dynamic elastic properties of coal laboratory ultrasonic velocity measurements of different types of coal demonstrate that their dynamic elastic properties depend on coal rank and applied effective pressure in spite of the growing interest in coal beds as targets for methane production the high abundance in sedimentary sequences and the strong influence that they have on seismic response little data are available on the acoustic properties of coal velocitiesweremeasuredincoreplugsparallelandperpendicular to lamination surfaces as a function of confining pressure up to 40 mpa in loading and unloading cycles pand s wave velocities and dry bulk and dry shear moduli increaseascoalrankincreases thus bituminouscoalandcannel show lower velocities and moduli than higher ranked coals such as semianthracite and anthracite the vp vs relationshipfordrysamplesislinearandcoversarelativelywide rangeofeffectivepressuresandcoalranks however thereis a pressure dependence on the elastic properties of coal for confiningpressuresbelow5 mpa thispressuresensitivityis relatedtothepresenceofmicrocracks finally thedatashow that coal has an intrinsic anisotropy at confining pressures above 5 mpa the closing pressure for most of the microcracks this intrinsic anisotropy at high pressures might be due to fine lamination and preferred orientation of the macerals

the influence of tectonic deformation on some geochemical properties of coals a possible indicator of outburst potential abstract nearly all outburst prone coal is known to have been tectonically deformed in fault and fold zones which underwent one or more episodes of strong structural deformation the physical properties of deformed coal such as strength coefficient and rate of gas desorption have been broadly studied and used to predict outbursts in the past however it can be difficult to reliably determine these physical coefficients from core sampling operations because the coal can be inadvertently pulverized during drilling the development of a new index which predicts the outburst potential of coal seams and is not influenced by sampling procedures could be beneficial to mining safety technology tectonic deformation may not only affect the original physical structure of a coal but also may bring about changes in chemical properties any chemical property with the potential to identify outburst prone coal must also be stable and independent of the physical changes imposed by drilling most of the chemical characteristics of coal display no obvious difference between normal undeformed coal which is not subject to outbursts and deformed coal however recent studies have shown that the chloroform extract yield is a very good geochemical index for differentiating these coals nineteen coal samples from five mines experiencing outbursts in the pingdingshan coalfield henan china were analyzed their mean maximum vitrinite reflectance in oil ranges from 0 97 to 1 28 all of the samples were prepared to 180 m 80 mesh us and subsamples were extensively extracted with chloroform in a soxhlet apparatus at 75 c the mean extract yield of the 10 deformed coals is 1 45 whereas that of the nine normal coals is 0 44 we conclude that deformed coal has a higher chloroform extract yield than equivalent coal which has not been tectonically disturbed chloroform extraction therefore can be used to recognize deformed coal and the potential to undergo further deformation chloroform extract yield is an accepted measure of the hydrocarbon generating potential of coals and other rocks the results presented here therefore suggest that tectonic deformation may modify the hydrocarbon generating potential of coals the adsorption of soluble organic matter expelled during and following tectonic deformation onto enhanced surface areas may have contributed to the higher extract yields of the deformed coal

the geometry of echelon fractures in rock implications from laboratory and numerical experiments abstract the traces of echelon joints veins and dikes in rock range from curving to straight theoretical analyses using boundary element numerical methods have concluded that straight open fractures imply a significant remote differential stress whereas curving traces imply a more nearly isotropic stress we present a series of laboratory experiments which investigate the two dimensional propagation paths of echelon fractures in pmma plates as a function of the applied biaxial loading and the initial geometry of a simple fracture array the experimental results support the theoretical conclusions and verify the accuracy of the numerical method at the grain scale rock does not rigorously conform to the assumptions of isotropy homogeneity and linear elasticity demanded by the numerical method nevertheless results from crack path stability theory suggest that small scale deviations of a fracture from the ideal path generally do not affect its large scale behavior fracture paths which become kinked or curved by local heterogeneities are found to self correct to a path governed by competition between the fracture tip and remote stress fields provided the remote differential stress is non zero this enhances our confidence that the numerical method can be used to produce and explain realistic fracture geometries in rock an unexpected experimental result is the non perpendicular intersection of fractures grown in the laboratory free surface boundary conditions require that the walls of an open fracture be free of shear stress the principal stresses are therefore aligned with the crack wall and we might consequently expect an approaching opening mode fracture either to intersect the free surface at a right angle or to turn away and follow an asymptotic nonintersecting path experimental and numerical modeling however shows how the near tip stresses generated by an approaching fracture dominate the local stress field and allow it to propagate along an oblique path very close to intersection with the adjacent free surface

late cadomian crustal tilting and cambrian transtension in the tepla barrandian unit bohemian massif central european variscides the cadomian basement of the tepla barrandian unit is characterized by a classic barrovian type metamorphism the degree of which increases considerably towards the west reaching amphibolite facies conditions in the domaz lice crystalline complex dcc the number and volume of plutons also increases towards the west the emplacement ages of the te s ovice granite and the mrac nice trondhjemite have been determined at 521 7 2 ma and 523 4 5 ma respectively applying conventional u pb analyses of zircons pervasive high temperature prolate fabrics and north northwest dipping dextral oblique slip shear zones within the mrac nice trondhjemite suggest a synkinematic melt emplacement within a lower cambrian transtensional setting transtension is probably related to early stage rifting that introduced the separation of the tepla barrandian unit as part of armorica from gondwana structural and petrological data of the country rocks show that the barrovian type metamorphism and two deformation stages d1 with unknown kinematics and d2 top to the north shearing are older than the melt emplacement and thus can be attributed to the cadomian orogeny the intrusion depth of both plutons is nearly the same ca 7 km although the degree of barrovian type metamorphism differs significantly within the country rocks this suggests late cadomian eastward tilting of the metamorphic isograd planes the weak post plutonic lower greenschist to subgreenschist facies folding and thrusting result from variscan northwest southeast compression

sill morphology and comparison of brittle and non brittle emplacement mechanisms magmatic sheet intrusions contribute significantly to the upper crustal magma transport network the emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation previous observations have highlighted the preponderance of brittle structures associated with shallow level sheet intrusions however recent studies have suggested that non brittle host rock behaviour also occurs particularly related to the formation of magma fingers during shallow level sill intrusion here we examine both brittle and non brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems non brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics purely brittle and non brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling incorporation of variable host material behaviours in numerical and analogue modelling tuned using direct field observations may consequently further our understanding of the controls on shallow level intrusion

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

variational phase field modeling of hydraulic fracture interaction with natural fractures and application to enhanced geothermal systems in every tight formation reservoir natural fractures play an important role for mass and energy transport and stress distribution enhanced geothermal systems egs make no exception and stimulation aims at increasing the reservoir permeability to enhance fluid circulation and heat transport egs development relies upon the complex task of predicting accurate hydraulic fracture propagation pathway by taking into account reservoir heterogeneities and natural or preexisting fractures in this contribution we employ the variational phase field method which handles hydraulic fracture initiation propagation and interaction with natural fractures and is tested under varying conditions of rock mechanical properties and natural fractures distributions we run bidimensional finite element simulations employing the open source software opengeosys and apply the model to simulate realistic stimulation scenarios each one built from field data and considering complex natural fracture geometries in the order of a thousand of fractures key mechanical properties are derived from laboratory measurements on samples obtained in the field simulations results confirm the fundamental role played by natural fractures in stimulation s predictions which is essential for developing successful egs projects

ductile normal faulting along the west bohemian shear zone moldanubian tepla barrandian boundary evidence for late variscan extensional collapse in the variscan internides structural and kinematic investigations of the west bohemian shear zone wbs clearly indicate late variscan orogen parallel wsw ene extension within the variscan internides along the wbs the western part of the tepla barrandian tb was downthrown to the east against the adjacent moldanubian according to seismic data the steeply east dipping wbs flattens with depth forming a prominent detachment zone the western part of the tb was tilted along this zone producing the patterns of metamorphic isograds the age of which is probably cadomian cross cutting relationships of wbs mylonites and carboniferous granites as well as the overall cooling ages of hornblende and mica suggest that ductile normal faulting along the wbs was active from about 330 to 310 ma

forms of hydraulic fractures in shallow fine grained formations hydraulic fractures have been created in fine grained formations at depths of 2 10 m to improve the performance of environmental remediation projects at dozens of locations and in a wide range of geologic conditions the effectiveness of a hydraulic fracture during remediation will depend primarily on its form that is its shape thickness orientation length width and location with respect to the borehole the forms of many hydraulic fractures have been determined by mapping exposures in excavations and by compiling split spoon sampling data these observations indicate that a typical hydraulic fracture at shallow depths is gently dipping slightly elongate in plan and slightly asymmetric with respect to the parent borehole shallow hydraulic fractures lift the ground surface to produce gentle domes and the pattern of uplift reflects the location and thickness of the fracture at depth the forms of hydraulic fractures created over a narrow range of depths at the same site are similar but the forms

granitoid magmatism of the nw bohemian massif revealed gravity data composition age relations and phase concept the late variscan granitoids of the nw bohemian massif northeast bavaria west bohemia constitute four partly contiguous granitoid complexes fichtelgebirge northern oberpfalz waidhaus rozvadov and bor incorporating more than 20 intrusive units based on gravity data the granites can be modeled as steeply inclined slab and wedge like bodies with thicknesses between 2 and 8 km a rough estimate of the total volume of the granites is approximately 18 000 km3 within the four areas named above composition ranges from less evolved dioritic rocks known as the redwitzite suite to highly evolved granites the redwitzites comprise metaluminous rocks with dominant i type features these rocks yield aberrantly old rb sr ages 545 415 ma low initial sr ratios 0 706 0 708 and high and variable nd t values 1 to 4 sr nd isotopes of the redwitzites show contamination trends towards the granites suggesting mixing between mantle magma and crustal granitic melts an older plutonic association granites of bor leuchtenberg weissenstadt marktleuthen zainhammer is mildly peraluminous displaying features of both i and s type granitoids these granites are characterized by lower carboniferous ages rb sr k ar u pb low to intermediate initial sr ratios 0 707 0 708 and high nd t values 2 to 4 which overlap with those of paragneisses from the zone of erbendorf vohenstrauss zev and from the western part of the tepla barrandian it is postulated that the older granites were formed either by partial melting of zev or tepla barrandian crust or alternatively of preexisting mature crust contaminated by mantle material the younger granites are strongly peraluminous and of s type they yield upper carboniferous rb sr and k ar ages and exhibit a range towards high initial sr ratios 0 710 0 720 and low nd t values 4 to 8 similar values are found in moldanubian paragneisses and in saxothuringian metasediments both of which provide potential source rock lithologies for these granites

saucer shaped sill with lobate morphology revealed by 3d seismic data implications for resolving a shallow level sill emplacement mechanism we use 3d seismic data to describe the 3d geometry of a large igneous intrusion the solsikke compound sill and address a number of issues related to sill emplacement the solsikke compound sill formed by amalgamation of a number of sills and exhibits a complex internal morphology dominated by saucer shaped depressions and linear discontinuities one of the saucer shaped sub elements of the compound sill the solsikke lobate sill has a previously unrecognized morphology it has a basal feeder and consists of a bifurcating network of interlinked lobe shaped sill segments we propose two models for the development of this intrusive style based on analogues from igneous systems and hydrofracturing experiments the lobate pattern indicates that the solsikke lobate sill was fed at its deepest point and adopted its geometry through outwards and upwards propagation the feeder location is coincident with a fault intersection suggesting that magma transport from the underlying source exploited the zone surrounding the intersection

the roles of elastic properties magmatic pressure and tectonic stress in saucer shaped sill growth near surface igneous sills commonly exhibit saucer like shapes formed due to interaction with the earth s surface once some critical sill length is reached relative to its depth sill geometry has been strongly linked to the host material conditions particularly in terms of the elastic properties and shear cohesion of the host rock operating as primary controls on sill geometry here we conduct dynamic numerical simulations for sill growth in the near surface in which we vary the host rock properties magma pressure profile internal to the sill p and the externally applied tectonic stress r to consider their contributions to sill geometry we find that elastic properties alone have little impact on sill geometry saucer shapes reflect the additive stress components of the magma overpressure within the sill and the tectonic stress controlled by the locus of the maximum energy release rate gmax initially gmax is in plane with the sill but deflects to 25 at a critical base length rc relative to depth due to interaction between the sill and the free surface increasing r decreases this angle and increases rc of the sill p controls sill growth rate but has little effect on overall geometry host rock cohesion and elastic properties control the absolute magnitudes of r required to effect a change in sill geometry plain language summary horizontal magma pathways sills are a crucial part of volcanic plumbing systems acting as potential feeder conduits to volcanic eruptions and as magma storage systems saucer shaped sills which exhibit a flat inner region and inclined outer region are a common type of magma pathway in the shallow crust models for saucer shaped sills both as physical analogue models or numerical simulations typically under predict the length of the inner flat region and over predict the outer inclined region models are typically too short and too steep here we use numerical simulation to investigate parameters that may control sill shape we find that the dominant controls on sill shape are the competing effects of 1 bending of the rocks above the sill which promotes a transition to inclined growth typically at 25 and 2 plate tectonic shortening which serves to decrease the angle of incline towards 0 when the horizontal force is high increasing the applied horizontal tectonic force can produce sills that are up to five times longer in the inner region before growing as inclined sills at 5 this matches very closely with observations of natural sills indicating that tectonic forces are an important consideration in the growth of sills

geometry and growth of sill complexes insights using 3d seismic from the north rockall trough doleritic sill complexes which are an important component of volcanic continental margins can be imaged using 3d seismic reflection data this allows unprecedented access to the complete 3d geometry of the bodies and an opportunity to test classic sill emplacement models the doleritic sills associated with basaltic volcanism in the north rockall trough occur in two forms radially symmetrical sill complexes consist of a saucer like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined commonly ragged outer rim bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano with an elongate concave upwards trough like geometry bilaterally symmetrical sills climb away from the magma source from which they originate both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge producing hybrid sill complexes radial sill complexes consist of a series of radiating primary flow units with dimensions up to 3 km each primary flow unit rises from the inner saucer and is fed by primary magma tube primary flow units contain secondary flow units with dimensions up to 2 km each being fed by a secondary magma tube branching from the primary magma tube secondary flow units in turn are composed of 100 m scale tertiary flow units a similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex this branching flow pattern as well as the interaction between flow units of varying orders provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger the data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature these features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening the branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex suggesting that the general features of the laccolith emplacement model also apply

magma and sediment i emplacement mechanism of late carboniferous tholeiite sills in northern britain president s anniversary address 1981 like other great tholeiite sheets of the world the midland valley sill and whin sill were emplaced in thick accumulations of sediments which at the time of intrusion were not much older nor had been orogenically deformed however the carboniferous sediments of northern britain had been deposited under the influence of continuous differential subsidence so that they were already disposed in syn sedimentary basins and swells when intrusion began by drawing palinspastic contours of the sills relative to a late westphalian marine band approximating to the surface at the time of emplacement it is established that the dolerites mainly follow bedding planes dipping at angles of as much as 5 down to the bottoms of the basins isopachs of the sills indicate a further relationship for the intrusions are thickest at the bottoms of the basins these facts are not explained by any intrusion mechanism previously postulated though there seems to be broad agreement as to the processes which have given rise to thinning and en echelon lensing at leading edges as well as to step and stair transgression of sediment bedding it is proposed that emplacement must have been controlled in part by gravitational flow down dip from feeder dykes which extended to between 0 5 and 1 0 km below the contemporary surface thereafter hydrostatic equilibrium was attained first by accumulation at the bottom of the basins and then by further advance up dip under pressure of head the sheets are so similar in aspect to flood basalts that it must be assumed that the sediments offered only low frictional resistance to splitting and flow

geochronology and geochemistry of eclogites from the marianske lazně complex czech republic implications for variscan orogenesis the marianske lazn complex mlc is located in the bohemian massif along the north western margin of the tepla barrandian microplate and consists of metagabbro amphibolite and eclogite with subordinate amounts of serpentinite felsic gneiss and calcsilicate rocks the mlc is interpreted as a metaophiolite complex that marks the suture zone between the saxothuringian rocks to the north west and the tepla barrandian microplate to the south east sm nd geochronology of garnet omphacite pairs from two eclogite samples yields ages of 377 7 and 367 4 ma samples of eclogite and amphibolite do not define a whole rock sm nd isochron even though there is a large range in sm nd ratio implying that the suite of samples may not be cogenetic eclogites do not have correlated nd values and initial 87sr 86sr ratios five of the eight eclogite samples have high nd values 10 2 to 7 1 consistent with derivation from a morb like source but variable 87sr 86sr ratios 0 7033 to 0 7059 which probably reflect hydrothermal seawater alteration three other eclogite samples have lower nd values 5 4 to 0 8 and widely variable 87sr 86sr ratios 0 7033 to 0 7096 such low nd values are inconsistent with derivation from a morb source and may reflect a subduction or oceanic island basalt component in their source the mlc is an important petrotectonic element in the bohemian massif providing evidence for cambro ordovician formation of oceanic crust and interaction with seawater late devonian frasnian famennian high and medium pressure metamorphism related to closure of a saxothuringian ocean basin early carboniferous visean thrusting of the tepla terrane over saxothuringian rocks and late visean extension

pore structure of sheared coals and related coalbed methane coalbed methane is considered to be one of the major contributors to global warming geological prospecting of the rich storage zone of methane is an important precondition for gas recovery projects shear zones along coal seams have long been considered as a major place where gas outbursts occur during mining but they also have a positive aspect in coalbed methane prospecting and production because of their great quantity of fractures and high methane content mercury penetrating experiments on a series of variously sheared coal samples from the pingdingshan coalfield china were performed the results showed that tectonically sheared coals possess three to eight times more porosity and two to ten times more specific surface area than their normal counterparts moreover brittlely deformed coals possess larger average fracture apertures representing a good condition for methane extraction whereas ductilely deformed coals show a fracture aperture even smaller than normal coals which can explain why intensely sheared coals become difficult for methane extraction the occurrence of a large number of tectonic fractures in a shear zone will make it easier for an artificial fracture to increase the permeability of coals in methane production therefore except for locally ductile deformation areas shear zones along coal seams are the best source and reservoir for methane gas production and if this methane is extracted it will help not only the reservoir but also protect the earth against global warming

experimental study on ultrasonic velocity and anisotropy of tectonically deformed coal abstract tectonically deformed coal tdc is defined as coal formed by various tectonic stresses as one of the key concerns in the formation and recovery of coal bed methane cbm from the tectonic deformation coal seams the texture and fractures of tdc present various features in different deformation environments and as a result the physical properties change therefore the identification of tdc is significant and can be obtained from the physical properties in this study fourteen representative tdc and two undeformed coal samples from the suzhou mining area in the east of north china plate were collected to investigate the geophysical recognition parameters of tdc by elastic properties such as the velocities p and s waves elastic parameters v p v s and poisson s ratio and velocity anisotropies the results show that the elastic properties of undeformed coal and tdc samples from different deformation environments exhibit significant difference normally the velocities and elastic parameters of undeformed coal have the highest values while the velocity anisotropy has the lowest value in brittle deformation environment the velocity and elastic parameters decrease while the velocity anisotropy ascends with increased deformation extent for the tdc samples from shear deformation environment the velocity anisotropies present the significant high values among the selected tdc samples in plastic deformation environment the elastic parameters gradually decrease with the deformation extent ascending while the velocity anisotropies are relatively high among the elastic properties the v p v s poisson s ratio and velocity anisotropy are sensitive to deformation type and extent of coal samples furthermore the development characteristics of coal structural fractures have a significant impact on the elastic properties of measured coal samples from different deformation environments in summary the results may provide reference parameters for future studies in cbm rock physics from the tectonic deformation coal seams

on origin of near axis volcanism and faulting at fast spreading mid ocean ridges at fast and superfast spreading mid ocean ridges such as the east pacific rise a plate boundary is defined by a narrow tens to hundreds of meters wide neovolcanic zone within which the bulk of the upper oceanic crust is created however detailed near bottom observations indicate that the volcanic construction may occasionally persist several kilometers off of the ridge axis it has been proposed that off axis volcanism manifests tapping of a wide melting region that supplies magma to the ridge axis or spatial migration of magmatic sources in the crust and upper mantle we demonstrate that off axis eruptions may be a natural consequence of variations in magma supply rate even if the ridge axis is stationary in space and the magma delivery is perfectly focussed at the ridge axis theoretical modeling and field observations indicate that off axis volcanism may result from magma emplacement in sills that propagate toward the surface after their characteristic horizontal size exceeds their emplacement depth volcanic construction and faulting due to sill intrusions may contribute to the formation of abyssal hills arguably the most abundant relief form on earth fl 2001 elsevier science b v all rights reserved

in situ identification of high vertical stress areas in an underground coal mine panel using seismic refraction tomography abstract because high stress anomalies can induce dynamic failures in the underground panels of coal mines the identification of high stress areas is critically important for mining safety we have identified areas of high vertical stress of an in situ longwall panel with seismic refraction tomography and interpreted our results using rock physics models constrained by core measurements since p and s velocities in rocks are stress sensitive mapping of them can provide useful information to identify areas of potential high stress we have inverted p and s velocities of main roof of an in situ panel with refraction tomography and converted them into vertical stress estimates using a calibration function from core measurements those estimates are classified into three groups high medium and low respectively identified zones of high vertical stress show qualitative agreement with monitored in panel microseismic data zones derived from p waves give a more plausible assessment than s waves we also discuss the link between high vertical stress areas and in panel faults because of the impact of the regional stress field and previously mined out voids the existing fault zone affects the redistribution of vertical stress in the underground panel

effects of structural deformation on formation of coalbed methane reservoirs in huaibei coalfield china tectonically deformed coal is defined as coal formed by superimposed reformations from tectonic stress the huaibei coalfield is typically composed of various tectonically deformed coals containing rich coalbed methane resources however the occurrence of coal seam in this area is complicated largely by the structural deformation which has not yet been evaluated systematically for exploration and exploitation of coalbed methane in this study tectonism in huaibei coalfield is discussed by combining systematic analyses on the occurrence of coal seams and the formation of coalbed methane reservoirs the study shows that with structural deformation in the study area the coal seams in huaibei coalfield are distributed in north south tectonic blocks and east west tectonic zones north tectonic block of huaibei coalfield is not favourable for exploitation of coalbed methane because of low gas content or disadvantageous structural conditions within the south tectonic block the east suzhou syncline contains high gas content but coal permeability is very low this area is generally not suitable for exploitation of coalbed methane and is a dangerous mining area due to gas outburst because of the widely developed mylonitic coals south suzhou and nanping synclines in the middle part of the south tectonic block are exposed to relatively weak structural deformations these synclines contain coals with high gas content and moderate permeability which are beneficial for exploration and exploitation of coalbed methane linhuan mining area in the south tectonic block is generally not suitable for exploitation of coalbed methane mainly because of well developed normal faults and interlayer slip structure and presence of mylonitic coal resulting in low gas content and poor structural conditions for mining coalbed methane in contrast guoyang mining area in the west part of the south tectonic block where tectonically deformed coal was generally underdeveloped is a potential area for exploration and exploitation of coalbed methane because of moderate gas content and possibly higher permeability of its coal

coronitic metagabbros of the marianske lazně complex and tepla crystalline unit inferences for the tectonometamorphic evolution of the western margin of the tepla barrandian unit bohemian massif

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

evaluation of coal texture distributions in the southern qinshui basin north china investigation by a multiple geophysical logging method abstract coal texture is indicative of coal mechanical strength which is important not only for evaluating coalbed methane cbm reservoir permeability but also for evaluating the possibility of coal and gas outbursts in underground coal mining this paper begins with a foundation of a geophysical logging based coal texture evaluation method that compares the digital logging data with the results from 108 coring samples then the method was applied to the analyses of coal textures in 39 cbm wells the results of which are discussed in terms of the vertical distribution of coal textures in the study area finally a ternary diagram based on thickness proportions of coal textures was used to identify reservoir compartments in the zhengzhuang field of the southern qinshui basin the results show that undeformed coals are easily distinguished from cataclastic and granulated coals because of the high den and gr of undeformed coals meanwhile cataclastic coal has lower response values of ac and lld than granulated coal which can be used in identifying cataclastic from granulated coal a multiple geophysical logging method combining the log data of den gr ac and lld was provided for predication of the coal textures in the zhengzhuang field the predicated results show that the coal seam can be vertically divided into three to eight sub layers with a typical interbedded pattern of undeformed and cataclastic coals on the upper and lower parts and granulated coal in the middle at a relatively large thickness the study area is divided into four major regions and 11 sub regions based on the classification of coal texture types the undeformed coal dominated region is located in the southwestern part of the study area indicating a low permeability in the coal reservoir the granulated coal dominated region is mainly in the northern and eastern parts of the study area and has resulted from deep burial and multi period structural activities the cataclastic coal dominated region is in the middle of the study area the coal reservoir in this region is possibly the most favorable for cbm production

a review of shear wave splitting in the crack critical crust summary over the last 15 years it has become established that crack induced stress aligned shear wave splitting with azimuthal anisotropy is an inherent characteristic of almost all rocks in the crust this means that most in situ rocks are pervaded by fluid saturated microcracks and consequently are highly compliant the evolution of such stress aligned fluid saturated grain boundary cracks and pore throats in response to changing conditions can be calculated in some cases with great accuracy using anisotropic poro elasticity ape ape is tightly constrained with no free parameters yet dynamic modelling with ape currently matches a wide range of phenomena concerning anisotropy stress shear waves and cracks in particular ape has allowed the anisotropic response of a reservoir to injection to be calculated predicted with hindsight and the time and magnitude of an earthquake to be correctly stress forecast the reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems this crack critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre fracturing deformation of the crust and for solid earth geophysics and geology we review past present and speculate about the future of shear wave splitting in the crack critical crust shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass there is some good news and some bad news for conventional geophysics many accepted phenomena are no longer valid at high spatial and temporal resolution a major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes however at least in some circumstances the behaviour of the rock in the highly complex inhomogeneous earth may be calculated and the response predicted opening the way to possible control by feedback the need is to devise ways to exploit these new opportunities in the crack critical crust recent observations from the smsites project at husavik in northern iceland gathered while this review was being written display the extraordinarily sensitivity of in situ rock to small changes at great distances the effects are far too large to occur in a conventional elastic brittle crust and their presence confirms the highly compliant nature of the crack critical crust

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago