clues to variability in arctic minimum sea ice extent received 11 august 2005 revised 20 september 2005 accepted 26 september 2005 published 2 november 2005 1 perennial sea ice is a primary indicator of arctic climate change since 1980 it has decreased in extent by about 15 analysis of new satellite derived fields of winds radiative forcing and advected heat reveals distinct regional differences in the relative roles of these parameters in explaining variability in the northernmost ice edge position in all six peripheral seas studied downwelling longwave flux anomalies explain the most variability approximately 40 while northward wind anomalies are important in areas north of siberia particularly earlier in the melt season anomalies in insolation are negatively correlated with perennial ice retreat in all regions suggesting that the effect of solar flux anomalies is overwhelmed by the longwave influence on ice edge position citation francis j a e hunter j r key and x wang 2005 clues to variability in arctic minimum sea ice extent geophys res lett 32 l21501 doi 10 1029 2005gl024376

stommel s box model of thermohaline circulation revisited the role of mechanical energy supporting mixing and the wind driven gyration the classical two box model of stommel is extended in two directions replacing the buoyancy constraint with an energy constraint and including the wind driven gyre stommel postulated a buoyancy constraint for the thermohaline circulation and his basic idea has evolved into the dominating theory of thermohaline circulation however recently it is argued that the thermohaline circulation is maintained by mechanical energy from wind stress and tides the major difference between these two types of models is the bifurcation structure the stommel like model has two thermal modes one stable and another one unstable and one stable haline mode whereas the energy constraint model has one stable thermal mode and two saline modes one stable and another one unstable adding the wind driven gyre changes the threshold value of thermohaline bifurcation greatly thus the inclusion of the wind driven gyre is a vital step in completely modeling the physical processes related to thermohaline circulation

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

arctic inversion strength in climate models recent work indicates that climate models have a positive bias in the strength of the wintertime low level temperature inversion over the high latitude northern hemisphere it has been argued this bias leads to underestimates of the arctic s surface temperature response to anthropogenic forcing here the bias in inversion strength is revisited the spatial distribution of low level stability is found to be bimodal in climate modelsandobservationalreanalysis products withlow levelinversionsrepresentedbyastableprimarymode over the interior arctic ocean and adjacent continents and a secondary unstable mode over the atlantic ocean averaging over these differing conditions is detrimental to understanding the origins of the inversion strength bias while nearly all of the 21 models examined overestimate the area average inversion strength conditionally sampling the two modes shows about half the models are biased because of the relative partitioning of the modes and half because of biases within the stable mode

a sea ice climate switch mechanism for the 100 kyr glacial cycles a box model of the ocean atmosphere sea ice land ice climate system is used to study a novel mechanism for self sustained oscillations of the climate system on a time scale of 100 000 years without external forcing the oscillation in land ice volume has the familiar sawtooth shape of climate proxy records the most novel aspect of the climate oscillations analyzed here is the crucial role played by the sea ice the sea ice acts as a switch of the climate system switching it from a growing land glaciers mode to a retreating land glaciers mode and shaping the oscillation s sawtooth structure a simple explanation of the 100 kyr timescale is formulated on the basis of the mechanism seen in the model finally rapid sea ice changes such as those seen in our model and their drastic effects on the climate system may provide an explanation to some of the rapid climate changes observed to be a part of the variability at all timescales in the paleorecord

spatiotemporal variation of fractal properties in the source zone of the 2001 mw 7 7 bhuj earthquake the kachchh seismic zone ksz in gujarat india has been experiencing earthquakes since the occurrence of the 2001 m w 7 7 bhuj mainshock which led to a homogeneous catalog of 2808 earthquakes of m w 3 0 between 2001 and 2011 this enabled us to investigate the spatiotemporal variation of fractal dimensions d b values and seismic velocities in the ksz through 3d mapping of these three independent parameters the estimated fractal dimensions for the gedi fault gf events range from 0 7 to 1 0 whereas those of north wagad fault nwf events vary from 1 2 to 2 4 the b values for gf events also show smaller values in comparison to the nwf events the d values associated with events occurring in the main rupture zone mrz of the 2001 mainshock vary from 1 6 to 2 1 whereas those associated with events occurring in the surrounding unrifted zones show a wider range of variation from 1 2 to 2 4 we also observe that events associated with the nwf satisfy the aki s relationship d 2 b aki 1981 whereas events associated with gf do not follow this relationship both b and d values tend to increase with an increase in the earthquake density which could be connected with the process of disintegration of crustal rocks in the mrz where large material heterogeneities in terms of low and high seismic velocity patches are being mapped through local earthquake velocity tomography through examining the temporal changes in b and d values we notice several episodes of abnormally low b and d values associated with the occurrences of bursts of seismic activity in 2001 2005 2006 2008 and 2010 this decrease in b and d values is attributed to a reduction in rock friction in the causative fault zone at 10 35 km depths probably due to the presence of metamorphic fluids or volatile co2 thereby enhancing the probability of occurrence of stronger earthquakes

formation of denmark strait overflow water by mixing in the east greenland current abstract hydrographic data and current meter records from the east greenland current collected during theperiod 1987 to 1989 around the latitude of the central greenland sea reveal the formation of a watermass having the characteristics of denmark strait overflow water dsow the downstream southwestward transport of this newly formed water mass can be substantial amounting to roughly halfof the outflow of dsow through denmark strait as reported in the literature the formation of dsow inthe east greenland current results from isopycnic mixing of recirculated atlantic water and upper arcticintermediate water substantial formation occurs when the neccessary conditions for baroclinic instabilityare satisfied and the current variability due to mesoscale eddies is high this is subject to significantchanges from year to year

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

instability of the thermohaline circulation with respect to mixed boundary conditions is it really a problem for realistic models abstract this comment discusses two issues raised by a recent study of the stability of the thermohaline circulation tziperman et al a numerical problem is pointed out that may have affected the results of the reported calculations in addition it is argued that the state transition of the model circulation found in the above study is triggered by a convective instability mechanism not the advective mechanism discussed by its authors should this be the case then the conclusion of tziperman et al that the ocean is close to a stability transition point must be questioned

evolution em signals before earthquakes in terms of mesomechanics and complexity abstract mhz to khz electromagnetic em anomalies have been detected worldwide over time intervals ranging from a few days to a few hours prior to near surface earthquakes eqs that have occurred on land with magnitude approximately six or larger the mhz radiation systematically appears earlier than the khz laboratory experiments on rock samples reveal a similar change in the frequency content during progressive deformation i e the emissions exhibit a frequency shift from mhz to khz just before failure of the samples herein we attempt to associate these consecutively emerging mhz and khz modes of the pre fracture em emission with successive distinct stages of the fracture preparation process and the associated fracture mechanisms we base our approach on synergetic principles of physical mesomechanics a universal principle of physical mesomechanics is that the plastic deformation of a solid is related to its loss of shear stability at the micro meso and macroscale levels global fracture is determined by the mechanism controlling the development of macroscale bands of localized deformation associated with meso and microscale relaxation processes the major result we obtain is that the shift from mhz to khz em activity may signal the transition of plastic flow localization from the mesoscale to the macroscale culminating in global fracture a complexity measure approximate entropy and a persistency anti persistency measure hurst exponent also give evidence of a two stage model of eq preparation process significant complexity decrease and accession of persistency can be confirmed in the strong khz em activity that emerges in the tail of the pre seismic em activity laboratory experiments on rock samples reveal similar symptoms of an imminent global instability

stochastic synthesis of earthquake catalogs a model of earthquake occurrence is proposed that is based on results of statistical studies of earthquake catalogs we assume that each earthquake generates additional a probability that depends on time as t 1 this assumption together with one regarding the independence of branching events on adjacent branches of the event tree is sufficient to permit the generation of complete catalogs of earthquakes that have the same time magnitude statistical properties as real earthquake catalogs if is about 0 5 the process generates sequences that have statistical properties similar to those for shallow earthquakes many well known relations are reproduced including the magnitude frequency law omori s law of the rate of aftershock and foreshock occurrence the duration of a recorded seismic event versus its magnitude the self similarity or lack of scale of rate of earthquake occurrence in different magnitude ranges etc a value of closer to 0 8 or 0 9 seems to simulate the statistical properties of intermediate and deep shocks a formula for seismic risk prediction is proposed and the implications of the model for risk evaluation are outlined the possibilities of the determination of long term risk from real or synthetic catalogs that have the property of self similarity are dim

rock fragmentation and particle size in crushed zones by faulting abstract the size distribution of fragments in the crushed zone adjacent to a fault and that of grains in a zone of very fine grained particles the fault gouge was determined for two different faults in central japan one fault has a wide ca 100 m zone of rock fragmentation between the fault gouge zone and the basement rock formation dimensions of the 50 largest rock fragments were measured in the field at locations within a continuous outcrop of this fault at some places bulk samples were also collected and the particle fragment and grain size distributions were determined in the laboratory the relationship between the logarithmic mean of the sizes of the largest 50 fragments and their distances from the fault suggests that size reduction of fragments is due to bulk crushing away from the fault and to surface grinding near the fault the other fault has no crushed zone of basement rocks but does have a 5 m wide zone of fault gouge ten samples of ca 200 g each and three bulk samples of ca

mechanisms of thermohaline mode switching with application to warm equable climates abstract a three box model of haline and thermal mode overturning is developed to study thermohaline oscillations found in a number of ocean general circulation models and that might have occurred in warm equable paleoclimates by including convective adjustment modified to represent the localized nature of deep convection the box model shows that a steady haline mode circulation is unstable for certain ranges of freshwater forcing vertical diffusivity a self sustained oscillatory circulation is found in which haline thermal mode switching occurs with a period of centuries to millennia it is found that mode switching is most likely to occur in warm periods of earth s history with relative to the present climate a reduced pole ndash uator temperature gradient an enhanced hydrological cycle and somewhat smaller values of oceanic diffusivities

a two stage model of fracture of rocks in this paper we propose a two stage model of rock fracture in the first stage cracks or local regions of failure are uncorrelated and occur randomly throughout the rock in response to loading of pre existing flaws as damage accumulates in the rock there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop based on statistical arguments a critical density of damage will occur where clusters of flaws become large enough to lead to larger scale failure of the rock stage two while crack interaction and cooperative failure is expected to occur within clusters of closely spaced cracks the initial development of clusters is predicted based on the random variation in pre existing flaw populations thus the onset of the unstable second stage in the model can be computed from the generation of random uncorrelated damage the proposed model incorporates notions of the kinetic and therefore time dependent nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation the advantage offered by this model is that its salient features are valid for fracture processes occurring over a wide range of scales including earthquake processes a notion of the rank of fracture fracture size is introduced and criteria are presented for both fracture nucleation and the transition of the failure process from one scale to another

seismicity patterns before the m 5 8 2002 palermo italy earthquake seismic quiescence and accelerating seismicity abstract seismic quiescence and accelerating seismic energy release are considered as possible spatio temporal patterns of the preparation process of the 6 september 2002 palermo italy earthquake m 5 8 the detailed properties of the quiescence are analyzed applying the rtl algorithm the rtl algorithm is based on the analysis of the rtl prognostic parameter which is designed in such a way that it has a negative value if in comparison with long term background there is a deficiency of events in the time space vicinity of the tested point the rtl parameter increases if activation of seismicity takes place the rtl algorithm identified that a seismic quiescence started from the beginning of november 2001 and reached its minimum at the end of may 2002 the palermo 2002 earthquake occurred 2 months after the rtl parameter restored its long term background level the application of a log periodic time to failure model gives a predicted in retrospect magnitude m 6 2 main shock on 5 may 2002

seismic imaging of the 2001 bhuj mw7 7 earthquake source zone b value fractal dimension and seismic velocity tomography studies abstract we use precisely located aftershocks of the 2001 mw7 7 bhuj earthquake 2001 2009 to explore the structure of the kachchh seismic zone by mapping the 3 d distributions of b value fractal dimension d and seismic velocities from frequency magnitude analysis we find that the catalog is complete above mw 3 0 thus we analyze 2159 aftershocks with mw 3 0 to estimate the 3 d distribution of b value and fractal dimensions using maximum likelihood and spatial correlation dimension approaches respectively our results show an area of high b d and vp vs ratio values at 15 35 km depth in the main rupture zone mrz while relatively low b and d values characterize the surrounding rigid regions and gedi fault gf zone we propose that higher material heterogeneities in the vicinity of the mrz and or circulation of deep aqueous fluid volatile co2 is the main cause of the increased b d and vp vs ratio values at 15 35 km depth seismic velocity images also show some low velocity zones continuing in to the deep lower crust supporting the existence of circulation of deep aqueous fluid volatile co2 in the region probably released from the eclogitasation of olivine rich lower crustal rocks the presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the mrz interestingly we observe that aki 1981 s relation d 2b is not valid for the spatial b d correlation of the events in the gf d2 1 2b zone however the events in the mrz d2 1 7b show a fair agreement with the d 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone d2 1 95b show a strong correlation with the aki 1981 s relationship thus we infer that the remaining parts of the aftershock zone are probably behaving like locked un ruptured zones where larger stresses accumulate we also propose that deep fluid involvement may play a key role in generating seismic activity in the mrz therefore a similar episode of deep fluid inflow could play a crucial role in causing the next strong earthquakes in the surrounding blocks of nwf

oceanic responses to gradual transitions of equator to pole temperature gradients summary responses of an ocean model to gradual transitions of equator to pole gradients show that several quasiequilibrium states within the thermally driven regime are generated under identical forcing conditions these different states are associated with different patterns the location and the penetration depth of oceanic convection small changes in the thermal forcing conditions can push the system into an oscillatory regime once in this regime oscillations appear to proceed as internal processes one important implication of these results is that the presentday ocean climate may not recover fully if the atmospheric coz level after doubling is lowered to the present day level

convective flow patterns in an eight box cube driven by combined wind stress thermal and saline forcing an eight box cube model ocean simulating the subpolar gyre in the north atlantic is formulated in order to understand how the wind induced horizontal gyre affects the thermohaline circulation and its catastrophe the model is forced from above by thermal conduction and fresh water flux the structure of the thermohaline circulation and its catastrophe during the process of gradually increasing or reducing the evaporation precipitation are examined the results indicate that although adding the third dimension and a wind driven horizontal gyre of medium strength splits the catastrophe into several separate ones only some of these catastrophes remain of significant amplitude with choice of parameters appropriate for the north atlantic the model predicts a single stable state circulating in the thermal sense sinking at the pole this can be driven smoothly to a reversed saline sense sinking at the equator without catastrophe by increasing the precipitation evaporation rate beyond 3 times the present day value

characteristics of the beaufort sea high abstract characteristics of the arctic ocean s beaufort sea high are examined using fields from the ncep ncar reanalysis at a 2 hpa contour interval the beaufort sea high appears as a closed anticyclone in the long term annual mean sea level pressure field and in spring in winter the beaufort sea region is influenced by a pressure ridge at sea level extending from the siberian high to the yukon high over northwestern canada as assessed from 6 hourly surface winds the mean frequency of anticyclonic surface winds over the beaufort sea region is fairly constant through the year while for all seasons a strong closed high can be interpreted as the surface expression of an amplified western north american ridge at 500 hpa there is some suggestion of a split flow where the ridge linked to the surface high is separated from the ridge to the south that lies within the main belt of westerlies the aleutian low in the north pacific tends to be deeper than normal when there is a strong beaufort sea high in

unified scaling theory for distributions of temporal and spatial characteristics in seismology abstract the paper describes the unified scaling theory for distribution functions of temporal and spatial characteristics in seismology it is based on the scaling of seismological characteristics calculated for various energy spatial temporal intervals the common mathematical methods for the scaling of distribution functions are developed the means to test possibility of such scaling are found as well the relationship between the unified scaling theory and other present scaling approaches is determined the theory is applied to two characteristics of different seismoactive regions the first characteristic is the waiting time between earthquakes t the second one is a new space parameter d min which is the minimum distance of a current seismic event to the nearest in space neighbor in an energy spatial temporal interval the distribution of the characteristics t and d min allows estimating the time interval to the next earthquake and the distance of the following earthquake from previous earthquakes thus these characteristics are very important for seismic hazard estimations scaling of distributions functions is proven to be successful for d min in all energy spatial temporal intervals and for t with variations of energy magnitude range the distribution function of t for various time domains was stable in only 60 of the cases and near to unstable for spatial variations

the effects of aqueous chemical environments on crack and hydraulic fracture propagation and morphologies the role of surface active aqueous environments in chemomechanical weakening of geologic materials is examined in light of the results of hydraulic fracture tests in sandstone calorimetric studies and crack propagation tests in synthetic quartz in hydraulic fracture tests mploying crab orchard sandstone it was found that the effective hydraulic fracture pressure was reduced over that attained with distilled water when 5 10 4 m aqueous solutions of dodecyl trimethyl ammonium bromide dtab were used as the hydraulic fracture medium the degree of branching of the fractures was also increased in the presence of the dtab solution previously reported crack propagation stress values in quartz exposed to distilled water and various dtab solutions displayed the same trend when examined in this study the cracks propagated in the presence of dtab solutions also displayed a greater degree of branching than those propagated in the presence of distilled water or the ambient atmosphere these results and results from calorimetric measurements of the heats of adsorption and desorption from quartz of distilled water and dtab are synthesized in a model relating the weakening and morphological effects to a reduction in the surface free energy of quartz due to adsorption of species from the chemical environment onto the surfaces of the quartz and sandstone

switching from seismic faulting to silent slips in harzburgite induced by h2o fluid at upper mantle pressures slow slip events frequently occur but regular earthquakes are much less active on the h2o fluid rich subduction interface at depths of 40 km the characteristic duration for silent earthquakes which are categorized as the great slow slip events is more than five orders of magnitude longer than that for regular earthquakes such phenomena are often attributed to the slippage of the softer part of the subduction interface but the impact of h2o fluid on aseismic slip is still unsolved here we conduct deformation experiments on water saturated harzburgite at pressures of 1 2 to 3 0 gpa and temperatures of 770 to 1250 k corresponding to the conditions of the lower part of the overriding plate just above the subduction interface we observe deformation of the harzburgite followed by silent faulting at a significantly low stress level down to 0 3 gpa under fluid bearing conditions even though many acoustic emissions are generated at the onset of faulting in fluid free harzburgite we find that the observed silent faulting is caused by the detachment of asperity contacts by high pore pressures and lubrication of the fault plane by a hydration reaction we therefore propose that h2o fluid may prevent the occurrence of regular intraslab earthquakes but trigger silent earthquakes

thermohaline circulation energetics and variability in a single hemisphere basin model a series of numerical experiments have been carried out to explore the variability of the thermohaline circulation and the energetics of halocline catastrophe it is found that when the amplitude of surface freshwater flux is smaller than a critical value the thermohaline circulation is in a thermal mode with deep water formed in the north when the freshwater flux amplitude is supercritical the thermohaline circulation does not reach a single steady state instead the model ocean is in a continuous transition between a slow quasi steady saline mode and an energetic unsteady thermal mode for cases with no wind stress the saline mode is characterized by sinking along the equator for cases with wind stress the saline mode is characterized by intermediate water formation at midlatitude during the saline mode phase the deep water gradually becomes warm and salty thus at the end of the saline mode phase within the northern basin there is cold and relatively fresh water lying on top of warm and salty water such a vertical structure is potentially very unstable because small perturbations can grow supported by the release of potential energy during strong cooling a quantity called the diabatic available potential energy index is introduced as an indicator for such convective instability thus a final equilibrium in the saline mode cannot be reached instead the model ocean flips to a very energetic thermal mode in which violent overturning destroys the vertical stratification after the energy is released the saline cell supported by precipitation in the subpolar basin advances southward and the model ocean returns to the saline mode the whole cycle will be repeated

validation and sensitivities of frontal clouds simulated by the ecmwf model abstract clouds simulated by the european centre for medium range weather forecasts ecmwf model are composited to derive the typical organization of clouds surrounding a midlatitude baroclinic system comparison of this composite of about 200 cyclones with that based on satellite data reveals that the ecmwf model quite accurately simulates the general positioning of clouds relative to a low pressure center however the optical depths of the model s high low clouds are too small large relative to the satellite observations and the model lacks the midlevel topped clouds observed to the west of the surface cold front sensitivity studies with the ecmwf model reveal that the error in high cloud optical depths is more sensitive to the assumptions applied to the ice microphysics than to the inclusion of cloud advection or a change of horizontal resolution from 0 5625 to 1 69 lat this reflects the fact that in the ecmwf model gravitational settling is the most rapid process controlling the abundance of ic

is the gulf stream responsible for europe s mild winters is the transport of heat northward by the gulf stream and north atlantic drift and its subsequent release into the midlatitude westerlies the reason why europe s winters are so much milder than those of eastern north america and other places at the same latitude here it is shown that the principal cause of this temperature difference is advection by the mean winds south westerlies bring warm maritime air into europe and north westerlies bring frigid continental air into north eastern north america further analysis of the ocean surface heat budget shows that the majority of the heat released during winter from the ocean to the atmosphere is accounted for by the seasonal release of heat previously absorbed and not by ocean heat flux convergence therefore the existence of the winter temperature contrast between western europe and eastern north america does not require a dynamical ocean two experiments with an atmospheric general circulation model coupled to an ocean mixed layer confirm this conclusion the difference in winter temperatures across the north atlantic and the difference between western europe and western north america is essentially the same in these models whether or not the movement of heat by the ocean is accounted for in an additional experiment with no mountains the flow across the ocean is more zonal western europe is cooled the trough east of the rockies is weakened and the cold of north eastern north america is ameliorated in all experiments the west coast of europe is warmer than the west coast of north america at the same latitude whether or not ocean heat transport is accounted for in summary the deviations from zonal symmetry of winter temperatures in the northern hemisphere are fundamentally caused by the atmospheric circulation interacting with the oceanic mixed layer copyright 2002 royal meteorological society

expansion of subarctic water masses in the north atlantic and pacific oceans and implications for mid pleistocene ice sheet growth 1 past surface ocean circulation changes associated with the mid pleistocene transition 0 9 0 6 ma were reconstructed in the northern north atlantic odp 983 and the northwest pacific odp 882 using proxies for subarctic subpolar water mass distributions c37 4 alkenone and sea surface temperature u37 both sites experienced a secular expansion of subarctic waters from 1 15 ma spanning both glacial and interglacial intervals after 0 9 ma low c37 4 at site 983 records a northward retreat of subarctic waters during interglacials in the atlantic while continued high glacial c37 4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late pleistocene ice sheets in contrast a secular decline in c37 4 occurred at site 882 from 0 9 to 0 5 ma marking a more gradual retreat of subarctic conditions in the pacific it is proposed that the expansion of subarctic waters between 1 15 and 0 9 ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere ocean circulation changes associated with the mid pleistocene transition that began as early as 1 2 ma

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

influences of precipitation on water mass transformation and deep convection abstractthe influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses making explicit their dependence on both geometric parameters such as basin area sill depth and latitude as well as on the strength of atmospheric forcing in addition to the properties of the convective water the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode high resolution numerical model calculations compare well with the theory for the properties of the convective water mass the strength of the meridional overturning circulation and also the shutdown of deep convection however the numerical model also shows that for precipitation levels that exceed this critical threshold the circulat

reconstruction of sea surface temperature salinity and sea ice cover in the northern north atlantic during the last glacial maximum based on dinocyst assemblages past sea surface conditions over the northern north atlantic during the last glacial maximum were examined from the study of 61 deep sea cores the last glacial maximum time slice studied here corresponds to an interval between heinrich layers h2 and h1 and spanningabout 20 16 ka on a 14c time scale transfer functions based on dinocyst assemblages were used to reconstruct sea surface temperature salinity and sea ice cover the results illustrate extensive sea ice cover along the eastern canadian margins and sea ice spreading only during winter over most of the northern north atlantic on the whole much colder winter prevailed despite relatively mild conditions in august 10 15 c at most offshore sites thus suggesting a larger seasonal contrast of temperatures than today lower salinity than at present is reconstructed especially along the eastern canadian and scandinavian margins likely because of meltwater supply from the surrounding ice sheets these reconstructions contrast with those established by climap on the basis of planktonic foraminifera these differences are discussed with reference to the stratigraphical frame of the last glacial maximum which was not the coldest phase of the last glacial stage the respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses which was apparently much more stratified than at present in the northern north atlantic thus preventing deep water formation

spatial and temporal patterns of earthquake distribution in soviet central asia application of pair analysis statistics we have examined the soviet regional earthquake catalog for central asia for the period 1962 to 1983 to characterize the spatial and temporal structure of the earthquake process in this highly active continental collision zone three areas of apparently homogeneous earthquake distribution were identified as characteristic of distinct seismic regimes 1 a segment of the range bounding gissar kokshal fault zone 2 the interior of the crystalline massif of the tien shan mountain range and 3 the tadjik depression fold thrust belt the pair analysis technique applied in our study compares the spatial and temporal distribution of pairs of earthquakes with those determined by uniformly distributed events in the same area and time interval we have found the earthquake distribution in this region to be dominated by significant nonrandomness in both space and time the spatial nonrandomness is manifested in two major ways spatial clustering appears to characterize the overall structure of the earthquake process in the region as it is observed regardless of the scale considered and even upon removal of foreshocks aftershocks and swarms from the catalog anomalies at larger distances could also be distinguished suggesting the existence of a regular spatial alternation of subareas of higher and lower levels of seismic activity the nonrandomness in temporal distribution of earthquakes is also characterized by clustering at short time intervals in contrast with the spatial patterns earthquakes appear to be randomly distributed in time after removal of foreshocks aftershocks and swarms

sea ice as the glacial cycles climate switch role of seasonal and orbital forcing a box model of the coupled ocean atmosphere sea ice and land ice climate system is used to study glacial interglacial oscillations under seasonally and orbitally varying solar forcing the dominant 100 kyr oscillation in land ice volume has the familiar sawtooth shape of climate proxy records and to zeroth order it does not depend on the seasonal and milankovitch forcing the sea ice controls via its albedo and insulating effects the atmospheric moisture fluxes and precipitation that enable the land ice sheet growth this control and the rapid growth and melting of the sea ice allow the sea ice to rapidly switch the climate system from a growing ice sheet phase to a retreating ice sheet phase and to shape the oscillation s sawtooth structure a specific physical mechanism is proposed by which the insolation changes act as a pacemaker setting the phase of the oscillation by directly controlling summer melting of ice sheets this mechanism is shown to induce deglaciations during periods of lower summer insolation superimposed on the 100 kyr are the linear milankovitch forced frequencies of 19 23 and 41 kyr the transition from 41 kyr glacial cycles to 100 kyr cycles one million years ago may be explained as being due to the activation of the sea ice switch at that time this would be the case if sea ice extent was more limited during the warmer climate of the early pleistocene

the instability of the thermohaline circulation in a low order model abstract although the instability of the thermohaline circulation has been widely observed in numerical ocean models theoretical advances have been hindered by the nonlinearity of heat and salt transports a circulation governed by lateral temperature and salinity gradients because the instability occurs initially in polar waters through the formation of haloclines and the halt of convection any explanatory model must have at least a surface and a deep layer the model proposed here two surface boxes above a deep one reduces to a 2 degrees of freedom dynamical system when convection is active and 3 degrees when it is interrupted the instability that is induced by a negative freshwater perturbation in polar waters has three stages the first stage is a rapid 5 yr adjustment to a transient thermal attractor that results from an approximate balance between heat advection and air sea heat fluxes the second stage is a slow evolution that self organizes near this attractor which preconditions the insta

past extent of sea ice in the northern north atlantic inferred from foraminiferal paleotemperature estimates 1 using 150 core top samples we developed a conservative but fairly robust new measure to reconstruct past changes in maximum seasonal sea ice distribution in the northern north atlantic hitherto a major unknown the proxy is based on similarity maximum modern analog technique simmax estimates of threshold temperatures near the sea surface sst today almost 100 of all sites with sst 2 5 c during summer 0 4 for winters 1978 1987 and 0 75 c for little ice age winters lie seaward of the sea ice margin when applied to 60 sediment records of the last glacial maximum this proxy shows that peak glacial sea ice was far more restricted than in the classic climap project members 1981 reconstruction during glacial summer sea ice only covered the arctic ocean and western fram strait the northern north atlantic and nordic seas were largely ice free and thus formed a high latitude moisture source for the continued buildup of continental ice sheets in contrast sea ice spread far south across the iceland faeroe ridge during glacial winter with an inferred patch of sea ice also in the central east atlantic near the center of the azores high a broad ice free channel extended from 50 to 60 n forming an ideal site for large scale convection of glacial upper north atlantic deep water the extreme seasonality in glacial sea ice formation and melt in the nordic seas implies a major consumption of the regional energy income

thermohaline catastrophe in a simple four box model of the ocean climate a four box model of the ocean is examined in which a surface and deep layer of equal thickness and large volume are connected to two polar reservoirs of smaller volume while the four reservoirs are thoroughly mixed there is no significant mixing between them exchange is due to flow between reservoirs with the flow out of or into the polar reservoirs driven by pressure gradients newtonian boundary conditions are imposed on the temperature and salinity of the surface layer and the two polar reservoirs the deep water is forced only by flows into it from other boxes the temperature and salinity forcing is applied with a different time scale for each variable when the time scales are nearly equal the system responds as a simple component fluid with a single solution for each forcing when the salinity time scale is long compared with temperature up to four multiple equilibria can be present for a given forcing these equilibria are unstable to finite amplitude perturbations and numerical solutions exhibit catastrophic transitions from one mode to another when the deep water formation is totally inhibited as a result of a transition the system can go into a long term climatic oscillation quasi periodic in nature the system possesses four attractors corresponding to deepwater formation in either both or neither of the two polar reservoirs

the rock fracture experiment with a drive control a spatial aspect abstract the statistical analysis of the space time distributions of acoustical signals emitted from the compressed samples of westerly granite is presented the samples were uniaxially loaded in two regimes one of which included a feedback loop controlled by the current acoustical emission ae activity the distribution of distances between newly appeared hypocenters follows the power law with the exponent that does not depend on the mode of loading in both regimes a transient period of the decorrelated accumulation of damaged sites was revealed between the initial and focal stages of the fracture process the hurst analysis indicates a more pronounced trend to planar organization of final damage structure in the case of ae controlled loading

load unload response ratio and accelerating moment energy release critical region scaling and earthquake prediction the main idea of the load unload response ratio lurr is that when a system is stable its response to loading corresponds to its response to unloading whereas when the system is approaching an unstable state the response to loading and unloading becomes quite different high lurr values and observations of accelerating moment energy release amr aer prior to large earthquakes have led different research groups to suggest intermediate term earthquake prediction is possible and imply that the lurr and amr aer observations may have a similar physical origin to study this possibility we conducted a retrospective examination of several australian and chinese earthquakes with magnitudes ranging from 5 0 to 7 9 including australia s deadly newcastle earthquake and the devastating tangshan earthquake both lurr values and best fit power law time to failure functions were computed using data within a range of distances from the epicenter like the best fit power law fits in amr aer the lurr value was optimal using data within a certain epicentral distance implying a critical region for lurr furthermore lurr critical region size scales with mainshock magnitude and is similar to the amr aer critical region size these results suggest a common physical origin for both the amr aer and lurr observations further research may provide clues that yield an understanding of this mechanism and help lead to a solid foundation for intermediate term earthquake prediction

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

low cloud boundary layer and sea ice interactions over the southern ocean during winter abstractduring austral winter a sharp contrast in low cloud fraction and boundary layer structure across the antarctic sea ice edge is seen in ship based measurements and in active satellite retrievals from cloud aerosol lidar and infrared pathfinder satellite observations calipso which provide an unprecedented view of polar clouds during winter sea ice inhibits heat and moisture transport from the ocean to the atmosphere and as a result the boundary layer is cold stable and clear over sea ice and warm moist well mixed and cloudy over open water the mean low cloud fraction observed by calipso is roughly 0 7 over open water and 0 4 0 5 over sea ice and the low cloud layer is deeper over open water low level winds in excess of 10 m s 1 are common over sea ice cold advection off of the sea ice pack causes enhanced low cloud fraction over open water and thus an enhanced longwave cloud radiative effect at the surface quantitative estimates of the surface longwave cloud radiative effect contr

maps of expected earthquakes based on a combination of parameters abstract the technique for compiling maps of expected earthquakes has been developed and tested retrospectively and in real time the conditional probability of future earthquakes was calculated based on geotectonic data geodetic measurements and spatio temporal variations of such seismic parameters as density of seismogenic faults slope of the recurrence curve number of events such as seismic quiescence and activation ratio of s and p wave travel times and seismic energy release the probability of detection the probability of false alarm the mean waiting time the mean waiting area and the prediction efficiency were estimated from the retrospective analysis of earthquakes with magnitudes m 5 0 the map of expected earthquakes for the caucasus in 1986 1990 was sent to local seismological institutes in 1985 three main zones with a high probability of future earthquakes were revealed on that map each of them has a size of about 10 4 km 2 several smaller zones have a mosaic like pattern and are distributed along tectonic faults and their intersections 10 of the territory is covered by areas with an earthquake probability of 3 5 times larger compared with random occurrence six earthquakes with magnitudes m 5 0 occurred in the caucasus in 1986 august 1989 their epicentres were located within 30 km of the corresponding waiting zones the biggest shock occurred in armenia on the 7th of december 1988 m 6 9 it destroyed the cities spitak leninakan and kirovakan a high probability zone appeared in that area in 1983 i e 5 years before the event showing a gradual growth both in amplitude and size up to 1988 in five other cases the anomalies appeared 1 2 years before the corresponding earthquakes this technique is now being tested in other seismic areas of the soviet union

arctic synoptic regimes comparing domain wide arctic cloud observations with cam4 and cam5 during similar dynamics 1 arctic cloud properties variability and sensitivity to surface conditions are strongly dependent on the synoptic regimes in which they exist and proper evaluation of modeled cloud properties against observations requires that the dynamic and thermodynamic environment be carefully accounted for in this study a k means clustering algorithm is used to sort arctic clouds observed by calipso into four distinct synoptic regimes three regimes largely associated with mid tropospheric subsidence or very weak uplift and separated by differences in lower tropospheric stability and one regime associated with mid tropospheric uplift boundary layer clouds are present within the three subsidence regimes with increases in stability relating to lower altitudes of the maximum cloud percentage in going from sea ice to open ocean the cloud amount increases at the lowest atmospheric level for all subsidence regimes except the least stable regime and the height of maximum low clouds rises for all subsidence regimes except the most stable regime within each synoptic regime clouds diagnosed from the calipso simulator in cam4 and cam5 forecast runs are then compared with observations compared with cam4 cam5 produces boundary layer clouds that are more similar to the observations and more closely captures the observed sensitivity of cloud properties to the underlying surface type however cam5 overestimates cloud percentages within the uplift regime the improved boundary layer turbulence and cloud microphysical parameterizations in cam5 yield a model that exhibits an improved sensitivity of arctic low level clouds to changes in lower tropospheric stability and surface type

rapid switch like sea ice growth and land ice sea ice hysteresis 1 rapid and extensive growth of sea ice cover was suggested to play a major role in the sea ice switch mechanism for the glacial cycles as well as on shorter millennial scales gildor and tziperman 2000 this mechanism also predicts a hysteresis between sea ice and land ice such that land ice grows when sea ice cover is small and withdraws when sea ice cover is more extensive the switch like sea ice growth and the hysteresis were previously demonstrated using a simple highly idealized box model in this work we demonstrate a switch like sea ice behavior as well as the sea ice land ice hysteresis using a coupled climate model that is continuous in the latitudinal dimension it is shown that the switch like sea ice growth occurs when the initial meridional atmospheric temperature gradient is not too strong it is also shown that the meridional extent to which sea ice grows in a switch like manner is not affected by the intensity of the thermohaline circulation which does however influence the climate cooling that is needed to trigger such rapid sea ice growth

the stability of thermohaline circulation in a two box model abstract in stommel s simple two box model which has provided an insight on the thermohaline circulation and climate instability mechanisms a linear mass transport was used however a scaling law based on geostrophy and advective diffusive heat balance suggests a nonlinear mass transport relation for the oceans by including this nonlinear mass transport relation to stommel s box model it is possible to study the effects of the thermocline which was not considered before on the stability of the thermohaline circulation while keeping the simplicity of stommel s box model the results were compared with those obtained with the traditional model using a linear mass transport relation the thermal mode circulation of the nonlinear model is significantly more stable than that of the linear model suggesting the thermohaline catastrophe is less likely to occur in the present north atlantic if the thermocline is considered in the nonlinear model the circulation removes density anomalies rapidly so that s

rock damage evolution as failure process of hierarchical structure abstract the present study is devoted to evolution of rocks in the fracture process initially the rock is considered as an ideal medium with no cracks rock formation is assumed in the form of a nested self similar hierarchical structure the hierarchical structure scheme is chosen in accordance with the experimentally verified criterion of fracture the failure probability of the lowest structure level represents a function of time temperature material parameters and loading conditions knowing the failure probabilities of each structure level allows one to calculate the stress dynamics in a rock material failure volumes for each hierarchy level energy release etc the influence of temperature type of the hierarchical structure rock material stress rate on the fracture dynamics is considered the results of calculations of the rock fracture dynamics are compared with the results of experiments this study can be seen as an attempt to explain the stability of the gutenberg richter law

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

multiple equilibrium states in combined thermal and saline circulation abstract structure and stability of the multiple equilibria of the thermohaline circulation am studied using 2 2 and 3 2 box models thermohaline catastrophe is a shallow phenomenon and its time evolution consists of three stages the search stage the catastrophic stage and the adjustment stage a 3 2 box model is introduced to permit fitting a somewhat less truncated form of freshwater forcing although the total number of possible modes of circulation increases quickly as the number of boxes is increased the grand thermal mode and grand saline mode remain some multiple solutions are found to be statistically improbable and they belong to the so called minor modes with the more realistic freshwater forcing appropriate for the present day north atlantic our simple 3 2 model predicts that the thermohaline cimulation is near a critical mate because a small increase in freshwater flux can cause the system to collapse from the present thermally dominated circulation to an intermediate mode of

hierarchy in earthquake size distribution abstract we propose a fault model in which there are a finite number of characteristic lengths between the smallest and the largest scales e g between a grain size and a size of great earthquakes a fault plane in one scale is segmented into blocks of statistically similar sizes by the barriers of statistically similar heights rupture expands by successively climbing the barriers the average barrier height is proportional to the average block size which defines the characteristic length of the relevant scale stresses before and after rupturing are assumed to be independent of earthquake size with these assumptions the probability for rupture to grow further is shown to be independent of the scale of barrier structure the rupture in one scale however tends to grow more easily as it grows so that once the rupture exceeds some critical size it no longer stops until it encounters the barriers in the next larger scale rupture grows by repeating this cycle which starts with rupturing of a unit block in one scale and ends with one in the next larger scale our model involves two parameters which must be determined empirically one is the length ratio r between two successive scales the other is the critical number of blocks n c which defines the critical size for unstable rupture growth in one scale we suggest values of 5 for both r and n c with these values our model explains a diversity of earthquake phenomena such as the magnitude frequency relation the seismic gap and the magnitude gap the magnitude difference between a main shock and its largest aftershock the occurrence of multiplet earthquakes the generation of high frequency seismic waves the incoherency of the near field acceleration and the recent observation by furumoto and nakanishi that the main rupture is often preceded by a precursory rupture whose time duration in general scales with seismic moment

imperfections of the thermohaline circulation latitudinal asymmetry and preferred northern sinking abstract the present atlantic thermohaline circulation is dominated by deep water formation in the north despite the fact that surface buoyancy forcing has relatively modest latitudinal asymmetry many studies have shown that even with buoyancy forcing that is symmetric about the equator spontaneous symmetry breaking can produce a single overturning cell with intense sinking in the north this occurs by salt advection at sufficiently large freshwater forcing in this symmetry breaking case a southern sinking solution and a symmetric solution are also possible a simple coupled ocean atmosphere model of the zonally averaged thermohaline circulation is used to examine the effect of latitudinal asymmetries in the boundary conditions the greater continental area in the northern hemisphere combined with the slight asymmetry in the observed freshwater flux induce a strong preference for the northern sinking solution examining the relation to the solution under symmetric conditions the salt advection mech

geometry segmentation and stress regime of the spitak armenia earthquake from the analysis of the aftershock sequence summary the aftershock sequence of the spitak earthquake as recorded by a dense portable network deployed around the source region is analysed in order to obtain a precise description of the mechanics of the rupture a collection of 708 well recorded events corresponding to a period of about two weeks is studied their hypocentres are accurately located and their focal mechanisms are calculated individually as well as by a joint procedure that permits us to estimate the stress regime the epicentral distribution of these aftershocks indicates that the fault at depth extends well beyond the surface rupture towards the west and northwest neotectonic and seismic observations permit us to identify five segments broken during the earthquake the southeastern one oriented n140 corresponds to the surface ruptures along the alavar right lateral shear fault the main surface ruptures between spitak and gekhasar correlate well with aftershocks showing a n120 trending fault surface dipping 50 to the ne and acting as a thrust with a right lateral component two similar segments towards the west are offset and hidden under active folds a fifth segment towards the nw corresponds to a right lateral blind shear fault buried in depth in the vicinity of the large pambak sevan fault 14 vertical sections across the fault including focal mechanisms illustrate these features a relocation of the main shock and aftershocks for the period before the installation of the portable network confirms the spatial extent of the seismicity the foreshock the main shock and the strongest aftershock 4min 20s after the main shock have approximately the same epicentre thus the rupture started at the crossing of the pambak sevan and alavar faults and propagated bilateraly from there although the seismic moment associated to the alavar branch is only about one sixth of the total moment the stress regime is one of triaxial compression with a a axis oriented n344 the same orientation is given by the microtectonic observations made on the central segment of the surface ruptures a result that agrees with previous estimates for the georgian caucasus

dynamics of microscale precursors during brittle compressive failure in carrara marble microscale heterogeneities influence failure mechanisms in the crust to track the microstructural changes in rock samples when loaded until failure we employed a novel experimental technique that couples dynamic x ray microtomography imaging with a triaxial deformation apparatus we studied the brittle failure of carrara marble under triaxial compression dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure we quantified the emergence of scaling relationships between microstructural parameters including total damage volume incremental damage volume the largest connected microfracture and the applied differential stress the total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase the growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure the microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure these characteristic features of brittle failure in carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition we also observed that very close to failure several power law relationships broke down which we interpret to be related to the coalescence of the largest microfractures in a finite size volume scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models our results show that precursors of macroscopic brittle failure in carrara marble follow predictable trends

a self exciting process of acoustic emission occurrence in steady creep of granite under uniaxial stress clustering of acoustic emissions ae in space and time was found in a laboratory experiment to investigate the stochastic process of ae occurrence event times of ae were measured during steady creep phases under different stress levels oshima granite was continuously subjected to constant uniaxial stress of different intensity the occurrence time of ae event was analyzed as a combination of a poisson process and a self exciting part in the latter events are excited by preceding events the self exciting character was more enhanced under higher crack density in accordance with a stronger concentration in hypocenter distribution at higher stress

intermediate depth earthquakes linked to localized heating in dunite and harzburgite earthquakes can occur at great depths in the earth within subducting tectonic plates deformation experiments suggest these deep earthquakes can be triggered by localized heating of the slabs under high pressures

an analysis of the process of acceleration of seismic energy emission in laboratory experiments on destruction of rocks and before strong earthquakes on kamchatka and in italy abstract the time to failure model is a technique in which a failure function is fitted to a time series of accumulated benioff strain before a large earthquake we analyze the relation of the time to failure model to the hypothesis of fractal structure of seismicity a power law failure function varnes 1989 bufe and varnes 1993 and its log periodic generalization sornette and sammis 1995 are discussed the results of application of the log periodic time to failure model to the analysis of the process of acceleration of seismic energy emission in the laboratory experiments on rock destruction and before strong earthquakes on kamchatka and in italy are presented

a triple sea ice state mechanism for the abrupt warming and synchronous ice sheet collapses during heinrich events 1 abrupt switch like changes in sea ice cover are proposed as a mechanism for the large amplitude abrupt warming that seemed to have occurred after each heinrich event sea ice changes are also used to explain the colder than ambient glacial conditions around the time of the glacier discharge the abrupt warming events occur in this mechanism owing to rapid sea ice melting which warmed the atmosphere via the strong sea ice albedo and insulating feedbacks such abrupt sea ice changes can also account for the warming observed during dansgaard oeschger events the sea ice changes are caused by a weak order of 5 sv response of the thermohaline circulation thc to glacier discharges the main point of this work is therefore that sea ice may be thought of as a very effective amplifier of a weak thc variability explaining the abrupt temperature changes over greenland synchronous ice sheet collapses from different ice sheets around the north atlantic indicated by some proxy records are shown to be possible via the weak coupling between the different ice sheets by the atmospheric temperature changes caused by the sea ice changes this weak coupling can lead to a nonlinear phase locking of the different ice sheets which therefore discharge synchronously it is shown that the phase locking may also lead to precursor glacier discharge events from smaller ice sheets before the laurentide ice sheet discharges the precursor events in this mechanism are the result rather than the cause of the major glacier discharges from the laurentide ice sheet

temporal variation of multifractal properties of seismicity in the region affected by the mainshock of the october 6 2000 western tottori prefecture japan earthquake m 7 3 1 the temporal variation of multifractal properties in spatial distribution of seismicity in the region affected by the main shock of the western tottori prefecture japan earthquake of october 6 2000 m 7 3 and its aftershock sequence are investigated we use earthquake catalog data from 1985 to 2001 in order to understand the process and mechanism preceding a large shallow earthquake a monotonous decrease of multifractal dimension dq with a wide range of q appeared clearly for about two years prior to this large shallow earthquake dq then increased to a maximum at the time of the main shock during the aftershock sequence dq oscillated between 2 0 and 0 7 the decrease and then increase of dq with respect to the spatial distribution of seismic events indicate clustering and declustering in multifractal structure respectively the temporal variation of dq reflects the accumulation and release of strain energy within the tectonic stress field

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

seismicity preceding volcanic eruptions new experimental insights a variety of seismic signals representing different physical mechanisms precedes volcanic eruptions the most meaningful signals are high and low frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice we provide experimental support for this association by reproducing magma migration while recording seismic signals opening fractures emit high frequency acoustic events while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation

seismicity in north eastern brazil fractal clustering and the evolution of the b value summary we analyse a catalogue of earthquakes recorded near joao camara brazil an intraplate area with a simple velocity structure and low attenuation the evolution of seismicity is characterized by the seismic b value and the fractal dimension of earthquake epicentre locations measured from sliding 100 event windows the events are divided into a number of spatial clusters using a nearest centroid sorting technique and two of these clusters are examined in detail one cluster characterized by intense activity shows a clear negative correlation between b value and fractal dimension of epicentre locations as has been predicted from simple mechanical models a second cluster shows a weak positive correlation and it is suggested that this might be explained in terms of fluid flow in the fault zone

analogy in precursors of dynamic events at different scales abstract this paper presents a study of the time space behaviour of certain physical parameters namely the number of pulses of acoustic and seismic emission the density of seismogenic ruptures and the b value in laboratory mine and field experiments during the preparation and development of dynamic events at different scales the preparation stage before failure in rock specimens mine shocks and large earthquakes was studied it was found that in all cases the fault density parameter varies from 3 to 8 before a dynamic event the variance of the number of elastic pulses of acoustic and seismic emission as a rule increases and the b value undergoes changes it is shown that the behaviour of the parameters under study does not qualitatively depend on the linear dimensions of the object being loaded the results obtained strengthen the physical basis for the further development of studies on the prediction of dynamic events

omori s power law aftershock sequences of microfracturing in rock fracture experiment a time series of acoustic emissions ae in basalt was measured under constant uniaxial compression some bursts of ae events considered to be the main shock and aftershock sequences were observed two models describing the aftershock sequences the exponential decay model n t k exp pt and the omori s power law model n t k c t p where n t denotes the occurrence rate of aftershocks at time t were examined with the progress of the fracturing process the bursts changed from the exponential decay type to omori s power law type and the p value of omori s power law aftershock sequences decreased these results indicate that microfracturing gains a longer tail with the evolution of the fracture process the reproduction of omori s power law aftershock sequences of ae events suggests that the self similarity of rock fracturing holds good over a range from microfracturing to large earthquakes

physical modeling of the formation and evolution of seismically active fault zones acoustic emission ae in rocks is studied as a model of natural seismicity a special technique for rock loading has been used to help study the processes that control the development of ae during brittle deformation this technique allows us to extend to hours fault growth which would normally occur very rapidly in this way the period of most intense interaction of acoustic events can be studied in detail characteristics of the acoustic regime ar include the gutenberg richter b value spatial distribution of hypocenters with characteristic fractal correlation dimension d hurst exponent h and crack concentration parameter pc the fractal structure of ar changes with the onset of the drop in differential stress during sample deformation the change results from the active interaction of microcracks this transition of the spatial distribution of ae hypocenters is accompanied by a corresponding change in the temporal correlation of events and in the distribution of event amplitudes as signified by a decrease of b value the characteristic structure that develops in the low energy background ae is similar to the sequence of the strongest microfracture events when the ar fractal structure develops the variations of d and b are synchronous and d 3b this relation which occurs once the fractal structure is formed only holds for average values of d and b time variations of d and b are anticorrelated the degree of temporal correlation of ar has time variations that are similar to d and b variations the observed variations in laboratory ae experiments are compared with natural seismicity parameters the close correspondence between laboratory scale observations and naturally occurring seismicity suggests a possible new approach for understanding the evolution of complex seismicity patterns in nature

multiple equilibria and transitions in a coupled ocean atmosphere box model abstract a six box model is employed as a prototype of the coupled atlantic ocean atmosphere system ice dynamics are excluded numerical integration of this system shows that different thermohaline circulation patterns are possible under the same forcing conditions they consist of a global thermal mode with oceanic poleward surface flow a global saline mode with equatorward surface flow and two intermediate modes that are combinations of the two global modes the stability of the modern day like intermediate mode to finite amplitude freshwater flux perturbations in the high latitude north atlantic meant as a model of glacial melting is explored it is found that freshwater fluxes of the proper inferred magnitude are close to critical and can induce a transition of the coupled system to a saline mode however paleoclimatic data argues the last deglaciation was subcritical further working in a realistic subcritical parameter regime the box model yields an unrealistic temperature record this argue

impact of reduced arctic sea ice on greenland ice sheet variability in a warmer than present climate a global climate model with interactive vegetation and a coupled ice sheet shelf component is used to test the response of the greenland ice sheet gis to increased sea surface temperatures ssts and reduced sea ice si cover during the mid pliocene warm period 3 ma as reconstructed from proxy records seasonally open water in the arctic and north atlantic are shown to alter regional radiation budgets storm tracks and moisture and heat advection into the greenland interior with increases in temperature rather than precipitation dominating the ice sheets response when applied to an initially glaciated greenland the presumed warm ice free pliocene ocean conditions induce rapid melting of nearly the entire ice sheet and preclude a modern like gis from re growing regardless of orbital forcing the sensitivity of greenland to imposed pliocene ocean conditions may have serious implications for the future response of the ice sheet to continued warming in the arctic basin