the drift of icebergs under wind action the steady motion of an iceberg under wind action is studied in the presence of a mixed layer analytical solutions are obtained when the iceberg depth is less than or much larger than the mixed layer depth a few numerical examples are given our results show that winds of medium or low strength have a limited effect on the motion of deep icebergs extending below the thermocline furthermore the larger the horizontal scale of the iceberg the smaller the wind drift hence for winds of less than 10 m s 1the trajectory of deep icebergs more than 1 km long is shown to be representative of geostrophic currents the effect of a possible lift force is also estimated

relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

wind drag coefficient over first year sea ice in the bering sea profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the bering sea and used to compute surface wind drag coefficients based upon 138 profiles for near constant ice conditions northeast winds of 3 15 m s 1 and near neutral stability the mean near neutral 10 m drag coefficient was 0 00309 0 00049 this is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice sixty five percent of the variance of this estimate is explained by orientation of the ice floe to the wind an additional 5 of the variance is explained by wind speed dependence provided that diabatic atmospheric stability over the bering sea ice pack is well correlated with low wind speed the significant ice advecting wind stress on the ice is determined from the neutral value of the drag coefficient a function of ice roughness length alone the ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

inversion of complex body waves ii abstract after our previous paper we developed a method to deconvolve body waves into a multiple shock sequence we first consider a general case where a rupture process consists of subevents with arbitrary source parameters and next a special case where a source process consists of subevents with two different fault mechanisms a simple criterion to check the significance of solution is given by a statistical consideration on the estimated values the method is applied to two large earthquakes the 1976 tangshan earthquake and the 1976 east turkey earthquake in both cases the earthquake sources consist of major strike slip events and minor thrust events the total seismic moments of the major events are comparable to the values obtained by surface wave analyses the 1968 borrego mountain earthquake is also analysed by the same method for comparison a single mechanism solution results in a good waveform match and no significant secondary mechanism is required for this event

ice physical properties structural characteristics and stratigraphy in hobson s choice ice island and implications for the growth history of east ward hunt ice shelf canadian high arctic

intra plate seismicity in the subducting philippine sea plate southwest japan magnitude depth correlations abstract recent studies of intra plate seismicity have focused on detailed earthquake locations and potential hypotheses for intermediate depth events three main competing hypotheses for intra plate events are 1 transformational faulting 2 shear melt instabilities and 3 dehydration reactions recent work using precise hypocenters and thermal petrological models indicates that the spatial distribution of intra plate events coincides with dehydration reactions these studies have mainly focused on the location of events and the proposed reactions with little attention given to the magnitude distribution of events presented here is a magnitude depth correlation associated with intra plate events for southwest japan earthquake hypocenters were obtained from relocating a data set consisting of japan meteorological agency jma seismicity data and japan university network earthquake catalog junec data from 1985 to 1996 were combined and relocated using a standard location routine hypoinverse that allows regional variations in velocity models and station corrections hypoinverse results show a well defined plane of seismicity associated with the subducting philippine sea plate the data were further relocated using a double difference relocation algorithm hypodd hypodd results show a magnitude depth correlation for kii peninsula and northern kyushu histogram plots indicate that events near the plate interface were generally magnitude 3 or less whereas most large events were located within the lower crust or possibly the subducting oceanic mantle this observation also appears to hold true for intra plate events beneath tohoku japan trench and hokkaido kuriles but is not clearly observed beneath the tokai region a dehydration reaction model can well explain the magnitude depth correlation

strain partitioning in the zone of transition from nankai subduction to izu bonin collision central japan implications for an extensional tear within the subducting slab abstract the izu bonin ridge collision with central japan is a type example of collision of two island arcs in a subduction context based on the analysis of active faults paleomagnetic data and recent seismicity in the northern tip of the izu bonin arc and the adjacent oceanic plate we propose a tectonic schema of the izu collision system and its transition to the nankai subduction to the west the dense gps network deployed in central japan allows us to constrain the kinematics of the different blocks identified this new kinematic model demonstrates the essential role of strain partitioning there as the northward component of the izu bonin arc motion is locked in the collision zone 30 of the convergence between the philippine sea plate and central japan is accommodated within the philippine sea slab along the zenisu east izu deformation system we show that this pattern of deformation is related to an extensional tear of the philippine sea slab propagating southward along the volcanic arc we discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the central japan convergence zone

stable isotope 18o 16o tracing of fresh brackish and sea ice in multi year land fast sea ice ellesmere island canada la salinite de la glace et les rapports 18 o 16 o ont ete mesures sur 12 carottes de glace prelevees sur la glace marine au large de la cote nord de ellesmere island canada les 3 types de glace douce saum tre et marine ont ete identifies dans les carottes en utilisant les rapports isotopiques 18 o 16 o l utilisation des mesures 18 o pour identifier la glace marine et saum tre est discutee la proportion de chaque type de glace presente est etablie et les implications pour les proprietes et la structure de l eau sous glaciaire sont presentees

arctic ice shelves and ice islands origin growth and disintegration physical characteristics structural stratigraphic variability and dynamics ice shelves are thick floating ice masses most often associated with antarctica where they are seaward extensions of the grounded antarctic ice sheet and sources of many icebergs however there are also ice shelves in the arctic primarily located along the north coast of ellesmere island in the canadian high arctic the only ice shelves in north america and the most extensive in the north polar region the ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands the tabular icebergs of the arctic ocean the present state of knowledge and understanding of these ice features is summarized in this paper it includes historical background to the discovery and early study of ice shelves and ice islands including the use of ice islands as floating laboratories for polar geophysical research growth mechanisms and age the former extent and the twentieth century disintegration of the ellesmere ice shelves and the processes and mechanisms of ice island calving are summarized surface features thickness thermal regime and the size shape and numbers of ice islands are discussed the structural stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described large scale and small scale dynamics of ice islands are described and the results of modeling their drift and recurrence intervals are presented the conclusion identifies some unanswered questions and future research opportunities and needs

ability of a global three dimensional model to locate regional events 1 we assess the ability of a global three dimensional 3d seismic model of the crust and upper mantle cub2 0 to locate seismic events using regional travel time data alone epicentral distances 20 assessments are based on a ground truth gt database comprising nearly 1000 uncommonly well located events which occur in 23 event clusters across eurasia and north africa groomed p and pn arrival time data observed at regional distances from individual events and 1000 empirical phase path anomalies produced from event clusters evidence is presented that supports the conversion of the shear velocities vs in cub2 0 to compressional velocities vp in the upper mantle using the thermoelastic properties of an assumed mantle composition rather than traditional empirical scaling relationships two principal results are presented first this 3d vp model fits the empirical p and pn phase path anomalies very well in both pattern and absolute level second location assessments demonstrate that intrinsic regional location accuracy is 5 km using the 3d vp model and 10 km using the 1d model ak135 these findings highlight the importance of gt databases in assessing regional travel time models and establish that a global 3d vs model together with vp inferred from it provides a solid basis on which to build improvements in regional location capabilities

an analytical model of iceberg drift abstractthe fate of icebergs in the polar oceans plays an important role in earth s climate system yet a detailed understanding of iceberg dynamics has remained elusive here the central physical processes that determine iceberg motion are investigated this is done through the development and analysis of an idealized model of iceberg drift the model is forced with high resolution surface velocity and temperature data from an observational state estimate it retains much of the most salient physics while remaining sufficiently simple to allow insight into the details of how icebergs drift an analytical solution of the model is derived which highlights how iceberg drift patterns depend on iceberg size ocean current velocity and wind velocity a long standing rule of thumb for arctic icebergs estimates their drift velocity to be 2 of the wind velocity relative to the ocean current here this relationship is derived from first principles and it is shown that the relationship holds in the limit of

tracking large tabular icebergs using the seawinds ku band microwave scatterometer abstract knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes originally designed to measure wind speed and direction over the ocean seawinds is a microwave scatterometer that operates at 13 4 ghz ku band on the quikscat satellite radar measurements from seawinds are collected and processed on a daily basis using resolution enhancement techniques to produce daily radar images because icebergs scatter microwave energy more than sea ice and sea water icebergs are detected as high backscatter targets surrounded by lower backscatter regions in daily seawinds images as a result iceberg positions are determined in real time and a time series of iceberg positions is maintained in an antarctic iceberg database by brigham young university s microwave earth remote sensing mers laboratory since seawinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage this paper demonstrates that seawinds is an excellent platform to detect and track large tabular icebergs these icebergs are generally larger than 5 km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice the number of icebergs tracked in the mers antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the national ice center the movement patterns of all icebergs detected by seawinds are also analyzed and 90 of icebergs are found to travel a counter clockwise path around antarctica and accumulate in the weddell and scotia seas iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs c 19a and a 22a using the mers database and through real time operational support of the 2005 2008 and 2009 nsf antarctic cruises iceberg positions are validated by using collocated high resolution satellite imagery and by navigating the nsf ships to physically intercept several large tabular icebergs in the weddell and scotia seas

the freshwater budget and under ice spreading of mackenzie river water in the canadian beaufort sea based on salinity and 18o 16o measurements in water and ice observations of salinity and oxygen isotope composition 18o were made for the beaufort shelf mackenzie estuary waters in september 1990 just prior to ice formation and for both the water column and ice in april may 1991 at the end of winter these measurements are used to determine the apportioning of fresh water in the estuary between its two main sources runoff and sea ice melt changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived two domains are considered in order to construct a freshwater budget for the mackenzie shelf the nearshore within which landfast ice grows in winter and the outer shelf most of the winter inflow from the mackenzie river appears to remain impounded as liquid under the ice within the landfast zone at the end of winter and about 15 of it is incorporated into the landfast ice oxygen isotopes 18o in ice cores collected from across the shelf record the progress beneath the ice of new mackenzie inflow as it invades the nearshore throughout winter rates of spreading are about 0 2 cm s 1 away from the coast and 1 3 cm s 1 along the coast as this inflow spreads across the shelf it progressively shuts off convection driven by brine production at locations within the landfast ice salinity and 18o in the offshore water column suggest that about 3 m of sea ice was formed in the outer shelf domain since both brine and newly formed sea ice can be advected off the shelf a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components

stress field observation and modeling from the nantroseize scientific drillings in the nankai trough system sw japan abstract many studies have investigated the stress state in terms of drilling projects in the nankai trough region the potential area for next devastating earthquakes to understand the stress state and the geologic properties in nankai several drilling projects have been conducted over time among these projects the nankai trough seismogenic zone experiment nantroseize included studies regarding stress orientations and magnitude estimations by logging data from the nankai trough due to limitations in technology of drilling and the data processing the actual stress orientation and the magnitude of the nankai trough at depth remains controversial in this study we discussed the stress state in each borehole and evaluated the stress state using various models our models evaluated stress states contributed by a slip deficit model in the nankai trough system and the coseismic dislocations of the two september 5th 2004 earthquakes compared to the stress estimation from logging data the simulated stress orientation could more or less explain the logging data at the nantroseize drilling boreholes based on these models the stress tensor in nankai can be extended from the boreholes to more dimensional area even the locations where no drilling has been reached

a simulation of small to giant antarctic iceberg evolution differential impact on climatology estimates we present a simulation of antarctic iceberg drift and melting that includes small medium sized and giant tabular icebergs with a realistic size distribution for the first time an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around antarctica the study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies we simulate drift and lateral melt using iceberg draft averaged ocean currents temperature and salinity a new basal melting scheme originally applied in ice shelf melting studies uses in situ temperature salinity and relative velocities at an iceberg s bottom climatology estimates of antarctic iceberg melting based on simulations of small 2 2 km small to medium sized 10 km and small to giant icebergs including icebergs 10 km exhibit differential characteristics successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58 s while less meltwater is released into the coastal areas this suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias they underestimate the northward mass transport and are thus closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model future ocean simulations will benefit from the improved meridional distribution of iceberg melt especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the antarctic ice sheet

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

characterization of the antarctic polar frontal zone to the north of south georgia in summer 1994 the polar front pf forms the southern boundary to the polar frontal zone pfz along the northern edge of the antarctic circumpolar current acc in a number of areas the position of the pf and thus the pfz is known to be influenced by topographic steering while local bathymetry has also been implicated in the movement and retention of various associated mesoscale features in this paper we examine the structure and position of the pf as it passes over the rugged bathymetry to the north of the scotia sea results are presented from an oceanographic transect crossing the pf to the northwest of south georgia and from a pair of shorter transects south of the pf but north and east of the first associated with the pf was a narrow high speed flow embedded in broader slower moving regions this high speed flow was found to have a geostrophic component of velocity that was slower than estimates for other regions of the pf comparisons with output from recent oceanographic models were found to be consistent with the physical observations a second examination of the region after a period of 30 days suggested that the surface expression of the pf had shifted southward by approximately 35 km but that the pf was essentially in the same position over the southern edge of the maurice ewing bank an advanced very high resolution radiometer image taken during the cruise provided additional information about the position of the surface expression of the pf and the extent of mesoscale features that were present to the north of the study area immediately to the north of south georgia water in the eastward flow of the acc meets colder more saline water flowing west along the north coast of the island the area where these two flows meet was found to be variable over the 30 day timescale of the cruise this area is known to be of major biological significance and variability in the local oceanography is possibly of crucial importance to many predator species breeding at the northern end of south georgia

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

crustal structure across the coseismic rupture zone of the 1944 tonankai earthquake the central nankai trough seismogenic zone 1 differences in the coseismic rupture process between the 1944 tonankai and the 1946 nankaido earthquakes have been studied by many fault models to understand what factors control coseismic rupture zones it is important to investigate differences in deep crustal structures of the rupture zones between the 1944 and 1946 earthquakes the previously published crustal structure of the rupture zone of the 1946 earthquake shows that the coseismic rupture extends to the neogene quaternary accretionary prism however little is known about the structure of the rupture zone of the 1944 earthquake to obtain a complete image of the seismogenic zone of the 1944 earthquake a wide angle seismic survey was performed across the presumed coseismic rupture zone of the 1944 earthquake from ocean to land our model for the crustal structure is based on ocean bottom seismographic data the crustal structure appears characteristic for subducting oceanic crust and a neogene quaternary accretionary prism bounded by an island arc crust the neogene quaternary accretionary prism reaches a maximum thickness of 7 km at 50 km distance landward from the deformation front the subducting oceanic crust can be traced down to 35 km the subduction angle becomes steeper landward reaching up to 11 beneath the island arc crust the depth of the top of subducting oceanic crust at the downdip limit of the rupture zone is 23 km while the updip limit is located beneath the island arc upper crust similar structures of the updip and downdip limits are also published for several other subduction zones

hypocenters in the nankai trough determined by using data from both ocean bottom and land seismic networks and a 3d velocity structure model implications for seismotectonic activity abstract we investigated the hypocenter distribution along the nankai trough off the kii peninsula japan by using data from both ocean bottom and land based seismic networks because seismic velocity structures differ greatly below land and ocean we used a 3d velocity model based on a structural model of the philippine sea plate phs which provides much more accurate estimations of source locations than 1d velocity models derived from either onshore or ocean bottom seismic data alone especially for sources between the coast and the trough axis we identified intensive seismic activity below the axis of the nankai trough which we interpreted to be aftershocks of the 2004 off the kii peninsula earthquakes m jma 7 1 7 4 and 6 5 but found much less seismic activity along the subducting phs the earthquake sources below the trough axis lie on dipping planes within the phs from which we inferred that a fracture zone is developing within the phs our estimated focal mechanisms for these earthquakes showed that their p axes were oriented north south to northeast southwest similar to those of the 2004 events which were rotated clockwise by 45 90 from the northwest southeast direction of convergence between the phs and the eurasian plates we consider that the fracture zone represents a boundary between the phs and the izu microplate which are converging in a north south direction and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

observed stress state for the iodp site c0002 and implication to the stress field of the nankai trough subduction zone abstract conducting a stress state analysis is one of major challenges for evaluating earth crust and formation conditions stress magnitude is especially essential to comprehend stress heterogeneity significant structural anisotropy and or pre existing fracture systems stress state is influenced by rock strength structural properties and near field principal stresses which impact borehole integrity during drilling factors that we can measure through logging while drilling lwd and measure while drilling mwd to better understand borehole conditions include mud weight overburden weight and velocity the lwd resistivity images in holes c0002a and c0002f of the nankai trough seismogenic zone experiment nantroseize indicate that most of the drillings in stable environments however the bottom hole assembly became stuck around 3 km depth in hole c0002p and did not reach the mega thrust fault we evaluated the stress state for the site c0002 by the geomechanical model with the breakout width and rock strength estimation we constrain the stress profiles in the drilled depth our analysis inferred that the instability of hole c0002p had been caused by an overpressure drilling fluid state and low horizontal principal stress furthermore we developed an optimally oriented plane oop model to exam the stress state in the site c0002 from nankai accretionary prism to the nankai trough subduction zone the normal faulting stress regime modeled from oop is consistent with the geomechanical model in site c0002 the horizontal principal stresses magnitude appears to less than the overburden weight above this subduction zone

air ice drag coefficients for first year sea ice derived from aircraft measurements turbulent flux measurements were made at four levels 42 90 195 and 340 m by the noaa p 3 aircraft over first year sea ice in the northern bering sea during february 1982 three profiles of momentum flux and mean wind were used to calculate an air ice drag coefficient cd of 3 0 6 10 3 referenced to a 10 m anemometer height the boundary layer was slightly unstable zi l 1 2 where zi was the inversion height of 660 m and l the monin obukhov length the mean wind speed at the 42 m height was 17 m s and the air temperature was 20 c from turbulent heat flux measurements the value of the bulk heat transfer coefficient ch was 0 73 1 6 10 3 giving a ch cd of 0 24 the bowen ratio was greater than 2 8 comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement which increases confidence in the calculations the geostrophic drag coefficient u g where u is the friction velocity and g is the geostrophic wind was 0 047 the turning angle of the surface wind measured by an anemometer at a height of 3 m on the ice was 32 and the ratio of surface wind speed to the geostrophic wind speed was 0 76

the 2004 earthquakes offshore of the kii peninsula japan hypocentral relocation source process and tectonic implication on 5 september 2004 two major earthquakes of mw 7 2 and mw 7 3 referred to as the foreshock and the mainshock hereafter occurred close to the nankai trough in southwest japan this earthquake sequence is located within the subducting philippine sea plate phs with an aftershock distribution that overlapped a portion of the source region of the 1944 tonankai earthquake mw 7 9 we relocate 53 events with magnitudes greater than 4 2 by combining a single event location method for depth and a multiple event location method for epicenter and origin time source mechanisms and rupture histories of the foreshock and the mainshock are investigated by using a waveform modeling method which allows for mechanism changes during the rupture process the mw 7 2 foreshock and the mw 7 3 mainshock are relocated in the uppermost mantle of the phs on primary high angle reverse faults focal mechanisms are consistent with the horizontal and vertical projects of the distribution of aftershocks we speculate that this earthquake sequence was due to the collision reaction between the phs and the zenisu ridge

a reassessment of outer rise seismicity and its implications for the mechanics of oceanic lithosphere we use body waveform modelling to constrain the source parameters of earthquakes occurring globally in oceanic lithosphere beneath the subduction zone outer rise and outer trench slope these data are then used to map the stress state in the lithosphere of the downgoing plate as it bends into the subduction zone our results provide new constraints on the faulting of oceanic lithosphere at the outer rise which is important for understanding the transmission of plate driving forces through the subduction system in all cases shallow normal faulting earthquakes are observed at the top of the plate and are separated in depth from any deeper thrust faulting earthquakes no temporal variation associated with large thrust faulting earthquakes on the subduction interface is seen in the depth extent of each type of faulting at the outer rise the transition depth from trench normal extension to compression is found to vary in agreement with models in which deformation is driven by the combination of in plane stresses and bending stresses resulting principally from slab pull combining the seismologically derived constraints on the thickness of the elastic core of the plate with estimates of the plate curvature we place upper bounds on the strength of the lithosphere at the outer rise which is required to be 300 mpa for a constant yield stress model or governed by an effective coefficient of friction of 0 3

application of an improved algorithm to high precision relocation of isc test events abstract new location features for possible implementation by the international seismological centre in its standard location procedures are tested using a set of 156 well located and geographically well distributed earthquakes and explosions the tests are performed using the engdahl et al engdahl e r van der hilst r d buland r p 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seism soc am 88 3295 3314 ehb location algorithm with the 1 d reference earth model ak135 kennett b l n engdahl e r buland r 1995 constraints on seismic velocities in the earth from travel times geophys j int 122 108 124 weighting by phase variance as a function of distance improves location accuracy by 7 use of later phase arrival times does not result in a significant improvement in location or depth for events with observing stations well distributed in azimuth however with application of an improved phase identification technique depth phases provide significantly better estimates of focal depth

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

drag measurements for first year sea ice over a shallow sea for a free drift case a method is developed for simultaneously determining air ca and water cw drag coefficients by solving the vertically integrated stress balance equation for sea ice the method allows the algebraic determination of ca and cw from measurements of relative wind and relative current at single reference levels from estimates of the densities of all three fluids and ice thickness and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements the method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag one shortcoming of the technique is that if the relative wind and current are colinear then only the ratio of ca and cw can be determined another is that the accelerations caused by other forces need to be independently determined an experiment was conducted on a single floe in the eastern bering sea over the continental shelf during march 1981 the site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10 20 m diameter floes both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site ca at 3 m was 4 55 10 3 by the profile method compared to 3 63 4 39 10 3 for slab depending on assumptions cw at 1 1 m by profile was 24 2 10 3 compared to 18 3 22 0 10 3 for slab the two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice the instantaneous stress balance on the floe included contributions from material acceleration coriolis force the two surface stresses and sea surface tilt relative to mean current and tide

tsunami scenarios based on interseismic models along the nankai trough japan from seafloor and onshore geodesy the recent availability of global positioning system acoustic seafloor geodetic observations enables us to resolve the spatial distribution of the slip deficit rate near the nankai trough southwestern japan considering a tectonic block model and the transient deformation due to the major earthquakes in this area the slip deficit rate between the two relevant blocks can be estimated in this study we remove the time dependent postseismic deformation of the 2004 southeastern off the kii peninsula earthquakes mjma 7 1 7 4 which had led to the underestimation of the slip deficit rate in earlier studies we model the postearthquake viscoelastic relaxation using the 3d finite element model with bi viscous burgers rheology as well as the afterslip on the finite faults the corrected global positioning system acoustic and land based global navigation satellite systems data are aligned to the existing tectonic model and used to estimate the slip deficit rate on the plate boundary we then calculate the coseismic displacements and tsunami wave propagation with the simple assumption that a hundred years of constant slip deficit accumulation was released instantaneously to evaluate the influence of uncertainties in the plate interface geometry on a tsunami model for the nankai trough we investigated two different geometries and performed checkerboard inversion simulations although the two models indicate roughly similar results the peak height of the tsunami wave and its arrival time at several points are significantly different in terms of the expected hazard

seismogenic zone temperatures and heat flow anomalies in the to nankai margin segment based on temperature data from iodp expedition 333 and thermal model the location of the seismogenic zone across the to nankai margin segment has been widely investigated using geodetic tsunami seismologic and heat flow data as well as thermal models seafloor heat flow measurements show large scatter raising questions about the thermal state of the incoming and overriding plates in this study new temperature and conductivity measurements recorded in the philippine sea plate psp and in the accretionary prism during iodp expedition 333 are integrated with recent data on the margin structure and seismicity to improve constraints on the thermal structure of the incoming plate and the subduction zone as well as the thermal conditions within the seismogenic zone iodp expedition 333 measurements provide heat flow values that are lower than the average of nearby seafloor measurements thermal modeling for the psp suggests that hydrothermal warming is insignificant in the trench thus an observed widespread positive thermal anomaly in the shikoku basin that peaks at the kashinozaki knoll more likely results from vigorous thermal convection in the upper mantle in back arc context the modeled thermal structure of the margin from the trench to the mantle shows a significantly colder interplate contact than in previous studies the seismogenic zone is likely to be 30 170 km from the deformation front corresponding to the 100 340 c temperature range the 1944 co seismic slip zone extends farther southward where temperatures are about 60 c slow slip earthquakes are located in the downdip transition zone between 340 and 440 c across the intersection of the moho and the megathrust fault this improved thermal structure from the trench to the mantle results mainly from a better estimate of oceanic plate age slab dip and sedimentation rate variations in the trench this last parameter cools the interplate contact until a depth of 35 km shifting the thermally defined seismogenic zone landward by 20 km and significantly diminishing its influence near the corner flow area

propagation mechanism of long period ground motions for offshore earthquakes along the nankai trough effects of the accretionary wedge a thick accretionary wedge with low seismic velocity overlying a subducting plate is an important factor affecting the amplitudes and durations of long period ground motions for great offshore earthquakes we performed a series of 3d long period ground motion simulations to obtain a better understanding of the effects of the accretionary wedge along the nankai trough japan the simulation results demonstrate that the accretionary wedge has the effect of decreasing the peak amplitude and velocity response but amplifying and elongating later phases of long period ground motions in the land area these effects depend significantly on the focal depth and are pronounced for shallow seismic sources the amplified and elongated later phases originate mainly from prominent basin induced surface waves excited near the trough axis we also identified hard sediments with intermediate s wave velocity in the accretionary wedge as a key layer that enhances the propagation of long period ground motions from offshore to onshore in the case of the nankai trough the hard sediments allow long period ground motions developed inside the accretionary wedge to be efficiently transmitted outward in the longer period than 10 s comparisons between the observed and simulated records suggest that for more accurate predictions of long period ground motions velocity structure models of not only the accretionary wedge but also the surrounding upper crust should be validated and revised using seafloor observations

massive ancient sea ice strata and preserved physical structural characteristics in the ward hunt ice shelf two sea ice layers one measured as 9 m thick the other at least 12 m thick and estimated to be 24 5 m thick have been located by ice core drilling in the west ward hunt ice shelf to examine the preservation of physical structu ral characteristics over long time intervals the crystal structure and brine volumes in the sea ice which possibly dates back to about 3000 bp have been studied the structural characteristics are immediately recognizable as those of undeformed congelation sea ice accreted by stefan growth brine volumes in the ancient sea ice are higher than those in modern multi year ice at the same temperature the preservation of brine over a time span of hundreds to thousands of years is attributed to an absence of surface meltwater to effect brine flushing and the very slow even negligible action of gravity drainage brine pocket migration and brine expulsion the congelation structures indicate that sea ice can grow by the stefan accretion mechanism to thicknesses exceeding the equilibrium thickness 2 5 5 m of most undeformed multi year ice the observed physical structu ral characteristics of the ward hunt sea ice strongly suggest that many of the properties attained by sea ice are permanent and not affected by slow acting physical processes

antarctic iceberg distribution and dissolution from ship based observations the australian antarctic program s iceberg dataset from ship based observations including information from the austral summer seasons 1984 85 to 1999 2000 is examined and used to extend earlier studies using snapshots of the iceberg population to provide an idea of the iceberg life cycle the distribution of icebergs between 60 and 1508 e is discussed in terms of calving regions and ocean currents temporal changes are also examined the discussion leads us to the point where we can define an area bounded to the north by the maximum sea ice limit and to the south by the antarctic divergence in which icebergs are confined as they drift eastward this allows estimation of total dissolution in terms of iceberg numbers and volume within 108 longitudinal sectors and with knowledge of drift speeds iceberg movement rates and freshwater input across the sector iceberg dissolution rates are found to be 0 03 0 05 m d 1 and the total mass contribution of fresh water to the ocean as the icebergs traverse our 308 of longitude study sector is 32 gt this amounts to a contribution equivalent to precipitation of 15 5 cm a 1 accounting for 2 of the total iceberg discharge from the antarctic ice sheet

evaluation of the relative contribution of meteorological and oceanic forces to the drift of ice islands offshore newfoundland on 29 april 2015 four beacons were deployed onto an ice island in the strait of belle isle to record positional data the ice island later broke up into many fragments four of which were tracked by the beacons the relative influences of wind drag current drag coriolis force sea surface height gradient and sea ice force on the drift of the tracked ice island fragments were analyzed using atmospheric and oceanic model outputs the sea ice force was calculated as the residual of the fragments net forces and the sum of all other forces this was compared against the force obtained through ice concentration dependent relationships when sea ice was present the sea ice forces calculated from the residual approach and concentration dependent relationships were significant only when sea ice was present at medium high concentrations in the vicinity of the ice island fragments the forces from ocean currents and sea surface tilt contributed the most to the drift of the ice island fragments wind however played a minimal role in the total force governing the drift of the four ice island fragments and coriolis force was significant when the fragments were drifting at higher speeds