upper mantle anisotropy beneath the geoscope stations seismic anisotropy has been widely studied this last decade particularly by measuring splitting of vertically propagating core shear waves the main interest in this technique is to characterize upper mantle flow beneath seismic stations on the other hand the major restriction in this method is that a single station gives a single anisotropy measurement alternative methods have been developed in order to avoid this restriction an accurate determination of upper mantle seismic anisotropy beneath a seismic station may allow one by doing anisotropy correction to characterize remote or deeper anisotropy the geoscope network is ideal for this purpose because it is composed of a large set about 26 of high quality broadband seismometers globally distributed and because some of these stations have run for more than 10 years and most of them for more than 5 years we selected about 100 events at each site generally of magnitude mb 6 0 and we performed systematic measurements of the splitting parameters fast polarization direction and delay time t on sks skks and pks phases splitting on oceanic islands has been difficult to observe owing to the low quality of the signal but also perhaps owing to complex upper mantle structures beneath the stations station kip kipapa hawaii in the pacific is the only oceanic geoscope station with a clear anisotropy we determined well constrained splitting parameters for 10 of the 17 continental stations that may be explained by a single anisotropic layer the poor correlation between fast polarization directions and the absolute plate motion together with the apparent incoherence between the plate velocities and the observed delay times suggest that a simple drag induced asthenospheric flow alone fails to explain most of the observations for some stations located on or near major lithospheric structures tam tamanrasset algeria for instance we observe a good correlation between fast polarization directions and regional structures at station scz santa cruz california we found clear variations of the splitting parameters as a function of the event backazimuth compatible with two layers of anisotropy three stations can canberra hyb hyderabad india and ssb saint sauveur badole france seem to be devoid of detectable anisotropy

quantification of rock mass damage in underground excavations from microseismic event monitoring abstract rock mass damage assessment is required for many applications in rock engineering practice including support design contamination transport control stope design amongst others while various methods such as displacement measurement seismic refraction and direct observation using borehole camera have been used relatively few efforts have been made to use microseismic monitoring to quantify the rock mass damage from laboratory tests it is well known that microseismic events are indicators of fracturing or rock damage as the rock mass is brought to failure at high stress by capturing the microseismic events underground excavation induced rock mass degradation or damage can be located but can the amount of damage in terms of changes to strength or deformation properties be measured in the present study a method of characterizing rock mass damage near excavations based on microseismic event monitoring is developed and a damage driven numerical model is presented that takes the microseismic data as input to determine the damage state described by fracture density the approach is built on the discovery that a realistic crack size corresponding to a seismic event can be established by applying a tensile cracking model instead of the traditional shear model commonly used in earthquake analysis the rock mass is softened by the introduction of cracks and this is simulated by a micro mechanics based constitutive model the material property input for the model are young s modulus poisson s ratio of the intact rock and information obtained from the monitoring of microseismic events such as the location and the source size of each event calculated from source parameters using data from the atomic energy of canada limited mine by experiment this model has been verified by investigating the linkage between microseismicity rock mass damage and ground deformation it is found that when damage related softening based on microseismic data is considered predicted rock mass displacements are in good agreement with extensometer measurements

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

seismic anisotropy of south african upper mantle xenoliths abstract seismic properties of six upper mantle xenoliths from south africa were determined both by laboratory measurements at elevated pressure and numerical calculations from petrofabric analyses in order to provide constraints on the structural interpretation of the field seismic data obtained in recent years the samples studied include harzburgite garnet harzburgite mica harzburgite lherzolite and garnet lherzolite average anisotropies calculated from petrofabrics are 5 4 for v p and 4 4 for v s ultrasonic measured anisotropies from xenolith rock cores are approximately 1 lower than calculated values this difference is likely due to simplifications in modal mineralogy used in the calculations and small amounts of alteration in the samples used in the velocity measurements comparison of laboratory data with the sks and p n data yields possible structural orientations in the upper mantle beneath the south africa continent our results suggest that foliation in the upper mantle is likely horizontal and the stretching lineation olivine a axis is oriented n30 e which coincides with the absolute plate motion apm of the south african continent it is apparent from our data that the fast s wave polarization depends on the propagation direction with respect to petrofabric orientations and does not always indicate the stretching lineation

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

sea ice atmosphere and upper ocean variability in the weddell sea antarctica a frequency domain singular value decomposition is performed on 20 years 1979 1998 of monthly sea ice concentration sea ice drift and sea level pressure data in the weddell sea antarctica interannual oscillations with periods of around 3 4 years are found to dominate the variability in this region anomalous atmospheric patterns periodically reach the weddell sea from the west and perturb the sea ice circulation and distribution in the weddell gyre through changes in the intensity and direction of the climatological winds sea ice accumulates in the southeastern weddell sea every 3 4 years owing to two atmospherically driven processes 1 weak ice export to the north due to a weak northward branch of the gyre driven by weak southerly winds and 2 large ice import from the east due to a strong east wind drift driven by strong easterly winds along the coast the opposite situation gives rise to a depletion of sea ice in the same region half a cycle later sea ice anomalies are then advected north northeastward before turning eastward in the gyre circulation the eastward propagation of ice anomalies along the ice margin accounts for the passage of the antarctic circumpolar wave through the atlantic sector of the southern ocean a low frequency signal is also detected in the weddell sea variations albeit rather speculatively in this 20 year long record sea ice variability on this timescale appears to be associated with a change in the shape and characteristics of the weddell gyre circulation around 1990 this mode of variability implicates feedbacks between the gyre and weddell deep water temperature variations whose impact is observed near the maud rise topographic feature

seismic anisotropy and mantle creep in young orogens summary seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere we discuss the origin of anisotropy at various depths and relate it to tectonic stress geotherms and rheology the anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine and may result from ductile deformation dynamic recrystallization or annealing anisotropy beneath young orogens has been measured for the seismic phase pn that propagates in the uppermost mantle this anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event and thus provides information on the process of mountain building whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts pn anisotropy is aligned parallel to the structural axis we interpret this to indicate mountainparallel ductile i e creeping deformation in the uppermost mantle that is a consequence of mountain perpendicular compressive stresses the preferred orientation of the fast axes of some anisotropic minerals such as olivine is known to be in the creep direction a consequence of the anisotropy of strength and viscosity of orientated minerals in order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal escape or extrusion tectonics to the uppermost mantle we present rheological model calculations to support this hypothesis mountain perpendicular horizontal stress determined in the upper crust and mountain parallel seismic anisotropy in the uppermost mantle require a zone of ductile decoupling in the middle or lower crust of young mountain belts examples for stress and mountain parallel pn anisotropy are given for tibet the alpine chains and young mountain ranges in the americas finally we suggest a simple model for initiating mountain parallel creep

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

fabric related seismic anisotropy in upper mantle xenoliths evidence from measurements and calculations the seismic properties and their directional dependence have been measured in four mantle peridotites from picritic tuffs vitim baikal region russia geothermobarometric data suggest a source depth for the xenoliths corresponding to the spinel garnet transition zone 40 90km the experimental data include the measurement of p and s wave velocities and densities at confining pressures to 600 mpa and temperatures to 600 c and the determination of velocity anisotropy and shear wave splitting the measured velocities are compared with velocity calculations based on lattice preferred orientation lpo of olivine orthopyroxene the modal composition of the rocks and the single crystal stiffness coefficients macroscopic velocity anisotropy is strongly controlled by the lpo of olivine measured 600 mpa room temperature and calculated p wave anisotropies compare fairly well although the experimentally determined velocities are markedly lower than the calculated velocities the correspondence between measured and calculated shear wave splitting data is less pronounced this is attributed to grain boundary effects retrogressive reactions interstitial glass incomplete crack closure and to the fact that the lpo of the cpx fraction has not been included in the calculation the magnitude of p wave anisotropy corresponds to that observed in mantle peridotites exposed at the surface ivrea zone northern italy ronda southern spain

pressure and temperature dependence of p and s wave velocities seismic anisotropy and density of sheared rocks from the sierra alpujata massif ronda peridotites southern spain seismic wave velocities and densities and their pressure and temperature dependence of rock samples recovered from surface exposures at the sierra alpujata were determined in order to better understand the petrological controls on velocity and density the rock samples studied are representative of the major lithologies of the ronda ultramafic body and its metamorphic aureole the suite of ultramafic rocks includes dunite harzburgite and lherzolite exhibiting different degrees of deformation and serpentinization the rocks representing the metamorphic aureole comprise coarse grained migmatites to ultramylonitic migmatites gneisses and eclogites the experimental data include measurements of elastic wave velocities vp vs and densities at confining pressures up to 600 mpa and temperatures up 600 c at 600 mpa the determination of the pressure and temperature derivatives of velocities and densities and the determination of velocity anisotropy average p and s wave velocities at 600 mpa for rocks of the ultramafic body vary from 6 47 to 8 22 km s 1 and 3 27 to 4 75 km s 1 respectively mainly due to different degrees of serpentinization maximum vp and vs anisotropy is about 8 0 and 9 5 respectively and is primarily related to the preferred orientation of olivine in rocks of the metamorphic aureole average p velocities are in the range 5 61 7 23 km s 1 and s velocities vary from 3 48 to 4 04 km s 1 p and s velocity anisotropy is highest about 6 4 and 4 6 in sheared rocks mylonites and is mainly due to the preferred orientation of biotite and sillimanite the geophysical significance of the experimental data is briefly discussed

contrasting seismic reflectivity of the lower crust and uppermost mantle between ne japan and sw japan as illustrated by petrophysical analyses of mafic and ultramafic xenoliths 1 petrophysical analyses of mafic and ultramafic xenoliths reveal large contrasts in acoustic impedance between the lower crustal rocks and uppermost mantle rocks both beneath ichinomegata crater in ne japan and beneath oki dogo island in sw japan in contrast to minor contrasts in acoustic impedance both among the lower crustal rocks and among the uppermost mantle rocks beneath ichinomegata crater relatively large contrasts in acoustic impedance are present beneath oki dogo island between granulite and olivine gabbro in the lower crustal rocks as well as between plagioclase bearing wehrlite and other cumulus peridotites in the uppermost mantle rocks based on the existing petrologic models of the lower crust and uppermost mantle beneath ichinomegata crater and oki dogo island we then constructed model structures of the lower crust and uppermost mantle beneath these two areas composed of units with randomly arranged 100 m thick foliation parallel horizontal layers of xenolith samples and used these model structures to examine the seismic reflectivity beneath these two areas the results suggest the presence of strong seismic reflectors between the lower crust and the uppermost mantle in both areas although no other recognizable seismic reflector is expected beneath ichinomegata crater many seismic reflectors due to the above contrasts in acoustic impedance are expected both in the lower crust and in the uppermost mantle beneath oki dogo island thus a remarkable contrast in seismic reflectivity in the lower crust and uppermost mantle is likely present between these two areas as well as between ne japan and sw japan

seismic monitoring system for landslide hazard assessment and risk management at the drainage plant of the peschiera springs central italy abstract the assessment of landslide hazards and design of strategies for managing the related risk have been widely studied topics in the scientific community due to the settlements infrastructures and tourist and cultural heritage sites that may be threatened by deformations involving unstable slopes engineering geological and geophysical techniques have been recently integrated in multidisciplinary approaches to study gravity induced slope instabilities and monitor their evolution the slope that hosts the peschiera springs drainage plant central italy is involved in a mass rock creep process associated with deep karst dissolution due to the importance of this infrastructure which provides water to the rome aqueduct an accelerometric network was installed in 2008 and a nanoseismic array was added in 2014 in this paper data recorded by the nanoseismic array were used to locate 397 microseismic events related to the slope instability process distinguished into two types with different waveforms 16 failures and 381 collapses the failures were distributed throughout the slope while the collapses exhibited two spatially separate clusters below the groundwater level at a depth where karst processes produce cavities the clusters were analysed as two distinct microseismic sources characterised by specific frequency magnitude curves of events that describe their attitude to produce events of different magnitudes regarding the accelerometric network an automated procedure was developed for quickly analysing the seismic records which include signals from teleseisms and near to far field earthquakes that can induce deformation in the landslide involved slope the results obtained by the two seismic monitoring systems were integrated with the aim of implementing a landslide hazard matrix based on the statistical frequency of the occurrence of such events and their probability of exceedance during a reference period providing a useful tool for managing the related landslide risk

on the forcing of planetary scale rossby waves by antarctica the propagation of rossby waves forced at high latitudes into middle and low latitudes is studied using the barotropic vorticity equation on the sphere ray tracing theory indicates that fundamental differences exist between the response of an atmosphere initialized with typical northern hemisphere winter flow and typical southern hemisphere winter flow to such a forcing with a substantial response more likely for the southern hemisphere case integrations with a fully nonlinear barotropic model confirm this suggestion and indicate that away from the local forcing region linear theory provides a good description of the response the most notable feature in the steady solutions is a split of the mid latitude jet close to new zealand the location of this split coincides well with a region where blocking is observed to be prevalent in the southern hemisphere

damage evolution and stability analysis of the jianchuandong dangerous rock mass in the three gorges reservoir area abstract to analyze the deformation mechanism and to evaluate the stability of a dangerous rock mass we investigated the jianchuandong dangerous rock mass jdrm in the three gorges reservoir area by generalizing the jdrm mechanical model we found that the damage and degradation of the base rock mass will eventually lead to its collapse the weight of the upper rock mass and the periodic change in the reservoir water level result in a weakened and increasingly damaged base rock mass based on data from laboratory tests we created constitutive damage models for the base rock mass under dry wet conditions applying these models allowed us to quantify the damage and the stability of the submerged dangerous rock mass over time in this new method the effective axial pressure can be determined from the damage variables and that pressure informs the stability of the dangerous rock mass this new modeling technique was validated by the similarity between our calculated constraints on the effective axial pressure of the jdrm and the actual on site pressure monitoring results furthermore because our new methodology reveals that the jdrm will become unstable after two dry wet cycles we recommend that measures be taken to reinforce the jdrm as soon as possible

a tensile model for the interpretation of microseismic events near underground openings for small scale microseismic events the source sizes provided by shear models are unrealistically large when compared to visual observations of rock fractures near underground openings a detailed analysis of the energy components in data from a mine by experiment and from some mines showed that there is a depletion of s wave energy for events close to the excavations indicating that tensile cracking is the dominant mechanism in these microseismic events

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

can the equatorial ocean quickly respond to antarctic sea ice salinity anomalies 1 el nino southern oscillation enso plays a critical role in many of the extremes or anomalies of climate causing floods droughts and the collapse of fisheries recent studies have revealed a statistically significant link between equatorial processes and sea ice anomalies in the southern ocean the generally accepted view is that the primary interaction of the equatorial and polar oceans takes place via the atmosphere indeed the lag in these processes is usually of the order of a few months and is much too quick to be connected with ocean currents the question is can climate anomaly signals effectively and rapidly propagate by another oceanic mechanism it is demonstrated that signals generated by anomalies in the antarctic sea ice cover salinity distribution can propagate in a wave like manner in the form of fast moving barotropic rossby waves such waves propagates from the drake passage to the western pacific in only few days this signal is reflected at the western boundary of the pacific and generates an coastally trapped kelvin wave moving equatorwards the resulting temperature anomaly propagates northwards along the western coastline to the vicinity of the equator and increases in amplitude in time the anomaly in the western edge of the equatorial pacific then begins to move eastward along the equator as a trapped equatorial wave after about 2 3 months this wave reaches the eastern coast this process is suggested as one possible direct mechanism by which the extra tropical ocean can induce anomalies in the equatorial ocean

teleconnections in the southern hemisphere abstract teleconnections are calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the southern hemisphere 10 90 s for five month winter and summer seasons the monthly means were calculated from australian analyses for the period from june 1972 to november 1980 zonally averaged anomalies at both sea level and 500 mb display an out of phase relation between low and high latitudes and in midlatitudes are negatively correlated with anomalies in the subtropics and polar regions in winter a striking zonal wavenumber 3 pattern is found over the southern ocean anomalies in 500 mb geopotential heights at 50 s 95 e 58 s 150 w and 38 s 15 w exhibit strong positive correlations while showing weaker negative correlations with heights over antarctica and in low latitudes a similar pattern appears in sea level pressure in summer anomalies in 500 mb geopotential height over the three subtropical continents appear to occur out of phase with anomalies over the su

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

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

structural characteristics of columnar jointed basalt in drainage tunnel of baihetan hydropower station and its influence on the behavior of p wave anisotropy abstract researches about the structural characteristics of rock mass are the basis for understanding their failure modes mechanism properties as well as evaluation of structural stability during the process of excavation natural columnar jointed basalt has complex structures and exhibits remarkable anisotropy and size effect in this study the observation window method was firstly applied to describe the natural columnar joints and pillar shapes at engineering scale and then the structural characteristics of columnar joints were analyzed the roughness of columnar joints scanned from large size rock core obtained at drainage tunnel 1 1 was secondly investigated based on the 3d scanning method some techniques such as field statistical analysis and ct scanning were used to analyse the characteristics of internal implicit joints in columnar jointed basalt thirdly the large scale columnar jointed basalt cores were tested by p wave which assisted to investigating the anisotropy of columnar jointed basalt the experimental and analytical results indicate that at the engineering scale natural columnar jointed basalt is heterogeneous exhibiting the features of mosaic structure and mainly quadrilateral in shape at the large size rock core scale the roughness of columnar joints is low with the value of 5 558 at the basalt column scale the internal implicit joints are not randomly distributed instead showing obvious tendency the internal implicit joints and columnar joints are important factors contributing to the special failure mode of columnar jointed basalt at the rock core scale with increasing angle between the p wave propagation direction and column the anisotropy of columnar jointed basalt core gradually increases and the degree of anisotropy is proportional to the number of columnar joints the internal implicit joints could also affect the p wave anisotropy of basalt column and the results in this study can provide some references for projects related to columnar jointed rock mass

mechanical behavior of structurally reconstructed irregular columnar jointed rock mass using 3d printing abstract baihetan hydropower station is one the most famous hydroelectric projects in china the columnar jointed rock mass cjrm is widely distributed in this area such as at the dam site and drainage tunnel the rocks surrounding cjrm are usually unstable due to its discontinuity therefore the investigation of mechanical properties of cjrm is essential to designing relevant structures in recent years several previous studies have been conducted to determine the mechanical properties of regular cjrm reconstructed using the mixture of water cement and sand however few studies have been conducted on the irregular cjrms formed in nature because of their structural uniqueness in this study the mechanical properties of irregular cjrms reconstructed using 3d printing technology was investigated and verified through laboratory test first the sampling window method was adopted to obtain the structural characteristics of columnar jointed basalts cjbs after this the mechanical properties i e uniaxial compressive strength ucs uniaxial tensile strength uts peak shear strength residual shear strength failure mode and acoustic emission ae characteristics of the reconstructed and natural cjbs in the laboratory tests were compared based on the similarity constant the results show that the mechanical properties of irregular cjrm reconstructed using 3d printing are consistent with the in situ specimens when considering the similarity constant finally based on a detailed discussion of the reconstructed and original irregular cjrm a new method to accurately reconstruct the structure of irregular cjrms using 3d printing is suggested and verified this method could be used to design irregular cjrms in rock engineering

sea ice atmosphere signal of the southern oscillation in the weddell sea antarctica abstract composite analysis of weekly ship and shore observations of the weddell sea pack ice for extreme events of the southern oscillation so occurring in the 1929 62 period reveals strong variations in ice water concentrations in the early and late summer melt season substantially reduced ice concentrations more open water occur in december and early january of warm el nino events yr0 compared with the summer before yr 1 and appear connected with the change to a stronger cyclonic atmospheric circulation over higher latitudes of the south atlantic similarly consistent meteorology sea ice associations appear to characterize the mid to late summer of warm so events yr0 compared with yr0 of cold events there is some evidence that the regionally dependent pressure and wind reversals and possibly the associated sea ice concentration changes in the weddell sector have become more marked during so events occurring since about the early 1950s some corroboration of changes in the sea ice

seismic anisotropy under extended crust evidence from upper mantle xenoliths cima volcanic field california abstract a model of p wave velocity anisotropy and shear wave splitting for upper mantle under extended crust is derived from comparisons of seismic field measurements and observed xenolith anisotropies seismic velocity measurements and anisotropies calculated from petrofabric measurements of 15 upper mantle xenoliths from the cima volcanic field eastern mojave desert california show average maximum anisotropies of 6 9 for v p and 4 5 for v s xenolith compressional wave velocities corrected for upper mantle temperature and pressure agree well with field observations in the vicinity of the cima volcanic field the velocities calculated from the olivine fabrics suggest that upper mantle foliations beneath the region are horizontal and lineations trend ene the fabrics are believed to originate from early cenozoic extension in the area which had the same trend as the lineations the unusually high upper mantle temperatures in this region apparently have not significantly affected upper mantle fabrics

response of the intertropical convergence zone to antarctic ice sheet melt past cooling events in the northern hemisphere have been shown to impact the location of the intertropical convergence zone itcz and therewith induce a southward shift of tropical precipitation here we use high resolution coupled ocean atmosphere simulations to show that reasonable past melt rates of the antarctic ice sheet can similarly have led to shifts of the itcz albeit in opposite direction through large scale surface air temperature changes over the southern ocean through sensitivity experiments employing slightly negative to large positive meltwater fluxes we deduce that meridional shifts of the hadley cell and therewith the itcz are to a first order a linear response to southern hemisphere high latitude surface air temperature changes and antarctic ice sheet melt rates this highlights the possibility to use past episodes of anomalous melt rates to better constrain a possible future response of low latitude precipitation to continued global warming and a shrinking antarctic ice sheet

style of active intraplate deformation from gravity and seismicity data the baikal rift asia to better understand how active deformation localizes within a continental plate in response to extensional and transtensional tectonics a combined analysis of high quality gravity bouguer anomaly and seismicity data is presented consisting of about 35000 earthquakes recorded in the baikal rift zone this approach allows imaging of deformation patterns from the surface down to the moho a comparison is made with heat flow variations in order to assess the importance of lithospheric rheology in the style of extensional deformation three different rift sectors can be identified the southwestern rift sector is characterized by strong gravity and topography contrasts marked by two major crustal faults and diffuse seismicity heat flow shows locally elevated values correlated with recent volcanism and negative seismic p velocity anomalies based on earthquake fault plane solutions and on previous stress field inversions it is proposed that strain decoupling may occur in this area in response to wrench compressional stress regime imposed by the india asia collision the central sector is characterized by two major seismic belts the southernmost one corresponds to a single steeply dipping fault accommodating oblique extension in the centre of lake baikal a second seismic belt is associated with several dip slip faults and subcrustal thinning at the rift axis in response to orthogonal extension the northern rift sector is characterized by a wide low bouguer anomaly which corresponds to a broad high topographic dome and seismic belts and swarms this topography can be explained by lithospheric buoyancy forces possibly linked to anomalous upper mantle at a more detailed scale no clear correlation appears between the surficial fault pattern and the gravity signal as in other continental rifts it appears that the lithospheric rheology influences extensional basins morphology however in the baikal rift the inherited structural fabric combined with stress field variations results in oblique rifting tectonics which seem to control the geometry of southern and northeastern rift basins

rockburst and microseismic characteristics around lithological interfaces under different excavation directions in deep tunnels abstract sandstone hard rock and siltstone relative soft rock appeared alternately during tunnel boring machine tbm excavation of two headrace tunnels at the neelum jhelum hydropower station in pakistan rockbursts occurred frequently near these sandstone siltstone interfaces seriously threatening the safety of personnel and equipment in situ rockburst investigations and microseismic monitoring were conducted to study the characteristics of these rockbursts and their associated microseismic activities around the lithological interfaces under different excavation directions i e the tbm passing though sandstone and siltstone in different sequences the results show that the rockburst frequency and intensity are greater during excavation from sandstone to siltstone than those during excavation from siltstone to sandstone within 15 m around the lithological interfaces moreover the number of miroseismic events the amount of microseismic radiated energy and the proportion of high energy or large microseismic events are higher during excavation from sandstone to siltstone than those during excavation from siltstone to sandstone in the selected zone in addition the differences in the rockburst and microseismicity characteristics between sandstone and siltstone are also analysed in the selected zone finally a simple 3d numerical model is employed to assess the rockburst risks in different excavation directions the results of which agree well with field rockburst results the formation mechanisms of different rockburst risks under the two excavation directions are discussed and analysed with microseismic data and numerical results this study may be valuable for predicting rockburst based on microseismic techniques and managing rockburst risks in similar projects

multi approach stability analyses of large caverns excavated in low angled bedded sedimentary rock masses in singapore abstract the first commercial underground rock caverns for hydrocarbon storage in south east asia the jurong rock caverns project jrc project have recently been completed in singapore the storage capacity of 5 caverns is 1 47 million cubic meters and 3 5 million cubic meters of rocks were excavated in this project geologically it was excavated in low angled bedded meta sedimentary mudstone pyroclastic rocks and sandstone although traditional arch roofed style excavations are typical for tunnel and cavern for stability condition flat roofed profiles tend to form in low angle stratified sedimentary rock mass in this study the stability of such flat roofed tunnel and cavern with structurally controlled stability was analyzed using geotechnical classification systems including the stability graph method analytical voussoir techniques and numerical models accordingly and once presented the main features of the project characterization of the rock masses is presented some classification system approaches providing a convenient but probably over estimated support and reinforcement recommendation are illustrated then basic wedge stability analysis is briefly illustrated voussoir analogue techniques are applied to unsupported cavern profiles showing instability but clear stability for the supported case discontinuous models of the final designed cavities are presented showing a good agreement with indicative measurements on place and stress distributions associated with the excavation sections are analyzed using examine2d to show that abutment relaxation was unlikely to occur in jrc project the study shows that classification systems are useful tools but application of analytical techniques and numerical models contribute to a better understanding of the excavation and reinforcement process

constraints on seismic velocity anomalies beneath the siberian craton from xenoliths and petrophysics high seismic vp velocity anomalies 8 7 9 0km s 1 have long been known about in regions of the uppermost mantle of the siberian craton often in association with kimberlite fields laboratory measurement of seismic properties of five xenoliths three peridotites and two eclogites from the udachnaya kimberlite under confining pressures up to 600 mpa were extrapolated to uppermost mantle p t conditions of 1500 mpa and 500 c however none of the velocities are high enough to explain the observations eclogites or peridotites are commonly considered to be the source of anomalous high velocities we prefer a peridotitic source to an eclogitic source due to the unusual chemistry and regional uniformity of eclogitic garnets required maximum velocity limitations on laboratory measurements of seismic properties of natural eclogites and purported abundance of eclogites in the lithosphere alternatively a highly depleted peridotite such as dunite or harzburgite can produce velocities high enough to match observations olivine petrofabrics in most peridotites including the three peridotites used in this study are great enough to produce the observed high velocities provided olivine petrofabrics are continuous enough and correctly oriented to be seismically detectable and the modal proportion of olivine is high there have been suggestions by other authors that the siberian upper mantle is highly depleted and that a lithosphere scale shear zone exists which may have acted to organize fabrics into segments large enough for detection anomalously high vp vs velocity ratios of greater than 1 8 are expected parallel to the olivine 100 maxima required to be present in a high velocity olivine dominated upper mantle vp vs velocity ratios can serve as a means of inferring large scale anisotropy when limited seismic data are available as in siberia 2006 elsevier b v all rights reserved

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

upper mantle seismic anisotropy in the intra continental kachchh rift zone gujarat india abstract shear wave splitting study of 411 sks skks phases covering backazimuth range of 13 to 305 recorded by 12 broadband stations in the kachchh rift has led to estimates of fast axis orientations and splitting times for 118 good measurements the average vector mean of fast axis orientation 86 14 corresponds to the e w axis of the kachchh rift and the delay time 1 6 s is attributed to the 184 km thick upper mantle layer with 4 anisotropy the anisotropic character observed for the kachchh rift kr is comparable to other continental rifts and these are related to the high temperature lattice preferred orientation fabric of olivine inherited from the mantle flows the source of the rift axis parallel anisotropy is traced to the rift parallel flows within the 76 6 km thick lithosphere additionally the rift parallel pockets of partial melts also induce anisotropy within the asthenosphere both these are inherited from the plume lithosphere interaction during the deccan reunion plume episode 65 ma

p and s wave anisotropy and shear wave splitting at pressure and temperature in possible mantle rocks and their relation to the rock fabric the seismic properties and their directional dependence have been measured in three potentially mantle derived rocks peridotite ivrea zone italy lherzolitic xenolith massif central france serpentinite the experimental data include the measurement of elastic wave velocities and densities at confining pressures up to 600 mpa and temperatures up to 600 c 600 mpa and the determination of velocity anisotropy and shear wave splitting the petrophysical data can be related to mineral composition and to microstructural characteristics of the rocks macroscopic anisotropy of p and s wave velocities is strongly controlled in the peridodites by the olivine and in the serpentinite by the serpentine antigorite lattice preferred orientation lpo respectively shear wave splitting was found to be an important characteristic of the anisotropic rocks the study shows that for the interpretation of shear wave splitting the direction of wave propagation in relation to the lpos of the major minerals and to the symmetry of their lattice fabric is of great importance in the ivrea peridotite exhibiting rhombic symmetry there is practically no shear wave splitting to be observed for s waves propagating parallel to the olivine 100 axes and the maximum shear wave splitting is not coupled with the direction of highest p wave velocity in the transversely isotropic massif central xenolith shear waves do not split when propagating parallel to the olivine 010 maximum coinciding with the direction of the radial symmetry axis of the olivine fabric the experimental data are principally in accordance with velocity calculations based on the measured olivine lpo and the olivine single crystal stiffness coefficients implications for the interpretation of seismic data are discussed

the dynamics of the antarctic circumpolar current abstract the dynamics of the antarctic circumpolar current acc in a near eddy resolving model of the southern ocean fram are investigated a streamwise coordinate system is used rather than a more conventional approach of considering zonally averaged quantities the motivation for this approach is the large deviation from a purely zonal flow made by the current comparisons are made with a zonal mean analysis of the same model it is found that the topographic form drag is the main sink of the momentum that is input by the wind however in contrast to a zonal mean analysis other terms namely horizontal mixing bottom friction and advection of momentum are no longer negligible the total effect of transient eddies is to produce a drag on the mean flow again in contrast to the zonally averaged case the vertical penetration of stress is considered a generalized formula is derived for the interfacial form stress averaged along a convoluted path and that includes nonquasigeostrophic effects the i

moment tensor inversion of induced microseisnmic events evidence of non shear failures in the 4 m 2 moment magnitude range to assess objectively the source mechanism of mining induced seismic events we developed an algorithm to invert for the moment tensor components from this inversion the ratio of isotropic deviatoric component in the source is obtained we are applying this method to microseismic events 4 m 2 recorded at the underground research laboratory url in pinawa manitoba where a tunnel is being excavated at 420 m depth to monitor the seismic activity induced by this opening an array of 16 triaxial accelerometers was installed around the planned tunnel results from the moment tensor inversion on a fist data set provide evidence of non shear failure mechanisms furthermore the location of events displaying a tensile component corresponds to a breakout observed underground in the roof of the tunnel

combined analysis of sks splitting and regional p traveltimes in siberia summary azimuthal anisotropy in the upper mantle of many continental regions is documented by swave splitting measurements with sks techniques here we present observations of splitting of the sks seismic phase at seismograph stations in the siberian platform where few such data were known previously the parameters of splitting are coherent the fast direction everywhere is around 150 and the delay of the slow split wave is close to 1 0 s these observations provide no constraints on the distribution of anisotropy with depth however the siberian platform is remarkable in that it is covered by a network of long range profiles where p waves from nuclear explosions are recorded at epicentral distances of 2000 km and more depending on epicentral distance these waves sample the upper mantle from the moho to the transition zone two profiles run approximately parallel to the fast direction of the azimuthal anisotropy whereas the directions of the two others are intermediate between the fast and slow we examine the observed p traveltimes for their dependence on the azimuth and epicentral distance with the available data on elastic anisotropy in mantle xenoliths the values of p wave anisotropy for horizontal propagation can be used to evaluate s wave splitting for vertical propagation it appears that the upper mantle between the moho and 150 km depth is responsible for not more than about 30 per cent of the large scale effect in the sks phase the major effect is accumulated in a broad low velocity zone the top of which is found at a depth of 150 km anisotropy within this zone can be caused by recent mantle flow a similar distribution with depth might explain discrepancies between the estimates of azimuthal anisotropy from phase velocities of surface waves and sks splitting in north america and south africa

seismic properties of lower crustal xenoliths from el hoyazo se spain experimental evidence up to partial melting abstract seismic techniques provide unique tools to investigate the structure and in combination with petrological geochemical and petrophysical study the composition of the lower crust controversies can be solved with comparative study of metamorphic terrains or xenoliths that occur adjacent to areas where seismic refraction reflection data are available xenoliths represent a direct sampling of the inaccessible lower crust at the time of the volcanism whilst exposed crustal sections can only be used as analogue of present day lower crust the present study is focused on the measurements of compressional wave velocities up to conditions exceeding the beginning of melting 950 c at 500 mpa confining pressure on three garnet biotite sillimanite metapelitic xenoliths recovered from the neogene dacites of el hoyazo se spain they preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction and represent the best example of partially molten lower crust in the alboran domain the influence of glass on vp is primarily reflected by anomalous positive dvp dt while heating with velocity increasing at 500 mpa from 4 98 to 5 50 km s 1 at room temperature to 5 85 6 79 km s 1 at 650 700 c this corresponds to the glass transition where all the grain boundaries and most of the pores within the glass are closed after this point the velocity decreases to 6 2 6 5 km s 1 at 950 c where re melting of the glass is achieved and additional partial melt produced on cooling the behavior is normal with negative dvp dt after the thermal treatment velocities are 30 higher 6 07 7 21 km s 1 and reveal that in the presence of intergranular melt velocity measurements at room temperature cannot be extrapolated to high temperatures p waves measured at melting conditions are in agreement with deep seismic refraction data and tomography in the area and corroborate the hypothesis that partial melts are actually present in alboran lower crust

a model of velocity structure beneath calabria southern italy based on laboratory data abstract laboratory velocity measurements of representative rock samples from across a nearly complete crustal section from the serre mountains of southern calabria have been carried out as an aid to interpreting in situ seismic velocity data the section is composed of interlayered acidic mafic and pelitic rocks metamorphosed to granulite and amphibolite facies conditions in addition a suite of post tectonic granitoids intrudes the section the experimental data include the measurement of compressional wave vp and shear wave vs velocities at confining pressure in conjunction with structural and stratigraphic field data the experimentally determined data are used to construct a seismic velocity model for the crust beneath calabria in the upper crustal levels vp and vs vary in different manners below the uppermost amphibolite facies gneisses a weak velocity inversion of vp is associated with the post tectonic granites at the granite granodiorite and the tonalite dioritic gneiss boundary vp increases in steps of about 200 and 300 m s respectively in contrast vs remains constant or even decreases slightly through this same sequence of rocks this contrasting behaviour is primarily related to the quartz feldspar ratio in the rocks the most pronounced velocity jump occurs at the top of the granulite facies metapelite unit here both vp and vs increase markedly due to mineralogic changes that accompany increasing metamorphic grade and the greater abundance of mafic and garnet bearing restites of partially melted pelite the mafic rocks of the lowermost crustal layer have p and s wave velocities that are significantly lower than those in the overlying metapelites the variation of poisson s ratio with depth suggests that this parameter which is a combination of vp and vs is more sensitive to lithology than the p and s wave velocities alone in rock units of upper and mid crustal levels with average p wave velocities

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

quantification and interpretation of seismicity abstract methods based on acoustic emission and microseismicity ae ms have proven to be valuable for monitoring microcracking at the underground research laboratory url in canada the source locations of the seismic events induced by the excavation have helped to map out the extent of the excavation damage disturbed zone edz around tunnels this paper describes methods for advanced processing and interpretation of ae ms data and the quantification of changes in material properties using velocity interferometry examples of methods that are generally not used routinely in the analysis of ae ms data are given these include 1 long term spatial and temporal source parameter trends and magnitude frequency studies 2 source mechanism analysis and 3 source location refinement by the use of relative location and clustering techniques results from these studies are shown to aid in the understanding of the effect of confining pressure on ae ms activity around tunnels and the mechanics of rock failure in the edz also the reduction of source location error is shown to be critical for delineating structures that may exist in clusters of ae ms data finally examples of the use of seismic sources to produce repeat measurements of seismic velocity along raypaths in 3d orientations through a rock mass are given this is found to be a highly sensitive method for quantifying changes in rock properties such as young s modulus as well as for modelling the change in crack density and saturation occurring in a rock mass with time

rapid ocean wave teleconnections linking antarctic salinity anomalies to the equatorial ocean atmosphere system the coupled climate model forte is used to investigate rapid ocean teleconnections between the southern ocean and equatorial pacific ocean salinity anomalies located throughout the southern ocean generate barotropic signals that propagate along submerged topographic features and result in the growth of baroclinic energy anomalies around indonesia and the tropical pacific anomalies in the ross bellingshausen and amundsen seas exchange the most barotropic kinetic energy between high and low latitudes in the equatorial pacific baroclinic kelvin waves are excited which propagate eastwards along the thermocline resulting in sst anomalies in the central and eastern pacific sst anomalies are subsequently amplified to magnitudes of 1 25 c by air sea interaction which could potentially influence other coupled pacific phenomena

seismic anisotropy beneath stable continental interiors a robust knowledge of seismic anisotropy beneath the continents is essential to our understanding of plate tectonic theory as anisotropy provides a unique constraint on the character of past and present deformation in the lithosphere and sublithospheric mantle this review paper summarizes the range of techniques currently available to image seismic anisotropy with passive source seismic data and addresses current issues surrounding the observation and interpretation of continental seismic anisotropy to this end we present case studies for four regions where seismic anisotropy has been extensively investigated in recent years eastern north america the canadian shield australia and southern africa based on this full suite of results we infer that stable continental regions generally contain seismic anisotropy that is clearly located within both the lithosphere and the sublithospheric mantle usually to depths of at least 200 km and perhaps more an implication of these results is that tectonic plates are at most only partially coupled to the underlying mantle the results from these case studies also demonstrate that while remarkable progress in seismic anisotropy imaging has been achieved in recent years it is clear that much more work will be required to adequately understand the origin of continental seismic anisotropy we suggest that a more robust characterization of anisotropic parameters can only be achieved by integrating complementary seismic datasets and by incorporating constraints from key related datasets from mineral physics magnetotellurics gravity and geodesy

physical properties of ultrahigh pressure metamorphic rocks from the sulu terrain eastern central china implications for the seismic structure at the donghai ccsd drilling site about 30 samples representing major lithologies of sulu ultrahigh pressure uhp metamorphic rocks were collected from surface exposures and exploration wells and compressional vp and shear wave vs velocities and their directional dependence anisotropy were determined over a range of constant confining pressures up to 600 mpa and temperatures ranging from 20 to 600 degreesc samples range in composition from acidic to ultramafic p and s wave velocities measured at 600 mpa vary from 5 08 to 8 64 km s and 2 34 to 4 93 km s respectively densities are in the range from 2 60 to 3 68 g cm 3 to make a direct tie between seismic measurements refraction and reflection and subsurface lithologies the experimental velocity data corresponding to shallow depths were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000 m chinese continental scientific drilling program ccsd crustal segment comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks the strongly reflective zone beneath the donghai drill site can be explained by the impedance contrasts between the different lithologies contacts between eclogite peridotite and felsic rocks gt gneiss granitic gneiss in particular may give rise to strong seismic reflections in addition shear induced lattice preferred orientation lpo related seismic anisotropy can increase reflectivity for the explanation of the high velocity bodies 6 4 km s around 1000 m and below 3200 m depth large proportions of eclogite peridotite about 40 and 30 vol respectively are needed c 2002 elsevier science b v all rights reserved

climate and biogeochemical response to a rapid melting of the west antarctic ice sheet during interglacials and implications for future climate interglacials onto the global climate carbon cycle system using the earth system model of intermediate complexity loveclim prescribing a meltwater pulse in the southern ocean that mimics a rapid disintegration of the wais a substantial cooling of the southern ocean is simulated that is accompanied by an equatorward expansion of the sea ice margin and an intensification of the southern hemispheric westerlies the strong halocline around antarctica leads to suppression of antarctic bottom water aabw formation and to subsurface warming in areas where under present day conditions aabw is formed this subsurface warming at depths between 500 and 1500 m leads to a thermal weathering of the wais grounding line and provides a positive feedback that accelerates the meltdown of the wais our model results further demonstrate that in response to the massive expansion of sea ice marine productivity in the southern ocean reduces significantly a retreat of the wais however does not lead to any significant changes in atmospheric co2 the climate signature of a wais collapse is structurally consistent with available paleoproxy signals of the last interglacial mis5e citation menviel l a timmermann o e timm and a mouchet 2010 climate and biogeochemical response to a rapid melting of the west antarctic ice sheet during interglacials and implications for future climate paleoceanography 25 pa4231 doi 10 1029 2009pa001892

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

stress estimated using microseismic clusters and its relationship to the fracture system of the hijiori hot dry rock reservoir a method for estimating the in situ stress state by analyzing microseismic clusters induced by hydraulic injections is proposed the method is based on focal mechanism analysis supplemented with microseismic doublet analysis the latter is used to discriminate between the fault plane and the auxiliary planes of the focal mechanism solution the method was applied to estimate the stress field within the hijiori hot dry rock geothermal reservoir and yielded results which were consistent with other estimates the mechanics of permeability creation within the reservoir during major hydraulic injections was then examined by evaluating the interaction of the inferred stress field with the natural fracture system the characteristics of the latter were determined by integrating information obtained from core samples acoustic borehole televiewer images and pressure temperature and spinner logs the results indicated that the observed microseismicity and orientation dependent permeability characteristics of the fracture population are well explained by shear failure inferred from coulomb s friction theory it is also shown that the growth direction of the reservoir is strongly controlled by the distribution of favorably oriented pre existing fractures and their interaction with the stress field

studies on temporal and spatial variation of microseismic activities in a deep metal mine abstract aiming at forecasting techniques of ground pressure hazards in deep metal mines a microseismic monitoring system was established at a deep stope in hongtoushan copper mine in china based on theories of geophysics and rock mechanics a forecasting approach was introduced using microseismic multi parameters including cumulative apparent volume energy index spatial correlation length fractal dimension and b value the approach was used to predict large scale fractures and ground pressure hazards in rock masses the results showed that microseismic activities were very weak before mining commenced however activities became significant when mining started when mining finished microseismic activities remained at a higher level for about one week then became weakened before large scale fractures occurred all microseismic multi parameters behaved differently the apparent volume and spatial correlation length were continually increasing while energy index fractal dimension and b value were gradually dropping to their minimum values therefore these parameters could be used as precursory indicators for great ground pressure hazards comprehensive analysis on microseismic multi parameters changes could improve reliability of forecasting which is of great significance to deep metal mines in managing ground pressure failure risks

a quick response of the equatorial ocean to antarctic sea ice salinity anomalies the potential mechanisms for a quick response of the equatorial ocean to processes occurring in the high latitude southern ocean have been investigated in the southern ocean at the drake passage latitudes there is an zonally unbounded channel the antarctic circumpolar current belt accb it is demonstrated that in a multiconnected domain such as the accb signals generated by anomalies in the southern ocean sea ice cover salinity distribution can propagate in a wave like manner in the form of fast moving barotropic rossby waves a disturbance induced near the drake passage is demonstrated to generate a rossby wave that propagates across the pacific in only a few days this signal is reflected at the western boundary of the pacific and generates an equatorward propagating coastally trapped kelvin wave the resulting temperature anomaly moves northward along the western coastline up to the vicinity of the equator and increases in amplitude over time the anomaly in the western edge of equatorial pacific then begins to propagate eastward along the equator as a trapped equatorial wave after about 2 3 months this wave reaches the eastern coast reflects and generates the coastal trapped wave which propagates north and south along the coastline in both hemispheres this process is suggested as one possible direct mechanism by which the extratropical ocean can induce anomalies in the equatorial ocean

temporal imaging of mine induced stress change using seismic tomography abstract in an effort aimed at monitoring mining induced stress changes that may influence ground failure the us bureau of mines conducted a series of active 3 d seismic tomographic surveys at the homestake lead south dakota and lucky friday mullan idaho mines existing rock bolts were used to mount geophones and as strike points for introducing seismic energy using a 3 6 kg sledge hammer travel time measurements were recorded spanning up to 160 m between drifts at several levels the tomographic uncertainty was minimized by computing iso velocity surfaces of constant probability based on statistics from multiple reconstructions and a threshold criteria periodic imaging using tomographic velocity surfaces demonstrated that temporal and spatial changes in the local stress field occurred in response to ground failure and stope advancement at a gold and silver mine respectively

about the lithospheric structure of central tibet based on seismic data from the indepth iii profile signals from 11 shots and 8 earthquakes and numerous teleseismic events were recorded along the 400 km seismic line indepth iii in central tibet and interpreted together with previous seismic and tectonic data the abnormal behavior of various mantle phases reveals a complex moho transition zone especially in the northern part of the line in the changtang block where the lower crust and the mantle show unusually low velocities a shingled appearance of pn and no low velocity layer in the upper crust the strong east west anisotropy in the changtang block is related to an easterly escape movement of the whole lithosphere facilitated by the warm and weak layers in the lower crust and the upper mantle bounded apparently by two prominent west east running fault zones

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

seismic properties of the upper mantle beneath lanzarote canary islands model predictions based on texture measurements by ebsd abstract we present a petrophysical analysis of upper mantle xenoliths collected in the quaternary alkali basalt fields series iii and iv from the island of lanzarote the samples consist of eight harzburgite and four dunite nodules 5 to 15 cm in size and exhibit a typical protogranular to porphyroclastic texture an anomalous foliation resulting from strong recovery processes is observed in half of the specimens the lattice preferred orientations lpo of olivine orthopyroxene and clinopyroxene were measured using electron backscatter diffraction ebsd in most samples olivine exhibits lpos intermediate between the typical single crystal texture and the 100 fiber texture occasionally the 010 fiber texture was also observed simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime probably dominated by a simple shear component under low strain rate and moderate to high temperature orthopyroxene and clinopyroxene display a weaker but significant texture the lpo data were used to calculate the seismic properties of the xenoliths at pt conditions obtained from geothermobarometry and were compared to field geophysical data reported from the literature the velocity of p waves 7 9 km s obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation our results are consistent with a roughly w e oriented fastest p wave propagation direction in the uppermost mantle beneath the canary islands and with the lithosphere structure proposed by previous authors involving a crust mantle boundary at around 18 km in depth overlaid by intermediate material between 11 and 18 km

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

estimating in situ rock stress from spalling veins a case study stress induced failures have typically been considered as engineering disasters in deep underground excavations this paper highlights the importance of stress driven rock failures as a means to estimate the in situ rock stress at the depth the method which is based on the observation and documentation of a failure mode referred to here as spalling in deep tunnels or caverns is put forward and presented to estimate the macro scale rock stress using the proposed method the orientation of the principal stresses in situ can be deduced by the spalling intensity and associated stress induced spalling veins in the rock mass surrounding the opening and the magnitude of the principal stresses can be estimated by the assumed crack initiation stress required to generate spalling in the given rock by careful documentation of spalling failure characteristic in the field a real case study at baihetan powerhouse site has been carried out and indicates that the proposed method is an available way to enriching recognition of in situ rock stress and a helpful supplement to traditional methods of stress measurements after strictly numerical verification analysis of the regional tectonic setting as well as measurements of in situ stress supports the results by the suggested approach

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

calibration of shear wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska abstract despite the abundance of measurements of shear wave splitting around the world some fundamental questions about its geological interpretation have not yet been answered in order to constrain 1 i the orientation and magnitude of s wave anisotropy 2 ii the thickness of the anisotropic layer and 3 iii the possible variation of the anisotropy with depth in the subcontinental upper mantle beneath active orogenic belts we have carried out a systematic investigation on shear wave properties of mantle xenoliths from recent alkaline basalts of the canadian cordillera and alaska it is found that the polarization direction of the fast s wave as well as the time delay t between the two arrivals are strongly dependent on the propagation direction with respect to the structural frame at a single station the variations of measured and t values for sks phases from different events can result from this dependence because the average grain size of olivine in upper mantle samples is commonly larger than 0 5 mm dislocation creep prevails over a thickness of at least 250 km and results in olivine lpo and hence anisotropy and shear wave splitting a single thick anisotropic layer in mountain parallel subvertical shear zones may cause high values of tgd while multiple subhorizontal layers will produce multiple splitting making the measurement and interpretation of s wave splitting difficult our results also suggest that the s wave splitting observed in cold old stable cratons such as the canadian shield is likely dominated by fossil anisotropy whereas that observed in hot active orogenic regions such as the northwest american cordillera and the tibetan plateau may be dominated by modern tectonic deformation in the lithosphere and flow in the asthenosphere

deformation forecasting and stability analysis of large scale underground powerhouse caverns from microseismic monitoring abstract to assess the stability of the underground powerhouse caverns and analyse the failure mechanism of the surrounding rock mass at the baihetan hydropower station in southwest china a high resolution microseismic ms monitoring system was implemented in the left bank underground powerhouse caverns based on the temporal and spatial distribution of ms events the correlation between ms activities and construction was established and three damage regions for the surrounding rock mass during excavation were identified ms clusters were found to occur most often in stress concentration regions of the underground powerhouse caverns and to result from various factors including excavation induced unloading and geological structure activation the seismic source parameters i e moment magnitudes and s wave to p wave energy ratios e s e p of the three ms clusters demonstrate the different failure modes and risks of the surrounding rock mass the temporospatial evolution of the ms activities apparent stress and cumulative apparent volume in localized rock mass during the period of a typical large deformation were used to develop a comprehensive analytical method for forecasting the deformation of the surrounding rock mass thus this comprehensive analytical method which incorporates ms monitoring conventional monitoring geological survey and construction is promising for identifying the damage zones and forecasting the macro deformation of the surrounding rock mass in underground powerhouse caverns subjected to excavation

equilibration temperatures and elastic wave velocities for upper mantle rocks from eastern australia implications for the interpretation of seismological models abstract this study integrates available geological geophysical and petrophysical data for deep seated lithologies which occur beneath eastern australia and which are accessible at the surface as xenoliths in basaltic host rocks it is shown that spinel lherzolite mantle wall rock occurs over a depth range commencing at about 30 km and extending to about 55 km this represents a temperature range of 850 1000 c acoustic wave velocity measurements were carried out on three types of spinel lherzolites and one mantle derived garnet pyroxenite the acoustic velocities range from 7 7 to 7 9 km s 1 for the pressure and temperature conditions beneath eastern australia derived from xenolith geothermobarometry these values demonstrate that the use of dunite as a generalised mantle rock results in overestimation of model mantle vp especially when used with a standard continental model geotherm the measured spinel lherzolites also show variable anisotropy in acoustic wave velocity 5 8 for these moderately foliated samples it is demonstrated that by using a combination of the measured acoustic velocities and single crystal elasticity data for constituent minerals it is possible to interpolate vp for a wide modal range of rock types relevant to the lower crust and upper mantle triangular grids which allow graphical estimation of vp for spinel lherzolites garnet lherzolites and garnet pyroxenites have been constructed the petrologic and petrophysical results are used to constrain models of the lower crust and upper mantle profiles based on available seismic data for eastern australia

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

upper mantle anisotropy beneath the altai sayan region of central asia abstract the altai sayan region of central asia is actively deforming despite its being located several thousands of kilometers away from the collisional front between india and eurasia to add constraints to the role of the upper mantle in this type of tectonic environment we analyzed intermediate period analogue records of sks and skks to determine the state of mantle anisotropy in this region we find that for all stations located in actively deforming areas the fast direction of anisotropy correlates well with indicators of cenozoic to the present day deformation and correlates with older structures only when they happen to align with younger ones the general east northeast trend of the fast direction of anisotropy in active regions also aligns with the principle extensional strain axis determined from earthquake moment tensors at one station nvs located outside of any actively deforming region the n s fast direction may correspond to the long wavelength strain field of the mantle beneath much of siberia these correlations along with the size of the delay times 1 2 s suggest that the anisotropy in the upper mantle beneath the altai sayan is responding to recent tectonic activity

seismic properties of the upper crust in the central friuli area northeastern italy based on petrophysical data abstract the compressional and shear wave velocities have been measured at room temperature and pressure up to 450 mpa on 5 sedimentary rock samples representative of the most common lithologies of the upper crust in the central friuli area northeastern italy at 400 mpa confining pressure the triassic dolomitic rock shows the highest velocities vp 7 km s vs 3 6 km s the jurassic and triassic limestones samples intermediate velocities vp 6 3 s vs 3 5 km s and the cenozoic and paleozoic sandstones the lowest velocities vp 6 15 km s vs 3 35 km s the paleozoic sandstone sample is characterized by the strongest anisotropy 10 and significant birefringence 0 2 km s is found only on the cenozoic sandstone sample we elaborated the synthetic profiles of seismic velocities density elastic parameters and reflection coefficient related to 4 one dimensional geological models extended up to 22 km depth the synthetic profiles evidence high rheological contrasts between triassic dolomitic rocks and the soft sandstones and the jurassic limestones the vp profiles obtained from laboratory measurements match very well the in situ vp profile measured by sonic log for the limestones and dolomitic rocks supporting our one dimensional modelling of the calcareous carbonatic stratigraphic series the vp and vs values of the synthetic profiles are compared with the corresponding ones obtained from the 3 d tomographic inversion of local earthquakes the laboratory vp are generally higher than the tomographic ones with major discrepancies for the dolomitic lithology the comparison with the depth location of seismicity reveals that the seismic energy is mainly released in correspondence of high contrast rheological boundaries

mechanical anisotropy of columnar jointed basalts an example from the baihetan hydropower station china abstract columnar jointed basalts are characterized by a self organized joint network of discontinuities and pose a difficult challenge for geotechnical engineering design due to their inherent anisotropic nature we explore here the anisotropic characteristics of the columnar basalt formation in the chinese baihetan hydropower station including aspects of the geometrical rock structure deformation and strength anisotropy site investigations reveal that a typical cross section of the columnar basalt blocks is mainly quadrangular and pentagonal with an average edge length of 0 152 m three types of joints with different macro and micro characteristics form the columnar jointed rock mass and are identified by scanning electron microscopy in situ ultrasonic tests further confirm that the columnar basalt prisms exhibit transverse isotropy with the plane of isotropy perpendicular to the column axis as can also be observed in the field strength anisotropy is confirmed by point load and uniaxial compression tests the mechanical and anisotropic characteristics of baihetan s jointed basalt mass can be explained by its multi scale joints pattern by means of goodman s stiffness equation we find that the anisotropic coefficients obtained for its deformability and strength are similar for all testing methods employed including in situ p wave velocity point load tests and uniaxial compression tests this result confirms the strong anisotropic effect in these rock masses and facilitates an issue that must be considered when assigning input parameters for various classification and numerical analyses schemes

volcanism of the baikal rift zone abstract the volcanism of the baikal rift zone is a specific case of intraplate volcanism where the tensional stress field in the lithosphere under the rift zone does not greatly exceed local tension in other volcanic regions of central asia in which rifting was not morphologically expressed the main phase of volcanism miocene pliocene preceded active extension and rift formation migration of volcanism from the periphery to the axial part of the rift as well as subsequent variation of the composition of volcanics from alkaline to tholeiitic are not specific to the baikal rift zone the volcanism of this zone and other interior regions of asia is considered to be a consequence not only of deep regional processes under volcanic areas connected to the formation and rise of a highly anomalous mantle but also of global processes caused by the indo eurasian collision which was responsible for the large scale deformations within the asiatic continent including tensional stress fields

coupled oscillations in antarctic sea ice and atmosphere in the south pacific sector interannual oscillations with period of about 3 6 years have dominated the winter atmospheric and ice variability in the ross amundsen and bellingshausen seas antarctica during 1979 1998 anomalies in sea ice concentration and drift propagate eastward in the winter ice pack coupled to sea level pressure anomalies this signal accounts for the ice and atmospheric components of the antarctic circumpolar wave during its eastward passage through the pacific sector of antarctica sea ice concentration anomalies at the ice margin seem to result from air ice sea interactions which involve both the dynamic effect of the anomalous wind driven ice motion and the thermodynamic ice growth and melting due to surface air and ocean temperature anomalies

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

assessing in situ microcrack damage using ultrasonic velocity tomography abstract to characterize the damage induced during excavation of a test tunnel in granite ultrasonic wave velocity and amplitude measurements were made in situ around one quadrant of the tunnel sixteen 1 m deep boreholes were drilled into the tunnel wall these boreholes spanned the region from tensile stress induced damage in the sidewall to compressive stress induced damage in the well developed notch measurements were made by pulsing a source transducer at numerous points within a given borehole and on the tunnel surface and then capturing the transmitted ultrasonic waves at transducers located in the adjacent borehole the travel times of the waves between sources and receivers were used to compute the average velocities and to construct two dimensional 2d tomographic images wave velocities and amplitudes in the tensile stress region are low and show significant anisotropy indicating the presence of oriented microcracks even as deep as 1 m from the tunnel wall velocities and amplitudes are higher in the compressive stress region and show lower anisotropy indicating the rock is relatively undamaged away from the tunnel wall the velocity anisotropy indicates that the dominant orientation of microcrack planes is everywhere tangential to the tunnel wall even though the minimum principal stress is tangential and tensile in the sidewall the distribution of microcracks inferred from these results is consistent with the extensive microseismicity detected during and after excavation and suggests that both the stress history and current stress state have impacted the current state of damage around the tunnel

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

petrographic interpretation of a complex seismic crust mantle transition in the central eastern alps abstract a recent reinterpretation of the existing dss profiles scarascia and cassinis tectonophysics 271 1997 157 188 led to a reconstruction of the moho boundary and of the lower crust in the central eastern alpine sector where the european and the adriatic domains are deeply indented in that work a complex crust mantle transition composed of alternating low and high velocity layers was observed in the deepest bottom of the european crust in the same work it was confirmed that the european lower crust beneath the alpine range is characterised by a very low seismic velocity while the velocity of the adriatic lower crust reaches the average values found in collisional belts the interpretation of these features has been performed employing a data base of ultrasonic seismic measurements the ivrea verbano zone has been assumed as an analogue of crust mantle transition a statistical approach was used to associate the bodies of the interpreted seismic models to the lithotypes a petrological model is attempted in order to suggest an explanation of the observed phenomena assuming physical and compositional constraints appropriate to the alpine collisional belt cumulitic peridotites and pyroxenites lenses in a gabbroic host rock fit the observed seismic structure of the crust mantle transition the upper mantle lies below a transition zone and is characterised by a velocity of 8 2 km s detected by p n phases in our study it is interpreted as a spinel to garnet peridotite the anomalous low velocity of the european lower crust is discussed but still remains an open subject

global teleconnections in response to freshening over the antarctic ocean abstract in this paper coupled ocean atmosphere responses to freshening over the antarctic ocean are investigated in a fully coupled model with a series of sensitivity experiments in the model 1 0 sv 1 sv 106 m3 s 1 of freshwater flux is uniformly imposed over the antarctic ocean for 400 yr while the ocean and atmosphere remain fully coupled both locally and elsewhere the model explicitly demonstrates that a freshening of the antarctic ocean can induce a significant local cooling coupled with an intensification of the westerly winds and expansion of sea ice furthermore the cooling can extend to the entire southern extratropical and tropical oceans coupled with an intensification of southeasterly trades and the equatorial trade winds some modest warm anomalies also occur in the northern extratropical oceans forming a sharp interhemispheric sst contrast a series of sensitivity experiments are conducted to understand the mechanisms responsible for transmitting the southern high latitude cooling

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

sea ice transports in the weddell sea time series of sea ice draft in the weddell sea are evaluated together with hydrographic observations satellite passive microwave data and ice drift for estimation of the freshwater fluxes into and out of the weddell sea ice draft is measured with moored upward looking sonars since 1990 along two transects across the weddell gyre one transect extending from the tip of the antarctic peninsula to kapp norvegia was sampled between 1990 and 1994 and covers the flow into and out of the southern weddell sea the other transect sampled since 1996 and extending from the antarctic continent northward along the greenwich meridian covers the exchange of water masses between the eastern and the western weddell sea in order to relate results obtained during the different time periods empirical relationships are established between the length of the sea ice season derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15 and 1 the annual mean ice draft and 2 the annual mean ice volume transport by using these empirical relationships estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period february 1979 through february 1999 wind and current force a westward ice transport in the coastal areas of the eastern weddell sea and a northward ice transport in the west during the 2 year period 1991 1992 the mean ice volume export from the weddell sea is 50 19 103 m3 s 1 this freshwater export is representative for a longer term 20 year mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19 103 m3 s 1 yielding an upper bound for the formation rate of newly ventilated bottom water in the weddell sea of 2 6 sv

microseismicity monitoring and failure mechanism analysis of rock masses with weak interlayer zone in underground intersecting chambers a case study from the baihetan hydropower station china abstract a weak interlayer zone wiz is a rock mass system with poor mechanical properties large scale random distribution water softening causing an adverse effect on the safety of the construction and project progress to investigate the fracture process and the mechanism of rock masses with wizs in the intersecting chambers during the excavation process in situ microseismic ms monitoring was carried out in the underground powerhouse on the right bank of the baihetan hydropower station china during the monitoring the spatio temporal evolution process of the microseismicity of the rock masses around the intersecting chambers was obtained during the excavation unloading of multiple working faces the spatial evolution of ms events illustrates the dynamic progressive characteristics of ms activities as they propagate and accumulate along the wiz and finally form a cluster zone the fracture mechanism of moment tensor inversion reveals the distribution and evolution of ms events with respect to different fracture types tensile fracture events are distributed near the free surface while non tensile fracture events are far from the free surface finally the study proposes support measures restraining fracture development in surrounding rock masses with wiz the effectiveness of reinforced support measures is verified by ms events and the deformation of surrounding rocks the results of the study are particularly valuable for the stability analysis excavation and support optimization of similar engineering studies