur face we relax this assumption and demonstrate the feasibility of seismic characterization of multiple fracture sets our technique relies on recent numerical findings indicating that multiple differently oriented possibly intersecting planar cracks embedded in an otherwise isotropic host rock result in a nearly orthorhombic or orthotropic effective medium here the governing parameters of crack induced orthotropy are estimated from 3d wide azimuth multicomponent seismic reflection data acquired over the tight gas rulison field in colorado we translate strong azimuthal variations of the normal moveout velocities intointerval crack densities fracture orientations type of fluid infill and velocities of p and s waves in an unfractured rock our inversion procedure identifies a set of cracks aligned in approximately west northwest east southeast direction in the western part

the aster spectral library version 2 0 abstract the advanced spaceborne thermal emission reflection radiometer aster on nasa s terra platform has been widely used in geological and other science studies in support of aster studies a library of natural and man made materials was compiled as the aster spectral library v1 2 and made available from http speclib jpl nasa gov the library is a collection of contributions in a standard format with ancillary data from the jet propulsion laboratory jpl johns hopkins university jhu and the united states geological survey usgs a new version of the library v2 0 is now available online or via cd which includes major additions to the mineral and rock spectra the aster library provides a comprehensive collection of over 2300 spectra of a wide variety of materials covering the wavelength range 0 4 15 4 m

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways

parameter estimation in orthorhombic media using multicomponent wide azimuth reflection data orthorhombic models with a horizontal symmetry plane adequately describe seismic signatures recorded over many naturally fractured reservoirs the inversion of wide azimuth traveltimes of pp and ss the fast s1 and slow s2 reflections are discussed for tsvankin s anisotropic parameters and the azimuths of the vertical symmetry planes of orthorhombic media if shear waves are not excited ss traveltimes can be found from pp and ps converted wave data which makes the method applicable to offshore surveys the feasibility of parameter estimation is strongly dependent on reflector dip and orientation for a horizontal reflector beneath a single orthorhombic layer the vertical velocities and reflector depth cannot be found from conventional spread reflection traveltimes alone if the reflector is dipping the inversion is ambiguous when the dip plane is close to one of the vertical symmetry planes of the orthorhombic layer above it the parameter estimation becomes possible if the dip direction deviates b

the clay mineralogy of sediments related to the marine mjolnir impact crater the 40 km diameter mjolnir crater is located on the central barents sea shelf north of norway it was formed about 142 2 6 myr ago by the impact of a 12 km asteroid into the shallow shelf clays of the hekkingen formation and the underlying triassic to jurassic sedimentary strata a core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high these beds are overlain by gravity flow conglomerates with laminated shales and marls on top here impact and post impact deposits in this core are studied with focus on clay mineralogy obtained from xrd decomposition and simulation analysis methods the clay sized fractions are dominated by kaolinite illite mixed layered clay minerals and quartz detailed analyses showed rather similar composition throughout the core but some noticeable differences were detected including varying crystal size of kaolinite and different types of illites and illite smectite these minerals may have been formed by diagenetic changes in the more porous fractured beds in the crater compared to time equivalent beds outside the crater rim long term post impact changes in clay mineralogy are assumed to have been minor due to the shallow burial depth and minor thermal influence from impact heated target rocks instead the clay mineral assemblages especially the abundance of chlorite reflect the impact and post impact reworking of older material previously an ejecta layer the sindre bed was recognized in a nearby well outside the crater represented by an increase in smectite rich clay minerals genetically equivalent to the smectite occurring in proximal ejecta deposits of the chicxulub crater such alteration products from impact glasses were not detected in this study indicating that little if any impact glass was deposited within the upper part of the crater fill crater fill deposits inherited their mineral composition from triassic and jurassic sediments underlying the impact site

impact generated hydrothermal systems capable of forming phyllosilicates on noachian mars the early history of the terrestrial planets was punctuated by a period of heavy bombardment frequent large impacts condensed in a short 0 02 0 5 ga long time period resulted in heavily cratered planetary surfaces in volatile bearing planetary crusts each of these large impacts created a volume of hot rock and melt that drove vast subsurface hydrothermal systems in mars basaltic crust these systems produced a variety of alteration phases the nature of which we explored with thermochemical modeling using the computer code chiller we found a variety of oxides hydroxides and hydrous and water free silicates resulting from the hydrothermal alteration the main hydrous silicates are serpentine chlorite nontronite and other clay minerals some of the resulting assemblages contain up to 15 wt bound water our results constrain the temperature and water rock ratio at the time of alteration and compare well to the mineral assemblages found on mars by omega observatoire pour la mineralogie l eau les glaces et l activite and crism compact reconnaissance imaging spectrometer for mars and therefore provide an interpretative framework for analyzing martian mineralogy from orbital data our results also provide a geological template needed to select landing locations for future missions that search for water and energy sources associated with potential habitats on early mars

phyllosilicates in the mawrth vallis region of mars 1 omega mars express has discovered large outcrops rich in phyllosilicates in the region of mawrth vallis mars around 20 w 25 n the region is located in noachian highly cratered terrains close to the limit of the martian dichotomy where the outflow channel mawrth vallis cuts the highlands we have examined this region using omega spectra of the surface from 0 9 m to 2 6 m with spatial sampling from 500 m to 3 km offering a full coverage of the region omega spectra show two broad bands centered at 1 m and 2 2 m revealing the presence of clinopyroxene on dark surfaces phyllosilicates have been identified by absorption bands at 1 4 m 1 9 m and 2 2 or 2 3 m comparison with laboratory spectra reveals similarities with al oh smectites such as montmorillonites or fe or mg oh smectites such as nontronite a precise location of the phyllosilicate rich areas on visible hrsc images indicates that they are placed exclusively on bright outcrops mostly on the plateaus dated to the noachian period on hrsc and moc images the phyllosilicate rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick the phyllosilicate rich unit corresponds to a geological unit more than 100 m thick over a horizontal extension approximately of 300 km 400 km this unit implies a large volume of altered rocks either in situ or after transport and deposition in noachian terrains revealing a different climatic and geologic environment from the present one

analysis of phyllosilicate deposits in the nili fossae region of mars comparison of tes and omega data abstract diverse phyllosilicate deposits discovered previously in the nili fossae region with near infrared reflectance data are a window into the complex history of aqueous alteration on mars in this work we used thermal infrared data from the thermal emission spectrometer tes in combination with near infrared data from the observatoire pour la mineralogie l eau les glaces et l activite omega to better constrain the mineralogy and geologic origin of these deposits we developed a tes spectral index for identification of clay minerals which correctly identifies the phyllosilicates in the nili fossae area and points to several other interesting deposits in the syrtis major region however detailed inspection of the tes spectral features of nili fossae phyllosilicates shows a feature at low wavenumbers 350 550 cm 1 that is not an exact match to any specific fe 3 al or mg rich phyllosilicate phase instead the feature is more similar to basaltic glass and may indicate that the phyllosilicates in this region are 1 rich in fe 2 based on similarity to trends seen in laboratory data of clay minerals 2 poorly crystalline extremely disordered and or 3 present within a matrix of actual basalt glass this feature is similar to spectral features seen in altered rocks in the columbia hills region of gusev crater by previous authors by calibrating measured spectral index values against mathematical spectral mixtures of typical martian dark surfaces and known abundances of alteration minerals we are able to estimate an enrichment in abundance of alteration minerals in the altered surfaces many dark noachian deposits in the nili fossae area are enriched phyllosilicates by 20 30 10 15 relative to dark volcanic surfaces in the same region the distribution and abundance of these phases indicates that alteration in the region was pervasive but did not completely erase the original mineralogy of what was likely an fe rich basalt protolith as a group the nili fossae phyllosilicate deposits are fundamentally different from those found in the mawrth vallis region nili fossae deposits have strong thermal infrared features related to admixed pyroxene plagioclase and occasionally olivine whereas the mawrth vallis deposits contain no mafic minerals comparison of tes and omega data also illustrates some more general differences between the datasets including the impact of physical character of the martian surface on detectability of minerals in each spectral range

interaction between near annual and enso modes in a cgcm simulation role of the equatorial background mean state abstract a 260 yr long coupled general circulation model cgcm simulation is used to investigate the interaction between enso mode and near annual variability and its sensitivity to the equatorial background mean stratification and seasonal cycles although the thermocline mean vertical structure of the model favors the high order baroclinic modes that are associated with the slow time scales of the coupled variability the simulated enso oscillates at a dominant quasi biennial frequency biases of the climatological velocity field are favorable to the dominance of the zonal advective feedback over the thermocline feedback the model exhibiting an overenergetic westward seasonal zonal current in the central western equatorial pacific and an upwelling rate that is about half the observations this sets the conditions for the enhancement of a near annual mode that is observed to oscillate at an 8 month period in the model using an intermediate coupled model of the tropical pacific where the climatologica

evolution of interdecadal variability in sea level pressure sea surface temperature and upper ocean temperature over the pacific ocean abstract interdecadal variability in sea level pressure slp and sea surface temperature sst anomalies in the pacific ocean was quasiperiodic from 1900 91 the coherent variability of this phenomenon is investigated using gridded observational data from the turn of the century sst and slp and of upper ocean heat content hs from the recent two and a half decades the nominal cycle in atmosphere ocean variables is roughly two decades long but growth and decay can happen on a shorter timescale e g half a cycle or so the authors divide the full cycle into four phases an onset phase during which a weak slp anomaly pattern off japan takes approximately 2 4 yr to expand eastward leads to large slp anomalies in the region of the aleutian low a quasi stationary growth phase with the midlatitude slp anomaly pattern in the eastern ocean intensifies over a 2 4 yr period the persistent slp anomalies evolve in concert with large sst and hs anomalies of the same polarity located to the south sout

composition and thermal inertia of the mawrth vallis region of mars from tes and themis data abstract clay mineral bearing deposits previously discovered on mars with near infrared 0 3 5 m remote sensing data are of major significance for understanding the aqueous history geological evolution and past habitability of mars in this study we analyzed the thermal infrared 6 35 m surface properties of the most extensive phyllosilicate deposit on mars the mawrth vallis area clay mineral bearing units which in visible images appear to be relatively light toned layered bedrock have thermal inertia values ranging from 150 to 460 j m 2 k 1 s 1 2 this suggests the deposits are composed of a mixture of rock with sand and dust at 100 meter scales dark toned materials that mantle the clay bearing surfaces have thermal inertia values ranging from 150 to 800 indicating variable degrees of rockiness or induration of this younger sedimentary or pyroclastic unit thermal emission spectrometer tes spectra of the light toned rocks were analyzed with a number of techniques but none of the results shows a large phyllosilicate component as has been detected in the same surfaces with near infrared data instead tes spectra of light toned surfaces are best modeled by a combination of plagioclase feldspar high silica materials similar to impure opaline silica or felsic glass and zeolites we propose three hypotheses for why the clay minerals are not apparent in thermal infrared data including effects due to surface roughness sub pixel mixing of multiple surface temperatures and low absolute mineral abundances combined with differences in spatial sampling between instruments zeolites modeled in tes spectra could be a previously unrecognized component of the alteration assemblage in the phyllosilicate bearing rocks of the mawrth vallis area tes spectral index mapping suggests that fe mg clays detected with near infrared data correspond to trioctahedral fe2 clay minerals rather than nontronite like clays the average mineralogy and geologic context of these complex interbedded deposits suggests they are either aqueous sedimentary rocks altered pyroclastic deposits or a combination of both

effective elasticity of rocks with closely spaced and intersecting cracks the noninteraction approximation nia is the simplest effective media theory that describes the overall elasticity of fractured rocks if the nia is used for fracture characterization its accuracy and the range of applicability must be estimated we do it by performing a series of 3d finite element simulations of effective elasticity for models that contain several sets of fractures embedded in otherwise isotropic host rock we intentionally place the cracks close to each other to create strong interactions in their local stress fields in addition we allow the cracks to intersect in such a way that they do not break a rock specimen apart perhaps surprisingly we find that fracture interactions and intersections have little influence on the effective elasticity and the nia performs well in all cases while it has a tendency to slightly underestimate the effective stiffnesses the incurred errors are small their typical magnitudes are just a few percent in the entire range of the crack densities expe