an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

fractal nature and scaling of normal faults in the espanola basin rio grande rift new mexico implications for fault growth and brittle strain abstract quaternary faults in the western espanola basin of the rio grande rift show a power law size displacement distribution suggesting that faulting in this region is scale invariant and that faults are self similar the power law or fractal distribution is characterized by fractal dimension of 0 66 to 0 79 and represents a young immature active fault population in a continental extensional regime based on this distribution it is estimated that unobserved faults with very small displacements account for up to 6 of the total strain since 1 2 ma total extension in this part of the basin has been at least 5 a direct correlation exists between maximum displacement and length of faults in this area suggesting that they obey a scaling relationship in which the ratio of log d max log l is 5 10 3 this ratio is nearly constant for faults whose lengths span three orders of magnitude indicating that there is no difference in the scaling relationship of displacement and length between faults of all sizes considering previous models these fault characteristics suggest that in the western espanola basin 1 host rock shear strengths are low 2 remote shear stresses were probably high and 3 most faults do not extend throughout the brittle crust finally displacement profiles on five of the largest faults arc asymmetric and show a rapid decrease in displacement from the point of maximum displacement toward the fault tip the fractal nature scaling relationship and distribution of displacement on faults are used to suggest that faults grew by nearly proportional increases in displacement and length perhaps by mechanisms dominated by propagating shear fractures rather than by linkage of pre existing joints or faults

geologic and geophysical investigation of two fine grained granites sierra nevada batholith california evidence for structural controls on emplacement and volcanism the johnson granite porphyry and the silver pass porphyry are two late stage porphyritic intrusions in the cretaceous sierra nevada batholith california both intrusions are characterized by fine grained textures miarolitic cavities pegmatite veins and abundant xenoliths microstructures in the johnson granite porphyry record magmatic flow magnetic fabrics in the johnson granite porphyry determined by anisotropy of magnetic susceptibility show that the poles to magnetic foliations define a nne ssw girdle and magnetic lineations plunge shallowly to moderately to the wnw and ese a gravity survey and three dimensional inversion indicate that the johnson granite porphyry is shallow and tabular extending to 1 5 km depth beneath the southwestern margin a second gravity anomaly was delineated southeast of the johnson granite porphyry suggesting the intrusion continues to depth the silver pass porphyry is deformed by the dextral rosy finch shear zone and records a gradient of high to low temperature solid state fabrics field and magnetic foliations in the silver pass porphyry are subvertical and lineations are shallowly plunging we propose that regional shear zones controlled the emplacement of these intrusions the johnson granite porphyry was emplaced in a three dimensional tension gash associated with the termination of the bench canyon shear zone the rosy finch shear zone facilitated the emplacement of the silver pass porphyry probably as a tension fracture associated with the shear zone the field observations and magnetic fabrics suggest that the johnson granite porphyry may record an extrusive event suggesting that volcanism may be related to deformation along active shear zones

some consequences of a proposed fractal nature of continental faulting a key question in the study of continental deformation concerns the preservation of undeformed regions sometimes quite large in the midst of otherwise penetrative deformation some authors1 have interpreted such regions as being relatively strong but we argue here that the existence of large undeformed regions might instead arise naturally from a fractal style of continental faulting a scaling analysis derived from laboratory simulations of the india asia collision2 5 yields a predicted distribution of undeformed regions which can be tested in the field we also show that if continental faulting is fractal in nature this will limit the validity of homogenization approaches to the modelling of continental deformation in which the rheology of the lithosphere is assumed to be homogeneous at scales larger than a threshold value

fractal analysis of fracture patterns using the standard box counting technique valid and invalid methodologies abstract on the basis of results of simple box counting analysis it has been suggested in several recent publications that natural fracture patterns are fractal fractal patterns are characterized by self similarity of structure on a range of scales and provide straight line distributions on box counting plots new analysis of a fracture pattern that provided the most convincing straight line box counting curve previously published shows that the curve is non linear and therefore that the fracture pattern is not fractal non linear box counting curves are also characteristic of other natural fracture patterns analysed but spurious linear curves can be obtained if the area analysed extends beyond the mapped area

unconventional geomechanical testing on coal for coalbed reservoir well design the alberta foothills and plains abstract one unconfined compressive strength ucs test and four high pressure triaxial stress tests were conducted on coal cores in order to best emulate the key issues regarding horizontal wellbore stability coal strength permeability change and coal fines generation during the life cycle of a coalbed methane reservoir the four non trivial stress paths were loading compression lc where the axial stress is increased while the confining stress is held constant loading extension le where the axial stress is held constant while the confining stress is increased unloading compression ulc in which the axial stress is held constant while the confining stress is decreased and unloading extension ule during which the confining stress is held constant while the axial stress is decreased the ucs test showed the expected fractured response of initial non linearity due to fracture closure followed by a linear portion at a certain axial stress and finally by brittle failure of the coal along each of the extension stress and also along the combined compression extension stress paths the coal did not show any visual signs of failure no coal fines were detected in the downstream accumulator subsequent to the permeability tests particle size distribution analysis following loading compression provided an estimate of the optimum diameter of the liner perforations test results showed that as the mean effective confining stress increased permeability decreased due to closure of cleats as the coal was loaded unloaded and reloaded along the same stress path a decrease in permeability below the original measured value permeability hysteresis was noted this could be attributed to one or a combination of two mechanisms deformation due to creep and or cleat damage from previous loading using the best fit approach a compressive hoek brown hb failure envelope was fit with intact parameters of geological strength index or gsi 85 d 1 0 ci 20 5 mpa m i 16 7 and a 0 5 assuming there was no anisotropy in the intact coal an extension envelope was fit using a gsi 55 thus the hb criterion in combination with the gsi can be used to capture the influence of both coal cleating and microfractures on its behaviour during drilling and production of the methane gas

coseismic growth of basement involved anticlines the northridge laramide connection seismogenic thrust faults in the transverse ranges of southern california may provide analogues for interpreting kinematic data from some laramide anticlines in the southern rocky mountains the 1994 northridge earthquake m w 6 7 occurred on a southwest dipping blind thrust fault beneath the transverse ranges and resulted in incremental growth of a basement involved fault propagation fold analyses of geodetic data and aftershock focal mechanisms show that deformation of the hanging wall block consisted of two major components 1 a large scale elastic strain characterized by horizontal shortening normal to the fault and horizontal lengthening parallel to the fault that was imposed by reverse slip on the underlying blind thrust during the main shock and 2 postseismic cataclastic flow with a geometry comparable to the coseismic strain including horizontal fault parallel lengthening of the hanging wall block which was accommodated at least in part by distributed aftershock activity fault and fold parallel lengthening strains similar to those observed during the northridge earthquake have been obtained by inversion of fault slip data from some laramide basement involved anticlines the northridge analogue suggests that distributed brittle faulting of the crystalline basement may reflect aftershock deformation during incremental growth of the laramide folds if so then the laramide structures provide examples now exposed by erosion of the mature internal structure of the active basement involved folds in the transverse ranges

fabric attractors in general triclinic flow systems and their application to high strain shear zones a dynamical system approach high strain zones may deform by flow with a triclinic symmetry this paper describes triclinic flow in a reference frame where instantaneous stretching axes isa are fixed the operation of triclinic flow is described in two ways first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain in monoclinic flow at least one of the eigenvectors of the flow coincides with one of the isa and one or two of the eigenvectors act as attractors of foliation or lineation elements in triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues controlling the flow are imaginary imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20 from one of the isa strong deviation from monoclinic flow is therefore possible but this will not produce permanent foliations or lineations for triclinic flow that does produce permanent fabrics the angle between isa and the fabric is so small that it is unlikely that it can be recognised in nature a discussion of the potential application of such results within real shear zones is presented

tabular fracture clusters dynamic fracturing produced by volatile expulsion sierra nevada batholith california abstract an undocumented type of fracture system tabular fracture clusters tfcs occurs in the cathedral peak granodiorite sierra nevada batholith ca tfcs are linear zones of sub parallel densely spaced fractures approximately 4 40 cm wide and 3 100 m long tfcs occur in highest density adjacent to the johnson granite porphyry which intruded the cathedral peak granodiorite individual fractures in tfcs exhibit only opening mode displacement microstructural analysis indicates that tfc fractures contain micro breccia of angular clasts of host rock fine grained zeolite and quartz are observed along many of the fractures within tfcs all of which are absent in the host rock the characteristics of tfcs suggest that they differ from previously documented fracture systems in the sierra nevada batholith the dense spacing nature of the fractures and association of tfcs with miarolitic cavities provide compelling evidence that tfcs formed in response to volatile overpressure from the adjacent johnson granite porphyry we attribute the formation of tfcs to dynamic fracturing based on the clustered nature of the extension fractures and the geometric similarities of tfcs to other dynamic fracturing arrays

geochemical and climate modeling evidence for holocene aridification in hawaii dynamic response to a weakening equatorial cold tongue abstract a 13 5 m sequence of holocene limnic sediments from a sinkhole on oahu hawaii provides a valuable paleoclimatic record for the central subtropical pacific 13 c analysis of plant leaf waxes n alkanes n c 27 n c 29 n c 31 and n c 33 is used to infer vegetative changes average 13 c values of the suite of n alkanes increase from approximately 31 0 5 at 10 ca kyr bp calibrated thousand years before present to about 27 0 5 by 6 ca kyr bp and then remain roughly constant until the polynesian arrival about 1 15 ca kyr bp the increase in 13 c values of n alkanes is interpreted to indicate a shift in the local vegetation from c 3 to c 4 dominated flora based on mass balance calculations the observed increase in the 13 c values translates to at least a doubling of the relative abundance of c 4 plants we argue that the expansion of c 4 plants was a response to decreased overall water availability aridification due to reduced wintertime precipitation model simulations of an orbitally induced increase in insolation along the equator during the holocene provide evidence for a wintertime drying trend in the eastern subtropical north pacific this trend is associated with boreal fall to winter warming of the cold tongue in the eastern equatorial pacific eep these model results provide a conceptual framework to explain a dynamic link between the reconstructed holocene drying trend in hawaii and orbitally forced climate change in the eep that is analogous to the modern el nino southern oscillation teleconnection

from fractures to flow a field based quantitative analysis of an outcropping carbonate reservoir abstract fractures can play an important role in the fluid storage migration properties of fault damage zones in this present contribution we document the role exerted by fractures on fluid flow in carbonate damage zones of hydrocarbon bearing km long oblique slip normal faults with 10 s of m throw the carbonate fault damage zones were analysed by mean of scan line surveys conducted in both tar free and tar rich outcrops in this way the relationships among the individual fracture characteristics length spacing aperture orientation connectivity and distance from slip surfaces pertaining to small faults of the fault damage zones and hydrocarbons have been established data obtained by scan line surveys were also used to compute the amount of fracture porosity the degree of fracture connectivity and based upon simple assumptions the orientation of the local hmax at times of faulting additionally scan line surveys were also carried out along outcrops exposing unfaulted carbonate host rocks the results of our computation are consistent with a carbonate host rock made up of a quite isotropic fracture array comprised of isolated and coupled fractures in which individual fracture sets have negative exponential spacing distributions in terms of fluid flow the fracture array of the carbonate host rock enhances the fluid storage conversely the fracture array of the fault damage zones is characterized by a pronounced anisotropy due to interconnected fractures which enhance the fluid migration fractures in the fault damage zones include those inherited from background deformation and others related to the faulting processes the latter fracture sets are characterized by power law spacing distributions in conclusion counter intuitively both fracture length and fracture spacing do not have any correlation with hydrocarbons in the fault damage zones on the contrary fracture anisotropy fracture spread and fracture orientation are positively correlated with hydrocarbons

mechanism for joint saturation in mechanically layered rocks an example from southern israel abstract over 700 joint spacings were measured along a 190 m scanline within a single limestone bed of the turonian gerofit formation southern israel by investigating joints belonging to a single systematic set confined to a bed of uniform thickness one can factor out the major influences of bed thickness lithology and mechanical properties on joint set development joint spacing distributions and fracture spacing ratios fsr vary dramatically along the length of the scanline and correlate directly with throughgoing fracture zones belonging to the same tectonic stress regime regions cross cut by fracture zones display narrower median joint spacings fsr of 1 3 and unimodal joint spacing distributions where fracture zones are absent joint spacings have wider medians fsr of 0 8 and multimodal distributions because fracture zones most likely represent areas of high strain and laboratory experiments demonstrate a systematic decrease in fracture spacing with increasing strain regions of the bed cross cut by fracture zones are likely at a more advanced stage of joint set development and hence closer to saturation than other regions joint saturation in the gerofit formation may be achieved by a shift in scale from single layer to multi layer jointing as the development of throughgoing joints prevents the formation of additional bedding confined joints

growth linkage and termination processes of a 10 km long strike slip fault in jointed granite the gemini fault zone sierra nevada california abstract field based structural analysis of an exhumed 10 km long strike slip fault zone elucidates processes of growth linkage and termination along moderately sized strike slip fault zones in granitic rocks the gemini fault zone is a 9 3 km long left lateral fault system that was active at depths of 8 11 km within the transpressive late cretaceous sierran magmatic arc the fault zone cuts four granitic plutons and is composed of three steeply dipping northeast and southwest striking noncoplanar segments that nucleated and grew along preexisting cooling joints the fault core is bounded by subparallel fault planes that separate highly fractured epidote chlorite and quartz breccias from undeformed protolith the slip profile along the gemini fault zone shows that the fault zone consists of three 2 3 km long segments separated by two zones of local slip minima slip is highest 131 m on the western third of the fault zone and tapers to zero at the eastern termination slip vectors plunge shallowly west southwest and show significant variability along strike and across segment boundaries four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at or below greenschist facies conditions taken together we interpret the fault zone to be a segmented linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations complex fault segment interactions and asymmetric slip distance profiles

quantification of fracture networks in non layered massive rock using synthetic and natural data sets abstract two quantitative measures correlation dimension and maximum lyapunov exponent are investigated for quantifying fracture spacing in massive non layered rock the correlation dimension a measure of fractal dimension characterizes some aspects of fracture distribution relative to other fractal methods used in structural geology the correlation dimension provides a more rigorous mathematical calculation of the fractal dimension and is particularly robust in cases where data is limited the maximum lyapunov exponent calculation also provides quantification of observed distributions of fracture spacing emphasizing variations in adjacent spacing measurements the two methods are tested on two different synthetic data sets to elucidate their usefulness in distinguishing between different distributions and their sensitivity to population size average fracture spacing and standard deviation both methods provide accurate results for small population sizes and for a range of average fracture spacings these methods are then used together to quantify two different fracture sets in the granitoids of the sierra nevada batholith the results indicate that the different fracture sets inferred to form from different tectonic processes have distinctive and quantifiable differences in patterns of fracture spacing

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

fault terminations and barriers to fault growth abstract field observations of strike slip faults in jointed granitic rocks of the central sierra nevada california combined with a mechanical analysis of fault interaction provide insight into how fault terminations vary with scale we document here a strike slip fault system 2 3 km long clustered about the west end of the fault system are several dozen faults that parallel the three main fault zones in the system we interpret this cluster of small faults as a barrier that inhibited growth of fault zones in the fault system a two dimensional mechanical analysis shows that a cluster of small faults flanking the tip of a large fault zone will tend to diffuse the stress concentration near the fault zone tip an analogous effect in engineering is known as crack tip shielding near tip stress concentrations promote fault growth and processes that decrease these stress concentrations inhibit fault growth as faults lengthen and grow they interact with features at greater distances and over a broader area so the potential for tip shielding effects will increase as fault length increases this effect can account for why the mechanisms and character of fault terminations would tend to vary as a function of scale

scaling of fracture connectivity in geological formations a new method to quantify fracture network connectivity is developed and applied to analyze two classical examples of fault and joint networks in natural geological formations the connectivity measure accounts for the scaling properties of fracture networks which are controlled by the power law length distribution exponent a the fractal dimension d and the fracture density the connectivity behavior of fracture patterns depends on the scale of measurement for a d 1 analysis of the san andreas fault system shows that a d 1 and that the connectivity threshold is reached only at a critical length scale in contrast for a typical sandstone joint pattern a d 1 which is on the cusp where the connectivity threshold is highly sensitive to the minimum fracture length in the system

brittle to ductile transition due to large strains along the white rock thrust wind river mountains wyoming abstract the deformed foreland of the rocky mountain cordilleras is characterized by major reverse faults that bring precambrian basement rocks to the surface the white rock thrust in the wind river mountains of wyoming is one such fault that developed at fairly shallow levels in the crust detailed study of grain size variations and textures within the fault zone provide a framework for discussion of the mechanics of movement along the fault textural criteria are suggested for distinguishing between dominantly brittle and dominantly ductile deformation a transition from brittle fracturing to ductile deformation is seen with increasing strain and resultant decrease in grain size along the fault zone diffusional creep in the final stages of deformation leads to strain softening and may allow large strains to take place along narrow zones at low deviatoric stresses this may be one way of obtaining large displacements along major faults at shallow levels in the crust

fractures and drainage in the granite mountainous area a study from sierra nevada usa abstract this paper provides an analysis of relationships between drainage patterns and fractures in the part of sierra nevada california north of the yosemite valley bedrock is cretaceous granite and cut by numerous lineaments of various orientation length and geomorphic expression we have mapped fractures and drainage lines from aerial photographs 1 40 000 scale in four test areas ranging in size from 32 5 to 266 km 2 azimuths are shown on rose diagrams for fractures and drainage lines and then visually and statistically compared the coincidence of drainage and fracture patterns is strong which implies causal relationships in plan the majority of valleys follow fractures even if this locally means a different orientation in respect to the regional slope arising from tectonic tilt of the range main streams occupy deeply incised troughs coincident with master fractures of regional extent among two principal fracture directions ssw nne to sw ne and wsw ene the former exerts more control on the drainage lines the presence of a central zone of structural weakness within the major valleys provided significant constraints for the course of glacial erosion and may explain why multiple pleistocene glaciers did not succeed in transforming valley cross sections into expected u shapes

fault size distributions are they really power law abstract power law fault size throw distributions spanning ca seven orders of magnitude are analysed using sample lines from seismic coal mine plan and outcrop data sets outcrop data sets generally have lower power law exponent values than seismic data sets consistent with a general decrease in exponent value with decrease in fault size if such a relationship does exist then probably it cannot be accounted for by sampling bias alone we suggest that either i fault size populations are not power law over a large scale range or ii they are power law but at smaller scales show a greater range of exponent values due to spatial clustering

strain and scaling of faults in the chalk at flamborough head u k analysis has been made of the orientations displacements and spacings of 1340 extensional faults with displacements of up to 6 m along an almost completely exposed 6 km length of cliff this data set has been used to study how fault populations account for strain in a region and to study relationships between different scales of fault strains have been estimated the maximum and intermediate extensions are sub horizontal with approximately equal extension e 0 01 in all horizontal directions it can be inferred that the minimum extension maximum compression was sub vertical but that the wide variety of fault orientations and cross cutting relationships resulted from variable horizontal extensions some faults have oblique slip slickenside lineations which imply a period of later dominantly nnw sse extension which possibly developed as the exposure scale faults linked up e w striking larger scale normal faults effectively forming a single wide fault zone graphs of displacement per unit distance are used to illustrate variations in displacement the scaling of fault displacement appears to follow a power law relationship the differences in orientation between the small scale and large scale faults precludes a simple estimation of the total strain over all scales

reactive transport modeling in fractured rock a state of the science review abstract the field of reactive transport modeling has expanded significantly in the past two decades and has assisted in resolving many issues in earth sciences numerical models allow for detailed examination of coupled transport and reactions or more general investigation of controlling processes over geologic time scales reactive transport models serve to provide guidance in field data collection and in particular enable researchers to link modeling and hydrogeochemical studies in this state of science review the key objectives were to examine the applicability of reactive transport codes for exploring issues of redox stability to depths of several hundreds of meters in sparsely fractured crystalline rock with a focus on the canadian shield setting a conceptual model of oxygen ingress and redox buffering within a shield environment at time and space scales relevant to nuclear waste repository performance is developed through a review of previous research this conceptual model describes geochemical and biological processes and mechanisms materially important to understanding redox buffering capacity and radionuclide mobility in the far field consistent with this model reactive transport codes should ideally be capable of simulating the effects of changing recharge water compositions as a result of long term climate change and fracture matrix interactions that may govern water rock interaction other aspects influencing the suitability of reactive transport codes include the treatment of various reaction and transport time scales the ability to apply equilibrium or kinetic formulations simultaneously the need to capture feedback between water rock interactions and porosity permeability changes and the representation of fractured crystalline rock environments as discrete fracture or dual continuum media a review of modern multicomponent reactive transport codes indicates a relatively high level of maturity within the yucca mountain nuclear waste disposal program reactive transport codes of varying complexity have been applied to investigate the migration of radionuclides and the geochemical evolution of host rock around the planned disposal facility through appropriate near and far field application of dual continuum codes this example demonstrates how reactive transport models have been applied to assist in constraining historic water infiltration rates interpreting the sealing of flow paths due to mineral precipitation and investigating post closure geochemical monitoring strategies natural analogue modeling studies although few in number are also of key importance as they allow the comparison of model results with hydrogeochemical and paleohydrogeological data over geologic time scales

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

fracture network of the ferron sandstone member of the mancos shale east central utah usa abstract the fracture network at the outcrop of the ferron sandstone member of the mancos shale was studied to gain an understanding of the tectonic history of the region and to contribute data to studies of gas and water transmissivity related to the occurrence and production of coal bed methane about 1900 fracture readings were made at 40 coal outcrops and 62 sandstone outcrops in the area from willow springs wash in the south to farnham dome in the north of the study area in east central utah two sets of regional vertical to nearly vertical systematic face cleats were identified in ferron coals a northwest striking set trends at a mean azimuth of 321 and a northeast striking set has a mean azimuth of 55 cleats were observed in all coal outcrops examined and are closely spaced and commonly coated with thin films of iron oxide two sets of regional systematic joint sets in sandstone were also identified and have mean azimuths of 321 and 34 the joints of each set are planar long and extend vertically to nearly vertically through multiple beds the northeast striking set is more prevalent than the northwest striking set in some places joints of the northeast striking set occur in closely spaced clusters or joint zones flanked by unjointed rock both sets are mineralized with iron oxide and calcite and the northwest striking set is commonly tightly cemented which allowed the northeast striking set to propagate across it all cleats and joints of these sets are interpreted as opening mode mode i fractures abutting relations indicate that the northwest striking cleats and joints formed first and were later overprinted by the northeast striking cleats and joints burial curves constructed for the ferron indicate rapid initial burial after deposition the ferron reached a depth of 3000 ft 1000 m within 5 2 million years m y and this is considered a minimum depth and time for development of cleats and joints the sevier orogeny produced southeast directed compressional stress at this time and is thought to be the likely mechanism for the northwest striking systematic cleats and joints the onset of the laramide orogeny occurred at about 75 ma within 13 7 m y of burial and is thought to be the probable mechanism for development of the northeast striking systematic cleats and joints uplift of the ferron in the late tertiary contributed to development of butt cleats and secondary cross joints and probably enhanced previously formed fracture sets using a study of the younger blackhawk formation as an analogy the fracture pattern of the ferron in the subsurface is probably similar to that at the surface at least as far west as the paradise fault and joe s valley graben farther to the west on the wasatch plateau the orientations of ferron fractures may diverge from those measured at the outcrop

using the continuum approach to model unsaturated flow in fractured rock the appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening a continuum model is calibrated against data generated with a high resolution model that created discrete flow and seepage behavior probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model the study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete calibration is a crucial step in this approach because it yields effective model related and process specific parameters the impact of discretization on the estimated parameters is discussed prediction uncertainty is evaluated by means of monte carlo simulations including both the impact of parameter uncertainties and the effect of local heterogeneity in this paper the advantages and limitations of the continuum approach are discussed from a practical perspective which includes a critical examination of project objectives data needs robustness of assumptions and prediction uncertainty

formation of joints in cooling plutons abstract the geometry age and mineralogy of steeply dipping joints in the lake edison granodiorite of california indicate that thermal stresses played a key role in the formation of the joints joint traces curve to approach the pluton boundary at high angles at both large and small scales and they generally terminate at or near the contact with an older pluton radiometric dates and the epidote and chlorite fillings of the joints tie jointing to the initial cooling of the pluton a thermo mechanical stress analysis assuming two dimensional conductive cooling predicts thermal stresses of several tens of mpa the same order of magnitude as plausible fluid pressures regional stresses and lateral normal stresses associated with the overburden the orientation of the joints can be accounted for rather well by the stress field formed by superposing a uniform regional stress field on the predicted thermal stresses the large scale pattern of the early joints in many plutons should be predictable based on a pluton s geometry its age relative to the adjacent rock and knowledge of the regional stress at the time of initial cooling these findings bear on issues pertinent to mining petroleum recovery nuclear waste repository siting and ground water flow

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation