slow fault propagation in serpentinite under conditions of high pore fluid pressure abstract the rupture localization and slip of faults in serpentinite were studied under varying pore fluid pressure conditions to understand deformation mechanisms potentially responsible for slow slip in fault zones experiments were conducted at a constant effective confining pressure of 10 mpa and under pore fluid pressures from 0 to 120 mpa and at temperatures from 23 to 110 c with no fluid pressure faulting occurs rapidly and audibly and the duration of failure increases monotonically with increasing fluid pressure and temperature although non dilatant during initial strain hardening the serpentinite dilates during strain weakening concomitant with fault rupture and slip non dilatant strain hardening occurs by microcracking along serpentine basal planes and grain boundaries and rarely in mode i orientations consistent with previous studies dilatant fault rupture produces a network of transgranular shear fractures in conjugate orientations generally with one dominant fracture structural observations show that as fluid pressure increases the number of transgranular fractures increases we propose that when faulting occurs over a distributed zone rather than a pre existing principal slip surface dilatant hardening causes deformation to migrate this process causes an increase in slip weakening distance and fracture energy at elevated fluid pressures that can lead to more stable failure further thermally activated processes caused deformation at propagating crack tips which also increases the slip weakening distance and the effective fracture energy with increasing temperature given the geologic settings for slow slip our results indicate that high fluid pressure distributed deformation and thermally activated processes may all contribute to slow fault rupture and slip

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

changes in the salinity and porosity of sea ice samples during shipping and storage a theoreti cal examination of salinity and porosity changes introduced in sea ice samples by brine expulsion and gas entrapment caused by thermal cycling during shipping and storage shows that in extreme cases such effects can be significant resulting in 15 reductions in porosity 1 more representative scenarios give porosity changes of less than 2 which assuming that ice property variations scale with n 1 2 result in property variations of less than 1

a numerical model of deformation and fluid flow in an evolving thrust wedge abstract to investigate deformation and fluid flow in an actively deforming tectonic wedge we model the evolution of a large two dimensional 100 km long 5 km thick mechanically and hydrologically homogeneous and isotropic pile of sedimentary strata that is deformed to become a thrust wedge we compare both dry and wet cases in order to illustrate 1 the relative importance of fluids on wedge evolution and 2 the effect of brittle deformation on fluid flow we use an elastic plastic constitutive relation including a mohr coulomb failure criterion and a non associated flow rule and coupled fluid flow with bulk rock properties that approximate typical foreland sedimentary strata simulations are made both with and without dilation the model is fully dynamic but inertial forces remain small results show that deformation within the wedge is accommodated by reverse slip movement on shear bands which migrate in both directions through the wedge as both fore and back thrusts the model has features predicted by the critical taper theory 1 overall wedge geometry 2 crudely self similar growth during evolution 3 more intense deformation toward the rear of the wedge the models show strong overall in sequence faulting behavior with major thrusts isolating relatively undeformed packages which are moved in a piggyback manner upon the active thrusts intermittent out of sequence faulting does however occur in order to maintain the wedge taper fluid flow in the deforming wedge is dominated by topography but is also strongly affected by dilational plastic deformation in all simulations there is focused fluid flow within fault zones when mechanical time stepping is shut off uncoupled flow systems evolve to steady state where inflow equals outflow by subtracting the two states we isolate the mechanical fluid response from the total coupled system response the mechanical fluid response is manifest as contours of head and pressure difference and focusing of fluid flow in areas of active deformation in non dilational simulations these zones are quite localized and are a result of the contrasting stresses in and adjacent to a brittle shear zone in simulations with dilation the zones of head and pressure difference are broad and regional in extent they are ten times greater in magnitude than in non dilation simulations and they track a rock damage front that moves through the wedge

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

off fault plasticity and earthquake rupture dynamics 2 effects of fluid saturation 1 we present an analysis of inelastic off fault response in fluid saturated material during earthquake shear rupture the analysis is conducted for 2 d plane strain deformation using an explicit dynamic finite element formulation along the fault linear slip weakening behavior is specified and the off fault material is described using an elastic plastic description of the drucker prager form which characterizes the brittle behavior of rocks under compressive stress when the primary mode of inelastic deformation is frictional sliding of fissure surfaces microcracking and granular flow in this part part 1 pore pressure changes were neglected in materials bordering the fault in part 2 we more fully address the effects of fluid saturation during the rapid stressing by a propagating rupture the associated undrained response of the surrounding fluid saturated material may be either strengthened or weakened against inelastic deformation we consider poroelastoplastic materials with and without plastic dilation during nondilatant undrained response near a propagating rupture large increases in pore pressure on the compressional side of the fault decrease the effective normal stress and weaken the material and decreases in pore pressure on the extensional side strengthen the material positive plastic dilatancy reduces pore pressure universally strengthening the material dilatantly strengthened undrained deformation has a diffusive instability on a long enough timescale when the underlying drained deformation is unstable neglecting this instability on the short timescale of plastic straining we show that undrained deformation is notably more resistant to shear localization than predicted by neglect of pore pressure changes

deep seismic imaging of the cadomian thrust wedge of northern brittany abstract the armor seismic profile ar1 ar2 crosscuts the major units of the cadomian domain 600 540 ma of northern brittany and extends the offshore swat 10 profile birps ecors program we thus have a combined 95 km long nnw sse section for describing the regional scale structure of the cadomian crust in the area following reprocessing and migration of the southern end of the swat 10 profile so that it could be compared with the ar1 ar2 armor profile a structural interpretation of the composite profile was carried out taking into account gravity modelling and magnetotelluric soundings the swat 10 armor profile reveals the existence of steeply dipping thrust faults in the upper crust representing a thrust wedge with a gently northwest dipping sole this cadomian thrust system continues below the unmetamorphosed brioverian and palaeozoic sediments of central brittany and beyond the southern end of the profile in the central armorican domain it supports previous interpretations of dominant oblique type thrusting during cadomian tectonics proposed on the basis of geological field evidence and confirms the existence of a major northwest dipping thrust fault that brings the volcanic arc formations of the saint brieuc unit onto the metasediments of the saint malo unit the profile also emphasises the regional extent of a thrust wedge at the scale of the whole cadomian domain of northern brittany

a new method for combining gravimetric and geological data abstract application of the gravity method to structural geology makes it possible to highlight local variations of the gravitational field that are caused by density heterogeneities related to the composition and structure of the crust these density heterogeneities and their boundaries which correspond to gravity discontinuities can be identified using the properties of the vertical and horizontal derivatives of the field gravity data on the huelgoat granite in the armorican massif france were subjected to a new two step geological analysis first the gravity discontinuities derived from bouguer anomaly data were automatically identified and second these discontinuities were combined with existing geological data the first step was made possible by a software program that defines and visualizes the gravity discontinuities through an automatic analysis of the horizontal and vertical gravity gradient functions the result is a map on which gravity discontinuities separate areas of different densities the vertical and horizontal derivatives of the field were computed from the gravity data using frequency domain transformations the second step corresponds to the geological interpretation of the gravity discontinuity map a petrostructural map is used which mainly shows the structure and the syntectonic internal fabric of the area along with fracture data obtained on the granite and its host rocks the latter illustrates late brittle deformation the petrostructural map is used to adjust and rearrange the gravity discontinuities in order to obtain a gravity image deduced from the fabric of the rocks a fabric gravity image after this a fracture gravity image is derived by using the fracture data as a filter to obtain priority directions in the gravity discontinuities superimposing the two images provides a structural sketch map that gives a more integrated insight into the ductile and brittle deformation of the area than can be obtained from field observations alone

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

u pb geochronology and hf nd isotope compositions of the oldest neoproterozoic crust within the cadomian orogen new evidence for a unique juvenile terrane new u pb dates combined with nd and hf isotopic data from rocks within the port morvan area of the baie de st brieuc region of brittany identify a unique portion of the neoproterozoic cadomia terrane two gneisses near port morvan yielded u pb dates of 754 6 0 8 ma and 746 0 0 9 ma ages that are more than 130 myr older than the oldest units formed during the main phase of early cadomian magmatism two trondhjemite boulders from the monogenetic facies of the cesson conglomerate yielded identical ages of 665 2 0 5 ma and 665 5 0 7 ma and a cobble from the polygenetic facies yields a 207pb 206pb date of 637 2 ma individual detrital zircons from a sandstone associated with the cesson conglomerates yield concordant u pb dates ranging from 650 3 ma to 624 1 0 6 ma initial nd values for the rocks in this region range from 5 0 to 6 6 indicative of a substantial input from depleted mantle initial hf values determined on zircons from these neoproterozoic rocks including the detrital zircons range from 6 7 to 14 5 consistent with the nd isotopic results maximum initial hf values for two 2 ga icartian gneisses considered basement to cadomia average 8 4 and 8 7 in contrast to the results of the port morvan rocks 616 608 ma syn tectonic intrusions from normandy and the british channel islands all have negative initial nd values 10 4 to 8 3 consistent with significant contamination by ancient crust such as the 2 ga gneisses the oldest arc related magmas should have interacted most extensively with cadomian basement buffering younger mantle derived magmas that were generated in subsequent magmatic episodes the rocks within the port morvan region are thus inconsistent as examples of the earliest cadomian intrusions as they show no evidence of interaction with 2 ga basement instead the older ages and mantle like isotopic composition of these rocks suggest they are part of an independent terrane that formed prior to and independently from the cadomian arc possible terrane scale structural boundaries have recently been identified including the newly recognized port morvan thrust fault and the nw dipping main cadomian thrust

a multilayer sigma coordinate thermodynamic sea ice model validation against surface heat budget of the arctic ocean sheba sea ice model intercomparison project part 2 simip2 data keywords sea ice reference epfl article 162504doi 10 1029 2004jc002328view record in web of science record created on 2011 01 24 modified on 2016 08 09

elementary theory of bed sediment entrainment by debris flows and avalanches 1 analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed sediment entrainment rates a preliminary analysis assesses the behavior of a coulomb slide block that entrains bed material as it descends a uniform slope the analysis demonstrates that the block s momentum can grow unstably even in the presence of limited entrainment efficiency a more detailed depth integrated continuum analysis of interacting deformable bodies identifies mechanical controls on entrainment efficiency and shows that entrainment rates satisfy a jump condition that involves shear traction and velocity discontinuities at the flow bed boundary explicit predictions of the entrainment rateeresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions for coulomb friction tractions predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden in the simplest scenario the bed sediment liquefies completely and the entrainment rate equation reduces toe 2 1gh1 cos 1 1 v 1 where is the slope angle 1 is the flow s coulomb friction coefficient h1 is its thickness 1 is its degree of liquefaction and v 1is its depth averaged velocity for values of 1ranging from 0 5 to 0 8 this equation predicts entrainment rates consistent with rates of 0 05 to 0 1 m s measured in large scale debris flow experiments in which wet sediment beds liquefied almost completely the propensity for bed liquefaction depends on several factors including sediment porosity permeability and thickness and rates of compression and shear deformation that occur when beds are overridden

fault geometry and mechanics of marly carbonate multilayers an integrated field and laboratory study from the northern apennines italy abstract sealing layers are often represented by sedimentary sequences characterized by alternating strong and weak lithologies when involved in faulting processes these mechanically heterogeneous multilayers develop complex fault geometries here we investigate fault initiation and evolution within a mechanical multilayer by integrating field observations and rock deformation experiments faults initiate with a staircase trajectory that partially reflects the mechanical properties of the involved lithologies as suggested by our deformation experiments however some faults initiating at low angles in calcite rich layers i 5 20 and at high angles in clay rich layers i 45 86 indicate the important role of structural inheritance at the onset of faulting with increasing displacement faults develop well organized fault cores characterized by a marly foliated matrix embedding fragments of limestone the angles of fault reactivation which concentrate between 30 and 60 are consistent with the low friction coefficient measured during our experiments on marls s 0 39 indicating that clay minerals exert a main control on fault mechanics moreover our integrated analysis suggests that fracturing and faulting are the main mechanisms allowing fluid circulation within the low permeability multilayer and that its sealing integrity can be compromised only by the activity of larger faults cutting across its entire thickness

an experimental method for testing soil mobility of landslides debris flows can travel great distances from their sources and pose hazards to communities downstream identification of soils susceptible to liquefaction during slope failure could aid in locating potential debris flow sources we used a modified version of the slump test typically used to measure the consistency of wet concrete mix to test the proclivity of soil to flow the method can be used to identify a threshold density below which a soil will flow under field saturated conditions we performed 51 soil mobility tests on 13 sandy and gravelly soils with 0 16 silt and clay fines and one sample with 72 fines collected from landslide and nonlandslide sites results are consistent with corresponding site porosity and failure mode for coarse grained soils threshold porosity for flow ranged from 0 39 to 0 65 highest failure velocities were associated with the loosest soils and soils with the lowest permeability failure velocities and modes observed in our tests were consistent with test results for identical soils in a large scale flume on thicker samples 0 65 m that approach average failure depths measured in the field 0 75 m this novel test was successfully designed as a rapidly conducted 24 h to prepare and test samples including overnight saturation low cost alternative to large diameter triaxial tests capable of testing gravelly soils that does not require a predefined shear rate allowing pore pressure to evolve as soil fails under self weight and drained conditions

optimum expulsion of brine from sea ice a simple model is constructed to exploit the concept of drainage trees as ob served during the process of expulsion for desal ination of sea ice linear analysis is used to gether with a consistent approximation procedure for solution of the system to determine critical minimum rayleigh numbers for the onset of insta bility it is found that the system functions optimally when there is both a finite angle of tilt of the drainage channel as well as no tilt at all the determination of the nonzero angle depends critically on the lateral mean density gradient and numerical values for critical an gles of inclination to the vertical obtained agree quantitatively with those reported

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

short paper cadomian terrane tectonics and magmatism in the armorican massif the north armorican composite terrane nw france is a collage of displaced terranes which result from the amalgamation of cadomian continental arcs and marginal basin complexes by sinistral transpression along a continental margin above a subduction zone early cadomian arc activity occurred at c 700 650 ma but terrane accretion did not occur until c 540 ma and post tectonic magmatism persisted well into the palaeozoic cadomian events thus span a considerably greater period than previously supposed

the aeromagnetic map of the french cadomian belt abstract in order to obtain an image of the subsurface of the armorican massif two detailed aeromagnetic surveys were combined to obtain an aeromagnetic map at 350 m altitude with an interpolated grid of 250 m 250 m the map shows good correlation between the magnetic anomalies and known geological structures and also distinguishes between long and short wavelength anomalies the long wavelength anomalies are associated with the overall subsurface arcuate structure of the cadomian belt the short wavelength anomalies are commonly associated with the lanvollon acid volcanic rocks and syntectonic diorites with one set of short wavelength anomalies in the east of the saint malo region being associated with dykes that are exposed onshore and continue offshore

effects of dilatant hardening on the development of concentrated shear deformation in fissured rock masses this study examines the effects of dilatant hardening on the development of concentrated shear deformation specifically the analysis considers the shear of an inelastic ally deforming rock mass containing a weakened layer of thickness h the presence of the weakened layer causes localization instability characterized by an unbounded ratio of a strain increment in the weakened layer to that in the far field to occur earlier than it would be predicted from the response of the material surrounding the embedded layer the development of instability in time depends on the ratio of the rate of imposed shear strain to that for fluid mass exchange between the layers c h2 where c is an effective diffusivity in the limit the pressure in the weakened layer is equal to that in the surrounding material and localization instability occurs at the peak of the drained stress strain curve for finite instability is delayed until the material in the weakened layer has been driven to the peak of its undrained dilatantly hardened stress strain curve the time delay between final instability and the time at which the weakened layer passes the peak of its drained stress strain curve is called the precursor time tpr because rapid straining of the weakened layer occurs during this period for small as appropriate for tectonic applications and most laboratory experiments a nonlinear asymptotic analysis predicts that where is the half width of the peak of the stress strain curve is the difference in the peak stresses of the rock mass and the weak layer divided by times the elastic shear modulus and is a nondimensional measure of the strength of dilatant hardening for a wide range of numerical values the precursor times are very short less than a few hours for tectonic strain rates and less than a few tens of seconds for typical laboratory strain rates

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

mirabilite solubility in equilibrium sea ice brines abstract the sea ice microstructure is permeated by brine channels and pockets that contain concentrated seawater derived brine cooling the sea ice results in further formation of pure ice within these pockets as thermal equilibrium is attained resulting in a smaller volume of increasingly concentrated residual brine the coupled changes in temperature and ionic composition result in supersaturation of the brine with respect to mirabilite na2so4 10h2o at temperatures below 6 38 c which consequently precipitates within the sea ice microstructure here mirabilite solubility in natural and synthetic seawater derived brines representative of sea ice at thermal equilibrium has been measured in laboratory experiments between 0 2 and 20 6 c and hence we present a detailed examination of mirabilite dynamics within the sea ice system below 6 38 c mirabilite displays particularly large changes in solubility as the temperature decreases and by 20 6 c its precipitation results in 12 90 and 91 97 reductions in the total dissolved na and so42 concentrations respectively compared to that of conservative seawater concentration such large non conservative changes in brine composition could potentially impact upon the measurement of sea ice brine salinity and ph whilst the altered osmotic conditions may create additional challenges for the sympagic organisms that inhabit the sea ice system at temperatures above 6 38 c mirabilite again displays large changes in solubility that likely aid in impeding its identification in field samples of sea ice our solubility measurements display excellent agreement with that of the frezchem model which was therefore used to supplement our measurements to colder temperatures measured and modelled solubility data were incorporated into a 1d model for the growth of first year arctic sea ice model results ultimately suggest that mirabilite has a near ubiquitous presence in much of the sea ice on earth and illustrate the spatial and temporal evolution of mirabilite within sea ice as it grows throughout an arctic winter reaching maximum concentrations of 2 3 g kg 1

gravity modellings of the cadomian active margin of northern brittany abstract the geometrical relationships existing between the saint brieuc saint malo and guingamp units which form the cadomian active margin of northern brittany have been determined by gravity analyses and 2 5d modelling correlated with other geophysical magnetic seismic etc and geological observations automatic structural analyses were performed before modelling to identify lateral gravity discontinuities averaged density measurements were used for 2 5d gravity modelling along six profiles across the arcuate geological and gravity shape of the cadomian basement this study allowed the third dimension to be obtained through correlating each profile with its neighbours we propose that orthogneiss formations equivalent to the port morvan orthogneiss constitute the saint brieuc upper crustal unit below the lanvollon formation 2 5d gravity modelling outlines downward geological differences in the western and eastern parts of the ploufragan complex as previously indicated by surface mapping these results stress the necessity for distinguishing between the guingamp and saint malo units

natural convection and dispersion in a tilted fracture in many geophysical situations fluid is contained in long narrow fractures embedded within an impermeable medium of different thermal conductivity and there may be a uniform vertical temperature gradient imposed upon the system we show that whenever the slot is tiled to the vertical convection develops in the fluid even if the background temperature increases with height

lithologic tomography an application to geophysical data from the cadomian belt of northern brittany france abstract a probabilistic description of subsurface lithologic structures can be established by inverting multidisciplinary geophysical data constrained by geological and geostatistical priors the methodology is based on the joint modelling of several media properties and on a statistical description of the relationships between them the information provided by the geophysical data and the geological and geostatistical priors is represented by probability density functions pdf that are combined into a posterior pdf composed by 1 a prior pdf in the space of the primary lithologic model parameters 2 a pdf of the secondary physical model parameters conditional to the primary model parameters and 3 a joint likelihood function that is the product of the independent likelihood functions for each observed geophysical field applying a markov chain sampling method enables a large sample of joint models to be generated from the posterior pdf the true configuration of the media is then determined from the representation of models pulled from the chain and the elaboration of statistics from the large sample of posterior joint models the method was used to invert gravity and magnetic data jointly characterising the mass density field the magnetic susceptibility field and the lithotype field along two 2 d sections of the geological units in the cadomian belt of northern brittany besides generating 10 6 joint models consistent with the observations and priors some features of the joint models and the statistical tomographic images provided additional insights to the geologic configuration of the area for example the main cadomian thrust shows an irregular geometry that could have resulted from the belt emplacement and or from variscan tectonism and the hercynian granitic intrusion shows a deep subsurface continuation the cosimulation of magnetic susceptibility and mass density inside each lithologic region was performed according to a multivariate gaussian model or a mixed multivariate gaussian functions model that was developed specially to describe multimodal distributed properties

analysis of water level changes induced by fault creep at parkfield california this paper demonstrates that the recovery rates of water level changes due to fault creep can be used to infer the position of the slipping zone relative to the well this technique is applied to five slip related water level changes observed in a well 460 m from the san andreas fault near parkfield california during january 1989 to july 1990 the water level changes are all characterized by a rapid drop in less than 8 hours and a slow recovery of 15 to 30 days the water level drop and the position of the well constrain right lateral slip to be predominantly to the southeast of the well the recoveries are modeled by pore fluid diffusion due to a plane strain dislocation in a porous fluid saturated elastic solid satisfactory agreement with the observations is obtained by assuming slip occurs instantaneously and extends indefinitely to the southeast of the well the extent of the slip northwest of the well which ranges from zero to 322 m is determined by fitting the variations in recovery times among the five events calculations are carried out for the limiting cases of both an impermeable and a permeable fault the permeability of the fault has little effect on inferences about the slip but the inferred horizontal diffusivity differs for the two cases 0 15 m2 s for the impermeable and 0 06 m2 s for the permeable for two of the events the magnitude and distribution of slip inferred from the water level changes agree well with that measured on two nearby creepmeters for a third event the agreement is moderately good discrepancies for the remaining two events suggest that the surface slip measured by the creepmeters may differ significantly from that near the 240 m depth of the well

seismic and geodetic signatures of fault slip at the slumgullion landslide natural laboratory 1 we tested the hypothesis that the slumgullion landslide is a useful natural laboratory for observing fault slip specifically that slip along its basal surface and side bounding strike slip faults occurs with comparable richness of aseismic and seismic modes as along crustal and plate scale boundaries our study provides new constraints on models governing landslide motion we monitored landslide deformation with temporary deployments of a 29 element prism array surveyed by a robotic theodolite and an 88 station seismic network that complemented permanent extensometers and environmental instrumentation aseismic deformation observations show that large blocks of the landslide move steadily at approximately centimeters per day possibly punctuated by variations of a few millimeters while localized transient slip episodes of blocks less than a few tens of meters across occur frequently we recorded a rich variety of seismic signals nearly all of which originated outside the monitoring network boundaries or from the side bounding strike slip faults the landslide basal surface beneath our seismic network likely slipped almost completely aseismically our results provide independent corroboration of previous inferences that dilatant strengthening along sections of the side bounding strike slip faults controls the overall landslide motion acting as seismically radiating brakes that limit acceleration of the aseismically slipping basal surface dilatant strengthening has also been invoked in recent models of transient slip and tremor sources along crustal and plate scale faults suggesting that the landslide may indeed be a useful natural laboratory for testing predictions of specific mechanisms that control fault slip at all scales

magnetic modelling in the french cadomian belt northern armorican massif abstract the french cadomian belt northern armorican massif constitutes an excellent area for studying panafrican orogenic processes in europe for which geophysical methods are useful for obtaining a realistic interpretation of the geological structures at depth magnetic modelling of the area to the west of saint brieuc bay was carried out to determine the geometry of the cadomian geological units modelling was computed along profiles extracted from the regional aeromagnetic map the shape of the magnetic bodies was determined with the help of interpretative geological sections and the total magnetization of the magnetic bodies was determined from a data base of about 350 rock sample measurements the measured susceptibility ranges from 0 15 10 3 si to 221 5 10 3 si the induced magnetization im 40 a m the natural remanent magnetization nrm is weak and shows varied directions it is therefore negligible at the formation scale and only the magnetic susceptibility was taken into account for modelling a computed mean im was attributed to each magnetic body in the model measurements of the magnetic properties and thin section observations of field samples show that magnetite is the main carrier of the magnetization the strong susceptibilities are consistent with ferromagnetic behaviour of multidomain grains whereas the weak susceptibilities accord with dominantly paramagnetic behaviour sample measurements show that the saint quay intrusion the acid part of the lanvollon formation and one of the three lenses of squiffiec metagabbro are the most highly magnetic formations magnetic modelling made it possible to estimate the long wavelength fold shape of the binic formation the basin within this formation reaches about 2 0 2 5 km depth the modelling also indicates that the saint quay intrusion cuts the binic basin at its centre with vertical contacts modelling shows that the intrusion is apparently composed of two imbricated magnetic bodies in its eastern part and of homogeneous magnetic bodies in its western part which is consistent with the geological observations the lanvollon formation exhibits an heterogeneous magnetic behaviour consistent with its lithology of intercalated acid and basic metavolcanic bodies magnetic modelling indicates a difference in thickness of the acid part of the lanvollon formation between the profiles of the binic basin area and those of the squiffiec plouha area this we interpret as reflecting an initial variation in the thickness of the acid volcanic bodies the binic and the squiffiec plouha profiles show that the southern boundary of the basic part of the lanvollon formation is probably vertical or steeply dipping to the north

pore pressure changes induced by slip on permeable and impermeable faults pore pressure changes due to a ramp introduction of slip on permeable and impermeable faults in a fluid saturated rock mass are calculated for the purpose of evaluating water well level fluctuations the calculations demonstrate the importance of coupling between deformation and fluid diffusion at observation points less than 5 4ct0 where c is the diffusivity and t0 is the rise time the decay of pore pressure in the results here is due entirely to fluid mass diffusion an approach that neglects diffusion and assumes that the pore pressure is proportional to the mean normal stress would predict a ramp pore pressure response at distances greater than 5 4ct0 the pore pressure decays so slowly that the neglect of diffusion may be appropriate for both permeable and impermeable faults the pore pressure decays more rapidly for shorter slip zone lengths and longer rise times however the pore pressure change calculated for the impermeable fault is larger particularly for observation points near the fault and decays less rapidly than for the permeable fault these differences suggest that fault permeability can be a significant factor in the response of water wells near faults and care should be used in inferring details of the slip distribution if hydrologic conditions are not known these results are applied to a water well level change observed by lippincott et al a satisfactory fit to the data is obtained by uniform slip over a fault length of about 1 5 km and a rise time of 8 hours although the slip magnitude is not well constrained by the fit the range of possible values includes the 0 5 to 1 0 cm inferred by lippincott et al using a different approach

off fault plasticity and earthquake rupture dynamics 1 dry materials or neglect of fluid pressure changes 1 we analyze inelastic off fault response during earthquakes spontaneous crack like rupture with slip weakening is modeled in 2 d plane strain using an explicit dynamic finite element procedure a mohr coulomb type elastic plastic description describes the material bordering the fault we identify the factors which control the extent and distribution of off fault plasticity during dynamic rupture those include the angle with the fault of the maximum compressive prestress the seismic s ratio and the closeness of the initial stress state to mohr coulomb failure plastic response can significantly alter the rupture propagation velocity delaying or even preventing a transition to supershear rupture in some cases plastic straining also alters the residual stress field left near the fault in part 1 we consider dry materials bordering the fault or at least neglect pore pressure changes within them part 2 addresses the effects of fluid saturation showing that analysis procedures of this part can describe undrained fluid saturated response elastic plastic laws of the type used are prone to shear localization resulting in an inherent grid dependence in some numerical solutions nevertheless we show that in the problems addressed the overall sizes of plastic regions and the dynamics of rupture propagation seem little different from what are obtained when we increase the assumed plastic hardening modulus or dilatancy parameter above the theoretical threshold for localization obtaining a locally smooth numerical solution at the grid scale evidence for scaling of some localization features with a real nongrid length scale in the model is also presented

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

physical models of earthquake instability and precursory processes this paper selectively reviews physical models of earthquake instability in these models instability arises as a result of interaction of a fault constitutive relation with deformation of the surrounding material that occurs in response to remote tectonic loading in contrast to kinematic models in which the fault slip is imposed it is calculated in physical models and consequently these models are essential for understanding precursory processes some kind of weakening behavior for the fault constitutive relation is required to produce an instability analogous to an earthquake two commonly employed idealizations discussed here are rate independent slip weakening and rate state dependent friction when these constitutive models are employed on surfaces embedded in elastic half spaces or layers possibly coupled to a viscoelastic substrate the results are capable of simulating realistically some aspects of earthquake occurrence common to all models is the prediction that earthquake instability is preceded by precursory slip which produces a departure of surface strain rate from the background level near the epicenter of a moderate to large earthquake the magnitude of this departure appears to be well within the range of current geodetic measurement accuracy and its duration is of the order of months to years however details depend on a variety of factors including the modelling of the constitutive relation near peak stress coupling of elastic crust to the asthenosphere and coupling of deformation with pore fluid diffusion

thermal conductivity of landfast antarctic and arctic sea ice 1 we present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures results from landfast first year fy ice near barrow alaska and mcmurdo sound antarctica are consistent with predictions from effective medium models but 10 15 higher than values from the parameterization currently used in most sea ice models we observe no previously reported anomalous near surface reduction which is now understood to have been an artifact nor a convective enhancement to the heat flow although our analysis is limited to temperatures below 5c at which brine percolation is restricted results for landfast multiyear my ice in mcmurdo sound are also consistent with effective medium predictions and emphasize the density dependence we compare these and historical measurements with effective medium predictions and the representation commonly used in sea ice models developed originally for my arctic ice we propose an alternative expression derived from effective medium models appropriate for both my and fy ice that is consistent with

depth and seasonal variations in the thermal properties of antarctic dry valley permafrost from temperature time series analysis 1 we present the first dedicated study of the thermal properties of perennially frozen ice cemented subsurface dry valley permafrost from time series analysis of 14 months temperature measurements we resolve depth and seasonal variations in the thermal properties at two nearby sites at table mountain with different origin composition and polygonal ground patterning we determine apparent thermal diffusivity atd profiles directly from thermistor array measurements at 13 5 cm depth intervals and 4 hour time intervals in the top 2 m we treat the system as purely conductive year round due to the cold temperatures and compare the performance of several common analysis schemes with a graphical finite difference method that we present in detail this comparison is facilitated by one site showing strong depth variations including an abrupt twofold increase in atd across a sharp compositional boundary we characterize the composition of the inhomogeneous ground from recovered cores and estimate an ice fractiondependent heat capacity in the range c 1 7 0 1 to 1 8 0 1 mj m 3 c 1 we calculate apparent thermal conductivity profiles that correlate very well with the core compositions the conductivity generally lies in the range 2 5 0 5 w m 1 c 1 but is as high as 4 1 0 4 w m 1 c 1 for a quartose sirius sandstone unit at one site the seasonal variation in the atd is consistent with its expected temperature dependence index terms 3299 mathematical geophysics general or miscellaneous 5134 physical properties of rocks thermal properties 5194 physical properties of rocks instruments and techniques keywords dry valleys antarctica thermal properties of frozen ground permafrost

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

non linear thermal transport and brine convection in first year sea ice we report the first results from a programme recently set up to directly measure the thermal conductivity of young sea ice an array of thermistors frozen into first year antarctic sea ice provides temperature against depth data which is fitted directly with a partial differential equation for heat conduction temperatures are recorded every hour at twenty vertical intervals of 100mm over a period of 5 months allowing accurate and direct estimation of the thermal conductivity preliminary results indicate that the thermal conductivity is in the expected range with some evidence of nonlinear effects deeper in the ice a larger variance in data is evident at higher temperature gradients and at greater depths in the ice preliminary modelling of the impact of brine migration on heat transport through first year sea ice is presented diffusion driven brine pocket migration is school of mathematical and computing sciences victoria university of wellington po box 600 wellington new zealand yphysics dept victoria university of wellington po box 600 wellington new zealand znew zealand institute for industrial research and development po box 31310 lower hutt new zealand

linkages between salinity and brine channel distribution in young sea ice a high resolution study of bulk salinity was undertaken on laboratory grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures ice samples at two different stages of development were compared with respect to physical state brine distribution and brine channel structures cold growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels areas of high bulk salinity are found to correspond directly to the positions of the brine channels and these areas are surrounded by ice that shows significant brine depletion it is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases the redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice the distribution of brine in warm ice is shown to be more homogeneous and independent of brine channel structures a number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution

3d volumetric modelling of cadomian terranes northern brittany france an automatic method using voronoi diagrams abstract an automatic method based on the use of voronoi diagrams is proposed for the 3d volumetric reconstruction of geological objects it enables volumes to be constructed starting from the combined use of geological maps and cross sections defined in multiple directions and can also take into account incomplete information on geological interfaces and faults the method is suitable for global modelling of a set of geological objects it gives a consistent 3d volumic partition of space according to geological information contained in the maps and the cross sections the method is described and applied to modelling the main domains of the cadomian collisional orogenic belt of panafrican age in northern brittany france thanks to the contrasting densities of the main units involved in the collisional process the gravimetric effect of the volumic model can be calculated its comparison with the observed anomaly allows us to discuss the validity of the geological model although some improvements appear to be necessary it is concluded that the method can make geological modelling more efficient through providing the possibility of rapidly testing many hypotheses

dynamic rupture through a branched fault configuration at yucca mountain and resulting ground motions we seek to characterize the likelihood of multiple fault activation along a branched normal fault system during earthquake rupture using dynamic finite element analyses this is motivated by the normal faults in the vicinity of yucca mountain nevada a potential site for a high level radioactive waste repository the solitario canyon fault scf a north south trending fault located approximately 1 km west of the crest of yucca mountain is the most active of these faults based on the results of previous branching work by kame et al 2003 branch activation in the hanging wall of a normal fault such as the scf may be possible for fast ruptures propagating near the rayleigh wave speed at the branch junction dynamic branch activation along a splay of the scf during a seismic event could have important effects on the rupture velocity and resulting ground motions at the proposed repository site we consider elastic as well as a pressure dependent elastic plastic response of the off fault material we find that based on the regional stress state in the area the only likely candidates for branch activation in the hanging wall of the scf are more steeply westward dipping intrablock splay faults we also find that the rupture velocity for an earthquake propagating updip along the scf must reach supershear speeds in order for dynamic branch activation to occur branch activation can have significant effects on the ground motions at the proposed repository site 1 km away from the scf beneath the crest of yucca mountain causing the repository site to experience a second peak in large vertical particle velocities elastic plastic response near the branch junction reduces peak ground velocities and accelerations at the proposed repository site

cadomian tectonics in northern brittany a contribution of 3 d crustal scale modelling abstract both available and newly acquired geological and geophysical data processed in the framework of the armor project have been used to construct a 3 d geometric and geological model of the cadomian domain of northern brittany the major results of the data processing are presented and discussed relative to a composite profile transecting the studied domain and constructed from the surface geology reflection seismics magnetotelluric soundings and gravimetric data they are then extrapolated at regional scale through a series of cross sections compiled from the surface geology and gravimetric data and calibrated onto the composite profile the 3 d crustal scale models were computed according to two procedures the first using a strim matra datavision modeler defines various interfaces through correlation between adjacent cross sections and is well adapted to the 3 d representation of geological structures the second based on voronoi diagrams leads to a volumetric model of the geological units and is a powerful tool for calculating 3 d geophysical responses of the model when the physical properties of the rock units are known the tectonic implications of the computed 3 d crustal scale geometry of the cadomian domain are then discussed in terms of volcanic arc thrusting with special emphasis being placed on the obliquity of the shortening direction by reference to the thrust fault trend finally the data are used to demonstrate the reactivation of some cadomian faults during the deposition of ordovician sandstones and following the emplacement of the paleozoic dolerite dyke swarm of northern brittany

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

refraction wide angle reflection investigation of the cadomian crust between northern brittany and the channel islands abstract a seismic refraction experiment has been carried out off the coast of northern brittany nw france to investigate the deep structure of the north armorican block the seismic source was an array of airguns and the shots were recorded simultaneously both by ocean bottom seismometers and land stations we present 2d velocity models computed from two crossing seismic refraction profiles labelled p1 and p2 and each about 135 km long oriented ne sw and nnw sse i e parallel and perpendicular respectively to the regional basement structures wide angle reflection profiles were also performed to extend the 2d structures to a 3d crustal interpretation observed and calculated p wave traveltimes were matched by forward modelling prior to their inversion in order to produce two crustal velocity models the model which best fit the data consists of 1 high basement velocities at the top of the crust except in an area with shallow seismic velocity which can be as low as 3 0 km s at the surface and possibly related to the existence of shallow paleozoic sedimentary basins 2 the mean crustal velocity ranges from 5 5 to 6 8 km s at a depth of 15 km depth 3 lower crustal velocities range from 7 0 to 7 5 km s at a depth of 35 38 km and then from 7 5 to 8 1 km s at the crust mantle boundary located between 35 and 38 km depth comparisons with the crustal section imaged by the coincident seismic vertical reflection profile swat 10 show a good correlation between velocity gradients and lower crustal reflectivity when compared to surrounding basement areas the north armorican cadomian crust displays a slightly thicker crust and also a thicker reflective lower crust which can be related to the relative preservation of this upper proterozoic block from later paleozoic and mesozoic tectonic episodes the crustal structure of the north armorican block thus appears to be an intercalated feature between the surrounding paleozoic areas and older shield or platform domains

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

lithospheric stress and deformation the study of the mechanisms magnitudes and modes of lithospheric stress and deformation occupies a central position in the discipline of tectonophysics it is therefore difficult in assembling a comprehensive review to place limits on what should be included for example one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors once admitting to the importance of rheological considerations in discussing stress and deformation one is then compelled to include information relating to the thermal state of the lithosphere since temperature is one of the foremost environmental variables controlling rheology furthermore lithospheric processes cannot be considered in isolation from those affecting the asthenosphere since surely there exists some coupling between the motion of the lithosphere and convection in the earth s interior in fact an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth the topic of this report cannot even be cleanly separated from reviews in other disciplines such as seismology and geodesy the magnitude and orientation of lithospheric stress is often indicated by earthquakes while lithospheric strain can be observed geodetically the philosophy i have adopted here is that some overlap with other review papers in this series is unavoidable and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere s state of stress and mechanisms of deformation i have however resisted the temptation to include extraterrestrial studies presumably covered in the planetary section despite the similar causes for deviatoric stress and deformational mechanisms operating on other terrestrial planets certainly ideas of how silicate materials behave and how lithosphere responds to internal forces benefit from the perspective of omparative planetology finally in defining the scope of this portion of the u s national report to the iugg i did not consciously exclude papers by non u s citizens work done at non u s institutions projects not funded by the u s government or however else foreign might be defined topics in geophysical research cannot be divided along political boundaries however i did not attempt to seek out articles written in languages other than english or published in journals not readily available in the united states and i apologise for this obvious shortcoming