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

the response of the coupled arctic sea ice atmosphere system to orbital forcing and ice motion at 6 kyr and 115 kyr bp abstract a coupled atmosphere mixed layer ocean gcm genesis2 is forced with altered orbital boundary conditions for paleoclimates warmer than modern 6 kyr bp and colder than modern 115 kyr bp in the high latitude northern hemisphere a pair of experiments is run for each paleoclimate one with sea ice dynamics and one without to determine the climatic effect of ice motion and to estimate the climatic changes at these times at 6 kyr bp the central arctic ice pack thins by about 0 5 m and the atmosphere warms by 0 7 k in the experiment with dynamic ice at 115 kyr bp the central arctic sea ice in the dynamical version thickens by 2 3 m accompanied by a 2 k cooling the magnitude of these mean annual simulated changes is smaller than that implied by paleoenvironmental evidence suggesting that changes in other earth system components are needed to produce realistic simulations contrary to previous simulations without atmospheric feedbacks the sign of the dynamic sea ice feedback is complicated and

constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

climate impacts of an ice sheet in east siberia during the last glacial maximum abstract recent evaluations of geomorphological evidence in east siberia strongly suggest that no ice sheet existed on the east siberian arctic shelf during the last glacial maximum lgm contrary to the hypothesis of some authors because most general circulation model gcm simulations of the lgm have included such an ice sheet the impact of an east siberian ice sheet is crucial for understanding previous model simulations of the lgm the experiments in this study use the global environmental and ecological simulation of interactive systems genesis 2 0 gcm and the equilibrium vegetation ecology eve vegetation model to simulate the lgm climate with previously published simulation and without new simulation an east siberian ice sheet most lgm simulations have shown increased southerly advection into beringia resulting from the dynamics of the continental ice sheets which acts to alleviate the hemispheric glacial cooling in beringia the east siberian ice sheet provides a secondary source of warm air advection into beringia in the simulation with an east siberian ice sheet a glacial anticyclone develops over the ice sheet during winter resulting in subsidence of air flowing off the ice sheet increased southerly advection along the western margin of the ice sheet and warming to the south of the ice sheet during summer the ice sheet blocks northerly flow from the arctic also resulting in warming south of the ice sheet the primary vegetation difference is in the ratio of tundra to polar desert the more mild climate with the ice sheet present produces more tundra and less polar desert

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

evidence for melt lubrication during large earthquakes 1 rotary friction experiments have been performed on westerly granite at start velocities of 2 0 4 0 m s 1 under loads of 250 500 n until the system stalls up to 4 s interface temperature velocity and force were measured at intervals of 0 2 milliseconds the results show that kinetic friction increases in direct proportion to temperature up to a critical value tcr whereupon the system changes from boundary lubrication slip strengthening to hydrodynamic lubrication slip weakening with an associated decrease in friction and temperature for westerly granite tcr is 1150 c this corresponds to the melting point of feldspar which constitutes 50 of the rock if tcr is exceeded in natural slip systems which will depend on rock type this can result in the generation of friction melt melt lubrication can explain the scaled energy of large earthquakes being 10 to 100 times more than that of small earthquakes

limitations of the system approach in geomorphology abstract a system is defined as a set of interrelated elements which function together as a whole for a statistical mechanical application of system theory it is assumed that the number of elements is large and that the interrelations are complex so that the individual interactions cannot be followed individually in detail under such circumstances the individual processes can be considered as quasi random i e as if they were stochastic and by the use of the limit theorems of probability theory statements can be made regarding the expected behavior of the system this approach however has its limitations the assumption that the individual processes are quasi stochastic does not necessarily hold there are many instances when the individual processes are uniform and correlated in this case they cannot under any circumstances be considered as quasi random this applies in geomorphology mainly in connection with structural and neo tectonic predesign the application of system theory in such circumstances leads to faulty results

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

fractal dimension of molten surfaces as a possible parameter to infer the slip weakening distance of faults from natural pseudotachylytes high velocity friction experiments on gabbro and monzodiorite using a rotary shear high velocity friction apparatus have revealed that frictional melting and progressive growth of a molten layer along a fault cause slip weakening eventually reaching a nearly steady state the melting surface at the host rock molten layer interface is initially very flat but it becomes more complex and rounded in shape towards the steady state owing to the selective melting of minerals with lower melting points and the gibbs thomson effect this change in the melting surface topography can be quantitatively expressed by the fractal dimension d as determined by the divider method from about 1 0 near the peak friction to around 1 1 near the steady state friction the ultimate fractal dimension at steady state friction tends to decrease with increasing heat production rate presumably due to more rapid and uniform melting a systematic correlation of d with mechanical behavior of the fault during frictional melting may provide a way of estimating slip weakening distance and heat production rate at steady state friction by measuring d for natural pseudotachylytes on slip surfaces with different displacements the weakening distance is of vital significance in relation to fault instability and the heat production rate is related to the fault strength the experimental studies point to ways to estimate these difficult quantities for natural faults

erosion triangular facets as markers of order in an open dissipative system the complexity and non linearity of the morphogenetic system which is responsible for shaping the earth s surface have been widely recognised by many authors who have documented the fractal nature of erosion in this paper two peculiar kinds of landforms are compared to point out ordered structures i e triangular facets that arise in different geomorphic systems due to the principle of morphologic convergence occurrence of triangular facets has been documented in mountainous areas in relation to base level changes and hydrographical network evolution similarly shaped landforms are present even in recent tectonic uplift areas along faults the spatial distribution of the two kinds of facets has been investigated in two river basins located in liguria northern italy and in a mountainous area in oman the results of this analysis document the different spatial features of the two kinds of facets

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

a diagnostic ice ocean model abstract a coupled ice ocean model suitable for simulating ice ocean circulation over a seasonal cycle is developed by coupling the dynamic thermodynamic sea ice model of hibler with a multilevel baroclinic ocean model bryan this model is used to investigate the effect of ocean circulation on seasonal sea ice simulations by carrying out a simulation of the arctic greenland and norwegian seas the ocean model contains a linear term that damps the ocean s temperature and salinity towards climatology the damping term was chosen to have a three year relaxation time equivalent to the adjustment time of the pack ice no damping however was applied to the uppermost layer of the ocean model which is in direct contact with the moving pack ice this damping procedure allows seasonal and shorter time scale variability to be simulated in the ocean but does not allow the model to drift away from ocean climatology on longer time scales for the standard experiment an initial integration of five years was per

laboratory observations of transient frictional slip in rock analog materials at co seismic slip rates and rapid changes in normal stress knowledge of frictional shear resistance and its dependency on slip distance slip velocity normal stress and surface roughness is fundamental information for understanding earthquake physics and the energy released during such events in view of this in the present study plate impact pressure shear friction experiments are conducted to investigate the frictional resistance in a rock analog material i e soda lime glass under interfacial conditions of relevance to fault rupture the results of the experiments indicate that a wide range of frictional slip conditions exist at the slip interface ranging from initial no slip and followed by slip weakening slip strengthening healing and seizure all during a single slip event the slip weakening phase is understood to be most likely due to thermal induced flash heating and incipient melting at asperity junctions while the slip strengthening slip healing phase is understood to be a result of coalescence and solidification of local melt patches on the slip interface in addition plate impact pressure shear normal stress change drop experiments are employed to probe the response of the slip interface due to sudden alterations in normal stress in particular the location timing of the stress drop is varied so as to investigate the behavior of the slip interface in its slip weakening slip strengthening healing phase or the seized phase in response to sudden drop in normal stress these experimental results provide a rich set of data to better understand the range of possible friction slip states that can be achieved and or critically examine existing dynamic friction models for fault slip behavior

snowball earth asynchronous coupling of sea glacier flow with a global climate model during snowball earth episodes of the neoproterozoic and paleoproterozoic limited amounts of tropical open ocean jormungand or tropical ocean with thin ice cover would help to explain 1 vigorous glacial activity in low latitudes 2 survival of photosynthetic life and 3 deglacial recovery without excessive buildup of atmospheric co2 some previous models have suggested that tropical open ocean or thin ice cover is possible however its viability in the presence of kilometer thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively here we describe a new method of asynchronously coupling a zonal sea glacier model with a 3 d global climate model and apply it to snowball earth equilibrium curves of ice line vs co2 are mapped out as well as their dependence on ocean heat transport efficiency sea glacier flow and other model parameters no climate states with limited tropical open ocean or thin ice are found in any of our model runs including those with sea glaciers if this result is correct then other refugia such as cryoconite pans would have been required for life to survive however the reasons for the differences between our results and others should first be resolved it is suggested that small scale convective dynamics affecting fractional snow cover in low latitudes may be a critical factor accounting for these differences

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

artificial generation of pseudotachylyte using friction welding apparatus simulation of melting on a fault plane a 150 m thick fused layer of rock has been produced by rotating two metadolerite core faces against each other at 3000 r p m under an axial load of 330 kg for 11 s using friction welding apparatus scanning electron microscopy and electron microprobe analysis reveal that the melt layer comprises sub angular to rounded porphyroclasts of clinopyroxene feldspar and ilmenite 20 m diameter derived from the host metadolerite set within a silicate glass matrix thermal calculations confirm that melting occurred at the rock interface and that mean surface temperatures in excess of 1400 c were attained the fused layer shows many textural similarities with pseudotachylyte described from fault zones morphologically the fused layer consists of a series of stacks of porphyroclasts welded together by melt to form build ups oriented at right angles to the friction surface there is also evidence of gouging ploughing and plucking as well as transfer and adhesion of material having occurred between the rock faces the mean surface velocity attained by the metadolerite 0 24 m s 1 and duration of the experiment are comparable with velocities and rise times of typical single jerk earthquakes occurring during stick slip seismic faulting within brittle crust i e slip rates of 0 1 0 5 m s 1 for say 1 10s in these respects the experiment successfully simulated frictional fusion on a fault plane in the absence of an intergranular fluid power dissipation during the experiment was about mw m 2 comparable only to very low values for earthquakes e g 1 100 mw m 2 for displacement rates of 0 1 0 5 m s 1 at shear stresses of 100 1000 bars this indicates that melting on fault planes during earthquakes should be commonplace field evidence however does not support this contention either pseudotachylyte is not being recognized in exhumed ancient seismic fault zones or melting only occurs under very special circumstances

sea ice dynamics in the weddell sea simulated with an optimized model the advection of sea ice and associated freshwater salt fluxes in the weddell sea in 1986 and 1987 are investigated with a large scale dynamic thermodynamic sea ice model the model is validated and optimized by comparison of simulated sea ice trajectories with observed drift paths of six buoys deployed on the weddell sea ice the skill of the model is quantified by an error function that measures the deviations of simulated trajectories from observed 30 day sea ice drift a large number of sensitivity studies show how simulated sea ice transports and associated freshwater salt fluxes respond to variations in physical parameterizations the model reproduces the observed ice drift well provided ice dynamics parameters are set to appropriate values optimized values for the drag coefficients and for the ice strength parameter are determined by applying the error function to various sensitivity studies with different parameters the optimized model yields a mean northward sea ice volume export out of the southern weddell sea of 1693 km3 in 1986 and 2339 km3 in 1987 this shows the important role of sea ice transport for the freshwater budget of the weddell sea and gives an indication of its high interannual variability

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

climate and ice sheet mass balance at the last glacial maximum from the genesis version 2 global climate model abstract at the last glacial maximum lgm about 21 000 calendar years ago 21 ka bp the overall mass balance of the laurentide and eurasian ice sheets should have been close to zero since their rate of change of total ice volume was approximately zero at that time the surface mass balance should have been zero or positive to balance any iceberg iceshelf discharge and basal melting but could not have been strongly negative in principle this can be tested by global climate model cgm simulations with prescribed ice sheet extents and topography we describe results from a suite of 21 ka bp simulations using a new global climate model genesis version 2 0 a with ssts prescribed from climap 1981 and predicted by a mixed layer ocean model and with ice sheets prescribed from clih the ice 4g peltier 1994 and climap 1981 reconstructions in common with previous gcm simulations using mixed layer oceans substantial cooling over and around antarctica occurs due to normal gcm dynamics and polar sea ice feedback without recourse to changes in thermohaline circulation we find slightly enhanced cooling and cloudiness over low latitude land masses compared to over ocean especially over the andes which decreases the disagreement with land based data and suggests that tropical climap ssts may only be 1 2 c too warm the gcm used here is well suited for ice sheet mass balance studies because i the surface can be represented at a finer resolution than the atmospheric gcm ii an elevation correction accounts for spectral distortions of the atmospheric gcm topography iii a simple post processing correction for refreezing of meltwater is applied and iv the model s precipitation and mass balances for present day greenland and antarctica are realistic however for all reasonable combinations of ssts and ice sheet configurations the predicted annual surface mass balances of the lgm laurentide and eurasian ice sheets are implausibly negative possible reasons for this discrepancy are discussed including increased ice age aerosols higher climap like ice sheet profiles in the few thousand years preceding lgm and a surge of the southern laurentide just before lgm to fleetingly produce the ice 4g profile at 21 ka bp

investigation of the dynamic sea ice component of a coupled atmosphere sea ice general circulation model this paper discusses the development of a coupled atmospheric ice model with a comprehensive ice dynamics cavitating fluid rheology and an open water parameterization the results center on the ice thickness and concentration distribution in the arctic basin where the inclusion of ice rheology has maximum impact the influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean ice drag coefficient under winter wind stress conditions the model had a tendency to buildup ice on the siberian coast the introduction of a partial slip condition at land ice boundaries in the model designed to prevent this buildup is discussed and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0 4 the ice model results are compared with the available observational data sets on ice thickness concentration and ice velocity fields to test the validity of the model simulations

the force balance of sea ice in a numerical model of the arctic ocean the balance of forces in the sea ice model of hibler 1979 is examined the model predicts that internal stress gradients are an important force in much of the arctic ocean except in summer when they are significant only off the northern coasts of greenland and the canadian archipelago a partition of the internal stress gradient between the pressure gradient and the viscous terms reveals that both are significant although they operate on very different timescales the acceleration term is generally negligible while the sum of coriolis plus sea surface tilt is small thus the seasonal average force balance in fall winter and spring is mostly between three terms of roughly equal magnitudes air drag water drag and internal stress gradients this is also true for the monthly average force balance however we find that there is a transition around the weekly timescale and that on a daily basis the force balance at a particular location and time is often between only two terms either between air drag and water drag or between air drag and internal stress gradients the model is in agreement with the observations of thorndike and colony 1982 in that the correlation between geostrophic wind forcing and the model s ice velocity field is high this result is discussed in the context of the force balance we show that the presence of significant internal stress gradients does not preclude high wind ice correlation a breakdown of the internal stress gradient into component parts reveals that the shear viscous force is far from negligible which casts strong doubt on the theoretical validity of the cavitating fluid approximation in which this component is neglected finally the role of ice pressure is examined by varying the parameter p we find a strong sensitivity in terms of the force balance as well as ice thickness and velocity

the effect of normal stress on the real area of contact during frictional sliding in rocks the real area of contact during frictional sliding has been determined as a function of changing normal stress in triaxial experiments through the use of thermodyes utilizing the technique described by teufel and logan in 1978 with saw cut surfaces inclined 35 to the load axis determinations were made for monolithologic sliding of tennessee sandstone and indiana limestone and dilithologic sliding of the same rocks confining pressures to 200 mpa were investigated at a constant shortening rate of 10 2 mm sec and at room temperature direct measurements were made of single asperity areas and the asperity density the product of these measurements gives the percent area of real contact across the sliding surface single asperity area and density are found to remain relatively constant during the displacement single asperity areas are in the ranges of 0 4 to 6 10 2 mm2 for sandstone 0 8 to 2 10 2 mm2 for limestone and 0 2 to 24 10 2 mm2 for sandstone sliding against limestone these values are smaller than the grain size of either rock the values increase with increasing normal stress for both monolithologic and dilithologic sliding in sandstone the asperity density increases from about 0 8 to 2 75 contacts per square millimeter in a logarithmic fashion monolithologic limestone has values of about 0 9 contacts per square millimeter and does not show significant change with increasing normal stress the percent area of real contact increases in all cases with average maximum values of 16 of the apparent area at a normal stress of 374 mpa in sandstone 18 at 25 mpa in limestone and 22 at 123 mpa in the dilithologic specimens the normal stress recalculated for the real area of contact approaches the unconfined compressive strength for sandstone and limestone

progressive flash heating and the evolution of high velocity rock friction accurate descriptions of strength evolution are required in predictive models of fault zone behavior during earthquakes at low sliding rates frictional resistance between fault rocks is much higher than the shear stress that is typically inferred to be present during earthquakes laboratory experiments confirm that the friction coefficient drops at high sliding rates and it is suggested that strengthening possibly related to an increase in the area of viscous melt patches may occur after this initial weakening stage most existing weakening mechanisms do not predict such strengthening which may exert an important control on the thickness of the shear zone we propose a micromechanical model of flash heating that describes how shear resistance evolves at the asperity scale as a result of distributed deformation over a weak layer that grows during the brief lifetime of each asperity contact beyond a threshold weakening velocity our model predicts that friction should decrease with slip rate since higher sliding speeds cause the weak layer to thicken more rapidly a comparison with published experimental data from a range of mineral systems shows good agreement with the model predictions the parameter choices that ensure good model fits to the laboratory friction data are consistent with a priori estimates for the onset of asperity melting at high contact normal stresses at higher sliding rates and or elevated temperatures our model predicts that the frictional rate dependence should transition from velocity weakening to become velocity strengthening because decreases in the contact lifetime with slip rate cause the average asperity strength to increase

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

melt welt mechanism of extreme weakening of gabbro at seismic slip rates a laboratory study of the frictional properties of the igneous rock gabbro at seismically relevant slip rates suggests that the initial weakening of a fault surface during earthquake rupture may be associated with hotspots and macroscopic streaks of melt which partially unload the rest of the slip interface

experimental and modeling study of the effect of fault roughness on dynamic frictional sliding abstract friction governs many processes in nature from the motion of glaciers and landslides to tremors and earthquakes the roughness of the sliding interfaces presumably affects their dynamics in particular the condition for stable or unstable sliding we investigate this issue by modeling numerically tri axial stick slip experiments on westerly granite samples with different levels of roughness the model accounts for surface roughness at the millimeter scale and assumes rate and state friction with enhanced dynamic weakening it reproduces key characteristics observed in the experiments such as sequences of fast stick slip events for smooth surface and sequence of slow slip events with small stress drop followed by a large stress drop unstable slip event for the rough interface the increase in loading stiffness due to the additional resistance from roughness can explain the initial slow slip the fast unstable event may be the result of the higher critical stiffness due to the increase of local normal tractions with slip as well as of the reduction of the loading stiffness due to contacts losses the study allows examining numerically the relationship between the frictional behavior on the interface and the apparent friction estimated from external loads we find that because of dynamic overshoot the reduction in apparent friction is larger than that of the actual friction coefficient on the interface

tectonic processes and geomorphological design abstract deep seated geodynamic processes are the cause of the existence of the geotectonic stress field the influence of the latter and therefore of deep seated processes in surface geomorphology is investigated it is noted that the features caused by deep seated geotectonic processes can be distinguished from those caused by exogenic agents weather erosion etc by their statistical characteristics all statistically systematic features are of geotectonic origin random features are of exogenic origin in this paper various types of morphological features are analyzed with regard to their origin it is shown that lineaments seen on air photographs may not be of recent geotectonic origin specific examples of such lineaments being erosion scarps are given next it is shown that the orientation patterns inherent in fluvial and glacial valleys are indeed affected to a large extent by neotectonic processes the same is naturally the case for rift valleys and chains of volcanoes a further interesting subject is presented by the so called tectonic landforms inselbergs cirques the shapes of mountain summits etc are all shown to be directly or indirectly caused by deep seated processes the mass movements on slopes are also of great importance although it is often thought that these are triggered by meteorological conditions it is shown that their basic design is influenced to a large extent by deep seated processes amongst other things this is borne out by a correlation between landslide and earthquake activity finally it is mentioned that the common joints on rock outcrops are also designed by the neotectonic stress field and that the latter can in fact be determined by an analysis of joint orientations in summary it may be stated that although exogenic agents may be responsible for many morphological features deep seated processes have nevertheless a great influence on the fundamental design of such features

calibration of water granite interaction with pressure solution in a flow through fracture under confining pressure fluid mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs to investigate the impact a preliminary study on water granite interaction in an undeformable fracture under confining pressure is conducted a 1 d flow and reactive transport model is therefore developed and validated against the experimental data in yasuhara et al appl geochem 26 12 2074 2088 2011 the model takes free face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account together with a nested well equipped geochemical system the simulation is implemented by fem based simulator opengeosys with a plugin module of iphreeqc for speciation calculation after calibration the predictions of effluent element concentrations are in good agreement with the measurements the study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts pressure solution at anorthite contacts may not take effect under experimental conditions because of the high level energy barrier to interpenetration and al bearing secondary minerals such as gibbsite may be formed in the current near equilibrium aqueous system the sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts

shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes as a result of the comminution that takes place over numerous earthquake cycles mature faults are characterized by thick layers of pulverized gouge with finite porosity that is saturated with water at seismogenic depths the heat generated during earthquakes raises the gouge temperature and thermal expansion of the pore fluid and surrounding solids produce elevated pore pressures that cause fault strength to decrease in the process known as thermal pressurization building upon this framework we describe a model that imposes a plane strain configuration and shows that the stress variations caused by porothermoelasticity promote the mohr coulomb failure of previously undeformed regions except in special cases where the friction is rate strengthening we find that the frictional strength must vary throughout the post failure region which we identify in our model with the shear zone we introduce a strain rate function that describes the overall influence of distributed slip on energy dissipation and fault strength as the shear zone thickness expands using typical fault parameters at 7 km depth the shear zone reaches several millimeters of thickness after 1 s sliding at an overall rate of 1 m s the expansion of the shear zone limits the temperature rise to several hundred degrees celsius and the average fault strength falls to about a tenth of the static frictional strength

flash weakening of serpentinite at near seismic slip rates 1 to investigate the processes responsible for dynamic frictional weakening in antigorite serpentinite we conducted single velocity and velocity stepping friction experiments at slip rates v from 0 01 to 0 4 m s 1 sliding displacements up to 40 mm and a normal stress of 5 mpa single velocity experiments demonstrate an approximately 1 v dependence of friction on velocity above a characteristic weakening velocity vw 0 1 m s 1 consistent with theoretical predictions for flash heating and subsequent weakening of asperities velocity stepping experiments impose stepwise increases in slip rate show stepwise weakening at slip rates above vw scanning electron microscopy of experimental fault surfaces reveals nanoparticle gouge textures at raised sites 10 m in diameter in tests that exhibit dramatic weakening furthermore x ray diffraction analyses of fault gouge from the sliding surface document the formation of significant talc in these tests indicating that weakening temperatures reached 500 c 700 c in contrast no talc is observed in samples for which v remained significantly below vw the observed value for vw is consistent with published microphysical models for flash weakening when independent constraints on the thermal stability and contact strength of antigorite are considered finally while serpentinite displays velocity strengthening behavior at plate tectonic slip rates our results indicate that seismic ruptures propagating into serpentinized regions in the shallow lithosphere may trigger seismicity or slow earthquakes after limited amounts of displacement

the high temperature liquid and glass heat contents and the heats of fusion of diopside albite sanidine and nepheline relative enthalpy and heat capacities of camgsi 2 o 6 di stable liquid and glass of kalsi 3 o 8 sa stable and supercooled liquid and glass of naalsi 3 o 8 ab liquid derived directly by melting solid albite of crystalline disordered albite itself and of naalsio 4 ne liquid and glass the effect of annealing at 981 k on the enthalpy of the glasses quenched from liquids at high temperature is relatively small ranging from 0 to 100 cal mol heats of fusion in kcal mol di 33 0 or 0 5 1665 k ab 15 0 or 0 5 1373 k sa 13 8 or 1 0 metastable 1473 k and ne 11 7 or 0 5 metastable 1750 k modified journal abstract

granular nanoparticles lubricate faults during seismic slip nanoparticles are known to form in narrow slip zones in natural and experimental fault zones but their possible role in dynamic weakening of faults during seismic slip remains almost unexplored we conducted friction experiments on periclase mgo nanoparticles 50 nm in average size at rates as high as 1 3 m s 1 a typical speed of seismic slip the nanoparticles were used as the initial gouge to avoid complexities arising from comminution and fluid release the dynamic friction decreased with increasing slip rate and the steady state frictional coefficient reduced to as low as 0 1 at a slip rate of 1 3 m s 1 flash heating is not effective for nanoparticles and we propose that development of slickensides and dominant operation of nanoparticle rolling cause such a weakening nanoparticle lubrication appears to be as effective as melt lubrication and thermal pressurization and the formation of nanoparticles in slip zones may be an important fault lubrication process

high pressure equation of state of molten anorthite and diopside new hugoniot equation of state data for molten diopside at 1773 k and molten anorthite at 1923 k are reported to 38 and 35 gpa respectively the diopside data initial density 2 61 mg m 3 are described by a straight line fit to the shock velocity particle velocity results of u s 3 30 1 44 u p km s 1 and our preferred fit to the anorthite data initial density 2 55 mg m 3 is given by u s 2 68 1 42 u p km s 1 reduction of the data to a third order birch murnaghan isentrope assuming the gruneisen ratio times the density is a constant and the mie gruneisen equation of state gives k 0s 22 4 gpa and k s 6 9 for diopside for anorthite we calculate k 0s 17 9 gpa and k s 5 3 the present data for diopside are used to calculate the diopside solidus at high pressures we expect the solidus to be shallow above 10 gpa but the lack of data on the variation of either the gruneisen parameters of the liquid and crystal or the heat capacity and thermal expansion at elevated pressures makes extrapolation of fusion curves uncertain solidus temperatures of 2400 2500 k and 2560 2705 k for diopside are calculated at 10 and 20 gpa respectively the new data are combined with those of rigden et al 1988 for the di 0 64 a 0 36 eutectic composition to examine the degree to which such liquids mix ideally with respect to volume up to 25 gpa for the eutectic composition at 1400 c we calculate the volumes of the an and di mix nearly ideally to 25 gpa we find that the ratio of the partial molar volumes of the oxides in silicate melts to that of the crystal oxides at 1673 k and 1 atm is 1 0 0 1 for a wide range of oxide components for the low pressure tetrahedrally coordinated oxides e g sio 2 al 2o 3 fe 2o 3 the ratio is 1 3 with respect to oxides such as stishovite corundum and hematite in which the cations are octahedrally coordinated by oxygens if changes in coordination of al and si from tetrahedral at low pressures to octahedral at high pressures occur in melts they do so gradually over an interval of 40 gpa although 1 atm bulk moduli for a wide compositional range of silicate melts are similar the differences in integrated compression to mixed oxide like high pressure configurations are reflected mainly by variations in k t k t is found to vary inversely with fraction of network forming initially tetrahedrally coordinated cations e g al 3 si 4 thus k t which may be uncertain by 1 5 is estimated to vary from 7 for molten anorthite enstatite and diopside to 8 for molten ferrosilite to 10 for molten forsterite and to 11 for molten fayalite

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

generation and crystallization of an amphibolite shear melt an investigation using radial friction welding apparatus a cylinder of amphibolite comprising the assemblage amphibole clinozoisite albite has been frictionally melted using radial friction welding apparatus this was achieved by rotating a steel ring at 750 rpm and a force of 98 kn for 10 s against a stationary steel casing which housed the rock sample the ring penetrated the casing then proceeded to rotate and compress the sample to 95 of its original volume until it cracked at right angles to its length this generated a whole rock silicate melt which injected the crack and on cooling produced glass crystallites and vesicles melting occurred in two stages an initial low pressure melting event with crystallization to augite fe rich anorthite followed by a high pressure melting event with crystallization to fassaitic clinopyroxene it is estimated that pressures of 0 5 gpa rising to 1 gpa were realized at the ring rock interface under these conditions fassaite superseded augite anorthite crystallization due to the increased solubility of ca tschermak s component in clinopyroxene the high pressure event provides a crude analogue for the frictional melting of basic rock at depths of 15 30 km in a seismogenic fault a situation realized along the slip zone between cold descending lithosphere and overlying mantle during subduction

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

frictional melting of peridotite and seismic slip 1 the evolution of the frictional strength along a fault at seismic slip rates about 1 m s is a key factor controlling earthquake mechanics at mantle depths friction induced melting and melt lubrication may influence earthquake slip and seismological data we report on laboratory experiments designed to investigate dynamic fault strength and frictional melting processes in mantle rocks we performed 20 experiments with balmuccia peridotite in a high velocity rotary shear apparatus and cylindrical samples 21 8 mm in diameter over a wide range of normal stresses 5 4 16 1 mpa slip rates 0 23 1 14 m s and displacements 1 5 71 m during the experiments shear stress evolved with cumulative displacement in five main stages stages 1 5 in stage 1 first strengthening the coefficient of friction increased up to 0 4 0 7 first peak in friction in stage 2 abrupt first weakening decreased to about 0 25 0 40 in stage 3 gradual second strengthening shear stress increased toward a second peak in friction 0 30 0 40 in stage 4 gradual second weakening the shear stress decreased toward a steady state value stage 5 with 0 15 stages 1 and 2 are of too short duration to be investigated in detail with the current experimental configuration by interrupting the experiments during stages 3 4 and 5 microstructural field emission scanning electron microscope and geochemical electron probe micro analyzer and energy dispersive x ray spectroscopy analysis of the slipping zone suggest that second strengthening stage 3 is associated with the production of a grain supported melt poor layer while second weakening stage 4 and steady state stage 5 are associated with the formation of a continuous melt rich layer with an estimated temperature up to 1780 c microstructures formed during the experiments were very similar to those found in natural ultramafic pseudotachylytes by performing experiments at different normal stresses and slip rates 1 the thermal as it includes the thermally activated first and second weakening slip distance to achieve steady state from the first peak in strength decreased with increasing normal stress and slip rate and 2 the steady state shear stress slightly increased with increasing normal stress and for a given normal stress decreased with increasing slip rate the ratio of shear stress versus normal stress was about 0 15 well below the typical friction coefficient of rocks 0 6 0 8 the dependence of steady state shear stress with normal stress was described by means of a constitutive equation for melt lubrication the presence of microstructures similar to those found in natural pseudotachylytes and the determination of a constitutive equation that describes the experimental data allows extrapolation of the experimental observations to natural conditions and to the study of rupture dynamics in mantle rocks