anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

the influence of microstructure on seismic wave speed anisotropy in the crust computational analysis of quartz muscovite rocks summary we study the influence of microstructural variables on seismic wave speed anisotropy in crustal rocks the bulk elastic properties and corresponding wave velocities are calculated for synthetic rock samples with varying amounts of muscovite and quartz different muscovite and quartzgrainorientationsandvaryingspatialdistributionsofthemuscovitegrainstoinvestigate the sensitivity of seismic wave speed anisotropy on these characteristics the asymptotic expansionhomogenizationmethodcombinedwithfiniteelementmodellingisusedtocalculate bulk stiffness tensors for representative rock volumes and the wave velocities are obtained from these tensors using the christoffel equation the aim of this paper is to 1 demonstrate how wave speeds computed from the rigorous asymptotic expansion homogenization method compare with those generated using stiffness tensors derived from commonly applied analytic estimates and 2 explore how different microstructural variables influence seismic wave speeds our results show that the muscovite grain orientations have a significant influence on the wave speeds increasing the modal fraction and alignment of muscovite grains leads to greater seismic anisotropy of the rock the p wave speed at an incidence angle of 45 between the

separating natural and anthropogenic vertical movements in fast subsiding areas the po plain n italy case the geological and the anthropogenic components of vertical movement act on different time scales millions to thousands years and hundreds to tens of years respectively this peculiarity has been used in order to separate the factors controlling sea level changes in the po plain area the component due to long term geological processes is calculated from stratigraphic data commercial wells and seismic lines adding to this long term component the contribution of pleistocene deglaciation obtained from analytical models an estimate of the total natural component of vertical velocities is obtained the validity of these values is confirmed by comparison with velocities obtained from archaeological data and detailed palynological and paleontological analyses the anthropogenic components can be inferred by comparison between the total natural vertical velocities we calculate and vertical velocities obtained from other data sets two applications are proposed using tide gauge records and geodetic data respectively

coastal dynamics under conditions of rapid sea level rise late pleistocene to early holocene evolution of barrier lagoon systems on the northern adriatic shelf italy this multidisciplinary case study of two preserved barrier systems combined the analysis of radiocarbon datings grain size distributions high resolution seismics and shelf bathymetry with reconstructions of palaeo environmental conditions tides waves sea level change and forward modelling of barrier lagoon systems to provide an integrated view of the coastal transgressive evolution of a large sector of the northern adriatic shelf between 15 and 8 ka bp palaeoenvironmental reconstructions point to increased tidal amplitude low energy wave climate and high rates of sea level rise up to 60 mm a during the formation of the oldest preserved barrier system not vert similar90 m water depth 14 3 cal ka bp a younger barrier system 42 m water depth 10 5 cal ka bp formed under conditions of lower tidal amplitude higher wave energy and a lower rate of sealevel rise 10 mm a forward modelling suggests that the probability of barrier island overstepping during transgression is inversely proportional to tidal amplitude if all other factors are assumed equal the oldest barrier lagoon system developed under conditions of large tidal amplitude which permitted rapid transgression however this system apparently failed to keep up with the anomalously high rate of sea level rise resulting from melt water pulse 1a the youngest barrier system appears to have drowned in place due to antecedent topography as the barrier system transgressed over an ancient pleistocene alluvial plain the rapid increase in backbarrier accommodation caused an abrupt disequilibrium between shoreface and backbarrier sedimentation which led to barrier overstepping although barsim modelling indicates that tidal deposition can reduce the probability of barrier overstepping there are other driving mechanisms in our case extremely rapid sea level rise and antecedent topography which are more determinative in explaining the transgressive coastal evolution of barrier lagoon systems in the northern adriatic sea grain size analysis of shoreface deposits sampled above the transgressive ravinement surface across the northern adriatic shelf indicate a distinct relation between the sediment grain size and the rate of sea level rise during deposition which implies that progressive sorting must have been highly effective

mica deformation fabrics and the seismic properties of the continental crust abstract seismic anisotropy originating within the continental crust is used to determine kinematic flow lines within active mountain belts and is widely attributed to regionally aligned mica however naturally deformed micaceous rocks commonly show composite e g s c fabrics it is necessary therefore to understand how both varying mica content and differing intensities of multiple foliations impact on seismic interpretations in terms of deformation fields an outcrop analogue for granitic mid crustal deformed zones is used here to calibrate the seismic response against both parameters seismic responses are modelled using crystallographic preferred orientations for polymineralic micaceous granitic gneisses measured using electron back scatter diffraction the sample results are generalised by modelling the effects of variations in modal composition and the relative importance of deformation fabrics of variable orientation so called rock and fabric recipes the maximum p and s anisotropy are calculated at 16 6 and 23 9 for single foliation gneisses but for mixed i e s c foliation gneisses these values reduce to 5 8 and 7 5 respectively furthermore mixtures of multiple foliations generate significant variations in the geometry of the seismic anisotropy this effect coupled with the geographical orientation of fabrics in nature can generate substantial variations in the orientation and magnitude of seismic anisotropy especially for shear waves as measured for the continental crust using existing receiver function and teleseismic near vertical incidence methods thus maps of seismic anisotropy varying with depth in deforming continents need not imply necessarily depth varying deformation kinematics and tectonic decoupling

the effect of oriented microcracks and crystallographic and shape preferred orientation on bulk elastic anisotropy of a foliated biotite gneiss from outokumpu abstract elastic anisotropy is an important property of crustal and mantle rocks this study investigates the contribution of oriented microcracks and crystallographic lpo and shape preferred orientation spo to the bulk elastic anisotropy of a strongly foliated biotite gneiss using different methodologies the rock is felsic in composition about 70 vol sio 2 and made up by about 40 vol quartz 37 vol plagioclase and 23 vol biotite measurements of compressional vp and shear wave vs velocities on a sample cube in the three foliation related structural directions up to 600 mpa and of the 3d p wave velocity distribution on a sample sphere up to 200 mpa revealed a strong pressure sensitivity of vp vs and p wave anisotropy in the low pressure range a major contribution to bulk anisotropy is from biotite importantly intercrystalline and intracrystalline cracks are closely linked to the morphologic sheet plane 001 of the biotite minerals leading to very high anisotropy at low pressure above about 150 mpa the effect of cracks is almost eliminated due to progressive closure of microcracks the residual pressure independent part of velocity anisotropy is mainly caused by the strong alignment of the platy biotite minerals displaying a strong spo and lpo calculation of the 3d velocity distribution based on neutron diffraction texture measurements of biotite quartz and plagioclase and their single crystal properties give evidence for an important contribution of the biotite lpo to the intrinsic velocity anisotropy confirming the experimental findings that maximum and minimum velocities and shear wave splitting are closely related to foliation comparison of the lpo based calculated anisotropy about 8 with measured intrinsic anisotropy about 15 at 600 mpa give hints for a major contribution of spo to the bulk anisotropy of the rock

modelling the anisotropic seismic properties of partially molten rocks found at mid ocean ridges abstract the problem of modelling the seismic properties of mid ocean ridge rocks of the axial magma chamber amc and the low velocity triangle lvt immediately below it has been addressed using two samples from oman ophiolite as examples the specimens are a layered gabbro from the lower oceanic crustal sequence and a harzburgite from the upper most mantle section at the palaeo ridge axis the seismic properties have been simulated at a temperature of 1200 c and pressure of 200 mpa so that the basalt melt is above its solidus various effective medium methods are discussed in the perspective of modelling rocks that have a strong background elastic anisotropy due to crystal preferred orientation cpo and an introduced anisotropy due to oriented melt filled inclusions calculations using various methods show a wide range of predicted melt fractions for a given seismic velocity the self consistent scheme scs and differential effective medium dem are compared in some detail a tensorial model was developed using a poro elastic method of gassman at low seismic frequency and a standard dem with isolated basalt inclusions at high frequency at low frequency the basalt pore fluid is considered to be everywhere connected and the pressure uniform whereas at high frequency basalt inclusions are isolated assuming the medium to be a standard linear solid the low and high frequency velocities were used to calculate the anisotropy of attenuation calculations with spherical basalt inclusions show that the seismic velocities decrease and attenuation increase with increasing melt fraction the symmetry of the background anisotropy due to cpo is preserved but gradually reduced with increasing melt fraction for the seismic velocities observed for the axial magma chamber amc with v p of 3 5 to 4 7 km s the model predicts 50 70 melt for the low velocity triangle lvt below the amc with v p of 4 8 5 6 km s the model predicts 35 50 melt predictions from the observed attenuations q 1 at the amc of 0 05 0 02 and in the lvt of 0 02 0 01 are around 60 and 45 melt respectively seismic anisotropy has been modelled with ellipsoidal basalt pancake shaped inclusions with their circular sections in the xy foliation plane only a 2 3 of ellipsoidal basalt inclusions are required to over print the anisotropy of the background medium there is a rapid decrease in v p and increase of q 1 for propagation normal to the foliation z with increasing axial ratio of the inclusions with increasing axial ratio the model predicts decreasing amounts of melt for given velocity v p in the z direction for the lvt only 15 25 melt is predicted for a 10 1 inclusion instead of the 35 50 of the spherical inclusion

the influence of heat and moisture fluxes from the ocean on the development of baroclinic waves abstract numerical experiments using a two dimensional primitive equation nonhydrostatic model with idealized thermodynamics are performed to study the behavior of baroclinic waves in an environment that is saturated and subject to sensible and latent heat fluxes from the lower boundary a slantwise convective adjustment is assumed to have occurred and reduced the base state to conditional symmetric neutrality the model s perturbations exhibit two distinct phases of growth an early stage of exponential growth in which all the heating is confined to the boundary layer followed by an explosive growth almost linear with time with deepening rates near or above the conventional definition of explosive cyclones the onset of the explosive phase coincides with a hurricane like structure in wind temperature and potential vorticity which includes a narrow maximum of e at the center of the perturbation that expands as the development continues an amplitude dependence for the transition to the explosiv

mica dominated seismic properties of mid crust beneath west yunnan china and geodynamic implications abstract measurements of crystallographic preferred orientations cpo and calculations of p and s wave velocities v p and v s and anisotropy were conducted on three quartz mica schists and one felsic mylonite which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern tibetan plateau results show that the schists have v p anisotropy av p ranging from 16 4 to 25 5 and maximum v s anisotropy av s max between 21 6 and 37 8 the mylonite has lower av p and av s max but slightly higher foliation anisotropy which are 13 2 18 5 and 3 07 respectively due to the lower content and cpo strength of mica with increasing mica content the deformed rocks tend to form transverse isotropy ti with fast velocities in the foliation plane and slow velocities normal to the foliation however the presence of prismatic minerals e g amphibole and sillimanite forces the overall symmetry to deviate from ti an increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast axis of feldspar aligns parallel to the slow axis of mica and or quartz the effect of quartz on seismic properties of mica bearing rocks is complex depending on its content and prevailing slip system the greatest shear wave splitting and fastest v p both occur for propagation directions within the foliation plane consistent with the fast pms s wave converted from p wave at the moho polarization directions in the west yunnan where mica amphibole bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation the fast pms directions are perpendicular to the approximately e w orienting fast sks s wave traversing the core as p wave directions indicating a decoupling at the moho interface between the crust and mantle beneath the region the seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear waves suffer little splitting

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

preferred orientation and elastic anisotropy of illite rich shale shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals this orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals a new method is introduced that uses high energy synchrotron x rays to obtain diffraction images in transmission geometry and applies it to an illite rich shale the images are analyzed with the crystallographic rietveld method to obtain quantitative information about phase proportions crystal structure grain size and preferred orientationtexture that is the focus of the study textures for illite are extremely strong with a maximum of 10 multiples of a random distribution for 001 pole figures from the three dimensional orientation distribution of crystallites and single crystal elastic properties the intrinsic anisotropic elastic constants of the illite aggregate excluding contribution from aligned micropores can be calculated by appropriate medium averaging the illitic shale displays roughly transverse isotropy with c11 close to c22 and more than twice as strong as c33 this method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

high resolution x ray texture goniometry high resolution x ray texture goniometry hrxtg significantly improves peak background ratios and allows for the determination of crystallographic preferred fabrics of small regions 1 mm2 in heterogeneously deformed rocks the basic instrument is a commercially available automated single crystal x ray diffractometer equipped with a mo source a stage for transmission mode was constructed that is driven by the original motors so the unit is fully computer controlled absorption corrections are calculated which removes the need for generally difficult to obtain empirical corrections this combined with equipment optimization enables us to use small irradiated volumes of rocks with variable compositions the advantage of hrxtg in heterogeneously deformed rocks is demonstrated in a cleaved mudstone analysis of 1 mm2 areas in a 2 cm bed showing a gradation from micaceous sandstone to slate reveals that fabric intensity of both mica and chlorite increases significantly dm from 0 64 to 1 03 and from 0 45 to 0 78 respectively without appreciable change in the oblate shape km of the fabric thus hrxtg can record a strain state at the mm scale of heterogeneously deformed rocks

impact of sea level rise on the morphological equilibrium state of tidal inlets abstract this study addresses the question whether the geomorphology of a tidal inlet i e the coastal inlet and associated tidal basin can maintain equilibrium under a rising relative sea level when a tidal inlet system is exposed to a constant rate of sea level rise slr the system will be permanently in a state that deviates from the equilibrium state corresponding to zero slr this is a physical requirement to create a permanent incentive to import sediment into the system in case the rate of sediment import matches the rate of sea level rise a new state of dynamic morphological equilibrium is reached if the actual import rate is less than this the system s morphological state will deviate increasingly from its equilibrium and finally degenerate in this case slr has exceeded an upper boundary named state limit denoted as slrlimit and the system will not be able to reach a state of dynamic morphological equilibrium any longer and drown because the slrlimit predictions are sensitive to a variation of internal sediment exchange rate and availability of sediment at the seaward boundary of the system we assess the slrlimit predictions quasi probabilistically to gain quantitative insight into the inherent uncertainties this technique leads to an estimate of the probability distribution for the slrlimit of two selected tidal inlet systems in the dutch wadden sea the calculated probabilities comply with the available fragmentary geological data which suggest that the former tidal inlets in the western region of the netherlands were drowned under the influence of a sea level rise of 80 cm to a few metres per century

absent anisotropy the paradox of the southern alps orogen 1 a high resolution active source dataset recorded across the southern alps of new zealand displays unusually strong s wave phases which show minimal shear wave splitting a suite of methods was used to analyse the data to minimize the uncertainty in the anisotropy measurements we use the silver and chan 1991 method cross correlation of stacked data and deconvolution in combination with the other methods the results were consistent at each station but differed between stations fault parallel fast directions with delay times of 0 0 08 s were calculated from the most impulsive s wave arrivals the crustal rocks from the southern alps are strongly anisotropic in the laboratory contrasting with results shown here the minimal delay times suggest that the shear waves are affected by multiple phases of deformation in the crust

elastic moduli of anisotropic clay claymineralsareimportantcomponentsinshales controlling their elastic properties and anisotropy the elasticity of crystalline clay minerals differs significantly from that of clay in situ because of the ability of clay particles to bind water in the majority of published works only isotropic moduli for in situ clays are reported however anisotropy is inherent in the clay elasticity we develop an inversion technique for determination of thestiffnesstensorofinsituclayfromtheshale sstiffnesstensor as an example we obtain the stiffness tensor of a water clay composite from the data on the water saturated greenhorn shale sample whose clay composition consists of almost equal amounts of illite and smectite and comparable amounts of kaolinite and chlorite the stiffness tensor of the water clay composite is found for the greenhorn shale with step by step inversion based upon an effective medium theory the inversion uses a nonlinear optimization technique with bounds imposed on the estimated parameters in the inversion we apply different approaches of the effective medium theory using a published method referred to here as the generalized singular approximation gsa the gsa method makes it possible to take into account the microstructure of shales the resulting elasticity constants of the anisotropic transversely isotropic in situ clay composite are c11 23 7 c33 8 5 c44 0 8 c66 5 7 and c13 3 1 in gpa and the density equals 2 17 g cm 3 the thomsen parameters for the clay composite are 0 89 3 10 and 0 34 the elasticity constants found for this clay composite can be used in the theoretical analysis of shales that have a similar composition of clay but with different mineral compositions the inversion technique developed can be used for general shale water clay composites when the mineral composition and orientation of the clay platelets are known

seismic anisotropy and its impact on imaging the shallow alpine fault an experimental and modeling perspective the transpressional alpine fault in new zealand has created a thick shear zone with associated highly anisotropic rocks low seismic velocity zones lvz and high seismic reflectivity are recorded in the alpine fault zone but no study has explored the underlying physical rock parameters of the shallow crust that control these observations protomylonites are the volumetrically dominant lithology of the fault zone here we combine experimental measurements of p wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged numerical models that account for the porosity free real samples fabric elastic tensors from ebsd are calculated by mtex and a finite element model fem while microfractures are modeled with differential effective media dem theory at effective pressures representative of the alpine fault brittle zone experimental wave speeds are lower than those predicted by mtex fem a possible dem model suggests that a combination of random and aligned microfractures with aspect ratios increasing with pressure can explain the experimental wave speeds for pressures 70 mpa such micro porosity in the form of foliation and mica basal plane parallel microfractures and grain boundaries is validated with synchrotron x ray microtomography and tem images finally by modeling anisotropy of seismic reflection coefficients with angle of incidence we demonstrate that the high reflectivity and lvz observed at the alpine fault can only be explained if this microporosity is accounted for throughout the brittle fault zone even at depths of 7 10 km

nanga parbat crustal anisotropy implications for interpretation of crustal velocity structure and shear wave splitting the nanga parbat haramosh massif repre sents a unique exposure of mid lower continental crust from beneath the himalayan orogen seismic velocity measure ments on a suite of quartzofeldspathic gneisses show up to 12 5 velocity anisotropy for compressional waves and up to 21 for shear waves the degree of anisotropy is a func tion of mica content and rock fabric strength over 30 of the samples have maximum compressional wave velocities of 6 4 6 5 km s velocities typically associated with more mafic lithologies these results have implications for the inter pretation of crustal velocity structure obtained from wide angle seismic surveys where in situ velocity measurements are made from refracted or turning rays that potentially spend a substantial portion of their travel path propagat ing in the foliation plane velocities determined from these surveys may overestimate mean velocities of crustal rocks with well developed horizontal fabric in addition crustal anisotropy due to the development of pervasive rock fabric has the potential to be a significant contributing factor to shear wave splitting observations

late glacial to preboreal sea level rise recorded by the rhone deltaic system nw mediterranean abstract a unique late glacial preboreal record of changes in sea level and sediment fluxes originating from the alps is recorded in the rhone subaqueous delta in the western mediterranean sea the compilation of detailed bathymetric charts together with high resolution seismic profiles and long cores reveals the detailed architecture of several sediment lobes related to periods of decreased sea level rise and or increased sediment flux they are situated along the retreat path of the rhone distributaries from the shelf edge and canyon heads up to the modern coastline they form transgressive backstepping parasequences across the shelf the late holocene highstand deltas being confined to the inner shelf the most prominent feature is an elongated paleo shoreface deltaic system with an uppermost sandy fraction remolded into subaqueous dunes a long piston core into the bottomsets of this prograding unit allows precise dating of this ancient deltaic system in seismic data it displays aggradation starting at 15 cal kyr bp followed by progradation initiated during the first phase of the younger dryas a period of reduced sea level rise or stillstand the delta kept pace with resumed sea level rise during the preboreal which is estimated at about 1 cm yr as a result of increased sediment supply from the alps melting of glaciers and more humid climate flushing the sediment down to the sea abandonment of the delta occurred around 10 500 cal yr bp that is to say about 1000 yr after the end of the younger dryas probably because of decreased sediment flux

predicting seismic properties from three dimensional microstructures a new look at an old quartzite the mylonitic cambrian quartzites moine thrust zone nw scotland have long been used to study microstructural and petrofabric evolution and to develop understanding of grain scale processes accommodating large scale displacements today structural geology is entering a new age of understanding of the basic processes involved in microstructural evolution due to the emergence of novel instrumental techniques and theoretical models it seems apposite therefore to re evaluate the microstructure of one example of this classic quartz mylonite from the stack of glencoul assynt using arguably the most important of these new techniques electron backscattered diffraction ebsd the three dimensional 3d microstructure and petrofabric of this rock was analysed using ebsd to 1 corroborate previous optical and x ray texture goniometry measurements 2 investigate the potential for sampling and or tectonic sectioning bias that may be introduced inadvertently into any petrofabric analysis and 3 predict its seismic properties it is found that microstructures do differ between orthogonal structural sections leading to variations in strengths of different components in the overall petrofabric that might impact on seismic properties the results emphasize the true 3d nature of microstructures and petrofabrics which can be recognized and accommodated more readily by this new generation of analytical techniques

petrofabric derived seismic properties of a mylonitic quartz simple shear zone implications for seismic reflection profiling the link between petrofabric lpo and seismic properties of an amphibolite facies quartzofeldspathic shear zone is explored using sem ebsd the shear zone lpo develops by a combination of slip systems and dauphine twinning with a maximum parallel to lineation x and c maximum normal to mylonitic foliation xy the lpo are used to predict elastic parameters from which the three dimensional seismic properties of different shear zone regions are derived results suggest that lpo evolution is reflected in the seismic properties but the precise impact is not simple in general the p wave velocity vp minimum is parallel to the a axis maximum the direction of maximum shear wave splitting avs is parallel to mylonitic foliation and the vp maximum and avs minimum are parallel to the c axis maximum the seismic anisotropy predicted is significant and increases from shear zone wall rock to mature mylonite p wave anisotropy ranges from 11 13 fast and slow shear waves anisotropy range from 6 15 and the magnitude of shear wave splitting ranges from 9 16 nevertheless such anisotropy requires a considerable thickness of rock with this lpo before it becomes seismically visible i e 100 s m for local earthquakes 10 s m for controlled source experiments however reflections and mode conversions provide much better resolution particularly across tectonic boundaries the low symmetry and strong anisotropy due to the lpo suggest that multi azimuth wide angle reflection data may be useful in the determination of the deformation characteristics of deep shear zones a number of factors may produce elastic anisotropy in rocks including variations in the spatial distribution of mineral phases layering grain size and shape fabrics grain boundary properties and the presence of oriented pores or fractures e g kern wenk 1985 mainprice et al 2003 in addition because elastic properties vary with respect to direction in single crystals the majority of rock forming minerals are elastically anisotropic e g christensen 1966 thus deformation processes such as dislocation creep which produce strong crystal lattice preferred orientations lpo in anisotropic minerals may also induce bulk elastic anisotropy it is no surprise therefore that petrophysical properties such as seismic velocities are often highly anisotropic in bulk rock aggregates e g babuska cara 1991 understanding of the impact of microstructural variables on elastic anisotropy has been obtained typically from experimental measurements of elastic properties of minerals or theoretical models that incorporate microstructural variables e g burlini kern 1994 wendt et al 2003 experimental studies have focused primarily on the influence of fractures or lpo on the elastic properties of minerals and rocks in particular the seismic properties can be measured via direct laboratory methods at ambient or elevated temperatures and pressures e g kern 1982 although it is often difficult or impossible to obtain the complete three dimensional property orientation distribution from a single experiment however see pros et al 2003 furthermore experimental investigation of seismic properties usually involves rocks in which all microstructural fabric elements contribute effectively masking any lpo component an alternative approach is to calculate the seismic properties of a rock aggregate from individual crystal orientation measurements incorporating the single crystal elastic constants and the lpo for each mineral weighted according to its modal content e g mainprice humbert 1994 the seismic phase velocities and anisotropies then can be calculated in every direction e g mainprice silver 1993 recently the advent of electron backscattered diffraction ebsd in the scanning electron microscope sem has made it possible to measure lpo in statistically viable numbers from different minerals within a rock aggregate whilst maintaining a oneto one relationship with other microstructural elements e g mainprice et al 1993 lloyd 2000 mauler et al 2000 bascou et al 2001 in this contribution the seismic properties of an amphibolite facies mylonitic quartz shear zone are predicted by averaging the single crystal elastic properties according to the sem ebsd derived lpo in order to study the relationship between microstructure petrofabric and seismic properties this approach illustrates the usefulness of integrating geological studies of rock microstructures and particularly petrofabrics with geophysical studies of seismic properties to obtain a fuller understanding of geodynamic processes

texture analysis of a muscovite bearing quartzite a comparison of some currently used techniques abstract four well established techniques were applied to determine the mineral textures of a muscovite bearing quartzite 1 directional measurements on an optical u stage 2 x ray 3 neutron and 4 electron diffraction ebsd techniques 1 and 4 are of the single grain type and techniques 2 and 3 of the statistical or volume type experimental pole density diagrams were compared by means of the construction of pole figure differences difference pole figures which led to the observation that ebsd and u stage derived pole figures agree well even in detail in contrast pole figures derived from x ray and neutron diffraction are clearly different from pole figures derived from the single grain techniques visible as pronounced preferred orientation in the difference pole figures specific properties of the applied techniques may be responsible for the observed differences such as 1 missing proportionality to the grain volume in the single grain methods 2 the accessible sample volume 3 erroneous data correction or 4 statistical errors also the method of data treatment which is basically different for the single grain and statistical methods should be considered when pole figures are evaluated apart from purely economical constraints and availibility of equipment the decision on the most suitable method for a texture determination should be based on the scientific goals and specific properties of particular techniques texture measurements of the statistical type are well suited for determination of bulk textures of rocks e g as required for the calculation of anisotropic physical properties of rocks whereas single grain measurements are advantageous for the investigation of local textures and texture forming mechanisms

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

directional dependence of p and s wave propagation and polarization in foliated rocks from the kola superdeep well evidence from laboratory measurements and calculations based on tof neutron diffraction we have measured p and s wave velocities on two amphibolite and two gneiss samples from the kola superdeep borehole as a function of pressure up to 600 mpa and temperature up to 600 degrees c the velocity measurements include compressional vp and shear wave velocities vs1 vs2 propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes the measurements are accompanied by 3d velocities calculations based on lattice preferred orientation lpo obtained by tof time of flight neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons the lpo based numerical velocity calculations give important information on the different contribution of the various rock forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy shear wave splitting and shear wave polarization to the structural reference frame foliation and lineation comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks foliation and lineation demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions the study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation respectively c 2005 elsevier b v all rights reserved

drowned shelf edge deltas barrier islands and related features along the outer continental shelf north of the head of de soto canyon ne gulf of mexico abstract four drowned shelf edge delta complexes two drowned shelf deltas three drowned barrier islands large areas of hardground and fields of bedforms on the mid and outer continental shelf and uppermost slope north of the head of de soto canyon ne gulf of mexico were mapped with high resolution multibeam echosounder deltas formed not during the last eustatic low stand but during one or more interstadials when eustatic sea levels were only 60 to 80 m below present sea level the barrier islands and deltas must have been cemented prior to rapid falls of eustatic sea level that occurred during global glaciations cementation is necessary to have preserved the barrier islands from erosion and subsequent destruction by the rapid sea level rise during the last deglaciation the preservation of the relict bathymetry is so good that features that superficially resemble trough blowouts are found in association with one of the relict barrier islands asymmetric bedforms on the midshelf in water depths of 50 to 60 m indicate transport directions to the sw but asymmetric bedforms in water depths of the upper slope between 100 and 120 m on the s and se flanks of the drowned shelf edge deltas indicate a different current direction a separate flow that is a continuation of a sw flowing current that was previously found on the upper slope off nw florida

high resolution compositional mapping of matrix phases implications for mass transfer during crenulation cleavage development in the moretown formation western massachusetts abstract high resolution compositional maps provide a new tool for investigating mass transfer during cleavage formation the moretown formation of western massachusetts contains a well developed crenulation cleavage with alternating mica rich crenulation limbs and mica poor crenulation hinges compositional mapping shows two generations of plagioclase the second of which was synchronous with the crenulation cleavage a significant amount of the syn crenulation plagioclase 10 20 modally grew in hinge domains a small amount of syn crenulation plagioclase 1 and a large amount of phengitic muscovite grew in limb domains the maps also show that uncrenulated domains experienced mass transfer and reactivation of older cleavages and thus cannot be used as undeformed reference domains for comparison with crenulated regions compositional mapping facilitates a new degree of integration between petrologic and structural analysis knowledge of the structural context of compositional domains allows better selection of phases and compositions for interpreting metamorphic reactions and linking metamorphism to deformational stages knowledge of syntectonic reactions provides new insights into mass transfer and volume change during deformation in the moretown formation plagioclase and phengite producing reactions play a large role in controlling the nature and magnitude of mass transfer but microstructures control the location of reactants and products within the evolving fabric

a determination of the three dimensional seismic properties of anorthosite comparison between values calculated from the petrofabric and direct laboratory measurements bernard eront and david mainprice zaboratoire de tectonophysique i h iversit montpe lier ii montpe lier france nikolas i christensen department of earth and atmospheric sciences purdue unh ersity west lafayette btdiana we have undertaken a coinparative study of the seisnfic properties of an anorthosite the seisnfic properties have been calculated froin the lattice preferred orientation lpo of plagioclase 90 by volume and olivine 10 by voluine and the elastic constants of these minerals laboratory measurements of vp 24 directions and vs 6 directions have been made on the same sample at room temperature and pressures up to 1 0 gpa the twe techniques agree with 0 1 km s for all orientations studied when the voigt averaging method is used hill and reuss averaging methods give calculated velocities significantly lower than the experimental ones a study of the difference between the velocity values given by the two methods reveals a systematically larger departure in orientations normal to the foliation the orientation dependent difference between the two tedmiques can be explained if there are small errors in the elastic constants for single crystal plagioclase used in the initial calculations the axial lpo symmetry of the plagioclase with all the crystallographic b axes parallel to the specimen symmetry axis allowed us to calculate c22 norinal to 010 directly from the laboratory measurement of vp some constraints can be put on c22 c44 c66 c12 and c23 on average our data require 10 modification of the single crystal constants reported by ryzhova 1964

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

numerical modeling of crenulation cleavage development a polymineralic approach abstract the finite element method was used to investigate how the elastic interactions of quartz and muscovite minerals affect grain scale stress and strain distributions at different stages of crenulation cleavage development the polymineralic structure comprises individual grains that were each assigned their own 3d stiffness tensor and orientation gradients in mean stress and volumetric strain within quartz grains develop between the limbs and hinges of microfolds at the earliest stages of crenulation development with higher values in the microfold limbs these gradients decrease with development of the crenulation cleavage as the microfold limbs become phyllosilicate rich p domains and the hinges become quartz and feldspar rich qf domains crystallographic orientations of the quartz grains have a relatively minor effect on the mean stress and volumetric strain distributions our findings are broadly consistent with both pressure solution and strain driven dissolution models for crenulation cleavage development however because crenulation cleavage development typically involves metamorphic reactions we favor a model in which dissolution is driven by those reactions and mass transfer leading to development of the mineralogically segregated fabric is driven by pore fluid pressure gradients that follow gradients in volumetric strain local concentrations of stress and strain across mineral interfaces may identify sites of enhanced reaction

constraint of lattice preferred orientation lpo on vp anisotropy of amphibole rich rocks summary the vp anisotropies of two amphibole rich rocks and two biotite amphibole rich rocks were measured under high pressure conditions up to 1 0 gpa and calculated based on the physical properties and lattice preferred orientation lpo of amphibole and biotite the results of these studies clearly demonstrated the strong effects of the lpo of amphibole and biotite on vp anisotropies previous studies pointed out the importance of 001 of amphibole and 001 of biotite for vp anisotropy in addition to these axes and poles 100 of amphibole strongly affected the vp anisotropy of the sample rocks

grain scale processes in actively deforming magma mushes new insights from electron backscatter diffraction ebsd analysis of biotite schlieren in the jizera granite bohemian massif abstract in the porphyritic jizera granite bohemian massif three distinct types of lattice preferred orientations of biotite grains were revealed in schlieren delineated magmatic structures using the electron backscatter diffraction ebsd method 1 biotite basal planes 001 reorient from schlieren subparallel near the schlieren base to schlieren perpendicular in the upper part of the schlieren both orientations share subhorizontal n s to nne ssw trending a axes 2 in some domains the a axes are steep and at a high angle to the schlieren plane while the c axes plunge shallowly and rotate around an ill defined a axis 3 in other domains the ebsd coincides with background magnetic fabric of the host granite revealed using the anisotropy of magnetic susceptibility ams method that is the a axes plunge shallowly to the se or nw while the c axes are subhorizontal and cluster around the ne sw trend these multiple biotite orientations in the schlieren are interpreted to reflect 1 velocity gradient in laminar magma flow along channel like conduits localized within the high strength host phenocryst framework 2 grain scale gravity driven constrictional deformation of the magma mush and 3 overprinting background tectonic deformation transmitted across large parts of the magma chamber prior to its final crystallization the grain scale mechanisms of biotite fabric acquisition in the schlieren presumably involved rotation of biotite crystals during flow with the biotite alignment reflecting the flow geometry and kinematics replaced after flow cessation by melt aided grain boundary sliding of those biotite crystals still enclosed in melt pockets within otherwise static highly crystallized magma mush the latter process was sufficient to reorient biotite grains but not to cause destruction of the schlieren using the jizera granite as a case example we argue that the lattice preferred orientation of mineral grains in mafic schlieren is highly sensitive to reorient in response to processes both associated with the schlieren formation e g localized magma flow and those that occur later and are superimposed onto the effectively solid high strength magma mush

strain localization and porphyroclast rotation it has been debated for decades whether rigid inclusions such as porphyroclasts and porphyroblasts do or do not rotate in a softer matrix during deformation experiments and numerical simulations with viscous matrix rheologies show ongoing rotation of circular inclusions whereas using mohr coulomb plasticity results in nonrotation because the rocks in which inclusions are found normally undergo deformation by dislocation creep we applied a full field crystal plasticity approach to investigate the rotation behavior of rigid circular inclusions we show that the inclusion9s rotation strongly depends on the anisotropy of the matrix minerals strongly anisotropic minerals will develop shear bands that reduce the rotation of inclusions inhibition of rotation can only occur after a significant amount of strain our results may help to explain why geologic rigid objects often show evidence for rotation but not necessarily in accordance with the viscous theory that is usually applied to these systems

the influence of crenulation cleavage development on the bulk elastic and seismic properties of phyllosilicate rich rocks abstract the anisotropy of seismic wave propagation is strongly influenced by the mineralogy and microstructure of rocks phyllosilicates are elastically highly anisotropic and are therefore thought to be important contributors to seismic anisotropy in the continental crust crenulation cleavage is one of the most common microstructural fabrics found in multiply deformed phyllosilicate rich crustal rocks we calculated the bulk elastic properties and resulting wave velocities for rock samples that preserved three different stages of crenulation cleavage development an initial planar foliation a moderately developed crenulation cleavage and a well developed crenulation cleavage mineral orientation maps were obtained using electron backscatter diffraction and calculations were made using asymptotic expansion homogenization combined with the finite element method the difficulties involved with sample preparation and data acquisition of phyllosilicate rich rock samples are also discussed we compare our results to more conventional methods for calculating an aggregate stiffness matrix from a mineral orientation map namely voigt and reuss averages these averages do not account for grain scale interactions and therefore deviate from the results calculated using asymptotic expansion homogenization our results show that the rocks characterized by a planar foliation and a moderately developed crenulation cleavage are highly anisotropic with p wave anisotropies up to 30 9 and s wave anisotropies up to 34 2 whereas the rock characterized by a well developed crenulation cleavage is only mildly anisotropic with a p wave anisotropy of 15 5 and s wave anisotropy of 10 7 progressive development of the fabric also causes the orientations of p and s wave velocity maxima and s wave polarization directions to change markedly despite the high anisotropy imparted by a planar schistosity the variety of folds and fabrics typically found in phyllosilicate rich rocks within larger scale crustal volumes will tend to mute the anisotropy possibly to the point of appearing nearly isotropic

sequential porphyroblast growth and crenulation cleavage development during progressive deformation abstract six stages of crenulation cleavage development during a single deformation event d2 can be recognised in both matrix and porphyroblast inclusion trails in the robertson river formation n e australia these stages progress from undeformed to crenulation and differentiated crenulation of s1 through development of differentiated crenulation cleavage s2 and differentiated schistosity s2 to homogeneous foliation s2 these rocks underwent prograde metamorphism during d2 and chloritoid garnet staurolite andalusite and sillimanite isograds have been mapped most rocks are rich in porphyroblasts which commonly contain well defined inclusion trails the geometry of these trails varies from one mineral type to the next depending on the timing of porphyroblast growth relative to the stage of crenulation cleavage development in the schistose matrix the deformation history involved progressive bulk inhomogeneous shortening and the strain is very heterogeneous on all scales partly as a consequence of this hence each of the six stages of crenulation cleavage development formed locally at various times during d2 therefore if a porphyroblast grew late in the deformation it could overgrow all stages of crenulation cleavage development including the very early ones the temperature increased during metamorphism in any one locality and consequently some porphyroblasts overgrew others that were unstable in the new conditions preserving them from destruction hence the precise timing of mineralogical reactions deduced from isograds and mineral chemistry relative to the stages in schistosity development can also be determined in the andalusite zone the sequence of porphyroblasts in decreasing order of age is biotite garnet biotite staurolite andalusite dissolution of garnet occurred during growth of staurolite and especially andalusite and dissolution of staurolite accompanied andalusite growth

characteristics of deep crustal seismic anisotropy from a compilation of rock elasticity tensors and their expression in receiver functions rocks in the continental crust are long lived and have the potential to record a wide span of tectonic history in rock fabric mapping rock fabric in situ at depth requires the application of seismic methods below depths of microcrack closure seismic anisotropy presumably reflects the shape and crystallographic preferred orientations cpos influenced by deformation processes interpretation of seismic observables relevant for anisotropy requires assumptions on the symmetry and orientation of the bulk elastic tensor we compare commonly made assumptions against a compilation of 95 bulk elastic tensors from laboratory measurements including electron backscatter diffraction ebsd and ultrasound on crustal rocks the majority of samples developed fabric at pressures corresponding to mid lower crustal depths tensor symmetry is a function of mineral modal composition with mica rich samples trending towards hexagonal symmetry amphibole rich samples trending towards an increased orthorhombic symmetry component and quartz feldspar rich samples showing a larger component of lower symmetries 77 of samples have a best fit hexagonal tensor with slow axis symmetry as opposed to mantle deformation fabric that usually has fast axis symmetry the best fit hexagonal approximation for crustal tensors is not elliptical but deviates systematically from elliptical symmetry with increasing anisotropy an observation that affects the magnitude and orientation of anisotropy inferred from receiver function and surface wave observations we present empirical linear relationships between anisotropy and ellipticity for crustal rocks the maximum out of plane conversion amplitudes in receiver functions scale linearly with degree of anisotropy for non elliptical symmetry the elliptical assumption results in a bias of up to 1 4 times true anisotropy

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

amphibole and lower crustal seismic properties abstract measurements of seismic anisotropy frequently offer insights of the deformation kinematics in situ within the earth in the continental crust seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation lpo of mica crystals however determinations of composition suggest that the deep continental crust contains rather little mica in this contribution the role of amphibole a far more plausible constituent especially for deep continental crust of basic composition is assessed a field analogue approach is adopted where the lpo are measured correlated with the strain state of the rocks and used to calculate the seismic properties the seismic properties may be up scaled through the specimen using the modal proportions of the constituent mineral phases to examine the role of composition in controlling the intensity of seismic anisotropy seismic properties are computed using an array of modal compositions so called rock recipes the case history comes from the central block of the lewisian of nw scotland where a regional basic dyke swarm the scourie dykes is locally deformed within amphibolite facies shear zones conditions that are representative of the deep crust shear strain profiles across a 100 m wide shear zone using deflected banding in the host gneisses yield values of 0

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

seismic anisotropy of shales shales are a major component of sedimentary basins and they play a decisive role in fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid lithology and pore pressure from seismic data and to understand time to depth conversion errors and non hyperbolic moveout a single anisotropy parameter thomsen s parameter is sufficient to explain the difference between the small offset normal moveout velocity and vertical velocity and to interpret the small offset avo response the sign of this parameter is poorly understood with both positive and negative values having been reported in the literature is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles if the ratio of the normal to shear compliance of the contact regions exceeds a critical value the presence of these regions acts to increase and a change in the sign of from the negative values characteristic of clay minerals to the positive values commonly reported for shales may occur misalignment of the clay particles can also lead to a positive value of for transverse isotropy the elastic anisotropy parameters can be written in terms of the coefficients w 200 and w 400 in an expansion of the clay particle orientation distribution function in generalized legendre functions for a given value of w 200 decreasing w 400 leads to an increase in while for fixed w 400 increases with increasing w 200 perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of w 200 and w 400 given by w max 200 10 8 2 and w max 400 3 2 8 2 a comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the w 200 w 400 plane defined by w 400 w 200 w max 400 w max 200

an experimental and numerical study of the microstructural parameters contributing to the seismic anisotropy of rocks 1 the elastic properties of rocks are influenced by several microstructural variables including the lattice preferred orientation and grain shape fabric of the mineral phases variations in the spatial distribution of the mineral phases the properties of the grain boundaries and the presence of porosity fractures consequently in principle directional variations in these variables can be inferred from seismic velocity anisotropy observations experimental seismic velocity measurements made on rocks of well characterized microstructure may be used to improve the quality of such interferences however since most rocks are microstructurally complex in order to interpret the measurements fully theoretical analyses which can accommodate all the relevant microstructural variables are required theoretical analyses of the requisite sophistication have only recently been developed we have tested one of these due to ponte castaneda and willis by using it to calculate the elastic properties of an upper mantle harzburgite and by then comparing the results with experimental velocity measurements to determine if the values of those microstructural variables which are difficult to quantify grain boundary properties fracture shape are physically realistic we find that they are and conclude that the ponte castaneda and willis analysis provides a powerful method for a more detailed assessment of the causes of elastic property anistropy in rocks than has previously been possible

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu

crustal structure of the eastern alps along the transalp profile from wide angle seismic tomography abstract the objective of the transalp project is an investigation of the eastern alps with regard to their deep structure and dynamic evolution the core of the project is a 340 km long seismic profile at 12 e between munich and venice this paper deals with the p wave velocity distribution as derived from active source travel time tomography our database consists of vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30 km wide corridor along the profile in order to derive a velocity and reflector model we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography 8000 travel time picks from dense vibroseis recordings provide the basis for high resolution in the upper crust explosion seismic wide angle reflection travel times constrain both deeper crustal velocities and structure of the crust mantle boundary with low resolution in the resulting model the adriatic crust shows significantly higher p wave velocities than the european crust the european moho is dipping south at an angle of 7 the adriatic moho dips north with a gentle inclination at shallower depths this geometry suggests s directed subduction azimuthal variations of the first break velocities as well as observations of shear wave splitting reveal strong anisotropy in the tauern window we explain this finding by foliations and laminations generated by lateral extrusion based on the p wave model we also localized almost 100 local earthquakes recorded during the 2 month acquisition campaign in 1999 seismicity patterns in the north seem related to the inn valley shear zone and to thrusting of austroalpine units over european basement the alignment of deep seismicity in the trento vicenza region with the top of the adriatic lower crust corroborates the suggestion of a deep thrust fault in the southern alps