acceleration spectra for subduction zone earthquakes we estimate the source spectra of shallow earthquakes from digital recordings of teleseismic p wave groups that is p pp sp by making frequency dependent corrections for the attenuation and for the interference of the free surface the correction for the interference of the free surface assumes that the earthquake radiates energy from a range of depths we apply this spectral analysis to a set of 12 subduction zone earthquakes which range in size from ms 6 2 to 8 1 obtaining corrected p wave acceleration spectra on the frequency band from 0 01 to 2 0 hz seismic moment estimates from surface waves and normal modes are used to extend these p wave spectra to the frequency band from 0 001 to 0 01 hz the acceleration spectra of moderate subduction zone earthquakes that is earthquakes whose seismic moments are less than 1027 dyn cm exhibit square or brune type spectra while the acceleration spectra of large subduction zone earthquakes that is earthquakes whose seismic moments are greater than 1027 dyn cm exhibit intermediate slopes where u 5 4 for frequencies from 0 005 to 0 05 hz for this set of earthquakes spectral shape appears to be a discontinuous function of seismic moment using reasonable assumptions for the phase characteristics we transform the spectral shape observed for large earthquakes into the time domain to fit ekstrom s 1987 moment rate functions for the ms 8 1 michoacan earthquake of september 19 1985 and the ms 7 6 michoacan aftershock of september 21 1985

global trends of sea surface gravity wave wind and coastal wave setup abstractassessing trends of sea surface wave wind and coastal wave setup is of considerable scientific and practical importance in view of recent and projected long term sea level rise due to glo

sensitivity of antarctic sea ice to the southern annular mode in coupled climate models we assess the sea ice response to southern annular mode sam anomalies for pre industrial control simulations from the coupled model intercomparison project cmip5 consistent with work by ferreira et al j clim 28 1206 1226 2015 doi 10 1175 jcli d 14 00313 1 the models generally simulate a two timescale response to positive sam anomalies with an initial increase in ice followed by an eventual sea ice decline however the models differ in the cross over time at which the change in ice response occurs in the overall magnitude of the response and in the spatial distribution of the response late twentieth century antarctic sea ice trends in cmip5 simulations are related in part to different modeled responses to sam variability acting on different time varying transient sam conditions this explains a significant fraction of the spread in simulated late twentieth century southern hemisphere sea ice extent trends across the model simulations applying the modeled sea ice response to sam variability but driven by the observed record of sam suggests that variations in the austral summer sam which has exhibited a significant positive trend have driven a modest sea ice decrease however additional work is needed to narrow the considerable model uncertainty in the climate response to sam variability and its implications for 20th 21st century trends

comparing trends in the southern annular mode and surface westerly jet abstractthis paper examines trends in the southern annular mode sam and the strength position and width of the southern hemisphere surface westerly wind jet in observations reanalyses and models from phase 5 of the coupled model intercomparison project cmip5 first the period over 1951 2011 is considered and it is shown that there are differences in the sam and jet trends between the cmip5 models the hadley centre gridded slp hadslp2r dataset and the twentieth century reanalysis the relationships between these trends demonstrate that the sam index cannot be used to directly infer changes in any one kinematic property of the jet the spatial structure of the observed trends in slp and zonal winds is shown to be largest but also most uncertain in the southeastern pacific to constrain this uncertainty six reanalyses are included and compared with station based observations of slp the cmip5 mean slp trends generally agree well with the direct observations despite some climatological biases

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

role of tropical variability in driving decadal shifts in the southern hemisphere summertime eddy driven jet abstractthe southern hemisphere summertime eddy driven jet and storm tracks have shifted poleward over the recent few decades in previous studies explanations have mainly stressed the influence o

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

extending the time range of apatite u th he thermochronometry in slowly cooled terranes palaeozoic to cenozoic exhumation history of southeast sweden the use of u th he thermochronometry in old slowly cooled terranes has long been debated hence studies of natural setting are needed to verify the expected diffusivity behaviour of helium our results demonstrate that the u th he method can be applicable to samples older than 200 ma and that available helium diffusion models can reproduce the results obtained from the age vs depth trends in addition the results shed some light on the cross validation with the apatite fission track thermochronometer u th he thermochronometry on apatites has been applied to samples taken from drill cores in the precambrian basement in southeast sweden to unravel the time of exhumation of the uppermost 1 3 km of the crust much of the phanerozoic exhumation history in sweden is poorly constrained due to a large hiatus in the sediment record results from the drill cores yield he ages decreasing with increasing depth from similar to 270 ma at the surface down to similar to 120 ma at 1700 in depth the age vs depth trend shows an inflection point at similar to 1400 in depth which coincides with the upper boundary of the present helium partial retention zone a period of slow exhumation similar to 17 m my probably linked to the isostatic uplift of the caledonian foreland basin is revealed by the upper section of the trend in the data the results demonstrate that the area has not been reheated since the mid permian this argues against the existence of a thick mesozoic sedimentary cover in this region which if present at all cannot have exceeded 100 in in thickness furthermore the age vs depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 ma the area has had no significant amount of sedimentation erosion or uplift since this time less

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

historical sam variability part i century length seasonal reconstructions seasonal reconstructions of the southern hemisphere annular mode sam index are derived to extend the record before the reanalysis period using station sea level pressure slp data as predictors two reconstructions using different predictands are obtained one jones and widmann jw based on the first principal component pc of extratropical slp and the other fogt on the index of marshall a regional based sam index visbeck is also considered these predictands agree well post 1979 correlations decline in all seasons except austral summer for the full series starting in 1958 predictand agreement is strongest in spring and summer hence agreement between the reconstructions is highest in these seasons the less zonally symmetric sam structure in winter and spring influences the strength of the sam signal over land areas hence the number of stations included in the reconstructions reconstructions from 1865 were therefore derived in summer and autumn and from 1905 in winter and spring this paper examines the skill of each reconstruction by comparison with observations and reanalysis data some of the individual peaks in the reconstructions such as the most recent in austral summer represent a full hemispheric sam pattern while others are caused by regional slp anomalies over the locations of the predictors the jw and fogt reconstructions are of similar quality in summer and autumn while in winter and spring the marshall index is better reconstructed by fogt than the pc index is by jw in spring and autumn the sam shows considerable variability prior to recent decades

the role of eddies in the southern ocean temperature response to the southern annular mode the role of eddies in modulating the southern ocean response to the southern annular mode sam is examined usinganoceanmodelrunatmultipleresolutionsfromcoarsetoeddyresolving thehigh resolution versionsof the model showan increase in eddy kinetic energy that peaks 2 3 yr after a positive anomalyin the sam index previous work has shown that the instantaneous temperature response to the sam is characterized by predominant cooling south of 458s and warming to the north at all resolutions the model captures this temperatureresponse this responseis also evidentin the coarse resolution implementation of the model with no eddy mixing parameterization showing that eddiesdo not play an important role in the instantaneous response on the longer time scales an intensification of the mesoscale eddy field occurs which causes enhanced poleward heat flux and drives warming south of the oceanic polar front this warming is of greater magnitude and occurs for a longer period than the initial cooling response the results demonstrate that this warming is surface intensified and strongest in the mixed layer non eddy resolving models are unable to capturethedelayededdy driventemperatureresponsetothesam theauthorsthereforequestiontheability

contrasting recent trends in southern hemisphere westerlies across different ocean basins many studies have documented the trends in the latitudinal position and strength of the midlatitude westerly jet in the southern hemisphere however very little attention has been paid to the long

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

changes in frequency size relationship from small to large earthquakes the constant b value observed in frequency magnitude distributions of earthquakes has been taken as an indication of self similarity at all magnitudes hence earthquake properties should scale uniformly in the same way from small to large earthquakes it has often been observed however that the seismic moment released in small earthquakes scales differently with rupture length than it does for large events1 2 where the crossover between small and large events is defined at a rupture dimension equal to the down dip width of the seismogenic zone a possible explanation for this contradiction is that frequency size distributions are biased by small earthquakes small events dominate most global earthquake catalogues because of the short time period covered another source of bias in size distributions is the saturation of earthquake magnitudes for large events here we correct biases in calculations of b values and present evidence for a change in b value in frequency size distributions we find that a break in self similarity from small to large earthquakes occurs at a point where the dimension of the event equals the down dip width of the seismogenic layer

application of an inhomogeneous stress patch model to complex subduction zone earthquakes a discrete interaction matrix approach in recent years it has been recognized that the level of shear and normal stress along a fault can vary thus the stress is spatially and temporally inhomogeneous moreover it has also been suspected that faults might interact in some way with the result that a variety of earthquake magnitudes might be produced along a given length of fault at varying times in order to explore these ideas we have developed a quantitative formalism which we call the interaction matrix method to express the influence of one fault upon another this matrix is calculated by use of the energy change for a system of interacting cracks or faults and therefore gives energy consistent results specifically the interaction matrix relates the area averaged stress on the fault segment to the area averaged slip state on all the other fault segments in the system since any fault can be subdivided into an arbitrary number of fault segments the interaction matrix can have arbitrary dimension in fact the continuum limit is recovered as the dimension of the matrix approaches infinity we combine this matrix method with a segmentation or patch model for earthquakes in which each discrete segment of a fault has the same coseismic stress change defined as the difference between the driving stress at which healing occurs minus the driving stress at which sliding starts each time it slips we show that slip on a patch during an earthquake can vary substantially depending on how it interacts with other nearby patches in this model it is quite possible for the spatial distribution of stress on the fault following an event to be again in a spatially inhomogeneous state rather than in a uniform state as is often assumed hence the seismic moment produced by an earthquake on a given set of patches can vary substantially depending on the sequence of sliding and healing on the different patches to apply these ideas we devised a means to calculate the interaction matrix elements and used them to quantitatively examine earthquake sequences off the colombia ecuador coast and in the nankai trough near japan

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

the role of oscillating southern hemisphere westerly winds southern ocean coastal and open ocean polynyas abstractan oscillation in intensity of the southern hemisphere westerly winds is a major characteristic of the southern annular mode its impact upon the sea ice ocean interactions in the weddell and ross seas is investigated by a sea ice ocean general circulation model coupled to an energy balance model for three temporal scales and two amplitudes of intensity we find that the oscillating wind forcing over the southern ocean plays a significant role both in regulating coastal polynyas along the antarctic margins and in triggering open ocean polynyas the formation of coastal polynya in the western weddell and ross seas is enhanced with the intensifying winds resulting in an increase in the salt flux into the ocean via sea ice formation under intensifying winds an instantaneous spin up within the weddell and ross sea cyclonic gyres causes the warm deep water to upwell triggering open ocean polynyas with accompanying deep ocean convection in contrast to coastal polynyas open ocean polynyas in the we

the nature of deep focus earthquakes wadati 1928 first proved convincingly that some earthquakes occur at depths well beneath the earth s crust he essentially proposed the nomenclature used today by the international seismological centre isc i e earthquakes with focal depths exceeding 300 km are deep earthquakes and those with depths between 70 and 300 km are intermediate earth quakes however when there is little reason to distinguish between the two groups both types are called simply deep earthquakes to avoid confusion in this paper we refer to those with focal depths exceeding 300 km as very deep earthquakes and those with focal depths between 70 and 300 km as intermediate earthquakes deep earthquakes are of interest for at least four reasons first they are exceedingly common between 1964 and 1986 they constituted no less than 22 of all earthquakes having mb greater than 5 0 in the isc catalog second they most often occur in association with deep ocean trenches and volcanic island arcs in subduction zones one of the great achievements of twentieth century geophysics was the recognition that their occurrence in inclined planar groups or wadati benioff zones apparently delineates the cold down going cores of convection cells in the uppermost mantle third seismologists use body waves of deep earthquakes dispro portionately more often than those of shallow earthquakes to inves tigate core mantle and crustal structure this is because a deep earth quakes often possess relatively more impulsive sources b their body phases traverse the heterogeneous uppermost mantle only once on the ray path from hypocenter to station and c surface waves do not contaminate these body phase arrivals on seismograms finally deep earthquakes are

a station based southern annular mode index from 1884 to 2005 atmospheric pressure observations from the southern hemisphere are used to estimate monthly and annually averaged indexes of the southern annular mode sam back to 1884 this analysis groups all relevant observations in the following four regions one for antarctica and three in the subtropical zone continuous surface pressure observations are available at a number of locations in the subtropical regions since the end of the nineteenth century however year round observations in the subpolar region near the antarctic continent began only during the 1940 60 period the shorter antarctic records seriously compromise the length of a traditionally estimated sam index to improve the situation proxy estimates of antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 208s this allows deriving a longer sam index back to 1884 several aspects of the new record its statistical properties seasonal trends and the regional pressure anomaly correlations are presented