an assessment of dynamically recrystallized grainsize as a palaeopiezometer in quartz bearing mylonite zones abstract recrystallized grainsize has been measured in quartz and in some cases feldspar in about 200 samples from 22 mylonite zones from 3 discrete tectonic settings 1 1 supracrustal low temperature shallow dipping thrusts 2 2 deeper level major 100 km thrusts in high grade metamorphic rocks and 3 3 steeply dipping fault zones in granite within a low grade palaeozoic fold belt the concept of a steady state dynamically recrystallized grainsize largely unaffected by post creep processes e g static grain growth receives strong support especially from the microstructures and the independence of finite strain and grainsize in most mylonite zones however the usefulness of this grainsize for predicting stress magnitudes is limited by the apparently independent influence of metamorphic environment on grainsize the available theoretical and empirical stress grainsize relationships do not account for these effects the concept of a steady state grainsize and the ease of accurate measurement offer a potentially powerful method for predicting stress intensity during deformation predicted deviatoric stresses have been computed using twiss theoretical model for comparison with other crustal stress estimates and most samples fall in the range from 20 to 150 mpa in a few cases where discrete high strain mylonite zones occur within contemporaneously regionally deformed rocks the recrystallized grainsize indicates that stresses were 1 5 to 2 times higher within the zones there is a clear need for improved theoretical and or empirical stress grainsize relationships for quartz and other minerals before extensive further application of this technique

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

the development of subgrain misorientations with strain in dry synthetic nacl measured using ebsd abstract the development of subgrain boundary misorientations with strain in dry synthetic nacl polycrystals deformed at elevated temperature has been investigated using electron backscattered diffraction ebsd at low natural strains up to 0 5 average misorientations of subgrain boundaries increase with strain and a power law relationship exists between strain and average misorientations the average misorientations are strongly influenced by grain orientation suggesting that the misorientation strain relationship may also be texture dependent in materials with high plastic anisotropy like nacl a slight grain size dependency of the average misorientations was observed the results indicate that with suitable calibration average subgrain boundary misorientations may offer a method for estimating the strain accommodated by dislocation creep in nacl and thus perhaps in other geological materials although current theories for polycrystalline plasticity imply that misorientations may also depend on stress in some situations

influence of deformation conditions on the development of heterogeneous recrystallization microstructures in experimentally deformed carrara marble recrystallized grains are potentially useful as indicators of palaeostress in naturally deformed rocks providing that well calibrated relationships palaeopiezometers exist between the recrystallized grain size and stress rocks can exhibit microstructures that are heterogeneous that is containing recrystallized as well as deformed grains and showing subgrains within grains that differ in size and character from the grain core to the mantle previous studies on palaeopiezometers only rarely took into account such heterogeneous microstructure we used electron backscattered diffraction ebsd to accurately quantify the heterogeneous microstructures in experimentally deformed carrara marble flow stress 15 85 mpa temperature 700 990 8c and natural strain 0 15 0 90 the sizes of bulges recrystallized grains and deformed grains have been measured we found that the overall character of the microstructures varies as a function of deformation conditions in heterogeneous samples showing core mantle microstructures the sizes of the bulges and recrystallized grains are independent of strain and show an inverse dependency on stress the recrystallized grains have been found to nucleate at grain boundary bulges our study illustrates that very different microstructures may develop in relation to the complexity of the recrystallization mechanisms we therefore suggest that piezometers should be calibrated and applied for a single type of overall microstructure

differential stress strain rate and temperatures of mylonitization in the ruby mountains nevada implications for the rate and duration of uplift kno ledge of the m agnitude of the differential stress during the formation of mylonitic rocks provides constramts on mechanical and thermal models for the exhumation of the metamorphosed footwalls of major low angle detachment faults we have analyzed the differential flow stress during the mylonitization of quartzose rocks in the ruby mountains nevada using grain size piezometers and kinetic laws for grain g owth quartzites from mylonitic shear zones in lamoille canyon and secret creek gorge have grain sizes of 91 151 m and 42 64 m respectively the peak temperature during mylonitization was 630 i 50 c and analysis of grain growth kinetics indicates that mylonitization continued during cooling to temperatures s450 c quartz grain size piezometers suggest that the mylonitization occurred under differential stresses crl cr3 of 38 64 mpa or maximum shear stresses of 19 32 mpa extrapolation of quartzite flow laws indicates that the mylonitization occurred at strain rates between 10 10 and 10 13 1 arguments presented m the paper suggest that the likely range of strain rates is 10 11 to 10 12 1 these strain rates are compatible with displacement rates of the order of 23 mm yr l along a 1 5 km thick simple shear zone such a shear zone dipping 15 would produce an uplift rate of 5 8 km m y 1 and a horizontal extensioo rate of 22 km m y l this uplift rate indicates that midcrustal mylonitic rocks could have been lifted up along a 1 5 km thick simple shear zone dipping 15 in 2 6 m y

subgrain rotation and dynamic recrystallization of olivine upper mantle diapirism and extension of the basin and range province abstract on the basis of an abrupt change of olivine grain size at certain depths in the upper mantle beneath the basin and range province in the western u s a mercier 1980b proposed that subgrain rotation sgr recrystallization had taken place above the grain size discontinuity and grain boundary migration gbm recrystallization at depths greater than the discontinuity the rotation of subgrains and the characteristics of dynamically recrystallized neoblasts of olivine were analyzed in a series of dunite samples deformed experimentally to compressive strains of about 15 60 whereas the rotation angle between adjacent subgrains increases with strain the mean rotation angle did not exceed 2 even in the most heavily deformed samples rotation angles between kink bands which formed at all experimental conditions also increase with strain at the highest strains rotations of up to 110 are not uncommon at low strains the dominant rotation axis between kinks is 001 and less frequently ovw at high strains uvw rotation axes are common neoblasts did form mainly on old grain boundaries and less frequently within old grains rotation axes between intragranular neoblasts and their hosts are of the type uvw and the rotation angles are always large features which seem to be inconsistent with sgr recrystallization and suggest gbm recrystallization neoblasts may have formed in highly strained regions of old grains where slip occurs with uvw rotation axes the olivine textures and fabrics of lherzolite nodules originating in the uppermost mantle above the grain size discontinuity are similar to those of nodules from the dreiser weiher germany mercier 1980b a study of dreiser weiher samples shows however that they have features difficult to reconcile with the sgr mechanism it is proposed here that gbm recrystallization occurred throughout a rising upper mantle diapir beneath the basin and range extension zone as the upward flow crossed the regional lithosphere asthenosphere boundary at about 65 km depth it diverged causing flow velocities to decrease abruptly and the strain rate dropped approximately by an order of magnitude as a consequence the differential stress decreased by about a factor of two and the olivine grain size increased by a factor of two

shallow velocity structure of stromboli volcano italy derived from small aperture array measurements of strombolian tremor abstract the properties of the tremor wave field at stromboli are analyzed using data from small aperture arrays of short period seismometers deployed on the north flank of the volcano the seismometers are configured in two semi circular arrays with radii of 60 and 150 m and a linear array with length of 600 m the data are analyzed using a spatiotemporal correlation technique specifically designed for the study of the stationary stochastic wave field of rayleigh and love waves generated by volcanic activity and by scattering sources distributed within the island the correlation coefficients derived as a function of frequency for the three components of motion clearly define the dispersion characteristics for both rayleigh and love waves love and rayleigh waves contribute 70 and 30 respectively of the surface wave power the phase velocities of rayleigh waves range from 1000 m sec at 2 hz to 350 m sec at 9 hz and those for love waves range from 800 to 400 m sec over the same frequency band these velocities are similar to those measured near puu oo on the east rift of kilauea volcano hawaii although the dispersion characteristics of rayleigh waves at stromboli show a stronger dependence on frequency such low velocities are consistent with values expected for densely cracked solidified basalt the dispersion curves are inverted for a velocity model beneath the arrays assuming those dispersions represent the fundamental modes of rayleigh and love waves

seasonality in particle motion of microseisms summary microseisms are a continuous source of seismic signal which mainly consist of rayleigh waves but are known to contain some other types of seismic waves we developed a simple processing procedure for single station three component seismic data which allows us to select rayleigh wave dominated portions application of this procedure to data from southern california led us to confirm that excitation of the secondary peak microseisms the predominant energy at about 0 15 hz occurs in coastal regions the source directions viewed at each station do not change very much throughout the year we also discovered that the ratio of the horizontal to vertical amplitudes in rayleigh waves termed h z in this paper is shown to have seasonal variations the h z estimates typically reach their maximum in winter and their minimum in summer seasonal variations are observed at most stations but peak to peak amplitudes of seasonal variations vary greatly from station to station ranging between 0 and 40 per cent two hypotheses were examined to explain this phenomenon the first hypothesis is that it is caused by seasonal changes in seismic velocities in a layer between the surface and the groundwater level the second hypothesis is that it is caused by seasonal changes in relative excitation of higher modes compared to dominant fundamental mode rayleigh waves the first hypothesis is not likely because predicted amplitudes of seasonal variations in h z are too small to explain observed variations the second hypothesis seems quite plausible if source regions move seasonally among regions with different ocean depths the technique developed in this paper however is not sufficient to answer this question conclusively

paleomagnetic secular variation and environmental magnetism of holocene age sediments from tulare lake ca abstract the lake level record from tulare lake ca has been shown to provide valuable constraints on late pleistocene and holocene runoff from the sierra nevada mountain range into the san joaquin valley of california one of the world s most prolific agricultural centers this project uses the magnetic properties of the tulare lake sediments in order to date the sediments and to constrain the relative lake level at the time of deposition shallowing lake conditions were identified leading up to a prominent unconformity magnetic mineralogy and grain size indicators primarily decreasing arm irm and s ratio values suggest coarser grain sizes and more oxidizing conditions approximately half of the samples possessed well behaved paleomagnetic directions suitable for paleomagnetic secular variation dating the results indicate that the sediments below the unconformity were deposited approximately 7600 8500 cal yr bp and the sediments above the unconformity were deposited approximately 2500 800 cal yr bp the ages of the corresponding sediments are consistent with the time intervals during which previous studies indicate that lake level was above the elevation of this site before and after a mid holocene regression

the role of recrystallisation on the deformation behaviour of calcite rocks large strain torsion experiments on carrara marble abstract the rheological microstructural and textural evolution of carrara marble was studied during experimental deformation in torsion up to very large shear strains 0 4 50 experiments were performed at constant angular displacement rates corresponding to shear strain rates of 6 10 5 3 10 3 s 1 a confining pressure of 300 mpa and temperatures of 500 600 and 727 c microstructures and crystallographic preferred orientations cpo were analysed using light microscopy and electron backscatter diffraction ebsd at all conditions deformation occurred dominantly by dislocation creep even up to very large shear strains after peak stresses 2 recrystallisation mostly by subgrain rotation caused weakening 5 20 grain size reduction and a change in the cpo a monoclinic cpo that formed at small strains at all temperatures evolved into two different large strain cpos at different temperatures at large strains even after complete recrystallisation the cpo continued to strengthen and a secondary foliation was formed at a steep angle to the shear zone boundary this secondary foliation was continuously reset by both subgrain rotation and grain boundary migration recrystallisation and eventually overprinted the primary foliation misidentifying the primary and secondary foliations could result in misinterpretation of the applied strain field more generally information about the amount of strain is lacking for microstructures and cpos of highly deformed ultramylonites

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

inversion of the hz ratio of microseisms for s wave velocity in the crust summary s wave velocity in the shallow crust is an important controlling parameter for ground motion amplification it is a key parameter for prediction of ground motion and thus for earthquake hazard mitigation in general shallow s wave velocity structure has often been obtained from phase velocity of microtremors and microseisms we present a new approach which directly inverts the ratio of horizontal to vertical amplitudes of microseisms which is referred to as the hz ratio in this paper our approach consists of i isolation of rayleigh wave dominant portions in seismograms by using the 90 degree phase shift between horizontal and vertical component ii measurement of the hz ratios as a function of frequency and iii iterative inversion for s wave velocity structure in the crust depth sensitivity kernels of the hz ratios for density p wave velocity and s wave velocity are derived by a numerical method examples of the application of this method to data in southern california show that the hz ratio data require modification of the standard seismic velocity model in this region southern california earthquake center community velocity model 3 0 or scec cvm in the upper 10 15 km the derived models show amplification of incident sh waves by factors of 2 8 relative to the prediction by the scec cvm the proposed approach has promise for applications to other regions in the world because microseisms are observed everywhere in the world the method may become even more powerful if it is combined with phase velocity data

holocene secular variation in western north america paleomagnetic record from fish lake harney county oregon an 8 9 m composite section of lake sediment from fish lake steens mountain southeastern oregon has provided a high resolution record of holocene geomagnetic secular variation in western north america the section is composed of overlapping core segments with stratigraphic control based on six tephra layers and other thin distinct bands and with age control from 37 radiocarbon dates the 455 paleomagnetic samples possess a strong and stable magnetic remanence which is carried by pseudo single domain magnetite paleomagnetic records for individual core segments show low scatter and high serial correlation and where the segments overlap there is excellent agreement between records the azimuthal orientation of the composite section was recovered from the known direction of the geomagnetic field at the time of the climactic eruption of mount mazama tephra which is present in fish lake both internal and external evidence including the correspondence with an archaeomagnetic record from the southwestern united states support the conclusion that the fish lake record represents the history of geomagnetic field behavior during at least the last 10 000 years b p analysis of that record reveals that the average geomagnetic direction can not be distinguished from that of a geocentric axial dipole field and that the overall circularity of the field was clockwise but the detailed behavior was quite complex angular standard deviations of both field directions and virtual geomagnetic poles differ significantly from the values predicted from theoretical models of secular variation but are consistent with those of other holocene records when the record from fish lake is compared to the proposed type curve for east central north america there is excellent agreement for the past 6000 years provided the curves are offset by about 400 years this offset corresponds to a rate of westward drift of about 0 062 yr beyond about 6000 radiocarbon years ago good agreement between the two curves occurs when there is no offset suggesting that the field was standing rather than drifting during this time

a fan dam for tulare lake california and implications for the wisconsin glacial history of the sierra nevada historic fluctuations and late quaternary deposits of tulare lake in the southern san joaquin valley indicate that maximum lake size has depended chiefly on the height of a frequently overtopped spillway this dependence gives tulare lake a double record of paleoclimate climate in the tulare lake region has influenced the degree to which the lake fills its basin during dry seasons and dry years during the past 100 000 130 000 yr incidence of desiccation of tulare lake inferred from stiffness mud cracks and other hand specimen properties has been broadly consistent with the lake9s salinity and depth inferred from diatoms and ostracodes and with regional vegetation inferred from pollen climate however also appears to control basin capacity itself tulare lake becomes large as a consequence of glacial outwash aggradation of its alluvial fan dam late wisconsin enlargement of tulare lake probably resulted from the last major glaciation of the sierra nevada the lake9s spillway coincides with the axis of the glacial outwash fan of a major sierra nevada stream moreover sediment deposited in the transgressive lake resembles glacial rock flour from the sierra nevada differential tectonic subsidence and deposition by a coast range creek facilitated the building of tulare lake9s fan dam during the late wisconsin but were less important than deposition of sierra nevada outwash four stratigraphically consistent 14 c dates on peat and wood give an age of 26 000 yr b p for the start of tulare lake9s late wisconsin transgression the last major sierra nevada glaciation tioga glaciation thus may have begun about 26 000 yr b p provided that vigorous glacial outwash deposition began early in the glaciation onset of the tioga glaciation about 26 000 yr b p is consistent with new stratigraphic and radiocarbon data from the northeastern san joaquin valley these data suggest that the principal episode of glacial outwash deposition of wisconsin age began in the san joaquin valley after 32 000 yr b p rather than at least 40 000 yr b p as previously believed an earlier enlargement of tulare lake probably resulted from a fan dam produced by the penultimate major tahoe glaciation of the sierra nevada average sedimentation rates inferred from depths to a 600 000 yr old clay and from radiocarbon dates indicate that this earlier lake originated no later than 100 000 yr b p the tahoe glaciation therefore is probably pre wisconsin

fast diffusion along mobile grain boundaries in calcite experimental measurements of grain boundary diffusion are usually conducted on static boundaries despite the fact that grain boundaries deep in the earth are frequently mobile in order to explore the possible effect of boundary mobility on grain boundary diffusion rates we have measured the uptake of 44ca from a layer of 44ca enriched calcite powder during the static recrystallization of a single crystal of calcite at 900 c a region about 500 m wide adjacent to the powder layer is heterogeneously enriched in 44ca and complex zoning patterns including sharp steps in composition and continuous increases and decreases in 44ca content are developed in metamorphic rocks these would normally be interpreted in terms of changes in pressure or temperature rayleigh fractionation or episodic fluid infiltration these explanations cannot apply to our experiments and instead the zoning patterns are interpreted as being due to variations in grain boundary migration rate we have applied an analytical model which allows the product of grain boundary diffusion coefficient and grain boundary width dgb to be calculated from the grain boundary migration rate and the compositional gradient away from the powder layer the value of dgb in the mobile grain boundaries is at least five orders of magnitude greater than the published value for static boundaries under the same conditions in order to allow the scale of chemical equilibrium and hence textural evolution to be predicted under both experimental and geological conditions we present quantitative diffusion regime maps for static and mobile boundaries in calcite using both published values and our new values for grain boundary diffusion in mobile boundaries enhanced diffusion in mobile boundaries has wide implications for the high temperature rheology of earth materials for geochronology and for interpretations of the length and time scales of chemical mass transport moreover zones of anomalously high electrical conductivity in the crust and mantle could be regions undergoing recrystallization such as active shear zones rather than regions of anomalous mineralogy water or melt content as is generally suggested

theories and applicability of grain size piezometers the role of dynamic recrystallization mechanisms abstract the average grain size d arising from dynamic recrystallization drx is often used as an indicator of flow stress however a theoretical basis for the scaling relation between d and has yet to be well established in this paper theories for the development of recrystallized grain size are reviewed and their applicability is examined special attention is paid to the dependence of the d relation on drx mechanisms steady state drx is classified into discontinuous drx with bulging blg nucleation grain boundary migration gbm and continuous drx with subgrain rotation sgr nucleation gbm the nucleation and growth model derived from derby ashby theory describes the former case whereas that derived from shimizu theory applies to the latter a static energy balance model derived from twiss theory is applicable to subgrain size but not to recrystallized grain size the lower limit of grain size is possibly constrained by a change in deformation mechanism from dislocation creep to diffusion creep because deformation induced grain size reduction ceases in the diffusion creep field scaling relations determined in the laboratory support the shimizu model in the case of sgr gbm the theoretical piezometer calibrated for quartz suggests significant temperature effects under low temperature metamorphic conditions

electron backscatter diffraction analysis to determine the mechanisms that operated during dynamic recrystallisation of quartz rich rocks abstract determination of the controlling nucleation and recrystallisation mechanisms from a samples microstructure are essential for understanding how the microstructure formed and evolved through time the aim of our research was to apply a quantified analytical approach to the identification of the controlling nucleation recrystallisation and microstructural modification mechanisms we used electron backscatter diffraction to quantify the microstructures of naturally deformed quartz rich rocks which were deformed at various temperature and pressure conditions our results show that ratios of the recrystallised grain size to the subgrain size with values less than 1 0 5 0 7 in the data presented here suggest bulge nucleation whereas ratios of 1 suggest subgrain rotation nucleation other supporting evidence for subgrain rotation nucleation is an increase in misorientation from the centre of an original protolith parent grain to the edge all samples show evidence for modification of the microstructure due to grain boundary sliding including increased misorientation angles between grains and movement of recrystallised grains between parent grains by systematically analysing sample microstructures it is possible to separate out evidence to determine the controlling nucleation and recrystallisation mechanisms as well as being able to identify microstructure modification mechanisms using microstructural quantification via ebsd allows a systematic methodology to analyse samples from any location from an objective viewpoint

the rambla highstand shoreline and the holocene lake level history of tulare lake california usa abstract the stratigraphy associated with a highstand wave cut shoreline and with sites farther out into the lake plain constrain the holocene lake level history of tulare lake california usa as follows seven to eight major fluctuations in lake level occurred during the past 11 500 yr lake level was generally higher during the early holocene prior to 6000 cal yr bp peaking in two highstands 65 70 masl at 9500 8000 cal yr bp and 6900 5800 cal yr bp thereafter it fluctuated at lower amplitude until reaching a major highstand during the most recent millennium between 750 and 150 cal yr bp two lake level rises of lower amplitude were centered on 3300 and 1600 cal yr bp at least three probably brief lowstands

a 9170 year record of decadal to multi centennial scale pluvial episodes from the coastal southwest united states a role for atmospheric rivers abstract a well dated 9170 calendar year before present cal yr bp paleohydrologic reconstruction is presented from lower bear lake in the san bernardino mountains of the coastal southwest united states this new multi proxy record is characterized by alternating organic rich carbonate rich sediment units interpreted to reflect hydrologically forced changes in the lake s depositional environment our interpretation of the proxy data indicates nine decadal to multi centennial pluvial episodes pe over the past 9170 cal yr bp of these nine inferred pluvials five are interpreted as more pronounced based on their combined proxy interpretations pe v 9170 8250 pe iv 7000 6400 pe iii 3350 3000 pe ii 850 700 and pe i 500 476 top of core cal yr bp the lower bear lake record indicates that the san bernardino mountains source region for the mojave river and its terminal playa was wet during the same periods within dating errors to several of the major pluvials proposed from the lakes in the sink of the mojave river our comparison extends north also to tulare lake which drains the southcentral western sierra nevada mountains this temporally and spatially coherent signal indicates that a similar climate forcing acted to increase regional wetness at various times during the past 9170 cal yr bp as originally proposed by enzel ely and colleagues e g enzel et al 1989 enzel 1992 ely et al 1994 enzel and wells 1997 we too contend that holocene pluvial episodes are associated with changing the frequency of large winter storms that track across a broad region at decadal to multi centennial timescales we build upon their hypothesis through the addition of new and better dated site comparisons recent advances in the understanding of atmospheric rivers and improved knowledge of the ocean atmosphere dynamics that caused the early 20th century western united states pluvial

paleowattmeters a scaling relation for dynamically recrystallized grain size during dislocation creep mineral grains often evolve to a stable size dictated by the deformation conditions we suggest that grain size evolution during deformation is determined by the rate of mechanical work provided that other elements of microstructure have achieved steady state and that the dissipation rate is roughly constant then changes in internal energy will be proportional to changes in grain boundary area if normal grain growth and dynamic grain size reduction occur simultaneously then the steady state grain size is determined by the balance of those rates a scaling model using these assumptions and published grain growth and mechanical relations matches stress grain size relations for quartz and olivine rocks with no fitting for marbles the model also explains scatter not rationalized by assuming that recrystallized grain size is a function of stress alone when extrapolated to conditions typical for natural mylonites the model is consistent with field constraints on stresses and strain rates

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

low temperature deformation of limestone isola palmaria northern apennine italy the role of primary textures precursory veins and intracrystalline deformation in localization abstract fine grained limestones of the tuscan nappe from isola palmaria northern apennine italy contain sporadically developed bedding parallel shear zones some of which exhibit well developed calcite mylonites the presence of shear zones that formed at temperatures less than 250 c allows the study of limestone deformation mechanisms active under low temperature upper crustal conditions two materially distinct types of shear zones developed during the syn nappe stage of deformation and have been characterized by integrated field strain microstructural optical microscopy cathodoluminescence transmission electron microscopy and ebsd fabric studies type a shear zones occur within decametre thick packages accommodating heterogeneously distributed strain in very fine grained limestone micrite type b shear zones are localized within calcite veins that develop into recrystallized calc mylonites both types form at the contact with dolomite although this does not play an important role in strain localization in both cases low temperature ductility occurs by extensive dislocation glide sustained by athermal network accommodated recovery although the end state microstructures of both shear zone types cannot be differentiated optically differences do exist in the crystallographic preferred orientations cpo and the grain boundary structure of deformed micrite and vein calcite deformed micrite grain boundaries are rich in voids consistent with extensive fluid flux that can enhance material transport and independent grain displacements while suppressing cpo development the crystallographically defined grain boundaries in recrystallized vein calcite suggest that lower grain boundary diffusivity enables more typical dislocation mediated cpo formation

grain boundary hierarchy development in a quartz mylonite abstract orientation contrast imaging using forescatter detectors and backscattered electron diffraction techniques in the scanning electron microscope have been used to investigate the boundary hierarchy characteristics of a quartz mylonite shear zone from torridon nw scotland the boundary hierarchy is defined as the relationship between the boundary misorientations their enclosed domain size and their frequency distribution by measuring the misorientation across every grain and subgrain boundary the characteristics of the boundary hierarchy can be found two microstructural domains were studied one partially recrystallized low strain domain with large relict grains and one fully recrystallized high strain mylonitic domain our results indicate that the processes of recovery subgrain rotation and grain boundary migration recrystallization each produce identifiable boundary hierarchy signatures in the relict quartz grains we have identified the processes of recovery and subgrain rotation in the recrystallized quartz a cyclic steady state exists between these and other processes coupling these data with traditional microstructural observations allows a more rigorous investigation into the development of a high strain fine grained mylonite from a coarse grained undeformed protolith we suggest that this type of detailed crystallographic microstructural analysis can greatly further our understanding of microstructural development in shear zones and may have implications for the effective use of sub grain size palaeopiezometers

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

optical microstructure of partly recrystallized calcite in some naturally deformed marbles abstract deformed marbles from the mt lofty ranges south australia have microstructures characterized by deformed relics of calcite interspersed with much finer grained recrystallized calcite and with minor quartz and diopside the deformed calcite relics contain numerous subgrains and show abundant evidence of strain induced migration of twin and grain boundaries new calcite grains have nucleated and grown preferentially along twins especially at twin intersections at grain and kink like boundaries and apparently randomly inside deformed relics optical microstructural evidence suggests that dynamic syntectonic recrystallization has taken place along with some static recrystallization probable mechanisms for the initiation of recrystallization include bulge nucleation and subgrain nucleation

microstructure mechanism map of dynamically recrystallized marble abstract the relative nucleus density rnd model of dynamically recrystallized grain size sakai t jonas j j 1984 dynamic recrystallization mechanical and microctructutal consideration acta metallurgica 32 198 209 was applied to experimentally and to naturally deformed marbles that have undergone dynamic recrystallization the model shows that a relationship between initial grain size d 0 and stable dynamically recrystallized grain size d s for a given value of temperature corrected strain rate z controls grain size evolution during dynamic recrystallization new microstructural mechanism maps mm maps for experimentally and naturally deformed marbles based on previously published data were defined in log grain size log z space and show two distinct regions of grain reduction and grain coarsening the boundary between these two regions corresponds to an equation relating dynamically recrystallized grain size and temperature corrected strain rate as proposed in this work the new mm map was used to trace semi quantitatively microstructural and grain size evolution in naturally deformed marbles that underwent dynamic recrystallization at different thermal conditions the boundary between grain coarsening and grain reduction does not necessarily coincide with the boundary between rotation and migration recrystallization mechanisms assessment of available natural data shows that the boundary condition d 0 2 d s between grain coarsening and grain reduction introduced by sakai and jonas sakai t jonas j j 1984 dynamic recrystallization mechanical and microctructutal consideration acta metallurgica 32 198 209 is not required for naturally deformed marble

characteristics of long period microtremors and their applicability in exploration of deep sedimentary layers abstract applicability of long period microtremors in inferring subsurface structure is examined using measurements of microtremors in the northwestern part of the kanto plain in japan short term continuous measurements of long period microtremors at both sediment and basement sites were taken a spectral peak at a period of 4 to 5 sec is stable with time while peaks at periods less than 2 sec are time variant suggesting a variation of microtremor sources however it was found that the spectral ratio between vertical and horizontal microtremors ellipticity at each site is stable with time good agreement was found between ellipticities of microtremors at the sediment site and those computed for rayleigh waves in which the structure of the sediments beneath the site was taken into account we also found that the ellipticities of rayleigh waves in earthquake ground motions were consistent with those of the microtremors these comparisons provide strong evidence that long period microtremors in the area studied consist mainly of rayleigh waves the ellipticity of microtremors was investigated by observing microtremors at temporary observation sites in the kanto plain where the sediment thickness varied from 0 to 1 km the subsurface structures were deduced by trial and error fitting of observed ellipticities with theoretical ellipticities that were calculated assuming rayleigh waves these results show that ellipticity of long period microtremors is effective for deducing structure from microtremor data at a single site

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

lake levels for the past 19 000 years from the tl05 4 cores tulare lake california usa geophysical and geochemical proxies abstract geochemical and geophysical proxy data from the tl05 4 lake plain cores of tulare lake california are reported on here representing most of the past 19 000 years the new record consists of carbon nitrogen ratios total organic carbon toc nitrogen n total inorganic carbon tic grain size and magnetic susceptibility analyses from samples taken at 1 cm intervals 45 yr sample age control is provided by 22 radiocarbon dates the first part of the record 19 0 14 5 cal ka bp consists of elevated sand and silt percentages and higher sedimentation rates interpreted as elevated runoff associated with melting of the tioga age sierra nevada ice cap the tic was undetectable and toc and n were low suggesting low productivity in a relatively sterile freshwater lake from 14 5 to 10 3 cal ka bp the deposits consisted of 50 clay and 50 silt with tic and toc extremely low which is consistent with a stable low productivity lake from 10 3 to 7 5 cal ka bp an initial pulse of fining upward sand gave way to increased clay deposition that suggests a lake transgression to a stable highstand coeval with the deep water event found in previously published records of tulare lake and other lakes from central and southern california including owens lake and lake elsinore a few hundred year duration spikes in tic centered at 8 0 cal ka bp is suggestive of evaporating lake conditions toward the end of this early holocene highstand tulare lake dropped quickly to a relative low at 7 5 cal ka bp but then lake level increased steadily until 3 0 cal ka bp high amplitude fluctuation in almost all proxies occurs from 2 5 to 1 8 cal ka bp at the end of the record suggesting that this time interval was characterized by rapid fluctuations in lake level tulare lake levels during the holocene vary in conjunction with sea surface temperature sst records from the ocean drilling program odp site 1017 located off the coast of central california which suggests that variations in ssts throughout the holocene drove changes in precipitation in the sierra nevada and hence tulare lake level since historic lake level histories have been shown to be directly related to stream discharge from the sierra nevada this observation will be integral in forecasting future decadal scale changes in southern san joaquin valley water supply due to anticipated climate change

last glacial maximum and holocene lake levels of owens lake eastern california usa abstract stratigraphic investigations of fluvio deltaic and lacustrine sediments exposed in stream cuts quarry walls and deep trenches east of the sierra nevada in owens valley near lone pine california have enabled the reconstruction of pluvial owens lake level oscillations age control for these sediments is from 22 radiocarbon 14 c dates and the identification and stratigraphic correlation of a tephra which when plotted as a function of age versus altitude define numerous oscillations in the level of pluvial owens lake during the latest pleistocene and early holocene we have constructed a lake level altitude curve for the time interval 27 000 cal yr bp to present that is based on the integration of this new stratigraphic analysis with published surface stratigraphic data and subsurface core data pluvial owens lake regressed from its latest pleistocene highstands from 27 000 to 15 300 cal yr bp as recorded by 15 m of down cutting of the sill from the altitudes of 1160 to 1145 m by 11 600 cal yr bp the lake had dropped 45 m from the 1145 m sill this lowstand was followed by an early holocene transgression that attained a highstand near 1135 m before dropping to 1120 m at 7860 7650 cal yr bp that had not been recognized in earlier studies the lake then lowered another 30 m to shallow and near desiccation levels between 6850 and 4300 cal yr bp fluvial cut and fill relations north of lone pine and well preserved shoreline features at 1108 m indicate a minor lake level rise after 4300 cal yr bp followed by alkaline and shallow conditions during the latest holocene the new latest quaternary lake level record of pluvial owens lake offers insight to the hydrologic balance along the east side of the southern sierra nevada and will assist regional paleoclimatic models for the western basin and range

large strain deformation studies using polycrystalline magnesium as a rock analogue part i grain size paleopiezometry in mylonite zones abstract the results of large strain deformation studies of polycrystalline magnesium are reported shear zones develop at temperatures below 0 65 tm for strain rates between 10 4 10 5 s 1 the zones are characterised by small recrystallised grains and are analogues of mylonite zones in crustal and mantle rocks their development is marked by a stress drop but the recrystallised grains in the zones do not re equilibrate and remain equilibrated to the peak stress however the recrystallised grains in the areas bordering the shear zones undergo a strain dependent coarsening and their sizes re equilibrate to the relaxed stresses at natural strains of 1 the geological implications of these results are discussed

effect of water on the strength and microstructure of carrara marble axially compressed at high temperature in this study we aimed to i answer the question if water affects the strength of marble deforming at high temperature and ii establish criteria that allow assessment of the role of water in microstructure development in marble samples of carrara marble were axially compressed at temperatures ranging 600 1000 8c and strain rate w10 k5 s k1 with or without addition of 0 4 2 1 wt water water added samples were found to be slightly weaker than dry samples microstructurally all samples showed grain flattening and twinning at 600 8c and dynamic recrystallization dominated by grain boundary migration at higher temperature grain boundaries in wet samples showed isolated or semi continuous remnants of fluid pockets the average grain roundness r and fractal dimension d relating grain diameter d and grain perimeter p pfd d for wet recrystallized samples were systematically lower than for dry samples at 600 8c high pore fluid pressure probably enhanced dilatation of wet samples and helped grain boundary sliding gbs thereby lowering the strength at higher temperature fluid enhanced grain boundary migration served as a recovery process reducing the contribution of gbs to creep overall water has little effect on strength and microstructure of marble experimentally deformed at high temperature q 2005 elsevier ltd all rights reserved

deformation and recrystallization mechanisms in actively extruding salt fountain microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size qum kuh central iran microstructural study of rocksalt samples from an active salt fountain qum kuh central iran enabled to identify the relative contribution of different deformation mechanisms on extrusive salt flow the microstructural study combined reflected and transmitted light microscopy of gamma irradiated thin sections textural analysis of digitized microstructures and electron back scattered diffraction ebsd deformation microstructures record the strongly variable deformation conditions of salt flow in the diapiric system from the diapiric stem towards the distal part of the mature viscous fountain high stress deformation conditions typical for diapiric stems are recorded in the small subgrains within the porphyroclasts of all documented samples recovery and recrystallization due to divergent and decelerating flow associated with differential stress drop in the salt extrusion above the diapiric orifice is reflected by abundant growth band microstructures this study reveals also evidence for penetration of rainwater into the salt mass and documents the switch from the dominant dislocation creep into dominant solution precipitation creep from the upper part to the distal part of the fountain this deformation mechanism switch is provided by influx of meteoric water and grain size decrease likely controlled by subgrain rotation and grain boundary migration recrystallization

stress dependence of microstructures in experimentally deformed calcite abstract optical measurements of microstructural features in experimentally deformed carrara marble help define their dependence on stress these features include dynamically recrystallized grain size dr subgrain size sg minimum bulge size l and the maximum scale length for surface energy driven grain boundary migration l taken together with previously published data dr defines a paleopiezometer over the range 15 291 mpa and temperature over the range 500 1000 c with a stress exponent of 1 09 ci 1 27 to 0 95 showing no detectable dependence on temperature sg and dr measured in the same samples are closely similar in size suggesting that the new grains did not grow significantly after nucleation l and l measured on each sample define a relationship to stress with an exponent of approximately 1 6 which helps define the boundary between a region of dominant strain energy driven grain boundary migration at high stress from a region of dominant surface energy driven grain boundary migration at low stress

a new perspective on paleopiezometry dynamically recrystallized grain size distributions indicate mechanism changes the dynamically recrystallized grain size is a material parameter associated with dislocation creep of crystalline solids that is especially important as a flow stress indicator via piezometer calibrations grain sizes have been measured in many studies of deformed rocks as well as metals and ceramics but global analyses of the frequency distribution of dynamically recrystallized grain sizes are lacking here we present the first systematic investigation of the recrystallized grain size distribution for quartz the grain diameters compiled from 555 samples of 31 studies of quartz mylonites deformed over a wide range of conditions extend from 3 m to 3 mm with distinct maxima at 10 20 m and 70 80 m and minima at 35 40 m and 120 m the frequency maxima correlate with distinct microstructures and the minima with the transitions between these microstructures which we interpret to result from the dominance of the recrystallization mechanisms of bulging subgrain rotation and grain boundary migration recrystallization these results demonstrate the necessity of distinct piezometer calibrations for different recrystallization mechanisms and highlight the importance of the recrystallized grain size for theoretical models of dynamic recrystallization

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

dynamic recrystallization of feldspar a mechanism for ductile shear zone formation feldspar aggregates experimentally deformed in the dislocation creep regime undergo dynamic recrystallization because recovery is difficult due to the limited climb of dislocations recrystallizing aggregates have a lower strength because of the cyclic production of small strain free grains and they develop a strong preferred orientation consistent with that observed in mylonites thus recrystallization accommodated dislocation creep may be responsible for the grain size reduction and strain softening that lead to the formation of many mylonites and ductile shear zones

microstructure and micromotion in recrystallization flow of octachloropropane a first look advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes and the effects of these processes upon various fabric elements this paper describes aspects of the microstructural evolution and associated small scale motion in a dynamically recrystallizing sheet of octachloropropane the material was deformed in progressive pure shear at 2 10 3 sec 1 with interruptions for photography and u stage measurement at 70 of its absolute melting temperature the dominant recrystallization process is migration of grain boundaries with consequent major adjustment of the shapes and sizes of grains but no marked change in the average grain size and no creation of new grains typical grains in the fully deformed material 30 bulk shortening have a composite structure with primitive high strain regions inherited directly from the undeformed state rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries an array of second phase marker particles permits distinction between grain boundary motion with and through the material and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient the markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains the central problem posed by the observations is to explain the direction and speed of each migrating boundary two hypotheses were tested neither with outstanding success one of these hypotheses is that grain boundary migration is part of a strain accomodation process that operates between grains stretching or shortening at different rates parallel to their mutual boundary

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

estimation of s wave velocity structures in and around the sendai basin japan using array records of microtremors we conducted array measurements of microtremors at six sites in and around the sendai basin to estimate deep s wave velocity structures above the seismological bedrock pre tertiary bedrock after estimating phase velocities of microtremors in the frequency range from about 0 5 to 3 hz we succeeded to estimate the deep structures above the pre tertiary bedrock at four soil sites kata okin arah and myg15 and only the upper part just beneath the pliocene layer at the other soil site trma using a rayleigh wave inversion technique at trma and a rock site tama we roughly estimate the deep s wave velocity structures using empirical site amplification factors derived from strong motion records the deepest bedrock depth is 1 km and the shallowest depth is 200 m among these six sites the difference of the bedrock depth between the eastern side and the western side of an active thrust fault the nagamachi rifu line is only 120 m the difference of the bedrock depth between two sites in the east of the basin reaches about 500 m although any geological boundaries or buried faults have not been mapped since the deep s wave velocity structure of the sendai basin had been basically unknown we delineate it for the first time in this article using array measurement of microtremors

dynamic recrystallization of wet synthetic polycrystalline halite dependence of grain size distribution on flow stress temperature and strain abstract it is often observed that dynamic recrystallization results in a recrystallized grain size distribution with a mean grain size that is inversely related to the flow stress however it is still open to discussion if theoretical models that underpin recrystallized grain size stress relations offer a satisfactorily microphysical basis the temperature dependence of recrystallized grain size predicted by most of these models is rarely observed possibly because it is usually not systematically investigated in this study samples of wet halite containing 10 ppm water by weight were deformed in axial compression at 50 mpa confining pressure the evolution of the recrystallized grain size distribution with strain was investigated using experiments achieving natural strains of 0 07 0 12 and 0 25 at a strain rate of 5 10 7 s 1 and a temperature of 125 c the stress and temperature dependence of recrystallized grain size was systematically investigated using experiments achieving fixed strains of 0 29 0 46 and one to a strain of 0 68 at constant strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c yielding stresses of 7 22 mpa the microstructures and full grain size distributions of all samples were analyzed the results showed that deformation occurred by a combination of dislocation creep and solution precipitation creep dynamic recrystallization occurred in all samples and was dominated by fluid assisted grain boundary migration during deformation grain boundary migration results in a competition between grain growth due to the removal of grains with high internal strain energy and grain size reduction due to grain dissection i e moving boundaries that crosscut or consume parts of neighbouring grains at steady state grain growth and grain size reduction processes balance yielding constant flow stress and recrystallized grain size that is inversely related to stress and temperature evaluation of the recrystallized grain size data against the different models for the development of mean steady state recrystallized grain size revealed that the data are best described by a model based on the hypothesis that recrystallized grain size organizes itself in the boundary between the grain size sensitive solution precipitation and grain size insensitive dislocation creep fields application of a piezometer calibrated using the recrystallized grain size data to natural halite rock revealed that paleostresses can vary significantly with temperature up to a factor of 2 5 for t 50 200 c and that the existing temperature independent recrystallized grain size stress piezometer may significantly underestimate flow stresses in natural halite rock

determination of shallow shear wave velocity profiles in the cologne germany area using ambient vibrations summary we have used both single station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of cologne germany from ambient vibration records based on fk analysis we assume that fundamental mode rayleigh waves dominate the analysed wavefield in the frequency range of 0 7 2 2 hz according to this view a close relation exists between h v spectral ratios and the ellipticity of the contributing rayleigh waves the inversion of the shape of h v spectral ratios then provides quantitative information concerning the local shear wave velocity structure however based on tests with synthetic data believed to represent a typical situation in the lower rhine embayment dispersion curves were found to provide stronger constraints on the absolute values of the velocity depth model than the ellipticities the shape of the ellipticities was found to be subject to a strong trade off between the layer thickness and the average layer velocity we have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities in order to test this method in practice we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available in order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half space model however owing to earlier studies from the region we assume a power law depth dependence for sediment velocities for all three sites investigated the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by budny from downhole measurements this is strong support for the interpretation of h v spectral ratios as rayleigh wave ellipticities for all three sites the predicted sh wave site amplification factors at the fundamental frequency are of the order of 5 6 with a slightly smaller value south of cologne

three dimensional s wave velocity structure in southern california 1 the three dimensional s wave velocity structure was constructed from rayleigh wave phase velocities measured using teleseismic trinet data the s wave velocity maps show some features that are much more distinct than previous tomographic results in southern california there is a clear seismic velocity contrast across the san andreas fault the north american plate side is systematically slower than the pacific plate side under the eastern california shear zone there are distinct slow velocity anomalies in the crust suggesting a close connection to lower viscosity crust previously concluded from observation of the post seismic deformation after the landers earthquake major upper mantle features include a fast velocity root under the transverse ranges which is the dominant feature in the upper mantle and a slow velocity anomaly under the salton trough our results support that the velocity contrast across the san andreas fault extends below the moho

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

quartz grainsize evolution during dynamic recrystallization across a natural shear zone boundary abstract although it is widely accepted that grainsize reduction by dynamic recrystallization can lead to strain localization the details of the grainsize evolution during dynamic recrystallization remain unclear we investigated the bulge size and grainsizes of quartz at approximately the initiation and the completion stages of bulging recrystallization across the upper boundary of a 500 m thick mylonite zone above the vincent fault in the san gabriel mountains southern california within uncertainty the average bulge size of quartz 4 7 1 5 m is the same as the recrystallized grainsize 4 5 1 5 m at the incipient stage of dynamic recrystallization and also the same within uncertainties as the recrystallized grainsize when dynamic recrystallization is largely complete 4 7 1 3 m these observations indicate that the recrystallized grainsize is controlled by the nucleation process and does not change afterwards it is also consistent with the experimental finding that the quartz recrystallized grainsize paleopiezometer is independent of temperature

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

rheological and microstructural evolution of carrara marble with high shear strain results from high temperature torsion experiments abstract this study investigated the rheological and microstructural evolution of carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice preferred orientation lpo are related to strain softening processes solid cylinders of carrara marble were deformed in torsion up to a shear strain of 11 at constant twist rates which correspond to a shear strain rate of 3 10 4 s 1 at the outer surface and at temperatures of 1000 and 1200 k 727 and 927 c respectively for the initial grain size of 150 m these conditions are within the dislocation creep regime substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000 k 1200 k a peak stress was reached at about 1 0 5 followed by moderate strain weakening an apparent steady state flow stress was obtained at high shear strain of 5 2 the stress exponent n decreased slowly with strain from 10 1 to 6 9 at 1000 k but it remained approximately constant at 1200 k n around 10 at the maximum reached shear strain of 11 8 5 the marble had almost completely recrystallized to a fine grain size of about 10 m 20 m a secondary foliation developed in the recrystallized matrix which is at a large oblique angle to the shear zone boundary szb lpo was measured by electron backscatter diffraction ebsd for both temperatures the lpo evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r 1014 parallel to the shear plane and a 1210 parallel to the shear direction it is concluded that strain weakening was associated with the development of a strong lpo during dynamic recrystallization to a finer grain size mechanical and microstructural steady state is only reached at large shear strain the steady state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite mylonites

synkinematic microscopy of transparent polycrystals abstract deformation of weak polycrystalline materials in thin section on the stage of a petrographic microscope offers insight into the origin of optical microstructures similar to microstructures in naturally deformed rocks sample materials used to date include several soft minerals ice carnallite bischofite nitratite and various organic plastic materials they can be simple sheared or pure sheared at temperatures to 300 c at a variety of strain rates using relatively simple and inexpensive apparatus the complete microstructural evolution can be recorded photographically along with the complete kinematic history research applications have focussed on dynamic recrystallization and progress has been made towards understanding how the average grain size is maintained constant in steady state recrystallization flow records have been obtained of the development of various crystal plastic microstructures and of lattice reorientation trajectories during flow teaching applications have begun to be developed and several videotapes are available future technical developments are expected to permit stress measurement or control during experiments and synkinematic recording of lattice reorientation numerous research areas invite attention these include investigation of the microstructural developments that precede faulting the behaviour of deforming crystal melt systems and the behaviour of dynamically reactive multi phase systems