the turbulent oscillator a mechanism of low frequency variability of the wind driven ocean gyres intrinsic low frequency variability is studied in the idealized quasigeostrophic midlatitude wind driven ocean gyres operating at large reynolds number a robust decadal variability mode driven by the transient mesoscale eddies is found and analyzed the variability is a turbulent phenomenon which is driven by the competition between the eddy rectification process and the potential vorticity anomalies induced by changes of the intergyre transport

long term behaviour of australian stable continental region scr faults abstract australia boasts arguably the richest late neogene to quaternary faulting record in stable continental region scr crust anywhere in the world variation in fault scarp length vertical displacement proximity to other faults and relationship to topography permits division of the continent according to fault character six onshore neotectonic domains are recognised with an additional offshore domain proposed by analogy with the eastern united states each domain relates to a distinct underlying crustal type and architecture broadly considered to represent cratonic non cratonic and extended environments in general greater topographic expression associated with faults occurring in extended crust relative to non extended crust suggests a higher rate of seismic activity in the former setting consistent with observations worldwide using the same reasoning non cratonic crust might be expected to have a higher rate of seismic activity than cratonic crust this distinction together with the variation in fault character between domains should be recognised in attempts to identify analogous systems worldwide a common characteristic of morphogenic earthquake occurrence in australia appears to be temporal clustering periods of earthquake activity comprising a finite number of large events are separated by much longer periods of seismic quiescence at the scale of a single fault and of proximal faults in several instances there is evidence for deformation at scales of several hundred kilometres switching on and off over the last several million years what is not clear from the limited palaeoseismological data available is whether successive active periods are comparable in terms of slip number of events magnitude of events etc regardless this apparent bimodal recurrence behaviour poses challenges for probabilistic seismic hazard assessment psha these rely on the simplifying assumption that large earthquake recurrence for long return periods is not random i e poissonian presently our ability to incorporate such time dependent models is limited by available data

a coupled decadal prediction of the dynamic state of the kuroshio extension system abstractbeing the extension of a wind driven western boundary current the kuroshio extension ke has long been recognized as a turbulent current system rich in large amplitude meanders and energetic pinched off eddies an important feature emerging from recent satellite altimeter measurements and eddy resolving ocean model simulations is that the ke system exhibits well defined decadal modulations between a stable and an unstable dynamic state here the authors show that the decadally modulating ke dynamic state can be effectively defined by the sea surface height ssh anomalies in the 31 36 n 140 165 e region by utilizing the ssh based ke index from 1977 to 2012 they demonstrate that the time varying ke dynamic state can be predicted at lead times of up to 6 yr this long term predictability rests on two dynamic processes 1 the oceanic adjustment is via baroclinic rossby waves that carry interior wind forced anomalies westward into the ke region and 2 the low frequency ke variability influenc

paleoliquefaction study of the clarendon linden fault system western new york state abstract the lack of earthquake induced liquefaction features in late wisconsin and holocene sediments in genesee wyoming and allegany counties suggests that the clarendon linden fault system clf did not generate large moment magnitude m 6 earthquakes during the past 12 000 years given that it was the likely source of the 1929 m 4 9 attica earthquake however the clarenden linden fault system probably is capable of producing future m 5 events during this study we reviewed newspaper accounts of the 1929 attica earthquake searched for earthquake induced liquefaction features in sand and gravel pits and along tens of kilometers of river cutbanks evaluated numerous soft sediment deformation structures compiled geotechnical data and performed liquefaction potential analysis of saturated sandy sediments we found that the 1929 m 4 9 attica earthquake probably did not induce liquefaction in its epicentral area and may have been generated by the western branch of the clarendon linden fault system most soft sediment deformation structures found during reconnaissance did not resemble earthquake induced liquefaction features and even the few that did could be attributed to non seismic processes our analysis suggests that the magnitude threshold for liquefaction is between m 5 2 and 6 that a large m 6 earthquake would liquefy sediments at many sites in the area and that a moderate earthquake m 5 5 9 would liquefy sediments at some sites but perhaps not at enough sites to have been found during reconnaissance we conclude that the clarendon linden fault system could have produced small and moderate earthquakes but probably not large events during the late wisconsin and holocene

the character and reactivation history of the southern extension of the seismically active clarendon linden fault system western new york state abstract integration of 11 types of data sets enabled us to determine the location character and fault history of the southern extension of the clarendon linden fault system clf in southwestern new york state the data sets utilized include detailed stratigraphic and fracture measurements at more than 1000 sites soil gas anomalies seismic reflection profiles well logs and lineaments on air photos topographic maps landsat and slar images the seismically active clf consists of as many as 10 parallel segmented faults across the fault system the fault segments are truncated by nw striking cross strike discontinuities csds the faults of the clf and intersecting csds form fault blocks that have semi independent subsidence and uplift histories east dipping reflectors in the precambrian basement indicate the southward continuation of thrusts of the intra grenvillian elzevir frontenac boundary zone these thrusts were reactivated during iapetan rifting as normal listric growth faults in ordovician black river to trenton time the southern clf segments experienced a second phase of growth fault activity with faults displaying a cumulative stratigraphic throw of as much as 170 m thrusting on the same east dipping precambrian reflectors typified the clf in taconic post trenton times detailed comparisons among the fault segments show that the fault activity in silurian and devonian times generally alternated between the western and central main faults in late devonian time the fault motion reversed from down on the east to down on the west about the time the appalachian basin axis passed across the clf in its westward migration the deep precambrian faults of the clf were thus reactivated as the appalachian basin developed in acadian times finally the clf thrust fault imaged on seismic line clf 1 offsets all bedrock devonian units thus significant motion occurred along this fault during late acadian or more likely alleghanian time

crustal velocity structure associated with the eastern tennessee seismic zone vp and vs images based upon local earthquake tomography we present three dimensional p and s wave velocity models for the active eastern tennessee seismic zone etsz using arrival time data from more than 1000 local earthquakes a nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters we image several velocity anomalies that persist through most of the inversion volume some anomalies support the presence of known features such as an ancient rift zone in northern tennessee other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies we image a narrow ne sw trending steeply dipping zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent new york alabama magnetic lineament the low velocity zone may have an apparent dip to the se at depths exceeding 15 km the low velocity zone is interpreted as a major basement fault juxtaposing granite rhyolite basement to the nw from grenville southern appalachian basement to the se relocated hypocenters align in near vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike slip fault we suggest that the etsz represents reactivation of an ancient shear zone established during formation of the super continent rodinia

investigating the predictability of north atlantic sea surface height interannual sea surface height ssh forecasts are subject to several sources of uncertainty methods relying on statistical forecasts have proven useful in assessing predictability and associated uncertainty due to both initial conditions and boundary conditions in this study the interannual predictability of ssh dynamics in the north atlantic is investigated using the output from a 150 year long control simulation based on hadgem3 a coupled climate model at eddy permitting resolution linear inverse modeling lim is used to create a statistical model for the evolution of monthly mean ssh anomalies the forecasts based on the lim model demonstrate skill on interannanual timescales mathcal o 1 2 years forecast skill is found to be largest in both the subtropical and subpolar gyres with decreased skill in the gulf stream extension region the ssh initial conditions involving a tripolar anomaly off cape hatteras lead to a maximum growth in ssh about 20 months later at this time there is a meridional shift in the 0 m ssh contour on the order of 0 5 circ 1 5 circ latitude coupled with a change in ssh along the us east coast to complement the lim based study interannual ssh predictability is also quantified using the system s average predictability time apt the apt analysis extracted large scale ssh patterns which displayed predictability on timescales longer than 2 years these patterns are responsible for changes in ssh on the order of 10 cm along the us east coast driven by variations in ekman velocity our results shed light on the timescales of ssh predictability in the north atlantic in addition the diagnosed optimal initial conditions and predictable patterns could improve interannual forecasts of the gulf stream s characteristics and coastal ssh

regional wave propagation in new england and new york we validate and improve 1d velocity models of the two main crustal provinces in the northeastern united states neus using seismograms from the 20 april 2002 m 5 au sable forks earthquake which is the largest earthquake in the region to be recorded by multiple recently deployed good quality regional broad band stations to predict and mitigate the effects of future earthquakes in the north eastern united states more information is needed regarding both the local earthquake sources and how seismic waves travel through the region we investigate the source and regional wave propagation for the au sable forks earthquake the earthquake epicenter is located near the boundary of two distinct geological provinces the appalachian new england and grenville new york we use a forward modeling approach to study the waveforms recorded at 16 stations located within 400 km of the epicenter we generate synthetic seismograms using the frequency wavenumber method testing several published models for the two provinces several models per form well at low frequencies 0 1 hz we refine these models and generate two alternative 1d crustal models for intermediate frequencies 1 hz of engineering interest our new grenville model performs better than previously published models for all six source station paths modeled in that province according to goodness of fit statistics variance reduction and correlation coefficient our alternative appalachian model improves the fit of synthetics to data for five of the ten paths modeled in that province from the results we identify two specific sources of wave field complex ities that should be investigated in future studies of earthquake ground motions in neus 3 azimuthal anisotropy in the appalachian province and complex wave paths along the boundary between the two provinces

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

interpretation of seismic and potential field data from western new york state and lake ontario abstract lithoprobe and industry seismic profiles have furnished evidence of major zones of easterly dipping grenville deformed crust extending southwest from exposed grenville rocks north of lake ontario additional constraints on subsurface structure limited to the postulated clarendon linden fault system south of lake ontario are provided by five east west reflection lines recorded in 1976 spatial correlations between seismic structure and magnetic anomalies are described from both lake ontario and the newly reprocessed new york lines in the paleozoic to precambrian upper crust the new york seismic sections show 1 an easterly thickening wedge of subhorizontal paleozoic strata unconformably overlying a precambrian basement whose surface has an apparent regional easterly dip of 1 2 minor apparent normal offsets possibly on the order of tens of meters occur within the paleozoic section the generally poorly reflective unconformity may be locally characterized by topographic relief on the order of 100 m 2 apparent local displacement on the order of 90 m at the level of the black river group diminishes upward to little or no apparent offset of queenston shale 3 within the limited seismic sections there appears to be no evidence that the complete upper crustal section is vertically or subvertically offset 4 dipping structure in the paleozoic strata 15 to 35 resembles some underlying precambrian basement elements 5 the surface continuity of inferred faults constituting the clarendon linden system is not strongly supported by the seismic data beneath the paleozoic strata the seismic sections show both linear and arcuate reflector geometry with easterly apparent dips of 15 to 35 similar to the deep structures imaged on seismic lines from nearby lake ontario and on lithoprobe lines to the north the similarity supports an extension of easterly dipping central metasedimentary belt structures of the grenville orogen from southern ontario to beneath western new york state from a comparison of the magnetic and gravity fields with the new york seismic sections we suggest 1 the largely nonmagnetic paleozoic strata appear to contribute negligibly to magnetic anomalies seismically imaged fractures in the new york paleozoic strata appear to lie mainly west of a positive gravity anomaly the relationship between magnetic and gravity anomalies and the changes in the geometry of interpreted precambrian structures remains enigmatic 2 north to northeast trending curvilinear magnetic and gravity anomalies parallel but are not restricted to the principal trend of the postulated clarendon linden fault system paleozoic fractures of the clarendon linden system may partly overlie a southward extension of the composite arc belt boundary zone

joint hypocenter velocity inversion for the eastern tennessee seismic zone a joint hypocenter velocity inversion for the eastern tennessee seismic zone etsz has resolved velocity features in basement rock below detached appalachian thrust sheets p and s wave arrival times from 492 earthquakes have been inverted for one 1 d and three dimensional 3 d velocity models to midcrustal depths the 3 d p and s wave velocity solutions are computed independly and are very similar in relation to the 1 d model velocity anomalies range from 8 to 16 in the first layer upper 5 km and between 7 in deeper layers prominent velocity anomalies parallel the seismic zone and are consistent from layer to layer the most persistent anomaly is a low velocity region that borders the seismic zone to the northwest and is flanked on either side by regions of anomalously high velocity the new york alabama ny al magnetic lineament coincides with or lies close to the southeast boundary of the prominent velocity low in both the p and s wave velocity images the spatial coincidence between velocity gravity and magnetic gradients suggests that major discontinuities are present in the basement relocation in the 3 d velocity model reduced the number of very deep earthquakes below 20 km and further accentuated differences in seismogenic properties on either side of the ny al lineament after relocation most earthquakes occur in a vertically bounded region roughly 30 km wide extending from 4 to 22 km in depth most earthquakes occur in regions characterized by either average velocity or small velocity anomalies

warm and saline events embedded in the meridional circulation of the northern north atlantic 1 ocean state estimates from 1958 to 2005 from the simple ocean assimilation system soda system are analyzed to understand circulation between subtropical and subpolar atlantic and their connection with atmospheric forcing this analysis shows three periods 1960s around 1980 and 2000s with enhanced warm saline waters reaching high latitudes alternating with freshwater events originating at high latitudes it complements surface drifter and altimetry data showing the subtropical subpolar exchange leading to a significant temperature and salinity increase in the northeast atlantic after 2001 the warm water limb of the atlantic meridional overturning cell represented by soda expanded in density salinity space during these warm events tracer simulations using soda velocities also show decadal variation of the gulf stream waters reaching the subpolar gyre and nordic seas the negative phase of the north atlantic oscillation index usually invoked in such variability fails to predict the warming and salinization in the early 2000s with salinities not seen since the 1960s wind stress curl variability provided a linkage to this subtropical subpolar gyre exchange as illustrated using an idealized two layer circulation model the ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal in this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax hence the polar front moves westward opening an enhanced northward access of the subtropical waters in the eastern boundary current

a three dimensional p wave velocity model for the charlevoix seismic zone quebec canada 1 a three dimensional p wave velocity model has been developed for the charlevoix seismic zone csz the csz is located along the st lawrence river 100 km northeast of quebec city canada and is one of the most active seismic zones in eastern north america five earthquakes with magnitudes equal to or exceeding 6 0 have occurred in the csz in historic time and around 200 earthquakes occur annually hypocenters are located in precambrian basement rocks basement rocks have been affected by numerous tectonic events including grenvillian collision iapetan rifting and meteor impact we performed a sequential tomographic inversion for p wave velocity structure based upon 3093 p wave arrivals from 489 earthquakes recorded by 12 stations high velocity is associated with the center of the impact crater the region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks an elongated high velocity region is present at midcrustal depths that trends parallel to the st lawrence river earthquakes avoid the high velocity body and separate into two bands one on either side of the feature larger earthquakes magnitude 4 have occurred along the northern edges of the high velocity region

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

a glacier flow model incorporating longitudinal deviatoric stresses le modele d ecoulement de glacier developpe introduit les effets de la composante longitudinale du deviateur des contraintes dans les equations les hypotheses sous jacentes peuvent etre appliquees au developpement de modeles pour des cas de figures variees ici elles sont envisagees pour des glaciers glissant en ecoulement plan a l etat stationnaire et non stationnaire le modele se ramene a une generalisation adequate de la theorie pseudo hydrostatique en ecoulement plan si la contrainte longitudinale deviatrice est negligee devant la contrainte de cisaillement basale

earthquakes and the cratonward limit of iapetan faulting in eastern north america the cratonward limit of large normal faults in the passive margin of the late proterozoic to early paleozoic iapetus ocean is a fundamental boundary for the assessment of seismic hazards in populous eastern north america earthquakes at five localities in the iapetan margin have been attributed to compressional reactivation of iapetan normal faults the northwesternmost locations of known iapetan faults both seismic and currently aseismic lie along a line from labrador to alabama this line coincides approximately with the northwestward transition from a more seismically active continental rim to a generally less active cratonic interior thus the northwestern boundary of iapetan faults separates two large regions of mostly different seismic hazard

rates and uncertainties on seismic moment and deformation in eastern canada 1 on the basis of earthquake statistics from the canadian earthquake hazard model we estimate the rates of seismic moment and deformation in seismic zones of eastern canada we use a logic tree approach to derive median values and 66 confidence intervals for models based on earthquake cluster distributions and geological and tectonic structures typical moment rates are low 0 1 1 1017 n m yr 1 equivalent to a magnitude mw 7 earthquake every 350 3500 years in each seismic zone in a few zones such as baffin bay moment rates reach 2 10 1017 n m yr 1 expressed in terms of relative velocity between zone boundaries seismic deformation rates are typically 0 2 0 5 mm yr 1 for a few regions of high seismicity such as baffin bay charlevoix or grand banks the relative velocities reach 1 2 mm yr 1 strain rates are typical of the intraplate environment 10 13 10 10 yr 1 with values locally as high as 10 8 yr 1 these rates give some insight into geodynamic aspects of the northeastern north america plate assuming that the seismic deformation rates represent long term deformation of the lithosphere they provide some constraint to the amplitude and variability of intraplate strain on a shorter timescale seismic strain rates can be compared with postglacial rebound predictions and might help constrain some aspects of these models because they reflect the seismic energy released over the last few hundred years our estimates in combination with geodetic measurements can also help constrain models of earthquake dynamics in eastern north america

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

dynamics of the gulf stream deep western boundary current crossover part ii low frequency internal oscillations abstract a low frequency oscillation in the gulf stream deep western boundary current dwbc system is identified and its influences on several important aspects of the basin scale circulation are investigated an eddy resolving regional primitive equation model is used to demonstrate that feedbacks between the gulf stream with its associated northern and southern recirculation gyres and the upper core of the dwbc can lead to self sustaining large amplitude internal oscillations of roughly decadal frequency the oscillator cycle is described as follows the upper core of the dwbc is entrained under the gulf stream through interaction with the eddy driven northern and southern recirculation gyres as described in part i of this study once entrained the low potential vorticity dwbc water stabilizes the gulf stream and suppresses the eddy fluxes that maintained the interior recirculation gyres this causes the upper dwbc to switch to a southward path along the western boundary thus removing the source o

subglacial hydrology for an ice sheet resting on a deformable aquifer glissements et deformation de la calotte de glace en relation avec le materiau de l aquifere et la densite des chenaux de drainage

on the recent destabilization of the gulf stream path downstream of cape hatteras mapped satellite altimetry reveals interannual variability in the position of initiation of gulf stream meanders downstream of cape hatteras the longitude where the gulf stream begins meandering varies by 1500 km there has been a general trend for the destabilization point to shift west and 5 of the last 6 years had a gulf stream destabilization point upstream of the new england seamounts independent in situ data suggest that this shift has increased both upper ocean deep ocean interaction events at line w and open ocean shelf interactions across the middle atlantic bight mab shelf break mooring data and along track altimetry indicate a recent increase in the number of deep cyclones that stir deep western boundary current waters from the mab slope into the deep interior temperature profiles from the oleander program suggest that recent enhanced warming of the mab shelf may be related to shifts in the gulf stream s destabilization point

relationship between observed upper mantle structures and recent tectonic activity across the southeastern united states the lithospheric structure of the southeastern united states is a product of earlier episodes of continental collision and breakup the region is located in the interior of the north american plate away from active plate margins however there is ongoing tectonism in the region with multiple zones of seismicity uplifting arches and cenozoic intraplate volcanism the mechanisms controlling this activity and the state of stress remain enigmatic two important factors are plate strength and preexisting inherited structures here we present new tomographic images of the upper mantle beneath the southeastern united states revealing large scale structural variations in the upper mantle examples include the relatively thick lithospheric mantle of stable north america that abruptly thins beneath the paleozoic appalachian orogeny and the slow upper mantle of the proterozoic reelfoot rift our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering this provides a viable explanation for seismicity uplifting and young intraplate volcanism we postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere we propose that piecemeal delamination has occurred beneath the region throughout the cenozoic removing a significant amount of reworked deformed mantle lithosphere ongoing lithospheric foundering beneath the eastern margin of stable north america explains significant variations in thickness of lithospheric mantle across the former grenville deformation front

the basement revealed tectonic insight from a digital elevation model of the great unconformity usa cratonic platform across much of north america the contact between precambrian basement and paleozoic strata is the great unconformity a surface that represents a 0 4 b y long hiatus a digital elevation model dem of this surface visually highlights regional scale variability in the character of basement topography across the united states cratonic platform specifically it delineates phanerozoic tectonic domains each characterized by a distinct structural wavelength horizontal distance between adjacent highs and or structural amplitude vertical distance between adjacent lows and highs the largest domain the midcontinent domain includes long wavelength epeirogenic basins and domes as well as fault controlled steps the pronounced change in land surface elevation at the rocky mountain front coincides with the western edge of the midcontinent domain on the basement dem in the rocky mountain and colorado plateau domains west of the rocky mountain front structural wavelength is significantly shorter and structural amplitude significantly higher than in the midcontinent domain the bordering basins domain outlines the southern and eastern edges of the midcontinent domain as emphasized by the basement dem several kilometers of structural relief occur across the boundary between these two domains even though this boundary does not stand out on ground surface topography a plot of epicenters on the basement dem supports models associating intraplate seismicity with the midcontinent domain edge notably certain changes in crustal thickness also coincide with distinct changes in basement depth

decadal predictability of the atlantic ocean in a coupled gcm forecast skill and optimal perturbations using linear inverse modeling abstract the decadal predictability of three dimensional atlantic ocean anomalies is examined in a coupled global climate model the third climate configuration of the met office unified model hadcm3 using a linear inverse modeling lim approach it is found that the evolution of temperature and salinity in the atlantic and the strength of the meridional overturning circulation moc can be effectively described by a linear dynamical system forced by white noise the forecasts produced using this linear model are more skillful than other reference forecasts for several decades furthermore significant nonnormal amplification is found under several different norms the regions from which this growth occurs are found to be fairly shallow and located in the far north atlantic initially anomalies in the nordic seas impact the moc and the anomalies then grow to fill the entire atlantic basin especially at depth over one to three decades it is found that the structure of the optimal initial conditio

transport of the north atlantic deep western boundary current about 39 n 70 w 2004 2008 abstract begun in spring 2004 a sustained measurement program line w is returning high resolution observations of the north atlantic s deep western boundary current dwbc southeast of new england the study focuses on the cold limb of the atlantic meridional overturning circulation near the boundary between the subpolar and subtropical gyres the field study consists of a 6 element continental slope spanning moored array on a line underlying an altimeter satellite ground track and periodic reoccupations of a full depth hydrographic section along the line extending from the continental shelf towards bermuda here data from the first 4 years of the array may 10 2004 april 9 2008 are analyzed along with 9 realizations of the section the array a mix of moored profiler and discrete fixed depth instrument moorings returned temperature salinity and horizontal velocity data with various temporal and depth resolutions after averaging to filter inertial tidal and other high frequency motions the combined moored data set was binned to the lowest common temporal resolution of 5 days the nominal burst sample interval of the moored profilers and interpolated to 2 dbar vertical resolution temperature salinity dissolved oxygen tracer chemical concentrations and direct velocity data were acquired on the hydrographic cruises the present work focuses on the 4 year mean and time varying meridional transport in 4 layers bounded by neutral density surfaces upper and classical labrador sea waters iceland scotland overflow waters and denmark strait overflow waters the 5 d 4 layer summed meridional transport estimates range between 3 5 and 79 9 sv with a record mean average transport of 25 1 sv and standard deviation of 12 5 sv bias adjustment to account for the finite width of the moored array increases the 4 layer mean transport estimate to 28 7 sv at time scales longer than about 1 month the variations in equatorward dwbc transport appear correlated with meridional position of the gulf stream north wall with stronger transport observed when the stream is displaced south

analysis of gps measurements in eastern canada using principal component analysis continuous global positioning system cgps position time series from eastern north america constrain the pattern and magnitude of regional crustal deformation initial analysis delineates consistent uplift patterns as expected from glacial isostatic adjustment gia predictions but the associated horizontal deformation is not definitive in part due to the short time periods for a significant number of the available stations we employ an eigenpattern decomposition in order to define a unique finite set of deformation patterns for this continuous gps data similar in nature to the empirical orthogonal functions historically employed in the analysis of atmospheric and oceanographic phenomena the method derives the eigenvalues and eigenstates from the diagonalization of the correlation matrix using a karhunen loeve expansion kle the kle technique is used to identify the important modes in both time and space for the cgps data modes that potentially include signals such as horizontal and vertical gia tectonic strain and seasonal effects here we filter both the vertical and horizontal velocity patterns on different spatiotemporal scales in order to study the potential geophysical sources after the removal of correlated and random noise the method is successful in disaggregating the linear vertical signal from more variable and less spatially correlated signals the vertical and horizontal results are compared to the predictions of the ice 3g gia loading model with a number of plausible mantle viscosity profiles the horizontal velocity analysis allows for qualitative differentiation between several potential gia models and suggests that with longer time series this technique can be employed to remove correlated noise and improve estimates of crustal strain patterns and their sources

northern north atlantic sea surface height and ocean heat content variability 1 the evolution of nearly 20 years of altimetric sea surface height ssh is investigated to understand its association with decadal to multidecadal variability of the north atlantic heat content altimetric ssh is dominated by an increase of about 14 cm in the labrador and irminger seas from 1993 to 2011 while the opposite has occurred over the gulf stream region over the same time period during the altimeter period the observed 0 700 m ocean heat content ohc in the subpolar gyre mirrors the increased ssh by its dominantly positive trend over a longer period 1955 2011 fluctuations in the subpolar ohc reflect atlantic multidecadal variability amv and can be attributed to advection driven by the wind stress gyre mode bringing more subtropical waters into the subpolar gyre the extended subpolar warming evident in ssh and ohc during the altimeter period represents transition of the amv from cold to warm phase in addition to the dominant trend the first empirical orthogonal function ssh time series shows an abrupt change 2009 2010 reaching a new minimum in 2010 the change coincides with the change in the meridional overturning circulation at 26 5 n as observed by the rapid rapid climate change project and with extreme behavior of the wind stress gyre mode and of atmospheric blocking while the general relationship between northern warming and atlantic meridional overturning circulation amoc volume transport remains undetermined the meridional heat and salt transport carried by amoc s arteries are rich with decade to century timescale variability

beyond goce for the ocean circulation estimate synergetic use of altimetry gravimetry and in situ data provides new insight into geostrophic and ekman currents accurate estimate of ocean surface currents is both a challenging issue and a growing end users requirement in this paper ocean currents are calculated at two levels surface and 15 m depth as the sum of the geostrophic and ekman components first a new global 14 mean dynamic topography called the cnes cls13 mdt has been calculated and is now available for use by the oceanographic community by exploiting information from surface drifters and argo floats the new mdt resolves spatial scales beyond the resolution permitted by the recent gravity and ocean circulation experiment goce geoid models 125 km associated mean geostrophic speeds in strong currents are increased by 200 on average compared to goce based mean currents in addition for the first time a two level monthly empirical ekman model that samples a spiral like behavior is estimated we show that combining both pieces of information leads to improved ocean currents compared to other existing observed products

earthquakes in the eastern great lakes basin from a regional perspective abstract this paper presents a summary of the seismicity and its relation to stress and geologic structures in the eastern great lakes basin eglb and compares it with that of other regions in the central and eastern north america cena the earthquakes scattered throughout the eglb are occurring at a rate somewhat less than that of the appalachians and along the atlantic seaboard paleoseismology studies suggest that the lower seismicity rate may be characteristic of the eglb since the late wisconsin north of the eglb earthquakes have primarily thrust mechanisms while to the south of the eglb most earthquakes are strike slip throughout the region including the eglb the average p axes of the earthquakes are oriented ne sw and are aligned with the direction of the current plate driving stress on a regional basis earthquakes are centered primarily in the precambrian basement beneath the paleozoic cover many of the earthquakes in the eglb have occurred in areas of preexisting faults at least some of which may have been active during past episodes of continental rifting for individual faults that have been studied in some detail however it is not clear whether earthquakes represent reactivations of local preexisting structures or nucleation of new ruptures in or near the old fault zones

effects of seismicity models and new ground motion prediction equations on seismic hazard assessment for four canadian cities seismicityratesandground motionpredictionequations gmpes arethe key uncertainties in probabilistic seismic hazard analysis psha we explore the impact of new findings and knowledge from seismological and ground motion studies on seismic hazard assessment for eastern and western canada updated information includes the reevaluation of seismicity rates and their interpretation in terms of seismic source zones and the use of new gmpes we refer to our model as an interim updated seismic hazard model as it does not treat all uncertainties comprehensively rather we address the impact of key uncertainties based on our updated interim seismic hazard model uniform hazard spectra uhs at four major cities across canada are obtained and compared with uhs in the current seismic hazard maps of canada 2005 2010 whicharebasedona1995seismichazardmodeldevelopedbythegeologicalsurveyof canada sensitivity analysis highlights the significant impact of seismicity smoothing in low to moderate seismic regions eastern canada while gmpes are important for all regions moreover our interim updated seismic hazard model can readily produce seismic hazard curves as well as seismic hazard deaggregation results for various site conditionsandformultipleprobabilitylevels thiscapabilityisessentialforcarryingout advanced earthquake engineering analyses

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

geographic deaggregation of seismic hazard in the united states the seismic hazard calculations for the 1996 national seismic hazard maps have been geographically deaggregated to assist in the understanding of the relative contributions of sources these deaggregations are exhibited as maps with vertical bars whose heights are proportional to the contribution that each geographical cell makes to the ground motion exceedance hazard bar colors correspond to average source magnitudes we also extend the deaggregation analysis reported in harmsen et al 1999 to the western conterminous united states in contrast to the central and eastern united states ceus the influence of specific faults or characteristic events can be clearly identified geographic deaggregation for 0 2 sec and 1 0 sec pseudo spectral acceleration sa is performed for 10 probability of exceedance pe in 50 yr 475 yr mean return period and 2 pe in 50 yr 2475 yr mean return period for four western u s cities los angeles salt lake city san francisco and seattle and for three central and eastern u s cities atlanta boston and saint louis in general as the pe is lowered the sources of hazard closer to the site dominate larger more distant earthquakes contribute more significantly to hazard for 1 0 sec sa than for 0 2 sec sa additional maps of geographically deaggregated seismic hazard are available on the internet for 120 cities in the conterminous united states for 1 sec sa and for 0 2 sec sa with a 2 pe in 50 yr examination of these maps of hazard contributions enables the investigator to determine the distance and azimuth to predominant sources and their magnitudes this information can be used to generate scenario earthquakes and corresponding time histories for seismic design and retrofit where fault density is lower than deaggregation cell dimensions we can identify specific faults that contribute significantly to the seismic hazard at a given site detailed fault information enables investigators to include rupture information such as source directivity radiation pattern and basin edge effects into their scenario earthquakes used in engineering analyses

seismotectonic characteristics of the lower st lawrence seismic zone quebec insights from geology magnetics gravity and seismics the estuary of the st lawrence river between baie comeau and sept iles is an area where 50 to 100 earthquakes are detected yearly this study defines the major lineaments of the precambrian basement and compares them with mapped faults where possible and examines their possible correlation with the local earthquakes onshore aerial photographs remote sensing images and field mapping are used to identify the geological structures of the precambrian basement while offshore they are interpreted from potential field magnetic gravity and a published synthesis of seismic reflection profiles the precambrian basement dips towards the southeast under the appalachian nappes with normal faults with kilometre scale throw and east west or ene wsw strikes onshore a system of normal brittle faults with a complex history of movements crosscuts both the precambrian basement and the overlying ordovician sedimentary cover most earthquakes occur beneath the st lawrence river at focal depths between about 7 and

seawater density variations in the north atlantic and the atlantic meridional overturning circulation seawater property changes in the north atlantic ocean affect the atlantic meridional overturning circulation amoc which transports warm water northward from the upper ocean and contributes to the temperate climate of europe as well as influences climate globally previous observational studies have focused on salinity and freshwater variability in the sinking region of the north atlantic since it is believed that a freshening north atlantic basin can slow down or halt the flow of the amoc here we use available data to show the importance of how density patterns over the upper ocean of the north atlantic affect the strength of the amoc for the long term trend the upper ocean of the subpolar north atlantic is becoming cooler and fresher whereas the subtropical north atlantic is becoming warmer and saltier on a multidecadal timescale the upper ocean of the north atlantic has generally been warmer and saltier since 1995 the heat and salt content in the subpolar north atlantic lags that in the subtropical north atlantic by about 8 9 years suggesting a lower latitude origin for the temperature and salinity anomalies because of the opposite effects of temperature and salinity on density for both long term trend and multidecadal timescales these variations do not result in a density reduction in the subpolar north atlantic for slowing down the amoc indeed the variations in the meridional density gradient between the subpolar and subtropical north atlantic ocean suggest that the amoc has become stronger over the past five decades these observed results are supported by and consistent with some oceanic reanalysis products

meltwater discharge through the subglacial bed and its land forming consequences from numerical experiments in the polish lowland during the last glaciation numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in nw poland primarily its flow pattern velocities and fluxes we have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady state and transient conditions the results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin all model runs show water discharge at the ice forefield driven by ice sheet thickness modulated down ice decreasing hydraulic heads in relation to non glacial times the transient 3d model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca 90 m below the ice bed interface and up to 40 km in front of the glacier comparison with empirical data suggests that depending on the model run only between 5 and 24 of the meltwater formed at the ice sole drained through the bed as groundwater this is consistent with field observations documenting abundant occurrence of tunnel valleys indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely in these areas the relief shows distinct palaeo ice lobes indicating fast ice flow possibly triggered by the undrained water at the ice bed interface owing to the abundance of low permeability strata in the bed the simulated groundwater flow depth is less than ca 200 m copyright 2009 john wiley sons ltd

role of large scale tectonic forces in intraplate earthquakes of central and eastern north america central and eastern united states ceus have experienced large intraplate earthquakes yet at present there is no comprehensive model to explain stresses strain and seismicity in this intraplate setting models to explain the intraplate stresses in ceus include glacio isostatic adjustment ridge push effects local stresses along preexisting fracture zones and large scale convection in this paper we present a self consistent model of the dynamics of ceus that explains the stress field responsible for these intraplate earthquakes the earthquakes represent slow ongoing deformation associated with forces arising from a combination of lithosphere topography and structure together with the effects of density driven mantle flow using gps data we calculate strain rates that are likely to arise from tectonic effects and conclude that intraplate strain rates associated with tectonic effects are unlikely to exceed 1 x 10 9 year 1 we test several models of lateral viscosity variations by comparing model stress orientation output with earthquake moment tensors shmax directions from stress inversion and p axes of earthquakes a model that satisfies stress and earthquake constraints and also strain rate magnitude constraints requires high viscosity 1025 pa s craton and old oceanic lithosphere of the western atlantic block and weaker 5 x 1024 pa s accreted appalachian terrane other strength contrasts within the lithosphere are likely present incorporation of these into future models using constraints from seismology along with refined geodetic measurements and improved estimates of crust and upper mantle densities is needed to further refine long term dynamic models and better evaluate the hazards associated with this very slow ongoing permanent deformation within the eastern and central united states