empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

semidiurnal tides on the laptev sea shelf with implications for shear and vertical mixing the arctic continental shelf seas hold a globally significant source of freshwater that impacts arctic ocean stratification circulation and climate this freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events as resolved by laptev sea microstructure observations the tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the laptev sea multiyear adcp mooring records from locations across the shelf reveal that semidiurnal tides are dominated by them2 and s2 constituents with the largest amplitudes on the outer shelf throughoutmost of the shelf tides are clockwise polarized and sheared by stratification as characteristic near the m2 critical latitude interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification setting lena river freshwater plume in all locations m2 tides are enhanced under sea ice and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure the main conclusions of this study are that i tides play a comparatively greater role year round on the outer shelf relative to the inner shelf ii a sea ice reduction will overall decrease the predictability of the currents especially on the inner shelf and iii the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure these combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater particularly on the inner shelf where the lena river first enters the laptev sea

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

repeatability study of seismic source signatures this study discusses the repeatability of source signature using the instantaneous phase as derived from the complex trace attributes the study is part of a very large 2 d seismic survey using sources of vibroseis and surface dynamite the field procedure consisted of recording the production record retaining the positions then repeat recording the same shake or shot the instantaneous phase was found to be the best measure for the difference between the first and the repeat records in addition to the instantaneous phase other analyses were used to evaluate changes in source signature results were tabulated for statistical comparisons and graded for quality excluding erroneous cases the remainder of poor repeatabilities were studied the analyses of near offset data seem to indicate that nonrepeatability of source signature relates mostly to changes in absorption and cohesion induced by elastic saturation at the near surface in general by time shifting and phase rotating the repeat record the difference in instantaneous phase tends to diminish the new idea of using instantaneous phase difference plots to evaluate repeatability offers improved evaluation of source signatures and can also be used to detect time lapsed changes in reservoir monitoring by evaluating repeatability and avoiding elastic saturation near the surface source signatures can be made more consistent thus increasing the resolution of stacked data for 2 d 3 d and 4 d seismic surveys

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

dipole anomaly in the winter arctic atmosphere and its association with sea ice motion abstract this paper identified an atmospheric circulation anomaly dipole structure anomaly in the arctic atmosphere and its relationship with winter sea ice motion based on the international arctic buoy program iabp dataset 1979 98 and datasets from the national centers for environmental prediction ncep and the national center for atmospheric research ncar for the period 1960 2002 the dipole anomaly corresponds to the second leading mode of eof of monthly mean sea level pressure slp north of 70 n during the winter season october march and accounts for 13 of the variance one of its two anomalous centers is stably occupied between the kara sea and laptev sea the other is situated from the canadian archipelago through greenland extending southeastward to the nordic seas the dipole anomaly differs from one described in other papers that can be attributed to an eastward shift of the center of action of the north atlantic oscillation the finding shows that the dipole anomaly also differs from

detailed structures of the subducted philippine sea plate beneath northeast taiwan a new type of double seismic zone we studied the detailed structure of the subducted philippine sea plate beneath northeast taiwan where oblique subduction regional collision and back arc opening are all actively occurring simultaneous inversion for velocity structure and earthquake hypocenters are performed using the vast high quality data recorded by the taiwan seismic network we further supplement the inversion results with earthquake source parameters determined from inversion of teleseismic p and sh waveforms a critical step to define the position of plate interface and the state of strain within the subducted slab the most interesting feature is that relocated hypocenters tend to occur along a two layered structure the upper layer is located immediately below the plate interface and extends down to 70 80 km at a dip of 40 50 below approximately 100 km the dip increases dramatically to 70 80 the lower layer commences at 45 50 km and stays approximately parallel to the upper layer with a separation of 15 5 km in between down to 70 80 km below that the separation decreases and the two layers seem to gradually merge into one wadati benioff zone we propose to term the classic double seismic zones observed beneath japan and kuril as type i and that we observed as type ii respectively a global survey indicates that type ii double seismic zones are also observed in new zealand near the southernmost north island cascadia just north of the mendocino triple junction and the cook inlet area of alaska all of them are located near the termini of subducted slabs in a tectonic setting of oblique subduction we interpret the seismogenesis of type ii double seismic zones as reflecting the lateral compressive stress between the subducted plate and the adjacent lithosphere originating from oblique subduction and the downdip extension from slab pulling force the upper seismic layer represents seismicity occurring in the upper crust of a subducted plate and or along the plate interface whereas the lower layer is associated with events in the uppermost mantle

the arctic circumpolar boundary current we present high resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the siberian and alaskan shelves in the arctic ocean thus far the arctic circumpolar boundary current acbc has been seen as comprising two branches the fram strait and barents sea branches fsb and bsb respectively here we describe a new third branch the arctic shelf break branch asbb we show that the forcing mechanism for the asbb is a combination of buoyancy loss and non local wind creating high pressure upstream in the barents sea the potential vorticity influx through the st anna trough dictates the cyclonic direction of flow of the asbb which is the most energetic large scale circulation structure in the arctic ocean it plays a substantial role in transporting arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum the simulations show the continuity of the fsb all the way around the arctic shelves and the uninterrupted asbb between the st anna trough and the western fram strait the bsb flows continuously along the siberian shelf as far as the chukchi plateau where it partly diverges from the continental slope into the ocean interior the alaskan shelf break current asc is the analog of the asbb in the canadian arctic the asc is forced by the local winds and high upstream pressure in bering strait caused by the drop in sea surface height between the pacific and arctic oceans

kara sea freshwater dispersion and export in the late 1990s 1 a regional coupled ice ocean model for the kara sea forced with boundary conditions from a large scale north atlantic arctic ocean model is used to study dispersion and export of freshwater from ob and yenisei rivers toward the arctic ocean and the laptev sea for the period 1996 2001 the years 1998 and 1999 were characterized by a strong positive sea level pressure slp anomaly in the siberian part of the arctic ocean owing to prevailing northeasterly winds the slp anomaly caused a blocking situation which suppressed the otherwise eastward freshwater export to the arctic ocean and laptev sea this reversal of the prevailing circulation scheme led to a dramatic freshening of the kara sea through accumulation of low saline river water in the central and western parts additionally the kara strait inflow from the barents sea which presents the main source for saline atlantic derived water was reduced and partly even reversed the suppressed freshwater export during winter 1998 1999 recovered in the following winter 1999 2000 when a significant pulse of low saline surface water left toward the laptev sea the variability of the river discharge plays a minor role for the investigated period because the interannual variability of runoff rates is generally too low to explain the observed hydrographic changes the results underline the importance of local shelf sea processes for the variability of the freshwater export from the arctic shelves to the central arctic ocean

the arctic circumpolar boundary current abstract the main water transformations in the arctic mediterranean take place in the boundary current of atlantic water which crosses the greenland scotland ridge from the north atlantic into the eastern norwegian sea it enters and flows around the arctic ocean before it exits the arctic mediterranean as the east greenland current primarily through denmark strait on route it experiences numerous branchings and mergings by examining how the properties of this circumpolar boundary current evolve it is possible to identify and describe the processes causing the water mass transformations in the arctic mediterranean it is also possible to follow the arctic ocean deep waters as they spread into the nordic seas and eventually provide 40 of the overflow water supplying the north atlantic deep water

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

the rupture process of the 1989 offshore ito earthquakes preceding a submarine volcanic eruption an earthquake swarm at the eastern offshore region of ito the izu peninsula started on june 30 1989 and became more active on and after july 4 the largest earthquake among the swarm mjma 5 5 occurred at 1109 jst 0209 ut on july 9 1989 and a second significant event followed 45 s later a remarkable volcanic tremor started on july 11 and a submarine eruption occurred just above the source region of the largest earthquake on july 13 in this paper we present a new inversion method to derive the source time function of rupture process the source time function is divided into several sections following an automatic algorithm and is interpolated with a cubic spline function the parameters which are the values and first derivatives at knots of the spline function are determined by minimizing a squared error between the observed and synthetic seismograms to demonstrate the performance of this method some numerical experiments simulations are carried out on near field seismic records applying this method to analysis of the two large earthquakes the detailed rupture processes are obtained a heterogeneous crustal structure near the volcanic area affects the rupture processes of these earthquakes the large stress drop due to the largest earthquake just beneath the submarine eruption point would assist a magma ascending and may have triggered the eruption 4 days after these earthquakes

seismic detection limits of small deep man made reflectors a test at a geothermal site in northern germany a key question for the development of geothermal plants is the seismic detection and monitoring of fluid injections at several kilometers depth the detection and monitoring limits are controlled by several parameters for example the strength of seismic sources number of receivers vertical stacking and noise conditions for a known reference reflector at 2 66 km depth at a geothermal site in northern germany the results of a simple surface seismic experiment were therefore combined with numerical forward modeling for different injection scenarios at 3 8 km depth the underlying idea is that changes of reflectivity from the injection at 3 8 km must be larger than the variance of the measurements to be observable assuming that the injection at 3 8 km depth would produce a subhorizontal disklike target with a fracture porosity of 2 or 5 the critical porosity the water injection volume has to be at least 443 and 115 m 3 respectively to be detectable from the surface if the injection on the other hand does not create subhorizontal but subvertical pathways or only reduces the seismic velocities via the increased pore pressure in the immediate vicinity of the bore hole the injection is undetectable from the surface the most promising approach is therefore to move sources and or receivers closer to the target that is the use of borehole instrumentation

time lapse crosswell seismic tomogram interpretation implications for heavy oil reservoir characterization thermal recovery process monitoring and tomographic imaging technology time lapse crosswell seismic data acquired with a cemented receiver cable have been processed into p and s wave tomograms which image heavy oil sand lithofacies and changes as a result of steam injection twenty seven crosswell surveys were acquired between two wells over a 3 5 month period before during and after a 34 day 30 mbbl 4770m3 steam injection cycle interpretation was based on correlations with reservoir data and models observation well data and engineering documentation of the production history and steam cycle baseline s and p wave tomograms image reservoir sand flow units and areas affected by past cyclic steam injection s wave tomograms define lithology and porosity contrasts between the excellent reservoir quality high flow turbidite channel facies and the interbedded low to moderate flow bioturbated levee facies the reservoir dip of approximately 20 is defined by the velocity contrast between lithofacies p wave baseline tomograms image lithology porosity structure an

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

the 1994 northridge california earthquake investigation of rupture velocity risetime and high frequency radiation a hybrid global search algorithm is used to solve the nonlinear problem of calculating slip amplitude rake risetime and rupture time on a finite fault thirty five strong motion velocity records are inverted by this method over the frequency band from 0 1 to 1 0 hz for the northridge earthquake four regions of larger amplitude slip are identified one near the hypocenter at a depth of 17 km a second west of the hypocenter at about the same depth a third updip from the hypocenter at a depth of 10 km and a fourth updip from the hypocenter and to the northwest the results further show an initial fast rupture with a velocity of 2 8 to 3 0 km s followed by a slow termination of the rupture with velocities of 2 0 to 2 5 km s the initial energetic rupture phase lasts for 3 s extending out 10 km from the hypocenter slip near the hypocenter has a short risetime of 0 5 s which increases to 1 5 s for the major slip areas removed from the hypocentral region the energetic rupture phase is also shown to be the primary source of high frequency radiation 1 15 hz by an inversion of acceleration envelopes the same global search algorithm is used in the envelope inversion to calculate high frequency radiation intensity on the fault and rupture time the rupture timing from the low and high frequency inversions is similar indicating that the high frequencies are produced primarily at the mainshock rupture front two major sources of high frequency radiation are identified within the energetic rupture phase one at the hypocenter and another deep source to the west of the hypocenter the source at the hypocenter is associated with the initiation of rupture and the breaking of a high stress drop asperity and the second is associated with stopping of the rupture in a westerly direction

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

reconciliation of crosshole seismic velocities with well information in a layered sedimentary environment in sedimentary environments horizontal fine layering can cause significant complications when analyzing and comparing seismic data with different frequencies and propagation directions at the whitchester test site three boreholes penetrate upper carboniferous cyclical sediments involving interbedded carbonates sandstones and mudstones with seismic velocities ranging from less than 3 0 km s in the mudstones to over 4 5 km s in the carbonates initial crosshole results from two boreholes approximately 200 m deep and 75 m apart showed a poor correlation with the borehole logs recorded in a third intermediate borehole furthermore the tomographic images were inconsistent with the expected geology the objective of this paper is to reconcile the crosshole seismic data with the borehole log information the borehole information must be upscaled to match the resolution of the crosshole experiment however upscaling techniques based on backus averaging lead to the prediction of significant anisotropy of the order of 20 in places with a vertical symmetry axis this anisotropy is a result of a combination of fine layering and the intrinsic mineral anisotropy measured on the core samples although it is the layer induced anisotropy that dominates at the crosshole frequencies of 400 hz this prediction was tested by including anisotropy parameters into the analysis of the crosshole data using anisotropic velocity tomography in the central part of the final anisotropic velocity tomograms where the ray coverage is adequate these crosshole results are consistent with the anisotropy predictions once the anisotropy was properly accounted for the tomographic images are consistent with the layered nature of the geology at the site and they show the location and throw of a known fault in the section we conclude that at this site and at crosshole frequencies seismic layer induced anisotropy plays a significant role and must be accounted for when processing and interpreting crosshole seismic data

gps observation of crustal deformation in the taiwan luzon region fifteen gps stations in the batan luzon area were surveyed three times during 1996 to 1998 in order to study crustal deformation in the taiwan luzon region the data from these annual surveys are processed together with data from 20 permanent stations in the taiwan area and igs stations in the asia pacific region we found that the chinese continental margin is moving in directions of 102 112 with rates of 11 12 mm yr relative to stable eurasia there is a significant southward increase in crustal motion with respect to eurasia along the n s trend of the luzon arc in the coastal range of taiwan the velocity is 53 mm yr in the direction 313 further south at two volcanic islands lanhsu and batan the velocities increase to 68 mm yr in the direction 306 and 81 mm yr in the direction 299 respectively in northern luzon the velocity reaches 86 mm yr in the direction 301 remarkable fault slips of 17 31 mm yr across the philippine fault system are detected

time lapse seismic reservoir monitoring time lapse seismic reservoir monitoring has advanced rapidly over the past decade there are currently about 75 active projects worldwide and more than 100 cumulative projects in the past decade or so the present total annual expenditures on 4 d seismic projects are on the order of 50 100 million us this currently represents a much smaller market than 3 d seismic but the use of 4 d seismic has grown exponentially over the past decade and is expected to continue to do so

kara sea freshwater transport through vilkitsky strait variability forcing and further pathways toward the western arctic ocean from a model and observations siberian river water is a first order contribution to the arctic freshwater budget with the ob yenisey and lena supplying nearly half of the total surface freshwater flux however few details are known regarding where when and how the freshwater transverses the vast siberian shelf seas this paper investigates the mechanism variability and pathways of the fresh kara sea outflow through vilkitsky strait toward the laptev sea we utilize a high resolution ocean model and recent shipboard observations to characterize the freshwater laden vilkitsky strait current vsc and shed new light on the little studied region between the kara and laptev seas characterized by harsh ice conditions contrasting water masses straits and a large submarine canyon the vsc is 10 20 km wide surface intensified and varies seasonally maximum from august to march and interannually average freshwater volume transport is 500 120 km3 a 1 0 53 0 08 sv with a baroclinic flow contribution of 50 90 interannual transport variability is explained by a storage release mechanism where blocking favorable summer winds hamper the outflow and cause accumulation of freshwater in the kara sea the year following a blocking event is characterized by enhanced transports driven by a baroclinic flow along the coast that is set up by increased freshwater volumes eventually the vsc merges with a slope current and provides a major pathway for eurasian river water toward the western arctic along the eurasian continental slope kara and laptev sea freshwater transport is not correlated with the arctic oscillation but rather driven by regional summer pressure patterns

pressure dependent seismic reflection amplitude changes in crystalline crust lessons learned at the continental deep drilling site ktb summary we conducted an active seismic experiment aimed at measuring changes in seismic reflection amplitudes as a consequence of fresh water injection and corresponding pressure changes at the german continental deep drilling site ktb the injection took place at the bottom of the 4 km deep pilot borehole in the se2 fault zone in crystalline rock units between the springs of 2004 and 2005 prior to the experiment theoretical calculations indicated a possible increase in the compressional wave reflection coefficient as a result of an injection induced reduction of the seismic velocities within the fault zone despite good repeatability of the emitted source signals the experiment suffered from missing the clear reflection signals expected from the fault zone with regard to seismic data from past experiments applying various data processing steps did not enhance the signals enough to obtain clear reflections or even pressure dependent reflection amplitude changes the signal to noise ratio remains smaller than the effects under observation provided that reflections are present in the data the error bar of the recorded signals is of the order of 100 per cent therefore we conclude that the experiment was not successful in seismically measuring pressure variations however important lessons for land seismic time lapse measurements in crystalline environments have been learned i the source should be capable of emitting frequencies below 30 hz ii the detector array setup proved to be partly questionable because in a scattering environment like the crystalline rocks at the ktb site the incidence of a plane wave precondition might be violated for high frequency signals iii near surface variations of elastic properties likely influence seismic monitoring iv using a step function that is a first order pressure discontinuity to model the subsurface pressure build up is very likely too simple an approach

observations of tidally induced currents over the continental slope of the laptev sea arctic ocean abstracttwo year long 2004 05 and 2005 06 records of currents from two moorings deployed at the continental slope of the laptev sea 78 26 n 125 40 e are used in order to define the properties of tidal currents in the upper 200 m ocean layer harmonic and spectral analyses of currents showed that the semidiurnal tidal constituent s2 dominates over the semidiurnal m2 and diurnal constituents this dominance of the s2 constituent in the tidal currents is due to resonant interaction of the superinertial wave with sloping bottom topography in contrast to the tidal currents sea level changes are dominated by the m2 constituent as seen from a tidal model by l padman and s erofeeva using assimilation of observational data strong anticorrelation 0 73 0 05 was found between the upper 50 m s2 current amplitudes and local sea ice concentration with fourfold from 2 0 to 8 5 cm s 1 amplification of tidal currents under ice free conditions this is probably due to a change of local resonance condit

time lapse crosswell seismic tomography to characterize flow structure in the reservoir during the thermal stimulation time lapse crosswell seismic tomography data recorded with an interval of six months indicate a strong directional thermal response in a fractured eolian sandstone reservoir at a five spot thermal stimulation site in the south casper creek oil field wyoming the seismic thermal response depicted on the tomogram and in conjunction with the geological data from cores and a wireline log reveals the multichannel flow mechanism in the reservoir formation the three factors that control steam or heat propagation are the fractures the directional permeability existing in the rock matrix and the fault crosswell tomograms imply that the primary fluid flow is through fractures oriented north south whereas the secondary fluid flow is through the matrix in the direction of maximum horizontal permeability the thermal response expressed on the tomogram infers that a fault oriented n80 degrees e offsets flow units and acts as a flow barrier or baffle the flow structure implied by the crosswell seismic tomography is strikingly different from the initial conjecture as deduced from engineering perception based on geological reasoning however the tomographic implications were supported by both a tracer test and fluid temperature measurements at the four producing wells around the injector

salinity trends on the siberian shelves 1 we present an analysis of observed long term 100 year salinity trends on the freshwater dominated siberian continental shelves a multiple regression was performed in the white sea ws the kara sea ks the laptev sea ls and the east siberian sea ess since 1930 the ws has gained freshwater while the ess has lost it consistent with river discharge trends over this period over the past 20 years increases in both river discharge and direct precipitation can explain observed salinity decreases in the ws but not in the ks salinity trends in the ls and ess indicate that ocean circulation plays a dominate role in these areas where in recent years freshwater has been diverted eastward along the coast rather than northward toward the deep ocean

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

the fate of terrigenous dissolved organic carbon on the eurasian shelves and export to the north atlantic dissolved lignin phenols chromophoric dissolved organic matter cdom absorption and fluorescence were analyzed along cross slope mooring locations in the barents laptev and east siberian seas to gain a better understanding of terrigenous dissolved organic carbon tdoc dynamics in arctic shelf seas and the arctic ocean a gradient of river water and tdoc was observed along the continental shelf eastward into the east siberian sea correlations of carbon normalized yields of lignin derived phenols supplied by siberian rivers with river water fractions and known water residence times yielded in situ decay constants of 0 18 0 58 yr 1 calculations showed 50 of annual tdoc discharged by siberian rivers was mineralized in estuaries and on eurasian shelves per year indicating extensive removal of tdoc bioassay experiments and in situ decay constants indicated a reactivity continuum for tdoc cdom parameters and acid aldehyde ratios of vanillyl v and syringyl s lignin phenols showed biomineralization was the dominant mechanism for the removal of tdoc characteristic ratios of p hydroxy p s and v phenols p v s v also identified shelf regions in the kara sea and regions along the western laptev sea shelf where formation of low salinity halocline waters lshw and lower halocline water lhw occurred the efficient removal of tdoc demonstrates the importance of eurasian margins as sinks of tdoc derived from the large siberian rivers and confirms tdoc mineralization has a major impact on nutrients budgets air sea co2 exchange and acidification in the siberian shelf seas

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

circulation in the northwest laptev sea in the eastern arctic ocean crossroads between siberian river water atlantic water and polynya formed dense water this paper investigates new observations from the poorly understood region between the kara and laptev seas in the eastern arctic ocean we discuss relevant circulation features including riverine freshwater atlantic derived water and polynya formed dense water emphasize vilkitsky strait vs as an important kara sea gateway and analyze the role of the adjacent 250 km long submarine vilkitsky trough vt for the arctic boundary current expeditions in 2013 and 2014 operated closely spaced hydrographic transects and 1 year long oceanographic mooring near vt s southern slope and found persistent annually averaged flow of 0 2 m s21 toward the nansen basin the flow is nearly barotropic from winter through early summer and becomes surface intensified with maximum velocities of 0 35 m s21 from august to october thermal wind shear is maximal above the southern flank at 30 m depth in agreement with basinward flow above vt s southern slope the subsurface features a steep front separating warm 0 58c atlantic derived waters in central vt from cold 1 58c shelf waters which episodically migrates across the trough indicated by current reversals and temperature fluctuations shelf transformed waters dominate above vt s slope measuring near freezing temperatures throughout the water column at salinities of 34 35 these dense waters are vigorously advected toward the eurasian basin and characterize vt as a conduit for near freezing waters that could potentially supply the arctic ocean s lower halocline cool atlantic water and ventilate the deeper arctic ocean our observations from the northwest laptev sea highlight a topographically complex region with swift currents several water masses narrow fronts polynyas and topographically channeled storms

atmospheric driven state transfer of shore fast ice in the northeastern kara sea received 9 september 2004 revised 19 april 2005 accepted 2 june 2005 published 21 september 2005 1 frequencies of observed occurrences of shore fast ice in the northeastern kara sea for each month during 1953 1990 reveal a multimodality of shore fast ice extent in late winter and spring the fast ice extent exhibits mainly three different configurations modes associated with the regional topography of coasts and islands these modes show fast ice areas equal to approximately 98 6 122 6 and 136 8 1000 km 2 analysis of the time series of fast ice extent shows that favorable conditions for expansion of fast ice seaward in winter and spring are met if the atmospheric circulation over the northeastern kara sea is controlled by the arctic high resulting in offshore winds and a significant up to 6 c decrease of the monthly mean surface air temperature in contrast the penetration of the icelandic low into the kara sea accompanied by arctic cyclones coming from the west is responsible for the partial breakup and decrease of fast ice extent in winter or spring

episodic warming of near bottom waters under the arctic sea ice on the central laptev sea shelf a multiyear mooring record 2007 2014 and satellite imagery highlight the strong temperature variability and unique hydrographic nature of the laptev sea this arctic shelf is a key region for river discharge and sea ice formation and export and includes submarine permafrost and methane deposits which emphasizes the need to understand the thermal variability near the seafloor recent years were characterized by early ice retreat and a warming near shore environment however warming was not observed on the deeper shelf until year round under ice measurements recorded unprecedented warm near bottom waters of 0 6 c in winter 2012 2013 just after the arctic sea ice extent featured a record minimum in the laptev sea early ice retreat in 2012 combined with lena river heat and solar radiation produced anomalously warm summer surface waters which were vertically mixed trapped in the pycnocline and subsequently transferred toward the bottom until the water column cooled when brine rejection eroded stratification

seismic attributes for monitoring of a shallow heated heavy oil reservoir a case study in production geophysics detecting the zones of production or constraining the in situ conditions within a reservoir are often of greater importance than obtaining highly resolved seismic structural images standard seismic data processing distorts the signal and limits the potential for extracting additional information especially for shallow targets an alternative shift stack procedure is applied in the processing of a shallow 12 fold 1 m common midpoint cmp spacing reflection profile acquired over a heated athabasca heavy oil sand reservoir the shift stack involves summing of cmp traces which have been flattened to an appropriate reference event simple modeling confirms that the prestack waveforms are better preserved by this process amplitude and frequency attributes are extracted from the reflection profile amplitudes of a continuous reservoir event vary by 600 over 35 m intervals along the profile bright spots correlate with heated regions apparent frequencies as measured by the instantaneous frequency and by short time window power spectral estimates of the subreservoir event are 20 30 hz lower in these same regions these diminished apparent frequencies most probably result from interference of the subreservoir reflection with events related to structural changes within the reservoir a complete interpretation of the results has not been attempted as knowledge of the in situ conditions is incomplete however changes in the seismic response at the well locations suggest that these attributes are useful in detection and mapping of heated zones the shiftstack procedure may also be useful in environmental and geotechnical applications

wind driven transport pathways for eurasian arctic river discharge distributions of temperature salinity and barium in near surface waters depth 50 m of the laptev sea and adjacent areas of the arctic ocean are presented for the summers of 1993 1995 and 1996 the tracer data indicate that while fluvial discharge was largely confined to the shelf region of the laptev sea in the summer of 1993 surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the laptev sea in the summers of 1995 and 1996 these distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central arctic basins from the laptev sea when southerly to southeasterly wind conditions prevail river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas these waters can then enter the interior arctic ocean via upper layer flow in the vicinity of the lomonosov ridge under other wind conditions river waters are steered primarily along the inner laptev shelf and into the east siberian sea as part of the predominantly eastward coastal current system these waters then appear to cross the shelf and enter the interior arctic ocean via upper layer flow aligned roughly along the mendeleyev ridge the extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle

cross shelf transport of warm and saline water in response to sea ice drift on the laptev sea shelf 1 oceanographic moorings and conductivity temperature depth ctd surveys from september 2009 to september 2010 are used to describe recent changes in the laptev sea hydrography and to highlight wind and ice driven surface ekman transport as the mechanism to translate these changes from the outer to the inner shelf bottom waters in february 2010 moored oceanographic instruments recorded a sudden increase in temperature 0 8 c and salinity 3 near the bottom of the inner laptev sea shelf such warm and saline waters had not been previously observed on the inner shelf in winter they likely originated from the basin and were first observed during a summer 2009 ctd survey in the northwestern shelf break region subsequently spreading east and shoreward across the laptev sea shelf the changes were introduced to the mooring site by the first of a series of bottom intensified flow events with velocities reaching 20 cm s 1 topographically guided along a relic submarine river valley each of the flow events coincided with negative pressure anomalies at the mooring site and offshore directed upwelling favorable winds and ice drift we suggest that the observations to first order resemble a simplified two dimensional two layered ocean where offshore surface ekman transport is compensated for by a barotropic shoreward response flow near the bottom in this paper we use one of the first comprehensive long term laptev sea datasets to highlight ice ocean atmosphere interactions in early and late winter and discuss the role of freshwater stratification and ice mobility on under ice circulation on the laptev sea shelf

waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes abstract yoshida s 1992 waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 45 59 we inverted teleseismic p waveforms to infer rupture processes of subduction zone earthquakes using green s functions computed for realistic seafloor topography because reverberations in the water layer near the source affect the teleseismic waveforms we modeled the seafloor by a series of several plane surfaces with appropriate dip and performed three dimensional ray tracing to compute green s functions from the gdsn seismograms spatial and temporal slip distributions were estimated for the 1986 andreanof islands earthquake m s 7 7 and the 1985 chile earthquake m s 7 8 to suppress unstable parts of the least squares solution we introduced some stabilizing constraints the 1986 andreanof islands earthquake was analyzed using two kinds of source models the first one has a prescribed rupture velocity and the second one allows any point to slip at any time the solutions by the two models gave similar patterns of slip distribution a relatively small subevent initially occurred and then a dominant subevent with a moment of about five times larger occurred with a center about 80 km west of the hypocenter for the 1985 chile earthquake a small initial subevent was also found and a major rupture with a ten times larger moment extended approximately from 20 to 70 km south of the hypocenter for both the earthquakes it was found that most of the one day aftershocks occurred in areas where a small moment was released during the main shock

landfast ice affects the stability of the arctic halocline evidence from a numerical model landfast ice covers large surface areas of the winter siberian seas the immobile landfast ice cover inhibits divergent and convergent motion hence dynamical sea ice growth and redistribution decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore in spite of the potentially large effects state of the art numerical models usually do not represent landfast ice in its correct extent a simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated arctic ocean are demonstrated the simulations suggest that the siberian landfast ice impacts the arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by redirecting river water to the canadian basin these processes strengthen the halocline in the canadian basin but erode its stability in the makarov and eurasian basins

investigation of the summer kara sea circulation employing a variational data assimilation technique 1 the summer circulations and hydrographic fields of the kara sea are reconstructed for mean positive and negative arctic oscillation regimes employing a variational data assimilation technique which provides the best fit of reconstructed fields to climatological data and satisfies dynamical and kinematic constraints of a quasi stationary primitive equation ocean circulation model the reconstructed circulations agree well with the measurements and are characterized by inflow of 0 63 0 8 0 51 sv through kara gate and 1 18 1 1 1 12 sv between novaya zemlya and franz josef land for mean climatologic conditions positive and negative ao indexes respectively the major regions of water outflow for these regimes are the st anna trough 1 17 1 21 1 34 sv and vilkitsky shokalsky straits 0 52 0 7 0 51 sv the optimized velocity pattern for the mean climatological summer reveals a strong anticyclonic circulation in the central part of the kara sea region of fresh water inflow rofi zone and is confirmed by adcp surveys and laboratory modeling this circulation is well pronounced for both high and low ao phases but in the positive ao phase it is shifted approximately 200 km west relatively to its climatological center during the negative ao phase the rofi locaion is close to its climatological position the results of the variational data assimilation approach were compared with the simulated data from the hamburg shelf ocean model hamsom and naval postgraduate school 18 km resolution nps 18 model to validate these models

the siberian coastal current a wind and buoyancy forced arctic coastal current we describe circulation and mixing in the siberian coastal current scc using fall shipboard measurements collected between 1992 and 1995 in the western chukchi sea the scc forced by winds siberian river outflows and ice melt flows eastward from the east siberian sea it is bounded offshore by a broad 60 km front separating cold dilute siberian coastal water from warmer saltier bering sea water the alongshore flow is incoherent because the current contains energetic eddies and squirts probably generated by frontal baroclinic instabilities these enhance horizontal mixing and weaken the cross shore density gradient along the scc path eventually the scc converges with the northward flow from bering strait whereupon it deflects offshore and mixes with that inflow deflection occurs where the alongshore pressure gradient vanishes that location varies on synoptic and seasonal timescales because this gradient depends on the winds buoyancy fluxes and the sea level difference between the pacific and arctic oceans deflection usually occurs on the chukchi shelf but the scc occasionally flows southward through bering strait such events are short lived 1 10 days and occur mainly in fall and winter under northerly winds scc transport is likely small 0 1 sv but its dilute waters could substantially freshen the bering strait inflow and affect the disposition of pacific waters in the arctic ocean arctic river outflows should preferentially form surface advected fronts rather than bottom advected fronts because vertical mixing energy is low on arctic shelves surface advected fronts are more susceptible to upwelling winds and for the scc the pressure gradient between the pacific and arctic oceans than bottom advected fronts the scc never developed in fall 1995 because of anomalously steady upwelling winds the western chukchi shelf could have formed upper halocline source water in the winter of 1995 1996

wind driven summer surface hydrography of the eastern siberian shelf 1 high interannual variability of summer surface salinity over the laptev and east siberian sea shelves derived from historical records of the 1950s 2000s is attributed to atmospheric vorticity variations in the cyclonic regime positive vorticity the eastward diversion of the laptev sea riverine water results in a negative salinity anomaly to the east of the lena delta and farther to the east siberian sea and a positive anomaly to the north of the lena delta anticyclonic negative vorticity results in negative salinity anomalies northward from the lena delta due to freshwater advection toward the north and a corresponding salinity increase eastward

three dimensional seismic monitoring of an enhanced oil recovery process seismic reflection data were used to monitor the progress of an in situ combustion enhanced oil recovery process three sets of three dimensional 3 d data were collected during a one year period in order to map the extent and directions of propagation in time acquisition and processing parameters were identical for each survey so that direct one to one comparison of traces could be made seismic attributes were calculated for each common depth point data set and in a unique application of seismic reflection data the preburn attributes were subtracted from the midburn and postburn attributes the resulting difference volumes of 3 d seismic data showed anomalies which were the basis for the interpretation shown in this case study profiles and horizon slices from the data sets clearly show the initiation and development of a bright spot in the reflection from the top of the reservoir and a dim spot in the reflection from a limestone below it interpretation of these anomalies is supported by informa

transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries a case study from the laptev sea abstract marine neodymium nd isotope and rare earth element ree compositions are valuable tracers for present and past ocean circulation and continental inputs yet their supply via high latitude estuaries is largely unknown here we present a comprehensive dissolved nd isotope expressed as end values and ree data set together with seawater stable oxygen isotope 18 o compositions of samples from the laptev sea recovered in two arctic summers and one winter the laptev sea is a shallow siberian shelf sea characterized by extensive river runoff sea ice production and ice transport into the arctic ocean the large variability in end 6 to 17 ree concentrations 16 to 600 pmol kg for nd and ree patterns is controlled by freshwater supply from distinct riverine sources and open ocean arctic atlantic water strikingly and contrary to expectations except for cerium no evidence for significant release of rees from particulate phases is found which is attributed to low amounts of suspended particulate matter and high dissolved organic carbon concentrations present in the contributing rivers essentially all shelf waters are depleted in light l rees while the distribution of the heavy rees shows a deficiency at the surface and a pronounced excess in the bottom layer this distribution is consistent with ree removal through coagulation of riverine nanoparticles and colloids starting at salinities near 10 and resulting in a drop of all ree concentrations by 30 with increasing salinity preferential lree removal is observable reaching 75 for nd at a salinity of 34 although the delayed onset of dissolved ree removal contrasts with most previous observations from other estuarine environments it agrees remarkably well with results from recent experiments simulating estuarine mixing of seawater with organic rich river waters in addition melting and formation of sea ice leads to further ree depletion at the surface and strong ree enrichment near the shelf bottom as a function of ice melting and brine transfer respectively the ice related processes significantly affect the distribution of dissolved rees in high latitude estuaries and likely also similarly contribute to the redistribution of other dissolved seawater constituents

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

evaluation of arctic sea ice thickness simulated by arctic ocean model intercomparison project models six aomip model simulations are compared with estimates of sea ice thickness derived from pan arctic satellite freeboard measurements 2004 2008 airborne electromagnetic measurements 2001 2009 ice draft data from moored instruments in fram strait the greenland sea and the beaufort sea 1992 2008 and from submarines 1975 2000 drill hole data from the arctic basin laptev and east siberian marginal seas 1982 1986 and coastal stations 1998 2009 despite an assessment of six models that differ in numerical methods resolution domain forcing and boundary conditions the models generally overestimate the thickness of measured ice thinner than 2 m and underestimate the thickness of ice measured thicker than about 2 m in the regions of flat immobile land fast ice shallow siberian seas with depths less than 25 30 m the models generally overestimate both the total observed sea ice thickness and rates of september and october ice growth from observations by more than four times and more than one standard deviation respectively the models do not reproduce conditions of fast ice formation and growth instead the modeled fast ice is replaced with pack ice which drifts generates ridges of increasing ice thickness in addition to thermodynamic ice growth considering all observational data sets the better correlations and smaller differences from observations are from the ecco2 and uw models

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

finite difference modelling of p wave scattering in the upper mantle summary scattering within the upper mantle is prominently documented in the so called high frequency teleseismic pn phase generated by velocity fluctuations in the upper mantle this phase is seen in many data sets from active and passive seismology whenever the source generated frequencies are high enough 5 10 hz to allow their observation at large distances 2000 km this phase appears in the recordings of the russian pne programme in other long range refraction experiments and in numerous recordings of earthquakes using a 2 d finite difference scheme we calculate complete synthetic seismograms in order to relate the scales of the fluctuation of the elastic parameters to wavefield properties we discuss the influence of critical parameters on the scattering properties of the upper mantle and on the propagation mechanism of the teleseismic pn variations in vertical and horizontal correlation lengths rms velocity fluctuations thickness of the heterogeneous layer and cross correlation of p and s wave velocities a teleseismic pn phase arises only if the velocity fluctuations are strong enough to cause multiple scattering and if the horizontal correlation length exceeds the vertical by an order of magnitude our favourite model for the russian pne profiles includes a 100 150 km thick zone of scatterers below the moho containing heterogeneities with a horizontal correlation length of 20 km a vertical correlation length of 0 5 km and an rms velocity perturbation of 2 per cent while keeping the p and s wave velocities correlated as the teleseismic pn is often observed this scale of velocity fluctuations seems to be characteristic of the uppermost mantle anisotropy is likely to contribute to the inferred velocity fluctuations

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

shallow crustal structure from short period rayleigh wave dispersion data in southwestern taiwan strong ground motions in the period range of 1 to 5 sec observed in taiwan in a dense network during the tapu earthquake ml 5 8 of 15 december 1993 were dominated by fundamental mode rayleigh waves the shallow crustal structure beneath this network was determined from the group velocity dispersion data using standard inversion techniques results show that an alluvial layer with a thickness of only about 160 m exists over the sedimentary structure in the western coastal plain a clear lateral variation in the shear wave velocity along a cross section perpendicular to the western structural grain ho 1982 was resolved for the purpose of retrieving the ground motions to confirm the proposed model forward modeling with a two dimensional finite element method was used and agreed well with the observed seismograms when slightly lower velocities than those of the inversions were used it is concluded that the velocity model estimated using group velocity data cannot definitively correspond to the real one at such short dis tances and in such a complex structure on the basis of quantitative simulations a very soft surface layer must be crucial in the interpretation of the slow wave trains with long duration and the rare prograde particle motions the results suggest that these surface waves may be generated by the conversion of body waves at the bound ary of the western coastal plain and foothills

a comprehensive view of kara sea polynya dynamics sea ice compactness and export from model and remote sensing data 1 the shelf seas of the arctic are known for their large sea ice production this paper presents a comprehensive view of the kara sea sea ice cover from high resolution numerical modeling and space borne microwave radiometry as given by the latter the average polynya area in the kara sea takes a value of 21 2 103 km2 9 1 103 km2 for winters jan apr 1996 97 to 2000 01 being as high as 32 0 103 km2 in 1999 2000 and below 12 103 km2 in 1998 99 day to day variations of the kara sea polynya area can be as high as 50 103 km2 for the seasons 1996 97 to 2000 01 the modeled cumulative winter ice volume flux out of the kara sea varied between 100 km3a 1 and 350 km3a 1 modeled high low ice export coincides with a high low average and cumulative polynya area and with a low high sea ice compactness in the kara sea from remote sensing data and with a high low sea ice drift speed across its northern boundary derived from independent model data for the winters 1996 97 to 2000 01

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

the spreading of a buoyant plume beneath a landfast ice cover abstractidealized numerical simulations using the regional ocean modeling system demonstrate the effects of an immobile landfast ice cover that is frictionally coupled to an underice buoyant plume established by river discharge the discharge rapidly increases and decreases over a 30 day period and has a maximum of 6000 m3 s 1 this study examined the response to a landfast ice cover of 26 km width and one that encompasses the entire shelf width the model setting mimics spring conditions on the alaskan beaufort sea abs shelf in comparison with the ice free case subject to the same discharge scenario underice plumes are broader and deeper and the downwave freshwater flux is substantially decreased and delayed multiple anticyclonic bulges form in the ice free case but only a single large bulge forms when ice is present these differences are because of the frictional coupling between the ice and plume which results in an ekman like underice boundary layer a subsurface velocity maximum and fricti

source process of the chi chi earthquake a joint inversion of strong motion data and global positioning system data with a multifault model the chi chi taiwan earthquake of 21 september 1999 was a large thrust earthquake that caused disastrous damage the surface fracture trace runs along the chelungpu fault which strikes n5 e along most of the faulting area but turns to the northeast while approaching its northern end it finally presents a horsetaillike faulting system and bends to an east northeast direction at the northern end both strong motion and global positioning system gps data recorded large displace ments in the northern part in this study we use a multifault model to simulate the observed large strong motion and gps data the results of the joint inversion reveal that in the southern part slip occurred mainly in the shallow portion reaching a maximum about 20 m on the ene fault where the rupture propagated to the deep part of the fault there was obviously slip vector rotation from south to north such that the slip on the branched fault plane was almost purely reverse faulting the seismic moment a total of 2 7 10 20 n m was released in less than 40 sec during the mainshock aftershocks occurred mainly in areas where little or no slip occurred slip vector rotation can be explained by the complexity of regional tectonic stress changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ene fault

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities