large sea ice outflow into the nares strait in 2007 1 sea ice flux through the nares strait is most active during the fall and early winter ceases in mid to late winter after the formation of ice arches along the strait and re commences after breakup in summer in 2007 ice arches failed to form this resulted in the highest outflow of arctic sea ice in the 13 year record between 1997 and 2009 the 2007 area and volume outflows of 87 103 km2 and 254 km3 are more than twice their 13 year means this contributes to the recent loss of the thick multiyear arctic sea ice and represents 10 of our estimates of the mean ice export at fram strait clearly the ice arches control arctic sea ice outflow the duration of unobstructed flow explains more than 84 of the variance in the annual area flux in our record seasonal stoppages are always associated with the formation of an arch near the same location in the southern kane basin additionally close to half the time another ice arch forms just north of robeson channel prior to the formation of the kane basin arch here we examine the ice export with satellite derived thickness data and the timing of the formation of these ice arches

regional bias in estimates of earthquake ms due to surface wave path effects continental earthquakes have long been known to have anomalously high surface wave magnitudes relative to their seismic moments a recent global study of shallow earthquakes by ekstrom and dziewonski 1988 confirmed this and found other regional systematic anomalies in the ms m relationship it is important to determine the source of these anomalies in order to understand the controls on earthquake source radiation and to obtain accurate estimates of historical seismic strain rates in this study the magnitudes of 82 earthquakes from eight different tectonic regions are recalculated using a simple surface wave path correction to determine whether path effects are responsible for the observed anomalies the magnitudes of continental earthquakes are reduced by an average of 0 2 magnitude units an improvement in fit to the global average significant at the 98 level surface wave path effects are clearly responsible for the high ms observed in continental areas there is a small decrease in scatter in the other areas but lateral refraction of the surface waves at plate boundaries prevents the simple correction from having a significant effect there is no evidence in the observed anomalies however for any dependence of earthquake source type on tectonic setting it is clear that to obtain reliable unbiased estimates of regional seismic strain rate and hazard a local moment magnitude relationship should be preferred to a global one

estimating sea ice area flux across the canadian arctic archipelago using enhanced amsr e 1 enhanced resolution advanced microwave scanning radiometer amsr e imagery is used to estimate daily sea ice area fluxes between the canadian arctic archipelago and the arctic ocean and baffin bay for the period september 2002 to june 2007 over the period amundsen gulf and m clure strait exported 54 103 km2 of sea ice area or roughly 77 km3 of sea ice volume each year into the arctic ocean export import into the arctic ocean through the queen elizabeth islands is small and uncertain since no estimates for july and august could be made due to atmospheric attenuation of the microwave signal lancaster sound exported 68 103 km2 of sea ice area or roughly 102 km3 of ice volume into baffin bay this produced a net loss of sea ice area of about 122 103 km2 or roughly 174 km3 a 1 which is presumed to be generated from within the archipelago itself mainly through the stationary and transient polynyas and leads that form each winter daily ice area fluxes for amundsen gulf ag and lancaster sound ls were as high as 2500 km2 d 1 and were event driven depending on synoptic scale atmospheric circulation and the mobility of the sea ice mean sea level pressure difference across each gate is moderately correlated with daily sea ice area fluxes despite the fact that free ice drift conditions are not always met in the region cross gradient and daily sea ice area flux for lancaster sound show a large number of counter gradient ice flux occurrences suggesting that local mesoscale winds nongeostrophic and perhaps ocean currents play a role in transporting sea ice through this gate monthly ice fluxes for the ag and ms gate were positively correlated with the ao index indicating that a strong beaufort sea high pressure and gyre correspond to more export into the beaufort sea monthly fluxes for the ls gate were positively correlated with the nao index indicating that strong southerly atmospheric circulation over baffin bay increases ice export into baffin bay from lancaster sound

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

multifrequency polarimetric synthetic aperture radar observations of sea ice the first known fully polarimetric airborne synthetic aperture radar sar data set of sea ice is introduced images were acquired in the beaufort bering and chukchi seas in march 1988 during a campaign for validation of defense meteorological satellite program special sensor microwave imager radiometer ice products statistics of the magnitude phase and polarization of complex backscattered signals recorded by the jet propulsion laboratory three frequency sar are examined in detail for various scenes with different ice characteristics the full stokes matrix information generated from c l and p band data characterize the scattering behavior of different ice types polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency fixed polarization micro wave radar a specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ers 1 5 3ghz vv polarization sar data such findings are consistent with theoretical model simulations of scattering characteristics of sea ice overall these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods

sea ice thickness in the eastern canadian arctic hudson bay complex baffin bay abstract past observations of sea ice thickness in the eastern canadian arctic eca have generally been restricted to drill hole measurements at a few local sites on landfast ice here we use data from the laser altimeter icesat and the radar altimeter cryosat 2 to present a 14 year record 2003 2016 of high resolution and spatially extensive ice thickness observations for the eca and identify 12 sub regions with distinct patterns the mean sea ice growth rate within the seasonally ice covered eca from november to april is 23 cm mo 1 565 km 3 mo 1 with the fastest increase in thickness occurring through strong ice convergence and deformation in eastern hudson bay and foxe basin our results demonstrate characteristically asymmetrical distributions of sea ice thickness in both hudson bay and baffin bay but in opposing directions in hudson bay the spring ice cover is 40 cm thicker in the eastern region compared to the northwestern region whereas in baffin bay the ice is 20 cm thicker in the western half of the bay compared to the eastern half in hudson bay we find that years with strong and positive ice drift vorticity i e cyclonic and convergent conditions correlate with increasingly asymmetrical sea ice covers with the level of west east asymmetry varying from 2 to 11 cm per 100 km however in baffin bay the ice drift vorticity is typically negative i e anticyclonic and divergent with no obvious link to the asymmetry of the spring ice cover finally we estimate that large interannual variations in spring sea ice volume within the eca lead to 15 variations in the volume of freshwater available at the ocean surface during summer

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

seismotectonics and the earthquake frequency magnitude distribution in the aegean area summary a study of aegean seismotectonics and the resulting frequency magnitude distribution on a broad scale is undertaken using the tectonic model of le pichon angelier this implies a tectonic moment release rate due to the spreading of the aegean of 17 8 times 1018 n m 1 yr 1 over the past 13 ma if stretching is due mainly to a series of normal faults dipping at about 45 in a seismogenic crust 10 20 km deep the moment magnitude relation from an instrumental magnitude catalogue is log m0 a bm with a 10 970 0 294 b 1 206 in si units this is established from 50 events of magnitude ms 5 3 whose scalar seismic moments m0 have been evaluated in a homogeneous manner for the region by spectral analysis of surface waves at 30 60 s period by contrast published body wave analyses from waveform modelling at 20 s period and moment tensor analyses seem to produce seismic moments which are lower by a factor of two or so on average this moment magnitude relation implies a seismogenic moment release rate due to stretching in the aegean of 14 times 1018 n m 1 yr 1 during the time period 1918 81 and 17 times 1018 n m 1 yr 1 for the period 1964 81 within a factor of two or so uncertainty this implies that the energy release in the brittle crust due to aegean spreading is substantially seismic within the stated accuracy and is also relatively stationary even when compared with the tectonic moment release rates a similar comparison using the same tectonic model shows that the subducting slab is sinking beneath the hellenic arc almost completely aseismically and that processes such as near vertical slab pull and confined thermal expansion could explain most of the observed seismic energy release by internal deformation of the slab the frequency magnitude statistics for the area of active extension has a characteristic earthquake of magnitude 7ms corresponding approximately to fault depths of 10 14 km for an aspect ratio of 2 and a strain drop of 10 4 this is close to the observed seismogenic depth 10 20 km for well determined earthquakes in the aegean area

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

sea ice circulation around the beaufort gyre the changing role of wind forcing and the sea ice state sea ice drift estimates from feature tracking of satellite passive microwave data are used to investigate seasonal trends and variability in the ice circulation around the beaufort gyre over the multi decadal period 1980 2013 our results suggest an amplified response of the beaufort gyre ice circulation to wind forcing especially during the late 2000s we find increasing anticyclonic ice drift across all seasons with the strongest trend in autumn associated with increased ice export out of the southern beaufort sea into the chukchi sea a flux gate analysis highlights consistency across a suite of drift products despite these seasonal anticyclonic ice drift trends a significant anticyclonic wind trend occurs in summer only driven in part by anomalously anticyclonic winds in 2007 across all seasons the ice drift curl is more anticyclonic than predicted from a linear relationship to the wind curl in the 2000s compared to the 1980s 1990s the strength of this anticyclonic ice drift curl amplification is strongest in autumn and appears to have increased since the 1980s up to 2010 in spring and summer the ice drift curl amplification occurs mainly between 2007 and 2010 these results suggest non linear ice interaction feedbacks e g a weaker more mobile sea ice pack enhanced atmospheric drag and or an increased role of the ocean the results also show a weakening of the anticyclonic wind and ice circulation since 2010 this article is protected by copyright all rights reserved

baffin bay ice drift and export 2002 2007 1 multiyear estimates of sea ice drift in baffin bay and davis strait are derived for the first time from the 89 ghz channel of the amsr e instrument uncertainties in the drift estimates assessed with envisat ice motion are 2 3 km day a persistent atmospheric trough between the coast of greenland and baffin island drives the prevailing southward drift pattern with average daily displacements in excess of 18 20 km during winter over the 5 year record the ice export ranges between 360 and 675 103 km2 with an average of 530 103 km2 sea ice area inflow from the nares strait lancaster sound and jones sound potentially contribute up to a third of the net area outflow while ice production at the north water polynya contributes the balance rough estimates of annual volume export give 500 800 km3 comparatively these are 70 and 30 of the annual area and volume exports at the fram strait

seasonal ice extent on the northeast newfoundland shelf over the northeast newfoundland shelf the main source of ice is advection from the north by winds and currents using historical ice charts it is shown that the advance of ice is limited by ice melt throughout the winter months when the ocean provides the only source of heat part of which is lost to the atmosphere and part of which goes to melting ice following techniques developed by maykut 1978 1982 the vertical growth of sea ice south of 55 n is examined in terms of the net heat loss from the ocean fw and the conductive heat flux fc through the ice to the atmosphere fc is estimated by assuming a linear temperature gradient through the ice from the freezing point of seawater at the underside of the ice to the surface temperature calculated by solving the radiation balance at the ice surface using monthly climatological data the flux fw is estimated from monthly averaged temperature profiles from station 27 off st john s newfoundland in the south and from historical data from the labrador shelf in the north the results suggest that in the north over bare ice growth of approximately 1 cm d might be sustained off hopedale 55 n for december through march while in the south off st john s an estimated melt rate of 5 cm d can be sustained throughout the winter months growth rates are strongly dependent on the depth of snow cover and the fraction of open water the flux fw reaches 250 w m 2 at station 27 in january and it is suggested that much of this heat is derived from summertime heating when the whole of the northeast newfoundland shelf is ice free

airborne observations of summer thinning of multiyear sea ice originating from the lincoln sea to better understand recent changes of arctic sea ice thickness and extent it is important to distinguish between the contributions of winter growth and summer melt to the sea ice mass balance in this study we present a lagrangian approach to quantify summer sea ice melt in which multiyear ice myi floes that were surveyed by airborne electromagnetic thickness sounding within nares strait during summer were backtracked using satellite imagery to a region in close proximity 3 20 km to spring ice thickness surveys carried out in the lincoln sea typical modal total myi thicknesses including 0 4 m snow ranged between 3 9 and 4 7 m in the lincoln sea during april ice only modal thicknesses were between 2 2 and 3 0 m in nares strait during august total thinning including snow and ice was 1 3 0 1 m including 0 4 0 09 m of snow melt and 0 9 0 2 m of ice melt this translates to a seasonal net heat input of 305 69 mj m2 262 60 mj m2 for ice only and seasonal net heat flux of 57 13 w m2 45 10 w m2 for ice only which is unlikely to be explained by solar radiation fluxes alone furthermore our approach provides an improvement on traditional ice mass balance buoy estimates because it integrates melt over larger spatial scales where melt can be highly variable due to differential melt experienced between melt ponds bare ice hummocks and ridges

recent changes in the exchange of sea ice between the arctic ocean and the canadian arctic archipelago 1 sea ice is exchanged between the arctic ocean and canadian arctic archipelago caa but has not been quantified over long time periods the corresponding mechanisms responsible for recent variability and change also remain unidentified to address this we estimated the sea ice area flux between the arctic ocean and the m clure strait and queen elizabeth islands qei from 1997 to 2012 for the months of may to november over the period there was a mean flux of 1 103 km2 21 103 km2 at the m clure strait and mean flux of 8 103 km2 8 103 km2 at the qei positive and negative flux signs correspond to arctic ocean ice inflow and outflow respectively the m clure strait had a mean flux of 5 103 km2 from may to september and a mean flux of 7 103 km2 from october to november the qei gates had a mean flux of 4 103 km2 from august to september with negligible ice exchange from may to july and october to november more frequent high sea level pressure anomalies over the beaufort sea and canadian basin since 2007 have reduced arctic ocean multiyear ice myi inflow into the m clure strait the presence of myi in the caa originating from the arctic ocean has been maintained by inflow at the qei which has increased since 2005 these recent increases in arctic ocean myi inflow into the qei can be attributed to increased open water area within the caa that have provided more leeway for inflow to occur

atmospheric controls on sea ice motion in the southern beaufort sea 1 the beaufort sea ice gyre is characterized in winter months by an anticyclonic regime associated with sea level pressure slp highs previous studies have shown instances of a reversal in this regime in summer months with the arrival of slp lows over the beaufort sea while also demonstrating a link to variations in lower stratospheric potential vorticity in this study we examine the role of relative vorticity in describing dynamic variability on weekly timescales from the surface to the middle stratosphere results from this analysis show that the beaufort gyre is characterized predominantly by anticyclonic activity throughout the year for the time interval considered from 1979 to 2000 with a summer reversal to cyclonic activity whose strength and duration varies between years these reversals coincide with reversals in slp based on a correlation analysis comparison of ice and atmospheric relative vorticity fields in the beaufort sea region bsr for all weeks from 1979 to 2000 indicates that sea ice and lower tropospheric processes are anticorrelated at zero time lag this is in contrast to relative vorticity fields at 10 mbar which exhibit maximum correlation between stratospheric and sea ice responses when 10 mbar leads ice relative vorticity by 2 6 weeks

characterization of arctic sea ice thickness using high resolution spaceborne polarimetric sar data in this paper we have investigated the relationship between the depolarization effects and the wintertime sea ice thickness in the landfast ice region where smooth thick first year ice fyi and deformed old ice coexisted by using c and x band spaceborne polarimetric synthetic aperture radar sar data radarsat 2 and terrasar x we have found a strong correlation between the in situ sea ice thickness and the sar derived depolarization factors copolarized correlation and cross polarized ratio the observed relationships have demonstrated not only a categorical difference between fyi and multiyear ice myi but also a one to one continuity in the scatter plots rather than being clustered it clearly shows that the observed correlations are not merely from the categorical difference in scattering mechanism between fyi and myi and that there might exist a one to one relationship between thickness and depolarization factors at least in our deformed ice case this suggests that depolarization factors could be effective sar parameters in the estimation of wintertime sea ice thickness numerical model simulations explained some portions of the correlation by employing multiple scattering on the sea ice surface and volume scattering within the low density subsurface layer

earthquake frequency and energy in greece abstract on the basis of a newly published revised earthquake catalogue for the greek area a study is made of its seismicity in terms of earthquake frequency and energy as functions of space time and magnitude in addition attempts are made to estimate the maximum possible magnitudes as functions of space the study is essentially a methodological experiment with tectonophysical and engineering results

multiyear sea ice export through the bering strait during winter 2011 2012 1 six ice beacons deployed in the beaufort sea during august 2011 tracked the anomalous export of multiyear sea ice from the chukchi sea through the bering strait to the bering sea between november 2011 and may 2012 these are the first observations in 34 years of ice beacon export through the bering strait using 34 years of passive microwave derived ice motion fields we find that during 2011 2012 southward ice motion in the chukchi sea persisted for a record six of seven months and that sea ice speeds were significantly faster than the long term mean the combination of increased ice speeds and reduced likelihood of ice arch development through the strait culminated in the record export of 13 5 103 km2 of sea ice through the bering strait monthly sea level pressure fields dominated by an aleutian low and siberian high show anomalies in december and january played a role in initiating this event and forced multiyear ice into the southern chukchi sea however these variations were small and typical of this area yet we find no evidence of a similar export event in the last 34 years even though the forcing was similar to the climatology this leads us to attribute this event to a change in the responsiveness of the arctic ice pack to typical forcing mechanisms

moment magnitude scaling in the aegean area abstract sixteen new determinations of scalar seismic moment from spectral modelling of rayleigh waves at 30 60 s period in the aegean area are presented when combined with earlier results obtained by a similar method the moment magnitude relationship from 50 events in the magnitude range 5 3 m s log m o 1 5 m s 9 198 0 317 for a constant stress drop dislocation model and m o in n m in contrast 15 published moments from body wave modelling at 20 s period and moment tensor inversion at periods greater than 45 s give log m o 1 5 m s 8 823 0 248 the surface wave results imply stress drops of 25 12 25 bar for the dislocation model and the body wave results imply systematically higher stress drops of 55 27 55 bar compared to 24 bar from field observation of the gulf of corinth sequence and 7 12 bar from inversion of body wave spectra and aftershock studies the latter are likely to be underestimates however the factor two scatter in the stress drops determined from the moment magnitude relation is much less than the factor four error in the estimated stress drop which might be introduced by model dependent systematics effects and these discrepancies may not be significant if the stress drop is free to vary then log m o 1 206 0 105 m s 10 970 0 632 surface waves log m o 1 160 0 181 m s 11 027 0 338 body waves this shows that the discrepancy between the two sets of results in negligible at m o 5 5 and thereafter increases slightly with earthquake size indicating that the underlying cause of the systematic difference in seismic moment for a given magnitude may be related to source size

the 2017 reversal of the beaufort gyre can dynamic thickening of a seasonal ice cover during a reversal limit summer ice melt in the beaufort sea during winter 2017 the semi permanent beaufort high collapsed and the anticyclonic beaufort gyre reversed the reversal drove eastward ice motion through the western arctic causing sea ice to converge against banks island and halted the circulation of multiyear sea ice via the gyre preventing its replenishment in the beaufort sea prior to the reversal an anomalously thin seasonal ice cover had formed in the beaufort following ice free conditions during september 2016 with the onset of the reversal in january 2017 convergence drove uncharacteristic dynamic thickening during winter by the end of march despite seasonal ice comprising 97 of the ice cover the reversal created the thickest roughest and most voluminous regional ice cover of the cryosat 2 record within the beaufort sea previous work has shown that winter ice export can precondition the region for increased summer ice melt but that a short reversal during april 2013 contributed to a reduction in summer ice loss hence the deformed ice cover at the end of winter 2017 could be expected to limit summer melt in spite of this the beaufort ice cover fell to its fourth lowest september area as the gyre re established during april and divergent ice drift broke up the pack negating the reversal s earlier preconditioning our work highlights that dynamic winter thickening of a regional sea ice cover for instance during a gyre reversal offers the potential to limit summer ice loss but that dynamic forcing during spring dictates whether this conditioning carries through to the melt season

single station attenuation measurements of high frequency rayleigh waves in scotland summary amplitude spectra derived from fundamental mode rayleigh waves generated by small underground and underwater explosions in scotland are analysed using a technique for measuring attenuation for a single sourcestation path the procedure estimates the average qi profile as a function of depth along an isoleted propagation path by correcting for known effects and mapping the function representing the remaining phenomena onto the corresponding data two methods of inversion are employed both giving similar results the technique is applied to explosion data recorded on the lispb and lownet arrays in scotland with epicentral distances of up to 85 km this yields well resolved single station qj values of between 0 02 and 0 09 in the top 400 m of the crustal area traversed by the waves the values at greater depth are weakly constrained but the qj estimates imply a decrease to 0 01 between 400 m and 800 m depth followed by an increase to 0 04 below 800 m the underground explosion spectra are modelled most accurately by a source time action in the form of an exponential step with an inverse timeconstant of 4s being optimum the mean source strength value of 1012nm agrees with a theoretical prediction based on the explosive yield a model consisting of a shock wave and ensuing negative pressure of 0 8 s duration is optimal for the underwater explosion data the mean source strength value is 107nm in close agreement with the theoretical prediction using known pressure data in both cases attenuation coefficients calculated using the qj models estimated from this analysis are consistent with the coefficients previously obtained in scotland using surface waves for pure geological provinces

response of sea ice drift to wind forcing on the northeastern newfoundland shelf observations of sea ice drift obtained with satellite tracked ice beacons in march april of 1988 and 1989 have been used to examine the response of sea ice drift to wind forcing over the northern newfoundland continental shelf the short term 5 20 days response of sea ice drift ranges from 2 6 to 5 4 of the local wind over much of the inner continental shelf which is comparable to that in the bering sea and the antarctic but larger than that in arctic sea ice drifts to the right of the local wind at angles ranging from 10 to 63 the response to wind forcing is largest near the ice edge both over the middle portions of the shelf and along the southern margins of the seasonal ice zone and during strong and steady wind of several days duration the large wind driven response of ice drift observed in this study in comparison with the arctic may result from 1 reduced levels of internal ice stress associated with the generally thin ice cover and lower areal concentration of sea ice 2 large atmospheric drag coefficients associated with the small ice floes in areas of comparatively higher ice concentration and 3 smooth ice bottom caused by melting in nearshore areas the ice to wind coupling is reduced owing to larger internal ice stresses experienced locally due to ice pileup

sea ice motion from low resolution satellite sensors an alternative method and its validation in the arctic 1 the retrieval of sea ice motion with the maximum cross correlation mcc method from low resolution 10 15 km spaceborne imaging sensors is challenged by a dominating quantization noise as the time span of displacement vectors is shortened to allow investigating shorter displacements from these instruments we introduce an alternative sea ice motion tracking algorithm that builds on the mcc method but relies on a continuous optimization step for computing the motion vector the prime effect of this method is to effectively dampen the quantization noise an artifact of the mcc it allows for retrieving spatially smooth 48 h sea ice motion vector fields in the arctic strategies to detect and correct erroneous vectors as well as to optimally merge several polarization channels of a given instrument are also described a test processing chain is implemented and run with several active and passive microwave imagers advanced microwave scanning radiometer eos amsr e special sensor microwave imager and advanced scatterometer during three arctic autumn winter and spring seasons ice motion vectors are collocated to and compared with gps positions of in situ drifters error statistics are shown to be ranging from 2 5 to 4 5 km standard deviation for components of the vectors depending on the sensor without significant bias we discuss the relative contribution of measurement and representativeness errors by analyzing monthly validation statistics the 37 ghz channels of the amsr e instrument allow for the best validation statistics the operational low resolution sea ice drift product of the eumetsat osi saf european organisation for the exploitation of meteorological satellites ocean and sea ice satellite application facility is based on the algorithms presented in this paper

toward a homogeneous moment magnitude determination for earthquakes in greece and the surrounding area a strategy is presented in order to produce a statistically homogeneous catalog of historical and present century earthquakes of the aegean area by expressing the size of all these earthquakes in the moment magnitude scale records of the mainka and wiechert intermediate period t 4 sec seismographs in athens have been used to calculate the magnitudes of earthquakes that occurred in greece and its surrounding area albania s yugoslavia s bulgaria and w turkey during the whole instrumental period since 1911 this magnitude m has also been used to derive empirical relations with macroseismic data it is shown here that m is equivalent to moment magnitude mw for a wide range of earthquake sizes 5 0 m 8 0 and to the surface wave magnitude ms for large earthquake sizes 6 m 8 0 it is also shown that the local magnitude ml for earthquakes in greece is half a unit smaller than the moment magnitude in the low magnitude range 4 5 ml 6 0 this could be attributed to a magnification smaller than the nominal for the wood anderson seismographs in greece v 1000 relations are also proposed to calculate moment magnitude when other magnitudes m ml ms and mb are known for earthquakes in greece

positive trend in the mean speed and deformation rate of arctic sea ice 1979 2007 using buoy data from the international arctic buoy program we found that the sea ice mean speed has substantially increased over the last 29 years 17 per decade for winter and 8 5 for summer a strong seasonal dependence of the mean speed is also revealed with a maximum in october and a minimum in april the sea ice mean strain rate also increased significantly over the period 51 per decade for winter and 52 for summer we check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing instead they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline increasing deformation means stronger fracturing hence more lead opening and therefore a decreasing albedo this accelerates sea ice thinning in summer and delays refreezing in early winter therefore decreasing the mechanical strength of the cover and allowing even more fracturing larger drifting speed and deformation and possibly a faster export of sea ice through the fram strait the september minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the arctic sea ice cover

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

seismic source parameters from a new dial up seismological network in greece a regional dial up pt telemetric network of eight digital short period seismic stations has been in full operation since the beginning of 1995 in greece during the first year of full operation three destructive earthquake sequences struck different regions of central and northern greece the dial up network managed to successfully record more than 85 of these seismic events including foreshocks main shocks and aftershocks and 45 of these events were selected in order to determine their seismic source parameters by spectral analysis the results show that seismic moment correlates very well with earthquake magnitude fault radius and fault displacement the determined scaling relations are in general agreement with those obtained by other studies for greek earthquakes that used different methodologies since digital seismic instrumentation is now expanding in greece these first results from spectral analysis of digital short period data can be considered useful for future seismic hazard studies

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

source processes of the 1981 gulf of corinth earthquake sequence from body wave analysis abstract teleseismic long period body waves from the 24 february 1981 gulf of corinth earthquake and its two principal aftershocks of 25 february 02h35m and 4 march 21h58m 1981 are studied to determine source characteristics focal mechanisms along with observed surface fault breaks suggest that the corinth earthquake sequence represents normal faulting due to the n s trending extension depths of the three shocks estimated by matching synthetic seismograms to observations are found to lie between 4 and 12 km the azimuthal variation of observed body wave duration indicates that the main shock is a multiple event and that the main rupture occurred about 3 to 4 sec after a relatively small foreshock and propagated toward the w nw seismic moments deduced from the body wave synthetics are 8 1 10 25 2 7 10 25 and 2 2 10 25 dyne cm for the main 25 february and 4 march shocks respectively average final displacements and stress drops are estimated to be 37 cm and 10 bars for the main shock for a circular fault of radius 15 km 22 cm and 8 bars for the 25 february shock and 18 cm and 7 bars for the 4 march shock for circular faults of radius 11 km the striking features of the earthquake sequence are the low stress drops of the main shock and its two principal aftershocks and the clear eastward migration of aftershock activities the unusually long source time function rise times 4 sec for the main shock 2 5 sec for both aftershocks and low stress drops suggest an overall slow energy release during the earthquake sequence

source mechanisms of recent earthquakes in the hellenic arc from broadband data three component long period seismograms from the global digital seismic network gdsn are used to determine the focal mechanisms of recent large mb 5 5 earthquakes in the hellenic arc using the relative amplitude method results are consistent with the regional stress regime obtained from other methods but they are better constrained broadband seismograms have been deconvolved from gdsn short period data and preliminary modelling of the p phases has been carried out using a two dimensional finite dislocation model this results in better fits to the data than earlier models using point source trapezoids as a source time function the relatively shallow hypocentral depths and stress drops typical of interplate contact zones 30 bar are consistent with previous observations this latter contrasts with the relatively low intraplate earthquake stress drops 15 bar reported for back arc events using the same technique

a catalogue of seismicity in greece and adjacent areas summary a new earthquake catalogue for greece has been formed to cover the instrumental period 1901 78 in particular 605 earthquakes for the period 1917 63 inclusive are relocated using first arrival data from the international seismological summary these relocations incorporate macro seismically and other well controlled master events into an ensuing joint epicentre determination technique the largest annual average shift is 165 km for 78 earthquakes during the decade after 1917 decreasing to 17 km for the later years 1957 63 magnitudes are redetermined mainly using readings from the swedish network and uppsala since as early as 1908 catalogue completeness exists for magnitudes around 5 5 for at least the last 60 years but magnitudes of about 4 7 are completely reported only during the most recent 15 years the new epicentral positions lead to a better delineation of the seismic zones than has previously been achieved the majority of shallow earthquakes are contained in a belt parallel to the hellenic arc which extends north into albania in the south east the epicentral locations give a more diffuse extension of this zone into the west coast of turkey depths of intermediate earthquakes along the hellenic arc tend to relocate to shallower depths in the south west part of crete no earthquake focus deeper than 100 km is found although in the south eastern section of the arc a tendency to increased depths is observed a second zone starts at leukas island in the west and extends through central greece to near volos on the east coast where it divides into two branches which are less well defined but which eventually join the seismicity of western turkey a third zone follows the saronikos and corinth gulfs

a two dimensional thermodynamic model for sea ice advance and retreat in the newfoundland marginal ice zone a time dependent two dimensional ice ocean coupled thermodynamic model is developed to study the ice edge advance and retreat development of the oceanic mixed layer and oceanic response to ice movement ice melt and heat balance in the newfoundland marginal ice zone the model domain is a vertical section of the ocean along the direction of the ice velocity initially the ocean is free of ice and has a deep mixed layer formed by winter surface cooling an ice sheet then moves into the domain from the upstream boundary at constant velocity it melts from the bottom and a shallow mixed layer beneath the ice is developed heat and buoyancy fluxes at the air sea and ice water interfaces and at the bottom of the mixed layer determine the melt rate and change of the mixed layer properties the ice edge reaches a maximum distance and starts to retreat when the ice is being melted by the warm water faster than it is being advected into the area the oceanic properties change with the ice movement during the advancing phase of the ice movement the heat loss to the ice bottom from ice melting exceeds the heat gain by surface heating and entrainment causing the mixed layer temperature to drop but since the buoyancy created by the melting is not sufficient to overcome the effect of wind mixing the mixed layer deepens rapidly during the retreating phase the mixed layer becomes shallower and warmer because of the increasing surface heating and buoyance production by ice melting the most important factors controlling the melt rate and the excursion distance are the air temperature and the ambient water temperature higher wind speeds increase the mixed layer depth but do not have a strong effect on the melt rate

montane forest root growth and soil organic layer depth as potential factors stabilizing cenozoic global change tree roots and their symbiotic fungal partners are believed to play a major role in regulating long term global climate but feedbacks between global temperature and biotic weathering have not yet been explored in detail in situ field data from a 3000 m altitudinal transect in peru show fine root growth decreases and organic layer depth increases with the cooler temperatures that prevail at increased altitude we hypothesize that this observation suggests a negative feedback as global temperatures rise the soil organic layer will shrink and more roots will grow in the mineral layer thereby accelerating weathering and reducing atmospheric co2 we examine this mechanism with a process based biological weathering model and demonstrate that this negative feedback could have contributed to moderating long term global cenozoic climate during major cenozoic co2 changes linked to volcanic degassing and tectonic uplift events

the large 1956 earthquake in the south aegean macroseismic field configuration faulting and neotectonics of amorgos island abstract new field observations of the seismic intensity distribution of the large m s 7 4 south aegean amorgos earthquake of 9 july 1956 are presented interpretations based on local ground conditions structural properties of buildings and peculiarities of the rupture process lead to a re evaluation of the macroseismic field configuration this together with the aftershock epicentral distribution quite well defines the earthquake rupture zone which trends ne sw and coincides with the amorgos astypalea trough the lateral extent of the rupture zone however is about 40 smaller than that predicted for aegean earthquakes of m s 7 4 this discrepancy could be attributed to sea bottom topography changes which seem to control the rupture terminations and to relatively high stressdrop with respect to other aegean earthquakes fault plane solutions obtained by several authors indicate either mainly normal faulting with a significant right lateral strike slip component or predominantly strike slip motion the neotectonism of amorgos island based on new field observations aerial photograph analysis and fault mechanisms is consistent with the dip slip interpretation the neotectonic master fault of amorgos and the 1956 seismic faulting appear to belong to the same tectonic phase ne sw strike and a southeasterly dip however the significant right lateral strike slip component supports the idea that the amorgos region deviates from the simple description for pure extension in back arc conditions

a source study of the thessaloniki northern greece 1978 earthquake sequence summary the thessaloniki northern greece earthquake sequence appears to have occurred along faults forming a graben structure this graben situated in the border region between the serbomacedonian massif and the vardar zone is bounded to the south west by clearly exposed north west striking north east dipping normal faults relative hypocentre determinations fault plane solutions surface faulting and the aftershock distribution suggest that some of these faults have been reactivated during the 1978 earthquakes the source parameters of the mainshock mb 6 1 ms 6 4 were determined by computing body wave synthetic seismograms in the time domain and comparing them with the observed this modelling constrained the orientation of faulting determined by the p wave fault plane solution it also constrained the source depth to 6 mp 2 km similar depths were calculated by a relative relocation method for the other three large events of the sequence the dislocation time function required for the far field had a total duration of 9 mp 1 5 s the body wave moment was 5 2 mp 1 8 times 1025 dyne cm for a fault length of 35 km and a fault width of 17 km both estimated from the aftershock distribution the static stress drop was found to be 4 bar an accelerograph record of the mainshock shows two distinct events 3 4 s apart these two events were unresolved by the long period data in the far field but the unusually long duration of the mainshock time function suggests an overall slow energy release which probably occurred as a sequence of events close in space and time seismic energy released in this fashion can account for waveform complexities observed at some stations

variability of nares strait ice flux 1 six years 1996 2002 of arctic ocean ice flux into the nares strait are estimated using radarsat ice motion this represents a first consistent multi year record of nares strait outflow for examination of seasonal and interannual variability across an 30 km gate at the entrance to robeson channel the average annual sept aug ice area flux is 33 103 km2 and ranges from 16 103 km2 in 2000 to 48 103 km2 in 1999 uncertainties in the 3 day ice displacements and ice flux are small assuming 4 m thick ice the average volume flux amounts to 130 km3 4 msv this is 7 of the mean annual fram strait ice flux seasonally ice flux is most active after july ceases after the formation of an ice arch in mid to late winter and re commences after breakup in summer the multiyear my ice coverage of the area poleward of the gate is high 80 south of the gate the my ice coverage is highly variable and the strait may be filled with multiyear or seasonal ice our estimates are placed in the context of others and uncertainties in the other components of canadian archipelago ice flux and are discussed

increasing mobility of high arctic sea ice increases marine hazards off the east coast of newfoundland heavy ice conditions along canada s east coast during spring 2017 presented hazardous conditions for the maritime industry and required the canadian coast guard to pull its research icebreaker ccgs amundsen off its scientific cruise to provide ice escort services and conduct search and rescue operations along newfoundland s northeast coast greater ice concentrations and a thicker ice pack than are typical of this area created the anomalous ice cover within this paper we present in situ observations of the ice cover confirming that pieces of multiyear sea ice from the high arctic were present within the ice cover and subsequently examine the transport pathway that connects the export of thick multiyear sea ice from the lincoln sea and canadian arctic archipelago to coastal communities in newfoundland we conclude with a discussion on how an increasingly mobile arctic sea ice cover may increase these ice hazards in the south

dicing with earthquakes the van group have been publicizing claims to be predicting earthquakes since 1981 their predictions of two basic parameters of earthquakes magnitude and location are very loosely constrained most van magnitude predictions are below 5 7 ms with a tolerance of 0 7 ms the uncertainty range spanned by a predicted magnitude is so enveloping that such forecasts cannot be viewed as plainly successful in terms of van s claims to spatial resolution these if successful might constrain the linear dimension of the source region of a magnitude 8 0 ms earthquake but do not adequately constrain a magnitude as large as 7 5 ms not only do van need to refine the tolerances in their magnitude and location predictions before careful judgements can be made but it is also necessary to provide an unambiguous statement of the prediction hypothesis used in relation to a pre published and communally archived dataset of complete seismic electric signal occurrences similar to seismological station bulletins

sea ice convergence along the arctic coasts of greenland and the canadian arctic archipelago variability and extremes 1992 2014 after the summer of 2013 a convergence induced tail in the thickness distribution of the ice cover is found along the arctic coasts of greenland and canadian arctic archipelago prompted by this a normalized ice convergence index ici is introduced to examine the variability and extremes in convergence in a 23 year record 1992 2014 of monthly ice drift large scale composites of circulation patterns characteristic of regional convergence and divergence are examined indeed the ici shows the june 2013 convergence event to be an extreme i e ici 2 furthermore there is a cluster of 9 months over a 17 month period with positive icis i e 1 following the record summer minimum ice extent smie in 2012 the imprint of ice dynamics from this cluster of positive icis likely contributed to higher smies in 2013 and 2014 the impact of convergence on smie is discussed and the increase in arctic ice volume in 2013 is underscored

fracture of summer perennial sea ice by ocean swell as a result of arctic storms 1 the arctic summer minimum sea ice extent has experienced a decreasing trend since 1979 with an extreme minimum extent of 4 27 106 km2 in september 2007 and a similar minimum in 2011 large expanses of open water in the siberian laptev chukchi and beaufort seas result from declining summer sea ice cover and consequently introduce long fetch within the arctic basin strong winds from migratory cyclones coupled with increasing fetch generate large waves which can propagate into the pack ice and break it up on 06 september 2009 we observed the intrusion of large swells into the multiyear pack ice approximately 250 km from the ice edge these large swells induced nearly instantaneous widespread fracturing of the multiyear pack ice reducing the large 1 km diameter parent ice floes to small 100 150 m diameter floes this process increased the total ice floe perimeter exposed to the open ocean allowing for more efficient distribution of energy from ocean heat fluxes and incoming radiation into the floes thereby enhancing lateral melting this process of sea ice decay is therefore presented as a potential positive feedback process that will accelerate the loss of arctic sea ice