elastic anisotropy of tambo gneiss from promontogno switzerland a comparison of crystal orientation and microstructure based modelling and experimental measurements author s vasin rn kern h lokajicek t svitek t lehmann e mannes dc chaouche m wenk hr abstract the authors 2017 felsic and mafic gneisses constitute large proportions of the upper and lower continental crust gneisses often display high anisotropy of elastic properties associated with preferred orientations of sheet silicates here we study the elastic anisotropy of a sample of tambo gneiss from promontogno in the central alps we apply optical microscopy time of flight neutron diffraction neutron and x ray tomography to quantify mineral composition and microstructures and use them to construct self consistent models of elastic properties they are compared to results of ultrasonic measurements on a cube sample in a multi anvil apparatus and on a spherical sample in an apparatus that can measure velocities in multiple directions both methods provide similar results it is shown that models of microstructure derived elastic properties provide a good match with ultrasonic experiment results at pressures above 100 mpa at a pressure of 0 1 mpa the correspondence between the model and the experiment is worse this may be caused by an oversimplification of the model with respect to microfractures or uncertainties in the experimental determination of s wave velocities and elastic tensor inversion the study provides a basis to determine anisotropic elastic properties of rocks either by ultrasonic experiments or quantitative models based on microstructures this information can then be used for interpretation of seismic data of the crust

petrographic and geochemical contrasts and environmentally significant trace elements in marine influenced coal seams yanzhou mining area china abstract the yanzhou mining area in west shandong province china contains coals of permian and carboniferous age the 31 and 32 seams of the permian shanxi formation and seams 6 15 17 of the carboniferous taiyuan formation were analyzed for coal petrology mineralogy and geochemical parameters the parameters indicate that the coal is high volatile bituminous in rank the coal is characterized by high vitrinite and low to medium inertinite and liptinite contents these properties may be related to evolution of the coal forming environment from more reducing conditions in a marine influenced lower delta plain environment for the early taiyuan coals to more oxidizing paleoenvironments in an upper delta plain for the upper shanxi coal seams the major mineral phases present in the coal are quartz kaolinite pyrite and calcite sulfur is one of the hazardous elements in coal the major forms of sulfur in coal are pyritic organic and sulfate sulfur pyritic and organic sulfur generally account for the bulk of the sulfur in coal elemental sulfur also occurs in coal but only in trace to minor amounts in this paper the distribution and concentration of sulfur in the yanzhou mining district are analyzed and the forms of sulfur are studied the sulfur content of the taiyuan coal seams is considerably higher than that of the shanxi coals organic sulfur content is positively correlated to total and pyritic sulfur the vertical variation of cu zn pb as th u and sulfur contents in coal seam 3 of the shanxi formation in the xinglongzhuang mine show that all these trace elements with the exception of th are enriched in the top and bottom plies of the seam and that their concentrations are also relatively high in the dirt bands within the seam the pyritic sulfur is positively correlated with total sulfur and both are enriched in the top bottom and parting plies of the seam the concentrations of the trace elements are closely related to sulfur and ash contents most of the trace elements are correlated with the ash content and may be associated with the mineral matter in the coal

leaching experiments to study the release of trace elements from mineral separates from chinese coals abstract leaching experiments were carried out for two samples of mineral separates from chinese coals for the purpose to simulate the release of trace elements in acid mine drainage the leaching solution has a ferric ion concentration of 10 3 m ph 2 the experiments were carried out at room temperature the grain size of the mineral separates is 75 130 m the behavior of the release of eight trace elements co ni zn cd al cr as and pb were measured during the period of 312h the results from four leaching tests using two samples with two solid to liquid ratios show that the concentrations of co ni zn and cd continuously increased during the leaching period and they were correlated with the sulfate content in the same leachate this indicates that the elements were released during the oxidation and dissolution of pyrite the elements were easily dissolved in the leaching solution on the other hand the concentrations of al cr as and pb in the leachates varied considerably under same leaching conditions and were sensitive to the condition of the leachate during the leaching process the release of these four elements was affected by the ph of the leachate and by absorption and co precipitation they are less likely to migrate therefore the release and migration of the eight elements in acid coal mine drainage are controlled mainly by three factors the oxidation of pyrite the ph of the leachate and mineralogy of country rocks

anisotropy of vp and vs in an amphibolite of the deeper crust and its relationship to the mineralogical microstructural and textural characteristics of the rock abstract laboratory seismic measurements of compressional v p and shear wave v s velocities have been carried out on a deformed amphibolite from the ivrea zone at pressures and temperatures up to 600 mpa and 600 c respectively amphibolite is considered to be an important rock of the deeper crust from crystallographic orientations of the component minerals hornblende plagioclase and diopside and the respective elastic constants we calculated the average elastic constants voigt average for the rock specimen compressional and shear wave velocities in three orthogonal directions normal and parallel to foliation measured at high confining pressure 600 mpa are in good agreement with the calculated velocity surface this suggests that seismic wave velocity anisotropy is controlled by preferred orientations of minerals in rocks texture at high confining pressure where the effect of microcracks on seismic wave velocities is eliminated in the amphibolite sample the velocity anisotropy is dominated by the texture of hornblende because of the strong preferred orientation and large volume fraction of this mineral species a large s wave splitting is documented in the directions parallel to the foliation particularly in the lineation which strongly argues against the microcrack origin of s wave splitting at least at conditions of high effective pressure

lithological control on shear wave velocity anisotropy in core samples from the taiwan chelungpu fault drilling project abstract the present study provides laboratory constrains on the in situ source of shear wave birefringence in siltstone and sandstone lithologies from the taiwan chelungpu fault drilling project tcdp bench top measurements at ambient pressure and temperature are performed across the end faces of vertically drilled samples while the polarization angle of the source and receiver is rotated from 0 to 360 in azimuth shear wave birefringence in siltstone is low 3 5 and controlled by low angle 30 bedding dip the sandstone samples exhibit moderate 15 shear wave anisotropy due to a network of vertical microcracks with normal about the bedding strike direction as related studies infer that the microcracks responsible for shear wave birefringence in sandstone are also open at depth our results suggest that anisotropy in borehole measurements can simply be accounted for by the observed siltstone and sandstone microstructures i e without invoking larger scale objects nor randomly oriented cracks fractures subjected to triaxial stress state

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

velocity anisotropy and shear wave splitting in rocks from the mylonite belt along the insubric line ivrea zone italy velocity anisotropy and shear wave splitting has been measured up to 600 mpa on seventeen mylonitic samples from the mylonite belt along the insubric line the rocks which range from felsic to mafic in composition have experienced large ductile strain seismic anisotropy a and shear wave splitting delta vs is significantly pressure dependent velocity anisotropies of p and s waves range from 9 to 27 vp and 10 to 25 vs at 10 mpa and from 4 to 15 and 6 to 17 at 600 mpa respectively oriented microcracks in addition to preferred orientation of anisotropic rock forming minerals contribute largely to velocity anisotropy and shear wave splitting in the low pressure range at high pressure 600 mpa where most of the cracks are closed velocity anisotropy and shear wave splitting is dominated by preferred mineral orientation texture the experimental data at 600 mpa are in fairly good agreement with velocity calculations voigt averages based on volume percentages of major minerals the stiffness tensor of respective rock forming minerals and the measured crystallographic orientation texture related reflection coefficients rc at the protolith mylonite interfaces normal incidence no density change are 0 04 vp and 0 03 vs for extremely anisotropic mylonites a approximate 12 calculations of the variation of reflection coefficients due to velocity anisotropy of p waves in mylonites of different lithologies literature data included give 90 less than 0 1 66 less than 0 05 and 44 less than 0 03 these results suggest that the directional variation of wave velocities in anisotropic mylonites alone does not provide the impedance contrast necessary to give rise for strong seismic reflections

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

a mineralogical and geochemical study of element mobility in sulfide mine tailings of fe oxide cu au deposits from the punta del cobre belt northern chile two flotation tailings sites ojancos and p cerda from the fe oxide cu au punta del cobre belt south of copiapo atacama desert northern chile are geochemically largely using sequential extractions and mineralogically compared main ore minerals are pyrite magnetite and or hematite and chalcopyrite gangue is dominantly calcite with minor quartz the host silicate assemblage is largely controlled by hydrothermal alteration and consists of variable amounts of the following minerals k feldspar ca amphibole biotite sericite chlorite tourmaline epidote quartz in this study both the ojancos and the p cerda tailings were deposited in valley dam impoundments and when they were filled new tailings were deposited upstream as a result high quantities of seepage migrated downstream into the older tailings impoundment at ojancos the recent upstream tailings have excess of acid potential 7 1 wt calcite and 3 5 wt pyrite whereas the older downstream tailings are characterized by alternations of several meter thick intervals with high neutralizing potential about 40 wt calcite and 2 wt pyrite and intervals with high acid potential about 3 wt calcite and 4 wt pyrite acid mine drainage amd with the precipitation of schwertmannite ph 3 15 and chalcoalumite ph 4 9 flows out at the interface between the uphill and downstream tailings strong downstream element transport is taking place and contributes to the formation of the cementation zone mainly gypsum ferrihydrite and goethite and locally jarosite in the older downstream impoundment the cementation zone ph 4 shows strong enrichment of heavy metals e g up to 6800 ppm cu 680 ppm zn 1100 ppm as mainly adsorbed and as secondary sulfides e g covellite in contrast at the p cerda tailings impoundment carbonates are homogeneously distributed and the overall neutralization potential exceeds the acid potential average of about 10 wt calcite and up to 2 5 wt pyrite the up to 5 m thick oxidation zones paste ph 6 9 8 3 at p cerda are characterized by interlayering of coarser dark gray unoxidized layers with fine grained fe iii hydroxide rich ochre to red brown colored horizons the hyperarid climate dries out first the coarse sulfide rich horizons of the tailings and limits so the oxidation which is restricted to the fine grained due to their higher moisture retention capacity however results indicate that during operation an important element transfer from the younger upstream tailings to the older downstream tailings impoundment took place possibly by sorptive transport at ferric polymers or colloids in the form of neutral mine drainage nmd this would explain the metal enrichments in the cementation zone which are mainly associated to the exchangeable fraction and not as secondary sulfides this results in both cases in ojancos mainly as amd and in p cerda mainly as nmd in fe iii input as ferric cation as ferric polymer or co3 complexes to the downstream impoundment this constitutes a very effective acid potential transfer to the older downstream material because oxidation via input of external fe iii produces 16 mol of protons per mol fes2 i e eight times more than via oxidation with oxygen in addition the created acidity favors dissolution of the abundant fe oxides magnetite and hematite of this ore deposit type providing so additional fe iii for sulfide oxidation

fabric changes and their influence on p wave velocity patterns examples from a polyphase deformed orthogneiss abstract the complete p wave velocity distribution preferred orientation of rock forming minerals and microcracks of two differently deformed orthogneisses from the kutna hora crystalline unit were investigated the complete symmetry of p wave velocities were determined as a function of confining pressure on the basis of 132 independent propagation directions up to 400 mpa the two samples are of almost identical mineralogical composition but exhibit different fabrics which can be related to different positions within a large scale fold structure the symmetry of the vp diagrams change from nearly transversely isotropic for the sample from the limb area to orthorhombic for the sample from the hinge zone which shows an additional crenulation cleavage this change of symmetry is observed at all pressure levels reorientation of the main velocity directions vpmin vpmax kpint between hinge and limb is controlled by the microcrack fabric and the texture of the rock forming minerals this can cause significant differences in reflectivity related to fabric changes within large scale folds

laboratory measurements of elastic anisotropy parameters for the exposed crustal rocks from the hidaka metamorphic belt central hokkaido japan summary to study crustal rock seismic anisotropy and its effect on seismic wave propagation we measure the seismic velocity anisotropy of two amphibolites one biotite gneiss and one biotite schist from the hidaka metamorphic belt in central hokkaido japan under confining pressures up to 150 mpa the rock microstructures show foliation and lineation characterized by lattice preferred orientation lpo of hornblende or biotite p and two s wave velocities are measured along the direction perpendicular to the foliation plane and two directions in the foliation plane perpendicular and parallel to the lineation we assume orthorhombic symmetry based on the rock microstructures and obtain tsvankin s anisotropic parameters an extension of thomsen s parameters for orthorhombic symmetry p and s wave phase velocity surfaces are calculated from anisotropy parameters and compared with the measured velocities along particular directions and with the velocity contour maps calculated from the voigt averages of singlecrystal elastic constants based on the orientation of measured lpo data qualitatively the measured velocity anisotropy agrees with the velocity contour calculated from the lpo data although large quantitative differences exist between them all anisotropy patterns can be approximated as transverse isotropy or its modification appearing as orthorhombic symmetry biotite schist containing 30 per cent volume ratio biotite shows strong s wave anisotropy and the phase velocity surfaces of p waves show a large deviation from ellipticity in the plane perpendicular to the foliation and parallel to the lineation in the same plane s waves show a singularity due to a large bulge of the sv velocity surface

mobility of trace and potentially harmful elements in the environment from high sulfur indian coal mines abstract coal mine rejects and sulfide bearing coals are prone to acid mine drainage amd formation due to aqueous weathering these acidic effluents contain dissolved trace and potentially harmful elements phes that have considerable impact on the environment the behavior of these elements in amd is mainly controlled by ph the focus of the present study is to investigate aqueous leaching of mine rejects for prediction of acid producing potential rates of weathering and release of phes in mine drainage mine reject mr and coal samples from the active mine sites of meghalaya india typically have high s contents 1 8 5 7 in mr and 1 7 4 7 in coals with 75 90 of the s in organic form and enrichment of most of the phes in rejects aqueous kinetic leaching experiments on mine rejects showed high acid producing potential and release of trace and potentially harmful elements the elements sb as cd cr co cu pb mn ni v and zn in mine sample leachates are compared with those in mine waters the concentrations of al si p k ti mn fe co ni cu zn and pb are found to increase with leaching time and are negatively correlated with ph of the solution the processes controlling the release of these elements are acid leaching precipitation and adsorption the critical loads of phes in water affected by amd are calculated by comparing their concentrations with those of regulatory levels the enrichment factors efs and soil pollution indices spis for the elements have shown that phes from coal and mine reject samples are mobilized into the nearby environment and are enriched in the associated soil and sediment

distribution isotopic variation and origin of sulfur in coals in the wuda coalfield inner mongolia china abstract this paper describes coal petrographic characteristics sulfur abundance distribution and isotopic signature in coals in the wuda coalfield inner mongolia northern china petrographic studies suggest that depositional environment influences petrographic composition the no 9 and no 10 coal seams which are thought to have formed on a tidal delta plain have high collodetrinite contents up to 66 1 indicating enhanced gelification and bacteria activity during coal accumulation and also have the highest sulfur content 3 46 and 3 42 both organic and pyritic sulfur isotope values 12 3 to 5 8 and 18 7 to 1 1 respectively are variable and generally tend to be more negative in high sulfur coals than those in low sulfur coals in the wuda coalfield the negative sulfur isotope values indicate that a large portion of sulfur in the high sulfur coals has a bacterial origin sulfur isotopic compositions and variations within the section were used to propose a model to explain the origin of sulfur in these coals the presence of pyritized rod like bacteria cyanophyte s gelatinous sheaths and degraded algae organic matter suggests that bacteria and perhaps algae may play an important role in the formation of these high sulfur coals

suggestions for a consistent terminology for seismic anisotropy seismic anisotropy is an unfamiliar concept to many geophysicists and the use of misleading and ambiguous terminology has made it more difficult to understand i suggest here a consistent terminology in which simple expressions have specific meanings similar to their colloquial meanings it is hoped that use of such language will help to make the increasing number of papers reporting seismic anisotropy more readily comprehensible to the non specialist this not a manual of anisotropy and it is not intended for theoreticians it is a list of terms which may make anisotropy a little easier to understand for those more familiar with wave propagation in isotropic solids

surface analysis of pyrite in the no 9 coal seam wuda coalfield inner mongolia china using high resolution time of flight secondary ion mass spectrometry abstract the chemical composition of pyrite in coal can be used to investigate its geological and mineralogical origin in this paper high resolution time of flight secondary ion mass spectrometry tof sims was used to study the chemical composition of various pyrite forms in the no 9 coal seam st d 3 46 from the wuda coalfield inner mongolia northern china these include bacteriogenic framboidal massive cell filling fracture filling and nodular pyrites in addition to fe 54fe 56fe 57fe other fragment ions were detected in bacteriogenic pyrites such as 27al si 28si 29si 30si 40ca cu 63cu 65cu zn 64zn 66zn 67zn 68zn ni 58ni 60ni 62ni and c3h7 tof sims images show bacteriogenic pyrites are relatively rich in cu zn and ni suggesting that bacteria probably play an important role in the enrichment of cu zn and ni during their formation intense positive secondary ion fragments from framboidal aggregates such as 27al 28si 29si alo ch2 c3h3 c3h5 and c4h7 indicate that formation of the framboidal aggregates may have occurred together with clay mineral and organic matter which probably serve as the binding substance the intense ions of 28si and 27al from massive pyrites also suggest that their pores incorporated clay minerals during crystallization together with the lowest 28si 23na value the intense organic positive secondary ion peaks from cell filling pyrites such as c3h3 c3h5 c3h7 and c4h7 indicate that pyrite formation may have accompanied dissolution or disintegration of the cell the intense p peak was observed only in the fracture filling pyrite and the highest 28si 23na value of fracture filling pyrite reflects its epigenetic origin together with xrd and rees data the stronger 40ca in nodular pyrite than other pyrite forms shows seawater influence during its formation

geochemistry of the late permian no 30 coal seam zhijin coalfield of southwest china influence of a siliceous low temperature hydrothermal fluid this paper describes the influence of siliceous low temperature hydrothermal fluid on the elemental concentrations and mineralogical characteristics of the late permian anthracitic ro max 3 58 coal seam no 30 from the zhijin coalfield in western guizhou province sw china coal samples were examined using instrumental neutron activation analysis inductively coupled plasma mass spectroscopy inductively coupled plasma atomic emission spectrometry x ray fluorescence powder x ray diffraction scanning electron microscopy equipped with energy dispersive x ray and isotope analysis the modes of occurrence of elements were determined using a sequential chemical extraction procedure the studies indicate that the no 30 coal seam has a very high content of veined quartz vol 9 4 whose isotope values of 30si and 18o are 0 6 and 15 4 respectively indicating that the quartz originated from siliceous low temperature hydrothermal fluid formation temperature 160 220 c rather than detrital material of terrigenous origin or magmatic hydrothermal inputs results of scanning electron microscopy equipped with energy dispersive x ray and sequential chemical extraction procedure show that the veined quartz is the dominant source of fe cu u pd pt and ir which are as high as 2 31 356 8 2 1 2 43 and 0 006 g g in this coal seam respectively the studies have also found that elements such as fe and cu are mainly in the veined quartz and they do not occur as sulfides in this coal seam in sharp contrast to many other coal seams in china the geochemical and mineralogical anomalies of the coal are attributed to the siliceous low temperature hydrothermal fluid

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

contamination of water and sediment in a desert stream by metals from an abandoned gold mine and mill eureka district arizona u s a abstract boulder creek comprises one of the major watercourses in an otherwise arid region of western arizona supporting a rich diversity of wildlife the abandoned hillside mine and mill complex on the banks of boulder creek consists of a series of tailings and waste piles collapsed adits and shafts and a dismantled mill the hillside mine extracted chiefly au and ag but the mill also processed a variety of base and precious metals from other mines in the region the non polluted stream water above the hillside complex is alkaline predominantly na ca hco3 in composition and well buffered polluted water enters the creek from two point sources a tailings pile and a collapsed adit the tailings seep has a ph of 2 4 and concentration in mg l up to 5240 so4 260 al 34 as 100 cu 610 fe 52 mn and 500 zn water from the collapsed adit has a ph of 5 4 and contains in mg l upt to 1480 so4 21 as 68 fe 45 mn and 9 5 zn but low concentrations of al and cu mixing of these waters with the oxygenated alkaline stream water causes a rapid downstream precipitation and sedimentation of the dissolved metals the reactions in the stream are the natural equivalents of the processes of aeration and liming which are used in water treatment

effect of darcy flux on the release of dissolved organic matter and nitrogen from coal gangue in a coal mine underground reservoir column experiments abstract underground reservoirs packed with coal gangue have been widely used to store and purify mine water in the coal mine areas of china however minimal information is available about the effects of pollutants released from the packed matrix on the quality of stored water column experiments were performed at 25 c and darcy fluxes of 0 39 0 73 and 1 56 cm h to investigate the effect of darcy flux on the dynamic changes of dissolved organic matter dom and nitrogen released from the packed coal gangue results showed that the values of dissolved organic carbon doc uv254 organic nitrogen org n nitrate and total dissolved solids tds in the effluent decreased rapidly within 3 7 pore volumes pv at the three darcy fluxes and then decreased slowly and tended to become stable during the column experiments however the effluent concentrations of nh4 n which is the major nitrogen released from the packed matrix and total nitrogen tn decreased and increased alternately which can be relative to the lithology mineral and chemical composition of the studied matrix the quantities of doc nh4 n org n and tn released from the studied matrix decreased with darcy flux suggesting a positive effect of hydraulic retention time hrt on the resolution of pollutants from the studied matrix moreover the microbial environment got weakened with an increase in darcy flux as confirmed by the variation trends of the biological autochthonous index bix and the fluorescence index fi thus the evident accumulation of no2 n and the highest content of no3 n were observed due to incomplete nitrate reduction with a low efficiency at 1 56 cm h the findings will be helpful in estimating the variation of water quality during the storage of mine water in a coal mine underground reservoir in china

the effect of oriented microcracks on seismic velocities in an ultramylonite the influence of oriented microcracks on the directional dependence of p and s wave velocities has been investigated in an epidote muscovite ultramylonite optical and sem studies revealed that the fabric of the mylonite is characterized by oriented intragranular and grain boundary cracks comparison of orientation patterns of cracks with calculated elastic properties voigt average of a model rock isotropic matrix ultramylonite crack geometry and laboratory seismic data indicates that wave propagation is particularly affected by oriented grain boundary cracks microcracks are most effective at low pressure and largely closed above about 200 300 mpa the residual part of velocity anisotropy observed above this crack closing pressure is mainly due to preferred mineral orientation in particular of mica maximum concentration of poles to 001 mica planes corresponds to the maximum of poles to oriented grain boundary cracks so that the effects of texture and oriented cracks on wave velocities line up giving rise to extreme values of velocity anisotropy and shear wave splitting at low pressure conditions

development of microcracks in granites during cooling and uplift examples from the variscan basement in ne bavaria germany abstract microcracks in two late variscan granites in ne bavaria provide information about regional paleostress directions and p t conditions during cooling and uplift in both granites three prominent generations of healed microcracks called ci cii ciii constitute an orthorhombic fabric the orientation of which is closely related to the mesoscopic joint pattern we present a model relating this orthorhombic crack fabric not only to external deviatoric stresses but also to internal stresses on the grain scale resulting from the strong thermal contraction of quartz relative to the feldspar framework at the deepest level 1 subvertical steep ci cracks developed normal to 3 and selectively in the quartz their formation caused a stress uncoupling of quartz aggregates from the external 3 direction so that further contraction of quartz produced steep cii cracks normal to 2 forming bridges between ci cracks at higher levels 2 subvertical the same process reactivated the ci cracks and now formed horizontal crack bridges ciii p t estimates based on fluid inclusion data and inferred geothermal gradients are 250 400 c at 1 5 3 kbar for ci cii cracks and 150 200 c at 1 2 kbar for ciii cracks the orientation of the younger open cracks which formed at higher crustal levels partly corresponds to the present regional stress field

repeating earthquakes and seismic potential along the northern longitudinal valley fault of eastern taiwan 1 the northern longitudinal valley fault in eastern taiwan creeps at the surface with a small rate of 1 cm yr but slips in large earthquakes to improve seismic hazard assessment it is important to comprehend the slip deficit rate distribution at depth we discovered 25 ml 2 1 4 6 repeating earthquakes in this area and inverted gps measurements for producing an image of the along strike spatial distribution of deep fault slip rates the repeating events are located at the depths of 10 22 km with 24 9 77 5 mm yr slip rates which are comparable with the gps derived slip rates of 47 5 5 8 mm yr at similar depth ranges based on distribution of gps derived slip deficits since 1951 the northern longitudinal valley fault has become capable of releasing stored strain in a future mw 7 3 earthquake

aligned fractures in carbonate rocks laboratory and in situ measurements of seismic anisotropy by vertical seismic profiling and shear wave analysis we show that a packet of carbonate reservoir rocks found at nearly 3000 m depth in the north german basin is seismically anisotropic for vertical paths of wave propagation the estimated velocity difference of the split shear waves is 10 no shear wave birefrigence is observed within the hangingwall which therefore has to be regarded as isotropic or transversely isotropic additional laboratory investigations of the petrography of drilled carbonate samples and of their seismic velocities show that the anisotropy is most probably caused by subvertical fractures with preferred azimuthal orientation the strike direction of the aligned fractures determined by analysis of split shear waves is approximately n55 e this value agrees with recently published directions of maximum horizontal tectonic stress in pre zechstein sediments in the eastern part of the north german basin but it is in contrast to the world stress map

seismic velocity anisotropy in mica rich rocks an inclusion model summary we calculated seismic wave velocity anisotropy caused by the preferred orientation of mica minerals by using the differential effective medium method dem spheroidal biotite crystals with their c axes coinciding with the symmetry axis of the spheroid are embedded in an isotropic matrix up to a volume ratio of 30 per cent all crystals are aligned with their c axes parallel to the symmetry axis of the effective homogeneous medium which shows transverse isotropy the effect of crystal shape on anisotropy was studied by changing the aspect ratio the ratio between the minor axis and the major axis of the spheroid from 0 01 flat spheroid to 1 sphere the s velocity anisotropy becomes large as the crystal shape becomes flat whereas the p velocity anisotropy shows only small changes with changes of the crystal shape in particular biotite generates large s wave anisotropy and the anisotropy becomes stronger as the aspect ratio of the biotite crystal becomes smaller when the volume ratio of the mica mineral is large the p wave phase velocity surface shows considerable deviation from the ellipse and the sv wave phase velocity surface forms a large bulge and crosses the sh wave phase velocity surface singularity in the plane including the symmetry axis these results show an interesting contrast when compared with the effect of crack or pore shape on seismic velocity anisotropy crack or pore shape affects the p velocity more than the s velocity we also calculated thomsen s anisotropic parameters e and as functions of the crystal aspect ratio and the mica volume ratio

crystallographic preferred orientations in eclogites a review abstract during the last decades processes taking place in subduction zones have been a topic of extensive debate there are many models on a tectonic scale but knowledge of deformation at microscopic levels is essential for an understanding of the processes involved crystallographic preferred orientation cpo investigations of minerals in eclogites yield the possibility to study deformation in the crustal part of subducted oceanic lithosphere as well as subducted continental units containing basic intrusions which are frequently exhumed during continental collision from cpo data of omphacite and garnet as well as other constituent minerals in eclogites conclusions on stress and strain at depth in currently active subduction zones can be drawn as the pressure temperature and strain path of the now exhumed rocks can be unraveled this contribution provides an overview of cpo studies of eclogites concerning slip systems deformation strain and other possible cpo forming mechanisms in all major constituent mineral phases in eclogites and the implications of these microstructural data on subduction zone processes are discussed nevertheless there are still many open questions and future research is essential

complete seismic properties obtained from microcrack fabrics and textures in an amphibolite from the ivrea zone western alps italy abstract laboratory seismic measurements of compressional wave velocities vp and shear wave splitting vs have been carried out on a clinopyroxene amphibolite from the ivrea zone western alps italy at pressures up to 600 mpa from the texture of the major minerals hornblende plagioclase and pyroxene and the respective elastic constants the elastic properties voigt average and seismic anisotropies were calculated at high confining pressure where the effect of microcracks is eliminated vp and shear wave velocities vs vss are in good agreement with the calculated velocities reflecting texture induced anisotropies microcracks are most effective at low confining pressure but are largely closed at about 200 300 mpa microscopic studies revealed that the crack fabric is characterized by oriented transgranular and cleavage cracks the bulk anisotropy at low pressure conditions was computed by superposing the texture induced anisotropy with the crack induced anisotropy these calculated values are consistent with the measured values indicating that anisotropy of vp and shear wave splitting is affected by both texture and oriented microcracks based on detailed fabric analyses the presented method allows to describe the complete elastic and seismic properties of crystalline rocks providing an ideal data basis for three dimensional seismic modelling to investigate the influence of anisotropic media on the reflectivity

shear wave splitting in the lower crust beneath the archean crust of southwest greenland abstract slant stacks of seismic data from rifted ancient archean crust along the southwest coast of greenland indicate that the lower crust is strongly seismically anisotropic the slant stack data show that a lower crustal wide angle s wave reflection has a different intercept time and ray parameter on the radial and transverse components from a receiver gather recorded on passcal reftek three component seismometers from the s wave analysis the continental crust is clearly seismically anisotropic above a high velocity wedge in the lower crust possibly magmatic underplating during late cretaceous labrador sea rifting heated the pre existing lower crust promoting plastic flow and enabling alignment of anisotropic minerals to produce the seismic anisotropy

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

shear wave evidence for an anisotropic lower crust beneath the black forest southwest germany abstract controlled shear wave sources a horizontal vibrator and dynamite were used in near vertical reflection studies to explore the nature of the reflective laminated lower crust in southwest germany the data reveal strong s wave reflections from the lower crust these lower crustal s reflections were not observed by previous wide angle surveys in the same region a laminated crustal model with isotropic layers and changing poisson s ratio cannot explain the differing near and far offset s response by introducing alternating anisotropic and isotropic lamellae this discrepancy may be resolved this seismic model is consistent with a petrological model of deformed amphibolites containing 10 30 of preferentially orientated hornblende observed amplitude differences in p and s wave reflections from the same depth in the lower crust suggest regions with a changing poisson s ratio

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact

velocity anisotropy in granodiorite and quartzite due to the distribution of microcracks summary the spatial anisotropy of p wave velocities was investigated in spherical samples of granodiorite and quartzite and correlated with the orientation of microcracks and grain boundaries determined optically by universal stage techniques the preferred orientation of normals to cleavage cracks of biotite and amphibole in granodiorite correlates well with the direction of maximum velocity increase under hydrostatic pressure although the minerals form only nine per cent of the volume irregular microcracks in an almost monomineral quartzite have only a very small effect on the velocity anisotropy although they are also preferentially oriented the nature of the microdiscontinuities is of primary importance for the velocity anisotropy observed at atmospheric and low hydrostatic pressures