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

thrust faults in southern illinois basin result of contemporary stress many north trending thrust faults have been observed in coal mines of southern illinois and adjacent western kentucky displacement ranges from less than an inch to about 3 m 10 ft no known ancient tectonic stress field or nontectonic process has been found to have produced these faults they correspond to the contemporary tectonic stress field in the region maximum horizontal compression along an axis trending slightly north of east this compression is thought to account for the preferred orientation of roof failure in underground coal mines jointing in roof shales and minor earthquakes in southern illinois

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

surface electric variations induced by deep hydraulic stimulation an example from the soultz hdr site 1 we carried out monitoring of surface electric potential variations at the soultz hot dry rock site france during a stimulation experiment where 23 000 m3 of water were injected in granite at 5 km depth we have observed a long period 9 10 days potential variation with a maximum amplitude of 5 mv thanks to the conductive well casing the start of this anomalous potential coincides with that of the water injection and its magnitude increases as more water is injected before returning toward its original value after shut in we interpret this anomalous potential as an electrokinetic effect which is caused by the injection of water circulating in deep fractures we modeled the pressure distribution during the stimulation and obtained the surface sp using electrokinetic coupling relationships we found that an in situ coupling coefficient of 1 mv mpa at the low end of laboratory values gives a good fit to the data

stratigraphic model for glacial eustatic pennsylvanian cyclothems in highstand nearshore detrital regimes lower distal positions on gently sloping shelves ramps affected by pennsylvanian glacial eustatic sea level fluctuation display classic marine transgressive regressive cyclothems which are separated by exposure surfaces or by shallow marine to thin terrestrial beds deposited at lowstand in contrast higher shelf proximal positions display marginal marine units and coastal plain coal beds deposited at marine highstand and separated by thicker terrestrial units both marine and terrestrial strata deposited in high shelf positions underwent significant fluvial incision and valley formation during long stands of lower sea level resulting in discontinuous erosional remnants and subsequent localized terrestrial deposition on irregular leached and eroded surfaces examples from the appalachian illinois and sydney basins display features such as erosional disconformities with rotated slumps buried hilltops preserving erosional remnants of marine units colluvially reduced landscape relief and buried

fault roughness at seismogenic depths from lidar and photogrammetric analysis fault surface roughness is a principal factor influencing earthquake mechanics and particularly rupture initiation propagation and arrest however little data currently exist on fault surfaces at seismogenic depths here we investigate the roughness of slip surfaces from the seismogenic strike slip gole larghe fault zone exhumed from ca 10 km depth the fault zone exploited pre existing joints and is hosted in granitoid rocks of the adamello batholith italian alps individual seismogenic slip surfaces generally show a first phase of cataclasite production and a second phase with beautifully preserved pseudotachylytes of variable thickness we determined the geometry of fault traces over almost five orders of magnitude using terrestrial laser scanning lidar ca 500 to 1 10 m is not anisotropic and less evolved than at smaller scales these observations are consistent with an evolution of roughness due to fault surface processes that takes place only at scales smaller or comparable to the observed net slip differences in roughness evolution between shallow and deeper faults the latter showing evidences of seismic activity are interpreted as the result of different weakening versus induration processes which also result in localization versus delocalization of deformation in the fault zone from a methodological point of view the technique used here is advantageous over direct measurements of exposed fault surfaces in that it preserves in cross section all of the structures which contribute to fault roughness and removes any subjectivity introduced by the need to distinguish roughness of original slip surfaces from roughness induced by secondary weathering processes moreover offsets can be measured by means of suitable markers and fault rocks are preserved hence their thickness composition and structural features can be characterised providing an integrated dataset which sheds new light on mechanisms of roughness evolution with slip and concomitant fault rock production

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

from spatial variation of fracture patterns to fold kinematics a geomechanical approach 1 a vertical compression parallel joint set apparently formed at sheep mountain anticline sma during the early laramide orogeny prior to significant folding field data indicate that these joints occur in fewer locations in the forelimb than in the hinge and backlimb using three dimensional elastic dislocation models we show that early slip along an underlying thrust fault can locally perturb the surrounding stress field inhibiting joint formation above the fault thus we are able to constrain the forelimb kinematics finding that the forelimb was originally located in the hangingwall above the thrust fault furthermore the mode of folding at sma is constrained the anticline developed with a fixed hinge and rotating limbs while the underlying basement rocks deformed internally

origin of the pennsylvanian coal bearing cyclothems of north america past controversy about the tectonic or eustatic origin of pennsylvanian cyclothems is resolved by regional basin subsidence analysis global paleoclimate paleogeography and plate tectonic evolution differences between marine carbonate kansas type cyclothems of the northern midcontinent and nonmarine clastic appalachian type cyclothems of the eastern united states are controlled by laterally changing flexural deformation during plate accretion into a supercontinent coupled with superposed glacial eustasy kansas type cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of north american margins these cycles are eustatic characterized by a periodicity comparable to milankovitch orbital parameters appalachian type cyclothems accumulated in response to episodic thrust loading during plate collisions that developed a series of flexurally deformed wide and shallow resurgent foreland basins this resurgent foreland basin evolution during paleozoic time increased crustal rigidity in the appalachians thus yoking the appalachian and illinois basins during pennsylvanian time with each thrust load foreland basin deepening favored transgressive cyclothem facies which changed to a regressive facies because sediment yield increased as denudation rates increased off uplifted orogens illinois type cyclothems are intermediate between the two end member processes of flexural tectonics and glacial eustasy characterizing appalachian type and kansas type cyclothems respectively thus the pennsylvanian coal bearing cyclothems of north america owe their origin to the remarkable coincidence of supercontinent development concomitant glaciation and eustatic sea level change and associated episodic thrust loading and foreland basin subsidence of small magnitude on progressively more rigid crust

postseismic stress and pore pressure readjustment and aftershock distributions abstract the time and spatial readjustment of stress and pore pressure due to a strike slip rupture are investigated by means of a model which treats the earth s crust as a linear poro elastic material infiltrated by fluids the analysis is based on a fundamental solution obtained by rice and cleary who treated the solid and fluid constituents as separately compressible the main shock is modeled as a sudden uniform stress drop and the resulting slip dislocation is maintained in time this suddenly introduced dislocation distribution sets up stress and pore pressure fields diffusion of fluid takes place from regions undergoing compression to regions undergoing dilation hence the stress and pore pressure fields evolve over time with time scales which depend on the flow parameters of the rock medium it is assumed that aftershocks occur when the coulomb stress defined as c n p where n and are the increase in normal stress and shear stress across a potential slip surface is a friction coefficient and p is the pore pressure increase exceeds the shear strength of the slip surface the coseismic elastic solution confirms the suggestion of spatial distribution of aftershocks by stein and lisowski the transient solution predicts a small rotation of the aftershock zone from the compression into the dilation region at the two ends of the main rupture whereas the aftershock zones for off fault aftershocks appear to expand and shift into the dilating regions a new plot is developed which provides a means to study the association between high coulomb stress increase with off fault aftershock locations the aftershock distributions of three earthquakes pasinler 1983 borrego mountain 1968 and haicheng 1975 are compared to the zones predicted by the model the earthquake aftershocks are skewed towards the dilatant regions and in some cases form distinct off fault clusters in the areas of high coulomb stress the ability of the model to provide a primary aftershock mechanism and the implications of this mechanism for material properties are discussed in the contexts of these sample earthquakes the model predicts the generally observed spatial expansion of the aftershock zones and suggests an explanation for the presence or absence of off fault aftershock clusters however the inaccuracy in location of aftershocks and the small magnitude change in predicted coulomb stress makes it difficult to confirm or disprove the theory that aftershock distributions are controlled by fluid flow

fluid rock interactions in the rhine graben a thermodynamic model of the hydrothermal alteration observed in deep drilling abstract deep drilling at soultz sous forets france on the western flanks of the rhine graben has penetrated hercynian granite underlying mesozoic sediments veins are present throughout the drilled granite and there are flows of warm water localized in fractures within the granite detailed mineralogical study of core material from the research drillhole eps 1 has been carried out in order to assess the alteration history of the soultz granite part of the crystalline basement of the rhine graben the results of the study have been used in conjunction with analyses of present day fluids from deep drilling in the rhine graben reported in the literature to model thermodynamically the alteration process and in particular to evaluate if it is likely to be continuing today reaction path calculations show that if deep basinal brines such as are known from sediments of the central rhine graben react with hercynian granite they will form different alteration assemblages depending on both the path that the fluid follows e g descending through sediments or through granite and the extent of preexisting alteration of the granite the calculations suggest that fluid now sampled from granite in eps 1 achieved its peak temperature c 200 c while within permo triassic sandstone the modeling also indicates that present day fluids from the rhine graben system are capable of producing the vein quartz and possibly also the baryte veins seen in the eps 1 core much of the alteration present in the granite in the vicinity of veins and fractures may have been produced by a flow regime similar to that prevailing today

organic matter in the soultz hdr granitic thermal exchanger france natural tracer of fluid circulations between the basement and its sedimentary cover abstract organic matter has been observed in cores of the soultz sous forets granite alsace france at depths between 2158 and 2160 m in a highly fractured and altered zone the granite is overlain by a 1400 m thick sedimentary cover containing petroleum pechelbronn oil field the soultz area is devoted to hot dry rock geothermics thanks to a high geothermal gradient up to 100 c km during drilling operations an artesian source produced oil in a fractured zone of the sedimentary cover buntsandstein its gas chromatography and mass spectrometry gc ms analysis revealed the presence of normal alkanes n alkanes i e linear hydrocarbons centered on c 17 branched alkanes with a major c 19 peak and few unsaturated hydrocarbons the aromatic fraction is present in small amounts in the soultz granite where it is altered organic matter is exclusively associated with tosudite interstratified clay mineral which crystallized in plagioclase sites during a hydrothermal alteration episode organic matter has been later displaced and concentrated along veinlets in which illite and carbonates have crystallized during another hydrothermal alteration stage the soluble organic matter analyzed by gc ms is composed of aliphatic acids n alkanes with a bimodal c 18 and c 24 c 25 centered distribution alkylbenzenes and aromatic acids organic compounds in the granite would either originate from a single source immature sediments or from two sources immature sediments and migration of the pechelbronn oil no real evidence was found to prove which hypothesis is the best one the presence of organic matter in the granite shows the importance of fluid flows between the sedimentary cover and the granitic basement through major fractures in addition the impregnation of plagioclase pseudomorphs with organic matter is made possible due to their high interconnection degree and to the intergranular microfracturation of the granite the succession of several hydrothermal events with different physico chemical characteris tics may also be inferred from the occurrence of organic matter found in association with neoformed clay minerals in the granite

elastic stress control on the pattern of tensile fracturing around a small fault network at nash point uk abstract complex trajectories of fault related opening mode fractures at nash point in south wales uk are consistent with elastic stress fields computed for the observed fault network subject to north south compression the linear elasticity theory is used to calculate local stress increments produced by slip on the fault network faults are assumed to be free of shear stress and to slip in response to some remote stress load brittle failure of rock within this stress field is determined according to a combined griffith coulomb criterion discrete fracture networks are simulated according to simple growth rules where fractures initiate according to the state of brittle failure and propagate along a surface normal to the direction of most tensile local stress results demonstrate the dominant opening mode fracture were caused by a uniform body force e g unloading and are just locally perturbed by the pre existing fault network fault heights of 2 3 times the mean fault block width and regional contraction along an azimuth of 180 10 are required to reproduce the observed fracture pattern independent kinematic analysis of nearby faults yield estimates of the azimuth of regional contraction of 170 180 some features in the observed fracture pattern are not well reproduced but these are small scale and related to small scale irregularities on the fault planes

fault slip distribution and fault roughness summary we present analysis of the spatial correlations of seismological slip maps and fault topography roughness illuminating their identical self affine exponent though the complexity of the coseismic spatial slip distribution can be intuitively associated with geometrical or stress heterogeneities along the fault surface this has never been demonstrated based on new measurements of fault surface topography and on statistical analyses of kinematic inversions of slip maps we propose a model which quantitatively characterizes the link between slip distribution and fault surface roughness our approach can be divided into two complementary steps i using a numerical computation we estimate the influence of fault roughness on the frictional strength pre stress we model a fault as a rough interface where elastic asperities are squeezed the hurst exponent h characterizing the self affinity of the frictional strength field approaches h h 1 where h is the roughness exponent of the fault surface in the direction of slip ii using a quasi static model of fault propagation which includes the effect of long range elastic interactions and spatial correlations in the frictional strength the spatial slip correlation is observed to scale as hs h 1 where hs represents the hurst exponent of the slip distribution under the assumption that the origin of the spatial fluctuations in frictional strength along faults is the elastic squeeze of fault asperities we show that self affine geometrical properties of fault surface roughness control slip correlations and that hs h given that h 0 6 for a wide range of faults various accumulated displacement host rock and slip movement we predict that hs 0 6 even if our quasi static fault model is more relevant for creeping faults the spatial slip correlations observed are consistent with those of seismological slip maps a consequence is that the self affinity property of slip roughness may be explained by fault geometry without considering dynamical effects produced during an earthquake

mechanical fault interaction within the los angeles basin a two dimensional analysis using mechanical efficiency 1 mechanical models examine deformation within eight different structural cross sections proposed by davis et al 1989 and shaw and suppe 1996 along a northeast southwest transect across the los angeles basin california horizontal contraction of the models constrained by geodetic measurements yields varying dip slip rates along frictionally sliding faults within the different cross sections mechanical efficiency analysis using effective stiffness and strain energy density assesses the overall fault system deformation as well as the partitioning of work between fault slip and host rock strain the cross section interpreted by shaw and suppe 1996 has the best fit to paleoseismically determined slip rates and the greatest mechanical efficiency greatest proportion of work toward fault slip however this model produces excessive reverse slip along the newport inglewood fault a modified fault configuration with a wedge or blind puente hills thrust fault rather than a ramp detachment configuration better matches the paleoseismic data with slightly lower mechanical efficiency slip rates in the mechanical models based on interpretations of shaw and suppe 1996 have much closer match to the geologically determined rates than those estimated from kinematic models this difference is due to 1 differing time spans of slip rate estimates and 2 deformable rather than rigid host rock in the mechanical models the mechanical efficiency analysis provides quantitative indicators of overall fault system deformation including the cumulative effect of interaction between individual faults assessment of effective stiffness and strain energy density furthers our understanding of two dimensional fault interactions in the los angeles basin and offers great potential for future applications

effects of late paleozoic foreland deformation on underground coal mine ground instability illinois and appalachian basins abstract slickensides are commonly associated with potentially hazardous ground conditions in underground coal mines investigations by the mine safety and health administration s roof control division indicate that slickensided drag folds in the immediate roof of pennsylvanian age coal seams represent instances of ground instability of various scales from skin control hazards to roof falls that block travelways and belt entries the occurrence of features in the roof of the illinois basin s springfield coal seam that are identical to structures interpreted as drag folds in pennsylvanian age coal measure rocks of the appalachian basin suggests that tectonic stress associated with the late pennsylvanian permian alleghanian orogeny was transmitted into the mid continent this paper relates slickenside occurrences in the pennsylvanian age springfield coal seam to local structural geologic features that are associated with the late pennsylvanian permian alleghanian orogeny because the slickensides discussed are interpreted to have formed in response to regional tectonic stress small scale controls on coal mine ground instability can be related to large scale regional tectonic processes field investigations indicate that mine wide geologic mapping of structural geologic features can be used to project zones of subtle yet problematic structural weakness in advance of face positions by incorporating this style of structural geologic hazard mapping in mine planning and operation miners can be prepared to install appropriate supplemental support or reduce the effects of structural weaknesses with local modifications to mine design

thrust fault nucleation due to heterogeneous bedding plane slip evidence from an ohio coal mine abstract shales often form the roof and floor rocks of coal mines in the appalachian basin from a geologic perspective these mines offer outstanding 3d exposures of fresh rocks otherwise only accessible via boreholes or heavily weathered surface outcrops and present an excellent opportunity to directly observe pristine in situ natural fractures in shale in carroll county ohio small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal shale contacts are steepest causing ground instability we hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state resulting in localized thrust fault development using borehole and in mine survey data we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations our modeling results suggest that inherited non planarity of contact surfaces influenced the nucleation of secondary faults simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures for mining purposes recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards

earthquakes as a coupled shear stress high pore pressure dynamical system the migration coalescence and localization of slip seismicity and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic increased pore pressure in discrete cells creates zones of low effective stress which induces slip that may propagate to surrounding cells depending on the local state of stress at slip stress is transferred using the solution for a rectangular dislocation in an elastic half space and pore pressures are redistributed by conserving fluid mass using simple assumptions about fault rheology and permeability it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events locked zones and large variations in fault strength the model evolves from a uniform shear stress state on a strong fault to a heterogeneous shear stress state on a weak fault

porosity and thermal conductivity of the soultz sous forets granite the success of the soultz sous forets hot dry rock project depends on the ability to maintain fluid circulation in a fractured granite fractures represent the main fluid pathways to understand the behavior of this granite in respect to thermal fluid rock interaction the important aspects are 1 the porous network around these fractures and 2 the thermal conductivity of the rock this granite is altered and composed of different weathered facies variations of porosity and thermal conductivity take place in regard to the alteration and fracturing of the granite two types of porosity measurements were performed mercury injection and water porosity on two samples sizes the two methods give similar porosity values between 0 3 and 10 thermal conductivity measurements were performed in two perpendicular directions to look at anisotropy with two methods at different scale and value ranges from 2 3 to 3 9 w m 1 k 1 optical scanning provides us with a good knowledge of local increase of thermal conductivity due to sealed fracture or quartz cemented matrix

constraints on mineralization fluid rock interaction and mass transfer during faulting at 2 3 km depth from the safod drill hole 1 mineralogical and geochemical changes in mudrock cuttings from two segments of the san andreas fault observatory at depth safod drill hole 3066 3169 and 3292 3368 m measured depth are analyzed in this study bulk rock samples and hand picked fault related grains characterized by polished surfaces and slickensides were investigated by x ray diffraction electron microscopy and geochemical analysis the elemental changes in fault related grains along the sampled san andreas fault are attributed to dissolution of detrital grains particularly feldspar and quartz and local precipitation of illite smectite and or chlorite smectite mixed layers in fractures and veins assuming zro2 and tio2 to be immobile elements systematic differences in element concentrations show that most of the elements are depleted in the fault related grains compared to the wall rock lithology calculated mass loss between the bulk rock and picked fault rock ranges from 17 to 58 with a greater mass transport in the shallow trace of the sampled fault that marks the upper limit the fault core the relatively large amount of element transport at temperatures of 110 114 c recorded throughout the core requires extensive fluid circulation during faulting whereas dissolution precipitation may be partly induced by the disequilibrium between fluids and rocks during diagenetic processes stress induced dissolution at grain contacts is proposed as the main mechanism for extensive mineral transformation in the fault rocks and localization of neomineralization along grain interface slip surfaces

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

hydromechanical properties and alteration of natural fracture surfaces in the soultz granite bas rhin france natural fractures are characterized by rough surfaces and complex fluid flows a large distribution of apertures residual voids within their walls and the presence of contact points in situ normal loads produce heterogeneous flows channeling the resulting permeabilities porosities or fluid rock exchange surfaces cannot be realistically modeled by parallel and smooth plate models four natural fractures are sampled at different depths and degrees of alteration in the soultz sandstone and granite eps1 drillhole soultz sous forets bas rhin france the fracture surfaces are measured with mechanical profilometry and maps of asperity heights xyz resulting local apertures xye are then calculated a statistical study of the surface profiles xz show that the fractures are more or less rough and tortuous according to the types of alteration altered samples are characterized by smoother surfaces of fractures such differences imply that i the average fracture aperture is not representative for the whole fracture and that ii the different local apertures should be integrated in hydraulic and mechanical models a hydraulic model finite difference calculations of fluid flow taking into account the elastic closure hertz contact theory of fractures with depth is used maps of contact points and relative local loads within the fracture planes are compared to flow maps they show different channeling of fluid flows strongly altered fractures are characterized by homogeneous fluxes despite the presence of numerous contact zones during the closure of fracture by contrast fresh fractures develop increasing fluid flow channels with depth fracture closure increasing normal stress does not systematically increase the channeling of fluid flow there is evidence for a general smoothing out of the irregularities of the fracture walls due to precipitation of secondary minerals indicating that the cubic law can be commonly valid also at great crustal depth but this validity depends on the degree of fracture alteration mineralogical and geochemical observations thus should be taken into account to perform more accurate permeability calculations and models of fluid circulation in fracture networks d 2002 elsevier science b v all rights reserved

microfracture pattern compared to core scale fractures in the borehole of soultz sous forets granite rhine graben france microfractures appearing in thin section as fluid inclusion trails in quartz crystals were studied in four core samples of soultz sous forets granite their orientations in four series of three mutually perpendicular thin sections were estimated using a previously described apparent dip method and a new method involving measurements of strike and apparent dips three samples display three microfracture sets and one sample displays two sets in all samples one set is nearly vertical and strikes n s in two samples one and two sets are nearly vertical and strike e w in two samples two sets strike nw se one is vertical the other dips gently to the ne or sw comparing microfracture and mesofractures sets in the same cores shows that 1 the n s microfracture set is always dominant at both scales and 2 all other microfracture sets have no mesoscopic counterpart the n s microfracture sets could have been created during e w extension of earliest cenozoic age rhine graben rifting differences between the two scales are explained by a 1 2 switching which occurred at the crystal scale and generated mutually perpendicular cracks

dating late quaternary planktonic foraminifer neogloboquadrina pachyderma from the arctic ocean using amino acid racemization the long term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the arctic ocean the racemization rates for aspartic acid asp and glutamic acid glu in the common taxon neogloboquadrina pachyderma were calibrated for the last 150 ka using 14c ages and the emerging quaternary chronostratigraphy of arctic ocean sediments an analysis of errors indicates realistic age uncertainties of about 12 for asp and 17 for glu fifty individual tests are sufficient to analyze multiple subsamples identify outliers and derive robust sample mean values the new age equation can be applied to verify and refine age models for sediment cores elsewhere in the arctic ocean a critical region for understanding the dynamics of global climate change

modeling of streaming potential responses caused by oil well pumping the occurrence of streaming potentials is directly related to movement of fluids in the subsurface to investigate whether streaming potential measurements in boreholes and at the surface can be used to monitor subsurface flow and detect subsurface flow patterns in oil reservoirs we model streaming potential responses caused by oil well pumping in monitoring wells and at the earth s surface since the model parameters permeabilities cross coupling properties and electric conductivities depend on a few basic rock physics parameters such as brine conductivity amount of water saturation and porosity the model parameters are evaluated self consistently using rock physics models using a threedimensional 3 d finite difference algorithm the governing differential equations that are drawn from nonequilibrium thermodynamics are solved numerically in three self consistent steps solution of the hydraulic problem computation of the streaming current sources based on the principle of conservation of char

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

hydrothermal alteration in anthracite from eastern pennsylvania implications for mechanisms of anthracite formation orthogonal joint sets cleat in anthracite rank coal beds from eastern pennsylvania contain two mineralogically and chemically different authigenic clay mineral assemblages in localities from all four anthracite fields the systematic cleat contains significant quantities 20 to 95 wt of authigenic rectorite sudoite or tosudite which are clay minerals primarily associated with hydrothermal veins and ore deposits the strike of systematic cleat in this region roughly parallels the inferred direction of lateral compressive stress during the alleghany orogeny the opposing nonsystematic cleat contains mostly authigenic nh 4 illite a clay that also occurs in the coal matrix all of these authigenic clay minerals formed during anthracitization t 200 c by replacement of kaolinite and quartz both of which formed during an earlier stage of coalification and are present in the joints and matrix of nearly all coal samples these distinct mineralogical structural relations are observed throughout the anthracite region and suggest that 1 mineralogical variations in the coal joints are related primarily to permeability variations that were controlled by the orientation of alleghanian stress fields 2 hydrothermal fluids passed through the systematic cleat during anthracitization and 3 hydrothermal alteration influenced diagenesis in this region hydrothermal alteration may be related to basin wide fluid migrations that were driven by alleghanian age uplift basinal fluid flow concentrated along permeable joints and detachment zones could have efficiently transported heat from depth and thereby increased the rate of coalification and decreased the postulated minimum depths at which anthracitization occurred perhaps 5km vs 6 10 km

structural geometry of raplee ridge monocline and thrust fault imaged using inverse boundary element modeling and alsm data abstract we model the raplee ridge monocline in southwest utah where airborne laser swath mapping alsm topographic data define the geometry of exposed marker layers within this fold the spatial extent of five surfaces were mapped using the alsm data elevations were extracted from the topography and points on these surfaces were used to infer the underlying fault geometry and remote strain conditions first we compare elevations extracted from the alsm data to the publicly available national elevation dataset 10 m dem digital elevation model ned 10 and 30 m dem ned 30 while the spatial resolution of the ned datasets was too coarse to locate the surfaces accurately the elevations extracted at points spaced 50 m apart from each mapped surface yield similar values to the alsm data next we used a boundary element model bem to infer the geometry of the underlying fault and the remote strain tensor that is most consistent with the deformation recorded by strata exposed within the fold using a bayesian sampling method we assess the uncertainties within and covariation between the fault geometric parameters and remote strain tensor inferred using the model we apply these methods to the raplee ridge monocline and find that the resolution and precision of the alsm data are unnecessary for inferring the fault geometry and remote strain tensor using our approach however the alsm data were necessary for the mapping of the spatial distribution of surface outcrops our models considered two scenarios one in which fault geometry and remote strains were inferred using a single deformed stratum and another in which all mapped strata were used in the inversion modeled elevations match those observed to within a root mean squared error of 16 18 m and show little bias with position along the fold both single and multilayer inversions image a fault that is broadly constrained to be 4 5 14 km in down dip height 13 30 km in along strike width with a tip line 2 0 9 5 km below the surface at the time of deformation poisson s ratio was not well resolved by the inversion the idealized elastic model is oversimplified when considering the complicated layered nature of this fold however it provides a good fit to the observations thus comparable surface displacements may be produced with a variety of rheological models so independent constraints on factors such as the fault geometry may be required to ascertain the appropriate rheology of the fold

rough faults distributed weakening and off fault deformation 1 we report systematic spatial variations in fault rocks along nonplanar strike slip faults cross cutting the lake edison granodiorite sierra nevada california sierran wavy fault and lobbia outcrops of the adamello batholith in the italian alps lobbia wavy fault in the case of the sierran fault pseudotachylyte formed at contractional fault bends where it is found as thin 1 2 mm fault parallel veins epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends we argue that the presence of fluids as illustrated by this example does not necessarily preclude the development of frictional melt in the case of the lobbia fault pseudotachylyte thickness varies along the length of the fault but the pseudotachylyte veins thicken and pool in extensional bends we conduct a quantitative analysis of fault roughness microcrack distribution stress and friction along the lobbia fault numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness resulting in an overall weaker fault than suggested by the corresponding static friction coefficient the models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip rather than being confined to the region close to the dynamically propagating crack tip

is the san andreas big bend responsible for the landers earthquake and the eastern california shear zone the occurrence of a series of earthquakes including the 1992 landers event the geodetic strain measurements and geologic studies in california s mojave desert prior to the earthquake have precipitated the idea for the existence of a relatively young right lateral shear zone in eastern california the so called eastern california shear zone using a boundary element method together with a fault propagation criterion based on the maximum distortional strain energy density we explored the possibility that the big bend along the san andreas fault may have perturbed and amplified the stress field around the bend thereby inducing a zone of shearing in a north northwest orientation at the southern end of the bend the simulated fault propagation path agrees well with the data and sheds light on the origin and nature of the seismicity north and east of the big bend of the san andreas

water rock interaction processes in the triassic sandstone and the granitic basement of the rhine graben geochemical investigation of a geothermal reservoir saline fluids have been collected in the rhine graben over the last two decades both from the triassic sandstone aquifer and the granitic basement down to a depth of 3500m their salinities and location are compared in order to distinguish the respective influences of temperature and host rock mineralogy in the water rock interaction processes the comparison shows that sulphates in the sedimentary formations were dissolved by the fluids which also led to br enrichment mica dissolution has strongly increased the rb and cs contents which then provide an indication of the degree of water rock interaction the sr isotopic ratios are used to compare the fluids with the granite minerals two relationships are revealed for the fluids in the sandstone and the granite one related to widespread mica dissolution which could have affected both the buntsandstein and the granite and the other to subsequent plagioclase dissolution which is observed only in the granite computations showed that 12 5g of mica and 1 658 of plagioclase per liter of fluid have been dissolved the nature of these two relationships suggests two different evolutions for the fluids and the individualization of the two reservoirs during the graben s history the cation concentrations are mainly controlled by temperature and are independent of the type of host rock equilibrium with the rock mainly caused ca and k concentration variations which has induced clear ca k and ca 18o k 18o correlations geothermometric computations indicate that with increasing depth the cations the silica and the 18o so4 geothermometers evolve towards a value close to 230 c this demonstrates the existence of a hot reservoir in the granite of the graben at a depth estimated at 4 5 5 km

the work budget of rough faults abstract faults in nature have measurable roughness at many scales and are not planar as generally idealized we utilize the boundary element method to model the geomechanical response of synthetic rough faults in an isotropic linear elastic continuum to external tectonic loading in terms of the work budget faults are generated with known fractal roughness parameters including the root mean square slope a measure of roughness amplitude and the hurst exponent h a measure of geometric self similarity energy within the fault models is partitioned into external work w ext internal elastic strain energy w int gravitational work w grav frictional work w fric and seismic energy w seis results confirm that w ext or work done on the external model boundaries is smallest for a perfectly planar fault and steadily increases with increasing this pattern is also observed in w int the energy expended in deforming the host rock the opposite is true for gravitational work or work done against gravity in uplifting host rock as well as with frictional work or energy dissipated with frictional slip on the fault and w seis or seismic energy released during slip events effects of variation in h are not as large as for but w grav w fric and w seis increase with increasing h with w int and w ext decreasing across the same range remarkably however for a narrow range of roughness amplitudes which are commonly observed along natural faults the total work of the system remains approximately constant while slightly larger than the total work of a planar fault faults evolve toward the most mechanically efficient configuration therefore we argue that this range of roughness amplitudes may represent an energy barrier preventing faults from removing asperities and evolving to smooth planar discontinuities a similar conclusion is drawn from simulations at relatively shallow depths with results showing that shallower faults have larger energy barriers and can be mechanically efficient at higher roughness amplitudes

zeolitization of basalts in subaqueous freshwater settings field observations and experimental study abstract zeolitization of volcanic flows was studied using both field observations and experimental investigations field observations show that basalt flows located in two areas massif central france and cascade range usa exhibit similar features of zeolitization associated with the interaction between flow rocks and fresh water as well as the thermal history of the volcanic sheet results are reported of an experimental study which determined the conditions of hydrothermal crystallization under constant pressure 200 bars in a thermal gradient at relatively low temperatures 140 200 c and 210 280 c two sets of experiments with two kinds of reactants mineral and bulk rock were conducted in sealed gold tubes containing deionized water ph 6 3 with a fluid rock mass ratio of 10 the starting materials correspond to different types of alteration conditions 1 a phillipsite plus kaolinite assemblage which represents the chemical limited system sio 2 al 2 o 3 cao k 2 o h 2 o 2 an alkaline basalt and 3 an obsidian two phenomena were found to depend upon the thermal gradient a parallel distribution of minerals implying local equilibria and a nonparallel phenomenon implying an irreversible process dissolutioncrystallization controlling the succession of crystallization field and experimental data demonstrated that zeolitization resulted from the combined effects of an initial thermal gradient between the base and the interior of the flow and its cooling history