the effect of rupture complexity on estimates of source size a general technique is proposed for estimating rupture geometry from measurements of body wave durations wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent respectively the complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity the shear waves radiated by eight moderate 3 6 ml 4 9 multiply recorded aftershocks of the 1975 oroville california earthquake are analyzed using measurements of the corner frequency the characteristic frequency the pulse duration and the signal duration comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size the difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases

absolute dating of permian ash fall in the rio bonito formation parana basin brazil abstract the rio bonito formation in southern parana basin contains a set of tonsteins interbedded with coal seams these tonsteins are composed mainly of kaolinite with zircon apatite and beta quartz paramorphs as accessory minerals and were interpreted as volcanic ashes deposited by ash falls over pits protected by barrier islands in a barrier lagoon system a u pb dating of zircons in the tonstein a which furnished an age of 267 1 3 4 ma early permian confirming previous age dates based on palynology and correlating them with one of the main periods of volcanic activity in the gondwana the source of the pyroclastic material was attributed to the early permian choiyoi magmatic arc in argentina developed during the sanrafaelic orogeny and with a main peak of volcanic activity between 260 and 272 ma

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

determination of spectral properties of earthquakes from their magnitudes abstract following the recommendation of the iaspei commission on magnitudes from 1967 p wave magnitudes of distant earthquakes are being computed with the aid of the calibration functions of gutenberg and richter 1956 with the development of the instrumental seismology especially in view of the availability of broad band recordings the question arises whether the functions are still adequate in this investigation new calibration functions for p and s waves are presented which are not only dependent on epicentral distance and focal depth but also on the period of the spectral component of the wave the determination of calibration functions is based on the currently most plausible global models for the velocity and anelasticity distribution taking into account the effective bandwidth of the instruments employed eventually leads to the so called spectral magnitudes from the spectral magnitudes m t the energy density spectrum e t of the respective wave can readily be computed the corresponding formula is e t 10 2m t 1 4 with e t in joules per hertz

the role of compressive stresses in jointing on vancouver island british columbia this study demonstrates that joint parallel compressive stresses were integral to the development of joint sets on vancouver island british columbia the mapped study area contains paleostress indicators in the form of calcareous concretions which have multiple internal fractures in precisely the same orientation as one of the surrounding joint sets in the sandstone matrix field and laboratory tests indicate that the stiffest concretions are the most likely to be fractured however results from numerical simulations using measured rock properties preclude an origin for the concretion fractures from either a far field uniaxial tensile or compressive stress fracturing is only found to be possible if the concretions possessed a lower poisson s ratio than the sandstone at the time of fracturing in the latter case a far field uniaxial compressive stress may have generated tensile effective stresses in the vicinity of high modulus concretions seeding the field site with an initial population of concretion fractures and joints given the close spacing of some joints their extension cannot be satisfactorily explained without invoking grain scale compression driven tensile fracturing mechanisms

detached neotectonic stress field in the northern jura mountains switzerland geodetically determined recent elevation changes plio pleistocene uplift history and quarternary fault movements suggest that the folded jura is neotectonically active this concept is supported by measurements of in situ rock stress in this region

subsurface fractures in situ stress and permeability variations in the walloon coal measures eastern surat basin queensland australia abstract in situ stress pattern and subsurface fractures control the production of coal seam gas csg reservoirs and hence comprehensive analyses are required for better development of these reservoirs the surat basin is a prolific csg province with major economic impacts in eastern australia recent studies have reported significant stress variations in this basin due to local geological structures however a systematic analysis of localised stress perturbations within the basin and their impacts on reservoir permeability have not been presented thus far in the published literature in this paper we combine different sets of data including conventional log data wellbore image logs 2d seismic lines and interpreted permeability from well test data in order to characterise the role of geological structures in the subsurface fluid flow of the walloon coal measures in eastern surat basin analysis of 7 3 km of borehole image log across 33 vertical wells revealed a regional ene wsw orientation of the maximum horizontal stress shmax in the study area however there are massive variability in the shmax orientation spatially and with depth analysis of 2d seismic lines highlight the role of geological structures in stress perturbation and the interpretation of natural fractures using image logs show that most of the open fractures are oriented sub parallel to the acute angle of local shmax orientation interpreted well test data in the study wells demonstrates that most of the high permeability data points are located where in situ stress rotation is observed this indicates the influence of local shmax orientation responding to geological structures on the subsurface fluid flow in the eastern part of the surat basin

occurrence of minerals within fractures and matrix of selected bowen and ruhr basin coals abstract late permian age samples of black coal from the coeval bandanna formation and baralaba coal measures of queensland s bowen basin as well as carboniferous coal from germany s ruhr basin were investigated this paper presents scanning electron microscope sem analysis of the mode of occurrence of minerals within these coals and characterisation of the natural fractures present within the samples the coal samples located proximal to orogenic fronts in both basins are structurally complex with multiple generations of mineralisation evident stable isotope analyses of carbonates from selected samples indicate that methanogenesis related co2 reduction has occurred at two of the bowen basin sampling locations ankerite precipitated from a magmatic fluid or basinal brine is associated with significant sulphide mineralisation within brecciated ruhr coal proximal to major fault intersections with anticlines and has been meteorically altered to ferroan calcite and sulphates in coal from immediately below the carboniferous cretaceous unconformity similar alteration has occurred within a bowen basin coal sample close to the present day land surface variation of mineralisation within both the cleats and the coal matrix occurs on a fine scale with crystals of multiple mineral species often being present within micrometres of each other

coal facies studies in brazil a short review coal facies studies in brazil have been done for south brazilian coal measures over the last 20 years using different methods for reconstructing paleoenvironments of peat formation and deposition the first studies were based on teichmuller s concept of macerals from 1984 to 1993 microlithotypes and palynomorphs were used according to the methodology described by hacquebard and donaldson in the 1990s a new method of interpreting paleoenvironments implementing organic geochemistry sequence stratigraphy and the use of biomarkers has become more common in the literature as well as the use of diessel s gelification index gi and tissue preservation index tpi

the amplitude spectra of p and s waves and the body wave magnitude of earthquakes abstract synthetic calibration functions for body wave magnitudes are presented they have been obtained from computations made under the assumption that the variation of amplitude spectra along the earth s surface is due to radial velocity heterogeneity and radial changes of the dissipation factor q inside the earth only the new calibration functions depend on the epicentral distance and the focal depth of the earthquake as well as on the period of the body wave under consideration no single calibration function exists which would produce magnitude figures identical for all fourier components of a body wave observations on several hundreds of strong earthquakes in recent years show that the p wave magnitudes vary systematically with the period of the wave with the application of the synthetic calibration function a general increase of the teleseismically determined p wave magnitudes with frequency is observed this fact reconciles acceleration response spectra from narrowband strong motion analyzers in the near field of an earthquake and spectral magnitudes determined from far field observations by sensitive narrow band seismographs the strength of high frequent spectral components generally exceeds the strength of low frequent components determined in both cases

appalachian stress study 1 a detailed description of in situ stress variations in devonian shales of the appalachian plateau we describe an experiment to measure variations in the state of stress within a horizontally bedded devonian shale sandstone limestone sequence in western new york a total of 75 stress measurements were made in three wells a kilometer or so apart using a wireline supported hydraulic fracturing system the stress profiles indicate that a major drop in horizontal stress level occurs in the generally massive shales this drop occurs principally across the lowermost member of a group of sand beds and corresponds to an offset in sh and sh of 3 5 and 9 mpa respectively above the sands thrust regime conditions prevail although the amount by which sh exceeds sv is undetermined since instantaneous shut in pressures isips were clipped at the level of sv due to fracture rotation below the sands the regime is strike slip with both horizontal stresses showing lateral uniformity despite substantial variations in topography the magnitude of sh in the sand beds themselves and a lower limestone remains at least as great as sv despite the decline in shale stress hence stress contrasts between these beds and neighboring shales become pronounced with depth the contrast in sh and sh between the lowermost sand and the immediately underlying shale is at least 6 and 14 5 mpa respectively sh levels in the lower strike slip regime are about 1 75 times greater than sh and are less than the value required to initiate slippage on favourably oriented frictional interfaces for the upper thrust regime and the sand and limestone beds however the inferred lower bound on sh is close to the slippage threshold for a coulomb friction coefficient of 0 6 the orientation of sh is ene with a standard deviation of 20 fracture traces were usually splayed occasionally spanning 30 of well bore no systematic correlation between mean orientation and lithology is evident significantly different orientations were obtained for adjacent tests in which almost identical islps were observed suggesting that the fractures quickly reorient themselves to propagate normal to the least principal stress direction similarly vertical traces were observed in those tests where isips apparently reflect sv suggesting that rotation to horizontal was rapid

controls on coal cleat spacing this study was undertaken to determine the relationship between cleat spacing cleat height and coal banding texture for queensland permian age coals of different rank four of which are presented here whereas relationships between cleat frequency and rank and with coal type or grade have been reported in the past relationships between the spacing and height among the different kinds of cleats are not quantitatively established for other layered sedimentary rocks joint or fracture spacing relates directly to both bed thickness and rock strength coal is similar to other layered rocks four major classes of cleats were distinguished which were separate data populations when cleat spacing was plotted against cleat height master cleats single vitrain layer cleats multiple vitrain layer package cleats and durain dull coal cleats understanding the relationship between cleat height and spacing for specific coals and the specific kinds of cleats within those coals will lead to more accurate predictions of cleat density and hence coal permeability this can improve modelling and prediction of methane gas deliverability in coal seams in the australian permian coals studied narrowly spaced cleats exist at all ranks but the distribution of cleat spacing with cleat height is what varies for specific cleat classes cleat spacing was found to be directly proportional to cleat height in most cases

seismic evaluation of differential tectonic subsidence compaction and loading in an interior basin quantitative analysis of depth converted reflection times defines long term differential motion across individual structures in a central appalachian interior basin known as the rome trough differential motion decreases exponentially with time rotation about a hinge defining the trough s west margin reached approximately 37 of total displacement in about 63 78 million years m y displacement across the trough s faulted east margin occurred more rapidly and reached 37 of the total in 13 51 m y a major fault in the interior of the trough developed rapidly with 37 of total displacement reached in from 16 to 23 m y longer term rotation across the west margin may be due to its participation in the overall subsidence of the craton during the paleozoic the time spanned by the formation of the east margin and interior faults was restricted to the cambrian in the northern part of the area but to the south movement along the east margin fault continued through the middle ordovician

joint development in perturbed stress fields near faults abstract field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories a progressive change in joint direction is observed from unperturbed regions away from faults to strongly perturbed zones adjacent to faults this indicates that the joint pattern can reflect perturbations of the regional stress field around faults in the examples the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock the corresponding joints converge at these points and are sub parallel to the fault along the remainder of the fault plane the possibility that a fault plane acts as a free surface contained within an elastic body is considered in this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault the free surface model seems to explain the metre scale curvature of joints in the vicinity of existing joints but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the earth s surface two examples are investigated from the lias of great britain at nash point and robin hood s bay both comprise sub horizontal strata of relatively homogeneous lithology and bed thickness which provide striking examples of joints developed near faults

stratigraphy and structure of coalbed methane reservoirs in the united states an overview stratigraphy and geologic structure determine the shape continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane coal in the united states is dominantly of pennsylvanian cretaceous and tertiary age and to date more than 90 of the coalbed methane produced is from pennsylvanian and cretaceous strata of the black warrior and san juan basins investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones coalbed methane production in the united states is mainly from foreland and intermontane basins containing diverse compressional and extensional structures balanced structural models can be used to construct and validate cross sections as well as to quantify layer parallel strain and predict the distribution of fractures folds and faults influence gas and water production in diverse ways however interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

spectral magnitudes magnitude spectra and earthquake quantification the stability issue of the corner period and of the maximum magnitude for a given earthquake abstract p wave magnitude spectra of a foreshock mainshock aftershock sequence on 7 and 8 may 1986 in the aleutian islands are determined using broad band seismograms recorded at the grf array the magnitude spectra are compared for different stations of the array the maximum magnitude is stable with a standard deviation below 1 the reliability of other source parameters fault length seismic moment and stress drop derived from the magnitude spectrum m f depends on the determination of the corner period different methods to derive the corner period are compared best suited and most stable is the one based on the formula t c 0 e s f df 0 e s f f df where es f 102mf 14 is the energy density spectrum of the p wave and mf the spectral p wave magnitude of the earthquake at the respective period

palynological biozones and radiometric data at the carboniferous permian boundary in western gondwana absolute radiometric data obtained recently in upper paleozoic basins of south america and southern africa are available to constrain the age of some palynological biozones defined in the western gondwana some dates obtained from argentina coincide with southern africa s and are useful to constrain the palynological associations in this way the permian argentinian lueckisporites weylandites lw biozone is compared with the lueckisporites virkkiae biozone of brazil and zone 3 of south africa on the other hand the palynofloras from dwyka south africa are comparable with argentinian and brazilian associations recovered near the carboniferous permian boundary tuffaceous intervals of the dwyka group in south africa suggest the beginning of that sequence at 307 ma reaching the 290 ma at the top the available palynological paleoenvironmental and radiometric data from these three western gondwanan areas are analyzed and compared 2006 international association for gondwana research published by elsevier b v all rights reserved

a late cenozoic regional mesofracture system in southern england and northern france the upper cretaceous and palaeogene rocks of s england and n france are cut by a nw trending system of fractures characterized by swarms of vertical extension joints accompanied by conjugate sets of hybrid and shear joints and normal mesofaults many major photolineaments exhibit the same nw trend as the fractures and are particularly conspicuous in n france where they are coincident with rectilinear drainage channels suggesting a relationship between fracture orientation and physiography in s england this relationship is absent possibly because of the influence of additional fracture systems related to major flexures trending obliquely to the nw se direction these major e w trending flexures and associated fracture systems were formed during the oligocene to early miocene 9helvetic9 phase of deformation and are cross cut obliquely by fractures in the nw trending system the nw trending fractures and lineaments are parallel to neotectonic normal faults in the lower rhine embayment and become less well developed to the west with increasing distance from these major structures the lower rhine faults were reactivated and propagated into the quaternary cover as a consequence of ne sw regional tension generated during the late neogene to recent 9jura9 phase of nw se alpine convergence the nw trending extensional structures in s england and n france are considered to be of about the same age and related to the same stress regime as the neotectonic normal faults of the lower rhine embayment however because fractures of the nw system cutting palaeogene sediments in se england are truncated by the erosion surface beneath the plio pleistocene red crag deposits it is possible that in england fracture initiation did not continue into quaternary times

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

fracture model of the upper freeport coal marshall county west virginia pilot ecbmr and co2 sequestration site a model discrete fracture or cleat network was developed for the pennsylvanian upper freeport coal seam at a carbon sequestration pilot site in southeastern marshall co west virginia u s a the model reservoir cleat network was developed using 3d seismic post stack processing and interpretation workflows combined with observations of fracture systems in the surrounding region the upper freeport coal is unminable in this area and served as a test for the feasibility of combined enhanced coalbed methane recovery ecbmr operations with co2 storage in unminable coals well log derived subsurface structure maps were used to calibrate 3d seismic time to depth conversion post stack processing was used to enhance and identify subtle discontinuities in the seismic data that could be related to field scale faults fracture zones or stratigraphic heterogeneity the cleat model was developed using power law fracture length and aperture distributions spatial variations of cleat intensity in the model were controlled using measures of localized structural discontinuity extracted from 3d seismic attribute workflows the cleat model identifies a permeable fracture facies within the reservoir most likely to be impacted by co2 injection and migration areas of concentrated seismic discontinuity bear some spatial association to areas of positive vertical deformation observed in a tiltmeter survey of the site and attributed to co2 injection the model could help focus time lapse processing and interpretation in regions estimated to have higher permeability and porosity and higher probability for change of acoustic properties in response to co2 injection and methane production the approach developed here has general applicability to identification of fracture facies and development of unconventional naturally fractured reservoirs in other lithologies and basins

mechanisms of natural fracturing in a sedimentary basin mechanisms of natural fracture generation in a sedimentary basin may be studied by the use of physical properties of sedimentary rocks and of pore fluid pressure the physical properties of rocks such as poisson s ratio and young s modulus under laboratory conditions are available but only a few of these are reported under subsurface conditions in this paper in situ values of poisson s ratio derived from analysis of artificial hydrofracturing data in the gulf coast are used for estimating horizontal stresses in both hydrostatically and abnormally pressured zones there in a tectonically relaxed basin such as the gulf coast the horizontal stress can be a function of vertical overburden stress fluid pressure and poisson s ratio the horizontal stress increases with depth in the hydrostatic pressure zone but is abnormally low in the abnormally pressured zone fracture pressure and its gradient given as a sum of least horizontal stress and fluid pressure is however not abnormally low in the abnormally pressured zone because the fluid pressure there is abnormally high this paper describes the in situ fracture pressure gradient estimated for the gulf coast area on the basis of models of vertical fluid charging through an aquifer and a fault system during continuous burial the depth at which the charged fluid pressure gradient exceeds the fracture gradient or the point of natural hydrofracturing is estimated after an erosional event the most significant decline of fracture pressure gradient is expected in the uppermost part of the original abnormal pressure zone hydrofracturing there could occur if an effective fluid is charging from deep to shallow through an aquifer or a fault system if the erosion continues to a point at which approximately two thirds of the total sediment thickness is removed the horizontal stress may become almost zero if such a stress condition is developed the sedimentary rocks become greatly relaxed possibly causing fractures

is there a genetic relationship between selected regional joints and contemporary stress within the lithosphere of north america on the appalachian plateau of new york ene striking joints parallel the mid continent contemporary stress field and do not correlate with other structures joints within ohio indiana michigan and west virginia also parallel the mid continent maximum horizontal compression as indicated by hydraulic fracture measurements in northern indiana where the contemporary stress field deviates significantly from the orientation of the mid continent stress the attitude of the joints deviates accordingly in addition to joints structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid continent stress field from this i conclude that these joints are mode i cracks whose orientation corresponds to the contemporary tectonic stress field in itself the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults and folds

reservoir parameters and maceral composition of coal in different carboniferous lithostratigraphical series of the upper silesian coal basin poland abstract laboratory tests were carried out on coal samples taken from mine openings of selected coal mines in the upper silesian coal basin the analyses involved maceral composition vitrinite inertinite and liptinite group and vitrinite reflectance on the one hand and reservoir parameters coal permeability and effective porosity on the other the results are compared samples with high values of coal permeability are characterized by vitrinite contents of ca 60 and samples with the lowest permeability by vitrinite contents of 40 the vitrinite rich bright coals are brittle and prone to crushing caused by tectonic pressures moreover coal permeability is more strongly anisotropic in the bright coals of the cracow sandstone and the mudstone series than in the dull coals of the upper silesian sandstone series in bright coals permeability is much along the direction parallel to vitrain layers good reservoir parameters such as permeability and effective porosity are crucial for fluid flow through the coal seams and thus successful coalbed methane exploitation in the upper silesian coal basin cracow sandstone and mudstone series with vitrinite rich coals should be a good target though serious geological problems must first be overcome

hydrologic properties of coal beds in the powder river basin montana i geophysical log analysis as part of a multidisciplinary investigation designed to assess the implications of coal bed methane development on water resources for the powder river basin of southeastern montana six wells were drilled through paleocene age coal beds along a 31km east west transect within the tongue river drainage basin analysis of geophysical logs obtained in these wells provides insight into the hydrostratigraphic characteristics of the coal and interbedded siliciclastic rocks and their possible interaction with the local stress field natural gamma and electrical resistivity logs were effective in distinguishing individual coal beds full waveform sonic logs were used to determine elastic properties of the coal and an attendant estimate of aquifer storage is in reasonable agreement with that computed from a pumping test inspection of magnetically oriented images of the borehole walls generated from both acoustic and optical televiewers and comparison with coal cores infer a face cleat orientation of approximately n338e in close agreement with regional lineament patterns and the northeast trend of the nearby tongue river the local tectonic stress field in this physiographic province as inferred from a nearby 1984 earthquake denotes an oblique strike slip faulting regime with dominant east west compression and north south extension these stress directions are coincident with those of the primary fracture sets identified from the televiewer logs and also with the principle axes of the drawdown ellipse produced from a complementary aquifer test but oblique to apparent cleat orientation consequently examination of these geophysical logs within the context of local hydrologic characteristics indicates that transverse transmissivity anisotropy in these coals is predominantly controlled by bedding configuration and perhaps a mechanical response to the contemporary stress field rather than solely by cleat structure published by elsevier b v

aliphatic and aromatic hydrocarbons in candiota coal samples novel series of bicyclic compounds abstract aliphatic and aromatic fractions obtained from nine samples taken from two different seams of five boreholes in the candiota coalfield lower permian were analysed by gas chromatography mass spectrometry the occurrence of the tetracyclic diterpenoids 16 h phyllocladane and ent 16 h kaurane among the aliphatic hydrocarbons and the tricyclic diterpenoids simonellite and retene in the aromatic hydrocarbon concentrates suggest an important input from conifers to the sedimentary biomass this may explain the origin of a novel series of saturated and aromatic bicyclic compounds detected in the extracts which may be structurally related to the same precursor possibly a conifer resin derived tricyclic diterpenoid

regional fractures ii fracturing of mesaverde reservoirs in the piceance basin colorado 1 cretaceous strata in the east central piceance basin of northwestern colorado were subjected to several phases of stress due to horizontal tectonic compression burial and uplift these rocks contain a regional set of west northwest extension fractures observed in abundant vertical and deviated core from the u s department of energy s multiwell experiment and slant hole completion test wells time depth relationships fracture orientation and fluid inclusion analyses indicate that the fractures formed at about 36 40 ma during a phase of increased laramide west northwest compression and in a pressure temperature regime compatible with the geologically reconstructed maximum burial depths this regional fracturing is an example of load parallel extension fracturing and basinwide dilatancy at depth under conditions of high pore pressure and anisotropic tectonically created horizontal stress

early jointing in coal and black shale evidence for an appalachian wide stress field as a prelude to the alleghanian orogeny early ene striking joints present coordinates within both pennsylvanian coal and devonian black shale of the central and southern appalachians reflect an approximately rectilinear stress field with a dimension 1500 km this appalachian wide stress field awsf dates from the time of joint propagation when both the coal and shale were buried to the oil window during the 10 15 m y period straddling the pennsylvanian permian boundary the awsf was generated during the final assembly of pangea as a consequence of plate boundary tractions arising from late stage oblique convergence where maximum horizontal stress s h of the awsf was parallel to the direction of closure between gondwana and laurentia after closure the awsf persisted during dextral slip of peri gondwanan microcontinents when sh appears to have crosscut plate scale trans current faults at around 30 sup o following 10 m y of dextral slip during tightening of gondwana against laurentia the awsf was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline shaped alleghanian map pattern seen today

candiota coalfield a world class brazilian coal deposit abstract the candiota coalfield is situated at the southwestern margin of the sul riograndense shield in the state of rio grande do sul south brazil the coal seams and associated sedimentary rocks occur in the rio bonito formation guata group of artinskian kungurian age lower permian the palynological assemblage found in the candiota coals is characterized by the predominance of pteridophytic spores pollen grains from gymnospermic vegetation as well as algae related elements are minor elements in the assemblage coal resources in the basin reach more than 12 billion t and the production of run of mine coal was about 1 500 000 t in 1989 several coal beds occur in the basin however only the candiota seam is exploited in an open cast mine the macroscopic seam section of the candiota seam shows a predominance of banded and dull coal which characterizes a mineral rich and vitrain poor coal vitrinite never reaches 50 and minerals vary from 36 to 50 under microscopic examination the coal is poor in inertinite when compared with other brazilian coals and the content of exinite is about 7 the composition of samples collected in various areas of the basin is very uniform as revealed by proximate analysis the coal is very high in ash yield and even the hand picked vitrain present values of about 12 the calorific value is very low 3 300 kcal kg for samples of run of mine coal with 52 ash based on data from both moisture and carbon contents of vitrain the candiota coal seam can be classified as equivalent to subbituminous a coal in the american standards for testing and materials classification

origin of reservoir fractures in little knife field north dakota thin vertical planar fractures observed in the mission canyon formation at the little knife field are naturally occurring and appear to be extension fractures the predominant east west trend of the fractures measured in oriented core from six wells parallels the contemporary maximum horizontal compressive stress in the williston basin the fractures occur only in carbonate units but within the carbonates their occurrence is not lithology dependent fracture density measured in cores of the reservoir carbonates averages 1 ft 3 m of fracture per 2 3 ft 7 m of core the formation and mineralization of reservoir fractures were the most recent diagenetic events in the mission canyon formation at little knife study of aqueous and hydrocarbon fluid inclusions associated with the fractures reveals 1 fractures formed after the strata were buried to at least their present depth of 9 800 ft 2 987 m which indicates their age is post mesozoic 2 the pore fluid pressure gradient was normal hydrostatic immediately after if not during fracture system development 3 formation water salinity has remained fairly constant since fracture initiation 4 migration of hydrocarbons into the reservoir probably preceded fracture genesis and 5 methane concentration may have decreased since fracture initiation

applications of twin analysis to studying meteorite impact structures abstract this paper describes a technique twin analysis of dolomite and calcite which was used to estimate the level of erosion of an impact crater if the age of impact is known the level of erosion gives the amount of sediments present at that time the estimate of the level of erosion and the presence or absence of tectonic strains in calcite constrains the age of impact this technique might also be useful in identifying deeply eroded impact structures twin analysis gives the greatest shortening direction e 1 tilt corrected e 1 directions converge at or above the present day surface if a shallow gas explosion or meteorite impact explains the structure rather than a deep gas or cryptovolcanic explosion the energy density recorded by twinning distinguishes an impact from a shallow gas explosion for structures 100 m diameter at serpent mound a well established impact structure e 1 directions converge at 1400 390 m 95 confidence interval of the mean above the present day structure and the sample closest to the center of the structure records an energy density of 1 7 10 7 j m 3 these results are consistent with previous studies showing that serpent mound is an impact e g r w carlton c koeberl m t baranoski g a schumacker discovery of microscopic evidence for shock metamorphism at the serpent mound structure south central ohio confirmation of an origin by impact earth and planet sci lett 162 1998 177 185 the level of erosion and other data suggests that serpent mound formed between 290 and 256 ma and was originally 8 5 to 11 km in diameter dolomite twinning is not observed at serpent mound suggesting that this technique may only be useful for studying larger more deeply eroded structures

recent stress field and neotectonics in the eastern jura mountains switzerland the regional stress field and its local variation were determined for the northern part of central switzerland fig 1 by using overcoring techniques doorstopper triaxial strain cell and observations of breakouts in deep boreholes the results are compared with fault plane solutions of earthquakes and with the orientation of horizontal stylolites in the northern part of central switzerland the nw se orientation of the maximum horizontal stress sh which is characteristic for central europe was observed only in the crystalline basement in the folded jura and south of it in one well the greatest principal horizontal stress above the triassic decollement horizon is oriented approximately in a n s to nne ssw direction this direction persists into the western tabular jura and the southernmost rhine graben only in the eastern part of the tabular jura the greatest principal horizontal stress shows a nnw sse to nw se orientation comparison of the near surface stress field as determined by in situ stress measurements and borehole breakouts with the directions of horizontal stylolites generated during the evolution of the folded jura indicates that the orientation of the recent stress field near the earth s surface is the same as that which prevailed during the upper miocene to lower pliocene the central part of northern switzerland is therefore the first area in central europe where it is possible to demonstrate that the near surface stress field is decoupled from that in the crystalline basement the difference in the orientation of the greatest principal horizontal stress is about 50

subsurface geology of the warfield structures in southwestern west virginia implications for tectonic deformation and hydrocarbon exploration in the central appalachian basin data from over 6000 wells and five multichannel reflection seismic lines were used to constrain the subsurface geometry of the warfield structures in southwestern west virginia within the central appalachian basin based on their vertical differences in geometry and structural styles we divided the warfield structures into shallow above the devonian onondaga limestone intermediate between the devonian onondaga limestone and the silurian tuscarora sandstone and deep below the ordovician trenton horizon structural levels shallow structures are related to the alleghanian deformation above the major detachment horizon of the devonian shales and consist of the warfield anticline with a 91 5 m closure and southeast dipping monoclines which aided the northwest migrati n and entrapment of oil and gas at the intermediate level the closure of the warfield anticline is lost because the alleghanian deformation is obscured below the major detachment of the devonian shales which explains the reduced production from the devonian and silurian reservoirs deep structures are characterized by an asymmetric half graben within a continental rift system known as the rome trough in which a thick sequence of sedimentary rocks exists to provide sources for overlying reservoirs although stratigraphic traps may be associated with thickness and facies changes the deep level is structurally unfavorable for trapping hydrocarbons based on changes we found in map trend we divided the warfield structures into a middle segment and southern and northern bends the middl segment is parallel to the new york alabama lineament a northeast trending magnetic gradient the southern and the northern bends are linked to the 38th parallel lineament a west trending fault system and the burning springs mann mountain lineament a north trending magnetic gradient respectively we propose a wedge tectonic model to explain 1 northern and southern bends of the warfield structures and hydrocarbon distribution in the subsurface of southwestern west virginia 2 vertical changes in geometry and structural style from the deeply buried half graben to the overlying asymmetric anticline and 3 geometric and kinematic relationship among the warfield structures the 38th parallel and the burning springs mann mountain lineaments

extensional failure and hydraulic valving at minas da panasqueira portugal evidence from vein spatial distributions displacements and geometries abstract at panasqueira portugal exceptional exposure and demonstrable vein connectivity allow robust characterisation of brittle elastic failure mechanisms in intrusive related environments extensional failure was driven by cycles of fluid injection hydraulic valving and vein growth under conditions with v 1 and differential stress

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

structure and tectonics of central and southern appalachian valley and ridge and plateau provinces west virginian and virginia the valley and ridge and eastern allegheny plateau from pennsylvania into tennessee is subdivided into distinct allochthonous sheets emplaced over an essentially featureless precambrian basement surface sheet development is related to variations in stratigraphic thickness and lithology as well as regional basement configuration three sheets control central appalachian structural style the massanutten blue ridge sheet is easternmost and is bounded on the west by the little north mountain pulaski fault system continuing westward into the plateau the martinsburg sheet contains anticlinoria and synclinoria uncut by major thrust faults both massanutten blue ridge and martinsburg sheets are seated in upper ordovician martinsburg reedsville shales the underlying waynesboro sheet is rooted in lower cambrian waynesboro rome shales and its imbrication has controlled the locations of major anticlinoria and synclinoria in the upper sheet within the southern appalachians greater imbrication of the lower sheet and increased thrust fault displacement at longitudinal ramps have destroyed the lateral continuity along strike of the central appalachian waynesboro and overlying martinsburg sheets there imbrication to the surface has formed the saltville sheet continuous into alabama as well as the st clair narrows copper creek cove mountain and st paul honaker sheets southwest of the trend change the holston stone mountain sheet adjacent to the blue ridge is rooted primarily in lower and middle cambrian strata and is underlain by the pulaski sheet in the westernmost sector of this region the pine mountain and richlands sheets are seated in devonian shales the pulaski and massanutten blue ridge sheets rooted primarily in upper ordovician shales form a continuous structural unit and include blue ridge and piedmont rocks

clastic dike swarms and the structural evolution of the foreland fold and thrust belt of the southern andes clastic dike swarms are intruded into a cenozoic foreland fold and thrust belt in southern chile the dike material consists of sandstone and conglomerate with clasts as much as 25 cm in diameter brecciated wall rocks are also found in the clastic matrix the dikes often exceed 50 cm in width and hundred of metres in length in outcrop and are oriented overwhelmingly transverse to fold axes and parallel to cross joints the dike swarms are concentrated near the toe of major thrusts where they are found injected into the hanging wall a regional axial planar spaced cleavage is developed in the clastic dikes and sills clearly postdating injection of clastic material dike injection postdates at least the initiation of extension fractures the cross joint set within the swarms the dike intrusions represent as much as 20 extension parallel to fold axes in addition to several percent extension represented regionally by the cross joints the structural features of the dike swarms and their geometric relationship to other structures suggest rapid single phase injection the arrival of the front edge of a thrust on an already highly overpressured sedimentary sequence would cause an instantaneous increase in the overburden pressure and therefore could result in injection of a dense slurry of wet coarse sediments along preexisting planes of weakness field relationships of mesoscopic structures suggest the following evolution cross joint development incipient cleavage development initiation of thrusting and buckling clastic dike injection regional spaced cleavage development and associated late stage tightening of folds

along axis segmentation and growth history of the rome trough in the central appalachian basin the rome trough a northeast trending graben is that part of the cambrian interior rift system that extends into the central appalachian foreland basin in eastern north america on the basis of changes in graben polarity and rock thickness shown from exploration and production wells seismic lines and gravity and magnetic intensity maps we divide the trough into the eastern kentucky southern west virginia and northern west virginia segments in eastern kentucky the master synthetic fault zone consists of several major faults on the northwestern side of the trough where the most significant thickness and facies changes occur in southern west virginia however a single master synthetic fault called the east margin fault is located on the southeastern side of the trough syndepositional motion along that fault controlled the concentrated deposition of both the rift and postrift sequences the east margin fault continues northward into the northern west virginia segment apparently with less stratigraphic effect on postrift sequences and a second major normal fault the interior fault developed in the northern west virginia segment these three rift segments are separated by two basement structures interpreted as two accommodation zones extending approximately along the 38th parallel and burning mann lineaments computer aided interpretation of seismic data and subsurface geologic mapping indicate that the rome trough experienced several major phases of deformation throughout the paleozoic from the early middle cambrian pre copper ridge deposition rapid extension and rifting occurred in association with the opening of the iapetus theic ocean at the continental margin the late cambrian middle ordovician phase copper ridge to black river deposition was dominated by slow differential subsidence forming a successor sag basin that may have been caused by postrift thermal contraction on the passive continental margin faults of the rome trough were less active from the late ordovician pennsylvanian post trenton deposition but low relief inversion structures began to form as the appalachian foreland started to develop these three major phases of deformation are speculated to be responsible for the vertical stacking of different structural styles and depositional sequences that may have affected potential reservoir facies trapping geometry and hydrocarbon accumulation

horizontal stress anisotropy and effective stress as regulator of coal seam gas zonation in the sydney basin australia abstract coal seam gas zonation in the sydney basin nsw australia is related to basin hydrodynamics and hydrochemical facies evolution along the flow path from the subcrop to the basin center biogenic methane corresponds with meteoric water under hydrostatic pressure and persists down to the top of the geopressured zone 800 to 1000 m thermogenic gases including wet hydrocarbons can reach up to relatively shallow horizons of less than 500 600 m depth in the transition zone between the top of the geopressured and base of the hydrostatic zone a mixed water and gas regime prevails comprising brackish waters and gases of mixed biogenic thermogenic and inorganic origins including co 2 mechanisms for and the role of stress in the development of this layered hydrogeological and gas environment are investigated in this paper the inverse relationship between effective horizontal stress and permeability in coals through regulation of cleat volumes is well documented and there is evidence of regionally compartmentalized stress regimes with depth within the sydney and other eastern australian coal basins this regional stress regime can be overprinted by the effect of localized geological features it is hypothesized that the in situ stress regime plays an important role in the regulation of groundwater flow regimes and extents resulting in the development of the reported gas content and compositional zonation analysis of regional gas and stress data obtained from public and private databases as well as literature supports this hypothesis changes in gas concentration and composition with depth correspond with discernable variations in horizontal stress anisotropy gas contents generally increase with depth down to a peak gas horizon below which concentrations decrease this peak gas zone is coincident with a horizontal stress anisotropy change from moderately high to low levels associated with reverse to strike slip faulting conditions respectively the stress release zone also marks the top of the thermogenic gas zone identified by the first appearance of ethane in the vertical profile this zone also hosts gases of mixed origins biogenic thermogenic and inorganic co 2 and represents a mixed transitional groundwater flow environment the base of the mixed gas zone is the top of the geopressured only flow associated with thermogenic gases and is signaled by the return to high stress reverse faulting conditions below 850 900 m depth in the sydney basin

delineation of the distinctive nature of tertiary coal beds abstract floral character in mires has changed progressively through time in the carboniferous pteridophytes sphenophytes and lycophytes were dominant but by the permian gymnosperms were an important component of mire flora during the early mesozoic gymnosperms remained the characteristic mire vegetation together with pteridophytes and conifers became dominant during the jurassic cretaceous and paleocene vegetation are similar with taxodiaceous flora being important in mire vegetation from the eocene onwards however angiosperms were increasingly dominant in mire communities and in the miocene herbaceous vegetation began to play a significant role together with these changes in floral character at least three aspects of coal character also appear to vary sequentially with time and are distinctive in the tertiary 1 proportions and thickness of vitrain banding 2 coal bed thickness and 3 proportions of carbonised material a compilation has been made of data from the coal literature comparing older coals with those of the tertiary in order to give a perspective in which to examine tertiary coals it was found that only tertiary coals contain significant proportions of coal devoid of vitrain bands in addition tertiary coals are the thickest recorded coal beds and generally contain low percentages of carbonised material many less than 5 as compared to older coals it is interesting to note that paleocene coal beds are similar to cretaceous coals in that they tend to be thinner and contain higher proportions of carbonised material than do younger tertiary coals the absence of vitrain bands in some tertiary coal beds is thought to result from the floras dominated by angiosperms which are relatively easily degraded as compared to gymnosperms the thickness of tertiary coals may be related to an increase in biomass production from the carboniferous through to the tertiary as plants made less investment in producing lignin an energy intensive process in addition with less lignin in plants easier degradation of biomass may have facilitated nutrient recycling which in turn led to greater biomass production increased biomass production may have also diluted the carbonised material present in some tertiary peats leading to lower proportions in the coal another possible cause of decreased carbonised components in tertiary coal is that decreasing lignin content resulted in decreased charring during fires as lignin is particularly prone to charring a third possibility is that the carbonised component of peat may be concentrated during coalification so that tertiary coals generally of lower rank than mesozoic or paleozoic coals contain a smaller fraction of carbonised plant material it is not at present clear which of these mechanisms may have affected carbonised material in peat and coal but it is clear that lignin type and content has had an important role in determining peat and coal character since the paleozoic

coal cleat domains and domain boundaries in the allegheny plateau of west virginia regional face cleats cutting pennsylvanian and permian coal seams in the allegheny plateau of west virginia can be divided into domains separated by boundaries that are sharply defined along most of their lengths domains and domain boundaries are established based on cleat trends number of regional cleat sets and relative chronology of cleat set development regional cleats of each set show a common trend and abutting relationships between multiple sets within a domain describe a progressive history of changing stress fields and cleat development boundaries dividing the in situ directions of horizontal principal stress are coincident with cleat domain boundaries suggesting a common and persistent controlling factor uniform trends of face cleats within domains and ab upt changes in cleat signature across domain boundaries can be spatially related to regional basement structures and a depositional hinge line within the coal bearing and underlying mississippian rocks in addition fold structures in coal and underlying sedimentary rocks across the allegheny plateau commonly terminate or change trend abruptly at joint domain boundaries in some cases regions of common fold trends in coal bearing rocks are contained within specific domains face cleat trends commonly differ from joint trends in rocks immediately bounding coal seams however one domain boundary in coal can be traced into mississippian rocks through the unconformity at the base of the pennsylvanian section in this case mississippian and pennsylvanian joint trends differ it follows tha joint domain boundaries can extend downward through rocks of different lithologies as well as coincide with conformable and unconformable stratigraphic boundaries

regional joint sets in the arabian platform as indicators of intraplate processes the eastern part of the saudi arabian craton is a platform underlain by gently tilted and horizontal mesozoic cenozoic sedimentary rocks everywhere more than 250 km distant from the zagros deformation front despite its tectonic simplicity the platform contains several laterally extensive but subdued structures and lineaments belonging to more than one system of fault zones and flexures new microtectonic observations of dominant sets of extension and conjugate hybrid joints permit regionally significant extension directions to be inferred and the origin of the macrostructures to be assessed the central arabian arch the e w crest of which coincides with an axis of mesozoic subsidence developed during the late cretaceous to eocene when the basin inverted as a consequence of the emplacement of ophiolite bearing nappes on the zagros and oman margins during arching there was strike parallel elongation of beds at the same time as the arch amplified the central arabian graben system evolved as a result of the northward displacement of an east arabian block or sheet that became detached across an arcuate separation zone which in the south is coincident with the crest of the arch an important neogene response in the arabian platform to ne sw shortening in the zagros ranges was the formation of a swarm of ne striking master joints and lineaments these structures reflect the diffuse and peripheral expansion of the foreland beyond the zagros deformation front

use of clay mineral alteration patterns to define syntectonic permeability of joints cleat in pennsylvania anthracite coal abstract joints cleat in pennsylvania anthracite contain two distinct clay mineral assemblages both of which formed by alteration of preexisting kaolinite at peak metamorphic conditions during the alleghanian orogeny the first assemblage nh4 illite or pyrophyllite quartz formed by reaction of kaolinite with methane rich fluids derived from within the coal the second assemblage sudoite tosudite rectorite berthierine formed by the reaction of kaolinite with ferromagnesian bearing hydrothermal fluids which must have come from outside the coal in an earlier paper we suggested that the first assemblage indicated clay diagenesis in low permeability environments and that the second assemblage indicated clay diagenesis in high permeability environments if this premise is correct then the distribution of clay mineral alteration assemblages serves to define syntectonic permeability variations in coal cleat the first assemblage dominates in the coal matrix itself in isolated cleat in cleat that parallel the regional trend of alleghanian folds and in the mirror portions of cleat oriented perpendicular to the fold trends suggesting that these regions are low permeability environments the second assemblage dominates in the hackle fringe of interconnected cleat that trend perpendicular to the strike of the appalachian orogen suggesting that these regions are high permeability environments our results emphasize that syntectonic cleat permeability is a function of cleat orientation macroscopic cleat interconnectivity and orientation as well as microscopic cleat surface morphology

controls on fracture distribution in cretaceous sedimentary rocks from the isfahan region iran in this study relationships between fracture patterns lithology thickness diagenetic processes and grain size are evaluated within cretaceous sediments in two sections of dizlu and kolah ghazi of isfahan this study area was selected based on its outcrops of different rock units and its well developed tectonic fractures the fracture patterns within stratigraphic units of these sections are studied using geometrical and statistical analyses this study finds that variable fracture spacing and fracture spacing ratios can be affected by lithology thickness grain size of sediments and diagenetic processes a study of fracture stratigraphy based on fracture pattern evaluation within different cropped out sedimentary rocks can be used to improve understanding of the same types of sedimentary rock units below the surface or throughout other sedimentary basins consequently this could improve information regarding storage and fluid flow pattern throughout sedimentary rocks in different regions even for subsurface purposes

structural controls on fractured coal reservoirs in the southern appalachian black warrior foreland basin abstract coal is a nearly impermeable rock type for which the production of fluids requires the presence of open fractures basin wide controls on the fractured coal reservoirs of the black warrior foreland basin are demonstrated by the variability of maximum production rates from coalbed methane wells reservoir behavior depends on distance from the thrust front far from the thrust front normal faults are barriers to fluid migration and compartmentalize the reservoirs close to the thrust front rates are enhanced along some normal faults and a new trend is developed the two trends have the geometry of conjugate strike slip faults with the same 1 direction as the appalachian fold thrust belt and are inferred to be the result of late pure shear deformation of the foreland face cleat causes significant permeability anisotropy in some shallow coal seams but does not produce a map scale production trend

spectral p wave magnitudes aki s ω square model and source parameters of earthquakes abstract the earthquake magnitude is a quantity sampling the spectrum of the far field radiation with a suit of properly defined magnitudes in a sufficiently broad range of frequencies the radiated spectrum can be restored and analyzed a method is proposed for the extraction of stress drop fault length and seismic moment from magnitudes on a routine basis thereby the theoretical spectrum as predicted by the square model of aki is utilized in applying the method to earthquakes which occurred in several parts of asia over a time span of 3 years it is shown that in most cases earthquakes in a given region are characterized by the same stress drop varying however from region to region in one region a change of the stress drop with time is found eventually indicating a change in the state of stress in the particular region during the time interval investigated

loading paths to joint propagation during a tectonic cycle an example from the appalachian plateau u s a abstract based on the timing of joint propagation during the history of burial lithification deformation and denudation of clastic rocks within sedimentary basins four types of joints may be distinguished tectonic hydraulic unloading and release tectonic and hydraulic joints form at depth prior to uplift in response to abnormal fluid pressures whereas unloading and release joints form near the surface in response to thermal elastic contraction accompanying erosion and uplift tectonic joints are distinguished from hydraulic joints in that tectonic compaction is a mechanism for achieving abnormal pore pressures leading to the propagation of the former whereas compaction by overburden loading leads to the abnormal pore pressures in the latter case the orientation of unloading joints is controlled by either a residual or contemporary tectonic stress whereas the orientation of release joints is controlled by a rock fabric examples of some of these joints are found within the devonian catskill delta of the appalachian plateau new york during the alleghanian orogeny tectonic joints cross fold joints formed under abnormal pore pressure as indicated by the observation that joints propagated in the siltstones before they developed in shales and by the cross cutting relationships of folds cleavage and joints this sequence is compatible with oil company hydraulic fracture data which show that the least principal stress within sandstone layers is less than that in the intercalated shale layers plumose structures indicate that the joints within siltstones propagated as discontinuous rupture events each of which affected less than a meter of bed length the discontinuous rupturing is compatible with models for natural hydraulic fracturing release joints strike joints post date the alleghanian orogeny as indicated by abutting relationships within the deeper parts of the devonian clastic section unloading joints are orthogonal to the contemporary tectonic stress field

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

cleats and their relation to geologic lineaments and coalbed methane potential in pennsylvanian coals in indiana abstract cleats and fractures in pennsylvanian coals in southwestern indiana were described statistically analyzed and subsequently interpreted in terms of their origin relation to geologic lineaments and significance for coal permeability and coalbed gas generation and storage these cleats can be interpreted as the result of superimposed endogenic and exogenic processes endogenic processes are associated with coalification i e matrix dehydration and shrinkage while exogenic processes are mainly associated with larger scale phenomena such as tectonic stress at least two distinct generations of cleats were identified on the basis of field reconnaissance and microscopic study a first generation of cleats that developed early on during coalification and a second generation that cuts through the previous one at an angle that mimics the orientation of the present day stress field the observed parallelism between early formed cleats and mapped lineaments suggests a well established tectonic control during early cleat formation authigenic minerals filling early cleats represent the vestiges of once open hydrologic regimes the second generation of cleats is characterized by less prominent features i e smaller apertures with a much less pronounced occurrence of authigenic mineralization our findings suggest a multistage development of cleats that resulted from tectonic stress regimes that changed orientation during coalification and basin evolution the coals studied are characterized by a macrocleat distribution similar to that of well developed coalbed methane basins e g black warrior basin alabama scatter plots and regression analyses of meso and microcleats reveal a power law distribution between spacing and cleat aperture the same distribution was observed for fractures at microscopic scale our observations suggest that microcleats enhance permeability by providing additional paths for migration of gas out of the coal matrix in addition to providing access for methanogenic bacteria the abundance distribution and orientation of cleats control coal fabric and are crucial features in all stages of coalbed gas operations i e exploration and production understanding coal fabric is important for coal gas exploration as it may be related to groundwater migration and the occurrence of methanogenic bacteria prerequisite to biogenic gas accumulations likewise the distribution of cleats in coal also determines pathways for migration and accumulation of thermogenic gas generated during coalification

p wave spectra for ml 5 foreshocks aftershocks and isolated earthquakes near parkfield california abstract wood anderson seismograms recorded at mount hamilton mhc 185 km 327 santa barbara sbc 180 km 158 and tinemaha tin 240 km 56 provide data for comparing p wave spectra for two immediate 17 min foreshocks one early 55 hr foreshock two aftershocks and two isolated parkfield earthquakes all are m l 5 0 shocks with epicenters within 7 km of the common epicenter of the 1934 and 1966 parkfield main shocks the set of events is well suited for testing the hypothesis that foreshocks are high stress drop sources calculated stress drops are controlled by source directivity at azimuths aligned with the fault break at mhc and sbc p wave radiation from the three foreshocks is focused along one fault trace azimuth suggesting that foreshock sources are characterized by pronounced unilateral rupture expansion at tin broadside to the fault where directivity has minimum effect on calculated relative stress drop the two immediate foreshocks are higher stress drop sources the early foreshock is a low to average stress drop source indicating the possibility that stress concentration is a rapidly occurring phenomenon in rupture nucleation alternatively the stress field is highly variable on the scale of 2 to 3 km in the focal region of an impending earthquake with a rupture length of 20 to 30 km

spectral and dynamic characteristics of strong earthquakes in the armenia upland and adjacent areas abstract the spectral and dynamic characteristics including magnitudes are determined for a number of strong earthquakes in the armenian upland and adjacent areas on the basis of the procedure developed at the usso the records of standard instruments and of tchiss instruments at the obninsk observatory are used the results are compared with similar estimates obtained from the data of the grafenberg observatory with application of the spectral magnitude approach it is shown for all the earthquakes considered that the periods of the maximum magnitudes at both observatories are largely in agreement dynamic characteristics such as seismic moments and the lengths of rupture from the obninsk observatory data generally agree with the cmt data and satisfy the relationship between the length of rupture and the surface wave magnitude riznichenko 1976

origin of fracture porosity example from altamont field utah the occurrence of natural fracture systems in subsurface rock can be predicted if careful evaluation is made of the geologic processes that affect sedimentary strata during their cycle of burial diagenesis uplift and erosional unloading variations in the state of stress within rock arise for example from changes in temperature pore pressure weight of overburden or tectonic loading hence geologic processes acting on a sedimentary unit should be analyzed for their several contributions to the state of stress and this information used to compute a stress history from this stress history predictions may be made as to when in the burial cycle to expect fracture joint formation what type of fractures extension or shear may occur and which geologic factors are most favorable to development of fractures a stress history is computed for strata of the naturally fractured altamont oil field in utah s uinta basin calculations suggest that fractures formed in extension that the well cemented rocks are those most likely to be fractured that fractures began to develop only after strata were buried to great depth and that the fracture system continued to develop as strata were uplifted and denuded of overburden geologic evidence on fracture genesis and development is in accord with the stress history prediction stress history can be useful in evaluating a sedimentary basin for naturally fractured reservoir exploration plays

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m

magnitude spectra and other source parameters for some major 1985 and 1986 earthquakes abstract broad band seismograms are used to determine the magnitude spectrum of an earthquake the spectrum represents the velocity amplitude density spectrum at the earthquake source scaled in magnitude units a method is presented to routinely utilize the magnitude spectrum for the independent determination of the seismic energy released the seismic moment the fault length and the stress drop the method is applied to six earthquakes in three different regions it is found that the stress drop is higher for the intraplate earthquake than for the interplate earthquakes also it is observed that the largest foreshock of an interplate earthquake has a clearly higher stress drop than the largest aftershock the results indicate that there are measurable regional differences in source parameters and that there are time variations in the parameters within each region

seismic estimates of stress release five seismic estimates of stress release are compared for eight multiply recorded aftershocks of the 1975 oroville california earthquake the dynamic stress drop the arms stress drop and the apparent stress provide stable estimates which are strongly correlated across the data set the uncertainties of these estimates the standard error of the mean divided by the mean are approximately 15 estimates of the brune stress drop are uncorrelated with estimates of the average static stress drop calculated from the seismic moments and the rupture geometries of the aftershocks determined from the signal durations of the recorded s waves the brune stress drops are most strongly correlated with the arms stress drops implying that the brune stress drop provides an estimate of the average dynamic stress drop as brune originally proposed

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

structural chronology of the alleghanian orogeny in southeastern west virginia the trend change between central and southern appalachian structures is sharply defined in southeastern west virginia there n30 35 e trends coincident with major central appalachian folds such as the browns mountain anticline end abruptly at n60 e trending southern appalachian structures along the st clair fault analysis of local and regional folds cleavage bedding perpendicular stylolite seams and bedding and fault slickenlines reveals that layer parallel shortening directed n10 30 w occurred in nonfolded greenbrier group mississippian carbonates well into the present appalachian plateau area this structural event is early and is associated with the evolution of southern appalachian folds and faults south of the st clair fault central appalachian folds and mesoscopic structures were superimposed on this early layer parallel shortening fabric this structural chronology indicates that southern appalachian folds and faults predated the development of central appalachian structures in the region

joint orientation in devonian rocks in the northern portion of the lower peninsula of michigan the orientations of 4 787 joints were measured at 43 separate locations in the area from charlevoix michigan to alpena michigan and north to the tip of the lower peninsula of michigan the sample localities are all in devonian carbonate rocks and shales of the michigan basin nearly all of the joints are vertical at least one major joint set is identifiable at each location and four major sets are present at more than half of the locations at 40 of the 43 sample localities there is a joint set with a strike of about 54 degrees n54 e at 35 locations there is a set striking about 133 degrees n47 w at 32 locations there is a set with a strike of about 92 degrees n88 w and a set with a strike of about 2 degrees no2 e is present at 31 sample localities mean orientation of any of the four joint sets does vary from location to location but is relatively consistent over the entire area for each of the sets fluctuations in mean orientation of any of the joint sets or the presence or absence of the joint sets is independent of formation lithology and distance between sample stations joint set orientation is independent of the regional strike around the michigan basin which varies from 54 degrees n54 e to 114 degrees n66 w within the study area the joint pattern does not appear to be related to structural trends previously postulated to exist in the precambrian basement of the area two of the joint sets may be related to major low amplitude folds in the paleozoic strata of the michigan basin in situ stress measurements show the orientation of maximum horizontal compressive stress to be compatible with these joint sets and the folds

orthogonal fracture systems at the limits of thrusting an example from southwestern wales abstract a well developed orthogonal vein system is located in the autochthonous foreland just beyond the limits of variscan thrusting in southwestern wales the two vein sets trend 200 and 290 perpendicular and parallel respectively to variscan structures the veins contain stretched quartz fibers indicating horizontal extensions of between 0 3 and 2 5 the 200 set has greater extension with a distinctive morphology including shorter more curvilinear fractures that have components of normal offset vein intersections are simple indicating episodic growth by alternating regional propagation of each set during propagation maximum compression was subvertical and the horizontal principal stresses switched direction with the alternation of set growth the system formed during waning variscan compression when the directions of horizontal principal stresses were still controlled by the tectonic compression the differential stress may have been greater during propagation of the 200 set this example indicates that orthogonal fracture systems in forelands beyond thrusting 1 are initiated by fracturing parallel to tectonic compression 2 form in a few stages that are controlled by changes in regional stress and 3 form during waning tectonic compression that controls fracture orientations

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry

fractures in the northern plains stream patterns and the midcontinent stress field fractures in late cretaceous to late pleistocene sediments in saskatchewan eastern montana and western north dakota form two vertical orthogonal sets trending northeast southwest and northwest southeast the pattern is consistent regardless of rock type or age except for concretionary sandstone both sets appear to be extensional in origin and are similar in character to joints in alberta modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures elevation variations on the sub mannville early cretaceous unconformity form a rectilinear pattern also parallel to the fracture sets suggesting that fracturing was initiated at least as early as late jurassic it may have begun earlier but there are insufficient data at present to extend the time of initiation we interpret the fractures as the result of vertical uplift together with plate motion the westward drift of north america the northeast southwest directed maximum principal horizontal

first r m hardy memorial lecture fracture lineament research and applications on the western canadian plains for parts of the western canadian plains high altitude airphotos and satellite images frequently show a simple pattern of preferred fracture lineament orientations fracture lineaments are composite linear topographic drainage vegetation moisture and tonal features a long search for their origin and repeating characteristics is described it is held that certain elements of fracture lineament networks are selectively inherited from preexisting regional fracture systems and structures in the underlying rocks and can therefore be correlated with subsurface geological hydrogeological and geophysical and near surface geochemical data a number of case studies illustrate how remotely sensed lineament data are applied in geological hydrogeological and geotechnical investigations for resource exploration development and management key words remote sensing fracture lineaments propagation hierarchy domain stress field salt tectonics data correlation application

interpretation of fracture and physiographic patterns in alberta canada abstract thousands of linear elements joint traces river trends and photolinears have been identified and statistically analysed in the province of alberta canada from the u s border to the fort mcmurray area a statistical evaluation was performed on the data by fitting dimroth watson distributions to groups of them it is suggested that the joints represent shear surfaces formed in a neotectonic stress field whose maximum compression is oriented normal to the front of the rocky mountains at least in the vicinity of that range further to the northeast the stress trajectories swing to e w and n s directions the river courses in alberta do not align themselves with the joints and are presumably controlled by the general slope of the land towards hudson s bay the photolineaments are features of uncertain origin and age