productivity controlled cold water coral growth periods during the last glacial off mauritania abstract article history received 17 june 2010received in revised form 29 october 2010accepted 11 december 2010available online 21 december 2010communicated by g j de langekeywords lopheliacold water coralscarbonate moundsbanda mound provincenw africaprimary productivity cold water corals are widely distributed along the atlantic continental margin with varying growth patternsinrelationtotheirspeci cenvironment here weinvestigatethelong termdevelopmentofcold watercoralsthat once thrived on a low latitude 17 40 n cold water coral mound in the banda mound province offmauritania duringthelastglacial interglacialcycle u thdatesobtained from20specimensofthecold watercoral lophelia pertusa revealed three distinct periods of coral growth during the last glacial at 65 to 57 kyr bp 45 to 32 kyr bp and 14 kyr bp thus comprising the cool periods of marine isotopic stages mis 2 4 thesecoral growth periods occur during periods of increased productivity in the region emphasizing thatproductivity seems to be the major steering factor for coral growth off mauritania which is one of the majorupwelling regions in the world this pattern differs from the well studied coral mounds off ireland where thecurrent regime predominantly in uences the prosperity of the cold water corals moreover coral growth offireland takes place during rather warm interglacial and interstadial periods whereas off mauritania coralgrowth is restricted to glacial and stadial periods however the on mound sedimentation patterns offmauritania largely resemble the observations reported from the irish mounds the bulk of the preservedsediments derives from periods of coral growth whereas during periods without corals hardly any netsedimentation or mound growth took place 2011 elsevier b v all rights reserved

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

precise determination of the open ocean 234u 238u composition uranium has a long residence time in the open oceans and therefore its salinity normalized u concentration and 234u 238u activity ratio expressed herein as 234u the deviation from secular equilibrium are assumed to be uniform the marine 234u 238u activity ratio is currently in radioactive disequilibrium and shows a 15 excess of 234u with respect to the secular equilibrium value due to continuous input from riverine sources knowledge of the marine 234u and how it has evolved through the quaternary is important for validating age accuracy in the u series dating of marine carbonates which is increasingly relied upon for providing a chronological basis in paleoclimate research however accurate and precise measurements of 234u are technically difficult thus existing compilations of the open ocean 234u value vary by up to 10 and the assumed uniformity in the oceanic 234u remains to be confirmed using mc icpms techniques and a suite of multiple faraday cups instead of the typical configurations based on a combined faraday cup multiplier array a long term reproducibility of better than 0 3 2 is achieved for 234u measurements applying these very high precision techniques to open ocean seawater samples an average 234u of 146 8 0 1 2 m n 19 is obtained these high precision seawater measurements yield an external reproducibility of better than 0 4 2 and show that the open oceans have a uniform 234u on the sub level these new data constrain the vertical mixing time of the open oceans to less than 1000 years

surface rupture during the 2010 mw 7 1 darfield canterbury earthquake implications for fault rupture dynamics and seismic hazard analysis the september 2010 m w 7 1 darfield canterbury earthquake in new zealand is one of the best recorded earthquakes of this magnitude the earthquake occurred on a previously unidentified fault system and generated a 29 5 0 5 km long surface rupture across a low relief agricultural landscape high accuracy measurements of coseismic displacements were obtained at over 100 localities along the greendale fault maximum net displacement d max 5 3 0 5 m and average net displacement d avg 2 5 0 1 m are anomalously large for an earthquake of this m w d max surface rupture length srl and d avg srl ratios are among the largest ever recorded for a continental strike slip earthquake geologically derived estimates of moment magnitude m w g are less than the seismologically derived m w derived using widely employed srl m w scaling regressions m w g is greater than m w using d max and d avg m w regressions the geologically derived static stress drop of 13 9 3 7 mpa provides a context with which to compare this earthquake rupture to interplate and intraplate ruptures of similar m w this data set provides fundamental information on fault rupture processes relevant to seismic hazard modeling in this region and analogous settings globally

mapping crustal stress and strain in southwest british columbia 1 this paper investigates the orientation and sources of stress in the forearc of the cascadia subduction zone in southwest british columbia using bayesian inversion results from focal mechanism data and comparing results with gps derived short term strain rates the subduction margin in this region includes a change in orientation from n s in washington state to nw se in british columbia over 1000 focal mechanisms from north american crustal earthquakes have been calculated to identify the dominant style of faulting and 600 were inverted to estimate the principal stress orientations and the stress ratio our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench from approximately margin normal along the coast to approximately margin parallel 100 150 km inland from the coast comparing stress orientations with gps data we relate the margin normal stress direction to subduction related strain rates due to the locked interface between the north american and juan de fuca plates just west of vancouver island further from the margin the plates are coupled less strongly and the margin parallel maximum horizontal compressive stress in the north american plate relates to the northward push of the oregon block which is also observed in the horizontal shortening direction of the residual strain rates after the subduction component is removed

holocene surface rupture history of an active forearc fault redefines seismic hazard in southwestern british columbia canada author s morell kd regalla c amos c bennett s leonard l graham a reedy t levson v telka a

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

variability of cold water coral mounds in a high sediment input and tidal current regime straits of florida cold water coral mound morphology and development are thought to be controlled primarily by current regime this study however reveals a general lack of correlation between prevailing bottom current direction and mound morphology i e footprint shape and orientation as well as current strength and mound size i e footprint area and height these findings are based on quantitative analyses of a high resolution geophysical dataset collected with an autonomous underwater vehicle from three cold water coral mound sites at the toe of slope of great bahama bank the three sites 80 km2 total have an average of 14 mounds km 2 indicating that the great bahama bank slope is a major coral mound region at all three sites living coral colonies are observed on the surface of the mounds documenting active mound growth morphometric analysis shows that mounds at these sites vary significantly in height 1 to 83 m area 81 to 6 00 000 m2 shape mound aspect ratio 0 1 to 1 and orientation mound longest axis 0 to 180 the autonomous underwater vehicle measured bottom current data depict a north south flowing current that reverses approximately every six hours the tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity an additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites at most locations sedimentation rate lags slightly behind mound growth rate causing mounds to develop into large structures where sedimentation rates are higher than mound growth rates sediment partially or completely buries mounds the spatial distribution and alignment of mounds can also be related to gravity mass deposits as indicated by geomorphological features for example slope failure and linear topographic highs in the three dimensional bathymetry in summary variability in sedimentation rates current regime and underlying topography produce extraordinarily high variability in the distribution development and morphology of coral mounds on the great bahama bank slope

the skipjack island fault zone an active transcurrent structure within the upper plate of the cascadia subduction complex abstract the skipjack island fault zone has been mapped in the san juan islands between vancouver island canada and the washington state mainland usa a decade ago interpretation of multibeam sonar seafloor imagery revealed that skipjack island an east west striking sedimentary bedrock outcrop was a fault controlled structural feature a major fault separates skipjack island from a deformed sedimentary bedrock outcrop on the seafloor to the north recently the skipjack island fault zone s morphology and extent have been explored both to the west and east of the island using multibeam echosounder bathymetry seismic reflection profiles and sediment cores the character of the skipjack island fault zone is well defined locally by the interpreted seismic reflection profiles which show active faults that displace sediments deposited since the last glacial maximum the central part of the fault zone near skipjack island appears as a near vertical structure in the shallow subsurface that has been subjected to left lateral motion as evidenced by a bedrock exposure on the seabed north of the island where folded strata bend eastward against the fault the result of drag from fault motion interpretations of recent geophysical data suggest an extension of the skipjack island fault zone farther to the west where it trends towards and possibly connects with the fulford fault on vancouver island and to the east where it either terminates north of lummi island or continues eastward onto the mainland the skipjack island fault zone is interpreted to be the northern boundary of the san juan archipelago with the devils mountain fault zone being the southern boundary both fault zones represent the longest continuous faults of the san juan archipelago this newly mapped fault zone and its zone of deformation to the north may represent the northern boundary of the cascadia forearc potential sesimicity of the skipjack island fault zone and its proximity to the steep unstable northeastern side of orcas island and the southern front of the fraser river delta poses a geohazads problem in the form of earthquakes landslides submarine slides and tsunamis

seismicity relocation and fault structure near the leech river fault zone southern vancouver island relatively low rates of seismicity and fault loading have made it challenging to correlate microseismicity to mapped surface faults on the forearc of southern vancouver island here we use precise relocations of microsciesmicity integrated with existing geologic data to present the first identification of subsurface seismogenic structures associated with the leech river fault zone lrfz on southern vancouver island we used the hypodd double difference relocation method to relocate 1253 earthquakes reported by the canadian national seismograph network cnsn catalog from 1992 to 2015 our results reveal an 8 10 km wide nne dipping zone of seismicity representing a subsurface structure along the eastern 30 km of the terrestrial lrfz and extending 20 km farther eastward offshore where the fault bifurcates beneath the juan de fuca strait using a clustering analysis we identify secondary structures within the nne dipping fault zone many of which are sub vertical and exhibit right lateral strike slip focal mechanisms we suggest that the arrangement of these near vertical dextral secondary structures within a more general ne dipping fault zone located 10 15 km beneath the leech river fault lrf as imaged by lithoprobe may be a consequence of the reactivation of this fault system as a right lateral structure in crust with a pre existing nne dipping structural fabric our results provide the first confirmation of active terrestrial crustal faults on vancouver island using a relocation method we suggest that slowly slipping active crustal faults especially in regions with pre existing foliations may result in microseismicity along fracture arrays rather than along single planar structures

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

sea level change and paleogeographic reconstructions southern vancouver island british columbia canada abstract forty eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern vancouver island british columbia sea level fell rapidly from its high stand of about 75 m elevation just before 14 000 cal bp 12 000 radiocarbon yrs bp to below the present shoreline by 13 200 cal bp 11 400 radiocarbon years bp the sea fell below its present level 1000 years later in the central strait of georgia and 2000 years later in the northern strait of georgia reflecting regional differences in ice sheet retreat and downwasting direct observations only constrain the low stand to be below 11 m and above 40 m analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the cascadia subduction zone however places the low stand at 30 5 m at about 11 200 cal bp 9800 bp the inferred low stand for southern vancouver island when compared to the sea level curve previously derived for the central strait of georgia to the northwest generates differential isostatic depression that is consistent with the expected crustal response between the two regions morphologic and sub bottom features previously interpreted to indicate a low stand of 50 to 65 m are re evaluated and found to be consistent with a low stand of 30 5 m submarine banks in eastern juan de fuca strait were emergent at the time of the low stand but marine passages persisted between southern vancouver island and the mainland the crustal uplift presently occurring in response to the late pleistocene collapse of the southwestern sector of the cordilleran ice sheet amounts to about 0 1 mm yr the small glacial isostatic adjustment rate is a consequence of low viscosity mantle in this tectonically active region

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

gps deformation in a region of high crustal seismicity n cascadia forearc we estimate the rate of crustal deformation in the central and northern cascadia forearc based on a combination of existing global positioning system gps velocity data along the cascadia subduction zone gps strain rates and velocities show that the northwestern washington southwestern british columbia region is currently shortening at 3 3 5 mm yr 31 in a n s direction in good agreement with inference from crustal earthquake statistics on the longterm the shortening rate is 5 6 mm yr 31 providing that the subduction related interseismic loading of the margin is purely elastic compared to the velocity of the oregon forearc with respect to north america v 7m m yr 31 this indicates that most of the forearc motion is accommodated in the puget georgia basin area corresponding to the main concentration of crustal seismicity the difference between the current and long term shortening rates may be taken up during subduction megathrust earthquakes thus these events could produce a sudden increase of n s compression in the puget sound region and could trigger major seattle fault type crustal earthquakes published by elsevier science b v

late mesozoic and possible early tertiary accretion in western washington state the helena haystack melange and the darrington devils mountain fault zone the helena haystack melange hh melange and coincident darrington devils mountain fault zone ddmfz in northwestern washington separate two terranes the northwest cascade system nwcs and the western and eastern melange belts wemb the two terranes of paleozoic and mesozoic rocks superficially resemble each other but record considerable differences in structural and metamorphic history the hh melange is a serpentinite matrix melange containing blocks of adjacent terranes but also exotic blocks of schistose metavolcanic rocks and jurassic tonalite and associated amphibolite the hh melange must have formed between early cretaceous and late middle eocene time because it contains tectonic clasts of early cretaceous shuksan greenschist and is overlain by late middle eocene sedimentary and volcanic rocks less certain constraints on its age are a tectonic clast of metarhyolite that yields 90 ma metamorphic ages and the presumption that the melange was emplaced before the outboard olympic terrane arrived at about 50 ma the apparent continuity of the hh melange and the decatur terrane of the san juan islands suggests that the melange is the strongly tectonized equivalent of the fidalgo ophiolite the out crop pattern suggests that the hh melange overlies rocks of the nwcs and it may have formed when the wemb terranes were thrust over rocks of the nwcs much of the exposed belt of the hh melange is overlain by late middle eocene feldspathic sandstone and volcanic rocks of the barlow pass volcanics of vance 1957a which are cut by numerous faults of the ddmfz paralleling the melange the barlow pass volcanics appear to overlie the straight creek fault without large offset but a displaced exotic block of amphibolite with attached early or early middle eocene sandstone in the melange suggests that strike slip movement along the ddmfz was synchronous with movement on the straight creek fault and stretched cobbles in the conglomerates of the barlow pass volcanics suggest post straight creek movement the possible continuation of the ddmfz to the northwest as the san juan and the west coast faults on vancouver island suggests that the structure has had a major role in the emplacement of all the westernmost terranes in the pacific northwest this major suture is strongly bowed to the northeast opposite the great oroclinal bend of the olympic terrane suggesting that the emplacement of that terrane may have deformed a once straighter strike slip zone

the southern whidbey island fault an active structure in the puget lowland washington information from seismic reflection profiles outcrops boreholes and potential field surveys is used to interpret the structure and history of the southern whidbey island fault in the puget lowland of western washington this northwest trending fault comprises a broad as wide as 6 11 km steep northeast dipping zone that includes several splays with inferred strike slip reverse and thrust displacement transpressional deformation along the southern whidbey island fault is indicated by along strike variations in structural style and geometry positive flower structure local unconformities out of plane displacements and juxtaposition of correlative sedimentary units with different histories the southern whidbey island fault represents a segment of a boundary between two major crustal blocks the cascade block to the northeast is floored by diverse assemblages of pre tertiary rocks the coast range block to the southwest is floored by lower eocene marine basaltic rocks of the crescent formation the fault probably originated during the early eocene as a dextral strike slip fault along the eastern side of a continental margin rift bending of the fault and transpressional deformation began during the late middle eocene and continues to the present oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation evidence for quaternary movement on the southern whidbey island fault includes 1 offset and disrupted upper quaternary strata imaged on seismic reflection profiles 2 borehole data that suggests as much as 420 m of structural relief on the tertiary quaternary boundary in the fault zone 3 several meters of displacement along exposed faults in upper quaternary sediments 4 late quaternary folds with limb dips of as much as 9 5 large scale liquefaction features in upper quaternary sediments within the fault zone and 6 minor historical seismicity the southern whidbey island fault should be considered capable of generating large earthquakes m s 7 and represents a potential seismic hazard to residents of the puget lowland

evidence for late holocene earthquakes on the utsalady point fault northern puget lowland washington trenches across the utsalady point fault in the northern puget lowland of washington reveal evidence of at least one and probably two late holocene earthquakes the teeka and duffers trenches were located along a 1 4 km long 1 to 4 m high northwest trending southwest facing topographic scarp recognized from airborne laser swath mapping glaciomarine drift exposed in the trenches reveals evidence of about 95 to 150 cm of vertical and 200 to 220 cm of left lateral slip in the teeka trench radiocarbon ages from a buried soil a horizon and overlying slope colluvium along with the historical record of earthquakes suggest that this faulting occurred 100 to 400 calendar years b p a d 1550 to 1850 in the duffers trench 370 to 450 cm of vertical separation is accommodated by faulting 210 cm and folding 160 to 240 cm with probable but undetermined amounts of lateral slip stratigraphic relations and radiocarbon ages from buried soil colluvium and fissure fill in the hanging wall suggest the deformation at duffers is most likely from two earthquakes that occurred between 100 to 500 and 1100 to 2200 calendar years b p but deformation during a single earthquake is also possible for the two earthquake hypothesis deformation at teeka trench in the first event involved folding but not faulting regional relations suggest that the earthquake s were m 6 7 and that offshore rupture may have produced tsunamis based on this investigation and related recent studies the maximum recurrence interval for large ground rupturing crustal fault earthquakes in the puget lowland is about 400 to 600 years or less

radiocarbon age constraints on rates of advance and retreat of the puget lobe of the cordilleran ice sheet during the last glaciation abstract calibrated radiocarbon dates of organic matter below and above till of the last fraser glaciation provide limiting ages that constrain the chronology and duration of the last advance retreat cycle of the puget lobe in the central and southeastern puget lowland seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17 420 90 cal yr b p which is the closest limiting age for arrival of the glacier near the latitude of seattle a time distance curve constructed along a flowline extending south from southwestern british columbia to the central puget lowland implies an average glacier advance rate of ca 135 m yr the glacier terminus reached its southernmost limit ca 16 950 yr ago and likely remained there for ca 100 yr in the vicinity of seattle where the glacier reached a maximum thickness of 1000 m ice covered the landscape for ca 1020 yr postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16 420 cal yr b p and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum the average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes

structural variation along the devil s mountain fault zone northwestern washington the eastern juan de fuca strait is subject to long term north south oriented shortening the observed deformation is interpreted to result from the northward motion of the oregon block which is being driven north by oblique subduction of the oceanic juan de fuca plate seismic data acquired during the seismic hazards investigation in puget sound survey are used with coincident first arrival tomographic velocities to interpret structural variation along the devil s mountain fault zone in the eastern juan de fuca strait the primary fault of the devil s mountain fault zone developed at the northern boundary of the everett basin during north south oriented tertiary compression interpretation of seismic reflection data suggests that based on their similar geometry including the large magnitude of pre tertiary basement offset the primary fault of the devil s mountain fault west of 122 95 w and the utsalady point fault represent the main fault of the tertiary devil s mountain fault zone the tertiary

holocene faulting in the bellingham forearc basin upper plate deformation at the northern end of the cascadia subduction zone 1 the northern cascadia forearc takes up most of the strain transmitted northward via the oregon coast block from the northward migrating sierra nevada block the north south contractional strain in the forearc manifests in upper plate faults active during the holocene the northern most components of which are faults within the bellingham basin the bellingham basin is the northern of four basins of the actively deforming northern cascadia forearc a set of holocene faults drayton harbor birch bay and sandy point faults occur within the bellingham basin and can be traced from onshore to offshore using a combination of aeromagnetic lineaments paleoseismic investigations and scarps identified using lidar imagery with the recognition of such holocene faults the northernmost margin of the actively deforming cascadia forearc extends 60 km north of the previously recognized limit of holocene forearc deformation although to date no holocene faults are recognized at the northern boundary of the bellingham basin which is 15 km north of the international border there is no compelling tectonic reason to expect that holocene faults are limited to south of the international border

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

azimuth dependent amplification of weak and strong ground motions within a fault zone nocera umbra central italy 1 during three moderate magnitude earthquakes occurred in september october 1997 in the central apennines italy accelerations larger than 0 5 g were recorded in the town of nocera umbra 10 to 15 km n nw of the epicenters the accelerograph is sited in a fault zone close to a n30 e tectonic contact six temporary seismological stations installed across the fault recorded 82 aftershocks occurred in two seismogenic zones the colfiorito sellano area s se of the array and the gualdo tadino area to the north the array data reveal large variations in terms of both peak ground motions and spectral amplitudes within the fault zone amplifications show a strong dependence on the source azimuth at the accelerograph site the effects are particularly large for events from s se peak ground motions are a factor of 14 larger than those of a reference site and conventional spectral ratios attain amplitudes as large as 50 at 7 hz along the n30 e direction of motion parallel to the strike of the fault nineteen strong motion accelerograms were then used to compare ground motion properties between weak and strong events up to m 0 1 2 x 10 25 dyn cm a particle motion analysis shows that the directional effect is also present in the strongest motions even though the amplification of peak ground motion decreases when m 0 increases results from stochastic simulations indicate that such a behavior is not due to nonlinearity applying the empirical weak motion transfer functions in a purely linear model the observed peak ground motions of the largest events are fit satisfactorily

analysis of field performance the thunder bay tunnel a numerical method for the calculation of the distribution of displacements for tunnelling in clays has been developed the method employs an orthotropic elastic perfectly plastic soil model that takes into account various sources of ground loss and soil lining interaction both undrained and drained analyses have been carried out and the results are compared with the measured soil displacements of two instrumented arrays at the thunder bay tunnel it is shown that the range of maximum settlements the shape of the settlement troughs and the pore pressure change as well as the magnitude and direction of spatial displacements obtained from the analyses compare reasonably well with the results of field measurements for both short and long term conditions key words tunnelling clays anisotropy elastic plastic displacements settlement trough thunder bay tunnel

coral mound development at the campeche cold water coral province southern gulf of mexico implications of antarctic intermediate water increased influence during interglacials abstract coral mounds formed by framework forming scleractinian cold water corals cwc mainly lophelia pertusa are a common seabed feature along the atlantic continental margins while coral mound areas in the ne atlantic reveal a climate dependent temporal pattern of cwc occurrence and mound aggradation that is related to distinct environmental conditions e g productivity water mass properties hydrodynamics the long term development of cwc and coral mounds at the western side of the atlantic is less well documented and understood here we present a 260 kyr coral record from the recently described campeche cwc province in the southern gulf of mexico combined with a reconstruction of the paleo environmental conditions for the last 140 kyr uranium series dating of 26 coral samples reveals that cwc growth predominantly coincided with interglacial periods highest vertical mound aggradation rates of 34 to 40 cm kyr 1 occurred during the holocene the reduced occurrence of cwc and the concurrent almost complete stagnation in mound aggradation during glacial periods could be linked to a diminished presence of antarctic intermediate water at those intermediate depths in which the coral mounds occur such setting would have caused a less dynamic bottom current regime resulting in a reduced food supply to the cwc along the campeche bank

the devils mountain fault zone an active cascadia upper plate zone of deformation pacific northwest of north america abstract the devils mountain fault zone dmfz extends east to west from washington state to just south of victoria british columbia in the northern strait of juan de fuca of canada and the usa recently collected geophysical data were used to map this fault zone in detail which show the main fault trace and associated primary and secondary conjugate strands and extensive northeast southwest oriented folding that occurs within a 6 km wide deformation zone the fault zone has been active in the holocene as seen in the offset and disrupted upper quaternary strata seafloor displacement and deformation within sediment cores taken close to the seafloor expression of the faults data suggest that the present dmfz and the re activated leech river fault may be part of the same fault system based on the length and previously estimated slip rates of the fault zone in washington state the dmfz appears to have the potential of producing a strong earthquake perhaps as large as magnitude 7 5 or greater within 2 km of the city of victoria

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

interaction between local tectonics and glacial unloading on the pacific margin of canada abstract variations in late quaternary coastal deformation along the pacific margin of canada reflect not only differences in glacial history but also local non glacial tectonics a forebulge developed to the north in the queen charlotte basin qcb from 13 2 until after 9 7 ka bp resulting in exposure of the currently submerged shelf whereas similar exposure was not evident to the south in the georgia basin a semi quantitative effective elastic lithosphere thickness of between 10 and 20 km is estimated for the qcb we propose that this warm relatively thin lithosphere combined with tectonic movement influenced crustal displacement particularly the decoupling of the north american plate along the queen charlotte qc fault which may have allowed the qcb to behave like a hinge in response to glacial unloading this would explain large magnitude crustal tilting 2 1 m km 1 observed adjacent to the qc fault the 50 m of depression observed in the early and mid holocene may imply that the western edge of the north america plate flexed down below present elevation producing a second wave of response to ice loading and unloading