timing and tectonic setting of grenvillian metamorphism constraints from a transect along georgian bay ontario systematic mapping of a transect along the well exposed shores of georgian bay ontario combined with the preliminary results of structural analysis geochronology and metamorphic petrology places some constraints on the geological setting of high grade metamorphism in this part of the central gneiss belt correlations within and between map units gneiss associations have allowed us to recognize five tectonic units that differ in various aspects of their lithology metamorphic and plutonic history and structural style the lowest unit which forms the footwall to a regional decollement locally preserves relic pre grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the grenvillian orogeny tectonic units above the decollement apparently lack the early granulite facies metamorphism out of sequence thrusting in the south produced a duplex like structure two distinct stages of grenvillian metamorphism are apparent the earlier stage c 1160 1120 ma produced granulite facies assemblages in the parry sound domain and upper amphibolite facies assemblages in the parry island thrust sheet the later stage c 1040 1020 ma involved widespread dominantly upper amphibolite facies metamorphism within and beneath the duplex deformation and metamorphism recently reported from south and east of the parry sound domain at c 1100 1040 ma have not yet been documented along the georgian bay transect the data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south east of the transect area with further advance to the north west during and after the waning stages of this deformation

introduction to this special section advances in seismic sensors seismic detectors have been around for centuries and seismic prospecting for many decades the variety of seismic sensors in modern surveys is dazzling they can measure particle velocity and acceleration pressure and pressure gradient strain and strain rate and multiple components z h1 h2 yaw pitch roll from near dc to hundreds or thousands of hertz in land marine borehole and extraterrestrial environments

vertical seismic optical profiling on wireline logging cable abstract vertical seismic profiles are usually acquired by deploying downhole seismic sensors below a wireline logging cable a seismic source is triggered at surface while recording the downhole vibration via the wireline cable in this paper an alternative approach based on distributed vibration measurement is tested using wireline deployment for the first time local axial strain of a multi kilometre fibre optic line is measured at intervals of approximately 1 m and processed to a spatial resolution of 10 m with sub nanometer strain resolution by an optical interrogation device distributed vibration acoustic sensing when deployed in a well the optical fibre line should be mechanically coupled to the borehole wall to generate valid seismic records a conventional vertical seismic profile was acquired with three component sensors in a vertical well near bottesford uk the impulsive seismic source was a novel portable airgun tank clear seismic reflections are observed within and below the borehole in agreement with surface seismic data a single shot generated equivalent data with an experimental optical wireline logging cable and an adequate optical interrogator at the surface the main difference between the two records is the presence of a strong tube wave in the optical profile which can be easily removed with conventional velocity filter processing corridor stacks from both conventional and optical profiles match each other and provide a reasonable tie to a nearby surface seismic line

the role of strain heating in the evolution of megathrusts on the basis of elementary energy considerations and the nonlinear temperature dependence of experimental flow laws a model is developed for the interplay of thermal and mechanical processes along megathrust systems the model is based on the observation that thrust systems involving large portions of the lithosphere have a two part history during the early history of movement dry lower crustal upper mantle rocks are deformed in a shear zone where because of the nonlinear effect of temperature dependent diffusion strain heating rates are directly controlled by the initial thermal state that is heating is insignificant if initial temperatures are high but where temperatures are low large temperature increases are possible as a result strain heating acts as a thermal buffer such that upon arrival of upper crustal rocks at depths of 20 km or more the temperatures along the thrust would be controlled largely by the rheology of hanging wall rocks rather than the initial thermal state moreover the relatively high melting temperatures for dry lower crustal upper mantle rocks implies that the temperatures achieved along the thrust should be relatively high as thrusting progresses this early history is successively eliminated as wet upper crustal rocks are emplaced beneath the preheated hanging wall the granitic melts that characterize many natural megathrust systems are probably generated when these wet metasedimentary rocks move beneath the hanging wall either by hydrous fluxing of the hot hanging wall or by melting in the highest grade footwall rocks rapid uplift implied by both metamorphic studies and preservation of the inverted metamorphic sequence is interpreted as a late phase event created by tectonic pileup beneath the thrust thorough testing of the model will require thorough assessment of the time dependent problem however one dimensional steady state models together with energy considerations indicate that the general model is allowable the concept of thermal buffering by strain heating is important because it implies that megathrust systems are a natural system where metamorphic temperatures are controlled by rock rheology hence they represent real world systems where a thermal and mechanical system are intimately linked this rationale is used to extend the model by indicating a method in which metamorphic conditions along exhumed megathrusts might be used as a natural constraint on experimentally determined flow laws

quartz microstructures and c axis preferred orientations in high grade gneisses and mylonites around the morin anorthosite grenville province quartz in deformed rocks from two large high grade shear zones around the morin anorthosite morin terrane grenville province displays distinctive microstructures as well as c axis preferred orientations in the west dipping morin shear zone east of the morin anorthosite four distinct quartz microstructures types 1 4 are identified based on deformation features and grain size the c axis orientations are characterized by a single maximum near the stretching lineation and two maxima in type 1 microstructure and by an asymmetrical single girdle in type 2 microstructure quartz c axes show crossed girdle pattern in type 3 microstructure both quartz microstructures and c axis preferred orientations suggest that crystal plastic slip and dynamic recrystallization are the dominant deformation mechanisms the asymmetry of c axis orientations with respect to the mylonitic foliation as well as the substructures developed in quartz indicates a dextral sense of shear in the morin shear zone type 4 micr

dynamic recrystallization and associated exsolution in perthites evidence of deep crustal thrusting mylonitic gneisses from parry sound ontario are intensely deformed and occur within a major deep crustal shear zone developed during thrusting of granulite facies rocks 800 c 900 1100 mpa northward onto an amphibolite facies terrane we have examined by optical and electron microscopy microstructures in perthites from these mylonites that preserve the deformation recrystallization cycle which operated during high ductility deformation of the crystals the exsolution and recrystallization microstructures are intimately associated exsolution in the perthites occurred in two stages a calcic plagioclase oligoclase exsolved first and subsequently coarsened and deformed during the single crystal ductility phase of shear zone deformation a progressive increase in size and boundary incoherence of oligoclase domains during deformation led to recrystallization of the host perthite crystals as discrete orthoclase and oligoclase grains the principal mode of recrystallization was subgrain rotation with a component of grain growth that followed the formation of mobile high angle boundaries misorientation of subgrains to form grains at the recrystallization front is abrupt and occurred over one or two subgrain diameters the second exsolution stage postdated perthite deformation and saw formation of fine albite lamellae in both host and recrystallized orthoclase temperatures inferred from the exsolution textures for independently determined confining pressures indicate that this deformation occurred under at least granulite facies conditions the perthites thus record deformation from crustal depths of the order of 34 42 km continental megathrusts such as the parry sound shear zone provide mechanisms for both the generation of large strains observed in otherwise nonductile minerals and the preservation of ensuing microstructures

the rheological evolution of brittle ductile transition rocks during the earthquake cycle evidence for a ductile precursor to pseudotachylyte in an extensional fault system south mountains arizona

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

amplification of seismic ground motion in the tunis basin numerical bem simulations vs experimental evidences this paper aims at the analysis of seismic wave amplification in a deep alluvial basin in the city of tunis in tunisia this sedimentary basin is 3000m wide and 350m deep since the seismic hazard is significant in this area the depth of the basin and the strong impedance ratio raise the need for an accurate estimation of seismic motion amplification various experimental investigations were performed in previous studies to characterize site effects the boundary element method is considered herein to assess the parameter sensitivity of the amplification process and analyse the prevailing phenomena the various frequencies of maximum amplification are correctly estimated by the bem simulations the maximum amplification level observed in the field is also well retrieved by the numerical simulations but due to the sensitivity of the location of maximum amplification in space the overall maximum amplification has to be considered the influence of the wave field incidence and material damping is also discussed

nonlinear seismic response for the 2011 tohoku earthquake borehole records versus one directional three component propagation models the seismic response of surficial multilayered soils to strong earthquakes is analyzed through a nonlinear one directional three component 1d 3c wave propagation model the three components 3c polarization of the incident wave are simultaneously propagated into a horizontal multilayered soil a 3d nonlinear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model the soil rheology is modeled by mean of a multi surface cyclic plasticity model of the masing prandtl ishlinskii iwan type its major advantage is that the rheology is characterized by few nonlinear parameters commonly available previous studies showed that when comparing one to three component unidirectional wave propagation simulations the soil shear modulus decreases and the dissipation increases for a given maximum strain amplitude the 3d loading path due to the 3c polarization leads to multiaxial stress interaction that reduces soil strength and increases nonlinear effects nonlinearity and coupling effects between components are more obvious with decreasing seismic velocity ratio in the soil and increasing vertical to horizontal component ratio for the incident wave this research aims at comparing computed ground motions at the surface of soil profiles in the tohoku area japan with 3c seismic signals recorded during the 2011 tohoku earthquake the 3c recorded downhole motion is imposed as boundary condition at the base of soil layer stack notable amplification phenomena are shown comparing seismograms at the bottom and at the surface the 1d 3c approach evidences the influence of the 3d loading path and input wavefield polarization 3c motion and 3d stress and strain evolution are evaluated all over the soil profile the triaxial mechanical coupling is pointed out by observing the variation of the propagating wave polarization all along the duration of seismograms the variation of the maximum horizontal component of motion with time as well as the influence of the vertical component confirm the interest of taking into account the 3c nonlinear coupling in 1d wave propagation models for such a large event

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

modest movements spectacular fabrics in an intracontinental deep crustal strike slip fault striding athabasca mylonite zone nw canadian shield geometry and strain partitioning within lower crustal intraplate strike slip shear zones can be extremely complex compared with analogous structural levels of interplate strike slip shear zones sited at plate margins striding athabasca mylonite zone canadian shield is a spectacular ca 500 km long granulite facies continental intraplate shear zone the shear zone is composed of middle archean granulite facies annealed mylonites ca 3 13 ga and late archean ca 2 62 2 60 ga granulite facies ribbon mylonite belts which thread a sinuous course along a chain of crustal scale lozenges cored by relatively stiff rocks of mafic to intermediate composition to the northeast the mylonites form a n s trending 5 10 km thick dextral strike slip belt to the southwest this bifurcates into a pair of conjugate strike slip shear zones overlain by a contemporaneous dip slip shear zone striding athabasca mylonite zone was kinematically inefficient as a strike slip fault and cannot have accommodated large wallrock displacements nevertheless spectacular granulite facies ribbon mylonites were formed throughout the shear zone reflecting the very high temperatures ca 850 1000 c high recrystallization rate strain rate ratios and the transpressive nature of the deformation wk 1 possibly accommodated by significant volume loss by magma migration

modelling strong seismic ground motion three dimensional loading path versus wavefield polarization seismic waves due to strong earthquakes propagating in surficial soil layers may both reduce soil stiffness and increase the energy dissipation into the soil to investigate seismic wave amplification in such cases past studies have been devoted to one directional shear wave propagation in a soil column 1d propagation considering one motion component only 1c polarization three independent purely 1c computations may be performed 1d 1c approach and directly superimposed in the case of weak motions linear behaviour this research aims at studying local site effects by considering seismic wave propagation in a 1 d soil profile accounting for the influence of the 3 d loading path and non linear hysteretic behaviour of the soil in the proposed 1d 3c approach the three components 3c polarization of the incident wave are simultaneously propagated into a horizontal multilayered soil a 3 d non linear constitutive relation for the soil is implemented in the framework of the finite element method in the time domain the complex rheology of soils is modelled by mean of a multisurface cyclic plasticity model of the masing prandtl ishlinskii iwan type the great advantage of this choice is that the only data needed to describe the model is the modulus reduction curve a parametric study is carried out to characterize the changes in the seismic motion of the surficial layers due to both incident wavefield properties and soil non linearities the numerical simulations show a seismic response depending on several parameters such as polarization of seismic waves material elastic and dynamic properties as well as on the impedance contrast between layers and frequency content and oscillatory character of the input motion the 3 d loading path due to the 3c polarization leads to multi axial stress interaction that reduces soil strength and increases non linear effects the non linear behaviour of the soil may have beneficial or detrimental effects on the seismic response at the free surface depending on the energy dissipation rate free surface time histories stress strain hysteresis loops and in depth profiles of octahedral stress and strain are estimated for each soil column the combination of three separate 1d 1c non linear analyses is compared to the proposed 1d 3c approach evidencing the influence of the 3c polarization and the 3 d loading path on strong seismic motions

extended iwan iai 3dxii constitutive model for 1 directional 3 component seismic waves in liquefiable soils applicationto the kushiro site japan the influence of pore water pressure has to be taken into account when the propagation of seismic waves in saturated soils is simulated because it controls the strength decrease during the dynamic process and can induce phenomena such as cyclic mobility and liquefaction the decrease of effective stresses leads to permanent deformation in the soil and damages to the surface structures this research aims at validating a 1 directional propagation model of 3 component seismic waves 1d 3c in a horizontally layered soil in the case of saturated soil a 3 d non linear elasto plastic model for soils is used and the variation of the shear modulus reduction curve with the pore water pressure is taken into account during the seismic event in the case of multiaxial stress states induced by a 3c seismic motion if no additional information is available the modulus reduction curves in shear and compression normalized with respect to the elastic moduli are assumed identical since the poisson s ratio is supposed to be constant during the process the multiaxial stress state in saturated soils induced by a 3c seismic motion is analysed for various stress paths the 1d 3c wave propagation model is used to compute the seismic response of the kushiro soil profile japan the stratigraphy and geotechnical properties are deduced from in situ and laboratory tests provided by the prenolin benchmark numerical results are in correct agreement with the records at the surface in terms of acceleration envelope

albite deformation within a basal ophiolite shear zone abstract albite mylonites at the base of the white hills peridotite ophiolite fragment at st anthony newfoundland formed during obduction at lower crustal p t conditions optical microstructures preserve a history of intracrystalline distortion recovery and cyclic dynamic recrystallization associated with hot working the crystallographic fabric is consistent with shear of the polycrystalline aggregate dominated by glide on 010 planes as is also indicated by tem observations slip systems implied by trace analysis and invisibility experiments using tem are b 101 010 b 001 010 and b 1 2 112 201 dissociated dislocations have separations ranging from 8 3 15 nm these separations are notably smaller than in more calcic plagioclases and indicate a relatively higher ductility for albite in the case of cross slip controlled creep the observed dislocation densities relate to a high stress strain rate pulse imposed on the dominant high temperature creep textures

natural deformation and recrystallization of some intermediate plagioclase feldspars abstract intermediate an25 an48 plagioclase feldspars from the nordre stromfjord shear zone central west greenland have undergone extensive ductile deformation by intracrystalline slip and by twinning the plagioclases were deformed under low granulite facies conditions optical substructures include undulatory extinction deformation bands subgrains and deformational twins mainly on the albite law dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation migration of a high angle boundary as a secondary mechanism in some cases recrystallization is accompanied by a small decrease in the an content which is thought to indicate prograde metamorphic conditions the plagioclases exhibit a good crystallographic preferred orientation which is compatible with 010 001 being the principal slip system quartz has in the same rocks undergone more plastic deformation and more extensive recovery than plagioclase this is at least in part due to the fact that most dislocations in plagioclase are dissociated

strong ground motion in the 2011 tohoku earthquake a one directional three component modeling local wave amplification due to strong seismic motions in surficial multilayered soil is influenced by several parameters such as the wavefield polarization and the dynamic properties and impedance contrast between soil layers the present research aims at investigating seismic motion amplification in the 2011 tohoku earthquake through a one directional three component 1d 3c wave propagation model a 3d nonlinear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model the soil rheology is modeled by mean of a multi surface cyclic plasticity model of the masing prandtl ishlinskii iwan mpii type its major advantage is that the rheology is characterized by few commonly measured parameters ground motions are computed at the surface of soil profiles in the tohoku area japan by propagating 3c signals recorded at rock outcrops during the 2011 tohoku earthquake computed surface ground motions are compared to the tohoku earthquake records at alluvial sites and the reliability of the 1d 3c model is corroborated the 1d 3c approach is compared with the combination of three separate one directional analyses of one motion component propagated independently 1d 1c approach the 3d loading path due to the 3c polarization leads to multiaxial stress interaction that reduces soil strength and increases nonlinear effects time histories and spectral amplitudes for the tohoku earthquake are numerically reproduced the 1d 3c approach allows the evaluation of various parameters of the 3c motion and 3d stress and strain evolution all over the soil profile

field testing of fiber optic distributed acoustic sensing das for subsurface seismic monitoring distributed acoustic sensing das is a relatively recent development in the use of fiber optic cable for measurement of ground motion discrete fiber optic sensors typically using a bragg diffraction grating have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old bostick 2000 and summary in keul et al 2005 however developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor mestayer et al 2011 miller et al 2012

field trial of seismic recording using distributed acoustic sensing with broadside sensitive fibre optic cables distributed acoustic sensing is an emerging technology using fibre optic cables to detect acoustic disturbances such as flow noise and seismic signals the technology has been applied successfully in hydraulic fracture monitoring and vertical seismic profiling one of the limitations of distributed acoustic sensing for seismic recording is that the conventional straight fibres do not have broadside sensitivity and therefore cannot be used in configurations where the raypaths are essentially orthogonal to the fibre optic cable such as seismic reflection methods from the surface the helically wound cable was designed to have broadside sensitivity in this paper a field trial is described to validate in a qualitative sense the theoretically predicted angle dependent response of a helically wound cable p waves were measured with a helically wound cable as a function of the angle of incidence in a shallow horizontal borehole and compared with measurements with a co located streamer the results show a similar behaviour as a function of the angle of incidence as the theory this demonstrates the possibility of using distributed acoustic sensing with a helically wound cable as a seismic detection system with a horizontal cable near the surface the helically wound cable does not have any active parts and can be made as a slim cable with a diameter of a few centimetres for that reason distributed acoustic sensing with a helically wound cable is a potential low cost option for permanent seismic monitoring on land

static recrystallization of vein quartz pebbles in a high pressure low temperature metamorphic conglomerate abstract microfabrics of quartz pebbles in hp lt c 1 gpa c 350 c metamorphic conglomerates are investigated the conglomerate was deformed by dissolution precipitation creep while the interior of the pebbles remained undeformed the different pebbles display a wide variety of quartz microstructures imported from the source rocks one type of pebble is derived from quartz veins it shows old grains with numerous fluid inclusions subgrains and undulatory extinction which are partly replaced by new grains devoid of inclusions and substructure free dislocation densities are on the order of 1012 m 2 in both grains we conclude that 1 the quartz vein underwent inhomogeneous crystal plastic deformation in the source rock 2 recrystallization took place by strain induced grain boundary migration starting from small crystalline volumes poor in defects 3 recrystallization was purely static and commenced during re burial of the conglomerate which 4 was simultaneously deformed by dissolution precipitation creep at low differential stress insufficient for crystal plastic deformation of quartz 5 fluid inclusions within old grains were eliminated and their fluid content was drained along the migrating high angle grain boundaries and 6 strain induced grain boundary migration ceased once the driving force became too low by static recovery concurrent to recrystallization within the deformed old grains

towards a more practical two feldspar geothermometer the thermodynamic basis of several recent attempts to formulate a simple two feldspar geothermometer is discussed together with a review of earlier empirical geothermometers and ones based on experimental studies in the ternary feldspar system it is shown that double binary thermometers which involve the combination of regular solution mixing models for the binary alkali feldspar system with ideal mixing in plagioclases do not give a satisfactory representation of two feldspar relations especially for albite rich compositions where a critical point exists thermometers based on mixing parameters for ordered alkali feldspar frameworks are even more unjustified both because low plagioclases are certainly non ideal and because of uncertainty in knowing the degree of al si order in the alkali feldspar when exchange equilibrium was achieved a thermodynamic thermometer requires knowledge of ternary activities which are at present unknown experimental determinations of relationships in the ternary feldspar system are reviewed and the correct general form of the thermometer constructed using mainly the experimental data of seck 1971a and smith and parsons 1974 chemographic tests for equilibrium between feldspar pairs are suggested and petrographie features discussed in an appendix new values are given of margules parameters calculated for binary disordered alkali feldspars from recent solvus data up to 15 kbars and their physico chemical basis examined we suggest that accurate representations of the mixing properties of disordered alkali feldspars using margules parameters are at present premature

shear criteria in the grenville province ontario canada abstract the grenville province of canada is a major proterozoic orogenic belt mapping and structural analysis shows that the central ontario segment of this belt is composed of a stack of imbricated thrust nappes separated by mylonite zones the mylonite zones were generated at high metamorphic grades and contain a distinctive assemblage of mesoscopic and microscopic asymmetric structures these structures include rotated tectonic inclusions rotated boudins and pinch and swell structures sheath folds rotated single crystal porphyroclasts single crystal fish and shear band foliation the shear asymmetry indicated by these structures is highly consistent between members of the assemblage and over a large area of the grenville province and shows that the thrust nappes were transported to the northwest the consistency of the structures is thought to be due to cyclical dynamic recrystallization leading to steady state foliations in the mylonites

deep crustal deformation textures along megathrusts from newfoundland and ontario implications for microstructural preservation strain rates and strength of the lithosphere lithospheric scale thrusts from the west newfoundland ophiolite belt white hills peridotite shear zone and the south western grenville province parry sound shear zone involve rocks of lower crustal and or upper mantle origin that exhibit intense crystal plastic deformation of plagioclase k feldspar orthopyroxene and clinopyroxene minerals that are commonly viewed as representative of low ductility phases the occurrence of this extreme deformation in shear zones that exhibit similar lower crustal syntectonic p t conditions suggests a phenomenological link between the megathrust environment and both the generation and subsequent preservation of the observed deformation microstructures an empirical homologous parameter is constructed in an attempt to characterize conditions for similar behaviour among different minerals and to explore the feasibility of refining a threshold recovery preservation condition within the megathrusts studied this parameter predicts at the estimated syntectonic temper

seismotectonics of the newport inglewood fault zone in the los angeles basin southern california the newport inglewood fault zone nif strikes northwest along the western margin of the los angeles basin in southern california the seismicity 1973 to 1985 of m l 2 5 that occurred within a 20 km wide rectangle centered on the nif extending from the santa monica fault in the north to newport beach in the south is analyzed a simultaneous full inversion scheme velest is used to invert for hypocentral parameters two velocity models and a set of station delays arrival time data from three quarry blasts are included to stabilize the inversion the first velocity model applies to stations located along the rim and outside the los angeles basin and is well resolved it is almost identical to the starting model which is the model routinely used by the cit usgs southern california seismic network for locating local earthquakes the second velocity model applies to stations located within the los angeles basin it shows significantly lower velocities down to depths of 12 to 16 km which is consistent with basement of catalina schist below the sediments in the western los angeles basin the distribution of relocated hypocenters shows an improved correspondence to mapped surface traces of late quaternary fault segments of the nif a diffuse trend of seismicity is observed along the inglewood fault from the dominguez hills across the baldwin hills to the santa monica fault in the north the seismicity adjacent to long beach however is offset 4 to 5 km to the east near the trace of the subsurface los alamitos fault the depth distribution of earthquakes along the nif shows clustering from 6 to 11 km depth which is similar to average seismogenic depths in southern california thirty nine single event focal mechanisms of small earthquakes 1977 to 1985 show mostly strike slip faulting with some reverse faulting along the north segment north of dominguez hills and some normal faulting along the south segment south of dominguez hills to newport beach the results of an inversion of the focal mechanism data for orientations of the principal stress axes and their relative magnitudes indicate that the minimum principal stress is vertical along the north segment while the intermediate stress is vertical along the south segment the maximum principal stress axis is oriented 10 to 25 east of north reverse faulting along the north segment indicates that a transition zone of mostly compressive deformation exists between the los angeles block and the central transverse ranges

ductility of garnet as an indicator of extremely high temperature deformation discoidal shaped garnets alm63 prp33 grs3 sps1 occur in the foliation plane of lineated quartzofeldspathic mylonites of the morin shear zone located along the eastern boundary of the morin anorthosite complex grenville province quebec the flattened shape of garnets records a component of coaxial strain x y z different from the dominant rotational shear strain x y z in this mylonite tem observations indicate dislocation slip and recovery to be the main mechanism for the deformation of garnet extrapolation of available experimentally determined flow laws to natural strain rates shows an inversion of flow strength between quartz feldspar and garnet garnet much stronger than quartz and feldspar at temperatures below 700 c becomes weaker than quartz and feldspar above 900 c the coaxial ductile strain recorded by the garnets could be produced by a local uncharacterized deformation under extremely high temperature conditions at the roof of the rising anorthositic diapir 1155 ma subsequent lower temperature rotational deformation is related to strike slip movement along the morin shear zone 1020 ma

mylonite fabric development on naxos greece abstract the miocene structural evolution of the metamorphic complex on naxos occurred within a mid to lower crustal sub horizontal shear zone the deformation style and the regional stress field in the aegean during the miocene are consistent with exhumation of the metamorphic complex during ductile crustal thinning deformation in this shear zone initiated possibly before and continued after the peak of localized high temperature barrovian style metamorphism kinematic indicators in non coaxial fabrics indicate that upper structural levels were displaced to the nne throughout the miocene structural history of the metamorphic complex this displacement was accompanied during its latter stages by compression in an e w direction

quartz deformation and the recognition of recrystallization regimes in the flinton group conglomerates ontario the clastic metasedimentary rocks that form the flinton group occur as arcuate belts within the grenville structural province southeastern ontario metamorphic isotherms transect these rocks and allow comparison of deformation over an approximate temperature range of 550 650 c two geometrically discrete but temporally continuous deformation phases contribute significantly to pebble deformation within the conglomeratic units there is a general increase in both finite strain over which there is a strong compositional control and the frequency of d2 minor structures with increasing metamorphic temperature d1 is characterized by the creation of a subgrain structure and progressive misorientation of the subgrains as strain accumulates ultimately this leads to formation of high angle boundaries defining recrystallized grains of a size similar to that of the precursor subgrains d2 produces a new finer subgrain structure elongated grains grain boundary migration bulging and small recrystallized gra

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at citronelle alabama a modular borehole monitoring concept has been implemented to provide a suite of well based monitoring tools that can be deployed cost effectively in a flexible and robust package the initial modular borehole monitoring system was deployed as part of a co2 injection test operated by the southeast regional carbon sequestration partnership near citronelle alabama the citronelle modular monitoring system transmits electrical power and signals fibre optic light pulses and fluids between the surface and a reservoir additionally a separate multi conductor tubing encapsulated line was used for borehole geophones including a specialized clamp for casing clamping with tubing deployment the deployment of geophones and fibre optic cables allowed comparison testing of distributed acoustic sensing we designed a large source effort 64 sweeps per source point to test fibre optic vertical seismic profile and acquired data in 2013 the native measurement in the specific distributed acoustic sensing unit used an idas from silixa ltd is described as a localized strain rate following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain improvement from repeated stacking of the source was observed conversion of the rebalanced strain signal to equivalent velocity units via a scaling by local apparent velocity allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity we see a very good match of uncorrelated time series in both amplitude and phase demonstrating that velocityconverted distributed acoustic sensing data can be analyzed equivalent to vertical geophones we show that distributed acoustic sensing data when averaged over an interval comparable to typical geophone spacing can obtain signal to noise ratios of 18 db to 24 db below clamped geophones a result that is variable with noise spectral amplitude because the noise characteristics are not identical with vertical seismic profile processing we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data along with improved upgoing reflection quality we conclude that the extra source effort currently needed for tubing deployed distributed acoustic sensing vertical seismic profile as part of a modular monitoring system is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones

cryptoperthites and cooling rate in a layered syenite pluton a chemical and tem study alkali feldspars in the klokken layered syenite south greenland are optically either coarse turbid deuteric patch perthites or clear unaltered fine braid microor cryptoperthites irregular clear volumes can be found in most turbid grains electron microscopy shows that all clear crystals or volumes are cryptoperthites in which the periodicity of the exsolution lamellae increases systematically with distance from the roof of the intrusion from 40 nm to 300nm they are composed of low albite and diagonally associated maximum microcline a secondary coarsening is responsible for optically visible braid microperthites the layered series consists of interleaved granular syenites and coarser grained laminated syenites with mineral layering microprobe analyses show a downward decrease in ca and ba in the granular syenite feldspars consistent with chilling from the roof inwards most laminated syenite feldspars contain 1 an increasing to 5 in mafic layers the periodicity of the exsolution lamellae in the laminated syenite feldspars is consistently up to twice that in adjacent granular syenites periodicity is not influenced by ab or or an content but high an feldspars have continuous zig zag intergrowths while others are more lozengeshaped lamellar periodicities largely reflect cooling rate in the pluton cooling times in the exsolution interval were probably about 103 104 years at the top of the series whereas existing experimental data suggest that the periodicities would be reached in a few days or years the periodicities at the top of the granular series are only slightly greater than experimentally determined initial wavelengths for spinodal decomposition suggesting that little or no coarsening occurred despite the long cooling times coarsening did occur lower in the pile framework ordering and twinning must slow or stop coarsening the difference in periodicity between the granular and laminated syenite series may be caused by differences in amount of water incorporated in the feldspar structure from the magma the exsolution of this water at low temperatures could be the cause of the deuteric unmixed patch perthites small volumes of cryptoperthite which have escaped deuteric unmixing may be common in igneous rocks in general and may be useful relative indicators of cooling rate

spectral element modelling of seismic wave propagation in visco elastoplastic media including excess pore pressure development numerical modelling of seismic wave propagation considering soil nonlinearity has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions indeed when strong ground motion propagates in saturated soils pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected here we model 1 d seismic wave propagation in linear and nonlinear media using the spectral element numerical method the study uses a three component 3c nonlinear rheology and includes pore pressure excess the 1 d 3c model is used to study the 1987 superstition hills earthquake ml 6 6 which was recorded at the wildlife refuge liquefaction array usa the data of this event present strong soil nonlinearity involving pore pressure effects the ground motion is numerically modelled for different assumptions on soil rheology and input motion 1c versus 3c using the recorded borehole signals as input motion the computed acceleration time histories show low frequency amplification and strong high frequency damping due to the development of pore pressure in one of the soil layers furthermore the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1c analysis and significant differences in surface displacements are observed between the 1c and 3c approaches this study contributes to identify and understand the dominant phenomena occurring in superficial layers depending on local soil properties and input motions conditions relevant for site specific studies

phase boundary mobility in naturally deformed high grade quartzofeldspathic rocks evidence for diffusional creep abstract grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern grenville province ontario canada suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep in these rocks quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions in the naturally deformed rocks however phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation i e in directions of inferred finite extension which implies that phase boundary motion and cusp formation occurred during deformation optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep however the morphology of quartz feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone we propose that phase boundary motion resulted from a diffusion assisted process involving dissolution at foliation parallel quartz feldspar phase boundaries mass transfer over length scales of the order of feldspar domain size 200 m or greater and precipitation at quartz feldspar phase boundary cusps this study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks it also has important implications for the natural rheological behavior of the mid and lower continental crust

influence of lateral heterogeneities on strong motion shear strains simulations in the historical center of rome italy abstract the influence of lateral heterogeneities on alluvial deposits is a topic of particular interest in the field of urban planning and engineering design of structures and infrastructures this work focuses on the effects of such heterogeneities on the shear strains produced within the recent alluvial deposits of the tiber river in the historical center of rome in case of the worst expected earthquake scenario to this aim a 3d engineering geology model of the subsoil is used to derive four geological sections across the tiber river valley as well as 48 soil columns to perform numerical simulations various models are considered a viscoelastic equivalent linear rheology in a 1d finite difference model for one component horizontal input a nonlinear elastoplastic model in a 1d finite element scheme for three component input and a nonlinear viscoelasto plastic rheology in a 2d finite difference model under one component horizontal input after comparing these different simulations results have shown that lateral heterogeneities play a key role with respect to the expected shear strains within multilayered soils to this aim some specific indexes are introduced to estimate the maximum shear strain mss concentration within the soil layers as well as to highlight their effect due to the stratigraphic position of the layers within the soil column independently from its depth a final differential index leads to the evaluation of the lateral heterogeneity effect on the estimated mss demonstrating their prevalent role with respect to the bedrock shape i e the angle of inclination of the buried valley slopes from these results an mss zoning map is obtained for the historical center of rome showing that the local seismic response should be modeled by assuming 1d or 2d conditions depending on the location considered

distributed acoustic sensing for reservoir monitoring with vsp 3d vsp has long been viewed as conceptually attractive for illuminating targets under complex overburden both for exploration purposes and for time lapse monitoring of reservoirs however the widespread use of 3d vsp has been hindered by the cost and risk of deploying geophones in a borehole and by the limited availability of accessible wells these hurdles are largely removed when acquiring downhole seismic with a new measurement called distributed acoustic sensing das

footwall rocks to the mid tertiary chemehuevi detachment fault a window into the middle crust in the southern cordillera crystalline rocks unroofed from the middle crust during tertiary crustal extension by the chemehuevi detachment fault record a complex history of comprises both subhorizontal and subvertically foliated mylonitic gneisses sharing a common gently sw plunging stretching lineation which are intruded by members of the voluminous laccolith shaped chemehuevi mountains plutonic suite proterozoic and mesozoic gneisses migmatites and early members of the chemehuevi mountains plutonic suite in the eastern chemehuevi mountains are deformed into a gently southwest dipping zone of protomylonite mylonite and locally ultramylonite in excess of 1 5 km thick a belt of steeply foliated mylonitic gneiss up to 5 km across traceable for 12 km along strike ne sw crops out in the northern part of the range this belt passes abruptly downward into the subhorizontal shear zone exposed in the eastern chemehuevi mountains a preliminary shear sense study indicates ne directed shear within the sub horizontal mylonitic rocks and sinistral shear parallel to the steeply foliated mylonites deformation in these two zones took place under upper greenschist to middle amphibolite facies conditions mylonitic deformation associated with the two shear zones was spanned by intrusion of the chemehuevi mountains plutonic suite cross cutting contacts within the suite indicate that ductile deformation occurred after intrusion of hornblende biotite granodiorite four zircon fractions from this unit are discordant but define a chord with a lower intercept of around 90 ma and an upper intercept of 1900 ma thirteen zircon fractions from two separate undeformed members of the suite biotite granodiorite and porphyritic biotite granodiorite are variably discordant but fractions for each unit define chords that yield latest cretaceous crystallization ages with upper intercepts of 1600 ma together these data constrain the timing of plutonism and ductile deformation with associated thick zones of fabric reorientation and mylonitic transposition to the late cretaceous superimposed on this fabric and involving all rocks types in the footwall are the localized brittle and ductile effects of the mid tertiary extensional deformation movement direction and the timing of mylonitic deformation in the chemehuevi mountains suggest that the effects of the cordilleran fold and thrust belt extends into the chemehuevi mountains region where it in part overlapped with and was heated by plutonism along the eastern margin of the mesozoic magmatic arc during late cretaceous time

nonlinear soil response a reality geotechnical models consistently indicate that the stress strain relationship of soils is nonlinear and hysteretic especially at shear strains larger than 10 5 to 10 4 nonlinear effects such as an increase in damping and reduction in shear wave velocity as excitation strength increases are commonly recognized in the dynamic loading of soils on the other hand these effects are usually ignored in seismological models of ground motion prediction because of the lack of compelling corroborative evidence from strong motion observations the situation is being changed by recently obtained data explicit evidence of strong motion deamplification accompanied by changes in resonant frequencies are found in the data from the 1985 michoacan mexico and the 1989 loma prieta california earthquakes the events recorded by the vertical and surface accelerograph arrays in taiwan as well as a number of other events throughout the world evidence of nonlinear behavior becomes apparent beyond a threshold acceleration of 100 to 200 gal nonlinearity is considerable in cohesionless soil but may be negligible in stiff soils the findings of recent years indicate that nonlinear site effects are more common than previously recognized in strong motion seismology

distributed acoustic sensing for reservoir monitoring with vertical seismic profiling distributed acoustic sensing is a novel technology for seismic data acquisition particularly suitable for vertical seismic profiling it is a break through for low cost on demand seismic monitoring of reservoirs both onshore and offshore in this article we explain how distributed acoustic sensing works and demonstrate its usability for typical vertical seismic profiling applications such as checkshots imaging and time lapse monitoring we show numerous data examples and discuss distributed acoustic sensing as an enabler of seismic monitoring with 3d vertical seismic profiling key words borehole geophysics acquisition seismics time lapse monitoring

ductile strain partitioning in micritic limestones calabria italy the roles and mechanisms of intracrystalline and intercrystalline deformation the apennine pollino ciagola limestone unit in northern calabria is characterized by subgreenschist heterogeneous ductile strain localized along narrow deformation zones at several stratigraphic levels paleogene conglomerates and jurassic calcareous breccias and ooidal packstones have been analyzed with the aim of characterizing the deformation of limestone as a function of the strain recorded by sedimentary markers reference sections parallel to principal finite strain planes were prepared at each locality for the study of specific parameters image analysis of polished sections by scanning electron microscopy sem was used to obtain the finite strain of calcite grains by rf harmonic mean and normalized fry methods for the range of grain sizes analyzed 1 10 m the ellipticity of calcite grains varies as a function of grain size according to a power law relationship from which the size of isometric grains is empirically predicted the finite strain ellipticity determined from single calcite

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

deformation of granitic rocks experimental studies and natural examples crustal deformation is inherently complex because the crust is inhomogeneous and anisotropic on a wide variety of scales advances in our understanding have come from a combination of field observations laboratory experiments and theoretical models what necessarily links all these investigations is a focus on process crystal plasticity dislocation creep is one of several grain scale deformation processes or mechanisms each process is dominant over a certain range of conditions in the crust has a particular form of the flow law and produces a characteristic set of microstructures characterizing the deformation mechanisms for different minerals over a range of conditions allows one to link the mechanical behavior or flow law associated with that process to the microstructures it produces the information on microstructures can be used to help interpret the thermomechanical history of naturally deformed rocks and flow laws can be used to create more realistic models predicting crustal behavior in different tectonic settings iterations among field theoretical and experimental approaches are critical for making progress in our understanding the deformation process of crystal plasticity is the main focus of this volume crystal plastic deformation of the crust is in many ways more complex than that of the mantle because most crustal rocks are polyphase aggregates and the strengths of common crustal silicates such as quartz feldspar and mica are very different at a given set of conditions yield strength envelopes for the crust as shown schematically in figure 1 are commonly plotted using the dislocation creep flow law for quartz which inherently assumes that quartz is the controlling phase and undergoes steady state flow but is the flow law for dislocation creep of quartz a good approximation for the deformation of a granite let alone a crustal plum pudding of regions and layers of different lithologies the crust

interaction of helically wound fibre optic cables with plane seismic waves distributed acoustic sensing is a novel technology for seismic acquisition in this technology strain changes induced by seismic waves impinging on an optical fibre are monitored due to the fact that glass is relatively rigid straight glass fibres are not sensitive to broadside waves we suggest using distributed acoustic sensing systems with fibres helically wound around cables one increases the fibre sensitivity to broadside waves by decreasing the fibre wrapping angle the angle between the fibre axis and the plane normal to the cable axis the optimal wrapping angle is chosen to minimize the impact of rayleigh waves on the signal measured this angle depends on the cable poisson ratio and it is approximately equal to 30 for cables composed of plastic for reliable detection of seismic waves one needs a good mechanical contact between the cable and the surrounding medium on the other hand the sensitivity of distributed acoustic sensing systems to primary waves can be significantly reduced if the cable is placed in a cemented borehole

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

matrix mosaics brittle deformation and elongate porphyroclasts granulite facies microstructures in the striding athabasca mylonite zone western canada abstract the late archean striding athabasca mylonite zone western canadian shield is a 400 km long linked system of granulite facies mylonite belts developed in the continental crust the granulite facies mylonites 800 1000 c at 0 8 1 1 gpa developed in subsets of the anhydrous mineral assemblage clinopyroxene orthopyroxene garnet plagioclase quartz hornblende comparison of the microstructures of the striding athabasca mylonites with published descriptions of natural and experimental deformation of geological and analogue materials at elevated homologous temperatures provides some insight into the role played by different processes in the development of the striding athabasca mylonites in addition to dislocation creep and dynamic recrystallisation extensive mass transfer occurred contemporaneously with brittle fracture and cataclasis during granulite facies metamorphism the microstructure and extreme phase dispersal in anhydrous polymineralic matrix mosaics is indicative of efficient grain scale and aggregate scale diffusion grain boundary mobility and mass transfer at relatively slow strain rates despite their annealed appearance the granoblastic matrix mosaics developed synkinematically deformation induced dilation may enhance metamorphic reactions where products are more voluminous than reactants in the porphyroclast population highly elongate 20 1 monocrystalline orthopyroxenes appear to be fragments of dismembered kinked parent grains rather than stretched porphyroclasts granulite facies mylonites should not be treated as direct analogues of greenschist facies mylonites in particular it is essential to evaluate the potential positive feedback between structural and metamorphic processes in highly strained high temperature shear zone rocks

the ductile shear zone in granitoid of the central anatolian crystalline complex turkey implications for the origins of the tuzgolu basin during the late cretaceous extensional deformation abstract the emizozu shear zone is the west northwest trending ductile shear zone within the agacoren granitoid in central turkey deformation that affected the granitoid along the emizozu shear zone resulted in mylonites with mylonitic foliation and stretching lineation the textural features of the deformed minerals suggest that mylonitization occurred under conditions of upper greenschist facies the shear indicators including asymmetric porphyroclasts oblique foliation and shear bands suggest a down dip top to the southwest displacement the orientation of stretching lineation as well as kinematic indicators indicates the extensional character of the emizozu shear zone although it is not precisely dated the available age constraints suggest that the zone formed at 78 71 ma according to field and micro structural data the agacoren granitoid was most likely emplaced during a regional deformation in central turkey and synchronously or shortly after was overprinted by the extensional emizozu shear zone the zone can also be correlated with the earlier stage development of the tuzgolu basin in central turkey

analysis of dynamic recrystallization and nucleation in a quartzite mylonite electron backscatter diffraction ebsd has been used to analyse a natural quartz mylonite from the stack of glencoul nw scotland this technique has been used to measure the misorientation between original protolith parent grains and recrystallized daughter grains the angle of misorientation is important because it has implications for the controlling recrystallization mechanism the sample exhibits approximately 65 a recrystallized microstructure the average neighbor daughter grain size is 12 m and the average subgrain size of the parent grain is 16 m the parent grains do not show a systematic increase in misorientation from the centre of the grain to the edges these data are inconsistent with the subgrain rotation recrystallization model we propose that recrystallization was facilitated by bulging during strain induced grain boundary migration however the majority of misorientations between the parents and their neighbouring daughter grains are in the range 10 30 requiring that another process has operated to rotate grains to higher misorientations with respect to their parents this process is likely to be grain boundary sliding

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

extreme ductility of feldspars from a mylonite parry sound canada abstract single feldspar crystals in mylonites from the grenville structural province of canada have accumulated extreme strains by ductile mechanisms the samples studied are from a deep crustal shear zone and were collected at parry sound ontario the mylonites were derived from granite and leucogabbro and the feldspar crystals originated in late syntectonic pegmatite dykes optical and transmission electron microstructures of microperthitic alkali feldspars show evidence of syntectonic and synchronous dislocation climb leading to recovery si al ordering and na k interdiffusion evidence for the operation of these processes is respectively ubiquitous subgrains development and coarsening of tweed texture and transition of monoclinic to triclinic k feldspar and exsolution domain reorganization these processes occurred concurrently with extreme straining of the host crystals by dislocation and diffusion mechanisms the effects of ductile deformation preserved in these crystals are quite different from those usually observed in feldspars the unusual microstructures are thought to be due to the conditions of high temperature and confining pressure which existed during deformation in concert with a deformation enhancing point defect chemistry possibly associated with incorporation into the crystals of a species of water

shearing during progressive retrogression in granitoids abrupt grain size reduction of quartz at the plastic brittle transition for feldspar the kashio shear zone chubu district japan affects the southeast margins of the ryoke granitic plutons as well as the ryoke metasedimentary rocks and is truncated by the median tectonic line near the shear zone centre coarse quartz grains within the granitic rocks have been dynamically recrystallized to quartz aggregates towards the pluton margins the grain size data show an abrupt reduction from various sizes 59 148 m to a steady state size around 35 m at approximately 400 m from the boundary of the granitic plutons without any tectonic boundary such as a fault being present this abrupt grain size reduction accompanies brittle deformation in feldspar that overprints earlier plastic deformation and develops strong mylonitic fabrics in contrast feldspar away from the pluton margins contains only weak microstructural evidence for plastic deformation and still locally preserves magmatic polycrystal structures amongst the inhomogeneously recrystallized quartz grains these features combined with an isochronological study suggest that the kashio shear zone began at high temperature 450 c as a ductile event that affected relatively wide regions in the ryoke granitic plutons before rapid cooling by ca 70 ma at this latter stage strong mylonitization at lower temperatures 300 c in a semiductile regime occurred in a narrow zone towards the shear zone centre here recrystallized quartz aggregates reached a steady state grain size by ca 60 ma that is cooling within the granitic plutons resulted in strain localization with the abrupt grain size reduction of quartz aggregates correlating with the plastic brittle transition of feldspar

deformation within part of a major crustal shear zone parry sound ontario structure and kinematics deformation within part of the parry sound shear zone pssz in the southwestern grenville structural province has been examined at the transition from mylonitized gabbroic anorthosite and orthogneiss within the body of the pssz to retrograde granulites in the immediate hanging wall detailed structural analysis shows a framework of internally deformed imbricate domains within the hanging wall granulites that are truncated by a major dislocation within the pssz mylonites deformation geometries within discrete hanging wall domains and the pssz exhibit strong similarities ascribable to a common deformation cycle that typically preserves three generations of overprinting structures this cycle comprises i formation of shear induced recumbent isoclinal folds and stretching lineations with concomitant transposition of compositional layering ii rotation of fold axes during noncoaxial shear into parallelism with the stretching lineation and formation of sheath folds and iii refolding about axes nearly