itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

paleostress adjacent to the alpine fault broader implications from fault analysis near nelson south island new zealand stress tensor determinations from probable mio pliocene age minor faults along the edge of the richmond block northwest of the alpine fault system of south island show pervasive thrusting rather than strike slip motion as proposed in some analyses this study with results almost identical to that of nicol and wise 1992 on the other side of the alpine marlborough fault system shows that the present pattern of regional compression at high angles to the alpine fault has persisted through much of the neogene over a width of about 150 km normal to the alpine fault zone one explanation might be san andreas type models invoking strike slip motion concentrated in fault zones by highly lubricating gouge coupled with strain partitioning to allow compression in adjacent regions to act at high angles to strike such models are difficult to apply to the new zealand example which now must include deformed forelands on either side of the zone but which shows little or no strike slip motion instead a model is proposed for a crustal scale flower structure to accommodate the along strike convergence of opposite dipping subducting plates a regional surface slab comprising marlborough and its adjacent forelands is undergoing compression normal to the strike of the system while semidetached deeper plate motion accommodates most of the fundamental converging oblique strike slip displacements

the nature of the plate interface and driving force of interseismic deformation in the new zealand plate boundary zone revealed by the continuous gps velocity field 1 new zealand straddles the boundary between the australian and pacific plates cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation with displacements on individual faults up to hundreds of kilometers however over periods of several years gps measurements show a remarkably smooth pattern of velocities we show here using a new method of back slip analysis that almost the entire plate boundary continuous gps velocity field can be predicted within measurement error from a simple model of elastic distortion due to deep slip on a single plate interface megathrust in the hikurangi and putsegur subduction zones or fault through continental lithosphere beneath the southern alps at the relative plate motion rates this suggests that the main driving force of plate boundary deformation is slip on the deeper moving part of the plate interface without buried creep in localized shear zones beneath individual surface faults the depth at which this deep slip terminates locking point line determines the width of deformation along the hikurangi margin there is also clockwise rotation of 150 km long segment of the fore arc wairoa domain at 4 5 1 ma relative to the australian plate about a pole in western north island model residuals in the velocity field are mainly a result of incomplete averaging of the cycle of slow slip events on the plate interface downdip of the locking point

modeling the instantaneous response of glaciers after the collapse of the larsen b ice shelf following the disintegration of the larsen b ice shelf antarctic peninsula in 2002 regular surveillance of its 20 tributary glaciers has revealed a response which is varied and complex in both space and time the major outlets have accelerated and thinned smaller glaciers have shown little or no change and glaciers flowing into the remnant scar inlet ice shelf have responded with delay in this study we present the first area wide numerical analysis of glacier dynamics before and immediately after the collapse of the ice shelf combining new datasets and a state of the art numerical ice flow model we simulate the loss of buttressing at the grounding line and find a good qualitative agreement between modelled changes in glacier flow and observations through this study we seek to improve confidence in our numerical models and their ability to capture the complex mechanical coupling between floating ice shelves and grounded ice

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

paleostress adjacent to the alpine fault of new zealand fault vein and styolite data from the doctors dome area doctors dome 75 km north of christchurch new zealand is an early pleistocene to recent structure being deformed along the southeast edge of the pacific australian plate boundary paleostress in the area has been determined in basement rocks of the mesozoic meta graywacke torlesse supergroup which lies unconformably beneath cretaceous and younger cover rocks pre late cretaceous multiple folding and bedding plane faulting produced a complex low grade metasedimentary basement with predominantly steeply plunging fold hinges and largely isotropic overall behavior with respect to later deformation probable late cretaceous wnw ese shortening and nne wsw extension of the basement produced widespread laumontite calcite and silica veins widespread but sparse slickensided minor fault surfaces are probably related to the same stress system during the late cenozoic dome stage basement was uplifted rotated and severely thrust along some of the range fronts to produce local high concentrations of small slickensided surfaces in the frontal areas inversion of basement fault data for the area indicates a general northwest compression with two peaks one wnw ese parallel to the shortening suggested by the older vein system and the other parallel to southeast northwest stylolite columns in the cover rocks this direction is approximately parallel to regional indicators of contemporary deformation in and adjacent to the alpine fault zone and suggests that the stress field affecting these rocks has not changed significantly since the late pliocene early pleistocene like the san andreas system this compression is at a high angle to the strike of the zone as a whole but is compatible with the direction of plate convergence and motion of the major faults between the overlapping ends of the alpine fault and the hikurangi subduction zone the alpine fault may become subhorizontal at middle lower crustal levels partially decoupling the crust from underlying structures and thus allowing oblique motion to be transferred directly onto the fault from the subduction complex while aiding the change from subduction to continental collision

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

spatiotemporal variations of snowmelt in antarctica derived from satellite scanning multichannel microwave radiometer and special sensor microwave imager data 1978 2004 1 we derived the extent onset date end date and duration of snowmelt in antarctica from 1978 to 2004 using satellite passive microwave scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data a wavelet transform based method was developed to determine and characterize melt occurrences about 9 12 of the antarctic surface experiences melt annually this is more than twice the surface melt extent measured in greenland seasonally surface melt primarily takes place in december january and february and peaks in early january regression analysis over the 25 year period of study reveals a negative interannual trend in surface melt nevertheless the trend inference is not statistically significant large year to year fluctuations characterize the interannual variability extremely high melt occurred in the 1982 1983 and 1991 1992 summers while extremely weak melt occurred in the 1999 2000 summer a strong correlation with air temperature suggests that the melt index can serve as a diagnostic indicator for regional temperature variations periodic melting has been observed over ross ice shelf ronne filchner ice shelf the west antarctic ice streams and outlet glaciers in the transantarctic mountains the antarctic peninsula west ice shelf shackleton ice shelf amery ice shelf and the ice shelf along the princess ragnhild coast experienced the most persistent and intensive melt and should be closely monitored for their stability in the future given the recent disintegration of the larsen ice shelf a and b

spectral discrimination between soviet explosions and earthquakes using short period array data summary spectral ratio discriminants are applied to 61 presumed nuclear explosions five large chemical explosions and 44 earthquakes in the soviet union recorded at the four uk teleseismic arrays the nuclear explosions were mainly from the shagan test site sts and from peaceful nuclear explosions pne ranging in magnitude from 4 2 to 6 2 the earthquakes were mostly located in the south central soviet union and range in magnitude from 4 4 to 5 9 for each event station pair the p wave spectrum is calculated out to 10 hz using a 5 s window from the time domain array beam and from a spectral stack the spectral ratios from the array beam in the 0 5 1 0 hz and 2 0 3 0 hz frequency bands appear to give the best discrimination performance at higher frequencies reduced signal to noise ratios particularly for the earthquakes result in fewer measurements and increased scatter in general the explosions are characterized by the existence of more high frequency energy than the shallow crustal earthquakes a least squares matrix factorization approach is used to separate out source and path effects the separation of earthquakes and explosions is generally quite good down to magnitude 4 5 where the two populations merge because of signal to noise problems the spectral values from the pnes shows increased scatter relative to those from sts presumably due to their wider range of emplacement conditions and geologic environment previous studies using regional phases indicate that nts explosions are deficient in high frequencies relative to western us earthquakes these contrasts in frequency content between nts and sts explosions may be caused by differences in the near source dynamic material response to the passage of the explosion shock wave or to depth dependent effects of q

continental heat anomalies and the extreme melting of the greenland ice surface in 2012 and 1889 recent decades have seen increased melting of the greenland ice sheet on 11 july 2012 nearly the entire surface of the ice sheet melted such rare events last occurred in 1889 and prior to that during the medieval climate anomaly studies of the 2012 event associated the presence of a thin warm elevated liquid cloud layer with surface temperatures rising above the melting point at summit station some 3212 m above sea level here we explore other potential factors in july 2012 associated with this unusual melting these include 1 warm air originating from a record north american heat wave 2 transitions in the arctic oscillation 3 transport of water vapor via an atmospheric river over the atlantic to greenland and 4 the presence of warm ocean waters south of greenland for the 1889 episode the twentieth century reanalysis and historical records showed similar factors at work however markers of biomass burning were evident in ice cores from 1889 which may reflect another possible factor in these rare events we suggest that extreme greenland summer melt episodes such as those recorded recently and in the late holocene could have involved a similar combination of slow climate processes including prolonged north american droughts heat waves and north atlantic warm oceanic temperature anomalies together with fast processes such as excursions of the arctic oscillation and transport of warm humid air in atmospheric rivers to greenland it is the fast processes that underlie the rarity of such events and influence their predictability

focal mechanisms of large earthquakes in the south island of new zealand implications for the accommodation of pacific australia plate motion b the plate motion model nuvel 1 predicts oblique convergence between the pacific and australian plates in the south island of new zealand we used p and sh body waveform analysis to constrain the focal mechanisms of the 15 largest earthquakes ms 5 8 that have occurred in this region since 1964 in order to see how the plate motion is accommodated at the southern end of the alpine fault convergence is achieved by oblique slip movement along a concentrated zone of deformation in the southern offshore region one event may be related to thrusting of the australian plate beneath the pacific plate and another strike slip event probably demonstrates movement on an active strike slip fault system parallel to but offset from the southern limit of the alpine fault this geometry provides a possible mechanism for the rapid uplift of the fiordland region deformation in the northern south island is more distributed in the south west marlborough region partitioning occurs between strike slip faulting in the se and reverse faulting farther nw in the buller region we suggest that the partitioning developed as a consequence of an increasing component of shortening that was accommodated by slip on reactivated pre existing normal faults in the buller region shortening in the buller region may have deflected the ne end of the alpine fault towards the nw forming the prominent bend the marlborough fault system with its youngest and most active faults to the se probably developed in an attempt to maintain a through going strike slip structure as each of the strike slip faults was transported towards the north west partitioning of the opposite polarity with reverse faulting se of the strike slip faulting occurs in north east marlborough the boundary between the two different styles of partitioning in ne and sw marlborough appears to coincide with a change in the nature of the downgoing slab and a change in strike of faults of the marlborough fault system a normal faulting earthquake on the northern edge of the chatham rise probably results from a complex interaction of the buoyant continental crust in that region with the subduction zone and the overlying marlborough fault system

foehn event triggered by an atmospheric river underlies record setting temperature along continental antarctica fondap conicyt chile 15110009 cr2 scientific committee on antarctic research scar university of wisconsin madison antarctic meteorological research center for the data set data display and information nsf grant ant 1535632 nlhpc

west antarctic surface melt triggered by atmospheric rivers recent major melting events in west antarctica have raised concerns about a potential hydrofracturing and ice shelf instability these events often share common forcings of surface melt like anomalous radiative fluxes turbulent heat fluxes and fohn winds using an atmospheric river detection algorithm developed for antarctica together with surface melt datasets we produced a climatology of atmospheric river related surface melting around antarctica and show that atmospheric rivers are associated with a large percentage of these surface melt events despite their rarity around 12 events per year in west antarctica atmospheric rivers are associated with around 40 of the total summer meltwater generated across the ross ice shelf to nearly 100 in the higher elevation marie byrd land and 40 80 of the total winter meltwater generated on the wilkins bach george iv and larsen b and c ice shelves these events were all related to high pressure blocking ridges that directed anomalous poleward moisture transport towards the continent major melt events in the west antarctic ice sheet only occur about a couple times per decade but a 1 2 c warming and continued increase in atmospheric river activity could increase the melt frequency with consequences for ice shelf stability atmospheric rivers associated with blocking events are related to a large fraction of the surface ice melt events in west antarctica suggest observation based analyses of atmospheric dynamics and west antarctic surface melt

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

strain distribution across the australian pacific plate boundary in the central south island new zealand from 1992 gps and earlier terrestrial observations as part of a geodetic experiment aimed at understanding the deformation associated with the australian pacific plate boundary in the south island of new zealand in 1992 we reoccupied using global positioning system gps techniques a first order triangulation and trilateration network established in 1978 between christchurch on the east coast and hokitika on the west the network crosses the south island a few tens of kilometers southwest of the region where the plate boundary changes from a single throughgoing oblique slip fault the alpine fault to a series of subparallel strike slip faults the marlborough faults the gps data have been analyzed as daily network solutions with about 12 stations in each solution rms repeatabilities for stations with multiple occupations are 4 mm 8 mm and 15 mm in the north east and vertical components respectively the observed strain across the network is consistent with the entire nuvel ia pacific australia plate velocity being accommodated on land across this part of the south island shear strain rates derived from the gps and terrestrial data show that the highest strain rate 0 4 rad yr occurs in the region of the southern alps and alpine fault this rate is about two thirds of the rate predicted from the nuvel ia plate velocity model assuming that all the plate boundary deformation occurs across this region implying that about two thirds of the plate motion is accommodated in the vicinity of the alpine fault significant shear strain rates greater than 0 2 rad yr are also observed farther east particularly in the region of the porters pass amberley fault zone demonstrating that this zone accommodates a significant part of the plate boundary deformation using dislocation modeling we show that the variation in fault parallel shear strain rates across the alpine fault is reasonably consistent with a nonoptimized dislocation model involving a 50 dipping fault that is presently locked to a depth of 12 km one explanation for this observation is that the upper 12 km of the crust in this area is storing most of the right lateral shear component of the relative plate motion as elastic energy that will be released in a future major earthquake the variation in the other component of shear strain which may be interpreted as fault normal relative contraction is not explained by a simple dislocation model implying that the normal component of plate motion is taken up in other ways

signal processing for indian and pakistan nuclear tests recorded at ims stations located in israel in compliance with the comprehensive nuclear test ban treaty ctbt the international monitoring system ims was designed for detection and location of the clandestine nuclear tests nt two auxiliary ims seismic stations mrni and eil deployed recently were subjected to detectability travel time calibration and discrimination analysis the study is based on the three recent 1998 underground nuclear explosions one of india and two of pakistan which provided a ground truth test of the existing ims these events attaining magnitudes of 5 2 4 8 and 4 6 correspondingly were registered by many ims and other seismic stations the mrni and eil broadband bb stations are located in israel at teleseismic distances from the explosions of 3600 2800 and 2700 km respectively where the signals from the tests are already weak the indian and the second pakistan nt were not detected by the short period israel seismic network isn using standard sta lta triggering therefore for the chosen ims stations we compare the sta lta response to the results of the more sensitive murdock hutt mh and the adaptive statistically optimal detector od that showed triggering for these three events the second pakistan nt signal arrived at the isn and the ims stations in the coda of a strong afghanistan earthquake and was further disturbed by a preceding signal from a local earthquake however the nt signal was successfully extracted at eil and mrni stations using mh and od procedures for comparison we provide the signal analysis of the cooperating bb station jer with considerably worse noise conditions than eil and mrni and show that od can detect events when the other algorithms fail using the most quiet eil station the most sensitive od and different bandpass filters we tried in addition to detect the small kazakh chemical 100 ton calibration explosion of 1998 with magnitude 3 7 at a distance approaching 4000 km the detector response curve showed uprising in the expected signal time interval but yet was low for a reliable decision after an nt is detected it should be recognized spectra were calculated in a 15 sec window including p and p coda waves the spectra for the first pakistan nt showed a pronounced spectral null at 1 7 hz for all three components of the eil station the effect was confirmed by observation of the same spectral null at the vertical component of the isn stations for this ground truth explosion with a reported shallow source depth the phenomenon can be explained in terms of the interference of p and pp phases however the spectral null feature considered separately cannot serve as a reliable identification characteristic of nuclear explosions because not all the tests provide the nulls whereas some earthquakes show this feature therefore the multi channel spectral discrimination analysis based on a spectral ratio of low to high frequency energy in the 0 6 1 hz and 1 3 hz bands and a semblance of spectral curves in the 0 6 2 hz band was conducted both statistics were calculated for the vertical component of the isn stations as well for the three components of the eil station the statistics provided a reliable discrimination between the recent nt and several nearby earthquakes and showed compliance with the former analysis of soviet and chinese nt where nuclear tests demonstrated lower values of energy ratio and spectral semblance than earthquakes accurate location of nt requires calibration of travel time for ims stations using known source locations iaspei91 travel time tables and neic origin times we calculated expected arrival time for the p waves to the eil and mrni stations and showed that the measured arrival time has a delay of about 4 sec similar results were obtained for the nearby pakistan earthquakes the analysis was complimented by the p travel time measurements for the set of semipalatinsk nt which showed delays of about 3 7 sec to the short period mbh station which is a surrogate station for eil similar delays at different stations evidence a path rather than site effect the results can be used for calibration of the ims stations eil and mrni regarding asian seismic events

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

a bayesian approach to determining and parametrizing earthquake focal mechanisms summary we develop a new probabilistic bayesian method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data we investigate the use of generalized matrix fisher distributions for parametrizing focal mechanism uncertainties the advantages of our approach are that it 1 models the data generation process and incorporates observational errors particularly those arising from imperfectly known earthquake locations 2 allows exploration of the entire parameter space 3 leads to natural point estimates of focal mechanism parameters 4 allows the inclusion of a priori information about the focal mechanism parameters and 5 allows the resulting posterior pdf to be well approximated by generalized matrix fisher distributions we present here the results of our method in two situations we first consider the case in which the seismic velocity of the region of interest described by a velocity model is presumed to be precisely known with application to seismic data from the raukumara peninsula new zealand we then consider the case in which the velocity model is imperfectly known with application to data from the kawerau region new zealand we find that our estimated focal mechanism solutions are for the most part consistent with all available polarity data and correspond closely to solutions obtained using established methods further the generalized matrix fisher distributions we examine provide a good fit to our bayesian posterior pdf of the focal mechanism parameters finally we demonstrate how informative prior distributions on focal mechanism parameters can be incorporated into our model

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

behavior of the brittle crust in wide plate boundary zones in wide and active continental plate boundary zones ductile flow in the deeper and strong parts of the lithosphere may control crustal deformation this is likely if average resistive shear stresses on faults in the brittle crust are much less than 108 pa and the underlying bulk effective viscosity is much greater than 1021 pa s in this case a simple model of distributed deformation referred to as the floating block model may be useful this treats the crust as an array of rotating and translating rigid blocks which are floating on an underlying continuous flow with a constant rheology the model is analyzed in detail in this paper because it has the potential to link detailed observations of crustal deformation with the large scale flow crustal blocks are defined by at least two sets of faults the kinematics of crustal deformation can be described in terms of the motions of these blocks both the relative motion on block boundaries faults and block tilting about a horizontal axis can be described in terms of the underlying flow and block rotation about a vertical axis however rotations about a vertical axis which are an important component of the crustal deformation will depend not only on the underlying flow but also on the shape orientation and arrangement of the crustal blocks the average rotation rate about a vertical axis over finite rotations will be significantly different from that predicted at any instant also the rotation history is considerably complicated if as is likely the underlying flow field or block shape has changed with time these aspects of crustal deformation are discussed with reference to real zones of active deformation in new zealand greece and western north america

the dynamics of western north america stress magnitudes and the relative role of gravitational potential energy plate interaction at the boundary and basal tractions summary we investigate the forces involved in driving long term large scale continental deformation in western north america and quantify the vertically averaged deviatoric stress field arising from internal buoyancy forces and the accommodation of relative plate motions in addition we investigate the ability of regional models to resolve the level of tractions acting at the base of the lithosphere we directly solve force balance equations for vertically averaged deviatoric stresses associated with differences in values of 1 lithospheric thickness times the gravitational potential energy per unit area gpe the gpe values are inferred using both the etopo5 topographic data set and the crust2 0 crustal thickness model deviatoric stresses associated with basal tractions are calculated globally with inputs determined from an isoviscous upper mantle 10 21 pa s 3 d large scale convection model in which mantle density variations were inferred from tomographic data and the history of subduction in a 211parameter iterative inversion we then solve for a stress field boundary condition by fitting stress field indicators i e the directions and relative magnitudes of the principal axes of kinematic strain rates magnitudes of the total vertically averaged deviatoric stress field sum of gpe solution with the boundary condition solution range from 5 to 10 mpa within a 100 km thick lithosphere these magnitudes are calibrated by the gpe differences along with the spatial variation in deformation style there is a trade off between the scaling of the basal traction deviatoric stress field and the boundary condition solution however the combined boundary conditions plus basal traction solution is robust in both magnitude and style and when added to the contribution from gpe differences provides a global minimum of misfit between the total deviatoric stress solution and the stress field indicators gpe variations account for 50 per cent of the deviatoric stress magnitudes driving deformation while boundary condition stresses account for the remaining 50 per cent of deviatoric stress magnitude by comparing possible end member strength profiles with our vertically averaged deviatoric stresses we infer that the bulk of the strength within the lithosphere in western north america lies within the brittle seismogenic layer

widespread movement of meltwater onto and across antarctic ice shelves surface water and its drainage across the surface of antarctic ice is shown to be widespread large scale and to have persisted for decades melt ponds and streams form across antarctica but their full extent and the duration of their existence have remained unclear now jonathan kingslake et al show that surface drainage systems including interconnected ponds and streams have existed for decades as far as 85 s and up to 1 300 metres elevation they show that surface water can be transported more than 100 kilometres creating pond networks almost 80 kilometres long although the implications of the findings for ice sheet dynamics are not explored the study demonstrates that surface water drainage is more extensive than previously thought and is probably a persistent feature of the antarctic ice sheet elsewhere in this issue robin bell et al report on the influence of surface meltwater on antarctic ice shelf stability and find that it might not be a universally destructive force as was previously thought surface meltwater drains across ice sheets forming melt ponds that can trigger ice shelf collapse1 2 acceleration of grounded ice flow and increased sea level rise3 4 5 numerical models of the antarctic ice sheet that incorporate meltwater s impact on ice shelves but ignore the movement of water across the ice surface predict a metre of global sea level rise this century5 in response to atmospheric warming6 to understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed yet despite extensive research in greenland7 8 9 10 and observations of individual drainage systems in antarctica10 11 12 13 14 15 16 17 we have little understanding of antarctic wide surface hydrology or how it will evolve here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds hereafter surface drainage as far south as 85 s and as high as 1 300 metres above sea level our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards surface drainage has persisted for decades transporting water up to 120 kilometres from grounded ice onto and across ice shelves feeding vast melt ponds up to 80 kilometres long large scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse as melt rates increase this century while antarctic surface melt ponds are relatively well documented on some ice shelves we have discovered that ponds often form part of widespread large scale surface drainage systems in a warming climate enhanced surface drainage could accelerate future ice mass loss from antarctic potentially via positive feedbacks between the extent of exposed rock melting and thinning of the ice sheet

foehn winds link climate driven warming to ice shelf evolution in antarctica rapid warming of the antarctic peninsula over the past several decades has led to extensive surface melting on its eastern side and the disintegration of the prince gustav larsen a and larsen b ice shelves the warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the southern annular mode sam which is thought to promote more frequent warm dry downsloping foehn winds along the lee or eastern side of the peninsula we examined variability in foehn frequency and its relationship to temperature and patterns of synoptic scale circulation using a multidecadal meteorological record from the argentine station matienzo located between the larsen a and b embayments this record was further augmented with a network of six weather stations installed under the u s nsf larsen ice shelf system antarctica project significant warming was observed in all seasons at matienzo with the largest seasonal increase occurring in austral winter 3 71 c between 1962 1972 and 1999 2010 frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales surface temperature and foehn winds were also sensitive to climate variability with both variables exhibiting strong positive correlations with the sam index concomitant positive trends in foehn frequency temperature and sam are present during austral summer with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves these observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the larsen b ice shelf

the role of atmospheric rivers in anomalous snow accumulation in east antarctica recent heavy snow accumulation events over dronning maud land dml east antarctica contributed significantly to the antarctic ice sheet surface mass balance smb here we combine in situ accumulation measurements and radar derived snowfall rates from princess elisabeth station pe located in the dml escarpment zone along with the european centre for medium range weather forecasts interim reanalysis to investigate moisture transport patterns responsible for these events in particular two high accumulation events in may 2009 and february 2011 showed an atmospheric river ar signature with enhanced integrated water vapor iwv concentrated in narrow long bands stretching from subtropical latitudes to the east antarctic coast adapting iwv based ar threshold criteria for antarctica by accounting for the much colder and drier environment we find that it was four and five ars reaching the coastal dml that contributed 74 80 of the outstanding smb during 2009 and 2011 at pe therefore accounting for ars is crucial for understanding east antarctic smb

origin of small scale segmentation and transpressional thrusting along the alpine fault new zealand the alpine fault is the major structural feature of the australian pacific plate boundary in the south island of new zealand geologic evidence suggests that half to three quarters of the plate boundary displacement is accommodated by movement on the fault detailed investigation of the central section of the alpine fault has revealed that it consists of oblique thrust sections striking 020 050 that are linked by subvertical right lateral faults striking between 065 and 090 the segmentation is on a scale of 1 10 km similarly oriented right lateral faults are abundant southeast of the alpine fault and are consistent with stresses induced in an elastic layer by an oblique slip ductile fault zone below propagation of the fault to the surface is predicted to result in an en echelon arrangement of strike slip and thrust segments it is suggested that the spatial distribution of segments is affected by the existence of deeply incised valleys in the hanging wall that disturb the stress field to depths of 1 4 km the segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes

quantifying vulnerability of antarctic ice shelves to hydrofracture using microwave scattering properties abstract recent ice shelf disintegrations on the antarctic peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture in this study we use active microwave scatterometry in time series to estimate melt season duration and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in antarctic ice shelf firn we demonstrate a physical relationship between melt days and firn ice backscatter using scatterometry and field data from greenland and apply the observed relationship to derive and map a vulnerability index for antarctica s ice shelves the index reveals that some remaining antarctic peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture we also show that the progression of an ice shelf towards vulnerability is affected by many factors such as surface mass balance internal stresses and ice shelf geometry

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

an analysis of spectral differences between nevada test site and shagan river nuclear explosions spectral ratio discrimination studies carried out on events located in the western united states and soviet union s u illustrate that pronounced differences in radiated explosion source spectra relative to nearby earthquakes exist between the two regions nevada test site nts explosions are characterized by the existence of more low frequency and or less high frequency energy greater low to high frequency spectral ratios than western u s earthquakes the opposite pattern is observed in the s u with nuclear explosions appearing to have more high frequency and or less low frequency energy than earthquakes these observations may be caused by at least two principal effects that are probably acting in parallel 1 variations in depth dependent effects of attenuation acting between the shallow explosions and deeper earthquakes and 2 differences in the dynamic response of the near source geology to the passing explosion shock wave anelastic synthetic seismogram calculations illustrate that depth dependent attenuation effects may explain the spectral observations however a number of observations using near and far field data from nts explosions suggest that near source effects are the dominant factor a quasi empirical explosion source model is proposed that simultaneously fits the spectral ratio data from both the u s and s u relative to earthquakes in each of the respective regions additionally the model fits the trends of the spectral ratios observed as a function of magnitude the key to the model is the shape of the pressure time history acting at the elastic radius for explosions detonated in weak porous rock the radiated shock wave divides into a two wave system consisting of an elastic precursor followed by a plastic wave the generation of this two wave system introduces a rise time into the pressure time history in the frequency domain a second corner frequency is established in a third order model with an 3 high frequency decay whose value is inversely proportional to the time separation of the two waves in higher strength saturated rocks or for overburied explosions the effective rise time is short and a second order model is appropriate with an 2 high frequency decay the second order model provides a good fit to the s u data in contrast a hybrid model is required to fit the nts data with an 3 high frequency decay for shallow explosions detonated in unsaturated tuff that evolves to an 2 decay as depth of burials reach higher strength saturated rocks below the water table

andersonian wrench faulting in a regional stress field during the 2010 2011 canterbury new zealand earthquake sequence the initial mw7 1 darfield earthquake sequence was centred west of christchurch city in the south island of new zealand but aftershocks including a highly destructive mw6 3 event eventually extended eastwards across the city to the coast the mainshock gave rise to right lateral strike slip of up to 5 m along the segmented rupture trace of a subvertical fault trending 085 58 across the canterbury plains for c 30 km in agreement with teleseismic focal mechan isms near field data however suggest that the mainshock was composite initiating with reverse slip north of the surface rupture stress determinations for the central south island show maximum compressive stress s1 to be horizontal and oriented 115 58 the principal dextral rupture there fore lies at c 3 08 to regional s1 the classic andersonian orientation for a low displacement wrench fault an aftershock lineament trending c 1458 possibly represents a conjugate left lateral strike slip structure this stress field is also consistent with predominantly reverse slip reactivation of nne ne faults along the southern alps range front the main strike slip fault appears to have a low cumulative displacement and may represent either a fairly newly formed fault in the regional stress field or an existing subvertical fault that happens to be optimally oriented for frictional reactivation

stress field and kinematics for diffuse microseismicity in a zone of continental transpression south island new zealand we analyze shallow 0 20 km microseismicity adjacent to the alpine fault in new zealand where there is oblique convergence of the australian and pacific plates focal mechanisms for 155 earthquakes june 2012 october 2013 are inverted to determine the orientation of the stress field this yields a principal horizontal axis of compression shmax 114 10 which cannot be explained in terms of the sum of stress from tectonic loading due to plate convergence indicated by gps observations and gravitational stresses the azimuth of slip vectors for individual focal mechanisms cluster perpendicular and parallel to the plate convergence vector these faults however strike at 45 to shmax from the stress inversion suggesting a very low coefficient of friction the earthquake slip directions may be kinematically controlled accommodating the plate convergence on a limited set of fractures similar to the segmentation for neotectonic faulting along the alpine fault which is partitioned into strike slip and thrust segments at a 1 10 km scale we suggest two possible controls on our calculated shmax azimuths firstly there may be a slight clockwise bias in the estimates of shmax from earthquakes slip may be occurring on a more limited range of fractures than assumed by the stress inversion method although this effect is likely to be relatively small 5 more importantly the components of the stress field may be relieved at different time scales during big earthquakes resulting in a residual stress field that varies significantly 15 on timescales of several large earthquakes

central west antarctica among the most rapidly warming regions on earth the west antarctic ice sheet is contributing to sea level rise but temperature trends in the region have remained uncertain a complete temperature record for byrd station in central west antarctica spanning from 1958 to 2010 establishes west antarctica as one of the fastest warming regions globally

a structural glaciological analysis of the 2002 larsen b ice shelf collapse this study provides a detailed structural glaciological analysis of changes in surface structures on the larsen b ice shelf on the antarctic peninsula prior to its collapse in february march 2002 mapped features include the ice shelf front rifts crevasses longitudinal linear surface structures and meltwater features we define domains on the ice shelf related to glacier source areas and demonstrate that prior to collapse the central larsen b ice shelf consisted of four sutured flow units fed by crane jorum punchbowl and hektoria green evans glaciers between these flow units were suture zones of thinner ice where the feeder glaciers merged prior to collapse large open rift systems were present offshore of foyn point and cape disappointment these rifts became more pronounced in the years preceding break up and ice blocks in the rifts rotated because of the strong lateral shear in this zone velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago we suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units this we believe was the result of ice shelf front retreat during 1998 2000 reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units ice shelf thinning and pre shelf break up glacier acceleration

enhanced seismic source discrimination using noress recordings from eurasian events summary the problem of discriminating between earthquakes and underground nuclear explosions is formulated as an exercise in pattern recognition approach analysis an advantage of our procedure is flexibility by combining both adaptive noise suppression and event classification incorporating feature selection criteria the analysis has been applied to a learning set of 44 nuclear explosions eight test sites and 35 earthquakes in eurasia recorded at the noress array fig 1 the signal features considered were the normalized power in eight spectral bands in the 0 2 5 0 hz range of the p wave 6 s and the p coda 30 s physically it means that we exploit potential differences in the shape of earthquake and explosion spectra respectively other features included are peak p and p coda amplitude frequencies and relative p p coda power these 19 features were extracted either from conventional array beam traces or the optimum group filtered traces ogf removal of coherent low frequency noise using the feature selection algorithm based on estimates of the expected probability of misclassification epmc only two to four features were needed for optimum discrimination performance the dominant features were coda excitation and p and p coda power at lower signal frequencies furthermore feature parameters extracted from the ogf traces had a slightly better performance in comparison to those extracted from beam traces finally there were no misclassifications for ogf derived features when the explosion population was limited to east kazakh events while including events from the other test sites lead to a decrease in discrimination power

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

an analysis of p wave amplitudes recorded by seismological stations in the ussr summary short period p wave amplitudes at soviet seismic stations are analysed to determine an amplitude distance curve in the range 0 180 from the ussr station amplitude terms corrected for crustal amplification effects are determined from seismic sources located between 30 and 90 a relationship between these station terms and regional p wave speed and regional heat flow is determined and is found to be in close agreement with similar observations in north america station amplitude terms were found to be reasonably uniform across the continental portion of the ussr but the baikal rift valley is characterized by very low p wave amplitudes and is the most significant feature discernible from the p wave amplitude terms

on the forces driving plate tectonics inferences from absolute plate velocities and intraplate stress summary absolute plate motions and intraplate stress both serve as tests of models for the forces acting on plate boundaries plate velocities relative to a presumedly fixed underlying mantle are calculated from the hypothesis that no net torque is exerted on the lithosphere intraplate stress is calculated by solving the equilibrium equations for thin elastic shells in the membrane state of stress the absolute velocity fields predicted from a wide assortment of physical and geological models are all very similar while the global pattern of absolute velocity is probably close to those predicted by such models the absolute motions do not therefore provide a strong test of the driving mechanism comparison of predicted intraplate stress with the long wavelength features of the global stress field however as determined by in situ measurements earthquake mechanisms and stressinduced geological structures does prove to be a powerful test of possible driving forces all absolute velocity models have several interesting properties lithosphere in the equatorial half of the earth is moving significantly faster than lithosphere in the polar half some connection to the earth s rotation is implied since this statement is demonstrably untrue for co ordinate poles much different from the geographic pole subducted slabs are characterized by a slow horizontal translation perpendicular to strike that is independent of the plate convergence rate confounding attempts to explain the dip angles of benioff zones in terms of a uniform vertical sinking and a variable absolute velocity for the overthrust plate ridges must migrate at a wide range of velocities relative to their underlying source of new lithosphere such rapid migration may be a necessary but is not a sufficient condition for ridge jumps force models considered in velocity and stress calculations include driving forces at spreading centres and subduction zones and various parameterizations of drag at the base of the lithosphere from the rms absolute velocities of individual plates there is a weak indication that pull by subducted lithosphere at trenches is an important driving force and that drag may be greater beneath continental than oceanic lithosphere the predicted intraplate deviatoric stress cannot match the well determined stress fields in north america and europe unless the driving force exerted at ridges is at least comparable in magnitude to other forces in the system the mid plate stresses are very sensitive to the nature of drag at the base of the lithosphere and thus measured stresses may ultimately provide a sensitive test of absolute plate velocities

microseismicity and stress in the vicinity of the alpine fault central southern alps new zealand 1 we investigate present day microseismicity associated with the central alpine fault and the zone of active deformation and uplift in the central southern alps using 14 months of data robust hypocenter locations have been obtained for 1800 earthquakes of magnitudes between 0 3 and 4 2 we derived a magnitude scale with a frequency dependent attenuation factor f 0f where 0 1 89 0 02 10 3 s km that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents the maximum depth of the seismicity varies systematically with distance from the alpine fault from 10 2 km near the fault to 8 2 km within 20 km and 15 2 km further southeast this distribution correlates with lateral variations in crustal resistivity earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities 100 m rocks at greater depth are too hot too fluid saturated or too weak to produce detectable earthquakes focal mechanism solutions computed for 211 earthquakes ml 0 44 exhibit predominantly strike slip mechanisms we obtain a maximum horizontal compressive stress direction of 115 10 from focal mechanism inversion this azimuth is consistent with findings from elsewhere in the central and northern south island and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief our stress estimates suggest that the alpine fault with a mean strike of 055 is poorly oriented in an andersonian sense but that individual thrust and strike slip segments of the fault s surface trace have close to optimal orientations

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

spectral discrimination analysis of eurasian nuclear tests and earthquakes recorded by the israel seismic network and the noress array abstract the energy spectral ratio and the innovative spectral semblance discriminants successfully performed previously on a local israeli events were verified on teleseismic short period recordings the events tested include 29 nuclear explosions and 41 earthquakes mb 5 2 6 5 mainly from china and kazakhstan recorded by the israel seismic network isn and the noress array a 15 s window comprising p and p coda waves was selected for the analysis the semblance statistic commonly used in seismic prospecting for phase correlation in the time domain was modified and utilized as a measure of coherency of the smoothed spectra across the network array the semblance and the average spectral ratio of low to high frequency energy were evaluated using a subset of 7 10 stations for a given event semblance and spectral ratio values calculated from isn seismograms were found to be higher for earthquakes where the analyzed waves are richer in low frequency energy and have more coherent spectral shapes than explosions these observations are contrary to those observed for local events the best performance is provided in the frequency bands 0 6 1 hz 1 3 hz for the ratio and 0 6 2 hz for the semblance joint application of the two discriminants showed almost full separation 95 between the two populations some explosions exhibited pronounced minima nulls near 1 hz which could be interpreted in terms of interference of p and pp waves from a source at the depth of several hundreds of meters nevertheless this feature could not be utilized as a discriminant many explosions revealed strong variability of this minimum across the isn network and some earthquakes also distinctly exhibited this feature the isn and noress discrimination performances were compared the latter records showed the same as the isn relation between spectral ratio values for earthquakes and explosions whereas the character of semblance was reversed the ratios in the frequency bands 0 6 0 8 hz 0 6 10 hz yield full separation of the two populations in general the spectral ratio performance appears to be better for noress recordings whereas the spectral semblance is better for the isn data

dynamics of the pacific north american plate boundary in the western united states the vertically averaged deviatoric stress tensor field within the western united states was determined with topographic data geoid data recent global positioning system observations and strain rate magnitudes and styles from quaternary faults gravitational potential energy differences control the large fault normal compression on the california coast deformation in the basin and range is driven in part by gravitational potential energy differences but extension directions there are modified by plate interaction stresses the california shear zone has relatively low vertically averaged viscosity of about 1021 pascal seconds whereas the basin and range has a higher vertically averaged viscosity of 1022pascal seconds

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

foehn warming distributions in nonlinear and linear flow regimes a focus on the antarctic peninsula the structure of lee side warming during foehn events is investigated as a function of cross barrier flow regime linearity two contrasting cases of westerly flow over the antarctic peninsula ap are considered one highly nonlinear the other relatively linear westerly flow impinging on the ap provides one of the best natural laboratories in the world for the study of foehn owing to its maritime setting and the larsen c ice shelf lcis providing an expansive homogeneous and smooth surface on its east side numerical simulations with the met office unified model at 1 5 km grid size and aircraft observations are utilized in case a relatively weak southwesterly cross peninsula flow and an elevated upwind inversion dictate a highly nonlinear foehn event with mountain wave breaking observed the consequent strongly accelerated downslope flow leads to high amplitude warming and ice shelf melt in the immediate lee of the ap however this foehn warming diminishes rapidly downwind due to upward ascent of the foehn flow via a hydraulic jump in case c strong northwesterly winds dictate a relatively linear flow regime there is no hydraulic jump and strong foehn winds are able to flow at low levels across the entire ice shelf mechanically mixing the near surface flow preventing the development of a strong surface inversion and delivering large fluxes of sensible heat to the ice shelf consequently in case c ice melt rates are considerably greater over the lcis as a whole than in case a our results imply that although nonlinear foehn events cause intense warming in the immediate lee of mountains linear foehn events will commonly cause more extensive lee side warming and over an ice surface higher melt rates this has major implications for the ap where recent east coast warming has led to the collapse of two ice shelves immediately north of the lcis

continent scale strike slip on a low angle fault beneath new zealand s southern alps implications for crustal thickening in oblique collision zones new zealand s southern alps lie adjacent to the continent scale dextral strike slip alpine fault on the boundary between the pacific and australian plates we show with a simple 2 d model of crustal balancing that the observed crustal root and erosion expressed as equivalent crustal shortening is up to twice that predicted by the orthogonal plate convergence since 11 ma and even since 23 ma when the alpine fault formed we consider two explanations for this involving a strong component of motion along the length of the plate boundary zone geophysical data indicate that the alpine fault has a listric geometry flattening at mid crustal levels and has accommodated sideways underthrusting of australian plate crust beneath pacific plate crust the geometry of the crustal root together with plate reconstructions requires the underthrust crust to be the hyperextended part of an asymmetric rift system which formed over 500 km farther south during the eocene the narrow remnant part today forms the western margin of the campbell plateau at 10 ma the hyperextended margin underwent shallow subduction in the puysegur subduction zone and then was dragged over 300 km along the length of the southern alps beneath a low angle 20 section of the alpine fault we speculate that prior to 10 ma more distributed lower crustal shortening and thickening occurred beneath the southern alps accommodating southward extrusion of continental crust in the northern part of the plate boundary zone providing a mechanism for clockwise rotation of the hikurangi margin

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

the seismic disturbance of 1976 march 20 elast kazakhstan earthquake or explosions summary on 1976 march 20 a seismic disturbance took place near an explosion test site in east kazakhstan ussr on the mb ms criterion this disturbance is identified as an earthquake however it has been suggested that the source may have been one or more explosions it is shown here that the polarities and relative amplitudes of the main arrivals on the short period p wave seismograms of the disturbance can be accounted for by assuming the source was an earthquake in a crust with some lateral variation in structure there is no evidence that the disturbance was anything other than a single earthquake

calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor

discrimination of nuclear explosions and earthquakes from teleseismic distances with a local network of short period seismic stations using artificial neural networks abstract seismic discrimination capability of artificial neural networks anns was studied using earthquakes and nuclear explosions from teleseismic distances the events were selected from two areas which were analyzed separately first 23 nuclear explosions from semipalatinsk and lop nor test sites were compared with 46 earthquakes from adjacent areas second 39 explosions from nevada test site were compared with 27 earthquakes from close by areas the basic discriminants were complexity spectral ratio and third moment of frequency the spectral discriminants were computed in five different ways to obtain all the information embedded in the signals some of which were relatively weak the discriminants were computed using data from six short period stations in central and southern finland the spectral contents of the signals of both classes varied considerably between the stations the 66 discriminants were formed into 65 optimum subsets of different sizes by using stepwise linear regression a type of ann called multilayer perceptron mlp was applied to each of the subsets as a comparison the classification was repeated using linear discrimination analysis lda since the number of events was small the testing was made with the leave one out method the ann gave significantly better results than lda as a final tool for discrimination a combination of the ten neural nets with the best performance were used all events from central asia were clearly discriminated and over 90 of the events from nevada region were confidently discriminated the better performance of anns was attributed to its ability to form complex decision regions between the groups and to its highly non linear nature

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

a bayesian approach to estimating tectonic stress from seismological data summary earthquakes are conspicuous manifestations of tectonic stress but the non linear relationships between the stresses acting on a fault plane its frictional slip and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress moreover observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations however by assuming that each earthquake in a small volume of the crust represents a single uniform state of stress the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated here we outline a probabilistic bayesian technique for estimating tectonic stress directions from primary seismological observations the bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation we show our bayesian formulation to be equivalent to a well known analytical solution for a single errorless focal mechanism observation the new approach has the distinct advantage however of including 1 multiple earthquakes 2 fault plane ambiguities 3 observational errors and 4 any prior knowledge of the stress field our approach while computationally demanding in some cases is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters such as seismic anisotropy and geodetic strain rate observations and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

observed antarctic interannual climate variability and tropical linkages abstractthis study reviews the mechanisms associated with antarctic tropical climate linkages and presents new analyses of the seasonality and spatial patterns of tropical climate signals in the antarctic for the late 1950s to the present tropical climate signals are primarily communicated to the antarctic via the pacific south america psa pattern and the southern annular mode sam the impacts of these circulation patterns and their tropical linkages are evident in regressions of seasonally stratified antarctic station temperature data and annually resolved ice core records on global fields of sea surface temperature sea level pressure and precipitation temperature and ice core anomalies in the antarctic peninsula region and adjoining areas of west antarctica are significantly impacted by the psa interpreted as a rossby wave train driven by anomalous tropical deep convection during enso events this pattern is most evident in the austral spring consistent with recent studies suggesting that atm

a focused look at the alpine fault new zealand seismicity focal mechanisms and stress observations the alpine fault is the pacific australian plate boundary in the south island of new zealand this study analyzes 195 earthquakes recorded during the 6 month duration of the southern alps passive seismic experiment sapse in 1995 1996 and two mr 5 0 earthquakes and aftershocks in 1997 which occurred close to the central part of the alpine fault precise earthquake locations are derived by simultaneous inversion for hypocenter parameters a one dimensional velocity model and station corrections together with focal mechanisms calculated using a first motion and amplitude ratio method these results provide a picture of the seismotectonics in the central south island over a 6 month period moment tensor inversions of three earthquakes provide an independent means of comparison to the focal mechanisms derived using the amplitude first motion method to validate our observations over time we compare the sapse seismicity with the seismicity recorded by the new zealand national seismic network nznsn and a local network at lake pukaki east of the southern alps 6 months versus 8 years our study indicates that the alpine fault releases elastic strain seismically from the surface down to 10 12 km depth between milford sound in the south and the hope fault in the north the seismicity rate of the alpine fault is low but comparable to locked sections of the san andreas fault with large earthquakes expected seismicity decreases north of bruce bay at the alpine fault and within a triangular region along the alpine fault located between the hope and porters pass fault zones we interpret this as the result of deformation distributed on the alpine fault and the hope and porters pass fault zones the base of the seismogenic zone is fairly uniform at 12 km 2km over large parts of the south island the high alps region has a shallower base of the seismogenic zone indicating localized elevated temperatures east of the alpine fault most of the study region deforms under a uniform stress field with a maximum principal horizontal shortening direction of 110o 120 o similar to geodetic observations and plate motions this confirms that the region is not undergoing strain partitioning the earthquake data show that the deformation away from the alpine fault is distributed on mainly nne trending thrust faults and strike slip transfer faults with a maximum seismogenic depth of 12km

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years