stable oxygen and carbon isotopes in late glacial holocene freshwater carbonates from belarus and their palaeoclimatic implications abstract four sets of 18 o and 13 c curves were derived from late glacial to mid holocene spring and lacustrine carbonates from belarus stratigraphic division was carried out by palynological studies and 14 c dating it was revealed that variations of isotopic compositions and the dynamics of terrestrial vegetation were affected to some extent by common climatic forcing birch expanded during relatively warm and or arid phases higher 18 o and or 13 c fir spread during relatively cold and or humid phases lower 18 o and or 13 c and grasses were abundant during relatively cold lower 18 o or arid phases higher 13 c a comparison of four pairs of 18 o and 13 c curves allowed the recognition of several palaeoclimatic events at a regional scale two main cold events interrupted by a warmer interval occurred in the younger dryas a short term episode of active permafrost decay at the end of the younger dryas and in the very beginning of the preboreal caused an abrupt rise of lake levels followed by their rapid fall a shift toward a lower precipitation evaporation balance and lower lake levels took place roughly in the middle of the boreal a trend of decreasing temperatures throughout most of the boreal culminated in a short lived very cold phase at 8100 14 c year bp or 9050 cal 14 c year bp according to the proposed age model in the atlantic 1 warmer phases were coincident with the phases of the lower precipitation evaporation balance an episode of significant short term warming occurred in the last third of the atlantic 1 correlation of the 18 o curve derived from authigenic calcites precipitated between the beginning of the preboreal 2 and the end of atlantic 1 in the ptich river valley with that from the gisp2 greenland ice core allowed good matching of the trends and spikes i e of the air temperature changes under assumption that the ages of the ptich pollen based time model are 600 1000 years too old

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

comparison of the microfracture localization in granite between fracturation and slip of a preexisting macroscopic healed joint by acoustic emission measurements experiments of fracturation and slip of a preexisting macroscopic healed joint have been performed under triaxial deformation on granite from mayet de montagne france this granite shows high grain scale inhomogeneity acoustic emissions have been recorded and hypocenters have been determined during the entire experiments for both rupture experiment and slip experiment precursory localization of microfractures in the final rupture plane has been observed in the early stage of deformation well before the dilatancy it is likely that not only initial closure of favorably oriented cracks but also breaking of partially cemented grains or slipping between grains may occur in the pseudoelastic phase and are already localized on the final rupture plane where the shear stress seems to be concentrate this behavior is observed in both cases where stress heterogeneity and rupture nucleation are controlled by 1 medium scale heterogeneity at the grain scale hs sample or 2 macroscopic heterogeneity in the form of a preexisting healed joint js sample the sample with the healed joint exhibited 1 6 times more acoustic emission events than the intact sample the presence of the healed joint significantly weakened the sample

a comparison of seismic and structural measurements of scaling exponents during tensile subcritical crack growth abstract the observed fractal nature of both fault length distributions and earthquake magnitude frequency distributions suggests that there may be a relationship between the structure of active fault systems and the resulting seismicity in previous theoretical work a positive correlation between the exponent d from the fracture length distribution and the seismic or acoustic emission ae b value has been inferred from a simple dislocation model of the seismic source here we present the first experimental evidence for a correlation between d and b from a series of tensile fracture mechanics tests on crystalline rock carried out in different environmental conditions both air dry and water saturated and at ambient temperature and pressure the microseismic acoustic emissions were monitored during subcritical crack growth under controlled conditions of constant stress intensity k i and quantitative analyses of the resulting fracture patterns were carried out on the same specimens it is found that ae b values ranging from 1 0 to 2 3 correlate negatively with the normalized stress intensity k i k ic where k ic is the fracture toughness of the specimen the microcrack length distribution exponent d ranges from 1 0 to 1 7 fluid presence has a first order influence on both the ae and structure produced in these experiments for experiments at low stress intensity or high fluid content the activation of the stress corrosion mechanism for k i k ic leads to a greater relative proportion both of small cracks and of low amplitude acoustic emissions reflected in higher values of d and b the exponent d is found to correlate positively with the ae b value

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

vegetation responses to rapid warming and to minor climatic fluctuations during the late glacial interstadial gi 1 at gerzensee switzerland abstract high resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to northgrip 1 a primary succession the vegetation responded to the rapid rise of temperatures around 14 685 yr bp with a primary succession on a decadal to centennial time scale the succession between ca 15 600 and 13 000 yr bp included 1 1 the replacement of shrub tundra by woodland of juniperus and tree birch around 14 665 yr bp 1 2 the response of juniperus pollen to the shift in oxygen isotopes in less than 20 yr 1 3 a sequence of population increases of hippophae rhamnoides ca 14 600 yr bp salix spp ca 14 600 yr bp betula trees ca 14 480 yr bp populus cf tremula ca 14 300 yr bp and pinus cf sylvestris ca 13 830 yr bp 2 biological processes plants responded to the rapid increase of summer temperatures on all organisational levels 2 1 individuals may have produced more pollen e g juniperus 2 2 populations increased or decreased e g juniperus betula later pinus and 2 3 populations changed their biogeographical range and may show migrational lags 2 4 plant communities changed in their composition because the species pools changed through immigration and local extinction some plant communities may have been without modern analogue these mechanisms require increasing amounts of time 2 5 processes on the level of ecosystems with species interactions may involve various time scales besides competition and facilitation nitrogen fixation is discussed 3 the minor fluctuations of temperature during the late glacial interstadial which are recorded in 18o resulted in only very minor changes in pollen during the aegelsee oscillation older dryas biozone gi 1d and the gerzensee oscillation gi 1b 4 biodiversity the afforestation at the onset of bolling coincided with a gradual increase of taxonomic diversity up to the time of the major pinus expansion

multiple oscillations during the preboreal as recorded in a calcareous gyttja kingbeekdal the netherlands abstract environmental changes occurring during the weichselian lateglacial to early holocene transition are supposed to be caused by rapid climate changes vegetation changes that occurred during the early holocene show a pattern of increased boreal forest development with dominance of birch friesland phase to a more open vegetation with an increase of predominantly grasses rammelbeek phase subsequently followed by renewed birch and later on pine forest development based on palynological evidence and botanical macrofossils the rammelbeek phase is supposed to have been caused by a change to dry rather than cold climate detailed 14c dating using a wiggle matched ams 14c chronology is used to place the vegetation changes in a time stratigraphic framework the rammelbeek phase can be placed to around 11 3 ka cal bp a direct correlation to the 11 2 ka event as recorded in the greenland ice cores is tempting in this paper we propose an alternative approach by using a common proxy registered in both ice core and terrestrial records based on oxygen isotopes a preboreal oscillation pbo appears to be present in many early holocene lacustrine carbonate rich records we used the 18o signal of calcareous lake deposits kingbeekdal southern netherlands in which biostratigraphically a rammelbeek phase is present the signal in the stable isotopes seems to correlate to the greenland ice core records this exercise shows that the pbo as recorded in the oxygen isotopes occurs not during the palynologically defined rammelbeek phase but early in the friesland phase moreover the palynological record of the kingbeekdal sequence shows at the level of the 18o reversal a distinct opening of the birch forest and a temporary disappearance of thermophilous taxa while the light requiring juniper increases this implies a more complex pattern of climate response registered by the different proxies as previously thought

holocene dynamics of the southern boreal forest in sweden holocene vegetation dynamics in the ecotone between the boreo nemoral and boreal forest were reconstructed from sediment cores of two small lakes using pollen and macrofossil analyses competition

biotic responses to rapid warming about 14 685 yr bp introduction to a case study at gerzensee switzerland abstract the late glacial climatic warming indicated in the greenland ice core record about 14 685 years before 1950 ad belongs to a type of very rapid high amplitude warming similar the onsets of dansgaard oeschger events during marine isotope stage 3 mis 3 in order to estimate the nature and rates of change of biotic responses to such a major climatic shift we need a reliable time scale as well as climatic indicators independent of the biota both are provided by a high resolution oxygen isotope record from precipitated carbonates of lake marl in gerzensee switzerland van raden et al 2013 this issue on the basis of the assumption of synchronous climatic changes between greenland and gerzensee the close correlation of the oxygen isotope changes at the two sites allows the use of the ngrip gicc05 timescale at gerzensee with the zero point at 1950 ad to maintain comparability with the numerous radiocarbon dates in europe the 18o record measured in precipitated carbonates is checked and refined by the 18o measured in mono specific ostracod samples von grafenstein et al 2013 in this issue the shift of 3 6 18o pdb in only about 112 years at the end of the gs 2 represents a very rapid temperature increase of at least 6 2 c this increase is confirmed by reconstructions based on transfer functions for pollen and chironomids by lotter et al 2012 possibly 4 7 c in the annual mean and 2 5 c in summer temperatures after this major shift the greenland late glacial interstadial gi 1 corresponding to the regional biozones bolling and allerod 18o records of both greenland and gerzensee exhibit four minor fluctuations about 1 0 1 2 18o of which the second and the fourth are especially clearly correlated with several of terrestrial records in the northern hemisphere the oxygen isotope record is used as a template for all these sediment and bio stratigraphies the biotic responses may include at least five types of process 1 changes in productivity of individuals within a year or two 2 changes in populations usually somewhat slower depending on life cycles and environmental constraints 3 changes due to migration often rather slow depending again on life cycles and environmental constraints 4 changes in the terrestrial and aquatic communities and 5 changes on the level of ecosystems including pedogenesis nutrient cycling and species interactions these biotic responses to the early rapid warming about 14 685 ka bp are elaborated in subsequent papers for plants chironomids ostracods and cladocera ammann et al 2013 a brooks and heiri in this issue von grafenstein et al in this issue novakova et al 2013 this issue in addition lake levels are reconstructed by magny 2013 this issue and vegetation dynamics and n2o emissions are modelled lischke et al 2013 pfeiffer et al 2013 the changes in the mammal fauna of the swiss plateau are summarized by nielsen 2013 this issue

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

microseismic properties of a homogeneous sandstone during fault nucleation and frictional sliding summary the formation and evolution of faulting in three initially intact oil saturated specimens of clashach sandstone is examined under conditions of constant strain rate loading at three different confining pressures simulating the effect of tectonic loading at different depths in the earth s upper crust after a fault is formed the specimens are slid for a time and then the initial confining pressure is increased to simulate the long term recovery of strength expected in the earth the differential stress u and natural acoustic emissions ae are measured during the three separate phases of fault nucleation sliding and strengthening at the end of each individual phase the fluid permeability is measured by a pulse decay technique at constant stress the ae are interpreted using a mean field theory for damage evolution which calculates a mean crack length c from the seismic event rate n and the b value and a mean energy release rate g from u and c c and g both increase non linearly in the nucleation stage and are associated with large fluctuations in the scaling exponent b in contrast the b value remains almost constant at a value near unity in the sliding phase even when the fault is mechanically strengthened small fluctuations in g observed during sliding may be associated with the breaking of individual asperities the relative stability of b combined with a relatively constant sliding stress implies that frictional sliding has all the hallmarks of a self organized critical soc phenomenon in contrast the fresh fracture of intact rock shows a continuum of states with power law scaling at a variety of b values where b is negatively correlated to g during the fault nucleation stage the implied subcritical crack growth index n obtained from the ae data shows a distinct break of slope during the failure of the intact specimens from n 2 consistent with a theoretical transition from stable damage to dynamic instability a possible mechanism is the transition from local mechanisms dominated by dilatant hardening negative feedback to microcrack coalescence positive feedback interpreted in this way the results imply that the organized coalescence of microcracks to form a fault occurs before the ultimate strength peak stress is reached this emphasizes the fact that local mechanisms of softening or hardening do not always scale simply to the macroscopic rheology in a heterogeneous medium the fluid permeability reduces steadily throughout all phases of deformation testament to the self sealing nature of deformation in porous sedimentary rocks

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

late quaternary expansion of norway spruce picea abies l karst in europe according to pollen data abstract lateglacial and holocene expansion of norway spruce picea abies l karst in europe is reconstructed in steps of 1000 radiocarbon years on the basis of pollen data collected from literature and databases pollen thresholds for the lateglacial of 0 1 2 5 and 10 and for the holocene of 2 were used spruce pollen representation and limitations of pollen data are discussed we assume that the 2 threshold tracks the advance of the main spruce front but might fail to detect small populations or those present in low density the history of spruce expansion was distinctly different in northern and southern parts of its range 1 in ne europe spruce expanded during the allerod reaching southwards to n byelorussia during the younger dryas spruce populations contracted north of ca 60 n but expanded strongly in the region approximately 53 60 n 23 32 e where they declined at the beginning of the holocene we infer that the lateglacial expansion in ne europe concerned mainly p abies subsp obovata 2 holocene expansion in n europe concerned mainly p abies subsp abies southward expansion within the northern range is continuing to the recent millennium 3 in central europe spruce expanded vigorously during the allerod contracted or stagnated during the younger dryas and then strongly re expanded during the preboreal following the simple expectation that climatic warming had a positive impact on its development 4 holocene westward and northward expansion of spruce in its southern range central europe was rapid 10 8 ka 14 c bp very slow 8 6 ka 14 c bp and rapid 6 5 ka 14 c bp when the present day western limits were reached 5 the 2 spruce pollen threshold is too high to detect the fact that the northern and southern ranges of spruce have joined in the holocene the persistence of low spruce abundance in the transitional area is explained mainly by the strong anthropogenic deforestation ever since spruce grew there

climate and vegetation dynamics in the tundra and forest zone during the late glacial and holocene abstract analysis of palynological successions has enabled reconstruction of climate variations throughout the late glacial and holocene in the tundra and forest zones of northern eurasia statistical analysis allows estimation of mean annual precipitation and mean annual and july temperatures based on palynological assemblages thus the dynamic relationships between climate and vegetation changes can be established throughout the late glacial and holocene climate fluctuations were more dramatic in eastern europe than in siberia primarily as a result of the influence of westerly air masses in contrast the autochthonous climate of siberia dominated by local air masses was less prone to influence from climate changes elsewhere in the northern hemisphere and shows only an attenuated younger dryas signal mid holocene warming characterizes all of northern eurasia although the regions of siberia most influenced by continental climates show less pronounced cooling during the later holocene sharp changes between summer monsoonal and winter anti cyclonic regimes characterize the pacific maritime region

quasi static fault growth and cracking in homogeneous brittle rock under triaxial compression using acoustic emission monitoring this paper describes the localization of deformation acceleration in the period prior to dynamic failure in hornblende schist rock under triaxial compression using acoustic emission ae monitoring rather than stabilize the failure process by controlling axial stress to maintain a constant rate of ae for monitoring ae hypocenters as in previous works e g lockner et al 1991 we have instead developed a rapid multichannel data collection system this enables us to elucidate the dynamics of fault nucleation under condition of constant stress creep loading which is a better approximation to low strain rate condition in the earth and allows both quasi static and dynamic crack growth to occur the waveforms of more than 8000 ae events which occurred mainly during a 15 s period were recorded on 32 channels with a sampling rate of 50 ns and mask time of 200 s hypocentral locations of ae sources revealed that the fault initiated at one end of the core and then propagated into the unfaulted rock with a process zone fault front of intense cracking we found that there were two different processes operating during the quasi static nucleation of a shear fault namely a process zone in front of the fault tip and a wake of damage zone following the process zone the process zone had the following features 1 major tensile cracking 2 low b value and fewer larger events and 3 strong self excitation the mechanism of crack interaction and fault growth was therefore a mutual enhancement on dilatation due to tensile cracking on the other hand the damage zone was characterized by 1 major shear cracking 2 low b value and more larger events and 3 weak self excitation indicating that in the damage zone following the development of a shear fault linkage between cracks became the major mechanism of crack interaction and fault development the mutual changes of b value and self exciting strength observed in our experiments seem to occur as a result of the hierarchy of fault growth which was not observed under slowed down loading conditions therefore our experimental results under a realistic approximation of the dynamic condition of the earth are meaningful for the problems of earthquakes as well as rock bursts

simulating fracture and friction of aue granite under confined asymmetric compressive test using clumped particle model abstract fracture and friction behaviors of aue granite erzgebirge germany under confined asymmetric load are simulated using a clumped particle model in contrast to conventional circular bonded particle assemblies clumped particle models consist of groups of neighboring individual particles tied together to mimic unbreakable larger grains of irregular shape clumps an optimized clumped model is used for all calculations which is calibrated by the strength and deformation data from laboratory data of uniaxial and triaxial compression at a first order approximation the simulated fracture paths obtained from the clumped particle model match the observed fracture paths from laboratory experiments at various confinements under low confinement b values shows low b values in the fracturing regime and higher b values during stick slip and frictional sliding post failure regime which are in accordance with the laboratory findings

pv frontogenesis and upper tropospheric fronts abstract upper tropospheric fronts and frontogenesis are viewed from a potental vorticity pv perspective the rudiments of this approach are to regard such a front as a zone of strong pv gradient on isentropic surfaces and to treat the accompanying frontogenesis as the process whereby this gradient is enhanced on tropopause transcending isentropic surfaces a case study suggests that this concept of pv frontogenesis provides a concise dynamically based definition of upper level frontal zones and a compact and transparent approach for diagnosing the frontogenesis the concept provides fresh insight on the dynamics of the upper level fronts and has the potential to shed light on related phenomena and processes

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

late glacial and holocene landscape dynamics in the southern taiga zone of east european plain according to pollen and macrofossil records from the central forest state reserve valdai hills russia abstract new pollen and macrofossil data are presented from three peat mires in the central forest state biosphere reserve southern valdai hills russia significant changes were recorded in the vegetation during the late glacial and the holocene caused by climate changes three main stages of wetland development clearly determined in the southern valdai hills were attributed to the boreal the onset of subboreal and the last two centuries intensive peat accumulation and forest paludification were induced by increasing humidity as a result of shifts in precipitation evaporation rate and probably of cooling and increased rainfall evidence of agricultural activity in places in the vicinity of the territories with traditional land use is preserved in pollen records since 2500 14 c bp however the forest ecosystems of the reserve were not significantly disturbed by anthropogenic activity until the last 200 150 years effective agriculture was possible in the southern valdai hills only from the 18th century

vegetation pattern and sedimentation changes in the context of the lateglacial climatic events case study of staroje lake eastern belarus abstract a lake sediment core collected from the staroje lake southeastern belarus reveals significant changes of the terrestrial and limnic environmental during the lateglacial and early holocene in the periglacial zone of the late weichselian glaciation the combination of lithological loss on ignition palaeobotanical pollen non pollen palynomorphs diatoms and isotopic 18o 13c 14c proxy parameters was applied for the reconstruction of the vegetation pattern and sedimentation regime the lateglacial pre interstadial gs 2 vegetation was dominated by mineral soil pioneers with scattered occurrence of pinus and betula an interstadial gi 1 dominated by pinus forest with increasing representation of open ground species since approximately 13 500 cal bp and lateglacial stadial gs 1 with recurring opening of the vegetation pattern with scattered tree patches including those of picea presence of pinus stomata confirms the local origin of this plant since the pre interstadial starting from the holocene birch later accompanied by other deciduous species ulmus alnus quercus corylus took over in the local vegetation structure isotopic records 18o 13c obtained on bulk carbonates as well as diatom data exhibit several shifts reflecting variations both in terrestrial and limnic environment distinct negative excursion of 18o curve recorded during the first half of the gi 1 event suggests intensive groundwater discharge accompanied by active transportation of detrital carbon in to the basin limited basin productivity is also indicated by lithological and diatom records since approximately 13 700 cal bp sedimentation regime in the lake stabilised and productivity of the basin started to increase in positive correlation with loi data a considerable decrease in 18o values punctuated by a rapid jump in the middle of the interval was recorded during the gs 1 stadial and could be associated with the deterioration of the environmental regime and degradation of the soil layer increasing erosion activity alongside the rising input of detrital carbonates into the basin the water table was low as indicated by diatom data recovery of the environmental regime preceded the gs 1 holocene boundary as is seen in lithostratigraphical and isotopic data during the early holocene stable isotopes show several episodes with altered levels suggesting instability of the environmental regime most probably related with the global climatic alterations

multidisciplinary investigations including stable isotope studies of thick late glacial sediments from tory hill co limerick western ireland abstract multidisciplinary investigations of a 10 m long marl rich late glacial core from tory hill co limerick have enabled environmental change including estimates of summer temperature st to be reconstructed for the late glacial period the sequence opens with fine partially laminated silt clay that has varve like microstructure a cold steppic environment from the final phase of the pleniglacial is represented here it is estimated to span almost 2000 years ca 16 9 15 cal ka b p ca 14 6 12 7 ka b p substantial development of woody vegetation is limited to the early part of the late glacial interstadial cf bolling this consists mainly of juniper and birch including tree birch betula pubescens as well as herb dominated communities these developments in vegetation and also the evidence from a variety of other proxies including stable isotope records 18o and 13c show that the thermal maximum was achieved early in the interstadial but st probably did not exceeded 14 c within this relatively warm period the various biological chemical and physical proxies suggest at least one substantial but short lived climatic oscillation the later part of the bolling allerod interstadial after ca 14 cal ka b p ca 12 ka b p began with a considerable and more or less sustained fall in temperature the low temperature regime was maintained until immediately before the younger dryas when a modest but distinct amelioration is recorded by all proxies this feature referred to as a pre younger dryas warming pydw and which is seen in land ocean and greenland ice core records from the northeast atlantic region has not been previously highlighted in the literature the younger dryas stadial when st may have fallen to ca 6 c has a distinctive pollen assemblage characterised mainly by gramineae thalictrum and artemisia but for reasons not readily explainable the early part of the stadial is not well defined in the stable isotope record as in most records from the northeast atlantic region the transition to the holocene is sharp and clearly recorded the importance of juniperus in the irish late glacial record as an indicator of temperature change is discussed and also the possible role played by ephedra and secale species at tory hill the apparent absence of temperature gradients within ireland is commented on and the evidence for much lower st in ireland compared with great britain is discussed

relative stress variations as determined by b values from earthquakes in circum pacific subduction zones abstract assuming a relation of b to stress state the possibility of globe wide stress variation and transmission was investigated the noaa earthquake data file served to determine the temporal change in b of log n a bm from 1963 to 1975 periods of six to eight years are observed in the b values stress pattern for most circum pacific areas south america tonga kermadec new hebrides kamchatka and eastern aleutians in the kurils fore and aftershock sequences of large earthquakes seem to mask any characteristic global pattern that might exist these sequences exhibit low b values high stress through the time of foreshocks and early stages of aftershocks followed by rapid increase in b values decrease in stress use of a worldwide earthquake data file clearly yields less resolution of the temporal b variation than the use of local network studies published by other authors incidental to the study 1124 earthquakes of the noaa data file yield the ms mb relations ms 1 16mb 0 835 for 4 5 mb 6 and log10ms 0 1432mb 0 0629 formb 6 with correlative coefficients of 0 994 and 0 992 respectively

b value aseismic deformation and brittle failure within an isolated geological object evidences from a dome structure loaded by fluid extraction studies of b values are usually performed either at rock sample scale laboratory experiments or at crustal scale earthquakes but interpretations at crustal scale are extrapolated from small scale experimental laws with well defined boundary conditions to a larger object with no clear boundary conditions we examine variations of the b value in time and space at spatial loxlox10 km3 and temporal 20 years scales intermediate between laboratory analyses and tectonic processes in a dome structure that is an isolated geological object with defined boundaries and known geomechanical properties seismic activity about 1000 events with magnitude 4 4 5 and aseismic displacements 6 7 cm of cumulative subsidence have been induced by gas extraction in an area where no displacement had previously been reported we find no agreement between temporal variations in b values and results from laboratory experiments there is no correlation between b values and stress histories nor between b values and the spatial migration of seismicity aseismic slips introduce anomalies in b value behaviour when seismic instabilities are a second order process compared to the whole deformation these observations imply that when changes in b values have been used for earthquake forecasting false alarms can be explained by the occurrence of aseismic displacement

a constitutive law for low temperature creep of water saturated sandstones an accurate predictive model for the long term strength of the continental lithosphere is important in a range of geophysical and geodynamic problems while laboratory experiments are consistent with mohr coulomb brittle faulting in the cold upper continental crust there is increasing evidence that time dependent processes may also be important in these rocks even at low temperature however there is some ambiguity as to the exact form of the constitutive law for describing time dependent behavior of upper crustal rocks here we present results of room temperature creep experiments on a suite of water saturated sandstones spanning a range of petrophysical and rheological properties and underlying deformation mechanisms on physical and microstructural grounds our analysis suggests that a modified power law creep of the form a d f where d is the differential stress and f is the long term failure fundamental strength provides a more complete description of the experimental data in particular the parameters can be used to differentiate between sandstone types with a f and varying systematically with cementation state rock rheology and confining pressure the fundamental strength f for time dependent deformation varies much more than the other parameters of the distribution making it a potentially sensitive indicator of underlying creep mechanisms further tests would be needed to prove the constitutive law on a wider range of rock types and to prove that the three parameter model is statistically better in the general case

monitoring fracture propagation in a soft rock neapolitan tuff using acoustic emissions and digital images sudden and unexpected collapses of underground cavities below the city of naples italy represent a serious safety hazard the collapses occur due to the detachment of large blocks from the cavity roofs walls and pillars often a long time after the original quarry excavation has been completed it is recognised that existing discontinuities e g fractures play an important role in the failure process by inducing local stress concentrations and reducing the overall material strength the larger fractures which ultimately lead to collapse occur through interaction propagation and coalescence of these discontinuities this paper presents recent results of experiments carried out on natural dry specimens of neapolitan finegrained tuff tuff to investigate the mechanisms involved in sample failure a better understanding of fracture development and rock bridge behaviour is gained through a combination of ae and photographic monitoring in an experimental program considering samples with artificial pre existing heterogeneities which simulate the in situ discontinuities for a range of rock bridge geometries the mechanisms and timing of different stages of the failure process are identified and characterised the results show that in general a classical description of failure for samples without artificial flaws or with only a single flaw is followed 1 crack closure 2 linear stress strain response and crack initiation with stable crack growth 3 crack damage and unstable crack growth leading to failure for samples with two artificial pre existing flaws the third phase is split into two parts and failure of the sample occurs only after both the unstable propagation of external wing cracks and coalescence of the internal cracks in the bridge in terms of the timing and duration of each phase it is seen that phases 1 and 2 have little dependence on the flaw configuration but phase 3 seems to depend directly on this in particular the angle in rock bridge between the inner tips of the pre existing flaws plays a key role phase 3 is shorter for 120 than for 105 these differences by bridge rotation which appears to take longer than the simpler mode of failure for 120 it has only been possible to determine the time ranges of interest using the ae signatures whilst the photographs allow the fracture geometry evolution to be described additionally the frequency character of ae events is investigated and shown to have significant potential for characterisation of ae source types and thus failure processes

early holocene terrestrial climatic variability along a north atlantic island transect palaeoceanographic implications a synthesis of the early holocene climatic development in the north atlantic region is presented based on three previously published lake records from southern greenland lake n14 iceland lake torfadalsvatn and the faroe islands lake lykkjuvotn the interval 11500 8500 cal bp has been divided into five phases with respect to the inferred strength of the north atlantic current nac and irminger currents ic phase 1 11 500 10 750 cal bp was characterised by the first establishment of the nac and ic in the vicinity of the studied sites interrupted by the preboreal oscillation around 11 200cal bp phase 2 10 750 10 100 cal bp was marked by a further warming step in southern greenland rather concordant with a change into colder and more variable winters on the faroe islands it is proposed that this could partly be related to a series of melt water outbursts disturbing the thermohaline circulation in the eastern atlantic ocean resulting in a warming trend in the western region during phase 3 10 100 9400cal bp the strength of the ic reaching northwestern iceland intensified a more stable regime in surface circulation was established at the onset of phase 4 9400 8900 cal bp in southern greenland and was followed by a change towards further warm conditions on iceland at the onset of phase 5 8900 8500 cal bp c 2007 elsevier ltd all rights reserved

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

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

the study of barrier fracture in relation to earthquake and rockburst prediction one of the simplest models of earthquakes and rockbursts was studied in laboratory conditions in which the fracture was initiated in a barrier between two preexisting faults the treated models were built of concrete during the construction of the models the stress concentrators were inserted inside the models this arrangement enabled the shear displacement to occur during uniaxial loading of the model the tests were made on the series of models the sizes of which were mutually varying more than one order in the process of the barrier fracture propagation the following were investigated the time and space changes of local deformations as well as the acoustic emission velocities and amplitudes of elastic waves electrical conductivity and proper electro induction the process of barrier fracturing can be understood in three fundamental stages in the course of the first stage the density of small tensile cracks increases considerably while the volume in which they exist is gradually enlarged in the second stage as the result of these cracks coupling longer shear cracks are created during the coupling due to the development of numerous regions of unstable deformation the zones of nonequal rigidity arise in the treated medium distributed within it in a mosaic like pattern in the third stage the main fracture is prepared and formed with simultaneous unloading of the surrounding medium the process of crack forming is gradually localized into a more narrow zone

on the spatio temporal distribution of acoustic emissions in two granitic rocks under triaxial compression the role of pre existing cracks we used a new rapid data acquisition system to examine the role of pre existing crack density in determining the mechanical properties of crystalline rock two similar coarse grained samples tsukuba granite tg and granitic porphyry gp were used in triaxial compression tests the main difference between the two rocks is that tg contains main large pre existing cracks whereas gp is almost crack free in our tests the two rocks showed significantly different behaviors in gp before the fault nucleation ae activity was low and showed increasing b values with increasing stress but in tg a large number of aes were observed and showed short term b value anomalies mutual fluctuations on a decreasing background the short term fluctuations of b values are closely correlated with those of the spatio temporal clustering of ae locations our results demonstrate 1 pre existing cracks are the most dominant factor of all heterogeneities that govern the fault nucleation process in laboratory rock samples 2 failure predictability is dependent on the pre existing crack density

acoustic emissions document stress changes over many seismic cycles in stick slip experiments 1 the statistics of large earthquakes commonly involve large uncertainties due to the lack of long term robust earthquake recordings small scale seismic events are abundant and can be used to examine variations in fault structure and stress we report on the connection between stress and microseismic event statistics prior to the possibly smallest earthquakes those generated in the laboratory we investigate variations in seismic b value of acoustic emission events during the stress buildup and release on laboratory created fault zones we show that b values mirror periodic stress changes that occur during series of stick slip events and are correlated with stress over many seismic cycles moreover the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop consequently b value variations can be used to approximate the stress state on a fault a possible tool for the advancement of time dependent seismic hazard assessment citation goebel t h w d schorlemmer t w becker g dresen and c g sammis 2013 acoustic emissions document stress changes over many seismic cycles in stick slip experiments geophys res lett 40 2049 2054 doi 10 1002 grl 50507

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form

inferring in situ stress changes by statistical analysis of microseismic event characteristics two commonly estimated fractal dimensions called b and d values represent statistical characteristics in the distribution of magnitude sizes b and spatial hypocenter locations d of microseismic events respectively we establish that the values of these two dimensions are related to specific stress regimes through the case study of a heavy oil field drained using cyclic steam stimulation we infer that the measured temporal variation in fractal dimension b is most likely due to significant changes in the local stress regime over a seven month period ranging from extensional faulting fractures opening via a strike slip regime to finally compressive faulting fractures closing the fracture dimension d indicates predominantly planar to spherical hypocenter spatial distributions in the first and last stages but changes to a more linear to planar spatial pattern in the intermediate strike slip regime when the vertical stress is anticipated to be in between the maximum and minimum horizontal stre