the origin of the dead sea rift abstract the dead sea rift is considered to be a plate boundary of the transform type several key questions regarding its structure and evolution are does sea floor spreading activity propagate from the red sea into the dead sea rift did rifting activity start simultaneously along the entire length of the dead sea rift or did it propagate from several centres why did the initial propagation of the red sea into the gulf of suez stop and an opening of the gulf of elat start using crustal structure data from north africa and the eastern mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half space the regional stress field in this region was calculated using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust by application of a strain dependent visco elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization corresponding to the high value of the damage parameter i e fault zones mathematical simulation of the plate motion and faulting process suggests that the dead sea rift was created as a result of a simultaneous propagation of two different transforms one propagated from the red sea through the gulf of elat to the north the other transform started at the collision zone in turkey and propagated to the south

frictional discharge at fault asperities origin of fractal seismo electromagnetic radiation abstract to investigate the relation between the rock friction and the fractal electromagnetic radiation before the main shock of earthquakes we conducted a friction experiment simulating the motion of an asperity on a fault plane and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals this indicates that frictional discharges plasma generations could occur locally at microscopic asperities on fault surfaces from concepts on the fractal size distribution and temporal evolution of fault asperities the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation benioff electromagnetic radiation prior to earthquakes

factors that control the angle of shear bands in geodynamic numerical models of brittle deformation abstract numerical models of brittle deformation on geological timescales typically use a pressure dependent mohr coulomb or drucker prager plastic flow law to simulate plastic failure despite its widespread usage in geodynamic models of lithospheric deformation however certain aspects of such plasticity models remain poorly understood one of the most prominent questions in this respect is what are the factors that control the angle of the resulting shear bands recent theoretical work suggest that both roscoe 45 coulomb angles 45 2 where is the angle of internal friction and arthur angles 45 4 where is the dilation angle as well as all intermediate angles are possible published numerical models however show a large range of shear band angles with some codes favoring arthur angles whereas others yield coulomb angles in order to understand what causes the differences between the various numerical models here i perform systematic numerical simulations of shear localization around an inclusion of given length scale both numerical element type geometrical and rheological viscoplastic versus viscoelastoplastic effects are studied results indicate that the main factor controlling shear band angle is the non dimensional ratio between the length scale of the heterogeneity d and the size of the numerical mesh x coulomb angles are observed only in cases where the inclusion is resolved well d x 5 10 and in which it is located sufficiently far from the boundary of the box in most other cases either arthur or roscoe orientations are observed if heterogeneities are one element in size coulomb angles are thus unlikely to develop irrespective of the employed numerical resolution whereas differences in element types and rheology do have consequences for the maximum obtainable strain rates inside the shear bands they only have a minor effect on shear band angles shear bands initiated from random noise or from interactions of shear bands with model boundaries or other shear bands result in stress heterogeneities with dimensionless length scales d x 1 2 such shear bands are thus expected to form roscoe or arthur orientations consistent with the findings in previous numerical models

large scale dynamics of the mesosphere and lower thermosphere an analysis using the extended canadian middle atmosphere model the extended canadian middle atmosphere model is used to investigate the large scale dynamics of the mesosphere and lower thermosphere mlt it is shown that the 4 day wave is substantially amplified in southern polar winter in the presence of instabilities arising from strong vertical shears in the mlt zonal mean zonal winds brought about by parameterized nonorographic gravity wave drag a weaker 4 day wave in northern polar winter is attributed to the weaker wind shears that result from weaker parameterized wave drag the 2 day wave also exhibits a strong dependence on zonal wind shears in agreement with previous modeling studies in the equatorial upper mesosphere the migrating diurnal tide provides most of the resolved westward wave forcing which varies semiannually in conjunction with the tide itself resolved forcing by eastward traveling disturbances is dominated by smaller scales nonmigrating tides and other planetary scale waves play only a minor role in the zonal mean zonal momentum budget in the tropics at these heights resolved waves are shown to play a significant role in the zonal mean meridional momentum budget in the mlt impacting significantly on gradient wind balance balance fails at low latitudes as a result of a strong reynolds stress associated with the migrating diurnal tide an effect which is most pronounced at equinox when the tide is strongest resolved and parameterized waves account for most of the imbalance at higher latitudes in summer this results in the gradient wind underestimating the actual eastward wind reversal by up to 40

empirical model of 90 120 km horizontal winds from wind imaging interferometer green line measurements in 1992 1993 an empirical model of horizontal winds is developed based on wind imaging interferometer windii green line observations between 90 and 120 km in 1992 1993 the model includes mean winds solar diurnal and semidiurnal tides and some planetary wave components as well as annual and semiannual variations in these fields its formulation is similar to that of hwm 90 and hwm 93 of hedin et al 1991 1996 but greatly modified and extended to use the higher resolution global wind measurements now available from windii while the technique will only reach fruition when results can be combined from the wind measurements of several years by the different instruments on the uars satellite this interim but updated model provides improved representation of the temporal and geographic variations of the wind fields compared to the current reference models the model generated climatological mean wind diurnal tides and some samples of the entire wind motion fields are presented and compared with the windii measurements and analysis results obtained from the data sets by different methods to check the consistencies between the model representations and the observations this study also reveals a dual cell structure in the meridional component of the diurnal tides with two amplitude maxima centered around 95 and 102 km near 20 latitude and strongly symmetric about the equator at equinox large interannual variabilities are found to exist in both diurnal wind components with maximum amplitudes of 40 and 55 m s for the zonal and meridional respectively at the vernal equinox of 1992

viscoelastic damage modeling of sinkhole formation abstract the sinkholes along the dead sea coast are observed in two main sedimentary environments alluvial fan sinkholes which usually form abruptly as deep 20 m and narrow 3 m sinkholes and mud flat sinkholes which usually form as shallow a few centimeters and wide 5 m sinkholes and deepen later the mechanical collapse of all sinkholes is triggered by cavities created by the dissolution of an underlying salt layer by relatively fresh groundwater the processes attributed to the mechanical formation of the sinkholes are viscous flow and brittle fracture failure we use a two dimensional viscoelastic damage rheology numerical model to quantitatively explain the brittle and ductile aspects of collapsed sinkholes three cases of the rheology of the collapsed sediments are simulated 1 damage controlled failure 2 viscoelastic controlled failure and 3 an intermediate damage viscoelastic case results show that viscoelasticity cannot be the sole process acting on the deformed layer because all sinkholes are characterized by sharp boundaries the damage accumulation progresses until arched cavities are created in the soil layer because of the geometric heterogeneity of the layer represented by the heterogeneity of the mesh smaller blocks continue to fall after the first breakup into the cavity advancing the arched cavity upwards this propagation finally stops when the cavity is shallow enough to hold the irregular arch the combination of these two processes creates competition within the stress reduction mechanism that may lead to either magnified or reduced deformation the deformation is magnified in high shear stress locations where the dispersion of the viscous flow spreads damage failure and it is reduced in low shear stress locations where viscous flow disperses shear stress before the onset of damage

mantle convection with a brittle lithosphere thoughts on the global tectonic styles of the earth and venus summary plates are an integral part of the convection system in the fluid mantle but plate boundaries are the product of brittle faulting and plate motions are strongly influenced by the existence of such faults the conditions for plate tectonics are studied by considering brittle behaviour using byerlee s law to limit the maximum stress in the lithosphere in a mantle convection model with temperature dependent viscosity when the yield stress is high convection is confined below a thick stagnant lithosphere at low yield stress brittle deformation mobilizes the lithosphere which becomes a part of the overall circulation surface deformation occurs in localized regions close to upwellings and downwellings in the system at intermediate levels of the yield stress there is a cycling between these two states thick lithosphere episodically mobilizes and collapses into the interior before reforming the mobile lid regime resembles convection of a fluid with temperature dependent viscosity and the boundary layer scalings are found to be analogous this regime has a well defined nusselt number rayleigh number relationship which is in good agreement with scaling theory the surface velocity is nearly independent of the yield stress indicating that the plate motion is resisted by viscous stresses in the mantle analysis suggests that mobilization of the earth s lithosphere can occur if the friction coeycient in the lithosphere is less than 0 03 0 13 lower than laboratory values but consistent with seismic field studies on venus the friction coeycient may be high as a result of the dry conditions and brittle mobilization of the lithosphere would then be episodic and catastrophic

scaling relations of earthquakes and aseismic deformation in a damage rheology model summary we perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function a new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities the formulation connects the damage rheology parameters with dynamic friction of simpler frameworks and the plastic strain accumulation is governed by a procedure that is equivalent to drucker prager plasticity the numerical simulations use variable boundary forces proportional to the slip deficit between the assumed far field plate motion and displacement of the boundary nodes these boundary conditions account for the evolution of elastic properties and plastic strain in the model region 3 d simulations of earthquakes in a model with a large strike slip fault produce scaling relations between the scalar seismic potency rupture area and stress drop values that are in good agreement with observations and other theoretical studies the area and potency of the simulated earthquakes generally follow a linear log log relation with a slope of 2 3 and are associated with stress drop values between 1 and 10 mpa a parameter space study shows that the area potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction more efficient healing and higher degree of seismic coupling

stable and unstable damage evolution in rocks with implications to fracturing of granite summary we address the relation between the rock rigidity and crack density by comparing predictions of a viscoelastic damage rheology model to laboratory data that include direct microscopic mapping of cracks the damage rheology provides a generalization of hookean elasticity to a non linear continuum mechanics framework incorporating degradation and recovery of the effective elastic properties transition from stable to unstable fracturing and gradual accumulation of irreversible deformation this approach is based on the assumption that the density of microcracks is uniform over a length scale much larger than the length of a typical crack yet much smaller than the size of the entire deforming domain for a system with a sufficiently large number of cracks one can define a representative volume in which the crack density is uniform and introduce an intensive damage variable for this volume we tested our viscoelastic damage rheology against sets of laboratory experiments done on mount scott granite based on fitting the entire stress strain records the damage variable is constrained and found to be a linear function of the crack density an advantage of these sets experiments is that they were preformed with different loading paths and explicitly demonstrated the existence of stable and unstable fracturing regimes we demonstrate that the viscoelastic damage rheology provides an adequate quantitative description of the brittle rock deformation and simulates both the stable and unstable damage evolution under various loading conditions comparison between the presented data analysis of experiments with mount scott granite and previous results with westerly granite and berea sandstone indicates that granular or porous rocks have lower seismic coupling this implies that the portion of elastic strain released during a seismic cycle as brittle deformation depends on the lithology of the region hence upper crustal regions with thick sedimentary cover or fault zones with high degree of damage are expected to undergo a more significant inelastic deformation in the interseismic period compared to intact crystalline rocks

a rheological model of a fractured solid abstract experiments to study the behavior of various materials point to the relation that exists between elastic properties and the type of stress the influence of the state of stress on the elasticity of a fractured material will be discussed for a physically non linear model of an elastic solid the strain dependent moduli model of material presented in this paper makes it possible to describe this feature of a solid it also permits to simulate a dilatancy of rocks a damage parameter introduced into the model using a thermodynamical approach allows to describe a rheological transition from the ductile regime to the brittle one and to simulate the rock s memory narrow fracture zone creation and strain rate localization additionally the model enables the investigation of the final geometry of fracture zones and also to simulate their creation process taking into account pre existing fracture zones the process of narrow fracture zone creation and strain rate localization was simulated numerically for single axis compression and shear flow

the processes controlling damage zone propagation induced by wellbore fluid injection summary induced seismicity by wellbore fluid injection is an important tool for enhancing permeability in hydrocarbon and geothermal reservoirs we model nucleation and propagation of damage zones and seismicity patterns for two dimensional plane strain configuration at a depth of 5 km using novel numerical software developed in the course of this study simulations include the coupling of poro elastic deformation and groundwater flow with damage evolution weakening and healing and its effect on the elastic and hydrologic parameters results show that the process occurring during fluid injection can be divided into four stages the duration of each stage depends on the hydrological and mechanical parameters initially fluid flows into the rock with no seismic events 5 to 20 hr at this stage damage increases from 0 to 1 creating two sets of conjugate zones four narrow damage zones thereafter the occurrence of seismic events and faulting begins and accelerates for the next 20 to 70 hr at the initial part of this stage two of the damage zones create stress shadows on the other two damage zones that stop progressing the velocity of the advancing damage is limited only by the rock parameters controlling damage evolution at the third stage which lasts for the following 20 30 hr damage acceleration decreases because fluid transport becomes a limiting factor as the damage zones are too long to efficiently transfer the pressure from the well to the tip of the damage zones finally the damage decelerates and even stops in some cases the propagation of damage is controlled and limited by fluid transport from the injection well to the tip of the damage zones becausefluid transport does not keep up with the dilatancy of the damage zones the time and distance of propagation depend on the damage permeability coupling and the remote shear stress higher remote shear stress causes shorter initial periods of no seismicity strong damage permeability coupling causes longer acceleration stage

micro and macroscopic models of rock fracture summary the anelastic deformation of solids is often treated using continuum damage mechanics an alternative approach to the brittle failure of a solid is provided by the discrete fiber bundle model here we show that the continuum damage model can give exactly the same solution for material failure as the fiber bundle model we compare both models with laboratory experiments on the time dependent failure of chipboard and fiberglass the power law scaling obtained in both models and in the experiments is consistent with the power law seismic activation observed prior to some earthquakes

extended canadian middle atmosphere model zonal mean climatology and physical parameterizations 1 this paper describes the energetics and zonal mean state of the upward extension of the canadian middle atmosphere model which extends from the ground to 210 km the model includes realistic parameterizations of the major physical processes from the ground up to the lower thermosphere and exhibits a broad spectrum of geophysical variability the rationale for the extended model is to examine the nature of the physical and dynamical processes in the mesosphere lower thermosphere mlt region without the artificial effects of an imposed sponge layer which can modify the circulation in an unrealistic manner the zonal mean distributions of temperature and zonal wind are found to be in reasonable agreement with observations in most parts of the model domain below 150 km analysis of the global average energy and momentum budgets reveals a balance between solar extreme ultraviolet heating and molecular diffusion and a thermally direct viscous meridional circulation above 130 km with the viscosity coming from molecular diffusion and ion drag below 70 km radiative equilibrium prevails in the global mean in the mlt region between 70 and 120 km many processes contribute to the global energy budget at solstice there is a thermally indirect meridional circulation driven mainly by parameterized nonorographic gravity wave drag this circulation provides a net global cooling of up to 25 k d 1

simulation of collision zone segmentation in the central mediterranean abstract collision processes between the african and european plates in the ionian sea offshore calabria and in sicily take place in several ways to the east normal subduction of oceanic crust underlying the ionian sea occurs underneath the calabrian arc whereas to the west continental collision between the pelagian block and the calabrian arc which extends from calabria to the northeastern tip of sicily and offshore of the island to the north gives rise to the maghrebian thrust belt on mainland sicily this belt consists mostly of stacked basinal and platform carbonates of mesozoic early tertiary age deposited along the africa passive margin no clear subduction characterizes the area north of the hybleandashmalta plateau where it collides with the maghrebian chain the origin of the hybleandashmalta plateau is unclear geophysical data indicate however that its crustal structure is different from that of the surrounding pelagian foreland crustal structure variations at the edge of the subducted african plate may thus cause the observed segmentation of the collisional arc system a computer model of the region was created to learn about the deformation and faulting processes in the region the simulation starts prior to the collision of the pelagian block with the calabrian arc with time the hybleandashmalta plateau collides with the northern crustal block and as a result a new simulated topography a new distribution of velocities and most important a new distribution of fracture zones are created a shear fracture zone is formed east of the hybleandashmalta plateau malta escarpment extending to the subduction zone at the calabrian arc a less active strike slip fracture zone is created west of the hybleandashmalta plateau an additional e w trending active fracture zone is creating in the southern part of the simulated area this feature may correspond to a fault zone which runs from the strait of sicily to the ionian sea

long term variability in the equatorial middle atmosphere zonal wind the high resolution doppler imager hrdi on the upper atmosphere research satellite uars has provided measurements of the horizontal wind field in the stratosphere mesosphere and lower thermosphere since november 1991 this data set which spans a period of more than 3 years has facilitated an investigation of the long term behavior of the background circulation on a nearly global basis at middle and high latitudes the zonal circulation is characterized by an annual oscillation at low latitudes 30 the most prominent long term variation above the stratopause is the mesosphere semiannual oscillation msao which maximizes near the equator at an altitude of between 80 and 85 km further analysis of the time series reveals an additional strong variation with an amplitude near 30 ms 1 and a period of about 2 years this feature shows the same altitude and latitude structure as the msao and exhibits a phase relationship with the stratospheric quasi biennial oscillation qbo observations from the christmas island mf radar 2 n 130 w confirm the presence of this mesospheric qbo mqbo these observations support recent findings from a modeling study which generates an mqbo via the selective filtering of small scale gravity waves by the underlying winds they traverse

zonal mean winds in the equatorial mesosphere and lower thermosphere observed by the high resolution doppler imager this paper presents analyses of mesospheric and lower thermospheric zonal mean winds observed by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars monthly averages of the equatorial zonal mean zonal winds are presented for january 1992 through june 1993 equatorial zonal winds in the 70 90 km region are dominated by a semiannual oscillation sao ranging from 30 m s 1 westerly to 100 m s 1 easterly at high latitudes the zonal wind variations are predominantly annual above 90 km the low latitude flow is easterly at all times punctuated by a small semiannual variation this behavior may be related to the deposition of momentum by the diurnal tides

evidence for coral island formation during rising sea level in the central pacific ocean the timing and evolution of jabat island marshall islands was investigated using morphostratigraphic analysis and radiometric dating results show the first evidence of island building in the pacific during latter stages of holocene sea level rise a three phase model of development of jabat is presented initially rapid accumulation of coarse sediments on jabat occurred 4800 4000 years b p across a reef flat higher than present level as sea level continued to rise during the highstand island margins and particularly the western margin accreted vertically to 2 5 3 0 m above contemporary ridge elevations this accumulation phase was dominated by sand size sediments phase three involved deposition of gravel ridges on the northern reef as sea level fell to present position jabat has remained geomorphically stable for the past 2000 years findings suggest reef platforms may accommodate the oldest reef islands in atoll systems which may have profound implications for questions of prehistoric migration through pacific archipelagos

hrdi observations of mean meridional winds at solstice abstract high resolution doppler imager hrdi measurements of daytime and nighttime winds at 95 km are used to deduce seasonally averaged eulerian mean meridional winds during six solstice periods these estimates are compared with seasonally averaged radar meridional winds and with results from dynamical and empirical wind models hrdi mean meridional winds are directed from the summer pole toward the winter pole over much of the globe peak equatorward winds of about 15 m s 1 are usually observed in the summer hemisphere near 30 a local minimum in the equatorward winds is often observed poleward of this latitude with winds approaching zero or reversing direction a similar structure is seen in contemporaneous radar winds this behavior differs from residual meridional wind patterns predicted by models the discrepancies may be related to gravity wave paramaterizations or a consequence of planetary wave influences

red sedimentary units as indicators of early pleistocene tectonic activity in the southern negev desert israel abstract alluvial units termed red units accumulated along the western margin of the dead sea rift dsr valley southern negev desert israel in the early pleistocene these sedimentary units consist of coarse to fine grained alluvium of local origin which contain calcic paleosols the sediments of the red units accumulated in stream valleys and newly forming semi closed local tectonic basins during a tectonic phase that deformed the western margin of the dsr as a result of this deformation the pliocene northward flowing regional drainage system of the southern negev disintegrated to the present northeast flowing ephemeral drainage systems of nahal zihor nahal hiyyon and nahal paran all of them draining to the arava valley in the dsr this change was induced by two deformation episodes 1 reactivation of the zihor and the milhan faults two major northeast trending tectonic lines and 2 east and northeast tilting of the entire region during upwarp arching of the central negev the paleosols of the red units are characterized by pedogenic features such as rhizoconcretions and bk horizons the paleosols developed in the alluvial sediments that were deposited and preserved in local small structural basins along the main fault lines and in reversed or abandoned westward flowing pliocene stream valleys formation of paleosols was initiated in the stream valleys when they attained a near horizontal gradient due to gradual eastward directed regional tilting followed by low rates of deposition the sections of the red units in the pliocene valleys were incised due to continuing tilting which completely reversed the primary westward gradient of the valleys and they were incised by new east and northeast flowing streams the red units have paleoclimatic implications since the middle pleistocene the southern negev has been characterized by gypsic and salic soils typical of an extremely arid climate while the calcic soils detected in the red units point to a semi arid climate this indicates a gradual transition from more humid conditions in the early pleistocene to the present extreme aridity therefore the red units reflect a distinct tectonic and climatic regime and can serve as regional morphostratigraphic marker of early pleistocene age in this paper we used this marker to reconstruct the tectonic deformation that established the present configuration of the southern negev terrain

satellite observations of mean winds and tides in the lower thermosphere 2 wind imaging interferometer monthly winds for 1992 and 1993 1 satellite observations of monthly i e 60 d averages centered on the 15th of each month zonal mean and migrating tide winds in the region of 90 120 km and 40 s 40 n from the wind imaging interferometer are presented the zonal mean zonal winds are characterized by annually varying eastward winds at midlatitudes with a maximum in summer and semiannually varying westward winds in the tropics with maxima at equinox below 105 km the zonal mean meridional winds are characterized by a summer to winter flow below 100 km at solstice and by a cell like structure at equinox the latter is the first such global observation of this tidally driven structure two distinct types of diurnal tide are observed an upward propagating one and an evanescent one of comparable magnitude the propagating tide which is dominant in the subtropics below about 105 km exhibits a semiannual variation with a primary maximum in march april and a secondary maximum in september october the evanescent tide which is dominant poleward of 20 n s and above 100 km has an annual variation with a maximum in the summer months the coupling of the two produces a double peaked structure in the vertical profile of the diurnal amplitude the semidiurnal tide is generally weaker than the diurnal tide the maximum semidiurnal winds are at 30 40 n s and at 105 110 km both zonal and meridional components are stronger in april september than in october march in both hemispheres but in the equatorial region in april september the meridional component has a maximum whereas the zonal component has a minimum

troposphere thermosphere tidal coupling as measured by the saber instrument on timed during july september 2002 1 coupling between the troposphere and lower thermosphere due to upward propagating tides is investigated using temperatures measured from the saber instrument on the timed satellite the data analyzed here are confined to 20 120 km altitude and 40 latitude during 20 july to 20 september 2002 apart from the migrating sun synchronous tidal components the predominant feature seen from the satellite frame during this period is a wave 4 structure in longitude with extrema of up to 40 50 k at 110 km amplitudes and longitudes of maxima of this structure evolve as the satellite precesses in local time and as the wave s responsible for this structure vary with time the primary wave responsible for the wave 4 pattern is the eastward propagating diurnal tide with zonal wave number s 3 de3 its average amplitude distribution over the interval is quasi symmetric about the equator similar to that of a kelvin wave with maximum of about 20 k at 5 s and 110 km de3 is primarily excited by latent heating due to deep tropical convection in the troposphere it is demonstrated that existence of de3 is intimately connected with the predominant wave 4 longitude distribution of topography and land sea difference at low latitudes and an analogy is drawn with the strong presence of de1 in mars atmosphere the predominant wave 2 topography on mars and the wave 2 patterns that dominate density measurements from the mars global surveyor mgs spacecraft near 130 km additional diurnal semidiurnal and terdiurnal nonmigrating tides are also revealed in the present study these tidal components are most likely excited by nonlinear interactions between their migrating counterparts and the stationary planetary wave with s 1 known to exist in the southern hemisphere during this period just prior to the austral midwinter stratospheric warming of 2002

fracturing process of granite inferred from measurements of spatial and temporal variations in velocity during triaxial deformations fracturing in fine grained homogeneous granite during triaxial deformation was investigated by measuring the spatial and temporal variations of elastic wave velocities velocities along 20 ray paths were measured with 12 piezoelectric transducers attached to a sample under confining pressures up to 400 mpa systematic velocity differences observed among the 20 paths apparently indicate the formation of a dilatant region near the surface of a sample the damaged region formed near the surface due to asymmetric development of dilatancy seemed to play an important role in controlling ultimate failure no evidence of the formation of a crack concentration zone adjacent to the ultimate fracture plane could be found before failure insofar as could be estimated from the velocity variations of elastic waves propagating along its plane however a highly concentrated region of cracks in which the fracture nucleated was generated in the damaged region at stresses of more than 97 99 of the ultimate strength in all the specimens based on tomographic images computed using an algebraic reconstruction technique the elastic waves were strongly affected by the damaged region even under the high confining pressures at which cracks are considered to close

self consistent generation of tectonic plates in three dimensional mantle convection abstract despite the fundamental importance of plates in the earth s mantle convection plates have not generally been included in numerical convection models or analog laboratory experiments mainly because the physical properties which lead to plate tectonic behavior are not well understood strongly temperature dependent viscosity results in an immobile rigid lid so that plates where included at all in 3 d models have always been imposed by hand an important challenge is thus to develop a physically reasonable material description which allows plates to develop self consistently this paper focuses on the role of ductile shear localization in two dimensional geometry it is well established that strain rate softening non newtonian rheologies e g power law visco plastic cause weak zones and strain rate localization above up and down wellings resulting in a rudimentary approximation of plates three dimensional geometry however is fundamentally different due to the presence of transform plate boundaries with associated toroidal motion since power law and visco plastic rheologies do not have the property of producing shear localization it is not surprising that they do not produce good plate like behavior in three dimensional calculations here it is argued that a strain rate weakening rheology previously shown to produce plate like behavior in a two dimensional sheet representing the lithosphere is a reasonable generic description of various weakening processes observed in nature one and two dimensional models are used to show how this leads to shear localization and the formation of faults this rheology is then applied to the high viscosity lithosphere of 3 d mantle convection calculations and the velocity pressure viscosity solution for the entire 3 d domain lid and underlying mantle is solved self consistently it is found that the lithosphere divides into a number of very high viscosity plates separated by narrow sharply defined weak zones with a viscosity many orders of magnitude less than the plate interiors broad weak zones with dominant convergent divergent motion above up and down wellings are interconnected by a network of narrow weak zones with dominant strike slip motion passive spreading centers are formed in internally heated cases while the resulting plates are not fully realistic these results show that self consistent plate generation is a realizable goal in three dimensional mantle convection and provide a promising avenue for future research

reef sedimentary accretion model reefsam understanding coral reef evolution on holocene time scales using 3d stratigraphic forward modelling abstract a detailed understanding of the development of coral reefs and their internal structure has important applications for predicting future reef trajectories in light of climate changes petroleum exploration and reconstructing past environmental changes such as sea level numerical computer modelling provides a quantitative means of testing and understanding reef processes and better predicting past and future reef development however most existing carbonate stratigraphic forward models sfms focus on the platform scale and several limitations in their simulation of important reef processes and reef scale features e g patch reefs sand aprons have been previously identified we present the reef sedimentary accretion model reefsam a new carbonate sfm designed to test new approaches to modelling processes important at the reef scale with the goal of better simulating reef features and evolution at higher temporal and spatial resolutions specific developments include a sediment transport model which calculates deposition based on a range of grain sizes additional controls on coralgal growth including wave energy and surface substrate specificity and model outputs showing categorized paleo conditions composition paleo depth and paleo energy along with numerous quantitative measures for objective comparison of model results to real world observational data which is often more abundant for modern holocene reefs than buried ancient reefs simulations of the well studied holocene one tree reef otr in the southern great barrier reef gbr showed improvements upon previous modelling attempts in both quantitative measures e g lagoon size or reef sea level catch up time and the ability to produce more realistic reef scale morphological features e g lagoonal patch reefs mostly sand filled lagoon and reef development characteristics e g transition from mostly vertical aggradation during sea level catch up to horizontal progradation afterwards controls on reef maturity lagoonal filling identified in previous modelling experiments were corroborated sensitivity testing also revealed a very high sensitivity to reef drowning these results indicate the new modelling approaches are viable and provide a way forward for future holocene reef evolution model development

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

evolving geometrical and material properties of fault zones in a damage rheology model we discuss numerical simulations of evolving fault zone structures in a 3 d lithospheric model with a seismogenic crust governed by a damage rheology that accounts for large strain associated with permanent brittle deformation results for the initial propagation of an existing narrow damage zone subjected to oblique loading exhibit strong asymmetry of the evolving damage with respect to the initial fault orientation and predict out of plane directions of the propagating damage zones the orientations of the simulated damage zones agree with analytical expectations based on fracture mechanics for the directions of wing cracks generated at the tips of a crack under mixed mode loading lithosphere scale numerical simulations for the long term evolution of a large strike slip fault zone produce initially a system of stepping en echelon segments associated with the asymmetric generation of new damage zones the simulated fault zone segments evolve with continuing deformation to a throughgoing localized structure large scale perturbation in the geometry of the moho interface together with the regional heat regime can reduce considerably the degree of localization of the fault zone structure and the associated deformation fields

geomorphology and sediment transport on a submerged back reef sand apron one tree reef great barrier reef back reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems the development of these features influences the evolution and defines the maturity of coral reefs however the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport current and wave conditions on a back reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron reef flats and lagoon the current and wave processes that may entrain and transport sediment were assessed using second order small amplitude stokes wave theory and shields equations the morphodynamic interactions between current flow and geomorphology were also examined the results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents a morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel like areas directing current off the sand apron towards the lagoon or the reef crest these results show that the short term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium

satellite observations of mean winds and tides in the lower thermosphere 1 aliasing and sampling issues 1 the canadian middle atmosphere model a general circulation model extending up to 200 km is used to analyze the impact of aliasing and data gaps on satellite observations of zonal mean winds and migrating tides in the lower thermosphere focus is placed on measurements from the wind imaging interferometer windii mock data sets are constructed by sampling daily zonal mean and migrating tides from the model like the satellite previously unverified assumptions that satellite observations of the zonal mean zonal winds and the meridional component of the diurnal tide winds are largely unaffected by aliasing are confirmed of the two the meridional component of the diurnal tide is more robust the amplitude of the zonal component of the diurnal tide is not strongly affected by aliasing tidal phase is nearly unaffected gaps in the windii data do not adversely affect the results provided sufficient local time coverage is available the analysis suggests that more subtle features in the windii observations such as the tidally driven cell like structures in the zonal mean meridional wind at low latitudes may be observable issues pertaining to the sampling interval and the use of daytime only data are also addressed sampling every second or third day provides nearly as good results as sampling every day and that using daytime only data results in substantial biases in the zonal mean zonal winds in the lower thermosphere the latter underscores the importance of the accurate removal of the migrating diurnal tide from climatologies generated from daytime only satellite data

numerical modelling of post seismic rupture propagation after the sumatra 26 12 2004 earthquake constrained by grace gravity data in the last decades the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle documenting new features of inter co and post seismic processes in particular since 2002 satellite mission grace provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the earth s gravity field including those caused by mass redistribution associated with earthquake processes when combined with gps measurements these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the sumatra 26 12 2004 earthquake indeed the observed post seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming burgers body rheology for the asthenosphere 60 220 km deep with a transient viscosity as low as 4 10 17 pas and constant 10 19 pas steady state viscosity in the 60 660 km depth range however even the low viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the grace gravity variations thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture post seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post seismic fault propagation has never been investigated numerically depth and size of localized slip area as well as rate and time decay during the post seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data in this paper we investigate post seismic rupture propagation by modelling two consequent stages first we run a long term geodynamic simulation to self consistently produce the initial stress and temperature distribution at the second stage we simulate a seismic cycle using results of the first step as initial conditions the second short term simulation involves three substeps including additional stress accumulation after part of the subduction channel was locked spontaneous coseismic slip formation and development of damage zones producing afterslip during the last substep post seismic stress leads to gradual 1 m slip localized at three faults around 100 km downdip extension of the coseismic rupture we used the displacement field caused by the slip to calculate pressure and density variations and to simulate gravity field variations wavelength of calculated gravity anomaly fits well to that of the real data and its amplitude provides about 60 per cent of the observed grace anomaly importantly the surface displacements caused by the estimated afterslip are much smaller than those registered by gps networks as a result cumulative effect of burgers rheology viscoelastic relaxation which explains measured gps displacements and about a half of gravity variations plus post seismic slip predicted by damage rheology model which causes much smaller surface displacements but provides another half of the grace gravity variations fits well to both sets of the real data hence the presented numerical modelling based on damage rheology supports the process of post seismic downdip rupture propagation previously hypothesized from the grace gravity data

role of modern climate and hydrology in world oil preservation the accumulation of oil requires a favorable source a reservoir good seal rock quality and suitably timed thermal history and structuring the accumulated oil especially its light fractions may be subsequently removed by hydrologically controlled processes such as water washing biodegradation and tilting of the oil water contact these processes are dependent on the climate in regions that have become increasingly cold or dry during late cenozoic time low rainfall low ground water flow rates and low input of nutrients and microorganisms have protected the oil in warm or temperate rainy climates high flow rates and high input of nutrients and microorganisms have led to partial or total removal of oil thus most of the rich 500 000 barrels day oil provinces on land are in cold or dry regions where water is recharged in highlands that receive little rain 500 mm yr such as texas oklahoma wyoming alaska s north slope california algeria libya egypt the middle east the volga ural basin and western siberia where upland recharge areas are warm or temperate and rainy as in the eastern united states western europe sub saharan africa brazil india and most of china rich oil provinces on land outside young deltas are rare and biodegradation is widespread 32 refs more 2 figs less

extreme longitudinal disturbances in the mesosphere and thermosphere observed with the wind imaging interferometer on uars 1 extreme longitudinal disturbances in the o 1s emission rate and horizontal winds in the mesosphere and thermosphere 90 180 km are identified on three march days in 1994 1996 and 1997 in the database of the wind imaging interferometer windii on the upper atmosphere research satellite uars this type of disturbance has a wave structure with apparent zonal wavenumber 1 and a very long vertical wavelength it generates longitudinal amplitudes of 70 photons cm 3 s 1 and 120 ms 1 in the o 1s volume emission rate and winds respectively and is strong enough to break the structures of migrating tides in the e region in the same longitudinal zone for day and night the zonal wind driven by this disturbance has the same phase suggesting a wave with s 1 and a very long period but the meridional wind has opposite phases suggesting a standing non migrating diurnal tide this super disturbance has not been observed before and fundamental questions about it await future investigation

atmospheric tide 2 the solar and lunar semidiurnal components solar and lunar semidiurnal wind and temperature oscillations from the surface to 400 km are simulated for average solar activity conditions utilizing the numerical tidal model described in part 1 hough mode decomposition of the solstitial solar semidiurnal tide excited by h2o and o3 insolation absorption below 80 km indicates that it is characterized by a predominance of 2 2 below 60 km about equal contributions of 2 2 2 3 and 2 4 between 70 and 90 km mostly 2 4 with some 2 5 and 2 2 between 90 and 120 km and a predominance of 2 2 above 140 km with secondary contributions from 2 3 and 2 5 the solstitial lunar semidiurnal tide is characterized by a predominance of 2 2 below 70 km 2 4 with secondary contributions from 2 2 2 3 and 2 5 between 80 and 110 km and by 2 2 with a fairly strong secondary contribution from 2 3 above 120 km similar descriptions for both the solar and lunar oscillations apply at equinox except that the asymmetric 2 3 and 2 5 modes are absent relative to the solar component lunar temperature and wind amplitudes are sufficiently large 20 in the lower and upper thermosphere to account for some of the observed variability previously attributed to the solar tide amplitudes of the 2 4 and 2 5 modes above 100 km are significantly affected by mesospheric eddy diffusion coefficients in excess of 2 106 cm s 1 the total solar semidiurnal exospheric temperature oscillation for average solar conditions ranges from 10 20 k poleward of 40 n to 40 60 k equatorward of 30 n and has its origin in three sources of excitation all of comparable importance 1 euv solar radiation absorption in the lower thermosphere 100 200 km 2 in situ momentum coupling due to the interaction of diurnal winds and diurnally varying ion drag and 3 tides propagating upwards from below 100 km in addition the calculations are compared with rocket meteor radar partial reflection thomson scatter and satellite data to evaluate the consistency of the model with observations

numerical modeling of the growth and drowning of hawaiian coral reefs during the last two glacial cycles 0 250 kyr 1 drowned coral reefs on rapidly subsiding margins possess a unique archive of sea level and climate changes generally unavailable from stable or uplifting margins using available field observations and sedimentary radiometric age and numerical modeling data we propose a new model of submerged reef development around hawaii during the last two glacial cycles 250 kyr this model provides a quantitative predictive stratigraphy for the reefs that we argue if drilled will yield new information on sea level and climate changes as well as coral reef response over the last 250 kyr comparing the observational and numerical modeling data combined with sensitivity testing we present our best case scenario for the evolution of the drowned lowstand reefs now at 400 h2 and 150 m h1 we find that growth rates of 2 5 2 85 m kyr for the main shallow reef building facies a subsidence rate of 2 5 m kyr and a variable basement substrate configuration best explain the observational data modeling of the internal stratigraphic succession of the reefs shows that the number and thickness of shallow reef units as well as the frequency and duration of subaerial exposure and reef drowning events are sensitive to the frequency and amplitude of eustatic sea level variations but not the rate of subaerial erosion h2 and h1 initiated growth during stable eustatic sea level conditions during highstands circa 222 ka mis7 and circa 126 ka mis5e respectively both h2 and h1 have a long and complex growth history growing episodically for 90 kyr precessional 20 kyr and higher frequency suborbital eustatic sea level fluctuations dominate with each reef experiencing repeated but brief 5 10 kyr drowning and subaerial exposure producing a complex layer cake stratigraphy of shallow 0 30 m coral reef units separated by either subaerial exposure horizons or thin intermediate 30 60 m coralgal units final drowning of h2 and h1 occurs during the penultimate 133 134 ka and last deglaciation 12 14 ka these findings are consistent with available age data and qualitative predictions of previous studies around hawaii

fractal patterns of fractures in granites abstract fractal measurements using the cantor s dust method in a linear one dimensional analysis mode were made on the fracture patterns revealed on two dimensional planar surfaces in four granites this method allows one to conclude that 1 the fracture systems seen on two dimensional surfaces in granites are consistent with the part of fractal theory that predicts a repetition of patterns on different scales of observation self similarity fractal analysis gives essentially the same values of d on the scale of kilometres metres and centimetres five orders of magnitude using mapped surface fracture patterns in a sierra nevada granite batholith mt abbot quadrangle calif 2 fractures show the same fractal values at different depths in a given batholith mapped fractures main stage ore veins at three mining levels over a 700 m depth interval of the boulder batholith butte mont show the same fractal values although the fracture disposition appears to be different at different levels 3 different sets of fracture planes in a granite batholith central france and in experimental deformation can have different fractal values in these examples shear and tension modes have the same fractal values while compressional fractures follow a different fractal mode of failure the composite fracture patterns are also fractal but with a different median fractal value compared to the individual values for the fracture plane sets these observations indicate that the fractal method can possibly be used to distinguish fractures of different origins in a complex system it is concluded that granites fracture in a fractal manner which can be followed at many scales it appears that fracture planes of different origins can be characterized using linear fractal analysis

the rise of solid state diapirs when magma inside a diapir solidifies it increases in density and becomes a stiff power law fluid if the diapir is still positively or negatively buoyant after solidification it will continue to rise or start to sink the results presented here suggest that solidified diapirs may rise sink a distance of up to a few kilometres in geologically reasonable times rocks and bubble and or crystal rich magmas behave as power law fluids this paper compares numerical results of viscosity and strain rate profiles across power law and newtonian diapirs and wall rocks the comparison shows that the core of power law diapirs deforms more slowly and the margins much faster than in newtonian diapirs this pattern of strain rate distribution leads to the often observed isotropic or weakly deformed core surrounded by a strongly sheared margin furthermore the results suggest that the strain rate of the ambient fluid wall rock is imposed across the contact into a power law diapir resulting in similar strains on either side of the contact and that power law wall rocks in contrast to newtonian wall rocks deform into a rim synform as the diapir rises

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

on the relation between seismic wave velocity and stress in a solid summary the paper considers a model comprised of variable moduli elastic solids incorporating fracturing caused by tectonic stress the model gives us a possibility to calculate the seismic velocities and crack distribution around density variations the results of numerical simulations are shown

dynamic rupture and seismic radiation in a damage breakage rheology model we present simulations of dynamic ruptures in a continuum damage breakage rheological model and waves radiated by the ruptures and observed in the far field the propagating rupture produces rock damage and granulation in the process zone ahead of the rupture front an expansion compaction process in the process zone leads to an isotropic source term while shear motion that accumulates behind the propagating front produces a deviatoric source term and shear heating behind the rupture front the process zone dissipation due to the damage breakage mechanism and the isotropic source component significantly affect the s p energy partitioning and the radiation patterns of the waves the calculated s p seismic energy ratio can be significantly lower than results of standard models with no damage breakage mechanism and no source volume components the p radiation pattern becomes more isotropic compared with the classical deviatoric solution with increased lobes at 45 to the direction of rupture propagation the s radiation pattern is affected more strongly by the damage breakage process in the source volume mainly within the process zone and is significantly different from classical deviatoric results the s waves propagate from the rupture front through the process zone unlike the p waves experiencing stronger dissipation so the s radiation pattern is more affected than the p radiation pattern hence analysis of p waves can provide more reliable results on rupture directivity than s waves

damage and plastic deformation of reservoir rocks part 1 damage fracturing in this series of studies we develop a numerical tool for modeling finite deformation of reservoir rocks we present an attempt to eliminate the main limitations of idealized methods for example elastic or kinematic that cannot account for the complexity of rock deformation our approach is to use rock mechanics experimental data and finite element models abaqus to generate realistic simulations the present numerical rheology incorporates the dominant documented deformation modes of rocks 1 rock mechanics experimental observations including finite strength inelastic strain hardening strength dependence on confining pressure strain induced dilation pervasive and localized damage and local tensile or shear failure without macroscopic disintegration and 2 field observations including large deformation distributed damage complex fracture networks and multiple zones of failure our analysis starts with an elastic plastic damage rheology that includes pressure dependent yield criteria stiffness degradation and fracturing via a continuum damage approach using the abaqus materials library we then use experimental results for berea sandstone in two configurations four point beam and dog bone triaxial to refine and calibrate the rheology we find that damage and fracturing patterns generated in the numerical models match the experimental features well and based on these observations we define damage fracturing the fracturing process by damage propagation in a rock with elastic plastic damage rheology in part 2 we apply this rheology to investigate fracture propagation at the tip of a hydrofracture

satellite observations of thermospheric tides results from the wind imaging interferometer on uars thermospheric winds measured by the wind imaging interferometer windii on the upper atmosphere research satellite are analyzed for migrating solar tides the data cover a 2 year period commencing february 1992 and are obtained from the atomic oxygen o 1s 557 7 nm emission which provides observations of the 90 to 200 km altitude range during daytime and the 90 to 110 km range at night the subtropical lower thermosphere is dominated by the diurnal propagating tide which exhibits a vertical wavelength of approximately 22 km grows in amplitude up to 95 km and decays rapidly above where molecular diffusion greatly reduces the vertical shears although the phase remains fairly uniform throughout the year a pronounced semiannual oscillation is observed in the diurnal tide amplitude at both 20 n and 20 s the meridional and zonal wind components attain their maximum values at equinox of approximately 70 and 40 m s respectively while the solstitial minima are nearly a factor of 2 smaller at 35 n the diurnal tide semiannual amplitude oscillation is still present in the lower thermosphere but above 100 km it is replaced by an annual cycle with a maximum in july and august this contrasts with 35 s where the july august peak is absent and the semiannual oscillation extends to 110 km at midlatitudes the zonal and meridional winds are of similar magnitude and no significant hemispheric asymmetries in amplitudes are observed in the lower thermosphere the semidiurnal tide amplitude exhibits an annual oscillation with maximum values of 30 to 40 m s occurring in june july near 100 km at 35 n 35 s and the equator a bimodal structure in the seasonal variation of the semidiurnal phase is observed this feature is characterized by rapid equinoctial transitions and is particularly well defined at the equator examination of the equatorial middle thermosphere indicates that the semidiurnal tide attains its maximum amplitude at 140 km and exhibits a vertical wavelength of approximately 60 km these findings indicate the predominance of the antisymmetric 2 3 hough mode in the tropics

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

brittle deformation and damage induced seismic wave anisotropy in rocks summary we study the relations between rock fracturing non linear deformation and damage and stress induced anisotropy of seismic waves by comparing theoretical predictions of a damage rheology model to results of laboratory experiments with granite samples the employed damage model provides a generalization of hookean elasticity to a non linear continuum mechanics framework of cracked media incorporating degradation and recovery of the effective elastic properties along with gradual accumulation of irreversible deformation beyond the elastic regime the model assumes isotropic distribution of local microcracks expressed in terms of a scalar damage variable but the non linear elastic response caused by the opening closure and evolution of the internal cracks is predicted to lead to seismic wave anisotropy we develop relations between the seismic wave anisotropy internal rock damage and stress field and test the viscoelastic damage rheology against sets of laboratory experiments with cylindrical granite samples the observed data include measurements of stress and strain in three loading cycles culminating in a final macroscopic failure together with measured wave velocities along and perpendicular to the axis of the cylinder using a single set of parameters the model fits well the overall evolution of the axial and transversal stress strain relations as well as the anisotropic elastic wave velocities during all cycles from the onset of fracturing in the first cycle until the macroscopic failure in the final cycle

cumulative benioff strain release modified omori s law and transient behaviour of rocks abstract irreversible thermodynamic theories with internal state variables can be used to derive a general constitutive law for both transient and steady state behaviours of rocks this constitutive law can represent the concepts of damage and damage evolution in either the fibre bundle model or continuum damage mechanics we have previously proposed an empirically based constitutive law for both the transient and steady state behaviours of rocks ultimately derived from laboratory experimental data we show here that this law is concordant with the general constitutive law derived from irreversible thermodynamic theories and that the relaxation modulus has a temporal power law that depends on a structural fractal property of rocks our constitutive law predicts forms for the cumulative benioff strain release for precursory seismic activations and the modified omori s laws of aftershocks both aspects of the temporal fractal properties of seismicity these seismic properties can also be derived by the fibre bundle model or continuum damage mechanics our model suggests that these time scale invariant processes of seismicity may be regulated by the fractal structures of crustal rocks

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

holocene reef accretion on the rodrigues carbonate platform an alternative to the classic bucket fill model carbonate platform evolution around the island of rodrigues southwestern indian ocean is reconstructed from cores recovered across the platform9s windward margin in contrast to the classic bucket fill model of carbonate platform evolution whereby platform filling occurs predominantly as a function of the lagoonward transport of sediment from the reef rim data from rodrigues demonstrate that the primary mode of platform filling was through reef progradation from the platform interior seaward indeed radiocarbon dates indicate that much of the platform interior had filled by 2000 cal calibrated yr b p data also indicate that the reef rim probably caught up with sea level only in the past 1000 yr and subsequent export of sediment from those areas into the lagoon has probably only become important during the final stages of the platform9s evolution we interpret this as a function of the platform margin reef9s catch up growth mode this would have allowed significant marine circulation within the platform interior thus promoting active reef growth prior to sea level being attained given that such catch up growth modes are widely recognized on many reef platform margins we suggest that this novel platform evolutionary model may have widespread applicability sounder resolution 10 cm were made at each core site and water depths were normalized to the tide curves and corrected to mean sea level msl is 1 872 m above chart datum all core depth measurements were uncompacted and were normalized to msl

holocene sediments of wistari reef towards a global quantification of coral reef related neritic sedimentation in the holocene wistari reef within the southern great barrier reef is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments the total global area of shallowly submerged coral reef has been quantified as 255 000 km 2 the question then becomes what additional area of sediment of significant thickness is associated with the measured shallow reef areas t at wistari reef the leeward sedimentary wedge has an area and a thickness that are roughly equal to the holocene sediments that have accumulated on the platform several important observations can be made from these data firstly the area of significant neritic carbonate sedimentation 1 m ka associated with coral reefs is near 500000 km 2 secondly the production rate of neritic carbonates at wistari reef is almost 50 less than the accumulation rate needed to obtain the volume of holocene reef sediments observed this implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid holocene c 2001 elsevier science b v all rights reserved

doppler imager wind measurements with simulations from the ncar thermosphere ionosphere mesosphere electrodynamics circulation model in this paper a comparison is presented between simulations of the diurnal and semidiurnal tides in the middle and upper atmosphere from the thermosphere ionosphere mesosphere electrodynamics general circulation model timegcm and satellite observations from the upper atmosphere research satellite uars high resolution doppler imager hrdi reasonable agreement is found between the model and observations for a march condition when a strong diurnal tide was observed the model is able to reproduce many tidal features at altitudes between 65 and 110 km as observed in the hrdi wind measurements of interest in these features is the shortening vertical wavelength of the 1 1 tide in the upper mesosphere and lower thermosphere which appears in both model simulations and the wind observations the hrdi data also show large longitudinal variations in the diurnal tide of which the amplitude can be as high as 50 of the migrating tide the wavelike structures in latitude and altitude dimensions suggest that the longitudinal variations are likely due to the presence of propagating nonmigrating tides in the upper mesosphere and lower thermosphere for further investigations of the observed tidal variability the model demonstrates great potential with the use of more realistic heating cooling and wave forcing schemes

faulting processes along the northern dead sea transform and the levant margin the northern dead sea transform is markedly different from the southern segments of the transform the strike of the transform changes in this area that forms a restraining bend and the displacement on it is much less than that on the southern and central dead sea transform the structure and evolution of the northern dead sea transform was simulated using a rheological model of a visco elastic material that takes into consideration the crustal structure variations in this area and the proximity to the collisional belts along the cyprean arc and the taurus mountains the simulation can explain the formation of the restraining bend known in this area as the yammuneh fault and the faulting along the northern levant continental margin providing that a simultaneous propagation of the dead sea transform from the north and south took place this suggests that restraining bends in general which are common features along continental transform faults are formed when two segments of a transform propagate toward each other

mid late holocene sea level variability in eastern australia a re analysis of sea level data from eastern australia based on 115 calibrated c 14 ages is used to constrain the origin timing and magnitude of sea level change over the last 7000 years we demonstrate that the holocene sea level highstand of 1 0 1 5 m was reached 7000 cal yr bp and fell to its present position after 2000 yr bp these findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional c 14 ages to calendar years during this 5000 year period of high sea level growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short lived oscillations in sea level of up to 1 m during two intervals beginning c 4800 and 3000 cal yr bp the rates of sea level rise and fall 1 2 mm yr 1 during these centennial scale oscillations are comparable with current rates of sea level rise the origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes including wind strengths ice ablation and melt water contributions of both greenland and antarctic ice sheets

3d modelling of rifting through a pre existing stack of nappes in the gulf of corinth greece a mixed analogue numerical approach the gulf of corinth is a young 1 ma active rift currently extending n00 which displays significant contrasts in structural style along strike a possible explanation for these variations is the presence of the phyllades nappe in the basement of the western part of the gulf previous 2d thermo mechanical models have shown that a strong strength contrast between this metamorphic unit and the rest of the basement can explain the kinematics and the spacing of the faults in the western part the rift however displays a wide variety of 3d features e g en echelon faulting n30 transverse normal faults that cannot be taken into account using 2d modelling to obtain 3d insights into the role of an inherited dipping weakness zone analogue sand and pdms experiments based on the results of the 2d numerical thermo mechanical model have been performed the analogue models show that a 308 discrepancy between the dipping direction of the weak nappe and the direction of extension leads to the formation of en echelon and n30 striking normal faults as observed in the gulf of corinth however fault spacing and graben width completely misfit both the data and the results of the thermo mechanical models on which the analogue experiments were based in order to understand those differences numerical mechanical benchmarks of the analogue experiments have been run to test different factors 3d lateral displacements values of the elastic parameters and bottom boundary conditions that could have affected the dynamics of the analogue model this approach highlights for our case study that the misfits are mostly related to the lack of isostatic compensation at the base of the analogue experiments

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

deformation and seismicity associated with continental rift zones propagating toward continental margins 1 we study the propagation of a continental rift and its interaction with a continental margin utilizing a 3 d lithospheric model with a seismogenic crust governed by a damage rheology a long standing problem in rift mechanics known as thetectonic force paradox is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism our modeling results demonstrate that under moderate rift driving tectonic forces the rift propagation is feasible even in the absence of magmatism this is due to gradual weakening and long term memory of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks we show that the style rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces but also on the rate of healing accounting for the memory effect provides a feasible solution for thetectonic force paradox our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin in such a case a new fault system is created perpendicular to the direction of the rift propagation these results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern

latitude and seasonal dependence of the semidiurnal tide observed by the high resolution doppler imager the high resolution doppler imager hrdi on the upper atmosphere research satellite uars has provided measurements of the horizontal wind field in the mesosphere and lower thermosphere mlt since november 1991 the observed dynamical patterns are dominated by the 1 1 diurnal tide but semidiurnal perturbations are also very prominent in the hrdi data particularly at latitudes greater than 40 this paper presents a preliminary study of the semidiurnal tide and discusses latitudinal and seasonal variations in the phenomenon regular seasonal changes are clearly detected and significant interhemispheric asymmetries have been identified in general the observed features are consistent with previous measurements and model results but some discrepancies have been found this new technique which brings a global perspective to the observation of mlt dynamics is complementary to the very detailed but localized radar data sets currently available and should provide important constraints for numerical models

tectonic stresses in the lithosphere various types of observables earthquake focal mechanisms in situ measurements and geological deformations give information about the large scale lithospheric stress field the latter has often been explained by postulating appropriate forces acting at the edges and beneath the plates this approach ignores the role of mass heterogeneities within the lithosphere here we analyze the effect of both boundary and internal forces on the stress pattern and show that both contributions are of comparable magnitude the presence of internal sources makes the problem three dimensional we show however that it can be reduced to a two dimensional plane stress formulation whereby the edge forces are expressed by the non hydrostatic stresses and the basal shear is increased by the addition of a term proportional to the gradient of the mean vertical stress for the oceanic lithosphere we derive a compression that increases with age the comparison with geophysical observables yields an upper bound of a few bars on the magniude of the basal drag for the continents we infer the existence of an underlying upper mantle somewhat denser than under oceans