rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

simulated ground motions for hypothesized mw 8 subduction earthquakes in washington and oregon the amplitude and duration of strong ground motions from hypothesized mw 8 subduction zone thrust earthquakes in the puget sound portland region were estimated using a semi empirical method the simulation procedure assumes the rupture surface may be represented by a grid of fault elements finite difference wave simulation in a detailed 2 d velocity structure identifies direct s and the moho postcritical reflection as the primary components of the s wave field at horizontal distances of 0 to 150 km green s functions containing these two arrivals are computed with generalized ray theory in an equivalent 1 d structure for each source element receiver propagation path scattering and attenuation structure are empirically modeled by the use of corrected accelerograms from mw 7 michoacan mexico and valparaiso chile aftershocks for the fault element source functions different site conditions are empirically included in the simulation procedure by using empirical source functions recorded on rock and soil sites spatial variations in slip on the fault asperities are introduced by weighting the fault elements the technique has been validated for large subduction zone earthquakes by modeling acceleration time histories and response spectra from the 1985 michoacan mw 8 0 and valparaiso mw 8 0 main shocks somerville et al 1991 fault models for the puget sound and portland regions and seismic velocity structure models have been adapted from published regional studies uncertainty in the location of the asperities on the fault surface results in a large degree of uncertainty in the simulated ground motions at a given site if distance is defined as the distance to the closest asperity then the variability in the ground motions is reduced indicating that this uncertainty can be lessened by constraining the depth of the asperity the ground motion estimates are relatively insensitive to the difference in fault dip between the puget sound and portland fault models the attenuation of peak acceleration with distance r from the fault asperity for a mw 8 subduction earthquake is given by in pga 1 5 3 33 in r 128 0 79 s where s is a site term equal to 0 for rock and 1 for soil when distance r is the distance to the fault plane the attenuation relation is in pga 2 8 1 26 in r 0 79 s formal estimates of uncertainty in the calculated ground motions have been obtained by estimating both parametric uncertainty from the range of source models of hypothesized cascadia subduction earthquakes and modeling and random uncertainty from the misfit between recorded and simulated ground motions of the 1985 michoacan and valparaiso earthquakes for periods less than 1 sec the estimated response spectral velocities on soil sites in the seattle olympia region are about twice those recorded during the 1949 olympia and 1965 seattle wadati benioff zone earthquakes and the durations of strong motion on rock sites are significantly longer 45 to 60 sec versus 10 to 15 sec

asynchronous behavior of outlet glaciers feeding godthabsfjord nuup kangerlua and the triggering of narsap sermia s retreat in sw greenland we thank w dryer and d podrasky for assistance with fieldwork and l kenefic for assisting with digitizing glacier front positions ch2 m hill polar services and air greenland provided logistics support the spot 5 images used for the 2008 dem were provided by the spirit program centre national d etudes spatiales france the digitalglobe worldview images used for the 2014 dem were obtained from p morin terminus positions were derived from landsat images courtesy of the u s geological survey funding was provided by the us national science foundation nsf office of polar programs opp grants nsf plr 0909552 and nsf plr 0909333 cassotto is supported by nasa under the earth and space science fellowship program grant nnx14al29h k k kjeldsen acknowledges support from the danish council research for independent research grant no dff 409000151 k kjaer is thanked for his support during the earlier phases of this study on ice weather stations are operated by geus denmark within the programme for monitoring of the greenland ice sheet promice j mortensen acknowledges support from iiknn greenland defrost project of the nordic centre of excellence program interaction between climate change and the cryosphere and the greenland ecosystem monitoring programme www g e m dk s rysgaard was funded by the canada excellence research chair programme additional funding was provided by the geophysical institute university of alaska fairbanks and greenland climate research centre scientific editor h fricker and reviewers h jiskoot and g cogley provided very constructive feedback that helped improve the paper

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

spring bloom dynamics in a subarctic fjord influenced by tidewater outlet glaciers godthabsfjord sw greenland in high latitude fjord ecosystems the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web however the environmental factors that control the timing and intensity of these spring blooms remain uncertain in 2013 we studied the spring bloom dynamics in godthabsfjord a large fjord system adjacent to the greenland ice sheet our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers a combination of out fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring april may which supplied nutrient rich water to the surface layer this surface water was subsequently transported out fjord and due to this circulation regime the biomass accumulation of phytoplankton was displaced away from the glaciers in late may the upwelling weakened and the dominant wind direction changed thus reversing the direction of the surface water transport warmer water was now transported toward the inner fjord and a bloom was observed close to the glacier terminus overall our findings imply that the timing intensity and location of the spring blooms in godthabsfjord are controlled by a combination of upwelling strength and wind forcing together with sea ice cover the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem

estimating ocean heat transports and submarine melt rates in sermilik fjord greenland using lowered acoustic doppler current profiler ladcp velocity profiles submarine melting at the ice ocean interface is a significant term in the mass balance of marine terminating outlet glaciers however obtaining direct measurements of the submarine melt rate or the ocean heat transport towards the glacier that drives this melting has been difficult due to the scarcity of observations as well as the complexity of oceanic flows here we present a method that uses synoptic velocity and temperature profiles but accounts for the dominant mode of velocity variability to obtain representative heat transport estimates we apply this method to the sermilik fjord helheim glacier system in southeastern greenland using lowered acoustic doppler current profiler ladcp and hydrographic data collected in summer 2009 we find a mean heat transport towards the glacier of 29 10 9 w implying a submarine melt rate at the glacier face of 650 m a 1 t he resulting adjusted velocity profile is indicative of a multilayer residual circulation where the meltwater mixture flows out of the fjord at the surface and at the stratification maximum

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

seismic attenuation in northeastern sonora mexico we studied the attenuation of local and regional earthquake body waves recorded by the seismic network of northeastern sonora mexico red sismica del noreste de sonora resnes the source station paths of the selected data set cover the epicentral region of the may 1887 m w 7 5 sonora earthquake we used the best located earthquakes recorded by resnes between 2003 and 2004 to analyze the spectral amplitude decay of body waves with hypocentral distance the database consists of 44 earthquakes with magnitudes between 1 8 and 3 2 and hypocentral distances between 25 and 150 km we calculated fourier spectral amplitudes from more than 400 records and defined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes at 23 individual frequencies between 0 4 and 63 1 hz we determined regional attenuation curves based on events located more than 100 km northwest of the center of the network and local curves based on earthquakes located near the fault zone that ruptured in the 1887 earthquake the obtained attenuation curves indicate that the spectral amplitudes decay faster in the area of the 1887 rupture than in the surrounding region to analyze the possible sources of attenuation we parameterized the attenuation functions considering three terms one that accounts for geometrical spreading another one for anelastic attenuation and a third for near surface attenuation we found the s wave quality factor q to be similar in both the general region and near the 1887 rupture however in the region of the 1887 rupture the near surface attenuation exceeds the regional average finally in the region of the 1887 rupture the nonparametric attenuation functions and the estimates of q indicate that at between 0 6 and 63 1 hz p waves attenuate more than s waves q p 20 8 f 1 1 whereas q s 83 8 f 0 9

heat salt and freshwater budgets for a glacial fjord in greenland abstractin greenland s glacial fjords heat and freshwater are exchanged between glaciers and the ocean submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration and observations of ocean heat transport are increasingly being used to infer the submarine melt rates the complete heat salt and mass budgets that underlie such methods however have been largely neglected here a new framework for exploring glacial fjord budgets is developed building on estuarine studies of salt budgets the heat salt and mass transports through the fjord are decomposed and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented this method is applied to moored records from sermilik fjord near the terminus of helheim glacier to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes throughout the year two different regimes are found in the nonsummer months advective transports are balanced by

local magnitude in northeastern italy we consider a large data set of waveforms 5053 recordings for the horizontal components and 9933 for the vertical to calibrate a local magnitude scale valid for northeastern italy in the hypocentral distance range of 10 250 km the data refer to 1096 events occurring in the period january 1995 to december 2002 in the area between 44 4 and 47 6 n and 10 1 and 15 7 e for each available signal we simulate the corresponding wood anderson seismogram using the geometrical mean of the two horizontal peaks we simultaneously estimate the distance attenuation the station correction terms and the magnitude of the events estimations are obtained with the standard parametric approach accounting for the geometrical spreading and the anelastic attenuation and by using two different methods of nonparametric regression based on a stepwise linear approximation and on kernel functions respectively the nonparametric solutions agree and show stronger attenuation in the first 70 km than what was found in central california furthermore a noticeable discontinuity occurs around 100 km because later phase arrivals such discontinuity is not fitted well by the parametric curve we investigate the effect of magnitude dependent attenuation on magnitude estimation we also account for the bias induced by data truncation i e data loss due to the limited dynamics of the instruments the analysis shows that at short distances the standard magnitude independent attenuation model underestimates high magnitudes e g by 0 49 units at 10 km for magnitude 5 5 and overestimates low magnitudes e g by 0 17 units at 10 km for magnitude 1 5 0 34 units if we extrapolate the relation down to magnitude 0 5 finally various factors suggest one should adopt the solution proposed in the literature to redefine the m l scale such that m l 3 corresponds to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance

21st century evolution of greenland outlet glacier velocities earlier observations on several of greenland s outlet glaciers starting near the turn of the 21st century indicated rapid annual scale and large 100 increases in glacier velocity combining data from several satellites we produce a decade long 2000 to 2010 record documenting the ongoing velocity evolution of nearly all 200 of greenland s major outlet glaciers revealing complex spatial and temporal patterns changes on fast flow marine terminating glaciers contrast with steady velocities on ice shelf terminating glaciers and slow speeds on land terminating glaciers regionally glaciers in the northwest accelerated steadily with more variability in the southeast and relatively steady flow elsewhere intraregional variability shows a complex response to regional and local forcing observed acceleration indicates that sea level rise from greenland may fall well below proposed upper bounds

the seasonal circulation of the glacier bay alaska fjord system the seasonal circulation in glacier bay an alaskan fjord system with active tidewater glaciers is derived from oceanographic data collected on 13 cruises from june 1964 to september 1967 the fjord bottom waters were renewed annually between november and april by saline intrusion over the 69 m deep entrance sill in february the inlet waters were homogeneous with temperature of 3 c and salinity of 31 0 freshwater runoff derived from melting glacial ice stored runoff and precipitation led to a pycnocline formation in april or may the deepening pycnocline cut off the saline intrusion at the entrance sill the period from april to november was characterized by the downward mixing of brackish surface waters some evidence is presented for mixing by tidally induced internal waves these waves oscillate at twice the tidal frequency and have amplitudes of at least 50m vertical diffusion coefficients of the order of 5 0 cm2s 1 are reported the topographic influence of the glaciated terrain and retreating glaciers on the fjord circulation is demonstrated

quantifying energy and mass fluxes controlling godthabsfjord freshwater input in a 5 km simulation 1991 2012 abstractfreshwater runoff to fjords with marine terminating glaciers along the greenland ice sheet margin has an impact on fjord circulation and potentially ice sheet mass balance through increasing heat transport to the glacier front here the authors use the high resolution 5 5 km hirham5 regional climate model allowing high detail in topography and surface types to estimate freshwater input to godthabsfjord in southwest greenland model output is compared to hydrometeorological observations and while simulated daily variability in temperature and downwelling radiation shows high correlation with observations typically 0 9 there are biases that impact the results in particular overestimated albedo leads to underestimation of melt and runoff at low elevations in the model simulation 1991 2012 the ice sheet experiences increasing energy input from the surface turbulent heat flux up to elevations of 2000 m and shortwave radiation at all elevations southerly wind anomalies and declining

near source attenuation of peak horizontal acceleration strong motion data recorded within 50 km of the rupture zone were used to study near source attenuation characteristics of horizontal peak ground acceleration for worldwide earthquakes of magnitudes 5 0 to 7 7 the data base consisted of 229 horizontal components of peak acceleration recorded from 27 earthquakes including the 15 october 1979 imperial valley earthquake these data were found to be adequately represented by the functional relationship pga a exp b m r c m d where pga represents the mean of the peak values scaled from the two horizontal components of each recording m is richter magnitude and r is distance from the fault rupture zone peak acceleration was found to be lognormally distributed with a standard error representing a 45 per cent increase in the median estimate the regression analysis statistically confirmed the results of earthquake simulation studies that have predicted peak acceleration to become independent of magnitude and distance in the near field an extensive sensitivity study showed that predictions based on our attenuation relationships are stable with respect to reasonable model and parameter variations an analysis of residuals was used to investigate the behavior of peak acceleration with respect to various earthquake site and recording parameters the more significant findings being 1 a similarity in the level of acceleration recorded on soil or rock 2 larger than average accelerations recorded at sites located on shallow soils or in areas of steep topography 3 larger than average accelerations associated with earthquakes having reverse fault mechanisms and 4 lower than average accelerations recorded in large embedded structures

ground motions from subduction zone earthquakes a total of 258 horizontal components of accelerogram data recorded at soil sites during thrust normal and strike slip earthquakes occurring in seven subduction zones around the pacific ocean were analyzed the results of statistical analyses of 5 per cent damped pseudo velocities psv computed from these accelerograms at 10 periods t between 0 1 and 4 sec indicated no significant differences in the average psv levels of the thrust normal and strike slip data from the northern honshu zone each of these groups of northern honshu data which together comprised one half of the total data base were fit equally well by the same attenuation model the analyses also revealed that at intermediate periods 0 8 t 3 sec the psv observed at stiff soil sites within the northern honshu nankai kuril mexico and alaska zones were on the average significantly greater than the psv observed at similar sites in the peru northern chile and new britain bougainville zones this observation indicates that differences in the source and or travel path characteristics between the two groups accounted for the differences in psv independent evidence supporting source differences is the correlation noted between psv in this period band and the characteristic source complexities for these zones which hartzell and heaton inferred from the teleseismic data of the larger magnitude earthquakes certain anomalous tectonic characteristics of the new britain bougainville zone were noted that may have contributed in some systematic manner to the relatively unusual spectral characteristics of the ground motions recorded on stiff soil sites within this zone some of the differences in the psv among the zones at intermediate and long periods were probably the result of differences in local geologic characteristics geology greatly influenced the mexican psv data from soft soil sites to a lesser extent geology probably affected the alaskan data which were recorded mostly on deep stiff soils and the new britain bougainville data recorded at yonki which is underlain by softer soil deposits

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

quantifying flow and stress in ice melange the world s largest granular material tidewater glacier fjords are often filled with a collection of calved icebergs brash ice and sea ice for glaciers with high calving rates this melange of ice can be jam packed so that the flow of ice fragments is mostly determined by granular interactions in the jammed state ice melange has been hypothesized to influence iceberg calving and capsize dispersion and attenuation of ocean waves injection of freshwater into fjords and fjord circulation however detailed measurements of ice melange are lacking due to difficulties in instrumenting remote ice choked fjords here we characterize the flow and associated stress in ice melange using a combination of terrestrial radar data laboratory experiments and numerical simulations we find that during periods of terminus quiescence ice melange experiences laminar flow over timescales of hours to days the uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate in addition the average force per unit width that is transmitted to the glacier terminus which can exceed 107 n m increases exponentially with the melange length to width ratio these buttressing forces are sufficiently high to inhibit the initiation of large scale calving events supporting the notion that ice melange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

spatially distributed runoff at the grounding line of a large greenlandic tidewater glacier inferred from plume modelling understanding the drivers of recent change at greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming a poorly constrained component of tidewater glacier processes is the near terminus subglacial hydrology here we present a novel method for constraining near terminus subglacial hydrology with application to marine terminating kangiata nunata sermia in south west greenland by simulating proglacial plume dynamics using buoyant plume theory and a general circulation model we assess the critical subglacial discharge if delivered through a single compact channel required to generate a plume that reaches the fjord surface we then compare catchment runoff to a time series of plume visibility acquired from a time lapse camera we identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface yet we observe no plume we attribute these observations to spatial spreading of runoff across the grounding line persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration

a study of site response and regional attenuation in the longmen shan region eastern tibetan plateau sw china from seismic recordings using the generalized inversion method abstract in this study more than 1600 seismic recordings from 88 small to moderate earthquakes during 2009 and 2013 which were recorded at 36 seismic stations were used to calculate the high frequency attenuation parameter 0 by comparing the 0 of six seismic stations with neighboring strong motion stations we observed that the surficial soil layers have aggravated the high frequency attenuation phenomenon besides we found that stations located in crustal low velocity anomaly areas maintained higher 0 and those located in high velocity anomaly areas tended to have lower 0 the correlation between 0 and s wave velocity anomaly showed that at the 0 10 km depth range the 0 values clearly decrease as the velocity anomaly increases the generalized inversion technique git was adopted to estimate the q f model of the sichuan basin sb and songpan garze orogen sgo in accompaniment with the site responses of 28 seismic stations the derived q f model were similar to those obtained from previous studies analyses of site responses revealed that the amplification curves and levels of sb and sgo were significantly different then site responses estimated from the genetic algorithm and git were compared the site response curves of most stations are similar for stations having significantly different site responses we investigated by comparing with the results obtained from accelerograms recorded at nearby strong motion stations by applying the horizontal to vertical spectral ratio hvsr method the results showed that site responses obtained from the git were closer to those of hvsr than those of the genetic algorithm

ocean circulation and properties in petermann fjord greenland the floating ice shelf of petermann glacier interacts directly with the ocean and isthought to lose at least 80 of its mass through basal melting based on three opportunisticocean surveys in petermann fjord we describe the basic oceanography the circulationat the fjord mouth the hydrographic structure beneath the ice shelf the oceanic heatdelivered to the under ice cavity and the fate of the resulting melt water the 1100 m deepfjord is separated from neighboring hall basin by a sill between 350 and 450 m deep fjord bottom waters are renewed by episodic spillover at the sill of atlantic water from thearctic glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier s grounding line about 500 m the fjord circulation isfundamentally three dimensional satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth with outflow on the northeast side tidal flowsare similar in magnitude to the geostrophic flow the oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting cold low salinity water originating in the surface layer of nares strait in winter intrudes farunder the ice this may limit basal melting to the inland half of the shelf the melt rate andlong term stability of petermann ice shelf may depend on regional sea ice cover andfjord geometry in addition to the supply of oceanic heat entering the fjord

subannual and seasonal variability of atlantic origin waters in two adjacent west greenland fjords greenland fjords provide a pathway for the inflow of warm shelf waters to glacier termini and outflow of glacially modified waters to the coastal ocean characterizing the dominant modes of variability in fjord circulation and how they vary over subannual and seasonal time scales is critical for predicting ocean heat transport to the ice here we present a 2 year hydrographic record from a suite of moorings in davis strait and two neighboring west greenland fjords that exhibit contrasting fjord and glacier geometry kangerdlugssuaq sermerssua and rink isbrae hydrographic variability above the sill exhibits clear seasonality with a progressive cooling of near surface waters and shoaling of deep isotherms above the sill during winter to spring renewal of below sill waters coincides with the arrival of dense waters at the fjord mouth warm salty atlantic origin water cascades into fjord basins from winter to midsummer we then use seaglider observations at davis strait along with reanalysis of sea ice and wind stress in baffin bay to explore the role of the west greenland current and local air sea forcing in driving fjord renewal these results demonstrate the importance of both remote and local processes in driving renewal of near terminus waters highlighting the need for sustained observations and improved ocean models that resolve the complete slope trough fjord ice system

estimating the diminution of shear wave amplitude with distance application to the los angeles california urban area the rate of decay with distance of shear wave amplitude computed from 20 sec s wave spectra is determined from terrascope records of small earthquakes in the greater los angeles area piecewise log linear interpolation functions and traditional diminution functions are used to fit spectral decay to a maximum distance of 150 km simultaneously isotropic source and receiver terms are determined separate branches of the spectral decay function are found for two categories of source depth greater than 10 km and less than 10 km in the hypocentral distance range of 20 to 150 km and in the frequency range of 0 5 to 8 0 hz an important result of the investigation is that the horizontal component decay rate associated with deeper crustal sources is generally greater than that associated with shallower sources and is greater than that which is estimated using more traditional models of spectral decay with distance the same behavior generally holds for vertical component spectra the variation in apparent attenuation rate with source depth should affect seismic hazard estimates associated with the rupture of blind thrust faults in the los angeles basin and vicinity the results of the inversions suggest that interpolation function representations of spectral decay are sensitive to perturbations of s wave amplitude due to crustal reflectors such as post critical s wave arrivals from mid crustal to deep crustal velocity interfaces

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

ice dammed lake drainage cools and raises surface salinities in a tidewater outlet glacier fjord west greenland the drainage of ice dammed lakes in the form of outburst floods in greenland is detected regularly by remote sensing and these events are expected to occur more frequently in a warmer climate however their impact on ice sheet stability and neighboring water bodies is still unknown in this interdisciplinary study we investigate lake drainages from the greenland ice sheet into a west greenland fjord by analyzing simultaneous time series of satellite observations and direct hydrographic measurements of temperature and salinity in the fjord satellite images show that in general lake drainages have occurred quasiperiodically during the last decade a particular sequence of drainage events was observed by satellite in 2009 and was analyzed together with the first direct hydrographic observations signs of ice dammed lake drainages were observed by a downstream mooring located just below the intertidal zone the release of freshwater occurred at the fjord subsurface at a tidewater outlet glacier the downstream in water sequence of property changes in relation to these drainage events was observed as an almost immediate decrease in surface layer temperature 2 c followed within a week by the arrival of a high saline pulse 5 units with elevated salinity lasting for several days during the passage during lake drainages large amounts of relatively warm and saline intermediate water are brought to the near surface layers by entrainment processes near the glacier front and this influences the hydrography of the fjord but also impacts the ecosystem through upwelling of nutrient rich intermediate water

a new attenuation relation for peak horizontal acceleration of strong earthquake ground motion in japan abstract a new attenuation relation for peak horizontal acceleration applicable to the near source region in japan is developed the data base consists of 1372 horizontal components of peak ground acceleration from 28 earthquakes in japan and 15 earthquakes in the united states and other countries coefficients describing the decrease in acceleration with increasing distance found by most previous studies of japanese data are significantly smaller than those found by analyzing individual earthquakes this phenomenon is examined and found to result from use of general nonstratified multiple regression analyses the present analysis uses a two step stratified regression procedure and an attenuation model that accounts for geometrical spreading and anelastic attenuation but has magnitude independent shape at very short distances the resulting relation in japan is log 10 a 0 41 m log 10 r 0 032 10 0 41 m 0 0034 r 1 30 where a is the mean of the peak acceleration from two horizontal components at each site cm sec 2 r the shortest distance between site and fault rupture km and m the surface wave magnitude the median estimate of peak horizontal acceleration at the source region is 620 cm sec 2 independent of earthquake magnitude effects of four different ground condition rock hard medium and soft soils on the attenuation relation are also examined average peak horizontal accelerations for the rock and the soft soil sites are 60 and 140 per cent respectively of the value predicted from the equation

subglacial drainage evolution modulates seasonal ice flow variability of three tidewater glaciers in southwest greenland b j d was funded in the form of a phd studentship provided by the scottish association for geosciences environment and society sages and the university of st andrews uk j m l is supported by a ukri future leaders fellowship grant no mr s017232 1 d f would like to acknowledge the support of this work through the epsrc and esrc centre for doctoral training on quantification and management of risk and uncertainty in complex systems environments grant no ep l015927 1

heat sources for glacial melt in a sub arctic fjord godthabsfjord in contact with the greenland ice sheet 1 recent warming of subpolar mode water off greenland has been suggested to accelerate the mass loss from tidal outlet glaciers of the greenland ice sheet we present a comprehensive analysis of water masses dynamics and interannual hydrographic variability in godthabsfjord a sill fjord in contact with tidal outlet glaciers on the west coast of greenland through seasonal observations we recognize an intermediate baroclinic circulation mode driven by tidal currents and an associated important local heat source for the fjord during summer this results in significant warming and freshening of the intermediate layer of the main fjord and the increase in heat content is equivalent to melting of 2 1 km3 of glacial ice this is comparable to 8 km3 glacial ice discharge estimated from the kangiata nun ta sermia calving front per year during winter the external heat source in the west greenland current enters the fjord as intermittent inflows of either cold 2 c dense water in pulses of 1 to 3 months duration four distinct circulation modes are observed in the fjord of which all can contribute to glacial ice melt an important aspect of the ice distribution in the fjord is that only a minor fraction is exported out of the fjord

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

seasonal variability of the circulation system in a west greenland tidewater outlet glacier fjord godthabsfjord 64 n many tidewater outlet glacier fjords surround the coast of greenland and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet thus fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet however very few observational studies describe the seasonal dynamics of fjord circulation here we present the first continuous current measurements april november from a deep mooring deployed in a west greenland tidewater outlet glacier fjord four distinct circulation phases are identified during the period and they are related to exchange processes with coastal waters tidal mixing and melt processes on the greenland ice sheet during early summer warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s 1 in late summer the average velocity decreases to 3 cm s 1 during a period with significant subglacial freshwater discharges during this period a large variability in current velocities is also observed the associated average heat transport in an intermediate depth range corresponds to 568 gw in early summer and is reduced to 287 gw in late summer these heat fluxes are at the higher end of previously reported fluxes our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and thereby potentially to glacial melt we suggest that intermediate heat transport may play a similar important role in other fjords around greenland

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

site response attenuation and source spectra of s waves along the guerrero mexico subduction zone acceleration spectra from nine earthquakes and up to 11 stations per earthquake are inverted to find the source spectra the site response and the quality factor q of s waves this method is applied to moderate earthquakes 4 0 0 8 hz does not follow a simple linear relation as observed in previous studies of attenuation in other regions when the source spectra are interpreted in terms of brune s model the stress drops obtained are less than 20 bars for the four larger events analyzed the site functions obtained indicate that although all the stations used are on rock the effect of the near surface geology caused important amplifications at some stations

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

nonparametric description of peak acceleration as a function of magnitude distance and site in guerrero mexico this article describes the peak accelerations observed on a network of strong motion accelerographs above the subduction zone in guerrero mexico as a function of magnitude and hypocentral distance our empirical description differs from regression analysis however in that it produces a table of values of peak acceleration for selected values of m and r and an interpolation rule to obtain peak acceleration at intermediate values with this approach the existence and extent of saturation of peak acceleration as magnitude increases is dictated by the data and unlimited flexibility is allowed in the distance dependence of the peak acceleration this nonparametric approach does not allow extrapolation beyond the range of the data and is thus most useful when the data spans a large magnitude and distance range after 7 yr of recording the digital guerrero accelerograph network has obtained enough data to test the concept the records include events with magnitudes ranging from under 3 to 8 1 with all magnitudes recorded at distances ranging from nearly directly above the rupture to distances where acceleration has become too small to trigger the instruments the data used in this study consist of 528 recordings each three components from 146 earthquakes that occurred between 1985 and 1990 all but one station are on rock sites since all the accelerograms are recorded by one of 30 stations there is an average of about 18 records for each station the results suggest that at short distances about 14 to 25 km from the fault as magnitude increases the peak horizontal acceleration saturates at about 20 g however unlike small earthquakes peak accelerations decrease very slowly with increased distance from the rupture in a large magnitude station corrections for peak acceleration reduced the rms misfit by about 15 for the horizontal component by 12 for the vertical component and by 21 for the ratio for some stations horizontal corrections are close to vertical corrections but others show very different site effects on horizonal and vertical components the ratios of peak vertical acceleration to peak horizontal acceleration show a very weak tendency to decrease as magnitude increases and this tendency is further reduced at most distances after correction for average site effects the average value of this ratio is 0 70 before the station correction after these corrections for 55 events with known stress drop the residual between the predicted peak acceleration and the observed peak acceleration is correlated with stress drop although scattered the observations are consistent with a theoretical prediction that amax 0 80

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

heat sources for glacial ice melt in a west greenland tidewater outlet glacier fjord the role of subglacial freshwater discharge the melting of tidewater outlet glaciers from the greenland ice sheet contributes significantly to global sea level rise accelerated mass loss is related to melt processes in front of calving glaciers yet the role of ocean heat transports is poorly understood here we present the first direct measurements from a subglacial plume in front of a calving tidewater outlet glacier surface salinity in the plume corresponded to a meltwater content of 7 which is indicative of significant entrainment of warm bottom water and according to plume model calculations significant ice melt energy balance of the area near the glacier showed that ice melt was mainly due to ocean heat transport and that direct plume associated melt was only important in periods with high meltwater discharge rates of 100 m3 s 1 ocean mixing outside of the plume area was thus the primary heat source for melting glacier ice

increasing meltwater discharge from the nuuk region of the greenland ice sheet and implications for mass balance 1960 2012 we assess the runoff and surface mass balance smb of the greenland ice sheet in the nuuk region southwest using output of two regional climate models rcms evaluated by observations the region encompasses six glaciers that drain into godthabsfjord rcm data 1960 2012 are resampled to a high spatial resolution to include the narrow relative to the native grid spacing glacier trunks in the ice mask comparing rcm gridded results with automatic weather station aws point measurements reveals that locally models can underestimate ablation and overestimate accumulation by up to tens of per cent however comparison with lake discharge indicates that modelled regional runoff totals are more accurate model results show that melt and runoff in the nuuk region have doubled over the past two decades regional smb attained negative values in recent high melt years taking into account frontal ablation of the marine terminating glaciers the region lost 10 20 km 3 w e a 1 in 2010 12 if 2010 melting prevails during the remainder of this century a low end estimate of sea level rise of 5 mm is expected by 2100 from this relatively small section 2 6 of the ice sheet alone

resolving bathymetry from airborne gravity along greenland fjords recent glacier mass loss in greenland has been attributed to encroaching warming waters but knowledge of fjord bathymetry is required to investigate this mechanism the bathymetry in many greenland fjords is unmapped and difficult to measure from 2010 to 2012 national aeronautics and space administration s operation icebridge collected a unique set of airborne gravity magnetic radar and lidar data along the major outlet glaciers and fjords in greenland we applied a consistent technique using the icebridge gravity data to create 90 bathymetric profiles along 54 greenland fjords we also used this technique to recover subice topography where warm or crevassed ice prevents the radar system from imaging the bed here we discuss our methodology basic assumptions and error analysis we present the new bathymetry data and discuss observations in six major regions of greenland covered by icebridge the gravity models provide a total of 1950 line kilometers of bathymetry 875 line kilometers of subice topography and 12 new grounding line depths

local coastal water masses control heat levels in a west greenland tidewater outlet glacier fjord fjords form the gateway between the open ocean and the greenland ice sheet gis and consequently play a crucial role for the stability of the ice sheet hydrographic observations especially with seasonal resolution from these fjords are limited making it difficult to assess linkages between the fjord coastal water masses and freshwater discharge from gis here we present a decade long monthly hydrographic time series from a southwest greenland fjord in direct contact with gis our observations reveal significant temporal and spatial water mass variations related to coastal glacial and atmospheric dynamics during winter the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures during summer runoff from gis leads to a pronounced freshening of the fjord in general the fjord s seasonal circulation system damps the seasonal variation in temperature in the fjord this leads to a seasonal temperature range in the intermediate layer in the inner part of the fjord that is half the observed range at the fjord entrance changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses where cold winter warm summer events decrease increase the mean water temperatures consequently these events play an important role in heat transport toward glacier termini

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

circulation and fjord shelf exchange during the ice covered period in young sound tyrolerfjord northeast greenland 74 n abstract fjords around greenland connect the greenland ice sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing runoff topography fjord shelf exchange tides waves and seasonal growth and melt of sea ice limited knowledge exists on circulation in high arctic fjords particularly those not impacted by tidewater glaciers and especially during winter when they are covered with sea ice and freshwater input is low here we present and analyze seasonal observations of circulation hydrography and cross sill exchange of the young sound tyrolerfjord system 74 n in northeast greenland distinct seasonal circulation phases are identified and related to polynya activity meltwater and inflow of coastal water masses renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale by the end of winter there is two layer circulation with outflow in the upper 45 m and inflow extending down to approximately 150 m tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the m2 tidal constituent 0 26 m s 1 and that residual currents 0 02 m s 1 were relatively small during the ice covered period tidal pumping a tidally driven fjord shelf exchange mechanism drives a salt flux that is estimated to range between 145 kg s 1 and 603 kg s 1 extrapolation of these values over the ice covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice covered period

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

subglacial discharge driven renewal of tidewater glacier fjords the classic model of fjord renewal is complicated by tidewater glacier fjords where submarine melt and subglacial discharge provide substantial buoyancy forcing at depth here we use a suite of idealized high resolution numerical ocean simulations to investigate how fjord circulation driven by subglacial plumes tides and wind stress depends on fjord width grounding line depth and sill height we find that the depth of the grounding line compared to the sill is a primary control on plume driven renewal of basin waters in wide fjords the plume exhibits strong lateral recirculation increasing the dilution and residence time of glacially modified waters rapid drawdown of basin waters by the subglacial plume in narrow fjords allows for shelf waters to cascade deep into the basin wide fjords result in a thin boundary current of shelf waters that flow toward the terminus slightly below sill depth wind forcing amplifies the plume driven exchange flow however wind induced vertical mixing is limited to near surface waters tidal mixing over the sill increases in fjord transport of deep shelf waters and erodes basin stratification above the sill depth these results underscore the first order importances of fjord glacier geometry in controlling circulation in tidewater glacier fjords and thus ocean heat transport to the ice

the 25 november 1988 saguenay quebec earthquake source parameters and the attenuation of strong ground motion the saguenay earthquake of 25 november 1988 occurred close to the southern margin of the saguenay graben in southern quebec it was caused by almost purely dip slip faulting centered at a depth of 26 km with a p axis oriented northeast southwest this faulting mechanism is similar to those of the larger historical earthquakes in eastern north america but the focal depth is substantially greater than all but one of these events the seismic moment estimated from regional pni waves and teleseismic long period body waves is 5 10 24 dyne cm corresponding to a moment magnitude of 5 8 the source duration of the earthquake is estimated to be 1 8 sec corresponding to a stress drop of 160 bars which is not significantly higher than the average stress drop of 120 bars estimated from previous large earthquakes in eastern north america in order to simultaneously match the recorded ground motion amplitudes of strong motion acceleration strong motion velocity and teleseismic short period and long period body waves it is necessary to use a source function having a complex shape that implies the presence of asperities and larger local stress drops the large set of strong motion recordings of the saguenay earthquake has been used to validate a procedure for estimating strong ground motion attenuation based on a simple wave propagation model the most important feature of the recorded strong motions is that their peak amplitudes do not decay significantly with distance inside 120 km but then decay abruptly beyond 120 km profiles of recorded accelerograms with absolute times indicate that at distances beyond 64 km the peak ground motions are due to strong postcritical reflections from velocity gradients in the lower crust the principal shear wave arrivals and the variation of their peak amplitudes with distance were reproduced in synthetic seismograms generated using a regional crustal structure model the critical distances for the postcritical reflections were short because of the deep focal depth of the event causing the elevation of ground motion amplitudes out to 120 km similar studies of earthquakes in other regions of eastern north america indicate that the strength of the postcritical reflections and the distance ranges over which they are dominant are controlled by the focal depth and crustal structure regional variations in crustal structure thus give rise to predictable regional variations in strong ground motion attenuation

on the seasonal freshwater stratification in the proximity of fast flowing tidewater outlet glaciers in a sub arctic sill fjord 1 the greenland ice sheet releases large amounts of freshwater into the fjords around greenland and many fjords are in direct contact with the ice sheet through tidewater outlet glaciers here we present the first seasonal hydrographic observations from the inner part of a sub arctic fjord relatively close to and within 4 50 km of a fast flowing tidewater outlet glacier this region is characterized by a dense glacial and sea ice cover freshwater from runoff subglacial freshwater sgfw discharge glacial and sea ice melt are observed above 50 90 m depth during summer sgfw and subsurface glacial melt mixed with ambient water are observed as a layered structure in the temperature profiles below the low saline summer surface layer 1 c intermediate water mass is a significant subsurface heat source for ice melt we analyze the temperature and salinity profiles observed in late summer with a thermodynamic mixing model and determine the total freshwater content in the layer below the summer surface layer to be between 5 and 11 the total freshwater contribution in this layer from melted glacial ice was estimated to be 1 2 while the corresponding sgfw was estimated to be 3 10 the winter measurements in the subsurface halocline layer showed a total freshwater content of about 1 and no significant contribution from sgfw