coulomb stress changes following the 2012 mw 7 8 haida gwaii canada earthquake implications for seismic hazard this article examines spatial changes to the local stress field resulting from the 28 october 2012 m w 7 8 haida gwaii earthquake off the west coast of moresby island british columbia this event occurred on a northeast dipping potentially blind thrust fault rather than on the subvertical queen charlotte fault qcf that represents the pacific north american plate boundary this was the largest earthquake along the canadian portion of this plate boundary since the 1949 m s 8 1 queen charlotte earthquake the u s geological survey coulomb software is used to quantitatively estimate the effect of the mainshock on the background stress field the known aftershock nodal planes and the nearby qcf we use two different mainshock finite fault models both of which are seismologically derived by lay et al 2013 and hayes 2013 separately and subsequently adapted by k wang to account for the motion detected at four nearby global positioning system stations see nykolaishen et al 2015 for more information we also use the best located set of aftershocks with information provided by a temporary array of ocean bottom seismometers results indicate an apparent clustering of aftershocks slightly seaward of the main thrust which is consistent with the modeled zone of promoted normal failure likely related to extension in the footwall using existing models we found a high number of aftershocks to be consistent with triggering by the mainshock suggesting that static stress is a dominant control in the months following a large earthquake in this area further we find loading greater than the triggering threshold on the qcf in an area interpreted as a seismic gap this work improves understanding of the evolving seismic hazard along the queen charlotte margin and tests the usefulness of coulomb modeling in this complex tectonic environment online material figures of focal mechanisms and maximum coulomb stress change and table of aftershock moment tensor parameters

anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

wave current bottom shear stresses and sediment resuspension in cleveland bay australia the bottom sediment resuspension is an important process in cleveland bay north australia hydrodynamics and suspended sediment concentrations ssc were measured from january to april 1993 during this field work two high sediment resuspension events were observed an iterative method of calculating the bottom shear stress under wave current motion has been applied using the calculated bottom shear stresses the resuspension mechanisms of bottom sediment in cleveland bay has been investigated by analysing data collected during two periods in january and march 1993 swell has been found to be the most important factor in sediment suspensions for both high ssc events wind waves have little effect on ssc levels tidal currents are too weak to stir up bottom sediment particles into the flow but affect the detailed ssc structure by tidal convection the critical shear stress for sediment resuspension in cleveland bay is about 2 0 n m2

triassic to neogene geologic evolution of the queen charlotte region a wealth of new geological and geophysical data from recent studies of the queen charlotte region are integrated into a coherent model in this paper we summarize these new studies and discuss possible correlations with other areas four tectonostratigraphic divisions are distinguished by stratigraphic structural and magmatic character and each is separated by a major unconformity the oldest division comprises widely distributed upper paleozoic through middle jurassic strata of wrangellia that accumulated in volcanic arc and stable shelf and basinal settings no significant deformation occurred in the queen charlotte islands region during the accumulation of these rocks a middle and upper jurassic assemblage comprises two plutonic suites and volcanic and epiclastic rocks the unconformity below the middle and upper jurassic assemblage marks a regional southwest vergent contractional deformation that is the most significant mesozoic or cenozoic deformation in the region jurassic plutons in the que

the winona basin structure and tectonics a compilation of published and new geophysical data from the winona basin off northern vancouver island has allowed a detailed interpretation of the sedimentary and tectonic history of the region to be made the basin is forming as a result of the asymmetric subsidence of a recently isolated lithospheric block that is slowly converging with the continental margin the crust beneath the basin is young 1 5 ma increasing in age from southeast to northwest and of normal oceanic thickness it is virtually non magnetic however probably because of its having been rapidly buried by turbidite sedimentation subsidence of the basin and uplift of the paul revere ridge began in the early pleistocene ca 1 8 ma and since that time up to 8 km of turbidite sediments has accumulated in the basin the nature of the fanning of the deposits suggests that the basin has been kept full throughout its history the minimum average supply rate necessary to accomplish this is about 70 106 mg year 1 this pleistocene ave

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

correlation of plate motions with continental tectonics laramide to basin range some of the major tectonic and magmatic events of the last 150 ma in the western cordillera can be correlated with a new model for the displacement histories between western north america and adjacent oceanic plates sierra nevada plutonism ended and laramide compression began during increasingly rapid convergence of the farallon plate with north america and during a moderate increase in the westward motion of north america in the hotspot reference frame the end of the laramide and beginning of widespread arc magmatism and extension correlates with slowing of both of these motions the spectacular slowing of faralion north america convergence is attributed to the decreasing age of the farallon plate entering the trench and thus to a change from negative to positive buoyancy the transition from widespread arc related magmatism and rapid extension to basaltic volcanism and moderate extension in the basin and range province finds no ready explanation in the plate motions of the pacific basin a change to oblique spreading in the basin and range province accompanied growth in length of the san andreas fault as the mendocino triple junction progressed northward

wave attenuation in the shallows of san francisco bay abstract waves propagating over broad gently sloped shallows decrease in height due to frictional dissipation at the bed we quantified wave height evolution across 7 km of mudflat in san pablo bay northern san francisco bay an environment where tidal mixing prevents the formation of fluid mud wave height was measured along a cross shore transect elevation range 2 m to 0 45 m mllw in winter 2011 and summer 2012 wave height decreased more than 50 across the transect the exponential decay coefficient was inversely related to depth squared 6 10 4 h 2 the physical roughness length scale kb estimated from near bed turbulence measurements was 3 5 10 3 m in winter and 1 1 10 2 m in summer estimated wave friction factor f w determined from wave height data suggests that bottom friction dominates dissipation at high rew but not at low rew predictions of near shore wave height based on offshore wave height and a rough formulation for fw were quite accurate with errors about half as great as those based on the smooth formulation for fw researchers often assume that the wave boundary layer is smooth for settings with fine grained sediments at this site use of a smooth fw results in an underestimate of wave shear stress by a factor of 2 for typical waves and as much as 5 for more energetic waves it also inadequately captures the effectiveness of the mudflats in protecting the shoreline through wave attenuation

in situ study of the spatiotemporal variability of sediment erodibility in a microtidal estuary abstract seabed erosion is a vital process for sediment transport in estuaries and coasts in this study we investigated the seabed erosion process and its spatiotemporal variability in the pearl river estuary china via in situ observations and laboratory experiments it is found that the seabed was more erodible in the channel than at the shoal in most cases due to the difference in sediment size in a neap spring neap tidal cycle a laminated seabed with different sediment ages was inferred to form due to deposition on flood tides and erosion on ebb tides the seabed was more erodible during spring tides than neap tides because of the difference in sediment availability at the unconsolidated fresh layer furthermore the erosion curve showed evident flood ebb asymmetry which was found to be related to the variations of sediment availability and bottom stress besides erosion experiments with different sediment consolidations revealed that sediment erodibility decreased with the growth of consolidation this study promotes our understanding on the spatiotemporal variability of sediment erodibility and has significant implications for simulation and prediction of estuarine sediment transport and morphological evolution

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

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

geological and geophysical characteristics of the tuzo wilson seamounts implications for plate geometry in the vicinity of the pacific north america explorer triple junction seamarc ii imagery seabeam bathymetry seismic reflection profiles and gravity and magnetic data are used to establish the tectonic significance of the tuzo wilson seamounts two submarine volcan

eocene basalts from the yakutat terrane evidence for the origin of an accreting terrane in southern alaska basalts from the yakutat terrane a composite oceanic and continental tectonostratigraphic terrane are chemically diverse large ion lithophile element lile depleted and lile enriched tholeiites interpreted as normal mid ocean ridge and oceanic island basalt that originated on seamounts near the kula farallon spreading center during the early to middle eocene coeval and geochemically similar basalts occurring sporadically in a linear belt from southern vancouver island to the southern oregon coast range are correlative with the yakutat terrane basalts both basaltic sequences were accreted to the continental margin during subduction of the kula farallon ridge and kula plate about 48 ma the yakutat basalts were emplaced along the coast of washington or british columbia the yakutat terrane probably originated during the neogene as a composite terrane when it was sliced off the continental margin and started to move northward along the queen charlotte fairweather transform fault toward its present location in southern alaska

modeling bottom roughness in the presence of wave generated ripples 1 near bottom wave current and microtopography measurements have been obtained at the leo 15 site off the southern coast of new jersey the measurements are used in conjunction with a recently calibrated continental shelf bottom boundary layer model to refine estimates of bottom roughness for a rippled bed under combined wave and current flows in the presence of nearly two dimensional wave generated ripples application of the grant and madsen 1979 type bottom boundary layer model produces estimates of the bottom roughness felt by the current that are several times greater than established formulations for rippled beds under waves modifying one of the primary length scales in the eddy viscosity profiles returns estimates that are more consistent with the wave roughness results application of the roughness model in conjunction with a refined empirical ripple geometry model produces highly accurate estimates of measured shear velocities and apparent roughnesses during a moderate storm the demonstrated accuracy of this simple combined roughness and ripple geometry formulation reveals its utility when considering applications of coupled bottom boundary layer shelf circulation models

spatial and temporal variation in cohesive sediment erodibility in the york river estuary eastern usa a biologically influenced equilibrium modified by seasonal deposition abstract sediment erodibility was measured at three sites in the york river a sub estuary of the chesapeake bay monthly to bimonthly from april 2006 through october 2007 erodibility at the three sites was similar during the summer and fall a site near the estuary mouth maintained this level of erodibility greater than 90 of the time while two sites in the more physically dominated mid estuary region exhibited a consistent and pronounced increase in erodibility in the late winter and spring weak to non existent correlations between bed erodibility solids volume fraction and surficial concentrations of organic matter colloidal carbohydrate and extracellular polymeric substances were not sufficient to explain the observed seasonal pattern in bed erodibility digital x radiographs revealed thick sequences 10 20 cm of laminated sediments at the surface in the middle estuary coincident with the period of highest erodibility and more biologically reworked sediment during the rest of the year suggesting that periodic rapid deposition introduced new sediment that was seasonally easy to erode the finding that seasonal deposition influenced erodibility at the mid estuary sites is consistent with previous results indicating the occasional presence of a secondary turbidity maximum comparison of the biologically reworked but still low erodibility condition in the york to other published chesapeake bay erodibility data revealed a consistent critical shear stress range and profile suggesting that this equilibrium critical stress profile may be representative of other similar estuarine environments in the absence of rapid deposition at relatively low stresses and in the absence of rapid deposition we speculate that burrowing and or pelletization may play a role in maintaining high equilibrium bulk water content without reducing the strength of the surface of the seabed

tertiary extension and tilting in the queen charlotte islands evidence from dyke swarms and their paleomagnetism the queen charlotte islands form the western margin of the tertiary queen charlotte basin which is situated on the western margin of the north american plate they contain seven major dyke swarms of late eocene to miocene age a period when the relative motions of the pacific and the north american plates in this region were dominantly dextral strike slip transform margin with intervals of highly oblique divergence and convergence within each swarm dykes have a systematic trend however trends vary from swarm to swarm indicating that the stress field varied a total of 678 cores 1352 specimens were collected from 129 dykes in six swarms over a distance of about 200 km magnetic stability is variable one hundred and one dykes yielded records of the paleofield data are also reported from an oligocene pluton 5 sites 27 cores 52 specimens and miocene lavas 8 sites 52 cores 101 specimens both normal and reversed magnetizations occur but irrespective of sign the mean directions of remanen

model based interpretation of sediment concentration and vertical flux measurements in a shallow estuarine environment a one dimensional numerical model describing tidally varying vertical mixing and settling was used to interpret sediment concentrations and vertical fluxes observed in the shoals of south san francisco bay by two acoustic doppler velocimeters advs at elevations of 0 36 m and 0 72 m above bed measured sediment concentrations changed by up to 100 g m 3 over the semidiurnal tidal cycle these dynamics were dominated by local resuspension and settling multiple particle class models suggested the existence of a class with fast settling velocities ws of 9 0 10 4 m s 1 in spring and 5 8 10 4 m s 1 in fall and a slowly settling particle fraction ws of 1 10 7 m s 1 in spring and 1 4 10 5 m s 1 in fall modeled concentrations of slowly settling particles at 0 36 m were as high as 20 g m 3 during fall and varied with the spring neap cycle while fine sediment concentrations in spring were constant around 5 g m 3 analysis of in situ water column floc size distributions suggested that floc properties in the lower part of the water column were most likely governed by particle size distribution on the bed and not by coagulation validating our multiple particle size approach a comparison of different sediment bed models with respect to model performance sensitivity and identifiability suggested that the use of a sediment erosion model linear in bottom shear stress b e m b c was the most appropriate choice to describe the field observations when the critical shear stress c and the proportionality factor m were kept constant

the composition and emplacement of basaltic magmas produced during the development of continental margin basins the gulf of california mexico the gulf of california is a region of active ensialic basin development and transform faulting legs 64 and 65 of the deep sea drilling project have demonstrated the diversity of basement stratigraphy drilling at sites 474 482 483 and 485 at the mouth of the gulf recovered massive basaltic flows and occasional pillow lavas and sills whereas drilling in the central part of the gulf in the guaymas basin recovered a sequence of sediments and massive doleritic sills very high sedimentation rates over 1000 m ma are characteristic of the guaymas basin and prevent extrusion of the basaltic magma onto the seafloor thus resulting in at least partial intercalation of oceanic layers 1 and 2 such a process of ocean crust formation could be locally important during the early stages of ocean and marginal basin development when sedimentation rates may be very high over 200 samples of basalts and dolerites from the gulf of california have been analysed by x ray fluorescence and neutron activation techniques basalts from the mouth of the gulf are tholeiitic and contain very low abundances of the more hygromagmatophile more hyg elements k rb ba th ta nb and light ree relative to the hyg elements y zr ti and heavy ree thus resembling depleted n type morb from elsewhere along the e pacific rise epr dolerites from the guaymas basin also have a tholeiitic chemistry and some epr basalt characteristics e g la n sm n

queen charlotte area cenozoic tectonics and volcanism and their association with relative plate motions along the northeastern pacific margin cenozoic relative plate interactions along the queen charlotte margin based on published models for the north america and northeast pacific plates are related to the tectonic and igneous history of the region plate motion models indicate convergence and subduction prior to the eocene since that time there has been transcurrent motion with varying small amounts of oblique extension or compression assuming that the pacific america farallon triple junction was to the south of the region a late miocene or early pliocene about 4 ma to present period of oblique convergence is well resolved the present queen charlotte fault zone along the west coast of the islands may have initiated more recently within the cenozoic transcurrent regime a period of oblique extension in the mid tertiary 36 20 ma in one model is supported by a variety of volcanic and tectonic evidence a small plate motion change at about 20 ma may have resulted in the transfer of the yakutat terrane from the north america plate to the pacific plate and the resulting motion of the terrane northwestward to its present position along the margin of alaska the onset of tertiary masset volcanism that is extensive on the queen charlotte islands corresponds within a few million years to the time of major plate reorganization at 43 ma that has tectonic expression around the entire pacific basin the period of most extensive masset volcanism and plutonism appears to correlate with the model oblique extension in the mid tertiary for one model the geochemistry and physical volcanology of the masset volcanic s are indicative of an extension regime the main syntectonic deposition in the queen charlotte basin skonun formation as inferred from seismic reflection and well data also appears temporally correlated with this time interval of oblique extension a variety of data including plate models dikes normal faults basin subsidence crustal thickness from seismic refraction and present and paleo heat flow indicate mid tertiary crustal extension of at least 20 in the queen charlotte region with up to 150 up to 2 5 in the main queen charlotte basin posttectonic basin subsidence and deposition may correlate with the model time interval of general transcurrent or oblique convergence motion from 20 to 4 ma more recent shortening deformation observed in outcrop and seismic sections of the northern parts of the basin may correlate with plate model oblique convergence from 4 ma to the present the latter convergence is associated with underthrusting that formed a trough or trench and an accretionary sedimentary prism off the west coast of the queen charlotte islands and with inferred uplift and erosion of the western part of the islands

tectonic history of the queen charlotte islands and adjacent areas a model the region including queen charlotte islands hecate strait and queen charlotte sound is underlain by two allochthonous terranes wrangellia and the alexander terrane the suture between them occurs in central graham island and central hecate strait and is coincident with the traces of the sandspit and rennell sound fault zones each of which developed in response to crustal rifting in queen charlotte sound during mid tertiary time the stratigraphic succession comprises four tectonic assemblages 1 the allochthonous assemblages comprise paleozoic rocks of the alexander terrane and upper triassic and jurassic rocks of wrangellia which on the basis of paleomagnetic and biogeographical data are clearly exotic the distribution of these terranes beneath queen charlotte sound and hecate strait is supported by geophysical information and subsurface data obtained from offshore wells 2 the suture assemblage is represented by extremely coarse conglomerates massive graywackes and turbidites of early cretac

reconciling late neogene pacific absolute and relative plate motion changes new models of pacific absolute plate motion relative to hot spots and models of relative plate motion involving the pacific plate all agree there was a significant change in the late neogene chron 3a 5 89 ma reflecting a more northerly absolute motion than previously determined as pacific absolute plate motion became slightly more northerly left stepping transform segments came under compression some left stepping segments became microplates with clockwise rotation others show clear evidence of compressional deformation conversely right stepping transforms came under tension and many developed intratransform spreading centers or show similar evidence for transform magmatism several large left stepping transform offsets represent portions of the nazca plate protruding into the pacific and as such act as obstacles to the more northerly pacific absolute plate motion we suggest these obstructions act to enhance the generally tensile equatorial pacific stress regime caused by distant slab pull as a consequence the greater french polynesia region has experienced diffuse volcanism that increased considerably following the chron 3a plate motion change we propose that since the hawaii emperor bend time the distant pacific slab pull and the friction between the large buoyant ontong java plateau and the northern margin of the australia plate have produced episodes of increased tensile stresses in the equatorial pacific we believe these stress excursions are responsible for much of the intraplate volcanism observed in a wide triangular region from samoa to the east pacific and pacific antarctic rises

simulating sediment transport processes in san pablo bay using coupled hydrodynamic wave and sediment transport models abstract san pablo bay is a tidal sub embayment of the san francisco estuary which is dominated by broad shallow shoals bisected by a deep channel under the conceptual model of sediment transport in san pablo bay proposed by krone 1979 sediment typically enters san pablo bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents numerical simulations of sediment resuspension due to wind waves and the subsequent transport of this sediment by tidal currents show that sediment concentrations and fluxes throughout the channel shoal system result from a complex temporal and spatial interaction of the waves and tides the three dimensional untrim san francisco bay delta model was coupled with the simulating waves nearshore swan wave model and the sedimorph morphological model to develop a three dimensional 3d hydrodynamic wind wave and sediment transport model of san francisco bay and the sacramento san joaquin delta the coupled model was validated using water level velocity wind waves and suspended sediment data collected in san pablo bay and then used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in san pablo bay under a range of tidal and wind conditions the model validation shows this modeling system can accurately predict hydrodynamics waves and suspended sediment concentration in san pablo bay the predicted bottom orbital velocities are elevated across the shoals during large wave events regardless of tidal stage but near low tide orbital velocities are increased even under low to moderate waves sediment fluxes between the shoals and the deeper channel are highest during spring tides and are elevated for up to a week following wave events even though the greatest influence of the wave event occurs abruptly

p wave velocity structure of the earth s crust beneath vancouver island refraction data were recorded from three shot points out to a maximum distance of 330 km as part of the 1980 vancouver island seismic project visp80 these vertical component data are partially reversed and so can be interpreted in terms of two dimensional structures by iterative modeling of p wave travel times and amplitudes the structure of the upper crust is the best constrained part of the model it consists generally of a gradually increasing velocity from 5 3 km s at the surface to 6 4 km s at 2 km depth to 6 75 km s at 15 5 km depth where the velocity increases sharply to 7 km s below 20 km depth the model becomes speculative because the data provide only indirect constraints on velocities at these depths an interpretation that fits the observed times and amplitudes has a low velocity zone in the lower crust and a moho at 37 km depth the only significant departure from this general structure is beneath the central part of vancouver island where the 15 5 km boundary in the model atta

sediment transport in the san francisco bay coastal system an overview abstract the papers in this special issue feature state of the art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal estuarine systems here we focus on the san francisco bay coastal system extending from the lower san joaquin sacramento delta through the bay and along the adjacent outer pacific coast san francisco bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries including a mining legacy channel dredging aggregate mining reservoirs freshwater diversion watershed modifications urban run off ship traffic exotic species introductions land reclamation and wetland restoration the golden gate strait is the sole inlet connecting the bay to the pacific ocean and serves as the conduit for a tidal flow of 8 10 9 m 3 day in addition to the transport of mud sand biogenic material nutrients and pollutants despite this physical biological and chemical connection resource management and prior research have often treated the delta bay and adjacent ocean as separate entities compartmentalized by artificial geographic or political boundaries the body of work herein presents a comprehensive analysis of system wide behavior extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining impact research of g k gilbert in the early 20th century

recent movements of the juan de fuca plate system analysis of the magnetic anomalies of the juan de fuca plate system allows instantaneous poles of rotation relative to the pacific plate to be calculated from 7 ma to the present by combining these with global solutions for pacific america and absolute relative to hot spot motions a plate motion sequence can be constructed this sequence shows that both absolute motions and motions relative to america are characterized by slower velocities where younger and more buoyant material enters the convergence zone pivoting subduction the resistance provided by the youngest portion of the juan de fuca plate apparently resulted in its detachment at 4 ma as the independent explorer plate in relation to the hot spot framework this plate almost immediately began to rotate clockwise around a pole close to itself such that its translational movement into the mantle virtually ceased after 4 ma the remainder of the juan de fuca plate adjusted its motion in response to the fact that the youngest material entering the subduction zone was now to the south differences in seismicity and recent uplift between northern and southern vancouver island may reflect a distinction in tectonic style between the normal subduction of the juan de fuca plate to the south and a complex underplating occurring as the explorer plate is overridden by the continent the history of the explorer plate may exemplify the conditions under which the self driving forces of small subducting plates are overcome by the influence of larger adjacent plates the recent rapid migration of the absolute pole of rotation of the juan de fuca plate toward the plate suggests that it too may be nearing this condition

suspended sediment storm modeling abstract a variety of sediment transporting storms was observed in the hebble long deployment indicating several distinct forcing mechanisms in particular some storms appear to originate locally gross and williams this issue in this paper a simple model of a locally forced storm is presented to elucidate the time dependent dynamics of erosion and deposition events in the deep sea based on these modeling efforts we make the following inferences storms exhibit peak sediment concentration before peak velocity this behavior is due to a limited amount of erodible bed sediment after near instantaneous erosion of the bed is complete fine sediment concentration in the water column drops due to dilution throughout a thickening turbulent mixed layer in the accelerating flow during and immediately after a storm event turbulence intensity above the 40 m thick momentum mixed layer can be sufficient to suspend fine particles in low concentration to elevations of 100 m above bottom or more following the storm the rate of sediment clearing depends on gravitational settling and the potential importance of additional turbulence driven deposition and aggregation mechanisms syn and post storm overthickening of the suspended sediment mixed layer relative to the ekman momentum mixed layer thickness as well as sensitivity of the post storm concentration profile to turbulence driven deposition can explain some complex features of near bed nepheloid layers in the hebble region observed by other workers validation of suspended sediment transport models is based on field observations obtained with light transmissometers transmissometer measurements of suspended sediment concentration depend in turn on calibration of instrument response to both mass concentration and particle size distribution by analyzing the temporal and spatial changes in mass concentrations with the model presented herein we calculate an operational calibration function during hebble storms this calibration function does not change by more than 30 due to particle sorting by turbulent suspension

interactions between waves sediment and turbulence on a shallow estuarine mudflat measurements were collected on a shallow estuarine mudflat in northern san francisco bay to examine the physical processes controlling waves turbulence sediment resuspension and their interactions tides alone forced weak to moderate currents of 10 30 cm s 1 in depths of 0 3 m and maintained a background suspension of 30 50 mg l 1 of fine sediment in the presence of wind waves bottom orbital velocities spanned 20 30 cm s 1 suspended sediment concentrations ssc at 15 and 30 cm above the bed cmab increased by 1 2 orders of magnitude and vertical gradients in ssc were strong enough to produce turbulence limiting stratification with gradient richardson numbers exceeding 0 25 simultaneously turbulent stresses decomposed from wave motions increased by an order of magnitude the apparent contradiction of energetic turbulence in the presence of strong stratification was reconciled by considering the turbulent kinetic energy tke budget in general dissipation and buoyancy flux were balanced by local shear production and each of these terms increased during wave events the classic wave current boundary layer model represented the observations qualitatively but not quantitatively since the velocity profile could not be approximated as logarithmic rather the mean shear was elevated by the stokes drift return flow and wind generated surface stress which diffused sediment upward and limited stratification our findings highlight a pathway for waves to supply energy to both the production and destruction of turbulence and demonstrate that in such shallow depths tke and ssc can be elevated over more of the water column than predicted by traditional models

sediment transport dynamics near a river inflow in a large alpine lake sediment dynamics were investigated in lake maggiore italy with field observations from october to mid december 2012 three moorings were deployed in pallanza bay a small embayment on the western side of the lake near the toce river inflow to measure temperature and currents throughout the water column and suspended sediment concentration ssc was estimated with acoustic instrumentation river intrusions are shown to dominate observed ssc although a small amount of sediment resuspension was observed at the site of the shallowest mooring during a large wind event that produced strong upwelling of the thermocline followed by downwelling although vertical turbulent sediment flux is typically assumed to indicate resuspension and the upward transport of sediment w c 0 downward turbulent sediment flux was observed w c 0 near the bed during the largest observed intrusion event the downward turbulent sediment flux significantly contributes to net deposition rates which are one order of magnitude larger than rates of erosion measured during the two major events observed horizontal transport of sediment occurs in vertically confined layers due to buoyancy driven intrusions beneath the intrusions sediment settles out of the water column at settling rates that appear to be constant with depth based on acoustic doppler current profiler backscatter measurements the effective settling velocities needed to produce the observed vertical transport of ssc during an inflow intrusion are one order of magnitude larger than those due to the stokes settling velocity ws alone particle flocculation and possible convective instabilities may play a role in generating the large observed effective settling rates

wind wave forced fine sediment erosion during the slack water periods in hangzhou bay china the shallow water wave simulation model swan incorporated with a simple fine sediment erosion model is applied to hangzhou bay china to model the horizontal distribution of the maximum bottom orbital velocity and corresponding fine sediment erosion rates induced by 1 southeasterly steady winds 5 20 and 30 m s 2 southwesterly steady winds 5 and 20 m s 3 northwesterly steady winds 5 and 20 m s 4 east southeasterly steady winds 5 and 20 m s 5 easterly steady winds 5 and 20 m s under closed and unclosed boundaries and 6 unsteady winds during the slack water periods results suggest 1 the steady wind wave induced maximum bottom orbital velocities and corresponding fine sediment erosion rates generally increased with the increasing steady winds 2 closed and unclosed boundary conditions had more significant influences on modeled fine sediment erosion rates under 5 m s easterly steady winds than 20 m s and 3 steady and unsteady wind wave induced maximum bottom currents could be significant in eroding fine sediment bed in hangzhou bay the results show implications for geomorphology sedimentology coastal erosion and environmental pollution mitigation in hangzhou bay

winter storms induced high suspended sediment concentration along the north offshore seabed of the changjiang estuary abstract fine grained sediments suspended in coastal waters play an important role in submarine topography evolution and associated environment changes the convergence of suspended sediments concentrated near the seabed results in high sediment concentration and contributes significantly to sediment transport in order to investigate the mechanism triggering high suspended sediment concentration ssc we deployed a tripod to the seabed to obtain in situ bottom boundary layer measurements of sediment dynamics and a buoy to the sea surface to collect meteorological and wave data at the northern changjiang river mouth from december 20 2015 to january 20 2016 the high ssc e g 3 g l events were observed together with fluid mud thicknesses of 4 16 cm near the seabed during neap tides when cold air intrusion generated winter storms and strong waves further we found that the high ssc event was mainly resulted from wind waves and sediment resuspension supported by local benthic fluid mud which was associated with three stages at the setting up stage the winter storm brought long duration of strong waves e g significant wave height 1 5 m more than 15 h resulting in a maximum wave current combined bottom shear stress of 3 2 pa and the increase of ssc to 1 g l at the reinforcement stage the strong waves and bottom shear stress lasted for several hours and further increased the ssc to 3 g l at the final decay stage wind waves and the maximum wave current shear stresses decreased significantly with the disappearance of high ssc thus there was no high ssc event observed even with strong wind waves during spring tides because strong wave duration was too short for the reinforcement process the sediment source for the high ssc events was mainly from bottom fluid mud resuspension as well as the advection transport from the adjacent subaqueous changjiang river delta

amount of extension on small faults an example from the viking graben extension estimates based on palinspastic restoration of only the largest faults in a deformed terrane may be significantly deficient due to neglect of small faults i e unsampled faults most of which have smaller displacements than do sampled faults small faults individually account for little extension but there may be large numbers of them the cumulative extension on small faults can be calculated from the fractal size distributions of fault displacements independent extension estimates support the inference from fault population statistics that small faults account for significant amounts of extension for example restorations of mesozoic faults interpreted from seismic reflection profiles across the viking graben in the north sea yield extension estimates that are only 40 75 of independent estimates the fractal size distribution of fault displacements in the viking graben is consistent with the hypothesis that the remaining 25 60 of extension resulted from displacements on small faults

episodic north america and pacific plate motions the north america plate motion for the period 20 0 m y is modeled by two absolute angular velocity vectors with a change occurring at about 9 m y the model incorporates new geologic constraints based on 1 the recognition of a discontinuity in north america plate motion at 9 m y 2 a reexamination of the iceland and yellowstone hotspot traces 3 improved delineation of the present north america pacific relative motion and 4 a revised history of pacific absolute motion the two stage model is consistent with several features of the late cenozoic geologic history of north america including geological observations relating to tectonism along a large portion of both the eastern and western boundaries of north america this plate model combined with a previously established pacific plate model makes specific predictions concerning the 15 0 m y history of the north america pacific plate boundary which compare favorably with the known history these models together resolve most of the discrepancies previously encountered between absolute and relative motion models of the two plates the implications of the north america plate model are the greatest for those events related to the 9 m y change in its motion among the geologic consequences of this change are rifting in the western united states intense compressional deformation along the northern caribbean plate boundary a hiatus in aleutian arc volcanic activity and a change in the orientation of the lesser antilles arc this picture reinforces the notion that the major plates behave rigidly and transmit stresses over great distances the predictive power of the model may help in interpreting the history of the north america plate boundary in those areas where clear observations are lacking an extra force needs to be applied to a plate to cause a change in plate motion by treating the plate as a rigid spherical shell overlying a uniformly viscous fluid we derive a simple class of forces sufficient to cause a given change in plate motion such force balance considerations indicate that an additional force applied in the northwest pacific region toward the northeast would result in the observed change in north america plate motion this force is surprisingly similar to that which apparently caused a large change in pacific plate motion about 5 m y later we propose that a common mantle process is responsible for both changes and is related to the ability of the northwest pacific subducted lithosphere to enter into the lower mantle

identify the impacts of waves and tides to coastal suspended sediment concentration based on high frequency acoustic observations abstract high frequency measurements of wind waves tides suspended sediment concentration ssc and turbulence were made using an autonomous meteorological station and optical and acoustic instruments over 34 days during january 20 february 23 2016 in heini bay yellow sea the responses of ssc on different dynamic processes are analyzed by decomposing the velocity and ssc fluctuations into wave and turbulent components in the presence of ssc fronts the horizontal advection by the reciprocating tidal flow would cause an asymmetry of ssc in a flood ebb tidal cycle the presence of swells induced intensified sediment resuspension and a flood ebb symmetry of ssc in the bottom boundary layer the net horizontal sediment fluxes were significantly increased in the presence of strong waves significant amount of suspended sediments were taken away from the study area implying the occurrence of coastal erosion

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

late neogene motion of the pacific plate oceanic crust between 38 s and 65 s along the pacific antarctic ridge records a complete history of neogene pacific antarctic motion we have modeled magnetic stages corresponding to portions of isochrons 1 2 2a 3 3a 4 and 5 from 17 high quality marine magnetic traverses of the ridge to determine the neogene finite rotation poles for this plate pair we chose to model velocities over time intervals of about 0 5 m y because this greatly increased the number of estimates of pacific antarctic plate velocity our analysis shows that a change in pacific antarctic relative motion occurred between chron 2a 3 40 ma and the beginning of chron 3 time 3 86 ma we used 203 estimates of pacific antarctic spreading velocity to calculate a 0 3 4 ma and 3 86 10 3 ma euler pole combined with tracks of seamounts that record the passage of the pacific plate over mantle plumes our data show that this change in relative motion corresponds to a change in the absolute motion of the pacific plate with respect to the hotspot frame of reference using these euler poles to calculate pacific antarctic africa north america circuit euler poles show that this recent change in pacific plate absolute motion corresponds to a change from strike slip to transpressive motion along the coastal california pacific north america plate boundary interestingly this age of increased tectonism agrees in time with deformation in new zealand and northern japan

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

variation in fold geometry in the yuso basin northern spain implications for the deformation regime first generation structures in greywackes of the yuso group from the cantabrian mountains of northern spain show a distinct variation in geometry with depth in a regional synclinal structure curavacas and lechada synclines they are easily distinguished from other deformation events in the structurally uppermost level we find flap folds flap folds are recumbent structures with the inverted limb preserved below this level cascade folds are found these structures have a vergence opposite to that of parasitic folds the nomenclature adopted is from harrison and falcon characteristically these structures have shallowly dipping axial surfaces in agreement with the shallow dip of the axial plane regional cleavage in the lowermost structural level upright parasitic folds with a steep cleavage are present the variation in fold geometry is accompanied by a general steepening of the regional cleavage with increasing depth in the absence of overprinting relationships the f1 fold geometries are included in a single deformation event the steepening of the cleavage with depth reflects the change in orientation of the maximum shortening direction from sub vertical in the upper part of the syncline to sub horizontal in the lower part with increasing depth the deformation regime during f changed from bending to buckling the deformation regime on the regional scale however is associated with basement subsidence and passive formation of the regional synclinal structure furthermore the absence of a distinct microfabric for the different f1 folds indicates that on a small scale a similar deformation regime was present we conclude therefore that the scale at which we study a structure only reflects the deformation regime at that particular scale consequently the overall deformation regime cannot be determined from single outcrops or microstructural analysis alone

characteristics of suspended particles at an 11 hour anchor station in san francisco bay california hourly measurements of suspended sediment in situ floc size distributions constituent grain size distributions total concentrations and average particle densities are presented for five depths from an 11 hour anchor station in san francisco bay the flocs formed well sorted distributions with modal sizes between 100 and 500 m whereas the disaggregated sediment was poorly sorted with about the same volume of material in all size classes and relatively little material coarser than 100 m for both types of size spectra concentrations at the coarse end of the size distribution fall off rapidly at a size range which varied with bottom shear stress the settling rates corresponding to the modal floc diameters were generally related to the maximum disaggregated diameters by a square relationship but turbulence appeared to limit floc size in the coarsest samples both the floc and disaggregated grain size vary with total concentration suggesting that flocs are relatively stable entities which do not change during alternating settling and resuspension

queen charlotte fault zone microearthquakes from a temporary array of land stations and ocean bottom seismographs a temporary array of land and ocean bottom seismograph stations was used to accurately locate microearthquakes on the queen charlotte fault zone which occurs along the continental margin of wester

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

sediment resuspension characteristics in baltimore harbor maryland abstract critical bed shear stress for sediment resuspension and sediment erosion rate were measured in situ at sites from inner to outer baltimore harbor using the vims sea carousel clay mineral contents and biological conditions were almost the same at the four study sites the experimental results indicated that the erosion rate increased from the outer harbor toward the inner harbor with a maximum difference of about 10 times at an excess bed shear stress of 0 1 pa the measured critical bed shear stress strongly depended on the existence of a fluff layer it was approximately 0 05 pa if a fluff layer existed and increases to about 0 1 pa in the absence of a fluff layer

turbulence dynamics at the shoal channel interface in a partially stratified estuary abstractturbulence observations at the shoal channel interface in south san francisco bay are described and analyzed in this work profiles of turbulent kinetic energy tke shear production and dissipation rate are estimated from adcp beam velocities over a nine day period during winter 2009 when the estuary was partially stratified the tke shear production profiles are consistent with a tidally driven bottom boundary layer except late in the ebb when shear production intensifies and the region of maximum production is located in the upper half of the water column a simple scaling for the depth averaged tke shear production based on bed friction performs well except during this late ebb period when it fails to predict the peak in shear production which suggests that a mechanism other than bottom drag drives turbulence dynamics during this period the profiles of tke dissipation rates also display a late ebb peak a lateral circulation develops at the shoal channel interface during this late ebb perio

the northern cascadia subduction zone at vancouver island seismic structure and tectonic history the structure and tertiary tectonic history of the northern cascadia subduction zone have been delineated by a series of new multichannel seismic lines acquired across the continental shelf to the

relationships between plate motions and late cretaceous to paleogene magmatism in southwestern alaska four major late cretaceous to paleogene magmatic belts have been recognized in southwestern alaska and tentative boundaries have been drawn for each the belts indicate minimum ages by which the tectonostratigraphic terranes they overprint must have been linked together though there has been significant postmagmatic tectonism the kuskokwim mountains belt 73 60 m y b p the alaska range belt 74 55 m y b p and the gulf of alaska belt 62 57 m y b p all may have been related to a period of rapid north northeastward motion of the kuia plate from about 74 to 56 m y b p the angle of convergence was low with respect to the present orientation of the belts suggesting the possibility of postmagmatic rotation of the belts a higher angle of convergence may have existed with respect to the alaska range belt a probable arc if postmagmatic rotation resulted from 300 400 km of right lateral displacement on the denali fault the gulf of alaska belt is in an anomalous forearc position with respect to the alaska range belt but probably formed by a convergence related mechanism the kuskokwim mountains belt is in an apparent back arc position but the mechanism of its origin is uncertain it may have been part of an unusually broad alaska range arc or less likely it may have been a separate arc magmatic quiescence occurred throughout south western alaska during a period of plate reorganization from about 56 to 43 m y b p a period which began with extremely rapid northward motion of the kuia plate magmatism resumed when the present period of rather slow northwestward pacific plate motion began at about 43 m y b p the aleutian arc probably formed at this time and has been episodically active in about the same location ever since

a sediment budget for the southern reach in san francisco bay ca implications for habitat restoration article i nfo the southbay salt pond restorationproject isoverseeing the restorationof about 6000 haof formercommercial salt evaporation ponds to tidal marsh and managed wetlands in the southern reach of san francisco bay sfb as a result of regional groundwater overdrafts prior to the 1970s parts of the project area have subsided below sea level and will require between 29 and 45 million m 3 of sedimentto raise the surfaceof the subsided areas to elevations appropriate for tidal marsh colonization and development therefore a sufficient sediment supply to the far south sfb subembayment is a critical variable for achieving restoration goals although both major tributaries to far south sfb have been seasonally gaged for sediment since 2004 the sediment flux at the dumbarton narrows the bayward boundary of far south sfb has not been quantified until recently using daily suspended sediment flux data from the gages on guadalupe river and coyote creek combined with continuous suspended sediment flux data at dumbarton narrows we computed a sediment budget for far south sfb during water years 2009 2011 a monte carlo approach was used to quantify the uncertainty of the flux estimates the sediment flux past dumbarton narrows from the north dominates the input to the subembayment however environmental conditions in the spring can dramatically influence the direction of springtime flux which appears to be a dominant influence on the net annual flux it is estimated that up to sev eral millennia may be required for natural tributary sediments to fill the accommodation space of the subsided former salt ponds whereas supply from the rest of the bay could fill the space in several centuries uncertainty in the measurement of sediment flux is large in part because small suspended sediment concentration differences between flood and ebb tides can lead to large differences in total mass exchange using monte carlo simulations to estimate the random error associated with this uncertainty provides a more statistically rigorous method of quantifying this uncertainty than the more typical sum of errors approach the results of this study reinforce the need for measurement of estuarine sediment fluxes over multiple years multiple hydrologic conditions to adequately detail the variability in flux additionally the timing of breaching events for the resto ration project could be tied to annual hydrologic conditions to capitalize on increased regional sediment supply published by elsevier b v

structure beneath queen charlotte sound from seismic refraction and gravity interpretations a combined multichannel seismic reflection and refraction survey was carried out in july 1988 to study the tertiary sedimentary basin architecture and formation and to define the crustal structure and associated plate interactions in the queen charlotte islands region simultaneously with the collection of the multichannel reflection data refractions and wide angle reflections from the airgun array shots were recorded on single channel seismographs distributed on land around hecate strait and queen charlotte sound for this paper a subset of the resulting data set was chosen to study the crustal structure in queen charlotte sound and the nearby subduction zone two dimensional ray tracing and synthetic seismogram modelling produced a velocity structure model in queen charlotte sound on a margin parallel line moho depth was modelled at 27 km off southern moresby island but only 23 km north of vancouver island excluding the approximately 5 km of the tertiary sediments the crust in the latter area is onl

uncertainties and implications of the late cretaceous and tertiary position of north america relative to the farallon kula and pacific plates we present updated global plate reconstructions and calculated uncertainties of the pacific kula and farallon vancouver plates relative to north america for selected times since 68 ma improved magnetic data from the indian ocean decrease the uncertainties in the global plate circuit approach these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots major differences between these results and those of others are due to our use of more detailed africa north america reconstructions separate vancouver and farallon plate reconstructions and the assumption of a rigid antarctica plate during cenozoic time the uncertainties in the relative positions of the pacific and north america plates since the time of anomaly 7 26 ma range up to 100 km in position or from 1 to 3 m y in time if the mendocino triple junction initiated at about 28 5 ma its position would have been at 31 3 n 130 km relative to fixed north america unacceptable overlap of oceanic crust of the pacific plate with continental crust of western north america in the anomaly 10 30 ma reconstruction is a minimum of 340 200 km along an azimuth of n60 e and may be accounted for by basin and range extension pacific north america displacement in the past 20 ma is found to be considerably less than that calculated by fixed hotspot reconstructions farallon vancouver north america convergence velocity decreased greatly between the times of anomalies 24 and 21 56 to 50 ma prior to the 43 ma age of the hawaiian emperor bend and the often quoted 40 ma end of the laramide orogeny a change in direction of farallon north america convergence occurred sometime between 50 and 42 ma and also may not correlate with the time of the hawaiian emperor bend the lack of data from subducted parts of the farallon and kula plates permits many possibilities regarding the position of the kula farallon ridge the age of subducted crust or the position of oceanic plateaus during the laramide orogeny leaving open the question of the relationship between plate tectonic scenarios and tectonic style during laramide time displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed north america during the interval between anomalies 30 31 and 18 68 to 42 ma are found to be pacific plate 1700 200 km northward farallon plate 3200 400 km northeastward vancouver plate 3000 400 km northeastward kula plate if attached to the pacific plate after a24 time 2500 400 km northward

wind enhanced resuspension in the shallow waters of south san francisco bay mechanisms and potential implications for cohesive sediment transport 1 we investigated the driving forces of sediment dynamics at the shoals in south san francisco bay two stations were deployed along a line perpendicular to a 14 m deep channel 1000 and 2000 m from the middle of the channel station depths were 2 59 and 2 19 m below mean lower low water respectively we used acoustic doppler velocimeters for the simultaneous determination of current velocities turbulence sediment concentration and fluxes maximum current shear velocities were 0 015 m s 1 at the station further from the channel closer to the shore and 0 02 m s 1 at the station closer to the channel peak wave induced shear velocities exceeded 0 015 m s 1 at both stations maximum sediment concentrations were around 30 g m 3 during calm periods root mean square wave height 0 10 g m 2 s 1 at the station further from the channel 0 36 m above the bed closer to the channel sediment concentrations and vertical fluxes due to wind wave resuspension were persistently lower maximum concentrations around 50 g m 3 and maximum fluxes around 0 04 g m 2 s 1 most resuspension events occurred during flood tides that followed wave events during low water although wave motions are able to resuspend sediment into the wave boundary layer at low tide the observed large increases in sediment fluxes are due to the nonlinear interaction of wind waves and the tidal currents

deep structure and structural inversion along the central california continental margin from edge seismic profile ru 3 deep penetration seismic reflection profile ru 3 crosses the central california continental margin revealing a subducted oceanic plate a modified accretionary prism and complex structures of the overlying sedimentary basins this structural framework was established by subduction processes during paleogene and earlier time and subsequently was modified by neogene transform motion combined with apparent components of extension and compression subducted rocks are indicated by deep gently dipping reflectors that extend beneath the continental margin for at least 38 km at a depth of about 15 km we interpret the subducted crust as either a part of the pacific plate or more likely a subducted fragment derived from the farallon plate a set of more steeply dipping deep events may indicate faulting within the subducted plate or its boundary with a no slab zone the overlying largely nonreflective layer of accreted material rapidly reaches 10 km in thickness landward of the paleotrench and increases to 15 km in thickness near the coast the santa lucia basin landward of the steep continental slope originated as a slope basin during paleogene subduction the lower strata of this basin were deposited onto and partially incorporated into the accretionary complex the offshore santa maria basin exhibits a variety of compressional structures that formed in the last 3 5 m y and whose locations correspond to an earlier framework of extensional faults structural inversion has occurred in miocene depocenters adjacent to the santa lucia bank fault and at the queenie structure miocene and lower pliocene strata also thicken toward the hosgri fault zone where subsequent compression is characterized by low angle thrusts and folding

basalt geochemistry of the explorer ridge area northeast pacific ocean forty two fragments of young fresh basalts dredged from the explorer ridge paul revere ridge fracture zone and dellwood knolls have been analysed for 34 major minor and trace elements and 87sr 86sr ratios have been determined in seven of the fragments the explorer ridge basalts have major element compositions similar to most mid ocean ridge basalts morb particularly to the iron rich basalts of the southern juan de fuca ridge the basalts exhibit variability in trace element content largely attributable to crystal fractionation at low pressure with respect to morb the incompatible minor and trace elements are weakly to strongly enriched in the explorer samples and are most strongly enriched in basalts from explorer deep adjacent ridge segments erupt basalts with variable incompatible element concentrations and ratios this could be an indicator of a chemically heterogeneous mantle source or may be the result of intermittent injection of enriched magmas from a hotspot beneath explorer deep

evidence of paleogene sedimentation on graham island queen charlotte islands west coast canada the palynomorph taxa ctenosporites eskerensis pesavis tagluensis and tilia spp demonstrate that an unnamed sedimentary unit in the union port louis well and float from mud bay creek skidegate i

basin filling related to the philippine sea plate motion in beppu bay southwest japan abstract strike slip basins are one of the most important accumulation spaces for sediment of terrigenous biogenic and volcanic origins and generally include large amount of event deposits although these event deposits are important basin filling process research on this topic particularly the effects of event deposits is insufficient in this study we discuss sedimentation features based on grain composition and other properties for ca 3000 year periods in beppu bay which is strike slip basin located at the western end of an arc bisecting dextral fault known as median tectonic line mtl associated with the northwestward subduction of the philippine sea plate this sediment is composed of hemipelagic clay and coarser event layers of turbidites referred to as types a b and c ash layers referred to as type d and other referred to as type e the turbidite event layers which accounted for 92 of the total major event layer with 1 cm thickness consist of particles related to volcanism including hydrothermal activity the events control the regional filling rate and transportation of coarse and heavy volcaniclastic materials in particular type a which accounted for 73 of the total major event layer thickness is likely induced by earthquakes related to the mtl according to its age as a result the basin filling processes are controlled mainly by tectonics related to the subduction of the philippine sea plate

modeling stratified wave and current bottom boundary layers on the continental shelf the glenn and grant 1987 continental shelf bottom boundary layer model for the flow and suspended sediment concentration profiles in the constant stress layer above a noncohesive movable sediment bed has been updated the reynolds fluxes for sediment mass and fluid momentum are closed using a continuous time invariant linear eddy viscosity modified by a continuous stability parameter to represent the influence of suspended sediment induced stratification throughout the constant stress region glenn and grant 1987 use a less realistic discontinuous eddy viscosity and neglect the stratification correction in the wave boundary layer for typical model parameters the two models produce currents above the wave boundary layer that are in better agreement than the suspended sediment concentrations within the wave boundary layer the differences are much greater for both the current and the sediment concentration this leads to significant differences in the sediment transport throughout the constant stress layer sensitivities of the updated model were examined on the basis of observed wave and current data acquired during storms on the inner continental shelf comparisons between the stratified and neutral versions of the updated model indicate that the stratified version produces a total depth integrated sediment transport that can be 2 orders of magnitude less than and time averaged shear velocities that can be nearly half of that predicted by the neutral version sensitivities to grain size distributions indicate that even a small amount of finer sediment can stratify the storm driven flows sensitivities to closure constants within the range of reported values also produce up to an order of magnitude variation in sediment transport illustrating the need for dedicated field experiments to refine further estimates of these parameters

reconstructing sediment age profiles from historical bathymetry changes in san pablo bay california abstract sediment age profiles reconstructed from a sequence of historical bathymetry changes are used to investigate the subsurface distribution of historical sediments in a subembayment of the san francisco estuary profiles are created in a grid based gis modeling program that stratifies historical deposition into temporal horizons the model s reconstructions are supported by comparisons to profiles of 137 cs and excess 210 pb at 12 core sites the predicted depth of the 1951 sediment horizon is positively correlated to the depth of the first occurrence of 137 cs at sites that have been depositional between recent surveys reconstructions at sites that have been erosional since the 1951 survey are supported by a lack of detectable 137 cs and excess 210 pb below the upper 6 16 cm of the core a new data set of predicted near surface sediment ages was created to illustrate an application of this approach results demonstrate other potential applications such as guiding the spatial positioning of future core sites for contaminant measurements

a revised estimate of pacific north america motion and implications for western north america plate boundary zone tectonics for the past 20 years much effort has been directed to determining the present day relative motion of the pacific and north american plates using two independent approaches one uses geologic observations and geodetic measurements along the san andreas fault and other faults in the plate boundary zone the other is based on plate motion models that incorporate spreading rates from marine magnetic anomalies transform azimuths and earthquake slip vectors geologic and geodetic studies find two principal elements of deformation slip along the san andreas of 34 mm yr directed n41 w and extension across the basin and range province of about 10 mm yr directed n56 w in contrast plate motion studies find 56 60 mm yr directed n35 w the discrepancy between these estimates a vector of about 15 mm yr oriented nearly due north is often attributed to a combination of slip along faults parallel to the san andreas and shortening normal to it here we revise the estimate of pacific north america motion by analyzing marine magnetic profiles from the gulf of california since 3 ma spreading has averaged 48 mm yr 10 mm yr slower than estimated before and consistent with the 49 mm yr spreading predicted by a new global plate motion model derived without any data along the pacific north america boundary the discrepancy with geodetic and geologic estimates is thus reduced to only 5 mm yr parallel to the san andreas 60 less than estimated before and 7 mm yr of shortening across the san andreas similar to prior estimates these results suggest that strike slip motion on faults west of the san andreas is less than thought before a conclusion consistent with geodetic seismological and other geologic observations

the mt edgecumbe volcanic field alaska an example of tholeiitic and calc alkaline volcanism major element trace element and isotopic composition data for lava samples have been collected from a holocene stratovolcano in southeastern alaska results indicate that a wide variation in chemical compositions exist 48 71 sio 2 10 14 16 mgo and the suite may be divided into two series on the basis of chemical mineralogical and isotopic characteristics the tholeiitic series lavas consist of generally phenocryst poor olivine basalts whose chemical and isotopic compositions are transitional between normal morb and lree enriched lavas of atypical areas such as the azores platform cao is high mgo feo 1 fe 2 o 3 k 2 o rb and sr are low while mgo and ni are high data show that the basalts are lree depleted and sr 87 sr 86 70304 the basalts compose 65 of the volcanic field and crystal fractionation appears to have produced the compositions of the more silicic basalts the calc alkaline series lavas are composed of basaltic andesites andesites and dacites of

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

change in motion of pacific plate at 5 myr bp alignments of volcanoes such as the hawaiian seamount chain record the passage of oceanic plates over mantle plumes or hot spots and changes in the orientation of a seamount chain may indicate changes in the direction of motion of the plate within the hotspot frame of reference1 this hypothesis can be tested for the pacific plate by comparing data from the hawaiian volcanoes with tectonic movements inferred from the geology of adjacent plates we have now found that the motion of the pacific plate changed to a more northerly direction 5 myr ago probably as a result of the detachment of a piece of pacific sea floor which had been subducted beneath the fiji plateau during the tertiary

the queen charlotte islands refraction project part i the queen charlotte fault zone the active margin between the continental north american plate and oceanic pacific plate west of the queen charlotte islands was the site of an extensive onshore offshore seismic refraction project

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

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