glacial to holocene implications of the new 27000 year dust record from the epica dome c east antarctica ice core insoluble dust concentrations and volume size distributions have been measured for the new 581 m deep dome c epica ice core antarctica over the 27000 years spanned by the record microparticle measurements from 169 levels to date confirm evidence of the drastic decrease in bulk concentration from the last glacial maximum lgm to the holocene interglacial by a factor of more than 50 in absolute value and of about 26 in flux unique new features revealed by the epica profile include a higher dust concentration during the antarctic cold reversal phase acr by a factor of 2 with respect to the holocene average this event is followed by a well marked minimum that appears to be concomitant with the methane peak that marks the end of the younger dryas in the northern hemisphere particle volume size distributions show a mode close to 2 m in diameter with a slight increase from the lgm to the holocene the lgm holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 m it changes from 50 to 6 glacial samples are characterised by well sorted particles and very uniform distributions while the interglacial samples display a high degree of variability and dispersion this suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into antarctica in the holocene than during glacial times assuming that southern south america remained the main dust source for east antarctica over the time period studied the higher dust content recorded during the acr which preceded the younger dryas period represents evidence of a change in south america environmental conditions at this time a wet period and likely mild climate in south america is suggested at circa 11 5 11 7 kyr bp corresponding to the end of the younger dryas the holocene part of the profile also shows a slight general decrease in concentration but with increasingly large particles that may reflect gradual changes at the source

10 be in ice at vostok antarctica during the last climatic cycle we have previously reported accelerator mass spectrometer measurements of the cosmogenic isotope 10be half life 1 5 myr in an 906 m ice core recovered at dome c antarctica1 in addition to an enhanced concentration during a period of reduced solar activity maunder minimum ad 1645 1715 2 we found substantially increased concentrations during that part of the core corresponding to the last ice age both effects have been confirmed and extended in greenland ice cores3 4 the recovery of a 2 083 m ice core at vostok antarctica5 together with an extended oxygen isotope chronology reported elsewhere in this issue6 permits an extension of 10be studies over the whole of the last climatic cycle 125 kyr we report here such measurements which show an excellent correlation with the oxygen isotope and thus presumably climate record over the whole of this period the results imply that precipitation rates in the antarctic during the last interglacial were similar to those of the holocene but were roughly halved during the last glaciation

teleseismic lg of semipalatinsk and novaya zemlya nuclear explosions recorded by the grf grafenberg array comparison with regional lg brv and their potential for accurate yield estimation acomparison of regional and teleseismic log rms root mean square lgamplitude measurements have been made for 14 underground nuclear explosions from the east kazakh test site recorded both by the brv borovoye station in kazakhstan and the grf grafenberg array in germany the log rmslgamplitudes observed at the brv regional station at a distance of 690 km and at the teleseismic grf array at a distance exceeding 4700 km show very similar relative values standard deviation 0 048 magnitude units for underground explosions of different sizes at the shagan river test site this result as well as the comparison of brv rmslgmagnitudes which were calculated from the log rms amplitudes using an appropriate calibration with magnitude determinations forpwaves of global seismic networks standard deviation 0 054 magnitude units point to a high precision in estimating the relative source sizes of explosions from lg based single station data similar results were also obtained by other investigators patton 1988 ringdalet al 1992 usinglgdata from different stations at different distances

calibration of mb pn mb lg scales and transportability of the m0 mb discriminant to new tectonic regions we have developed mo mb relationships for earthquakes and explosions in central asia using regional waveform data from the chinese broadband digital station wmq regional magnitude scales mb pn and mb lg were established by 1 determining the attenuation rates of pn and lg waves 2 calibrating the mb pn against the teleseismic rob and 3 applying nuttli s method to determine m b from the lg waves seismic moments for earthquakes and explosions were obtained by applying the bolt and herraiz 1983 method calibrated using cmt moments for earthquakes and regional moment estimates of the soviet joint verification experi ment jve explosion the results show that mo mb pn relationships for central asian earthquakes and explosions are in excellent agreement with the relationships for the western united states this demonstrates that the mo r discriminant is transportable to other regions and supports theoretical claims patton and walter 1993 that mo m b are directly comparable for explosions detonated in different emplacement media successful application depends upon correcting the mb pn for the magnitude bias known to exist between the shagan river test site and the nevada test site nts in general region specific mb bias must be accounted for whenever regional mag nitude scales are calibrated against teleseismic rob as pointed out by douglas and marshall 1996 transporting mo mb lg can be problematic because attenuation rates based on coda waves or lg waves from earthquakes may not necessarily apply to lg waves from explosions and vice versa this is demonstrated for the western united states where the coda q measured from explosion data is much lower than the coda q from earthquake data we show that mb lg for earthquakes located close to nts is greatly overestimated using the q values determined from the coda of nts explosions this is apparently not a problem for lg calibration in central asia perhaps because of differences in velocity and or q structures for the two regions other important considerations are the character of lg propagation on short paths 400 km for nts explosions versus long paths 1000 kin for east kazakh explosions and the properties of coda wave spreading as a function of distance and velocity structures for different tectonic regions

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

late quaternary grounded ice extent in the filchner trough weddell sea antarctica new marine geophysical evidence the last glacial maximum lgm ca 23 19 ka bp extent of grounded ice in the filchner trough a major cross shelf trough extending seaward from the filchner ice shelf in the southern weddell sea has been much debated here we present data from the first extensive multibeam swath bathymetry and sub bottom acoustic profiling surveys in the filchner trough that include several parallel survey lines with overlapping swaths we interpret these new data combined with published observations and radiocarbon dates from sediment cores as indicating that the grounding line in the filchner trough during the lgm advanced beyond the middle shelf probably to within 40 km of the shelf break and possibly reached the shelf break three different hypotheses are discussed that could reconcile this interpretation with interpretations based on ice coring and surface exposure age data that lgm ice surface elevations in areas draining into the filchner and ronne ice shelves were no more than a few hundred metres higher than today 1 ice plain conditions extended along most of the filchner trough 2 the ice shelf advanced and thickened so that it touched down on the continental shelf for a short period 3 lgm ice drainage pathways in the interior of the weddell sea embayment were different from those observed today

regional seismic characteristics of the 9 october 2006 north korean nuclear test we investigate the regional seismic signature of the 9 october 2006 north korean nuclear test broadband regional data for the nuclear test and a group of earthquakes close to the test site were obtained between december 2000 and no vember 2006 epicentral distances from the stations to the test site are between 371 and 1153 km we first use these regional events to calibrate the lg wave magnitude in the network then the network is used to calculate mblg 3 93 for the north ko rean nuclear explosion using a modified fully coupled magnitude yield relation the yield of the north korean nuclear test is estimated to be 0 48 kt because of large uncertainties in the source depth the estimate is preliminary the p s type spectral ratios pg lg pn lg and pn sn are calculated for the nuclear explosion and a group of earthquakes close to the test site at frequencies above 2 hz the network averaged p s spectral ratios clearly separate the 9 october 2006 explosion from the regional earthquakes our result indicates that a single blast explosion in the north korea re gion shows different seismic characteristics from an earthquake any well coupled single blast explosion detonated in this region with yield similar to that for the north korean nuclear test has a large probability of being identified by a regional seismic network such as the one adopted in this study

modeling the evolution of antarctic ice sheet over the last 420 000 years implications for altitude changes in the vostok region a new thermomechanical three dimensional model designed to simulate the evolution of the antarctic ice sheet over long time periods is presented this model incorporates the various types of ice flow found in antarctica relatively slow inland ice flow that is essentially due to ice deformation fast ice flow in the regions with ice streams and ice shelf flow by coupling these three types of flow it is possible to predict grounding line migration simulations covering four glacial interglacial cycles have been conducted by forcing this model with a temperature record from vostok and a sea level record from marine cores our findings indicate that grounding line migration induced by sea level changes is the primary factor governing the evolution of the antarctic ice volume on the other hand the altitude of the ice sheet surface at vostok is driven by accumulation rate variations the amplitude of the altitude change does not exceed 150 m and is very similar for all the sites located on the antarctic plateau

synchronizing ice cores from the renland and agassiz ice caps to the greenland ice core chronology 1 four ice cores from the agassiz ice cap in the canadian high arctic and one ice core from the renland ice cap in eastern greenland have been synchronized to the greenland ice core chronology 2005 gicc05 which is based on annual layer counts in the dye 3 grip and ngrip ice cores volcanic reference horizons seen in electrical conductivity measurements ecm have been used to carry out the synchronization throughout the holocene the agassiz ice cores have been matched to the ngrip ice core ecm signal while the renland core has been matched to the grip ice core ecm signal thus tying the cores to gicc05 furthermore it has been possible to synchronize the renland ice core to ngrip gicc05 in the glacial period back to 60 000 years b2k years before a d 2000 on the basis of a matching of transitions between stadials and interstadials this work brings the total number of ice core records that have been rigorously tied to the gicc05 timescale up to nine renland annual layer thicknesses are increasing with depth during the period from 7 to 8 5 ka b2k a highly unusual observation only matched by a similar thickness increase in the glacial section of the renland core some 60 ka ago annual layer thicknesses in the agassiz ice cores point to a well developed raymond bump in the agassiz ice cap

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

application of nuttli s method to estimate yield of nevada test site explosions recorded on lawrence livermore national laboratory s digital seismic system methods utilizing lg waves for estimating yields of underground nuclear explosions have attracted considerable attention for their accuracy claims of portability and suitability for low yield test ban verification in this study the method developed by nuttli is applied to a large dataset of nevada test site explosions recorded on livermore s digital seismic system the purpose was to check the reproducibility of nuttli s results and to verify the accuracy of mb lg to estimate yield at high and low yield levels portability of the method is examined from the perspective of variability of the magnitude yield relations as a function of station site and source geology the results of this study show accuracies of about a factor of 1 6 in yield at the two sigma level for shots below the water table in source regions exhibiting more or less uniform coupling at nevada test site there are three such source regions pahute mesa areas 19 and 20 northern yucca including areas 2 and 9 and southern yucca including areas 3 4 and 7 there is no apparent degradation in accuracies at low yields 1 to 10 kt variations in source coupling were observed as a function of shot location and as a function of the medium s gas porosity for shots in tuff the effect of gas porosity was not observed for shots in alluvium which have uniformly low coupling compared to shots in tuff variations in magnitude yield relations were observed from station to station while the four station network average magnitudes are more robust and agreed well with nuttli s magnitude yield relations thus portability to other test sites should be considered guardedly optimistic requiring geologic and seismic data related to coupling in each source region and sufficient numbers of stations four or five to estimate a robust network magnitude taken all together the findings of this study lend support to this method as a viable means of monitoring a threshold test ban or low yield threshold test ban

a comparison of regional phases from underground nuclear explosions at east kazakh and nevada test sites abstract analysis of regional data from east kazakh ussr and nevada test site nts underground nuclear explosions suggests possible mechanisms for the generation of both low and high frequency lg spectral characteristics of pn and lg phases from 25 soviet nuclear shots recorded at the chinese digital seismic network cdsn station wmq are analyzed for their dependence on parameters such as m b generally related to shot depth and spatial location shagan versus degelen test sites the observed results are compared with those from the nevada test site nts where the near source conditions are better known the average amplitude ratio pn lg is found to be stable with m b but to vary strongly with frequency for both shagan and yucca flat explosions of similar yield the reduction in amplitude over the frequency range of about 1 to 5 hz is considerably larger for lg than for pn the low frequency lg appears to be generated by the scattering of explosion generated rg into s especially for the shagan river explosions for which good agreement between observation and theory is observed this mechanism also provides a possible explanation for the stability of lg as an estimator of explosive yields because the scattering should be expected to occur over a large region of the shallow crust another important result supported by theory is that the higher frequency lg is strongly dependent on the source medium velocity at higher frequencies 3 to 7 hz the amplitude ratios pn lg for explosions from shagan degelen pahute mesa and yucca flat test sites show significant differences that appear related to differences in their source medium velocities the observed large differences in the relative spectral content of pn and lg from east kazakh and nts explosions are mainly due to the vast differences in the crustal structure of the two test sites

attenuation of multiphase surface waves in the basin and range province part i lg and lg coda summary broad band data recorded by the lawrence livermore laboratory network are used to investigate whether or not lg q and lg coda q have similar values in the basin and range province of north america in order to retrieve spectral estimates of the broad band lg and lg coda signals a hybrid method is used which retains high fidelity at lower frequencies while strongly smoothing the spectral estimates and minimizing the number of spectral points at high frequencies a stochastic approach is used to model the lg signal and ambient noise and to analyse results from two station determinations of lg q in the basin and range the effects of ambient noise frequency dependent station site response and focusing defocusing on lg q inversion are analysed it is shown that after averaging spectral ratios determined from repeated observations over four two station paths a modest site effect will not cause significant errors in the resulting lg q relation using this inversion scheme and spectral ratio estimates averaged over those paths at frequencies between 0 2 and 2 5 hz we obtain the relation qlg f 267 f 56 f0 37 0 06 for the basin and range province further constraints on lg q were obtained from lg coda which due to the natural averaging effect of scattering is insensitive to effects of focusing defocusing to investigate the validity of the single isotropic scattering model for lg coda in the basin and range province we calculated ischrons for scatterers corresponding to later lg coda signals as required by the single scattering model it is found that when significant portions of these isochrons are oceanic lg coda amplitude decay becomes irregular and abnormally slow suggesting a strong scattering reflection effect caused by the rapidly changing crustal structure along the coast applying the single isotropic scattering model to lg coda records with isochrons mostly confined to the continental crust results in q f 275 f 26 f 0 36 0 03 which is nearly identical to our qlg relation this indicates that even in a complicated geological province a joint interpretation of the dynamic properties of lg and lg coda can be successful and fruitful inconsistent lg q and coda q relations found in earlier studies in the basin and range province may be attributed to different settings of parameter trade offs different seismic phases or different dynamic properties being used

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

a 420 000 year deuterium excess record from east antarctica information on past changes in the origin of precipitation at vostok here we present and analyze the complete vostok ice cores deuterium excess record which spans the last four climatic cycles back to 420 000 years b p to extract paleoclimate information from this record we use isotopic modeling showing that changes in deuterium excess d d 8 18o of vostok precipitation reflect changes in the average temperature of oceanic moisture sources over the last 250 000 years the deuterium excess is strongly anticorrelated with changes in earth s obliquity this reflects changes in the relative contribution of low and high latitudes to the vostok precipitation resulting from changes in the latitudinal annual mean insolation gradient governed by the obliquity however this modulation by obliquity is not observed prior to 250 000 years b p we attribute this difference to the ice flow the deeper ice under vostok station having accumulated in a location upstream vostok receiving precipitation from different oceanic origins despite this difference between the earlier and the later portions of the record the deuterium excess changes during all the glacial inceptions are similar in amplitude and timing relative to the deuterium decrease the glacial inceptions are characterized by high deuterium excess indicating the significant role of the tropics in supplying moisture to the already cold poles

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

velocity map of the thwaites glacier catchment west antarctica the two dimensional surface velocity of thwaites glacier west antarctica was mapped with 23 ascending and 22 descending orbit european remote sensing satellite synthetic aperture radar ers sar interferograms time range 1995 2000 the velocity map covers 175 500 square km from the amundsen coast to the southern turning point of the satellite orbit and comprises over 80 of the thwaites catchment

m b pn scale for the korean peninsula and site dependent pn amplification the korean peninsula is located in the far eastern eurasian plate margin where crustal structures vary laterally causing significant raypath dependent modulations of crustal phases the discriminative variations of crustal phases hinder application of conventional local magnitude scales in the continental margin the mantle lid phase is less affected by the crustal structures than the crustal phases providing a better constraint to magnitude estimation a regional body wave magnitude scale based on the mantle lid p wave pn mb pn is developed for regional events around the korean peninsula the mb pn scale is determined to be mb pn 0 380 0 299 log a 2 012 0 122 log d where a is the peak to peak pn amplitude in m and d is the epicentral distance in km the mb pn estimates of regional events around the korean peninsula are determined the mb pn estimates are compared with other available magnitude estimates mb lg ml the influence of structures beneath stations on pn amplification is investigated from inter station magnitude residuals a characteristic spatial variation of inter station magnitude residuals with strengths mostly between 6 and 6 but with maximum strengths of 10 is observed the inter station magnitude residuals appears to be correlated well with geological and seismic structures in the crust

holocene volcanic history as recorded in the sulfate stratigraphy of the european project for ice coring in antarctica dome c edc96 ice core 1 a detailed history of holocene volcanism was reconstructed using the sulfate record of the european project for ice coring in antarctica dome c edc96 ice core this first complete holocene volcanic record from an antarctic core provides a reliable database to compare with long records from antarctic and greenland ice cores a threshold method based on statistical treatment of the lognormal sulfate flux distribution was used to differentiate volcanic sulfate spikes from sulfate background concentrations ninety six eruptions were identified in the edc96 ice core during the holocene with a mean of 7 9 events per millennium the frequency distribution events per millennium showed that the last 2000 years were a period of enhanced volcanic activity edc96 volcanic signatures for the last millennium are in good agreement with those recorded in other antarctic ice cores for older periods comparison is in some cases less reliable mainly because of dating uncertainties sulfate depositional fluxes of individual volcanic events vary greatly among the different cores a volcanic flux normalization volcanic flux tambora flux ratio was used to evaluate the relative intensity of the same event recorded at different sites in the last millennium normalized flux variability for the same event showed the highest value in the 1100 1500 ad period this pattern could mirror changes in regional transport linked to climatic variations such as slight warming stages in the southern hemisphere southern hemisphere medieval warming like period

a first step to reconciling the grip and gisp2 ice core chronologies 0 14 500 yr b p abstract 18o records from the gisp2 and grip ice cores are widely used as benchmark paleoclimate chronologies but there are significant differences between the two time scales the present study shows that offsets between the two chronologies over the past 14 500 yr do not accumulate gradually but appear over two short intervals of 100 200 yr an initial offset of 80 yr occurs close to 3300 3400 yr b p and another 100 yr of slip appears at the start of the younger dryas since these discrepancies are localized resolving them may be far easier than if large sections of both cores required reexamination

rapid sea level rise from a west antarctic ice sheet collapse a short term perspective will worldwide sea level soon rise rapidly because of a shrinkage of the west antarctic ice sheet wais here i give a personal perspective of that probability the crucial question is not whether large changes in ice mass can occur but how likely it is that a large rapid change say a several fold increase in the 20th century rate of about 2 mm a 1 will occur in the next century or two from awest antarctic cause twenty years ago weertman proposed that a marine ice sheet is inherently unstable but weertman s analysis was based on a simple model of a marine ice sheet that did not include fast flowing wet based ice streams which are now known to dominate the grounded ice sheet modern analyses do not definitively determine just how ice streams affect the stability of the wais but it can at least be said that there is no compelling theoretical reason to expect a rapid rise in sea level from the wais triggered by ice shelf thinning of the three main ice drainage systems in the wais the one that flows into pine island bay might be a particularly likely site for accelerated flow since there is no ice shelf to restrain the inflowing ice streams yet measurements show that this system is not significantly out of mass balance if the ross embayment system which has undergone several sudden glacial reorganizations in the last thousand years were unstable one might expect a history of large changes in the total outflow of ice into the ross ice shelf yet the total outflow in the ross embayment has remained relatively unchanged despite the large internal perturbations a fact that points to a stable not an unstable system study of the third major drainage from the wais into the ronne ice shelf also suggests that there is no gross discordance between the present velocity vectors and flow tracers in the ice shelf although the evidence is limited in the light of the evidence for recent stability it is difficult to see how climate warming whether anthropogenic or natural could trigger a collapse of the wais in the next century or two thus i believe that a rapid rise in sea level in the next century or two from a west antarctic cause could only occur if a natural not induced collapse of the wais were imminent based on a concept of pseudo random collapse once per major glacial cycle i estimate the chances of that to be on the order of one in a thousand

magnitude estimation and source discrimination a close look at the 2006 and 2009 north korean underground nuclear explosions north korea detonated its first known nuclear device a moderate sized event in the northeastern corner of the korean peninsula on 9 october 2006 a second one several times more powerful was set off nearby on 25 may 2009 both were recorded at high signal to noise ratio snr by a modern broadband 0 03 30 hz network of seismographs deployed since 2004 along the sino korean border and by station mdj due north of ground zero spanning a wide range of station azimuth 259 11 the near regional 1 3 3 3 paths are all purely continental and away from continental margins making the resulting data uniquely suited for assessing the capabilities of an out country network to verify the compliance by north korea with a future comprehensive nuclear test ban treaty the mblg magnitudes for the 2006 and 2009 nuclear explosions were determined anew giving 4 32 0 13 and 4 86 0 13 respectively we show that the ms mblgmethod correctly differenti ates these nuclear explosions from natural earthquakes although the differentiation was not achieved in studies based on published mblg values an analysis of the pg lg ratio derived from recordings of the two nuclear tests and of four regional earthquakes selected for their comparable magnitudes 4 2 mb 4 8 reveals that the ratios associated with the explosion and earthquake populations showed surpris ingly little overlap for a broad frequency range of 3 to 11 hz in principle ms mb can also be used to correctly identify the nuclear tests as explosions but the mb measure ment for such moderate sized events is not as robust as the mblg measurement rendering this traditionally favored method less practical

attenuation of crustal waves across the alpine range we present observational evidence of an anomalous propagation of lg waves across the south western part of the alpine range and we use numerical simulations to model these observations we consider a set of 48 earthquakes which occurred in switzerland northern italy and southeastern france and were recorded by the french laboratoire de detection et de geophysique and northwest italian istituto geofisico di genova seismic networks while the amplitude of the pn phase is stable throughout the region studied lg wave amplitude undergoes strong variations we map this anomaly in lg wave propagation by dividing the region into a grid and attributing to each cell a value equal to the mean value of the lg pn amplitude ratios computed for all the paths which cross this cell the image obtained shows that the extinction of lg waves occurs in a limited region of the western alps which corresponds to the zone of highest positive bouguer anomaly this zone located to the east of the high peaks of the massifs cristallins externes does not correspond either to the region of the highest topographies or to the one of the deepest moho at a frequency of 2 hz the crustal waves that cross this anomalous region have amplitudes divided by more than 10 with respect to waves that propagate along other paths in order to investigate the cause of the anomaly we perform numerical simulations of sh wave propagation through a model of the western alps which includes the main characteristics of the geological structure our results indicate that the geometrical effect of the lateral variations of the medium does not account entirely for the actual vanishing of crustal waves the simulation predicts a decay of the amplitude by only a factor between 2 and 3 the introduction of corrugation in the interface shapes further adds to the decay however other sources of attenuation such as anelasticity or severe heterogeneity must be invoked to explain fully the observations

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

remote sensing of glacier and ice sheet grounding lines a review abstract the precise positioning and long term monitoring of the grounding line forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers is critical for assessing ice sheet glacier stability ice sheet glacier mass balance calculations and numerical ice modelling however mapping of the grounding line is a challenging task since it is a subglacial and transient feature remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position the large variety of methods products and publications as well as an inconsistent use of terminology additionally complicate the topic we present the first detailed review of existing remote sensing techniques and data for grounding line mapping benefits and limitations of the different techniques and data sources are discussed and illustrated with examples we identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products rather new methods like sentinel 1 sar synthetic aperture radar differential range offset tracking drot and pseudo crossover radar altimetry pcra offer the potential for recent measurements and to fill gaps in some areas nevertheless there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate differential sar interferometry dinsar on a continental scale

regional coda q variations in the western alps northern italy abstract to study the microseismicity of the central segment of the western alps a local temporal seismic network of six stations was installed in addition to the regional centralized network operating in the area in 3 months about 220 shocks with magnitude ranging between 1 0 and 3 8 have been analyzed and located the epicenter distribution shows a possible subdivision into seismogenetic bands this subdivision is also recognizable from the spectral characteristics of the analyzed seismic signals a study of the wave attenuation in a restricted area well covered by the local network was carried out through a coda analysis the results show strong spatial qc variations in agreement with the strong lateral heterogeneities that characterize this area in particular the brianconnais domain the crystalline massifs and the inner part of the alpine arc appear to behave as decreasing attenuation bands

regional observations of the second north korean nuclear test on 2009 may 25 summary the suspicious seismic event that occurred in the northern korean peninsula on 2009 may 25 was declared to be the second underground nuclear test nk2nd by north korea we investigated the characteristics of nk2nd using seismic signals recorded at regional distance stations in south korea and china the pn lg ratios of nk2nd definitely discriminate this event from two nearby natural earthquakes at frequencies above 4 hz full moment tensor inversion of full waveform data shows that nk2nd had a very large isotropic component pure isotropic moment tensor inversion also resulted in good recovery of observed waveforms with clear indication that nk2nd was explosive in origin the moment magnitude mw from the full moment tensor inversion was estimated to be 4 5 and network averaged values of 4 6 and 3 6 were calculated for rms mb lg and ms vmax respectively although mb ms signature has been considered one of the most reliable discriminants for separating explosions and earthquakes this signature showed poor discrimination in the case of nk2nd the pn lg ratios and moment tensor inversion give more reliable evidence than does the mb ms for classifying the suspicious event in the northern korean peninsula as a possible explosion the characteristics of nk2nd are also quite similar to those of the first north korean nuclear test on 2006 october 9

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

comparison of holocene electrical records from dome c and vostok antarctica as part of the european project for ice coring in antarctica a new deep ice core is being drilled at dome c two electrical methods have been used on the core drilled so far a new design of electrical conductivity method ecm instrument and a traditional dielectric profiler the two profiles are very similar in both peaks and background consistent with acidity being the dominant influence on both in this part of the record the dome c records have been compared to ecm records from vostok and a tentative match has been made between them this suggests a long term average ratio of accumulation rate of 1 36 between this dome c core and vostok and that the dome c core analyzed so far to 358 m probably includes the very end of the glacial holocene transition

yield estimation of the 25 may 2009 north korean nuclear explosion we collect nine vertical component broadband seismograms from the 25 may 2009 north korean nuclear explosion for a regional seismic network in which eight stations also recorded the 9 october 2006 north korean nuclear test comparing the observed waveforms and spectra from the two events we estimate that the amplitudes of the records from the second event are approximately five times those from the first one additionally we use 599 vertical broadband seismograms from 82 regional events recorded on the regional network between december 1995 and may 2009 to calibrate the network lg wave magnitude the calibrated network is used to calculate the lg wave body wave magnitude m b lg 4 53 for the 25 may 2009 north korean nuclear explosion based upon 15 first arrivals from the two north korea nuclear explosions the regional pn velocity in the northeast china north korea region is calculated to be 8 0 km s this result along with the regional geological structures suggests that the north korean test site nkts is located at a relatively stable continental region we thus use a modified fully coupled magnitude yield relation to estimate the explosion yield and the result shows that the yield of the 25 may 2009 north korean nuclear test is approximately 2 35 kt under the minimum burial depth assumption online material epicentral parameters computed m b lg and corrected m b lg for 82 events used in the study

evidence of bias in estimations of earthquake size magnitudes of earthquakes determined using traditional methods show systematic deviations dependent on tectonic setting from accurate estimates of earthquake size magnitudes are overestimated for most of the continental earthquakes underestimated for mid oceanic ridges and differences of varying sign are obtained for subduction zones this is important in evaluating the seismic risk or consideration of effects such as the seismic versus aseismic strain release as seismic moments determined from magnitudes can be wrong by as much as a factor of four

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

a tentative chronology for the epica dome concordia ice core a tentative age scale edc1 for the last 45 kyr is established for the new 788 m epica dome c ice core using a simple ice flow model the age of volcanic eruptions the end of the younger dryas event and the estimated depth and age of elevated 10be about 41 kyr ago were used to calibrate the model parameters the uncertainty of edc1 is estimated to 10 yr for 0 to 700 yr bp up to 200 yr back to 10 kyr bp and up to 2 kyr back to 41 kyr bp the age of the air in the bubbles is calculated with a firn densification model in the holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum

empirical path and station corrections for surface wave magnitude ms using a global network summary one of the most commonly used methods of estimating the size of shallow earthquakes is the surface wave magnitude scale ms it has been known since the inception of the scale that the ms of a seismic disturbance recorded at different stations can vary due to path propagation and station terms but it has been difficult to quantify these variations on a global basis because until recently there has been no attempt to record ms in a uniform way on a worldwide network here we use ms measurements within the reviewed event bulletin reb of the international data centre idc which is produced to help monitor compliance with the comprehensive nuclear test ban treaty ctbt the idc collects waveforms from the as yet incomplete seismological network of the international monitoring system ims and ms is then measured using an automatic algorithm providing a unique set of surface wave observations in this paper we show that the ms values reported in the reb show distinct geographic variations we present preliminary attempts to model these observations in terms of a set of station corrections and a 2 d model which can be used to predict path corrections for ms the model shows a striking correlation with the known tectonic regions of the earth suggesting that this type of data set may provide a valuable tool for investigating shallow earth structure after modelling the residuals show some systematic patterns which cannot be explained using the model basis we have used these residuals are presumably due either to source radiation patterns or to complicated propagation effects not allowed for in the model such as refraction at ocean continent boundaries from the ctbt monitoring viewpoint ms station and path corrections are valuable because they should improve the effectiveness of event screening using mb ms however we recommend that implementation of such corrections should wait until the full seismological network of the ims is in place and until a fuller understanding of path effects on ms is available in particular it is vital that path propagation effects do not distort station corrections and that earthquake radiation patterns should not influence corrections which may be applied to surface waves from suspected explosions

sulfur cycle at last glacial maximum model results versus antarctic ice core data for the first time an atmospheric general circulation and sulfur chemistry model is used to simulate sulfur deposition in antarctica at the last glacial maximum lgm dimethylsulfide dms emitted by phytoplankton is the dominant source of atmospheric sulfur in antarctica once in the atmosphere it is oxidized into sulfur aerosols which are measured in ice cores such measurements allow for validating climate and chemistry models for glacial interglacial changes our glacial simulations test the effect of a recent re evaluation of glacial sea ice coverage on dms sources and sulfur aerosol deposition using the present day oceanic concentrations of dms the model reproduces observed glacial and interglacial sulfur concentrations in the ice this result suggests that climate change at the lgm did not greatly impact on dms production in the oceanic sectors where sulfur aerosols deposited in central east antarctica originate from

stratigraphic correlations between the european project for ice coring in antarctica epica dome c and vostok ice cores showing the relative variations of snow accumulation over the past 45 kyr 1 high resolution chemistry analysis and electrical measurements performed on two ice core records european project for ice coring in antarctica epica dome c and vostok spanning the last 45 kyr allow stratigraphic correlations by matching volcanic events several common events were identified along the two ice cores on the basis of acidity and sulphate spikes in snow layers timescales were matched through comparison with isotope d profiles and using the antarctic cold reversal acr minimum a 10be peak and a dust spike as temporal checkpoints ratios of relative snow accumulation at the two sites during the holocene in the glacial interglacial transition and in the last part of the glacial period were reconstructed by finding the best fit between dome c and vostok depths recording the same events after accounting for thinning of the layers as they are buried within the glacier the dome c vostok accumulation ratio expected to be roughly constant from the conventional accumulation temperature isotope approach is 1 12 for the glacial period but increases to as much as 1 44 for a large part of the holocene glaciological effects mainly related to the geographic origin of the vostok ice along the ridge b vostok axis can account for only a minor fraction of this change instead we argue that accumulation variability between the cores stems from differential changes in atmospheric circulation during these respective climatic periods at the two sites regional changes in atmospheric circulation are proposed with a negative anomaly in dome c a positive accumulation anomaly in vostok or a combination of both during glacial climate our approach may help to improve ice core dating by 1 revealing anomalies in accumulation rate estimation based on the classical thermodynamic method and 2 supporting the necessity to take into account contributions due to changes in atmospheric circulation processes

inland thinning of pine island glacier west antarctica the pine island glacier pig transports 69 cubic kilometers of ice each year from 10 of the west antarctic ice sheet wais it is possible that a retreat of the pig may accelerate ice discharge from the wais interior satellite altimetry and interferometry show that the grounded pig thinned by up to 1 6 meters per year between 1992 and 1999 affecting 150 kilometers of the inland glacier the thinning cannot be explained by short term variability in accumulation and must result from glacier dynamics

regional magnitude scaling transportability and ms mb discrimination at small magnitudes data sets of mb pn and mb lg measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude w and event discrimination at small magnitudes compilations of published measurements are provided for eastern north american and central asian earthquakes and new measurements are reported for earthquakes located in western united states statistical tests on w mb relationships show that the mb lg scale of nurru 1973 is transportable between tectonic regions and a single unified w mb lg relationship satisfies observations for m 6 5 in all regions a unified relationship is also developed for nuclear explosions detonated at the nevada test site and test sites of the former soviet union regional mb for explosions scale at higher rates than for earthquakes and of significance is the finding that mb pn for explosions scales at a higher rate than mb lg a model is proposed where differences in scaling rates are related to effects of spectral overshoot and near field rg scattering on the generation of pn and lg waves by explosions for earthquakes mb pn and mb lg scale similarly showing rates near 1 0 or 2 3 log1omo seismic moment

regional relationships among earthquake magnitude scales various magnitude scales commonly used and the interrelationships among them are reviewed it is shown that problems exist with all of the magnitude scales being used in the united states when using regional catalogs for example it is often necessary to determine how the reported magnitudes were determined often such information is not available although the potential errors are quite large both the ms and the mb scales were designed to be universal scales however both ms and mb magnitudes are often determined beyond the applicable range of the equations used to define the two scales furthermore the ms magnitudes are not generally available for moderate to small earthquakes in most earthquake catalogs the mb magnitudes are more generally available than ms values however there is also much greater variation in the way mb is determined in particular a significant change in the mb scale occurred in the early 1960 s when the world wide standard seismograph network wwssn was established this change in instrumentation used to determine mb values had a significant effect on estimated magnitudes post 1960 values are lower and the saturation level of the mb scale the older longer period instruments recorded larger mb magnitudes than can be recorded with the wwssn instruments in addition great care must be taken when selecting the mb magnitudes of western u s earthquakes because the values are often in considerable error owing to the fact that they were determined at distances less than 25 and were not properly corrected for attenuation in the upper mantle or asthenosphere the seismic body wave magnitude mb of an earthquake is strongly affected by regional variations in the q structure composition and physical state within the earth therefore because of differences in attenuation of p waves between the western and eastern united states a problem arises when comparing mb values for the two regions a regional mb magnitude bias exists which depending on where the earthquake occurs and where the p waves are recorded can lead to magnitude errors as large as unit there is also a significant difference between mb and ml values for earthquakes in the western united states an empirical link between the mb of an eastern u s earthquake and the ml of an equivalent western earthquake is given by ml 0 57 0 92 mb east this result is important when comparing ground motion between the two regions and for choosing a set of real western u s earthquake records to represent eastern earthquakes

characteristics and sources of tephra layers in the epica dome c ice record east antarctica implications for past atmospheric circulation and ice core stratigraphic correlations thirteen discrete air fall tephra layers were identified in the last 200 000 yr section of the epica dome c ice record drilled in the east antarctic plateau 75 06 s 123 21 e quantitative grain size glass particle morphology and the grain discrete major element composition of the glass fraction of these layers were investigated through comparison with literature data on the rock composition of quaternary volcanic centres located within and around antarctica five tephra layers were attributed to south sandwich volcanoes in the south atlantic ocean two to south shetland volcanoes northern antarctic peninsula two to andean volcanoes and four to antarctic marie byrd land and melbourne provinces the abundance of layers originating in the southern part of the atlantic confirms that westerly atmospheric circulation spiralling towards east antarctica prevailed over the last 200 ka moreover the record of events from antarctic centres suggests that atmospheric trajectories from west to east antarctica can also be significant a few ash layers are geochemically distinct and appear equivalent to levels from vostok and dome fuji deep ice records located ca 600 km and ca 2000 km respectively from dome c on the antarctic plateau these layers provide unambiguous markers for future correlation with other antarctic ice cores and circumpolar marine climatic records they also provide reliable constraints to get a common timescale by glaciological modelling and represent a first step towards absolute ice core dating

ice core evidence for secular variability and 200 year dipolar oscillations in atmospheric circulation over east antarctica during the holocene two holocene ice core records from east antarctica vostok and epica dome c were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per 50 years a series of volcanic markers randomly distributed over the common part of the ice cores from 9 8 to 3 5 kyear bp ensures accurate relative dating 33 years dust size records from the two sites display oscillations structured in cycles with sub millennial and secular scale frequencies that are apparently asynchronous the power spectra of the composite sum of the two dust size records display spectral energy mostly for 150 to 500 year periodicities on the other hand the 200 year band is common to both records and the 200 year components of the two sites are out of phase 100 year lead or lag over 5 5 kyear a phenomenon also reflected by a significant 99 conf lev band in the power spectra of the composite difference of the two size records during long range transport mineral dust originating from the southern hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport relatively coarse dust is associated with air mass penetration from the middle lower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the antarctic plateau a hypothesis already proposed for the changes that occurred during the last glacial maximum to holocene transition delmonte et al 2004b moreover we assume that the overall fluctuation of air mass advection over antarctica depends on the meridional pressure gradient with respect to low latitudes i e the antarctic oscillation aao we therefore suggest a regional variability in atmospheric circulation over east antarctica the 150 500 year power spectrum of the composite parameter represents the long term variability of the aao imprinted by secular internal oscillations probably related to the southern ocean climatic system on the other hand the dust composite parameter suggests a persistent atmospheric dipole over east antarctica delivering coarser finer dust particles alternatively to vostok and dome c regions with a bi centennial periodicity indeed a seesaw phenomenon in dust size distribution was already observed at three east antarctic sites during the last deglaciation delmonte et al 2004b and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole interestingly the parameter shows a pronounced 200 year oscillation mode throwing new light on the unresolved question of a possible relationship between climate and solar activity

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

evidence for rapid retreat and mass loss of thwaites glacier west antarctica thwaites glacier the second largest ice stream in west antarctica drains an area of 166 500 2000 km2 which accumulates 55 5 gt a 1 or 60 6 km3 ice a 1 into the amundsen sea unrestrained by an ice shelf using interferometric synthetic aperture radar insar data collected by the european remote sensing satellites ers 1 and 2 in 1996 an output flux of 71 7 gt a 1 or 77 8 km3 ice a 1 is estimated at the grounding line where ice thickness is deduced from hydrostatic equilibrium a similar flux 70 7 gt a 1 or 76 8 km3 ice a 1 is obtained at a gate located 20 km upstream where ice thickness was measured in 1978 by ice sounding radar total accumulation in between the two gates is 1 6 gt a 1 or 1 8 km3 ice a 1 ice discharge therefore exceeds mass accumulation by 30 15 and thwaites glacier must be thinning and retreating at present the insar data show that the glacier floating ice tongue exerts no back pressure on the inland ice calves into tabular icebergs along a significant fraction of its grounding line and has a grounding line thickness which exceeds a prior calculated limit for stability glacier thinning is confirmed at the coast by the detection of a 1 4 0 2 km retreat of its grounding line between 1992 and 1996 with insar which implies 3 2 0 6 m ice a 1 thinning at the glacier center and less near the sides these results complement the decimeter scale annual surface lowering observed with satellite radar altimetry several hundred km inland of the grounding line the magnitude of ice thinning estimated at the coast however rules out temporal changes in accumulation as the explanation for surface lowering ice thinning must be due to changes in ice flow

dust transport to dome c antarctica at the last glacial maximum and present day the antarctic polar ice core records show large changes in the concentration of dust over glacial interglacial timescales this paper explores how much of this variation is due to changes in the transport of dust from arid regions to the ice cores back trajectories initialised from the site of dome c ice core antarctica are calculated using an offline trajectory code forced by modelled winds output from the ukmo unified model running under present day and lgm boundary conditions as well as comparing the present day and lgm back trajectories their seasonal and interannual variability is also explored the results suggest that the patagonian provenance of the dome c dust can be understood in terms of the atmospheric transport whereas the total change in dust concentration requires changes to the sources or sinks

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

on the representation of ice shelf grounding zones in sar interferograms we investigate limitations of the one dimensional elastic beam model to detect grounding line and thickness of an ice shelf from a differential interferogram spatial limitations due to grounding line curvature and variable ice thickness are analyzed by comparison with two dimensional plate flexure temporal limitations from the tide dependent shift of the grounding line are analyzed by superpositions of four tidal flexure profiles representing differential interferograms i at scales greater one ice thickness seaward protrusions of the grounding line are well represented by the elastic beam model while landward embayments of the same scale produce significant misplacements 10 per cent of the ice thickness ii for reasonable spatial variations of shelf thickness the elastic beam model gives reliable estimates of grounding line position and unfractured mean ice thickness near the grounding line iii for about 20 per cent of superpositions of four tidal flexure profiles the resulting grounding line misplacements exceed the physical tidal shift of the grounding line by factors 2 for differential tide levels 2 km examples of real interferometric profiles from west antarctic ice shelves corroborate our results

dating the vostok ice core by an inverse method using the chronological information available in the vostok records we apply an inverse method to assess the quality of the vostok glaciological timescale the inversion procedure provides not only an optimized glaciological timescale and its confidence interval but also a reliable estimate of the duration of successive events our results highlight a disagreement between orbitally tuned and glaciological timescales below 2700 m i e 250 kyr b p thousands of years before present this disagreement could be caused by some discontinuity in the spatial variation of accumulation upstream of vostok moreover the stratigraphic datings of central greenland ice cores grip and gisp2 appear older than our optimized timescale for the late glacial this underlines an unconsistency between the physical assumptions used to construct the vostok glaciological timescale and the stratigraphic datings the inverse method allows the first assessment of the evolution of the phase between vostok climatic records and insolation this phase significantly varies with time which gives a measure of the nonlinear character of the climatic system and suggests that the climatic response to orbital forcing is of different nature for glacial and interglacial periods we confirm that the last interglacial as recorded in the vostok deuterium record was long 16 2 2 kyr thousands of years however midtransition of termination ii occurred at 133 4 2 5 kyr bp which does not support the recent claim for an earlier deglaciation finally our study suggests that temperature changes are correctly estimated when using the spatial present day deuterium temperature relationship to interpret the vostok deuterium record

the stability of rms lg measurements and their potential for accurate estimation of the yields of soviet underground nuclear explosions data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the soviet union and china observations of root mean square rms lg wave signals for soviet underground nuclear explosions at the shagan river test site in east kazakhstan show that the relative amplitudes of the rms signals at stations in norway the ussr and china are very similar for different explosions the standard deviation of the differences being only about 0 03 in logarithmic units i e magnitude units this is consistent with earlier observations comparing norsar and graefenberg array data and the observed scatter is significantly lower than has been reported for lg data from nevada test site explosions in view of the excellent correspondence found by nuttli 1986 and patton 1988 for lg versus yield at nevada this indicates that rms lg has a potential for yield estimation with very high accuracy at shagan river our study has shown that a selected stations in the ussr and china situated at regional distances provide a much improved signal to noise ratio of the lg phase for events at shagan river as compared to norsar array data b the scaling of rms lg amplitudes between different sized events recorded at the same single station site appears to be consistent with that of norsar indicating a remarkable degree of precision in single station measurements of lg signal c rms lg amplitude measurements for the best of these stations may be made at 1 5 to 2 0 magnitude units lower than at norsar or graefenberg allowing a much lower threshold for lg based yield determination and d the p wave detection capabilities of these single stations do not match those of the noress and arcess arrays thus teleseismic signals continue to be important for detection of small nuclear explosions our conclusion is that lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high quality digital in country seismic stations and when calibrated by access to independent nonseismic yield information for a few nuclear explosions at the test sites of interest in the context of monitoring a low yield threshold test ban treaty it will in addition be important to take into consideration various environmental conditions in the testing area such as the possible presence of cavities and to devise appropriate procedures for on site observations in this regard

gcm simulations of the last glacial maximum surface climate of greenland and antarctica the lmdz variable grid gcm was used to simulate the last glacial maximum lgm 21 ky bp climate of greenland and antarctica at a spatial resolution of about 100 km the high spatial resolution allows to investigate the spatial variability of surface climate change signals and thus to address the question whether the sparse ice core data can be viewed as representative for the regional scale climate change this study addresses primarily surface climate parameters because these can be checked against the limited ice core record the changes are generally stronger for greenland than for antarctica as the imposed changes of the forcing boundary conditions e g sea surface temperatures are more important in the vicinity of greenland over greenland and to a limited extent also in antarctica the climate shows stronger changes in winter than in summer the model suggests that the linear relationship between the surface temperature and inversion strength is modified during the lgm the temperature dependency of the moisture holding capacity of the atmosphere alone cannot explain the strong reduction in snowfall over central greenland atmospheric circulation changes also play a crucial role changes in the high frequency variability of snowfall atmospheric pressure and temperature are investigated and possible consequences for the interpretation of ice core records are discussed using an objective cyclone tracking scheme the importance of changes of the atmospheric dynamics off the coasts of the ice sheets especially for the high frequency variability of surface climate parameters is illustrated the importance of the choice of the lgm ice sheet topography is illustrated for greenland where two different topographies have been used yielding results that differ quite strongly in certain nontrivial respects this means that the paleo topography is a significant source of uncertainty for the modelled paleoclimate the sensitivity of the greenland lgm climate to the prescribed sea surface conditions is examined by using two different lgm north atlantic data sets

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

holocene electrical and chemical measurements from the epica dome c ice core the comparison between electric electric conductivity measurement ecm and dielectric profiling dep and chemical sulphate and chloride depth profiles along the first 400 m of the epica dome c ice core revealed a very good fit especially for peaks related to volcanic emissions from the comparison between these profiles a dominant contribution of sulphuric acid to the ionic balance of antarctic ice for the holocene was confirmed a progressive increase with depth was observed for chloride concentrations showing a change of relative contribution between sulphate and chloride a higher increase of chloride was evident between 270 and 360 m depth probably due to a change in source or transport processes or to an increase of the annual snow accumulation rate the dep ecm and sulphate ice signatures of tambora ad 1816 and el chichon ad 1259 eruptions are described in detail a characteristic peak series due to hcl deposition was identified at 103 109 m depth from the ecm dep and chloride profiles

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

yield estimation using regional mb pn seismic yield estimation at regional distances will become increasingly important in monitoring a low yield threshold test ban lyttb in order to investigate seismic yield estimation using regional data we have examined regional mb pn values for a large population of nevada test site nts underground nuclear explosions that occurred in widely varying geologic media with a range of yields from less than 1 kt to 300 kt magnitude yield relationships were developed using data from a set of pre 1985 events calibration set to obtain an independent estimate of the uncertainty in estimating yields of events at nts using mb pn alone the calibrated relationships were applied to a set of post 1984 events prediction set we found that the average uncertainty in the yield estimate based on a weighted combination of the yield estimates from the four livermore nts network lnn seismic stations is about 1 8 at the 2 level if data are available from all four lnn stations the uncertainty is about 1 7 at the 2 level by including a term for the gas filled porosity of the rock near the working point in the magnitude yield relationship we were able to develop a single relationship valid for events both above and below the water table as well as those in alluvium and tuff we have found however systematic differences in the relationships for events in yucca flat pahute mesa and rainier mesa

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

glacial interglacial changes in ocean surface conditions in the southern hemisphere the stable isotope signatures of oxygen and hydrogen in the water of preserved ice and snow are both widely used to infer local temperatures of past environments a derived quantity based on these two signatures the deuterium excess 1 provides additional palaeoclimatic information2 3 4 as this parameter depends on the meteorological and oceanic characteristics of the water s source regions in particular their temperature2 3 and relative humidity4 published studies mainly focus on records from the past 40 000 years here we present a deuterium excess history obtained from ice cores from vostok east antarctica spanning the full glacial interglacial cycle of the past 150 000 years the deuterium excess record shows a strong anticorrelation with the earth s orbital obliquity 41 000 year periodicity and values are markedly higher during the cold stage 5d following the last interglacial than during the other cold stages we interpret the relationship with obliquity as resulting from changes in the latitudinal insolation gradient affecting ocean surface conditions and thus the delivery of moisture to the polar region we argue that the high 5d values relative to other cold stages are driven by relatively less moisture delivered from high latitudes and more from low latitudes the deuterium excess in antarctic precipitation thus provides long term spatially integrated information on ocean surface conditions and ocean atmosphere circulations in the southern hemisphere

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

atmospheric decadal variability from high resolution dome c ice core records of aerosol constituents beyond the last interglacial along the epica dome c ice core we measured concentrations of different water soluble aerosol constituents and deduced total depositional flux records here we present high resolution sodium calcium ammonium and nitrate data covering the last 173 000 years the first three of these species are passive tracers and reveal source and long range transport changes whereas nitrate is deposited reversibly however it can be used to check isotope derived accumulation rate estimates a prerequisite to calculate total depositional fluxes during the last two transitions from glacial to interglacial periods changes in the total depositional flux differ strongly for different aerosol species the largest changes are observed in the terrestrial aerosol proxy non sea salt calcium only moderate changes occur in the marine sea salt indicator sodium while ammonium a proxy for marine bioproductivity remains rather constant in agreement with previous studies we find that only considerable glacial interglacial changes at both the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes the unprecedented high resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period on the one hand we find occasional fast shifts occurring within a few years here we present such an event in the calcium record from the penultimate glacial period on the other hand we examine variation coefficients and pairwise correlation coefficients both determined in 200 year windows they generally reveal only moderate changes during glacial periods slightly lower variation coefficients are found concurrent with slightly higher correlation coefficients which points to a more uniform and stronger coupled atmospheric long range transport of the different aerosol species to the east antarctic plateau and less influence of cyclonic activities during cold periods the opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the last interglacial period the marine isotope stage 5 5 this period reveals no evidence for abrupt climatic changes in any of the species however the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase this pattern is explained by significantly reduced sea ice production in the indian southern ocean sector which is believed to be the dominant source of sodium deposited in dome c during warm periods

lg body wave magnitude scaling for the continental margin around korea and japan regional body wave magnitude scalings are essential for quantification of small and moderate size earthquakes that are observed only up to regional distances crustally guided shear waves lg develop stably at regional distances in continental crusts and are minimally influenced by the source radiation patterns lg body wave magnitude scalings m b lg are widely used for assessment of sizes of regional crustal events the m b lg scaling has rarely been tested in continental margins where lg waves are significantly attenuated due to abrupt lateral variation of crustal structures we test the applicability of m b lg scaling to the eastern margin of the eurasian plate around the korean peninsula and japanese islands both third peak and root mean square rms amplitudes of lg vary significantly according to the crustal structures along raypaths causing apparent underestimation of m b lg implementation of raypath dependent quality factors q allows accurate estimation of m b lg retaining the transportability of m b lg in the continental margin around korea and japan the calibration constants for an rms amplitude based m b lg scaling are not determined to vary by region in the continental margin due to complicated crustal structures the calibration constants are determined to be distance dependent both the third peak amplitude based and rms amplitude based m b lg scalings yield accurate magnitude estimates when raypath dependent quality factors are implemented

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

the pinatubo eruption in south pole snow and its potential value to ice core paleovolcanic records snow samples collected in the 1996 austral summer at south pole show that sulfate concentrations in snow and by inference sulfur aerosol concentrations in the antarctic atmosphere were elevated from the end of 1991 to mid 1994 over a stable non volcanic background the new data support earlier findings that the june 1991 pinatubo eruption and the hudson eruption in the same year deposited volcanic sulfate and tephra in south pole snow and provide strong evidence of the global distribution of volcanic materials from the pinatubo eruption in this study snow samples were taken in six snow pits spatially distributed around the south pole station in order to evaluate the local spatial variability of volcanic signals due to glaciological variables such as snow accumulation rates and snow redistribution by wind after initial deposition the results indicate that pinatubo sulfate flux varies by as much as 20 throughout a 400 km2 area centered around the south pole station this glaciological variability probably represents the likely range of volcanic signals due to variations in snow deposition and post depositional changes the pinatubo eruption provides an unprecedented opportunity to estimate aerosol mass loadings by explosive volcanic eruptions found in antarctic ice cores via a quantitative relationship between aerosol mass loadings and sulfate flux in antarctic snow here the satellite estimated pinatubo so2 emission and the measured volcanic sulfate flux in snow with an assumed linearly quantitative relationship are used to calculate so2 loadings for several well known volcanic eruptions in the past 300 years covered by a shallow 42 m south pole firn core drilled in 1996 the errors for the calculated mass loadings are estimated by means of the glaciological variability associated with pinatubo volcanic flux

acceleration of pine island and thwaites glaciers west antarctica recent satellite investigations revealed that in the 1990s the grounding line of pine island and thwaites glaciers west antarctica retreated several km the ice surface on the interior of the basins lowered 10 cm a 1 and pine island glacier thinned 1 6 m a 1 these observations however were not sufficient to determine the cause of the changes here we present satellite radar interferometry data that show the thinning and retreat of pine island glacier are caused by an acceleration of ice flow of about 18 2 in 8 years thwaites glacier maintained a nearly constant flow regime at its center but widened along the sides and increased its 30 15 mass deficit by another 4 in 4 years the combined mass loss from both glaciers if correct contributes an estimated 0 08 0 03 mm a 1 global sea level rise in 2000

shear wave attenuation in the lithosphere beneath italy and surrounding regions tectonic implications more than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances 250 1400 km by the italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves lg and sn respectively the crustal phase lg efficiently propagates through the relatively stable adriatic continental crust while it is not observed along propagation paths crossing major physiographic features like the apennine chain and the basinal domain of the tyrrhenian and ionian seas similar to lg efficient sn propagation is observed in the uppermost mantle beneath the po plain and the adriatic sea efficient sn transmission is also observed across the northern ionian sea and sicily and in the area between sardinia and the northern coasts of africa sn are efficiently transmitted across the sicily channel and rather efficient sn propagate beneath the ligurian sea on the contrary inefficient sn transmission characterizes the uppermost mantle beneath the apennines the western margin of the italian peninsula and the southern tyrrhenian sea shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle probably related to the present day extension along the apennine chain and in the tyrrhenian basin this interpretation is consistent with the presence of extensive neogene and quaternary volcanic activity in these areas and related high heat flow proposed lithospheric delaminatioh processes beneath the apennines and subduction beneath the tyrrhenian sea can reasonably explain the observed high attenuation zones in the uppermost mantle in contrast a high strength mantle lid is inferred to underlay the po plain the adriatic sea and the northern ionian sea the available waveforms also indicate that a continuous mantle lid is present beneath sicily and the extensional domain of the sicily channel as well as in the marine area south of sardinia

glacial interglacial variations in central east antarctic ice accumulation rates past rates of ice accumulation in central east antarctica are defined poorly for the last glacial period ice cores from which current estimates are based are limited in number there is one deep ice core at vostok station one at dome f and two others currently being extracted at dome c and dronning maud land and are restricted spatially they are one dimensional here spatial variations in ice accumulation rates during the last glacial are calculated from isochronous internal ice sheet layering measured by airborne ice penetrating radar data the layers are used to identify the stratigraphy around five east antarctic ice domes isochrons are dated by linking them to the vostok ice core and in one case the epica dome c ice core this chronostratigraphy allows the depth age function to be identified across the ice sheet a simple ice flow model using the depth age measurements as input is then used to determine the spatial and temporal variation in east antarctic ice accumulation over the last glacial cycle the lowest rates of ice accumulation were predicted in the full glacial period to the south of dome a and ridge b there are two possible explanations for this 1 the ice divide topographies may have caused a precipitation shadow in the ice age 2 with the expansion of the ross ice shelf the area to the south of dome a and ridge b would be at the very centre of the ice sheet and hence at a maximum distance from the ocean moisture source r 2002 elsevier science ltd all rights reserved

a transportable mb lg scale for central europe and implications for low magnitude ms mb discrimination summary we have extended the mb lg method of nuttli using root mean square rms amplitudes corrected for noise and a 1 dependence for geometrical spreading lg waves recorded on the german regional seismic network grsn for earthquakes in south central europe were used to develop an mb lg formula requiring a new calibration constant crms to keep rms mb lg on the same baseline as nuttli s traditional formula based on 3rd peak amplitudes grsn stations had to be calibrated for site terms and for lg attenuation lateral variations in lgq appear to be significant across the study area and a regional q model consisting of constant q partitions north south and in the central alps was developed using measurements based on interstation and two event single station methods when plotted against surface wave estimates of mw rms mb lg measurements in central europe are found to be consistent with mw mb lg relationships for north america and southern asia thus supporting the transportability of our mb lg formula frequency wavenumber processing of grafenberg array data enabled us to extract rayleigh waves for small events and regional ms were measured using the marshall and basham formula our ms mb lg relationship extends to ms 2 5 and agrees well with observations in other regions including the western united states the discrimination potential of ms mb lg observations was examined under realistic monitoring conditions where path corrections were inferred from earthquake data and applied uniformly to natural sources and explosions under these conditions mb pn p are greater than mb lg for large nts explosions however ms mb scaling slopes are steeper for p waves than they are for lg and ms mb observations for nts explosions converge near mb 4 thus allowing for measurement errors and additional uncertainty in mb pn due to regional bias there is little difference in the discrimination potential for pn and lg waves at small magnitudes as such a regional ms mb discriminant based on lg might be preferred owing to the better detectability of lg waves for small earthquakes these results need to be confirmed for explosions at other test sites compared to teleseismic experience regional ms mb observations extend the discrimination capability to lower magnitudes by at least one ms unit

glaciological advances made with interferometric synthetic aperture radar spaceborne interferometric synthetic aperture radar insar techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half revolutionizing the study of ice dynamics spaceborne interferometry has contributed to major progress in many areas of glaciological study by providing the first comprehensive measurements of ice stream flow velocity over the major outlets of greenland and antarctica revealing that ice stream and outlet glacier flow can change rapidly months to years improving understanding of several ice sheet and ice shelf processes providing velocity for flux gate based mass balance assessment mapping flow of mountain glaciers and capturing the geomorphic traces of past ice flow we review the basic technique development the measurement characteristics and the extensive set of results yielded by these measurements