the formation of longitudinal fronts in a coastal plain estuary longitudinal estuarine fronts aligned parallel to the axis of the estuary are characteristic of the york river their time scale for genesis and decay is of the order of hours they are usually located at the inner edge of the shoals or over the main channel field measurements have shown marked intratidal differences in density and current speeds across this estuary these can be correlated with changes in depth and the strength of the advective processes differential advection between the channel and shoal regions when acting upon a constant longitudinal density gradient is shown to be of sufficient magnitude to generate strong lateral density gradients and thus fronts at particular times within the tidal cycle

structure seismicity and thermal regime of the queen charlotte transform margin 1 this study examines structural seismicity thermal and current deformation constraints on the tectonic regime of the queen charlotte margin located off the northwest coast of canada the margin is primarily a transcurrent boundary between the oceanic pacific plate and the continental north america plate but plate motion models indicate 20 of current oblique convergence that initiated 5 myr the estimated 120 km of convergence has been variously explained as accommodated by underthrusting or by crustal shortening the near vertical queen charlotte transcurrent fault and lack of wadati benioff earthquakes argue against underthrusting however structural models for the margin from receiver function and refraction studies show little evidence of crustal thickening the pattern of landward decreasing heat flow gravity anomalies an accretionary prism landward of the trench or trough down bowing ocean crust and sediments horizons and a variety of other geophysical evidence support underthrusting receiver function analysis on teleseismic data indicates a 10 km thick low velocity layer at 35 km depth dipping 20 to the east which is interpreted as underthrusting oceanic crust the heat flow across the fault zone rapidly decreases landward in agreement with predictions from a finite element thermal model of underthrusting

paleomagnetism and 40ar 39ar chronology of lavas from meseta del lago buenos aires patagonia 1 as part of a larger project investigating paleosecular variation in south america 36 paleomagnetic and geochronology sites were sampled on meseta del lago buenos aires 47 s 289 e 200 km east of the active plate boundary in southern patagonia basaltic lavas sampled range from late miocene to late pleistocene yet most of the individual lavas are younger than 3 3 ma thirty eight isochron ages determined via 40ar 39ar incremental heating experiments frame a detailed stratigraphy the isochron ages range from 66 9 4 1 ka for scoria cones and a youthful lava flow in the rio pinturas valley to 10 12 1 35 ma for thick plateau forming lavas exposed along the se edge of the meseta the last 3 3 myr is characterized by seven episodes of volcanism at ca 3 2 3 0 ma 2 4 ma 1 7 ma 1 35 ma 1 0 ma 750 ka 430 330 ka and 110 ka the bulk of lavas forming the surface of the meseta erupted in the last 1 7 my all sites have stable magnetization and after step demagnetization using either thermal or alternating field techniques yield characteristic directions held by magnetite and or titanomagnetite ten sites have distinct transitional directions defined by pole latitudes 55 and associated ages indicate possible connections to known reversals within the matuyama chron including the onset of the jaramillo subchron 1 016 0 01 ma the cobb mountain subchron 1 25 0 03 ma the ontong java 1 event 1 37 0 03 ma and the termination of the olduvai subchron 1 72 0 02 ma remaining sites are divided into normal 14 sites and reversed polarity 12 sites at 95 confidence mean normal and reversed directions overlap the mean direction for 26 sites is i 63 0 d 3 4 95 5 4 which is indistinguishable from the expected geocentric axial dipole paleosecular variation measured by the dispersion of virtual geomagnetic poles about the rotation axis is higher than expected at 20 0 model g using data for the past 5 myr predicts a dispersion of 17 this discrepancy may be due to true dispersion of the field in southern south america or it may be an artifact of inadequate sampling

density driven exchange flow in terms of the kelvin and ekman numbers 1 the pattern of density induced flow influenced by basin s width friction and earth s rotation is investigated as a function of the ekman ek and kelvin ke numbers a semianalytical solution is used to determine the conditions under which the density induced exchange flow is vertically sheared or horizontally sheared solutions are obtained over diverse laterally varying bathymetries it is found that the exchange flow is horizontally sheared under high frictional conditions ek 1 independently of the width of the basin ke the horizontally sheared pattern describes inflow in the channel and outflow over shoals with the inflow occupying the entire water column the exchange flow pattern is also horizontally sheared under weak friction ek 0 and in wide ke 2 basins in that case however the outflow is concentrated on the left looking into the basin in the northern hemisphere portion of the cross section and inflow appears on the right also under weak friction the exchange pattern becomes more vertically sheared with outflow at surface and inflow underneath as the width of the basin becomes small ke 1 bathymetry is not very influential in the weak friction exchange patterns finally under moderate friction 0 01 ek 0 1 the exchange pattern is both horizontally and vertically sheared for all widths the horizontally sheared pattern is best defined in wide basins high ke whereas the vertically sheared pattern practically dominates in narrow basins low ke these findings allow classification of various estuaries in the ek ke parameter space

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

the preservation potential of coastal coseismic and tsunami evidence observed following the 2012 mw 7 8 haida gwaii thrust earthquake abstract we describe near field coseismic and tsunami evidence collected following the 28 october 2012 m w 7 8 thrust earthquake that occurred offshore western haida gwaii british columbia and discuss factors that influence its extent and preservation potential observations indicate minor geomorphic and sedimentological impacts on the rugged and unpopulated west coast of the islands despite widespread coastal coseismic subsidence 0 5 m triggered landslides and tsunami waves exceeding 3 m in runup maximum 13 m along 230 km of coastline evidence left by the tsunami was minimal likely because it occurred during a low tide that restricted its onshore reach its flow depth and its capacity to entrain and transport significant amounts of clastic sediment sources of which are minimal or absent on the dominantly steep rocky coastline it is unlikely that subaerial evidence of coseismic subsidence and tsunami inundation will be recognizably recorded in the coastal stratigraphy of western haida gwaii due to the relatively small magnitude of subsidence a lack of suitable coastal environments such as tidal marshes to record paleoelevation differences sedimentation rates that are too low to bury a paleoseismic or paleotsunami record and long term relative sea level fall leading to erosion and bioturbation a higher preservation potential is likely for tsunami deposits in coastal lakes ponds and bogs as well as coseismic slope failure deposits offshore in lakes and in sheltered fjords our findings imply that large tsunamigenic earthquakes are likely undersampled in the paleoseismic record of haida gwaii and of other plate margins with similar characteristics

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

transverse structure of wind driven flow at the entrance to an estuary nansemond river 1 observations of current velocity profiles were combined with an analytical solution to study the transverse partition of the wind driven flow in an estuary the nansemond river which is a tributary of the james river in the chesapeake bay observations spanned two periods of nearly 3 months in autumn winter of 2003 2004 and spring summer 2004 the wind driven circulation consisted of downwind flow over the shoal and upwind flow in the channel at the entrance to the estuary this pattern developed mainly with landward winds and provided observational evidence that sustains analytical and numerical model results the transverse structure of the flow showed synoptic temporal variability 3 7 days which corresponded to the variability of winds and sea level synoptic variability seemed to be more influential in autumn winter than in springsummer however variability of 1 2 days was persistent in both periods of observation also the transverse structure of the wind driven flows was linked to a counterclockwise recirculation pattern previously observed with survey data part of the flow going into the tributary over the shoal might recirculate and form or enhance the outflow in the channel as suggested by the temporal scale of the wind the recirculation might weaken or even reverse direction every 3 7 days at the entrance to the estuary further detailed studies are needed to better define the extent of this recirculation

effects of bathymetry friction and rotation on estuary ocean exchange an analytical model that includes pressure gradient friction and the earth s rotation in both components of the flow is used to study the transverse structure of estuarine exchange flows and the nature of transverse circulation in estuaries of arbitrary bathymetry analytical results are obtained for generic bathymetry and also over real depth distributions and are compared with observations this study extends previous efforts on the topic of transverse structure of density induced exchange flows in three main aspects 1 the analytical model explores any arbitrary bathymetry 2 the results reflect transverse asymmetries relative to a midchannel centerline associated with the effects of the earth s rotation and 3 the transverse circulation produced by the analytical model is examined in detail analytical results over generic bathymetry show in addition to the already reported dependence of exchange flow structure on the ekman number two new features first the transverse structure of along estuary flows shows the earth s rotation effects even in relatively narrow systems thus producing transverse asymmetries in these flows the asymmetries disappear under strongly frictional high ekman number conditions thus illustrating the previously documented pattern of inflow in channels and outflows over shoals for typical estuaries second transverse flows resemble a sideways gravitational circulation when frictional effects are apparent ekman number greater than 0 1 responding to a transverse balance between pressure gradient and friction these transverse flows reverse direction under very weak friction and reflect coriolis deflection of along estuary flows that is geostrophic dynamics all examples of observed flows are satisfactorily explained by the dynamics included in the analytical model

geographical distribution of transitional vgps evidence for non zonal equatorial symmetry during the matuyama brunhes geomagnetic reversal abstract paleomagnetic records of the matuyama brunhes polarity reversal obtained recently from the northern equatorial and southern latitudes of the atlantic sector display a distinct symmetry with respect to the equator the virtual geomagnetic pole vgp paths from the mid latitude sites in the northern and southern hemispheres dsdp site 609 and core v16 58 are nearly coincident tracking northward through the americas the vgp path from the equatorial site odp site 664 tracks northward through eastern asia nearly antipodal to the other two paths modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records these results are consistent with the bulk of the data available from other records of this polarity transition suggesting that the transitional vgps during this reversal tend to fall along two distinct longitudinal bands the grouping of transitional vgps suggests that there is a strong geographical control over the reversal process an apparent correlation between the longitudinal bands of transitional vgps and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core mantle boundary 1 suggests that the processes which cause these flux concentrations may have influenced the geometry of the matuyama brunhes transitional field

spatiotemporal distribution of events during the first week of the 2012 haida gwaii aftershock sequence abstract we systematically relocated the 2012 haida gwaii aftershock sequence by re examining continuous seismic waveforms of the canadian national seismographic network cnsn because of the sparse station density in the source area and the offshore location of the majority of events precise determination of hypocenters is extremely challenging constraints on the back azimuth and incident angle of ray paths were derived from the cross correlation of three component waveforms and incorporated into the locating process to improve the results we located 1228 aftershocks for the first week after the mainshock effectively double the size of the cnsn routine earthquake catalog the distribution of aftershocks tends to form two linear trends roughly parallel to the strike of the plate margin in the northwest southeast direction the trend located updip from the mainshock within the subducting pacific plate appears to have three clusters spanning a lateral distance of 80 km the other trend coincides with the surface trace of the queen charlotte fault qcf spanning the northern two thirds of the main rupture zone the overall area of aftershock distribution is 120 km 40 km aftershocks overlap the southern part of the estimated rupture zone of the 1949 earthquake with no activity in the seismic gap farther to the south therefore it is likely that the 2012 earthquake only partially released the accumulated stress on the strike slip transform fault system in this scenario the possibility of a major strike slip earthquake along the southernmost part of the qcf should not be ignored online material table of source parameters of relocated mainshock and aftershocks

wind modifications to density driven flows in semienclosed rotating basins abstract an analytical two dimensional model is used to describe wind induced modifications to density driven flows in a semienclosed rotating basin wind stress variations produce enhancement inversion or damping of density driven flows by altering the barotropic and baroclinic pressure gradients and by momentum transfer from wind drag the vertical structure of wind induced flows depends on h the nondimensional surface trapping layer where is the inverse of the ekman layer depth d and h is the maximum water depth for h 5 wind driven flow structures are similar to the ekman spiral for h 2 wind driven flows are unidirectional with depth the relative importance of density to wind forcing is evaluated with the wedderburn number w 1 h2d which depends on water density mean depth h a proxy of the baroclinic pressure gradient d and wind stress because d depends on and therefore on the eddy viscosity of water az wind speed and az both modify w moreover wind direction alters w by

modeling influence of stratification on lateral circulation in a stratified estuary abstract the dynamics of lateral circulation in the passaic river estuary is examined in this modeling study the pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining during highly stratified ebb tides the lateral circulation exhibits a vertical two cell structure strong stratification suppresses vertical mixing in the deep channel whereas the shoal above the halocline remains relatively well mixed as a result in the upper layer the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg this density gradient drives a circulation with surface currents directed toward the shoal and the currents at the base of the pycnocline are directed toward the thalweg in the lower layer the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide a lateral baroclinic pressure gradient is a dominant dri

magnetostratigraphy of the apalos formation early pleistocene evidence for pulsed uplift of cyprus 1 landscape formation on cyprus is controlled by processes directly linked to the uplift and unroofing of the troodos ophiolite complex since mainly early miocene times understanding the island s geology and dating individual tectonic events will help in differentiating between tectonically controlled uplift and eustatic sea level or climatic changes in order to improve the timing of these events a magnetostratigraphic study was carried out on two terraces in the mesaoria basin of central cyprus at vlokkaria southwest of nicosia an artificial cliff exposes the sedimentary apalos formation of early pleistocene age a nearby section situated on a terrace probably postdating the vlokkaria section was sampled at kokkinos remanence carrying minerals are end member magnetite and maghemite formed by exsolution and oxidation from ophiolitic titanomagnetite hematite as a late alteration product is also present alternating field demagnetized paleomagnetic samples yield predominantly reversed polarities interpreted to have been acquired as early detrital remanent magnetization during the matuyama chron two zones of normal polarity within the apalos formation are interpreted to correlate to the olduvai and jaramillo subchrons pre apalos marine sediments at the bottom of the vlokkaria section show transitional polarity behavior and therefore might correlate with the onset of the reunion event results from the kokkinos section are exclusively of normal polarity which has been acquired during the brunhes chron sedimentation rates derived from these magnetostratigraphic results are in the order of 3 6 cm kyr with a marked increase to 50 cm kyr just below the matuyama jaramillo polarity transition which is interpreted to reflect increased uplift of the source area and supports the hypothesis of pulsed uplift of the troodos ophiolite complex

dipolar reversal states of the geomagnetic field and core mantle dynamics palaeomagnetic records from lavas suggest that at least two specific inclined dipolar field configurations have dominated the reversal process for the past ten million years these long lived states provide a way to explain directional rebounds aborted reversals and the recording in sediments of what appear to be preferred longitudinal paths of the virtual geomagnetic pole the polar orientations correlate with near radial flux concentrations recognizable when today s field is stripped of its axial dipole and with lower mantle seismic anomalies suggesting a tie to deep earth dynamics

wind driven modifications to the residual circulation in an ebb tidal delta arcachon lagoon southwestern france a combination of observations and analytical solutions was used to determine the modifications caused by wind forcing on the residual or nontidal circulation in an ebb tidal delta observations were obtained in the lower arcachon lagoon southwestern france the basic nontidal circulation was established with acoustic doppler current profilers adcps that were i moored in the delta s two deepest channels and ii towed along a cross lagoon transect the bathymetry of the lower lagoon or ebb tidal delta featured two channels north pass 9 m and south pass 20 m the basic nontidal circulation consisted of mostly inflow with weak surface outflow in the south pass and laterally sheared bidirectional flow dominated by outflow in the north pass analytical solutions and comparison of observed dynamical terms suggested that in addition to the conventionally accepted influence of tidal nonlinearities density gradients contributed to the basic nontidal circulation in the lagoon observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes this response was supported by an analytical solution to wind driven flows over the bathymetry of the transect sampled the response to seaward winds was to enhance inflow in south pass and reduce outflow in north pass landward winds caused diminished inflow in south pass and increased outflow in north pass

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

short polarity intervals within the matuyama transitional field records from hydraulic piston cored sediments from the north atlantic abstract detailed sampling of two short magnetozones within the matuyama chronozone recorded at dsdp site 609 49 86 n 335 77 e confirms that one the cobb mountain subchronozone 1 12 ma is a very short full normal polarity interval and that the other the older interval is a record of a geomagnetic excursion which occurred at approximately 1 55 ma the cobb mountain subchron lasted approximately 25 000 years one third the duration of the jaramillo subchron the normal polarity interval is bounded by two transition zones which document an antisymmetry in the sequence of directions in the reverse to normal and normal to reverse polarity transitions we interpret the antisymmetry as reflecting a dependence upon the sense of the reversal without significant changes in the relative contributions of non dipole terms the polarity interval recorded at 1 55 ma lasted only 8 800 years with what may be regarded as full polarity directions observed across only 3 cm of stratigraphic section this feature is interpreted as an excursion of the geomagnetic field and appears to be correlative with the gilsa subchron similarities between the transition bounding these two magnetozones suggest that these features occur as the result of the same process or triggering mechanisms in the earth s outer core

timing of quaternary geomagnetic reversals and excursions in volcanic and sedimentary archives abstract we review the ages of quaternary magnetic polarity reversals and magnetic excursions improvements in radioisotopic 40ar 39ar dating of reversals and excursions reflect the use of multi collector mass spectrometers along with ultra low backgrounds laser based incremental heating methods and adoption of 28 201 ma for the fish canyon sanidine fcs standard age kuiper et al 2008 these improvements have brought 40ar 39ar ages of reversals and excursions into close correspondence with astrochronological ages based on the correlation of 18o data to lr04 lisiecki and raymo 2005 and in a few cases correlation to ice core chronologies ages of two polarity reversals the matuyama brunhes boundary and base olduvai are at odds with ages given in popular geomagnetic polarity timescales sedimentary records of the laschamp and iceland basin excursion are numerous and widespread and attest to global manifestation and global synchronicity of these excursions records of other quaternary excursions are less numerous the blake excursion 115 ka has been recorded in north atlantic sediments chinese loess indian ocean volcanics and spanish speleothems the santa rosa excursion 932 ka has been recorded in north atlantic and phillipine basin sediments as well as in volcanic rocks from new mexico and galapagos the punaruu excursion 1115 ka has been observed in sediments from the north atlantic and california margin as well as in volcanic rocks on tahiti uniformity of individual excursion ages using astrochronological 40ar 39ar and u th methods argues for synchronous global manifestation of excursions strengthening the usefulness of magnetic excursions and reversals in quaternary stratigraphy

introduction to the special issue on the 2012 haida gwaii and 2013 craig earthquakes at the pacific north america plate boundary british columbia and alaska the 27 october 2012 m w 7 8 haida gwaii thrust earthquake and the 5 january 2013 m w 7 5 craig strike slip earthquake are the focus of this special issue they occurred along the transform boundary between the pacific and north american plates fig 1 the most identifiable feature of the plate boundary the strike slip queen charlotte fault might be viewed as typical of continent ocean transform faults because it separates the continental crust of the north american plate from oceanic crust of the pacific plate for most of its length however the current relative plate motion of about 5 cm yr is highly oblique to the queen charlotte fault causing a transpressive plate boundary in the region figure 1 location map for the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig earthquakes which occurred on the pacific north american plate boundary approximate rupture zones for the two events are shown in yellow whereas other significant events on the plate boundary are depicted by their aftershock zones red 1949 queen charlotte fault orange 1970 cape st james blue 1972 sitka the epicentral positions are given by stars and the focal mechanisms are plotted in a lower hemisphere projection the black arrows indicate pacific north american relative motion the queen charlotte terrace is located west of the queen charlotte fault and is interpreted to be a narrow accretionary prism inset the earthquakes occurred offshore the western margin of northern north america barbs indicate subduction of the juan de fuca jdf plate and smaller plates beneath north america at the cascadia subduction zone csz transform plate boundaries between continental and oceanic crust are often depicted as both simple and common in reality such continent ocean transform boundaries are neither for example the san andreas fault in california carries continental crustal fragments along with it on the seaward side

shear wave velocity structure in the vicinity of the 2012 mw 7 8 haida gwaii earthquake from receiver function inversion abstract the thrust mechanism of the 2012 m w 7 8 haida gwaii earthquake suggests convergence across the transpressive pacific north america plate boundary in the region is accommodated by underthrusting with important consequences for seismic and tsunami hazard analysis this article investigates the crustal structure and extent of subduction beneath haida gwaii by nonlinear inversion of receiver function data processed from teleseismic recordings at five land based seismograph stations three of these stations were deployed since the 2012 earthquake to extend coverage to the southeast and have not been analyzed previously the inversions provide estimates of the shear wave velocity structure beneath much of moresby island results indicate a positive velocity contrast at approximately 18 26 km depth interpreted as a shallow continental moho a 12 17 km thick low shear wave velocity zone is also identified which increases in depth from 25 to 42 km along the direction of plate convergence which is interpreted as subducting oceanic material these results provide the first evidence that the subducting oceanic plate extends beneath the entirety of moresby island

the matuyama brunhes boundary interval 500 900 ka in north atlantic drift sediments summary ocean drilling program odp sites 984 and 983 located on north atlantic sediment drifts provide high resolution records across the matuyama brunhes boundary at odp site 984 bjorn drift iceland basin the mean sedimentation rate in the 500 900 ka interval is 12 cm kyr 1 based on an age model derived by matching the planktonic and benthic oxygen isotope records to an ice volume model the matuyama brunhes polarity transition at site 984 as defined by virtual geomagnetic polar vgp latitudes 50 has an apparent duration of 7 kyr with a mid point at 773 5 ka compared with 772 5 ka at neighbouring site 983 outside the polarity transition at both sites 984 and 983 excursions in vgp latitudes to values 20 at 540 590 and 670 ka correspond to troughs in the palaeointensity record new u channel palaeomagnetic data across the matuyama brunhes boundary for working and archive halves of core sections from three holes at both sites 984 and 983 augment data published by channell lehman 1997 and are compared with back to back 1 cm 3 discrete samples clusters of vgps in the south atlantic and northeast asia in both u channel and discrete sample records imply that polarity transition fields have characteristics similar to the modern non axial dipole nad field

observations on the characteristics of the exchange flow in the dardanelles strait 1 a mooring section at each end of the dardanelles strait was deployed by the naval research laboratory on 28 29 august 2008 and maintained until 11 october 2009 each section was equipped with two bottom mounted barny moorings and a vertical string that together delivered concurrent bottom pressure temperature salinity and almost full water column current velocity observations these observations at the mooring sections indicated that on longer timescales monthly or longer the exchange through the dardanelles strait showed little variability and had a two layer structure with brackish waters moving approximately southward in the upper layer and more saline aegean waters flowing roughly northward underneath on shorter time scales synoptic there were pronounced fluctuations in both layers in the northern section some manifested as almost simultaneous reversals of the flow direction in both layers with lighter upper layer waters backing into the sea of marmara and dense lower layer waters moving toward the aegean sea in the southern section some of the exchange variability consisted of a three layer flow structure with upper brackish and bottom salty layers moving toward the aegean sea and a middle salty layer flowing toward the sea of marmara this three layer exchange persisted from a day to a week synoptic flow variability in the upper layer was partly related to both the along strait wind stress and the bottom pressure anomaly gradient while lower layer current fluctuations were coherent with the bottom pressure anomaly gradient

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

three dimensional wind driven flow in an elongated rotating basin abstract the wind driven circulation in lakes lagoons estuaries or coastal embayments is described with a linear steady three dimensional barotropic model in an elongated basin of arbitrary depth distribution on an f plane with rotation the vertically averaged velocity scales with the ekman depth rather than the maximum depth h0 as in the case without rotation near the closed ends of the basin the flow turns in viscous boundary layers because the length of the turning areas depends on the sign of the bottom slope and on the ratio of the ekman depth to h0 there is a striking contrast between the turning areas on either side of an observer looking toward the end of the basin in the northern hemisphere the turning area on the left is broad of order 1b where b is the basin half width the turning area on the right is narrow of order b and dynamically equivalent to the western boundary current in models of the wind driven ocean circulation ekman solutions are used to describe the ve

basement and regional structure along strike of the queen charlotte fault in the context of modern and historical earthquake ruptures the queen charlotte fault qcf is a dextral transform system located offshore of southeastern alaska and western canada accommodating 4 4 cm yr of relative motion between the pacific and north american plates oblique convergence along the fault increases southward and how this convergence is accommodated is still debated using seismic reflection data we interpret offshore basement structure faulting and stratigraphy to provide a geological context for two recent earthquakes an m w 7 5 strike slip event near craig alaska and an m w 7 8 thrust event near haida gwaii canada we map downwarped pacific oceanic crust near 54 n between the two rupture zones observed downwarping decreases north and south of 54 n parallel to the strike of the qcf bending of the pacific plate here may have initiated with increased convergence rates due to a plate motion change at 6 ma tectonic reconstruction implies convergence driven pacific plate flexure beginning at 6 ma south of a 10 bend the qcf which is currently at 53 2 n and lasting until the plate translated past the bend by 2 ma normal faulted approximately late miocene sediment above the deep flexural depression at 54 n topped by relatively undeformed pleistocene and younger sediment supports this model aftershocks of the haida gwaii event indicate a normal faulting stress regime suggesting present day plate flexure and underthrusting which is also consistent with reconstruction of past conditions we thus favor a pacific plate underthrusting model to initiate flexure and accommodation space for sediment loading in addition mapped structures indicate two possible fault segment boundaries along the qcf at 53 2 n and at 56 n

rapid response to coastal upwelling in a semienclosed bay bays estuaries forced by local wind show bidirectional exchange flow when forced by remote q3 wind they exhibit unidirectional flow adjustment to coastal sea level acoustic doppler current profiler observations over 1 year show that the ria de vigo iberian upwelling responds to coastal wind events with bidirectional exchange flow the duration of the upwelling and downwelling events estimated from the current variability was 3 3 days and 2 6 days respectively vectorial correlations reveal a rapid response to upwelling downwelling in which currents lag local wind by 6 h and remote wind by 14 h less than the ekman spinup 17 8 h this rapidity arises from the ria s narrowness nonrotational local response equatorward orientation additive remote and local wind responses depth greater than the ekman depth penetration of shelf circulation into the interior and vertical stratification shear reinforcing shelf circulation similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow

intertidal biological indicators of coseismic subsidence during the mw 7 8 haida gwaii canada earthquake the 28 october 2012 m w 7 8 haida gwaii earthquake was a megathrust earthquake along the very obliquely convergent queen charlotte margin of british columbia canada coseismic deformation is not well constrained by geodesy with only six global positioning system gps sites and two tide gauge stations within 250 km of the rupture area to better constrain vertical coseismic deformation we measured the upper growth limits of two sessile intertidal organisms which are controlled by physical conditions relative to sea level at 25 sites 5 months after the earthquake we measured the positions of rockweed fucus distichus 617 observations and the common acorn barnacle balanus balanoides 686 observations the study focused on the western side of the islands where rupture models indicated that the greatest amount of vertical displacement but we also investigated sites well away from the inferred rupture area to provide a control on the upper limit of the organisms unaffected by vertical displacement we also made 322 measurements of sea level to relate the growth limits to a tidal datum using the tpxo7 2 tidal model rather than ellipsoid heights determined by gps three methods of examining the data all indicate 0 4 0 6 m subsidence along the western coast of moresby island as a result of the 28 october 2012 haida gwaii earthquake our data are within the errors consistent with data from two campaign gps sites along the west coast of haida gwaii and with rupture models that indicate megathrust rupture offshore but not beneath the islands

the october 28 2012 mw 7 8 haida gwaii underthrusting earthquake and tsunami slip partitioning along the queen charlotte fault transpressional plate boundary the pacific north american plate boundary is undergoing predominantly right lateral strike slip motion along the queen charlotte and fairweather transform faults the queen charlotte fault qcf hosted the largest historical earthquake in canada the 1949 m s 8 1 strike slip earthquake which ruptured from offshore northern haida gwaii several hundred kilometers northwestward on january 5 2013 an m w 7 5 strike slip faulting event occurred near the northern end of the 1949 rupture zone along central and southern haida gwaii the relative plate motion has 20 oblique convergence across the left stepping plate boundary there had been uncertainty in how the compressional component of plate motion is accommodated the october 28 2012 m w 7 8 haida gwaii earthquake involved slightly 20 oblique thrust faulting on a shallow 18 5 northeast dipping fault plane with strike 320 parallel to the qcf consistent with prior inferences of pacific plate underthrusting beneath haida gwaii the rupture extended to shallow depth offshore of moresby island beneath a 25 30 km wide terrace of sediments that has accumulated in a wedge seaward of the qcf the shallow thrusting caused seafloor uplift that generated substantial localized tsunami run up and a modest far field tsunami that spread across the northern pacific prompting a tsunami warning beach closure and coastal evacuation in hawaii although ultimately tide gauges showed less than 0 8 m of water level increase the mainshock rupture appears to have spread with a 2 3 km s rupture velocity over a length of 150 km with slip averaging 3 3 m concentrated beneath the sedimentary wedge the event was followed by a substantial aftershock sequence in which almost all of the larger events involve distributed intraplate normal faulting extending 50 km oceanward from the qcf the highly oblique slip partitioning in southern haida gwaii is distinctive in that the local plate boundary parallel motion on the qcf may be accommodated either by infrequent large strike slip ruptures or by aseismic creep as seems to be the case for deeper oblique relative plate motion beneath haida gwaii while the sedimentary terrace accumulates plate boundary perpendicular compressional strain that releases in almost pure thrust faulting earthquakes seaward of the qcf

tidal and nontidal exchange at a subtropical inlet destin inlet northwest florida abstract a tidal cycle study at destin inlet northwest florida investigated intratidal and residual flow structures for the first time across the inlet underway current velocity profiles were combined with hydrographic station profiles at neap tides to document the appearance of tidal fronts the distribution of tidal currents across two cross sections and the residual or non tidal flow structure at the same cross sections intratidal variations of water density and velocity showed the presence of fronts both in 1 late ebb early flood and 2 late flood early ebb tidal stages late ebb early flood tidal intrusion fronts brought about depth independent changes in water density 10 kg m 3 in

the last two geomagnetic polarity reversals recorded in high deposition rate sediment drifts high resolution records of geomagnetic polarity transitions are rare owing to the difficulty of preserving in the geological record details of a process with a duration of only a few thousand years lavas can record the instantaneous field on cooling but lava records are themselves discontinuous and therefore polarity transition fields are seldom captured sedimentary records are more continuous but typical deep sea sedimentation rates of a few cm kyr 1are too low to record transition fields adequately here we report transition records from north atlantic drift deposits with high sedimentation rates 12 cm kyr 1 at the ocean drilling program sites 983 and 984 virtual geomagnetic polar vgp paths are similar within and between sites for the last two geomagnetic reversals attesting to a memory effect spanning back to back reversals the complex vgp paths feature two vgp clusters one located in northeastern asia and the other in the south atlantic ocean off south america and provide a link between the longitudinally constrained transitional vgps often recorded in sediments1 2 which represent highly smoothed renditions of transition fields and the scattered transitional vgps3 and vgp clusters4 observed in lava records

records of the cobb mountain subchron from the bermuda rise odp leg 172 abstract duplicate records of the cobb mountain subchron were obtained from two holes holes 1063b at 33 41 204 n 57 36 w and 1063c at 33 41 181 n 57 36 w drilled in a sediment drift at ocean drilling program odp site 1063 on the northeast bermuda rise we sub sampled the cores from both holes using u channels up to 1 5 m long samples with 2 2 cm cross section focusing on continuous sampling through the late matuyama interval containing the cobb mountain subchron results of standard progressive alternating field demagnetization experiments reveal that these sediments generally have a stable characteristic component after removal of a low coercivity drilling overprint additional discrete samples 7 cm 3 oriented cubes used in progressive thermal demagnetization studies display similar behavior by taking duplicate sets of u channels we were able to identify and remove several measurement artifacts such as edge effects that affect measurements made near the ends of the u channel samples the upper normal to reverse polarity transition was not obtained because of a coring gap or an interval of coring deformation after removing measurement artifacts the records from the two holes were stacked to obtain a composite record virtual geomagnetic poles vgps computed from the composite record follow a path through the central pacific during the lower polarity transition very similar to vgp paths from cobb mountain subchron records from other sites around the world furthermore the vgps cluster near southern africa early in the reversal process and then group in a nearly antipodal patch in the north pacific late in the reversal taken together these records indicate that the transitional field remained nearly dipolar through the polarity reversal or at least during the beginning and end of the reversal when the field was dominated by an axial dipole tilted about 20 40 to the spin axis if a tilted dipole is an inherent part of the initiation and ending of a reversal it may help explain why many sediment recorders which are thought to smooth the field record antipodal vgp paths through many reversals

the lateral density distribution in a partially mixed estuary abstract the density distribution across the york river is characterized by distinct inhomogeneities especially in the upper 2 m of the water column the pattern of variability is repetitive and closely correlated with the semi diurnal tidal cycle and water depth in the shallow areas the water column remains vertically well mixed at all times the density differences are greatest at times of minimum currents at slack before flood the least dense water is located in a lens over the main channel towards the end of the flood cycle and at slack before ebb this is reversed with the least dense water situated over the shoals these density differences result in horizontal pressure gradients which at times may be of sufficient strength to generate localized lateral circulations such circulation patterns would form zones of convergence or divergence across the estuary depending on the particular density distribution

buoyancy driven current during cooling periods in ise bay japan 1 the cooling effect on buoyancy driven current is studied in the coastal embayment of ise bay japan by applying knowledge derived from studies of convection in a rotating fluid this convection process is highly sensitive to the presence of inhomogeneities in the preexisting stratification and to differential buoyancy loss on freshwater input the bay water is divided into two regions that differ in their response to the cooling from the surface one region represents a river plume which in effect shields the deeper regions from the cooler surface in the other region convective mixing is active although the mixed water forms and becomes extensive in this convection region the mixed water hardly develops in the river plume region the subsequent differential deepening of the mixed water causes gravitational circulation and yields a mixed water lens which has a reversed dome shape and rotates anticyclonically in a thermal wind balance in the mixed water lends nonvanishing stratification remains because of the rotational effect the location of the mixed water lens and associated anticyclonic circulation determines the basin wide circulation during cooling periods

estimating coseismic coastal uplift with an intertidal mussel calibration for the 2010 maule chile earthquake mw 8 8 abstract coseismic coastal uplift has been quantified using sessile intertidal organisms after several great earthquakes following fitzroy s pioneer measurements in 1835 a dense survey of such markers may complement space geodetic data to obtain an accurate distribution of fault slip and earthquake segmentation however uplift estimates based on diverse intertidal organisms tend to differ because of few methodological and comparative studies here we calibrate and estimate coastal uplift in the southern segment of the 2010 maule chile earthquake m w 8 8 using 1100 post earthquake elevation measurements of the sessile mussel perumytilus purpuratus this mussel is the predominant competitor for rocky shores all along the pacific coast of south america where it forms fringes or belts distinctively in the middle intertidal zone these belts are centered at mean sea level and their width should equal one third of the tidal range we measured belt widths close to this value at 40 of the sites but overall widths are highly variable due to the unevenness in belt tops belt bases in turn are rather regular belt top unevenness apparently results from locally enhanced wave splash whereas belt base evenness is controlled by predation according to our measurements made beyond the earthquake rupture the belt base is at the bottom of the middle intertidal zone and thus we propose to estimate coastal uplift using the belt base mean elevation plus one sixth of the tidal range to reach mean sea level within errors our estimates agree with gps displacements but differ from other methods comparisons of joint inversions for megathrust slip suggest combining space geodetic data with estimates from intertidal organisms may locally increase the detail of slip distributions

the tectonic and geomagnetic significance of paleomagnetic observations from volcanic rocks from central afar africa deformation throughout afar over the past 2 myr has been characterized by widespread and intense crustal fragmentation that results from inhomogeneous extension across the region in eastern afar this situation has evolved to localized extension associated with the westward propagation of the gulf of aden gulf of tadjurah seafloor spreading system into the asal ghoubbet rift during the gradual process of rift propagation and localization crustal blocks in eastern afar sustained clockwise rotations of 11 to better understand the processes of rift propagation and localization and how they affect the rest of afar we have collected and analyzed over 400 oriented paleomagnetic samples from 67 lava flows from central and southern afar unlike eastern afar the mean paleomagnetic direction from central afar indicates that vertical axis rotations are statistically insignificant 3 6 4 4 though small clockwise rotations 8 are permitted thus propagation and localization in central afar have not had the same influence in causing crustal block rotations or perhaps more likely have not reached the same stage of evolution as seen in eastern afar in addition several of the lava flows record intriguing geomagnetic field behavior associated with polarity transitions excursions or large secular variation events interestingly the transitional or anomalous virtual geomagnetic poles vgps tend to cluster in two nearly antipodal regions one in the northern pacific ocean and the other in the southwest indian ocean one lava flow has recorded both of the antipodal transitional components with the two components residing in magnetic minerals with unblocking temperatures above and below 500 c respectively reheating and partial remagnetization by the overlying flow cannot explain either of the transitional directions because both differ significantly from that of the reversely magnetized overlying flow the high temperature component gives a vgp in the northern pacific whereas the lower temperature component gives a nearly antipodal vgp south of cape town south africa hence the configuration of the geomagnetic field appears to have jumped nearly instantaneously from a northern hemisphere transitional state to a southern hemisphere one during this normal to reverse polarity transition

the importance of tidal and lateral asymmetries in stratification to residual circulation in partially mixed estuaries measurements collected in the york river estuary virginia demonstrate the important impact that tidal and lateral asymmetries in turbulent mixing have on the tidally averaged residual circulation a reduction in turbulent mixing during the ebb phase of the tide caused by tidal straining of the axial density gradient results in increased vertical velocity shear throughout the water column during the ebb tide in the absence of significant lateral differences in turbulent mixing the enhanced ebb directed transport caused by tidal straining is balanced by a reduction in the net seaward directed barotropic pressure gradient resulting in laterally uniform two layer residual flow however the channel shoal morphology of many drowned river valley estuaries often leads to lateral gradients in turbulent mixing tidal straining may then lead to tidal asymmetries in turbulent mixing near the deeper channel while the neighboring shoals remain relatively well mixed as a result the largest lateral asymmetries in turbulent mixing occur at the end of the ebb tide when the channel is significantly more stratified than the shoals the reduced friction at the end of ebb delays the onset of the flood tide increasing the duration of ebb in the channel conversely over the shoal regions where stratification is more inhibited by tidal mixing there is greater friction and the transition from ebb to flood occurs more rapidly the resulting residual circulation is seaward over the channel and landward over the shoal the shoal channel segregation of this barotropically induced estuarine residual flow is opposite to that typically associated with baroclinic estuarine circulation over channel shoal bathymetry

paleomagnetic transition records of the cobb mountain event from sediments of the celebes and sulu seas the cobb mountain cm event is a short normal polarity interval within the matuyama chron just before the jaramillo subchron this event was found in the sediments of site 767 in the celebes sea and site 768 in the sulu sea during odp leg 124 reversal depth and age relation analysis gave ages of 1 11 and 1 10 m y ago for the onset and termination of this event we used discrete samples and high density pass through measurements to study the behavior of the geomagnetic field crossing this event although the two sites are very close to each other the records of the transitional fields were found to be quite different they are also very different from another cm event record from the north atlantic ocean based on the transition data we conclude that the transitional fields for the cm event were non axisymmetric one brief reverse in direction called rebound was found within the onset reversal at site 767 the absence of this feature at site 768 raises an interesting question concerning the source for rebounds

subsidence and thermal history of queen charlotte basin a tectonic model for the formation subsidence and thermal history of queen charlotte basin is developed based upon regional geological and geophysical data subsidence data from offshore wells in hecate strait and queen charlotte sound and thermal criteria derived from present heat flow and vitrinite reflectance information queen charlotte basin is seen to have resulted from two distinct mechanisms 1 during a period of broad regional uplift rifting and crustal extension occurred in queen charlotte sound up to about 17 ma ago and the queen charlotte islands were displaced northwards toward their present position by transcurrent motion along the louscoone inlet sandspit fault system the rifting generated a significant thermal anomaly and a restricted deep basin as a consequence of crustal thinning and subsequent thermal cooling 2 beginning about 6 ma ago oblique underthrusting commenced along the margin resulting in flexural uplift of the western part of the queen charlotte islands and comp

observed flow variability along the thalweg and on the coastal slopes of the gulf of finland baltic sea abstract bottom mounted adcp measurements from 10 installations collected between 2009 and 2014 and each lasting several months are analysed in order to distinguish between different flow regimes and to detect variability a along the thalweg of the elongated basin with different regimes in summer and in winter and b on the coastal slopes in the deep thalweg area the mean flow speed amounts to 6 13 cm s 1 whereas the maximum speeds appear in winter near the bottom of the basin and in summer within the halocline around 70 m depth the mean zonal flow component reveals a nearly depth uniform inflow during winter and a layered inflow outflow during summer in years where up estuary w to sw winds are stronger during the summer inflow dominates in upper layers and anti estuarine outflow dominates in deeper layers this causes the export of a salt wedge and the weakening of haline stratification infra low frequency zonal currents i e excluding topographic waves etc with periods of less than 10 days have a structure which is uniform with depth for 53 of the time in winter in summer a layered structure is present 65 of the time however during both periods the reversed estuarine flow inflow in upper layers and outflow in the bottom layer appears on average for 30 of the time the deep flow zonal component is well correlated with westward winds during summer r 0 84 and south westward winds during winter r 0 77 on the coastal slopes the speed of the currents are lower than in the thalweg region and they decay with depth in the vertical the flow exhibits a layered structure in both the winter and summer seasons

evidence for underthrusting beneath the queen charlotte margin british columbia from teleseismic receiver function analysis summary the queen charlotte fault zone is the transpressive boundary between the north america and pacific plates along the northwestern margin of british columbia two models have been suggested for the accommodation of the 20 mm yr 1 of convergence along the fault boundary 1 underthrusting 2 internal crustal deformation strong evidence supporting an underthrusting model is provided by a detailed teleseismic receiver function analysis that defines the underthrusting slab forward and inverse modelling techniques were applied to receiver function data calculated at two permanent and four temporary seismic stations within the queen charlotte islands the modelling reveals a 10 km thick low velocity zone dipping eastward at 28 interpreted to be underthrusting oceanic crust the oceanic crust is located beneath a thin 28 km eastward thickening 10 continental crust

40ar 39ar chronology and paleomagnetism of quaternary basaltic lavas from the persani mountains east carpathians abstract quaternary volcanism in the persani mountains forms an na alkali basaltic province inside the bend area of the carpathians in the southeastern part of europe previous k ar ages and paleomagnetic data reveal several transitional virtual geomagnetic poles which were tentatively associated with the cobb mountain subchron and a brunhes chron excursion we report a new paleomagnetic and rock magnetic study coupled with 40ar 39ar geochronology to better constrain the age of geomagnetic reversals or excursions that might be recorded and the timing of volcanism of the paleomagnetic directions obtained from sampled lava flows 4 are reversed polarity 19 are normal polarity and 16 have transitional polarity 40ar 39ar plateau ages determined from incremental heating experiments on groundmass indicate that two of the reversely magnetized lavas erupted at 1142 41 and 800 25 ka four of the normally magnetized lavas erupted at 1060 10 1062 24 684 21 and 683 28 ka and two transitionally magnetized lavas formed at 1221 11 and 799 21 ka both the new 40ar 39ar ages and the paleomagnetic data suggest at least five episodes of volcanic activity with the most active periods during the jaramillo and brunhes chrons this results shows that the last phases of alkalic and calc alkaline magmatism in the south east carpathians were contemporaneous the age of the older transitionally magnetized lava flow is within error of recent unspiked k ar and astrochronologic ages for the reversal that defines the onset of the cobb mountain normal polarity subchron the age of the younger transitional lava is similar to that of an excursion that preceded the matuyama brunhes polarity reversal and which has come to be known as the matuyama brunhes precursor omitting the excursion data the dispersion of the virtual geomagnetic poles around 19 is larger than the expected value around 45 n from the global compilation but closer to the value obtained only from the time averaged geomagnetic field initiative studies

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

gps observations of crustal deformation associated with the 2012 mw 7 8 haida gwaii earthquake abstract on 28 october 2012 an m w 7 8 earthquake occurred off the west coast of haida gwaii british columbia although past large events at this margin reflect strike slip motion between the pacific and north american plates e g 1949 m s 8 1 this earthquake involved low angle thrust faulting with a slip direction almost perpendicular to the margin a consequence of slip partitioning at this obliquely convergent margin to refine regional source models we investigated the coseismic and postseismic displacements using a network of global positioning system gps sites coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south southwest with 30 cm of subsidence the only continuously recording gps station on haida gwaii at the time of the earthquake about 80 km from the epicenter provides a robust coseismic displacement estimate of 22 cm to the south southwest the coseismic results are consistent with a shallow dipping thrust rupture underlying the queen charlotte terrace immediately seaward of the queen charlotte fault these results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm with a systematic along strike variation in azimuth from south southwest to southeast from north to south in the study area besides viscoelastic stress relaxation these postseismic trends may indicate afterslip on the deeper plate interface beneath northern moresby island and possibly aseismic slip along the queen charlotte or subparallel faults offshore of southern moresby island online material figures of three component daily position estimates from bernese analysis at global positioning system tracking stations on haida gwaii and the adjacent mainland

subtidal exchange in eastern long island sound abstractlong island sound lis is a large and wide macrotidal estuary with distributed river inputs including the connecticut river the largest freshwater source that flows into the eastern lis near the mouth in 2010 shipboard surveys of salinity temperature and currents were collected along an across estuary transect in eastern lis numerical model results are compared to these observations and used to study the spatial and temporal variability of salinity velocity and freshwater and salt fluxes over a 4 yr period for all low wind conditions observations and model results indicate an outward flowing low salinity wedge on the south side with an inward flowing higher salinity area underneath and to the north observations and model results during the low wind surveys indicate that stratification substantially decreases with increased tidal amplitude and decreased river discharge the velocity field is less variable among surveys model analysis indicates strong sensitivities to both tides and

odp site 1063 bermuda rise revisited oxygen isotopes excursions and paleointensity in the brunhes chron an age model for the brunhes chron of ocean drilling program odp site 1063 bermuda rise is constructed by tandem correlation of oxygen isotope and relative paleointensity data to calibrated reference templates four intervals in the brunhes chron where paleomagnetic inclinations are negative for both u channel samples and discrete samples are correlated to the following magnetic excursions with site 1063 ages in brackets laschamp 41 ka blake 116 ka iceland basin 190 ka pringle falls 239 ka these ages are consistent with current age estimates for three of these excursions but not for pringle falls which has an apparent age older than a recently published estimate by 28 kyr for each of these excursions termed category 1 excursions virtual geomagnetic poles vgps reach high southerly latitudes implying paired polarity reversals of the earth s main dipole field that apparently occurred in a brief time span 2 kyr in each case several times shorter than the apparent duration of regular polarity transitions in addition several intervals of low paleomagnetic inclination low and negative in one case are observed both in u channel and discrete samples at 318 ka mis 9 412 ka mis 11 and in the 500 600 ka interval mis 14 15 these category 2 excursions may constitute inadequately recorded category 1 excursions or high amplitude secular variation

frictional estuarine flow in juan de fuca strait with implications for secondary circulation estuarine flow in juan de fuca strait is highly seasonal in nature and an appreciable along channel surface pressure gradient is coincident with the peak fraser river discharge an upper layer momentum balance requires the vertical eddy viscosity av to be of the order of 0 02 m2 s 1 slightly larger than implied by conventional empirical formulae and used in current models mixing in an estuarine channel and a large vertical eddy viscosity should lead to significant cross channel flows this secondary circulation which may resemble internal ekman layers and intrusions of water mixed at the sloping sides of the strait is much less understood than the basic along channel estuarine exchange unfortunately historical current meter data in juan de fuca strait are of insufficient spatial resolution to show the predicted patterns

comment on the lau basin cobb mountain records by abrahamsen and sager abstract the cobb mountain subchron is one of the few short polarity intervals for which transition records have been obtained both from a wide geographical distribution and from different types of paleomagnetic recorders these records exhibit vgp paths that are remarkably similar given the wide geographic distribution of these sites the similarity in vgp paths is most simply interpreted as the presence of very large scale if not dipolar symmetries in the transitional fields only the records from western california and the lau basin exhibit vgp paths that are markedly different from the others new dates for the punaruu lavas suggest that they recorded a new geomagnetic cryptochron rather than the cobb mountain singer b s hoffman k a chauvin a coe r s 1999 dating transitionally magnetized lavas of the late matuyama chron toward a new 40 ar 39 ar timescale of reversals and events j geophys res 104 679 693 this new age indicates a revised correlation of some of the other california records whose ages agree better with the punaruu cryptochron a re examination of the lau basin records reveals that much of the difference between these and the other records results from a bias introduced when the paleomagnetic data were smoothed reanalysis of these records shows that the lau basin vgp paths are very similar to those obtained from western pacific and the north atlantic

40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited new 40 ar 39 ar age determinations on sanidine from the rhyolite of alder creek california indicate a 1 186 0 006 ma age for the cobb mountain normal polarity subchron the new age is statistically older 0 05 than the previously reported k ar age 1 12 0 02 ma and agrees with the age suggested by the astronomical polarity time scale incomplete extraction of radiogenic 40 ar 40 ar from the sanidine is the most likely reason for the disparity between the 40 ar 39 ar and k ar ages because the cobb mountain subchron is a worldwide short duration event and because no widely used interlaboratory 40 ar 39 ar standard younger than 27 ma exists we propose that sanidine from the rhyolite of alder creek be considered for use as a new quaternary 40 ar 39 ar mineral standard

a comparison of mechanical thickness estimates from trough and seamount loading in the southeastern gulf of alaska the southern portion of the kodiak bowie seamount chain in the southeastern gulf of alaska presents a unique opportunity to investigate loading on young oceanic lithosphere oceanic lithosphere younger than 25 ma is loaded both by sediments in a deep offshore trough and by seamounts 100 200 km offshore free air gravity anomaly values associated with the trough range from 90 mgal over the trough to 25 mgal over the offshore flexural high whereas values associated with the volcanic loading range from 80 mgal over the seamounts to 10 mgal over their associated moats these anomalies are modeled first using elastic beam theory gravity anomalies associated with the trough are modeled in terms of elastic bending of a sediment filled trench elastic thicknesses associated with the trough range from 12 to 22 km with an estimated uncertainty of 5 km seamounts are approximated as a series of stacked finite cylinders gravity highs over the seamounts are used to model density while gravity patterns associated with the moat and peripheral bulge are used to model the elastic thickness along the seamount chain elastic thicknesses along the seamount chain range from 2 to 5 km estimated uncertainty range 0 to 7 and 0 to 10 km respectively to investigate differences in elastic thickness estimates between the trough and seamount models we incorporate the effects of finite yield strength curvatures implied by the elastic beam models are used to calculate mechanical bending stresses bending moments calculated from elastic beam models and yield envelope models agree for flexure models at the queen charlotte trough and most seamounts the mechanical thickness corresponds to the depth to the 700 c isotherm assuming a dry olivine rheology and a simple cooling model for oceanic lithosphere our results imply that the strength of the lithosphere calculated for both seamount and trench loading corresponds to the same isotherm

an overview of the 28 october 2012 m w 7 7 earthquake in haida gwaii canada a tsunamigenic thrust event along a predominantly strike slip margin the boundary between the pacific and north america plates along canada s west coast is one of the most seismically active regions of canada and is where canada s two largest instrumentally recorded earthquakes have occurred although this is a predominantly strike slip transform fault boundary there is a component of oblique convergence between the pacific and north america plates off haida gwaii the 2012 mw 7 7 haida gwaii earthquake was a thrust event that generated a tsunami with significant run up of over 7 m in several inlets on the west coast of moresby island several over 6 m with a maximum of 13 m damage from this earthquake and tsunami was minor due to the lack of population and vulnerable structures on this coast

exchange fluxes between the ria de vigo and the shelf a bidirectional flow forced by remote wind 1 in the ria de vigo western coast of the iberian peninsula the seasonal pattern associated with shelf winds at these latitudes produces upwelling downwelling episodes that affect the residual circulation the aim of this paper is to go deeply into the interaction between remote winds and the dynamics of the ria aided by an inverse model in the galician r ias the box models inverse models have been developed from a two dimensional 2 d point of view since the classical baroclinic residual circulation in positive estuaries has a vertical distribution freshwater outflow through the surface layer and inflow through the bottom layer however recent work in the ria de vigo has shown the existence of a 3 d residual circulation in the seaward region of the ria during upwelling downwelling conditions a coastal jet enters leaves the ria through the northern mouth and leaves enters through the southern mouth the inverse model developed in this paper is a 3 d kinematic box model based on tracer and volume balances with the constraint of nonnegative vertical exchange coefficients the fluxes obtained confirm during some periods the 3 d residual circulation overlying the classical 2 d scheme it is shown how the 3 d pattern affects the inner ria causing transversal differences in the flow field in addition the model results have been helpful in the discussion of a possible barotropic bidirectional flow associated with remote winds the results have set the basis for the existence of a bidirectional flow originated by a barotropic interaction with the shelf upwelling

paleomagnetic record at odp site 980 feni drift rockall for the past 1 2 myrs 1 a detailed record of variations in the direction and intensity of the geomagnetic field over the past 1 2 myrs has been obtained from an 120 m thick sedimentary section cored at odp site 980 on the feni drift north atlantic the record has high resolution due to high mean sedimentation rates 11 3 cm kyr for the brunhes chron and 5 5 cm kyr for the matuyama chron paleomagnetic measurements every 1 cm along u channel samples and high quality isotopic age control the iceland basin event is manifest by virtual geomagnetic poles crossing the equator at 190 ka the base of the recovered section lies immediately below the cobb mountain subchronozone that occurs within marine isotope stage 35 normalized remanence data can be correlated to paleointensity records from odp sites 983 and 984 700 km to the nw from site 980 and with lower resolution paleointensity data from the pacific ocean differences between the site 980 paleointensity record and the pacific records are attributed to variable sedimentation rates variable quality age control and inadequacies in the normalization procedure used to derive the paleointensity proxies

tidal riverine and wind influences on the circulation of a macrotidal estuary abstractthe effect of tides river wind and earth s rotation on the three dimensional circulation in the dee a macrotidal estuary are investigated using a fine resolution model the interactions of the large tidal amplitude currents river and wind generated circulation require baroclinic and unsteady studies to properly understand the estuarine dynamics assessment of the model skill has been carried out by model observation comparisons for salinity which is the main control for density surface elevation current and turbulence stationary nondimensional numbers were only partially able to characterize the dynamics in this real complex macrotidal estuary at low water tidal straining and constrained river flow cause stratification large spatial variability occurs in the current and residual patterns with flood dominated maximum values occurring within the tidal channels the tides control residual circulation by modulating stratification through tidal straining and bathymetric constraint on

first field evidence of coseismic land level change associated with the 25 december 2016 mw 7 6 chiloe chile earthquake assessments of megathrust earthquake rupture patterns provide fundamental insights into the processes that control the seismic cycle along subduction zones when large earthquakes occur in regions with sparse geodetic networks as was the case for the magnitude mw 7 6 chiloe chile earthquake of 25 december 2016 estimates of vertical coseismic deformation from fixed intertidal biotic indicators provide important evidence that help to constrain fault slip ten months after the chiloe earthquake we observed a white fringe of bleached coralline algae corallinaceae along the southeastern coastline of isla quilan south of isla de chiloe killed by reduced tidal wetting resulting from coseismic land uplift our quantitative measurements of the vertical extent of algal mortality provide the first field based report of the effects of the 2016 earthquake we infer isla quilan coseismically uplifted by 25 8 14 3 cm the vertical extent of mortality vem and the aspect compass direction of the bedrock surface are uncorrelated but we find that exposure to waves and shielding from insolation may prevent or delay mortality focusing on sites sheltered from waves we demonstrate that with a large number of measurements 100 land level changes as low as 25 cm may be quantitatively assessed the absence of bleaching on isla de chiloe may reflect the smaller magnitude of coseismic uplift at this location or the lack of suitably sheltered bedrock surfaces previously published fault dislocation models are consistent with our field observations however the coralline algae data are on their own insufficient to discriminate between competing hypotheses over the amount of fault slip by combining our field data with space geodetic data in a model that uses detailed fault geometry we constrain peak slip to 3 m approximately 80 of the maximum cumulative plate convergence since the last great earthquake in the region

a quantitative comparison of two paleomagnetic records of the cobb mountain subchron from north atlantic deep sea sediments we present a new paleomagnetic record of the cobb mountain subchron obtained from deep sea sediments cored at ocean drilling program site 647 in the southern labrador sea the details of the transitional field behavior documented by this record appear to be very similar to those recorded in a previously published record of this subchron obtained at deep sea drilling project dsdp site 609 in the north atlantic clement and kent 1987 we used a quantitative correlation technique martinson et al 1982 to establish statistically the degree of similarity between these two records and thereby constrain the spatial variability in these transitional fields the error in the alignments is reduced significantly by aligning records of virtual geomagnetic pole positions rather than directions indicating that these records document such large scale changes in the fields that we can not distinguish them from dipolar changes given the proximity of these two sites these replicate records of the cobb mountain subchron provide evidence that deep sea sediments are capable of providing high resolution records of geomagnetic field behavior a reexamination of the sequence of polarity transitions recorded at dsdp site 609 in light of these results suggests the presence of two preferred transitional field configurations the field appears to change from one configuration to the other for several reversals and then back to the original configuration suggesting that a geographical influence on the reversal process persists through this sequence the variability in these reversal records provides insights into the response of the geodynamo to this geographical influence

source characteristics of the 2012 haida gwaii earthquake sequence abstract all the significant m l 4 events in the 2012 haida gwaii earthquake sequence are systematically relocated and their moment tensor solutions are determined from waveform inversion the focal mechanism of the mainshock shows low angle thrust faulting along a shallowly dipping plane with a strike parallel to the queen charlotte fault qcf consistent with the inference of pacific plate underthrusting beneath the overriding north american plate the epicenter of the mainshock is located 5 km landward northeast of the surface trace of the qcf suggesting the nucleation of the rupture was near the bottom of the seismogenic locked interface significant aftershocks appear to cluster on the periphery of the main rupture zone with most events located immediately seaward of the deformation front the majority of these events show normal faulting mechanisms that are probably associated with the bending stress within the pacific plate near the deformation front several normal and strike slip events at greater depths within the subducted pacific slab show a consistent pattern of t axis in the down dip direction implying the subducted plate is under a stress regime of down dip extension only a few strike slip events were observed along or near the qcf the limited size and distribution of these events suggest that most of the elastic strain accumulated along the qcf was not released during the 2012 haida gwaii sequence major strike slip earthquakes are likely to occur along the southernmost part of the qcf system in the future

effect of the earth s rotation on the circulation in regions of freshwater influence recent surveys in various regions of freshwater influence have shown considerably different flow patterns in each region an analytical model including viscous effects and the earth s rotation is proposed to examine the along channel flow pattern and to explain the differences model results show that the flow pattern is strongly dependent on the ekman number e with a large ekman number e 1 the system is governed by gravitational circulation and thus horizontal density gradients in along channel direction are important the whole water column is in the ekman layer and consequent jet inflow penetrates the surface over a deep depression if the bottom topography varies in a cross channel direction with an intermediate ekman number e 0 1 this jet inflow concentrates in the lower layer in which the viscosity still plays an important role the flow in the upper layer is on the other hand determined by the geostrophic balance the contribution by the geostrophic flow becomes larger so that the cross channel density gradients are important when die ekman number is small e 0 01 since the ekman layer is clung to the bottom the jet inflow exists only in the thin bottom layer the hydrographic and acoustic doppler current profiler surveys were conducted in ise bay japan both the density structure and the flow pattern were different from those observed in many drowned river valleys a strong jet inflow existed in the lower layer over the depression while the flow in the upper layer suggested anticyclonic circulation the estimated ekman number is 0 07 in the bay and thus the observed pattern is consistent with the model result when e 0 1

queen charlotte fault zone heat flow measurements the heat flow pattern from the deep sea across the queen charlotte terrace to the west coast of the queen charlotte islands has been determined through 20 marine heat flow measurements and by 11 borehole measurements at one land site there is a continuous transition from very high deep sea heat flow through intermediate values on the terrace to low continental heat flow the deep sea values are scattered probably reflecting hydrothermal circulation in the crust but their mean is in agreement with the theoretical value for the 7 ma deep sea oceanic crust the mean heat flow at the land site of 47 mw m 2 is similar to the average for the coast insular belt to the south and east the measurements on the 30 km wide 2 km deep terrace are less scattered and much lower than those on the deep sea floor the main thermal contrast is at the seaward edge of the terrace rather than near the coast where the earthquakes of the main plate boundary are located numerical models suggest that no reasonable steady stat