the effect of rupture complexity on estimates of source size a general technique is proposed for estimating rupture geometry from measurements of body wave durations wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent respectively the complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity the shear waves radiated by eight moderate 3 6 ml 4 9 multiply recorded aftershocks of the 1975 oroville california earthquake are analyzed using measurements of the corner frequency the characteristic frequency the pulse duration and the signal duration comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size the difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases

climate records covering the last deglaciation the oxygen 18 oxygen 16 ratio of molecular oxygen trapped in ice cores provides a time stratigraphic marker for transferring the absolute chronology for the greenland ice sheet project gisp ii ice core to the vostok and byrd ice cores in antarctica comparison of the climate records from these cores suggests that near the beginning of the last deglaciation warming in antarctica began approximately 3000 years before the onset of the warm bolling period in greenland atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

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

source parameters of intermediate depth vrancea romania earthquakes from empirical green s functions modeling abstract several source parameters source dimensions slip particle velocity static and dynamic stress drop are determined for the moderate size october 27th 2004 mw 5 8 and the large august 30th 1986 mw 7 1 and march 4th 1977 mw 7 4 vrancea romania intermediate depth earthquakes for this purpose the empirical green s functions method of irikura e g irikura k 1983 semi empirical estimation of strong ground motions during large earthquakes bull dis prev res inst kyoto univ 33 part 2 no 298 63 104 irikura k 1986 prediction of strong acceleration motions using empirical green s function in proceedings of the 7th japan earthquake engineering symposium 151 156 irikura k 1999 techniques for the simulation of strong ground motion and deterministic seismic hazard analysis in proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering integrated training in earthquake risk reduction practices kefallinia 453 554 is used to generate synthetic time series from recordings of smaller events with 4 mw 5 in order to estimate several parameters characterizing the so called strong motion generation area which is defined as an extended area with homogeneous slip and rise time and for crustal earthquakes corresponds to an asperity of about 100 bar stress release miyake h t iwata and k irikura 2003 source characterization for broadband ground motion simulation kinematic heterogeneous source model and strong motion generation area bull seism soc am 93 2531 2545 the parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and msk intensity pattern inversion for the 1977 event using a genetic algorithm the strong motion recordings of the analyzed vrancea earthquakes as well as the msk intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas which corresponds to small asperities with high stress drops 300 1200 bar and high particle velocities 3 5 m s these results imply a very efficient high frequency radiation which has to be taken into account for strong ground motion prediction and indicate that the intermediate depth vrancea earthquakes are inherently different from crustal events

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

modeling north american freshwater runoff through the last glacial cycle the northern hemisphere ice sheets decayed rapidly during deglacial phases of the ice age cycle producing meltwater fluxes that may have been of sufficient magnitude to perturb oceanic circulation the continental record of ice sheet history is more obscured during the growth and advance of the last great ice sheets ca 120 000 20 000 yr b p but ice cores tell of high amplitude millennial scale climate fluctuations that prevailed throughout this period these climatic excursions would have provoked significant fluctuation of ice sheet margins and runoff variability whenever ice sheets extended to mid latitudes giving a complex pattern of freshwater delivery to the oceans a model of continental surface hydrology is coupled with an ice dynamics model simulating the last glacial cycle in north america meltwater discharged from ice sheets is either channeled down continental drainage pathways or stored temporarily in large systems of proglacial lakes that border the retreating ice sheet margin the coupled treatment provides quantitative estimates of the spatial and temporal patterns of freshwater flux to the continental margins results imply an intensified surface hydrological environment when ice sheets are present despite a net decrease in precipitation during glacial periods diminished continental evaporation and high levels of meltwater production combine to give mid latitude runoff values that are highly variable through the glacial cycle but are two to three times in excess of modern river fluxes drainage to the north atlantic via the st lawrence hudson and mississippi river catchments averages 0 356 sv for the period 60 000 10 000 yr b p compared to 0 122 sv for the past 10 000 yr high amplitude meltwater pulses to the gulf of mexico north atlantic and north pacific occur throughout the glacial period with ice sheet geometry controlling intricate patterns of freshwater routing variability runoff from north america is staged in the final deglaciation with a stepped sequence of pulses through the mississippi st lawrence arctic and hudson strait drainages

statistics of small earthquakes and frequency of occurrence of large earthquakes along the mexican subduction zone abstract the validity of the gutenberg richter g r frequency magnitude relation over a wide range of magnitudes is usually accepted and the statistics of small earthquakes is often extrapolated to predict the frequency of occurrence of large earthquakes we take noaa and pde data from 1963 to 1981 related to the mexican subduction zone h 65 km and convert m b to m s in the range of 3 3 m b 5 7 for this conversion we use regression of m s on m b for mexican and central american events as well as an m s m b regression based on worldwide data wyss and habermann 1982 we also take into account the standard error in m s this may be important since the number of events decreases as m b increases the m s data of 18 5 yr is normalized to 75 5 yr and is compared to the statistics of observed large earthquakes m s 6 4 for the period 1906 to 1981 it is found that the g r relation in the range 4 5 m s 6 0 when extrapolated grossly underestimates the observed frequency of large earthquakes m s 6 5 for the oaxaca and jalisco regions there is strong evidence that the plate interface in the oaxaca region consists of a few 3 or 4 large fault zones each of which cyclically ruptures over its entire dimension without giving rise to smaller events in the manner implied by the g r relation the result is of profound importance in seismic risk analysis and in the understanding of fault mechanics this phenomenon has been reported for only a few regions e g turkey bath 1981 japan wesnousky et al 1983 it may have escaped detection in other regions due to a variety of causes the most important being the long recurrence periods of large earthquakes

on the hydrological cycle under paleoclimatic conditions as derived from agcm simulations the atmospheric hydrological cycle is compared for different time slices of the late quaternary simulations have been conducted with an atmospheric circulation model at t42 resolution and we have performed a global evaluation of the atmospheric water vapor transport the water export from the atlantic catchment area important for driving the large scale thermohaline ocean circulation is analyzed in detail for the last glacial maximum lgm we examine the model s sensitivity with respect to tropical cooling relative to the climap reconstruction which is motivated by recent data we find that the lgm experiment with tropical cooling is in better agreement with proxy data available our experiments indicate that the water vapor transport is strongly affected by three mechanisms continental drying eddy moisture transport and changes in the tropical circulation except for the continental drying and the blocking effect of the laurentide ice sheet the hydrological cycle is substancially different for both lgm experiments we find that the hydrological system is rather sensitive to tropical temperature change which is important to understand paleoclimate and future climate changes

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

the last glacial maximum climatic conditions on easter island abstract the aim of this paper is to refine previous estimates of last glacial maximum lgm climatic conditions for easter island samples were analysed for fossil pollen from the lower half of a 13 40 m sediment core rra5 this part of the core includes a time span from ca 28 000 10 000 14 c bp the results show that during this period there were three different climatic conditions first a time span from ca 28 000 23 200 14 c bp with slightly cooler and probably drier conditions relative to present day second a more cool and dry climatic condition from ca 23 200 14 700 14 c bp the second time span had two peak points at ca 22 100 and 17 150 14 c bp it seems that the coolest and driest conditions occurred at 17 150 14 c bp third a warm and wet climate started at ca 15 000 14 c bp and continued until the end of the period studied 10 000 14 c bp in all the time covered in this study there was an inverse relationship between values of palmae and poaceae while poaceae and tubuliflorae shrubs show similar variations the temperature estimations that are presented by different authors based on oxygen isotopes are for approximately 4 c cooling at the lgm however the empirical values derived from the pollen evidence suggest only ca 1 9 c cooling this is in agreement with recently obtained values from tropical lowlands

glacial surface temperatures of the southeast atlantic ocean a detailed record of sea surface temperature from sediments of the cape basin in the subtropical south atlantic indicates a previously undocumented progression of marine climate change between 41 and 18 thousand years before the present ky b p during the last glacial period whereas marine records typically indicate a long term cooling into the last glacial maximum around 21 ky b p consistent with gradually increasing global ice volume the cape basin record documents an interval of substantial temperate ocean warming from 41 to 25 ky b p the pattern is similar to that expected in response to changes in insolation owing to variations in earth s tilt

earthquake recurrence of a particular type the recurrence relation for turkish earthquakes expressed as the single frequency versus magnitude dependence exhibits significant maxima and minima reflecting true physical conditions various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity the results may be applicable to regions with high seismicity

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

seismic fluids and percolation theory we present a first attempt at a quantitative assessment of seismic fluid flux it is assumed that during an earthquake slipped regions experience transient high permeability high porosity and high pressure gradients which rapidly redistribute fluid we use percolation theory to model the size distribution of such slip planes interseismic fluid migration along background pressure gradients is ignored to render the problem tractable we make a number of assumptions regarding fluid movement fluid is transported from a well supplied reservoir across the fault plane to an efficient sink the system reaches steady state with a linear fluid concentration function across the fault using probability methods we obtain a simple relation between fluid flux slip rate and fracture porosity it is then a straightforward matter to calculate the total seismic fluid throughput for a region such estimates agree well with water rock ratio and other data

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

glacial terminations as southern warmings without northern control the timing and mechanisms of the transition from a glacial to an interglacial state are controversial an analysis of antarctic ice core records indicates that glacial terminations may begin as millennial scale warmings in the southern hemisphere that unlike previous events are not reversed by abrupt warming in the northern hemisphere

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

fracture coalescence as a mechanism for earthquakes observations based on mining induced microseismicity abstract microseismic events with magnitudes less than zero recorded within a volume at depth in an underground mine are used to evaluate failure conditions associated with a magnitude 2 9 event rockburst the approach incorporated several independent methods of analysis including the principal component analysis pca of seismicity focal mechanisms stress inversion underground in situ stress measurements and structural mapping and three dimensional numerical modelling derived stresses a good correlation was found between stress inversion and pca derived microseismic failure planes and structural mapping and between the in situ principal stress orientations and those obtained through stress inversion and numerical modelling a few days prior to the large event and during the aftershock sequence a change in microseismic failure plane orientation to a shallower dip angle than mapped underground was found to coincide with the numerical modelling derived plane of maximum slip potential this orientation along with measured fracture characteristics persistence and spacing and an increase in event clustering into the plane suggests that the formation of the large event plane of rupture was likely related to the coalescence of mapped fractures an observed reduction in stress release accompanying the increased tendency towards planarity prior to the large event indicates that the development of a large rupture surface occurred under an increased effective shear stress build up as part of the earthquake generation process and the process of coalescence can be considered as the breakage of barriers new fracture growth accompanied by an increase in the effective shear stress on the remaining asperities pre existing fractures

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

reconciling bolling warmth with peak deglacial meltwater discharge paleoclimatic data indicate warm conditions during the bolling period whereas climate modeling studies predict significant cooling triggered by the concomitant deglacial meltwater flux into the atlantic ocean we suggest that the lack of an adequate representation of deep water flow over the greenland scotland ridge in ocean circulation models can account for this discrepancy

asperity distribution and percolation as fundamentals of an earthquake cycle abstract a seismic cycle model is proposed based on the existence of an asperity space strength distribution along the fault plane and the applicability of the percolation theory to earthquakes as suggested by vrancea seismotectonic data two seismic regions somewhat decoupled are emphasized in the lower lithosphere roughly between 80 and 110 km and between 120 and 170 km depth and an asperity magnitude quasi independent dimension of 0 3 0 4 km is determined for small to moderate earthquakes accordingly two concepts are introduced 1 the active zone a distinct fault region able to generate a major earthquake by percolation and characterized by a specific background seismicity total area and maximum possible magnitude 2 the asperity cell an elementary local stress inhomogeneity of an active zone generating weak to moderate events percolation requires the presence of a critical stress free surface 44 of the active zone area the model explains the non linearity of the frequency magnitude relationship and enables the estimation of the major earthquake magnitude domain in each zone the computed maximum possible magnitudes are mw 7 6 and mw 7 8 respectively in agreement with historical data a complex form of the recurrence period of earthquakes in the major magnitude domain is determined ranging from about 40 to 100 years irrespective of the seismic zone it follows that the seismic activity per unit area is invariant in both zones this result is considered to be a consequence of an intrinsic material property the scale invariance of the fragmentation process in the lithospheric material different aspects related to the discrete structure of the active zone and the fractal dimension of faulting are also discussed from the point of view of this model

the glacial thermohaline circulation stable or unstable 1 the stability of the glacial thermohaline circulation thc with respect to north atlantic freshwater input is examined using a global ocean general circulation model it is found that the quasi equilibrium hysteresis behaviour is much less pronounced under glacial conditions than under present day conditions and the existence of multiple equilibria requires an anomalous freshwater inflow the results may help to assess the effect of iceberg invasions and meltwater events suggesting that the thc is prone to instability during a deglaciation phase when the atlantic meridional overturning is weakened under full glacial conditions however the thc is mono stable and even extreme freshwater pulses are unable to exert a persistent effect on the conveyor

numerical simulation of the earthquake generation process a numerical algorithm is proposed for the simulation of the earthquake process during a seismic cycle the algorithm is based on a heterogeneous discrete model of the fault plane and assumes there are two kinds of seismicity background crack like earthquakes and asperity like events an active zone of the fault contains an asperity distribution with a characteristic elementary area the background seismicity randomly develops shear stress free surfaces which tend to surround the asperities as in a 2d percolation process the model parameters are taken from observations on the vrancea romania intermediate depth seismic region the results emphasize the significant role of the geometry in the mechanism of the seismic failure the algorithm predicts the nonlinear behavior in the frequency magnitude distribution the decrease of theb slope associated with the asperity like events the magnitude range of major earthquakes and their recurrence times

influence of vertical mixing on the thermohaline hysteresis analyses of an ogcm the thermohaline hysteresis response to varying north atlantic freshwater forcing is studied by means of a three dimensional global ocean general circulation model ogcm the influence of vertical diffusivity is examined using a wide range of mixing coefficients for sufficiently large vertical diffusivity the model shows a pronounced hysteresis behavior so that two equilibrium states of the thermohaline circulation are found one mode with intense deep water formation in the north atlantic on mode and one mode with strongly reduced convective activity off mode by decreasing the diffusivity the two branches of the hysteresis merge in addition the effect of numerical diffusion is analyzed by applying different advection schemes a positive feedback between overturning strength and the numerical diffusivity of upstream advection is found resulting in a reduced stability of the on mode comparing the results with those from zonally averaged models exhibits substantial differences regarding the stability properties of the thermohaline circulation freshwater transports by horizontal gyres have an important effect on the overturning circulation in the ogcm

greenland temperature response to climate forcing during the last deglaciation greenland ice core water isotopic composition 18 o provides detailed evidence for abrupt climate changes but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns we investigate greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean atmosphere climate model contrary to the traditional 18 o interpretation the younger dryas period was 4 5 2 c warmer than the oldest dryas due to increased carbon dioxide forcing and summer insolation the magnitude of abrupt temperature changes is larger in central greenland 9 to 14 c than in the northwest 5 to 9 c fingerprinting a north atlantic origin simulated changes in temperature seasonality closely track changes in the atlantic overturning strength and support the hypothesis that abrupt climate change is mostly a winter phenomenon

early cretaceous gangdese retroarc foreland basin evolution in the selin co basin central tibet evidence from sedimentology and detrital zircon geochronology the selin co basin in the northern lhasa terrane includes more than 3000 m of upward coarsening lower cretaceous strata and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc uranium lead u pb ages were determined for 435 detrital zircons from the lower cretaceous strata in the selin co basin relative probability of detrital zircon ages shows the eshaerbu formation was rich in zircon grains with the age of 125 140 and 160 180 ma and the duoni formation was dominated by one main age cluster of 125 150 ma analysis of the potential provenances suggests the early cretaceous zircon grains were primarily derived from the gangdese magmatic arc to the south the youngest zircon ages in the lowermost exposure of the eshaerbru formation are c 130 ma providing a maximum depositional age of sediments in the selin

spatial seismicity variations and asperities in the new hebrides seismic zone the term asperity has been used in many recent studies to describe sections of faults with higher strength than the surrounding zones the level of background seismicity expected in such zones is unclear they may appear as quiet zones because of high strength or active zones because of high stress in this work the problem of seismicity levels in asperities is addressed by identifying regions of anomalously high or low seismicity and comparing the locations of these regions with the locations of asperities as determined from other observations the regions of anomalously high or low seismicity are identified using a quantitative technique which relies on spatial rate comparisons done with the z test for a difference between two means this technique allows the determination of the significance of spatial rate differences and the uniqueness of zones of outstanding seismicity four active zones which make up 10 and eight quiet zones which make up 16 of the length of the new hebrides seismic zone were recognized using this technique asperities in the new hebrides seismic zone were identified using characteristics which include large event initiation and stopping clusters of aftershocks and moderate events foreshock activity and earthquake stress drops eight regions which showed two or more of these characteristics were identified they make up 34 of the length of the seismic zone the overlap between the asperities and the active and quiet regions provides a test of possible relationships between these zones thirty four percent of the asperity area is active as opposed to the 10 expected and 6 of the asperity area is quiet as opposed to the 16 expected this suggests that in the asperities in the new hebrides seismic zone stress concentration overcomes increased strength and that phenomena other than increased strength can cause seismic quiescence nearly all of the asperities in the new hebrides seismic zone show high background seismicity or high stress drops which suggests that likely zones of mainshock initiation can be identified using background seismicity

source parameters of mining induced seismic events an evaluation of homogeneous and inhomogeneous faulting models for assessing damage potential source parameter estimates based on the homogeneous and inhomogeneous source models have been examined for an anomalous sequence of seven mine induced events located between 640 and 825 m depth at strathcona mine ontario and having magnitudes ranging betweenmn 0 8 and 2 7 the derived brune static stress drops were found to be similar to those observed for natural earthquakes 30 bars whereas dynamic stress drops were found to range up to 250 300 bars source radii derived from madariaga s model better fit documented evidence of underground damage these values of source radii were similar to those observed for the inhomogeneous model the displacement at the source based on the observed attenuation relationship was about 60 mm for three magnitude 2 7 events this is in agreement with slip values calculated using peak velocities and assuming the asperity as a brune source within itself 72 mm by using madariaga s model for the asperity the slip was over 3 times larger than observed peak velocity and acceleration scaling relations with magnitude were investigated by incorporating available south african data appropriately reduced to canadian geophysical conditions the dynamic stress drop scaled as the square root of the seismic moment similar to reported results in the literature for crustal earthquakes this behavior suggests that the size of the asperities responsible for the peak ground motion with respect to the overall source size follow distributions that may be similar over a wide range of magnitudes measurements of source rupture complexity ranging from 2 to 4 were found to agree with estimates of overall source to asperity radii suggesting together with the observed low rupture velocities 0 3 to 0 6 that the sources were somewhat complex validation of source model appropriateness was achieved by direct comparison of the predicted ground motion level to observed underground damage in creighton mine located within the same regional stress and geological regime as strathcona mine close to the source 100 m corresponding to relatively higher damage levels a good agreement was found between the predicted peak particle velocities for the inhomogeneous model and velocities derived based on established geomechanical relationships the similarity between asperity radii and the regions of the highest observed damage provided additional support for the use of the inhomogeneous source model in the assessment of damage potential

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

stress in the descending relic slab beneath the vrancea region romania we examine the effects of viscous flow phase transition and dehydration on the stress field of a relic slab to explain the intermediate depth seismic activity in the vrancea region a 2 d finite element model of a slab gravitationally sinking in the mantle predicts 1 downward extension in the slab as inferred from the stress axes of earthquakes 2 the maximum stress occurring in the depth range of 70 km to 160 km and 3 a very narrow area of the maximum stress the depth distribution of the annual average seismic energy released in earthquakes has a shape similar to that of the depth distribution of the stress in the slab estimations of the cumulative annual seismic moment observed and associated with the volume change due to the basalt eclogite phase changes in the oceanic slab indicate that a pure phase transition model cannot solely explain the intermediate depth earthquakes in the region we consider that one of the realistic mechanisms for triggering these events in the vrancea slab can be the dehydration of rocks which makes fluid assisted faulting possible

synchronous timing of abrupt climate changes during the last glacial period abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records but our understanding of their absolute timing and regional synchrony is incomplete our compilation of 63 published independently dated speleothem records shows that abrupt warmings in greenland were associated with synchronous climate changes across the asian monsoon south american monsoon and european mediterranean regions that occurred within decades together with the demonstration of bipolar synchrony in atmospheric response this provides independent evidence of synchronous high latitude to tropical coupling of climate changes during these abrupt warmings our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice core chronologies

a renormalization group approach to the stick slip behavior of faults we treat a fault as an array of asperities with a prescribed statistical distribution of strengths when an asperity fails the stress on the failed asperity is transferred to one or more adjacent asperities for a linear array the stress is transferred to a single adjacent asperity and for a two dimensional array to three adjacent asperities using a renormalization group rg method we investigate the properties of a scale invariant hierarchical model for the stochastic growth of fault breaks through induced failure by stress transfer an extrapolation to arbitrarily large scales shows the existence of a critical applied stress at which the solutions bifurcate at stresses less than the critical stress virtually no asperities fail on a large scale and the fault is locked above the critical stress asperity failure cascades away from the nucleus of failure we interpret this catastrophic failure as an earthquake and it corresponds to the transition from stick to slip behavior on the fault thus the stick slip behavior of most faults can be attributed to the distribution of asperities on the fault we propose our stochastic mechanism as an alternative to the traditional hypotheses for the stick slip behavior of faults a major advantage of our approach is the inclusion of scale invariance thus the observed frequency magnitude relation for seismicity is a natural consequence of our basic hypothesis

frequency moment distribution of earthquakes in the aleutian arc a test of the characteristic earthquake model the frequency moment distribution of earthquakes is derived for discrete regions of the entire aleutian arc both for segments which have ruptured in historic times and those regions which have been identified as seismic gaps this distribution is then compared to the moment of the largest event in the respective region or for gaps the largest event which is likely to occur based on a plate kinematic model of accumulated moment data for this study are based upon three data sources instrumental data are utilized for the 18 yr subsequent to the establishment of the world wide standardized seismograph network wwssn data for events of magnitude 7 and greater have been carefully collected and are presumed to be complete for the time period 1899 to present the last data set is comprised of the largest event in each region either an actual earthquake or the moment estimate based on current plate slip rates data were normalized to the recurrence time of the largest event in the respective zone in all cases the data seriously underestimate the largest moment event indicating that a characteristic earthquake model is appropriate for individual fault zones however if the data are combined for the entire arc the largest event is closely predicted this indicates that a b value model may be utilized only for regions in which there is a distribution in the size of earthquake producing faults

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

depth distribution of local stress inhomogeneities in the vrancea region romania corrected displacement amplitude spectra of weak and moderate ml 2 5 5 0 vrancea earthquakes h 0 201 km exhibit an obvious shape with two comer frequencies and two slopes this behavior is related to local inhomogeneities within the seismic zone and a heterogeneity parameter e is defined as the fraction of the complete stress drop released during earthquake barrier model or the ratio of the asperity to source radii asperity model the parameter e is evaluated as the ratio of the first corner frequency versus the second one and it ranges from 0 50 to 0 15 the heterogeneity appears to increase with increasing magnitude e decreases suggesting that the earthquakes represent the failure of asperities this behavior is not evident for the events in the 30 50 km depth interval a mostly crack origin of earthquakes in this zone is suggested this region is found to be more homogeneous and able to decouple the seismic activities in the crust and sinking slab the depth distribution of local inhomogeneities within the region is heterogeneous the crust and two intermediate depth intervals 90 110 km and 120 160 km are the most heterogeneous and have occurrence potential for moderate earthquakes the two intermediate zones show the highest activities which are slightly decoupled due to a more homogeneous layer 110 120 km

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

frequency magnitude distribution of earthquakes in vrancea relevance for a discrete model a high resolution analysis of a homogeneous and complete data set of intermediate depth microearthquakes h 60 km extending over an interval of 9 3 years emphasizes a significant deviation at low magnitudes ml 4 in a linear frequency magnitude distribution it appears as a distinct change in the slope of the cumulative distribution and as a seismicity deficit followed by a relative enhancement in the corresponding noncumulative curve this is in agreement with the presence of two characteristic mechanisms and allows the identification of both the magnitude threshold of asperity like earthquakes and the transition zone ml 3 3 3 9 from crack like earthquakes background seismicity to asperity like events these features are better pointed out on well individualized active zones the background seismicity shows a tremendeous decrease in its b slope from 1 03 to 0 57 during a 6 year interval before the occurrence of a major earthquake in 1986 mw 7 3 followed by a fast recovery to 1 03 in 2 years after this event such a behavior could be correlated to the continuous growth of the shear stress free surface on the fault as in a percolation process followed by its sudden diminution due to the locking of the fault the above results provide relevance for the discrete character of faulting and enable a coherent modeling of the earthquake generation process from microearthquake to major event scale lengths

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases