a new indicator of movement direction during orogenesis measurement technique and application to the alps the orientation of axes of sigmoidal staircase or spiral inclusion trails within porphyroblasts provides an indicator of the direction of movement during deformation that is synchronous with metamorphism a simple technique is presented in detail to find this axis in 3d by radially sectioning a horizontal slab cut from an oriented sample when viewed from one direction the switch in asymmetry of the porphyroblast inclusion trails in these sections defines the trend of the axis further radial sectioning of a vertical slab cut parallel to this trend determines the plunge of this axis this technique is independent of the model adopted for the formation of sigmoidal or spiral shaped inclusion trails and can be used to evaluate the mechanism by which they form it can also be used to evaluate theories of folding and orogenesis measurements of spiral and sigmoid axes in garnet porphyroblasts from the european alps show that they reflect the movement of the african plate relative to europe better than linear indicators preserved within the same rocks

prediction of coal seam details and mining safety using multicomponent seismic data a case history from china abstractwith the increasing mining depth of coal mines geologic hazards have become the main source of accidents for this reason coal seam prediction requires more assessment parameters such as the degree of anisotropy vp vs value and elastic modulus these parameters are difficult to determine using only the pp wave we have inverted and interpreted multicomponent seismic data acquired from a 2 56 km2 area in the guqiao mine located on the southern margin of the north china plate under the constraints of drill log and rock physics test data the production coal seam 11 2 of the mine located in the permian formation was our focus of this study and our objective was to determine the structure fracture development thickness surrounding rock lithology roof stability and mining safety of the seam to achieve this we first performed an analysis of s wave splitting and joint pp and ps wave inversions the inversion results were then combined to derive additional parameters such as the vp vs

mimicking syntectonic growth cordierite overgrowth of earlier rotated staurolite porphyroblasts strain caps and deflected foliation monoclinic shape fabrics and inclusion trail geometries of porphyroblasts are regarded as reliable shear sense indicators provided that timing and sequence of growth can be established in the southern bossost dome of the central pyrenees staurolite and cordierite porphyroblasts in mica schists contain inclusion trails oblique to but continuous with the external foliation indicating porphyroblast rotation straight inclusion trails in staurolites record growth between formation of the main schistosity and subsequent shear i e an intertectonic origin strain caps and deflection of foliation around porphyroblasts show a distinct asymmetry with uniform sense of shear cordierite porphyroblasts are significantly larger than staurolites and contain curved inclusion trails which would suggest syntectonic growth and a similar shear of sense however staurolite and cordierite do not belong to the same paragenesis and textural evidence corrosion of staurolite rims and relict inclusions in cordierites suggest partial consumption by cordierite complete overgrowth of staurolite with preservation of its inclusion trails and adjacent foliation deflection results in curved inclusion trails that mimic syntectonic growth of cordierite actually the larger cordierites statically overgrew rotated staurolites during post tectonic contact metamorphism

natural metastable reactions involving garnet staurolite and cordierite implications for petrogenetic grids and the extensional collapse of the betic rif belt medium grade metapelites of the torrox unit betic rif belt s spain contain mineral assemblages consisting of garnet grt staurolite st cordierite crd biotite kyanite sillimanite andalusite muscovite ms and quartz qtz and record complex reaction processes of cordierite growth through garnet and staurolite decomposition the reaction textures the chemical composition of the reactant and product phases including fe mg mn partitioning and the results of equilibrium thermodynamic calculations indicate that these cordierite bearing assemblages are largely deviated from equilibrium furthermore the actual cordierite forming reactions as estimated from the assemblage and associated textures conflict with the predictions of thermodynamically based petrogenetic grids for the model pelite system kfmash either those that predict the stable coexistence of cordierite muscovite plus garnet or staurolite or those that do not foresee a field of stability for these types of assemblages this conflict is explained in terms of cordierite growth at ca 575 c and 2 5 kbar through metastable reactions whose operation was conditioned by the relict persistence of higher pressure phases garnet and staurolite and phase compositions e g muscovite and biotite after fast decompression this interpretation militates against the existence of a wide p t range of stable coexistence at low p of crd ms qtz grt st in medium grade metapelites of normal composition i e poor in zn and or mn the triggering of metastable cordierite forming reactions and the preservation of even subtle disequilibrium features associated to them indicate that the rocks underwent fast near isothermal decompression from ca 12 kbar down to 2 3 kbar then rapid cooling these inferences agree with independent evidence indicating that termination of alpine metamorphism in the western betic rif belt was related to the extensional collapse of thickened crust and that the latter had consisted of a single continuous event

limitations of waveform modelling of long period seismograms summary in recent years the use of synthetic seismograms calculated for radially stratified models has gained increasing popularity as a means of placing further constraints on the velocity structure of the earth s mantle such synthetics do however have a number of limitations at short periods 1 s the amplitudes as well as the wave shapes of travel time branches are affected by seismograph siting the structure immediately beneath the seismograph and any laterally heterogeneous structure in the mantle later arrivals can also be masked by signal generated noise and by extended source times at longer periods 20 s the larger wavelengths reduce the sensitivity of amplitudes and waveforms to contarninating effects as a result the use of long period synthetics can only lead to the resolution of the gross features of the earth s interior

tectonic levels in the palaeozoic basement of the pyrenees a review and a new interpretation reply abstract two different structural domains developed during the main hercynian deformation events were recognized by de sitter zwart in the hercynian basement of the central pyrenees a deep seated level infrastructure made of medium to high grade metasediments and orthogneisses with dome shaped gently dipping foliations contrasts with a shallow level suprastructure of low to very low grade metasediments with rather steep foliations since the recognition of this structural zonation different interpretations have been proposed disagreements concern timing of deformation and tectonic regime considered to be prevalent of the structural development of each tectonic level the proposed interpretation regards the progressive development and differentiation of both structural domains and considers the following factors to be significant for the structural arrangement of the pyrenean segment of the hercynian belt an increase with depth of the horizontal shear component of deformation related to tangential and transcurrent tectonics a marked inhomogeneity of deformation and penetrability of related foliations and the gradual evolution from an earlier compressive crustal shortening event to a late transpressive event responsible for crustal shortening and trend parallel stretching

application of a high resolution seismic investigation in a greek coal mine high resolution seismic methods were applied to map the detailed structure and thickness of the domeniko coal basin central greece and to search for lateral discontinuities such as pinch outs and faults extensive tests were performed to optimize recording parameters and equipment reflection events which can be attributed to coal layers can be interpreted from depths of approximately 30 to 150 m on cdp stacked and inverted sections several low throw faults have been interpreted from the sections results obtained from the high resolution seismic reflection survey combined with drillhole information clearly revealed the 3 d model of the coal field using geostatistical methods the results of the high resolution reflection seismic survey were combined with the information from the borehole program to clearly reveal the 3 d model of the basin

analysis of broadband seismograms from the chile eru area broadband seismograms recorded at the graefenberg grf array in germany are analyzed these data from the chile peru area have often a very complicated signature we have attempted to identify pp using theoretical seismograms a third phase besides p and pp which may have higher frequencies was discovered in a number of broadband records interpretations that relate this phase to the source or the structure are discussed our preferred interpretation is an s to p conversion at the bottom of the descending plate

progressive deformation of a zone of magma transfer in a transpressional regime the variscan merens shear zone pyrenees france the ew striking variscan merens shear zone msz located on the southern border of the aston dome pyrenees corresponds to variously mylonitized gneisses and plutonic rocks that are studied using the anisotropy of magnetic susceptibility ams technique the plutonic rocks form ew striking bands with from south to north gabbro diorites quartz diorites and granodiorites the msz underwent a mylonitic deformation with an intensity progressively increasing from the mafic to the more differentiated rocks the foliations are ew to nw se striking and subvertical a first set of lineations shows a moderate wnw plunge with a dextral reverse kinematics more recent subvertical lineations correspond to an uplift of the northern compartment to the east the msz was cut by a n120 e striking late shear band separating the msz from the querigut pluton the different stages of mylonitization relate to late variscan dextral transpression this regime allowed the ascent of magmas along tension gashes in the middle crust we interpret the msz as a zone of magma transfer which fed a pluton now eroded that was similar to the querigut and millas plutons located to the east we propose a model of emplacement of these plutons by successive pulses of magmas along en echelon transfer zones similar to the msz

enhancing the detection of small coal structures by seismic diffraction imaging abstract faults are the most important geological structures that need to be detected in any modern underground coal mining project even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production while seismic surveys are usually successful at locating faults with throws greater than 5 10 m reliable techniques for resolving more subtle faults dykes and other minor features are yet to be developed in seismic data there are two types of seismic energy signatures that can be used for subsurface imaging specular reflections and diffractions specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal rock interfaces specular reflections are used in conventional seismic reflection surveys diffractions are generated by local discontinuities caused by surface roughness faults dykes and fractures in this paper we describe the use of a moving average error filter which along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections can be used to effectively extract diffraction signals from post stack reflection seismic data by identifying diffractions small faults and other minor features that are elusive using conventional seismic reflection processing can be detected suggesting that diffraction imaging may be a superior method to seismic reflection imaging both synthetic and real 2d and 3d coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection it is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m

the vibroseis system a high frequency tool exploration methods are extended to their limits as we continue the search for energy resources successful application of high frequency seismic method requires evaluating each element in the seismic acquisition system and ensuring that each part of the system contributes to the success of the method this extends from seismic signal generation through data processing where good equipment performance and correct parameter selections are required the vibroseis system depends upon the ability of vibrators to generate synchronous repeatable sweeps over the frequency range of interest to support our high frequency seismic efforts conoco inc has developed and built a new high frequency vibrator this paper includes some of the consideration used in building the vibrator along with typical baseplate responses showing excellent drive levels to the design goal of 200 hz with an excellent source available correct application is essential to assure retention of high frequency data recording offsets ar

premine study of shallow coal seams using high resolution seismic reflection methods geological investigations in the illinois basin coalfields have shown that significant differences in safe and economical exploitation of coal depends directly on accurate mapping of the roof rock overlying the seam as well as on geological structures in the coal measures in roof rock transition zones above the herrin no 6 coal where the nonmarine energy shale changes to the anna shale a change often occurs from low to high sulfur coal and from low to high stability roof rocks in many instances use of borehole data alone is inadequate to locate these features in advance of mining high resolution seismic reflection data collected near harco illinois were used as part of premine planning to help predict roof instability areas of low sulfur coal and geologic disturbances several faults channels and facies changes affecting the herrin no 6 and the springfield no 5 coal seams at depths of 137 m and 167 m respectively were interpreted and modeled one and two dimensional synthetic seismo

high resolution 3 d seismic survey over a coal mine reserve area in the u s a case study a high resolution three dimensional 3 d seismic survey was conducted in advance of coal mine development in the illinois basin in may 1989 to better define a geologic structure with the potential to adversely affect longwall mining conditions the 3 d seismic data indicate that an abrupt change in seam elevation or roll encountered near the northern property line trends south into the reserve area and then turns southeast a personal computer based workstation was used to integrate borehole and seismic data for modeling in which 3 d block diagrams of the calculated seam elevations were generated the block diagrams show a steep slope on the west flank of the roll that gradually decreases as the roll turns to the southeast the survey also reveals a geologic structure beneath the roll at an estimated depth of 46 62 m horizontal time slice sections of this feature suggest the presence of a paleochannel that meanders on a similar course as the roll which apparently was connected to a larger paleochannel system a conoco high frequency vibroseis unit was successfully used as the seismic source to generate the high frequencies necessary to detect and resolve the thin coal beds

upper mantle modelling using long period sh body wave trains abstract the resolution of fine shear velocity structure in the upper mantle is difficult because of the low signal to noise conditions in most recordings of short period s waves and the poor resolving power of long period s data the resolution obtainable from the latter could be improved if a greater proportion of the sh body wave train at distances less than about 40 presumably comprised of arrivals from a variety of multiple paths through the upper mantle could be separated into its component signals attempts at deconvolving these wave trains by standard techniques however usually result in noisy spike sequences which are extremely difficult to interpret the authors have devised an empirical method of decomposing an sh body wave train into its component arrivals based on sequential removal of the response wavelets from the train although the method is approximate in that it assumes the absence of phase distortion it provides clear spike sequences which can be used to derive a starting model for the application of refinement techniques application of the method to sh wave trains recorded at norsar from mediterranean earthquakes has enabled the construction of an sh velocity model for the upper mantle beneath eastern europe in which the discontinuity profile is strikingly similar to those of recent detailed p velocity models for the upper mantle beneath central australia

subduction of the nazca plate beneath peru as determined from seismic observations a detailed reinvestigation of seismicity in the southern half of peru using data from a local seismic network and a focal mechanism study using p wave first motions reveal that for the first 100 km of descent the slab as defined by this seismicity enters at a normal dip angle near 30 and that below this depth it is bent to a nearly horizontal angle this horizontal slab extends eastward for about 300 km and then dips steeply below the thick continental lithosphere scsp observations are found to be consistent with the profile of the subducting plate as determined from the local seismicity beneath the region from southern peru to northern chile the nazca plate descends with an almost constant dip angle 30 down to at least 300 km depth between the 30 dipping plate in southern peru and the horizontal profile beneath central peru there is a contortion over a 100 km wide continuous lateral section of the subducting plate we infer that at least in the upper 150 km depth range the descending nazca plate is contorted rather than torn

advances in seismic reflection profiling for us coal exploration the utilization of seismic reflection methods in us coal exploration increased during the last decade as evidenced by the number of publications and papers presented at technical meetings the increased application of innovative techniques adapted from the petroleum industry has resulted in improvements in seismic data acquisition processing and interpretation the objective of this paper is to present some advances in the application of high resolution seismic reflection methods to us coal exploration since they were adopted in the mid 1970s

the mylonite zones in the pyrenees and their place in the alpine tectonic evolution abstract in the pyrenees the development of mylonites zones is one of the most striking structural features two sets of mylonites of regional extent have been recognized large longitudinal e w to n110 e trending zones e g merens fault and north pyrenean fault and oblique nw se trending zones cross cutting both the hercynian and the post hercynian terrains the longitudinal zones limit the major structural zones of the pyrenees and are associated with nw se en echelons folds in the mesozoic terrains and rotations of rootless plutonic or gneissic massifs acting as competent inclusions in a more ductile matrix in the hercynian basement the oblique mylonite zones limit map scale fold bands and appear as the sheared limbs of these folds the age of the oblique zones and of the major movements along the longitudinal zones is clearly alpine and the en echelons folds seem to have controlled the sedimentation during the upper albian and possibly during the upper cretaceous early movements along the longitudinal zones may have been hercynian the analysis of the structures at all scales leads us to interpret these mylonite zones and associated structures as the ultimate result of a transcurrent simple shear acting during the whole mesozoic period this strike slip shearing was probably associated with an extension perpendicular to it from the permian to the upper cretaceous and then to a shortening component also perpendicular to it from the late cretaceous to the eocene the development of the mylonite zones appears to have predated the major alpine thrusting but to have been reactivated during this thrusting acting as initiation sites for the thrusts or as oblique ramps in the case of the oblique mylonite zones

tomographic imaging of rock conditions ahead of mining using the shearer as a seismic source a feasibility study roof falls due to poor rock conditions in a coal longwall panel may threaten miner s life and cause significant interruption to mine production there has been a requirement for technologies that are capable of imaging the rock conditions in longwall coal mining ahead of the working face and without any interruption to production a feasibility study was carried out to investigate the characteristics of seismic signals generated by the continuous coal cutter shearer and recorded by geophone arrays deployed ahead of the working face for the purpose of seismic tomographic imaging of roof strata condition before mining two experiments were conducted at a coal mine using two arrays of geophones the experiments have demonstrated that the longwall shearer generates strong and low frequency 40 hz seismic energy that can be adequately detected by geophones deployed in shallow boreholes along the roadways as far as 300 m from the face using noise filtering and signal cross correlation techniques the seismic arrival times associated with the shearer cutting can be reliably determined it has proved the concept that velocity variations ahead of the face can be mapped out using tomographic techniques while mining is in progress

rotation of irregular staurolite porphyroblasts in a simple shear dominated shear zone controlled by initial growth orientation and aspect ratio abstract in a mica schist unit of the bossost dome central pyrenees spain idioblastic interkinematic staurolite porphyroblasts with straight inclusion trails s i have rotated with respect to the main schistosity in the same sense by different amounts orientation data of 600 porphyroblasts were obtained from planes parallel to stretching lineation xz perpendicular to lineation yz and parallel to schistosity xy interpenetrating growth twinning resulted in highly irregular shapes with aspect ratios r a ranging from 1 to 5 initial random porphyroblast growth is inferred from variable length axis la s i angles maximum rotation of 120 is observed in blasts with s i oriented orthogonal to the mineral long axis implying a shear strain of 4 3 in simple shear flow absence of back rotation is indicative of dominant simple shear flow w k 0 8 0 9 elongated porphyroblasts r a 3 with s i parallel to la have rotated very little because they were already in a stable position when shearing commenced rotation of staurolite porphyroblasts was possible because decoupling between blasts and matrix was weak and no significant strain partitioning had developed the wide variety of shapes with different aspect ratios formed by simple blasts and interpenetrating growth twins of staurolite are potential shear strain and vorticity gauges

shallow seismic reflection investigations of coal in the sydney basin surface reflection profiling with the mini sosie technique successfully mapped shallow coal seam structure in the western sydney basin new south wales several minor faults and zones of fracturing were detected in regions of thick triassic sandstone cover data quality was poor and unsuitable for geologic interpretation synthetic seismograms based on nearby borehole and petrophysical control show excellent agreement with the mini sosie sections and illustrate the deleterious filtering effects of coal seams and sequences to establish a phenomenological basis for seismic wave propagation in shallow coal measures two vertical seismic profiles vsps which used small explosive charges were recorded with high spatial and temporal sampling numerous multiple reflections were observed in the downgoing wave display the isolated upgoing waves were migrated to yield blurred images of the main coal seams the subsurface velocity function also deduced from the vsp shows broad correlation with the geologic log

synthetic seismogram images of upper mantle structure no evidence for a 520 km discontinuity seismological data used by shearer 1990 1991 to infer the existence of a seismic discontinuity at 520 km depth are compared with complete long period bodywave seismograms calculated for the international association of seismology and physics of the earth s interior 1991 iaspei9l earth model the iaspei9l model does not contain a seismic discontinuity at or near 520 km depth the observed p and sh multiples caused by topside reflections and ss precursors caused by underside reflections from the 410 km and 660 km discontinuities are well reproduced by the synthetic stacks the synthetics exhibit clear phase extrema between these reflections that correlate well with similar features in the observed waveform stacks

40ar 39ar age of mylonites along the merens fault central pyrenees seven mylonitic samples and two coarse muscovites from the central pyrenees have been dated by the 40ar 39ar method whole rock specimens of mylonite were cut out of thin section chips allowing complete characterisation of mineralogy and texture several specimens showed rising staircase patterns in the range 50 90 ma with much higher ages in the highest temperature steps this is believed to reflect mixing of argon released from micas with excess argon contained in plagioclase and released mainly at high temperatures one biotite quartz mylonite gave a plateau age of 93 2 ma other inferred mica ages are about 60 73 ma for biotite and 50 60 ma for muscovite it is probable that biotite contains excess argon and that 50 ma approximates to the cooling age in the mylonites one coarse muscovite collected immediately below the major merens shear zone gave a hercynian plateau age while another collected within the merens zone gave a partially reset hercynian age taken together the data indicate that the shear zones were active in alpine times 100 ma and probably about 50 ma ago they are believed to have formed during the early stages of eocene compression in the pyrenees deformation and resultant uplift probably terminated an important thermal event in this part of the pyrenean basement which may have begun at the time of the mid cretaceous north pyrenean metamorphism 90 100 ma

polymetamorphism and ductile deformation of staurolite cordierite schist of the bossost dome indication for variscan extension in the axial zone of the central pyrenees the bossost dome is an e w trending elongated structural and metamorphic dome developed in cambro ordovician metasedimentary rocks in the variscan axial zone of the central pyrenees a steep fault separates a northern half dome cored by massif granite from an e w trending doubly plunging antiform with granitic sills and dykes in the core to the south the main foliation is a flat lying s 1 2 schistosity that grades into a steeper dipping slaty cleavage at the dome margins three major deformational and two metamorphic phases can be differentiated s 1 2 schistosity is an axial planar cleavage to w vergent recumbent folding that probably occurred in mid westphalian time peak regional metamorphism m 1 is characterized by static growth of staurolite and garnet following thermal relaxation of the previously thickened crust strong non coaxial deformation recording uniform top to the se extension during d 2 a is preserved in staurolite garnet schists in a 1 5 km thick shallowly se dipping zone in the southeastern dome a 500 m thick contact aureole m 2 was imprinted on the regionally metamorphosed rocks following the intrusion the bossost granite during d 2 b more coaxial deformation prevailed during synkinematic growth of m 2 phases in the inner part of the contact aureole around the northern part of the dome where it obliterated d 2 a fabrics progressive non coaxial deformation continued in the southeastern antiform and is recorded by late synkinematic growth of cordierite successive overprinting of the m 1 staurolite garnet assemblage by andalusite and cordierite of m 2 is preserved in the southern part the assemblage muscovite cordierite staurolite biotite is considered metastable given the low mn and zn contents of staurolite and cordierite and interpreted as the result of prograde metamorphism during decompression p t conditions during m 2 were approximately 3 kbar and 600 c pervasive crenulations and mesoscopic to regional southerly verging folds are the result of d 3 nne ssw compression post dating ductile deformation and contact metamorphism polymetamorphic assemblages of the bossost dome preserve a regionally confined zone of ese directed extensional shearing within an overall n s compressional setting exact timing of extensional shearing is not known but can be constrained by recumbent folding during the mid westphalian and granitic intrusions which confine it to late carboniferous time c 305 ma crustal scale flat lying extensional shear zones with similar orientation and time frame are observed in the hospitalet massif of the eastern axial zone this suggests that crustal extension though probably restricted by regional strain partitioning over orthogneiss or intruding granitic bodies within an overall compressive setting was not uncommon in late carboniferous time in the axial zone of the pyrenees

zooming on northern cap de creus shear zones abstract the northern cap de creus shear belt provides fine examples of shear zones developed at different scales in rocks bearing pre existing penetrative foliations the shear zones developed under retrograde metamorphic conditions and they are preferentially located in crystalline schists lower grade metasedimentary rocks accommodated deformation by folding the shear zones are linked in an anastomosing framework with self similar properties they are interpreted to have formed as the result of a progressive wrench dominated deformation affecting anisotropic rocks a progressive non coaxial deformation regime is considered responsible for the development of the complex kinematic pattern wherein shear zones with opposite senses of shear may come to lie in close parallelism in such a framework individual shear zones are characterised by marked strain gradients not only across the shear zone but also along it these features together with the geometrical analysis of shear zone marginal domains indicate that these structures developed with a component of shortening across the shear zones the shear zones are interpreted to have nucleated as buckling instabilities that gradually evolved to become shear zones approaching the simple shear model microstructural and quartz c axis fabric analyses indicate that shear zone formation is associated with strong strain partitioning on all scales

synthesis of complete sh seismograms summary a method for calculation of theoretical sh waves in a laterally homogeneous layered medium is presented the sh wave trains are complete i e they include surface waves as well as body waves the sh displacements are calculated for two point sources a single horizontal force and a shear dislocation of arbitrary orientation both buried in the layered half space numerical problems are discussed the correctness of the method is ascertained by its ability to reproduce complete synthetic sh seismograms published elsewhere in the literature several examples demonstrate that our method is well suited for crustal studies as well as for teleseismic studies of the upper and lower mantle

pseudomorphs and associated microstructures of western maine usa abstract in metapelitic rocks of western maine a pluton related m3 metamorphic gradient ranging in grade from garnet to upper sillimanite zone was superposed on a fairly uniform m2 regional metamorphic terrain characterized by the assemblage andalusite staurolite biotite garnet as a result m2 assemblages re equilibrated to the p t and ah2o conditions of m3 and both prograde and retrograde pseudomorphism of m2 porphyroblasts occurred the type of pseudomorph and degree of development is directly related to the rock s position within the m3 metamorphic gradient a function of its proximity to the mooselookmeguntic pluton several hinge zones occur in which the m3 minerals that pseudomorphed a particular m2 phase change for example m2 garnet was replaced by m3 chlorite or biotite depending on its position within the m3 gradient similarly in a transition zone between m3 upper staurolite and lower sillimanite zones m2 staurolite was stable and shows m3 growth rims downgrade from this transition zone staurolite was pseudomorphed by chlorite and muscovite whereas upgrade the pseudomorphs contain muscovite and some biotite m3 pseudomorphs commonly retain crystal shapes of the original m2 porphyroblasts reflecting relatively low regional deviatoric stress during and after m3 although evidence for textural disequilibrium is common chemical equilibrium was closely approached during m3 this study demonstrates for m3 that 1 the pseudomorphic replacement was a constant volume process and 2 fabrics produced by tectonic events can be erased by subsequent deformation and or sufficiently intense subsequent recrystallization

modeling studies of interference reflections in thin layered media bounded by coal seams high resolution seismic data collected over a major u s coal basin indicated potential complex problems associated with interference reflections these problems differed from those normally encountered in the exploration of oil and gas because of differences in the geologic boundary conditions modeling studies were conducted to investigate the effects of overlapping primary reflections and the composite reflection that result from stacking individual wavelets a modified empirical formula of lindseth s linear relationship between acoustic impedance and velocity is used to extrapolate velocity information from density logs to provide appropriate geophysical properties for modeling the synthetic seismograms generated from density and synthetic sonic logs correlated well with the processed seismic data a 150 hz ricker wavelet is used to convolve with the computer models and the models showed that certain anomalous composite reflections result from the superposition of overlapping primary reflections de

locating faults in underground coal mines using high resolution seismic reflection techniques a high resolution seismic reflection technique was used to locate faults in coal seams that were not visible on the surface and could only be observed in underground coal mines an 8 gauge buffalo gun built by the research and development department of consolidation coal company was used as the seismic source the coal seam at a depth of 700 ft produces a reflection with a predominant frequency of about 125 hz the high resolution seismic data permitted faults with vertical displacements of the same magnitude as the seam thickness to be detected at depths of several hundred feet beneath the surface several faults were detected and interpreted from the seismic sections and the magnitudes of their displacement were estimated by matching the recorded seismic data to synthetic seismic data subsequent underground mine development in the study area confirmed two interpreted faults and their estimated displacements mining engineers were able to use the information provided by the seismic survey to plan an