post glacial relative sea level isostasy and glacial history in icy strait southeast alaska usa abstract we use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level rsl history in northern southeast alaska rsl fell below its present level around 13 900 cal yr bp suggesting regional deglaciation was complete by then rsl stayed at least several meters below modern levels until the mid holocene when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby glacier bay this fluctuating rsl rise likely reflects the episodic but progressive advance of ice in glacier bay that started around 6000 cal yr bp after that time rsl low stands probably signaled minor episodes of glacier retreat thinning that triggered isostatic rebound and land uplift progressive down fjord advance of the glacier bay glacier during the late holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly only after the glacier reached an exposed position protruding into icy strait ca ad 1750 did its terminus succumb a century before the climate changes that marked the end of the little ice age to the catastrophic retreat that triggered the rapid isostatic rebound and rsl fall occurring today in icy strait

little ice age subsidence and post little ice age uplift at juneau alaska inferred from dendrochronology and geomorphology abstract application of dendrochronology and geomorphology to a recently emerged coastal area near juneau alaska has documented a little ice age lia sea level transgression to 6 2 m above current sea level the rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century based on a sea cliff eroded into late pleistocene glaciomarine sediments land began emerging between a d 1770 and 1790 coincident with retreat of regional glaciers from their lia maximums this emergence has continued since then paralleling regional glacier retreat total juneau uplift since the late 18th century is estimated to be 3 2 m the rate of downward colonization of newly emergent coastline by sitka spruce during the 20th century closely parallels the rate of sea level fall documented by analysis of local tide gauge records 1 3 cm yr regional and glacier bay lia loading and unloading are inferred to be the primary mechanisms driving subsidence and uplift in the juneau area climate change rather then regional tectonics has forced relative sea level change over the last several hundred years

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

tide gauge records of uplift along the northern pacific north american plate boundary 1937 to 2001 1 vertical crustal motions at 15 sites along the northern pacific north america plate boundary are determined using relative sea level changes from tide gauge records our analysis is based on monthly mean sea levels from which barometric pressure and seasonal effects are removed the records are corrected for common mode oceanographic variations these records are statistically examined for non linear behavior related to glacial isostatic tectonic and postseismic effects to estimate land uplift rates the local effect of global sea level rise is removed from the relative sea level rates slow rates of vertical motion are observed along the southern strike slip plate boundary the extremely rapid uplift of the northern strike slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater glacier retreat in glacier bay and regional post little ice age deglaciation isostatic modeling indicates a mantle viscosity of 2 1019 5 1019 pa s similar to that found elsewhere along the pacific north america plate margin at yakutat near the transition of plate motion from strike slip to subduction complex non linear behavior is evident with a significant change in uplift rate following the 1979 st elias earthquake non linear uplift rates are predominant within the 1964 great alaskan earthquake near field rapid uplift at kodiak during a 3 5 year period starting mid 1964 totaled 47 8 cm anchorage seward and seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid 1972 since mid 1972 uplift rates have increased steadily at anchorage seward cordova and valdez during this period nikiski and kodiak show decreasing uplift rates

tsunami history of an oregon coastal lake reveals a 4600 yr record of great earthquakes on the cascadia subduction zone bradley lake on the southern oregon coastal plain records local tsunamis and seismic shaking on the cascadia subduction zone over the last 7000 yr thirteen marine incursions delivered landward thinning sheets of sand to the lake from nearshore beach and dune environments to the west following each incursion a slug of marine water near the bottom of the freshwater lake instigated a few year to several decade period of a brackish 4 salinity lake four additional disturbances without marine incursions destabilized sideslopes and bottom sediment producing a suspension deposit that blanketed the lake bottom considering the magnitude and duration of the disturbances necessary to produce bradley lake s marine incursions a local tsunami generated by a great earthquake on the cascadia subduction zone is the only accountable mechanism extreme ocean levels must have been at least 5 8 m above sea level and the cumulative duration of each marine incursion must have been at least 10 min disturbances without marine incursions require seismic shaking as well over the 4600 yr period when bradley lake was an optimum tsunami recorder tsunamis from cascadia plate boundary earthquakes came in clusters between 4600 and 2800 cal yr b p tsunamis occurred at the average frequency of 3 4 every 1000 yr then starting 2800 cal yr b p there was a 930 1260 yr interval with no tsunamis that gap was followed by a 1000 yr period with 4 tsunamis in the last millennium a 670 750 yr gap preceded the a d 1700 earthquake and tsunami the a d 1700 earthquake may be the fi rst of a new cluster of plate boundary earthquakes and accompanying tsunamis local tsunamis entered bradley lake an average of every 390 yr whereas the portion of the cascadia plate boundary that underlies bradley lake ruptured in a great earthquake less frequently about once every 500 yr therefore the entire length of the subduction zone does not rupture in every earthquake and bradley lake has recorded earthquakes caused by rupture along the entire length of the cascadia plate boundary as well as earthquakes caused by rupture of shorter segments of the boundary the tsunami record from bradley lake indicates that at times most recently 1700 yr b p overlapping or adjoining segments of the cascadia plate boundary ruptured within decades of each other

seismicity in the st elias region of northwestern canada and southeastern alaska abstract low level monitoring in the st elias region between september 1978 and march 1981 has identified two principal zones of seismicity that are consistent with the historical pattern of seismicity at higher magnitude levels the most active zone follows the plate boundary along the coast of southeast alaska a recurrence relation based on completeness over varying time intervals is log n m 0 74 m 3 77 a less active zone is observed generally following the duke river and dalton segments of the denali fault system through the southwest yukon instead of continuing into chatham strait this trend of seismicity turns south into the glacier bay region to connect with the fairweather fault north of cross sound the seismicity and high rate of uplift observed in the glacier bay region is probably the result of convergence across the fairweather fault north of cross sound the recurrence relation for the denali zone is log n m 0 90 m 3 77 a similiar recurrence curve is found for activity with magnitudes down to about 2 0 observed over the 39 month low level monitoring program the rate of activity in the denali zone appeared to decrease for a period of about 1 yr following the 28 february 1979 m 7 2 st elias earthquake the rate of aftershock activity was also found to vary with the b value decreasing throughout the sequence only minor seismicity is observed northeast of the denali fault system in the southwest yukon and east of chatham strait in northwest british columbia a prominent cluster east of juneau near the british columbia border may be related to volcanic activity a 5 week microearthquake survey over a 40 km segment of the denali fault system found activity in a highly faulted zone about 15 km wide at depths of less than about 15 km a composite p nodal solution indicates motion on either east west or north south striking planes neither of which are consistent with the general trend of the denali system in the area an average slip rate of no more than about 1 mm yr is estimated from the seismicity for the denali fault system through the southwest yukon an estimate of the minimum present accumulated elastic strain suggests the potential for a magnitude 6 1 2 earthquake

late neoproterozoic paleogeography of the southeastern new england avalon zone insights from u pb geochronology and paleomagnetism integrated geochronologic and paleomagnetic investigation of the arc related lynn and mattapan volcanic complexes around boston massachusetts establishes a neoproterozoic paleopole for the southeastern new england avalon zone four new u pb zircon dates obtained using isotope dilution and thermal ionization mass spectrometry id tims methods range from 597 4 1 5 ma to 595 7 1 6 ma in agreement with published lynn mattapan results of ca 596 ma the mean direction calculated from the a component of magnetization at nine lynn mattapan sites has a declination d of 319 9 and an inclination i of 57 0 95 7 4 the paleopole based on this mean direction is 206 e 60 n these results pass both reversals and fold tests and are regionally consistent among lithologies that include basalt andesite rhyodacite and rhyolite which represent both volcanic and subvolcanic phases most sites also contain stable b and c magnetic components with directions that suggest ordovician to permian remagnetizations a broadly comparable a component direction with d 109 0 and i 63 4 95 9 4 n 11 samples was obtained from one site in the squantum member of the roxbury conglomerate maximum age of 593 ma overlying the volcanic sequence the lynn mattapan results indicate that southeastern new england occupied a mid latitude position at ca 595 ma similar to those reported from avalonian terranes in maritime canada the most likely peri gondwanan position for avalonia consistent with these paleomagnetic data lies off the west african margin using poles from the east sahara craton egypt and the rio de la plata craton brazil has permitted reconstruction of west gondwana without recourse to laurentian proxies

paleomagnetism of the sierra de las animas complex southern uruguay its implications in the assembly of western gondwana global paleogeographies in the neoproterozoic are poorly known in particular the assembly of gondwana at the end of the proterozoic is controversial in order to constrain the kinematic evolution of the rio de la plata craton a paleomagnetic study was carried out in the vendian to cambrian sierra de las animas magmatic complex exposed in southeastern uruguay 34 7 s 55 3 w one hundred and forty seven samples from 23 sites were studied these included two sites on the vendian glaciogenic sediments of the playa hermosa formation after stepwise af and thermal cleaning a characteristic remanence was isolated at several sites according to the available isotopic data for the complex and the correlation between remanence directions and lithologic type and age two paleomagnetic poles were computed for the sierra de las animas complex sa1 338 1 e 5 9 n dp 19 6 dm 26 7 n 7 sites mean declination 44 5 mean inclination 58 0 95 18 1 with a likely age around 520 ma shows a distribution of vgps that suggests a remanence acquisition that spanned a long time during a period of fast apparent polar wander for gondwana sa2 250 9 e 16 9 s dp 15 9 dm 21 5 n 6 sites mean declination 95 3 mean inclination 58 5 95 14 5 corresponds to a likely age around 550 ma and falls close to a pole of similar age from the congo craton this suggests that the rio de la plata craton was at that time part of gondwana and confirms previous postulates that a single apwp can be defined for the supercontinent since 550 ma a preliminary mean geomagnetic pole obtained from the playa hermosa formation ph 198 4 e 43 0 s dp 8 6 dm 16 0 n 6 samples mean declination 226 0 mean inclination 24 2 95 15 0 is consistent with a previous pole of 595 ma from the campo alegre ca lavas and may suggest if confirmed that the glaciogenic deposits were produced at low to intermediate latitudes despite high uncertainties a new speculative model on the process of assembly of gondwana is proposed

natural hazards extreme events and mountain topography the hazard of any natural process can be expressed as a function of its magnitude and the annual probability of its occurrence in a particular region here we expand on the hypothesis that natural hazards have size frequency relationships that in parts resemble inverse power laws we illustrate that these trends apply to extremely large events such as mega landslides huge volcanic debris avalanches and outburst flows from failures of natural dams we review quantitative evidence that supports the important contribution of extreme events to landscape development in mountains throughout the world and propose that their common underreporting in the quaternary record may lead to substantial underestimates of mean process rates we find that magnitude frequency relationships provide a link between quaternary science and natural hazard research with a degree of synergism and societal importance that neither discipline alone can deliver quaternary geomorphology stratigraphy and geochronology allow the reconstruction of times magnitudes and frequencies of extreme events whereas natural hazard research raises public awareness of the importance of reconstructing events that have not happened historically but have the potential to cause extreme destruction and loss of life in the future

a modern analogue for plant colonization of palaeotsunami sands in cascadia british columbia canada the sediment stratigraphy of a modern analogue for pioneer plant colonization of palaeotsunami sands near tofino british columbia canada shows that a sand outcrop is continuous with a buried sand stratum deposited by tsunamis of the ad 1700 cascadia earthquake plants growing on the sand outcrop form a low marsh community that includes triglochin maritimum salicornia virginica spergularia canadensis puccinellia pumila and plantago maritima in contrast low marshes on muddy substrates include only carex lyngbyei although carex lyngbyei colonizes low marsh on mud it is restricted to middle marsh or higher elevation communities on sand with two way indicator species analysis twinspan and detrended corre spondence analysis dca plant cover abundance clearly distinguishes sandy from muddy low marsh a finding that suggests that particle size influences plant colonization twinspan and dca show that pollen spectra of the sandy marsh surface resemble fossil pollen of sediments that immediately over

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

were they all giants perspectives on late holocene plate boundary earthquakes at the northern end of the cascadia subduction zone abstract the relative magnitude of plate boundary earthquakes at the northern end of the cascadia subduction zone was assessed from the temporal concordance between the ages of coseismically buried late holocene soils in southwest washington their counterparts in central and southern cascadia offshore turbidites and paleoseismic deposits on the west coast of vancouver island only three of the seven buried soils in southwest washington that can be reliably traced as buried soils or paleotsunami deposits in the coastal lowlands of south central and southern cascadia have well dated counterparts in northern cascadia the three wide ranging events date from cascadia earthquakes y 250 cal bp u 1260 cal bp and n 2520 cal bp all three likely ruptured the entire plate margin and therefore potentially qualify as giants m w 9 deposits that may derive from tsunamis generated by earthquakes s 1570 cal bp l 2870 cal bp and j 3360 cal bp can also be found in northern cascadia but the ages of these deposits are not yet well enough constrained to determine whether they are coeval with their southern counterparts earthquake w 850 cal bp appears to be present in the northern cascadia paleoseismic record but yields considerably older ages than in central cascadia and may be missing from southernmost cascadia the onshore record of an offshore turbidite t2 displays a similar spatio temporal pattern to that of earthquake w

fault slip and seismic moment of the 1700 cascadia earthquake inferred from japanese tsunami descriptions 1 the 1700 cascadia earthquake attained moment magnitude 9 according to new estimates based on effects of its tsunami in japan computed coseismic seafloor deformation for hypothetical ruptures in cascadia and tsunami modeling in the pacific ocean reports of damage and flooding show that the 1700 cascadia tsunami reached 1 5 m heights at seven shoreline sites in japan three sets of estimated heights express uncertainty about location and depth of reported flooding landward decline in tsunami heights from shorelines and post 1700 land level changes we compare each set with tsunami heights computed from six cascadia sources each source is vertical seafloor displacement calculated with a three dimensional elastic dislocation model for three sources the rupture extends the 1100 km length of the subduction zone and differs in width and shallow dip for the other sources ruptures of ordinary width extend 360 670 km to compute tsunami waveforms we use a linear long wave approximation with a finite difference method and we employ modern bathymetry with nearshore grid spacing as small as 0 4 km the various combinations of japanese tsunami heights and cascadia sources give seismic moment of 1 9 1022 n m equivalent to moment magnitude 8 7 9 2 this range excludes several unquantified uncertainties the most likely earthquake of moment magnitude 9 0 has 19 m of coseismic slip on an offshore full slip zone 1100 km long with linearly decreasing slip on a downdip partial slip zone the shorter rupture models require up to 40 m offshore slip and predict land level changes inconsistent with coastal paleoseismological evidence

active tectonics of the st elias orogen alaska observed with gps measurements 1 we use data from campaign and continuous gps sites in southeast and south central alaska to constrain a regional tectonic block model for the st elias orogen active tectonic deformation in the orogen is dominated by the effects of the collision of the yakutat block with southern alaska our results indicate that 37 mm yr of convergence is accommodated along a relatively narrow belt of n nw dipping thrust faults in the eastern half of the orogen with the present day deformation front running through icy bay and beneath the malaspina glacier near the bering glacier the collisional thrust fault regime transitions into a broad northwest dipping decollement as the yakutat block basement begins to subduct beneath the counterclockwise rotating elias block the location of this transition aligns with the gulf of alaska shear zone implying that the pacific plate is fragmenting in response to the yakutat collision our model indicates that the bering glacier region is undergoing internal deformation and could correspond to the final stage of offscraping and accretion of sediments from the yakutat block prior to subduction predicted block motions at the western edge of the orogen suggest that the crust is laterally escaping along the aleutian fore arc

coseismic subsidence in the 1700 great cascadia earthquake coastal estimates versus elastic dislocation models seismic hazard assessments for a cascadia subduction zone earthquake are largely based on the rupture area predictions of dislocation models constrained by geodetic and geothermal data this paper tests the consistency of the models for the 1700 great cascadia earthquake with compiled coastal coseismic subsidence as estimated from paleoelevation studies coastal estimates have large uncertainties but show a consistent pattern greatest coseismic subsidence 1 2 m occurred in northern oregon southern washington subsidence elsewhere was 0 1 m elastic dislocation models constrained by interseismic geodetic and thermal data are used to predict the coseismic subsidence for two likely strain accumulation periods of i 800 and ii 550 yr of plate convergence and for uniform megathrust slip of 10 20 30 and 50 m the former two models provide a better and equally good fit predicted subsidence is in broad agreement with marsh estimates discrepancies exist however at the ends of the subduction zone in the south misfit may be due to breakup of the gorda plate the discrepancy in the north may be explained if the 1700 event released only part of the accumulated strain there consistent with long term net uplift in excess of eustatic sea level rise the coseismic slip magnitude estimated by comparing uniform slip model predictions with marsh coseismic subsidence estimates is consistent with the m 9 earthquake indicated by japanese tsunami records the coseismic slip was greatest in northern oregon southern washington declining to the north and south

great cascadia earthquakes and tsunamis of the past 6700 years coquille river estuary southern coastal oregon cascadia subduction zone earthquakes dropped tidal marshes and low lying forests to tidal flat elevations 12 times in the last 6700 cal yr b p at the coquille river estuary in southwestern oregon the youngest buried soil preserved in tidal marsh deposits near the estuary mouth records the a d 1700 earthquake that ruptured the entire cascadia margin eleven other buried marsh and upland soils found in tributary valleys of the estuary provide repeated evidence for rapid lasting relative sea level rise interpreted as coseismic subsidence additional stratigraphic criteria supporting a coseismic origin for soil burial include lateral soil correlation over hundreds of meters fossil diatom assemblages that indicate a maximum of 1 2 3 0 m of submergence and sand deposits overlying buried soils consistent with earthquakeinduced tsunamis that traveled 10 km up the estuary twelve earthquakes occurred in the last 6500 6720 cal yr b p recurring on average every 570 590 yr intervals between earthquakes varied from a few hundred years to over 1000 comparisons of the coquille record to earthquake histories from adjacent sites in oregon southwestern washington and northwestern california suggest that at least two earthquakes in the last 4000 yr did not rupture the entire length of the subduction zone an earthquake 760 1140 cal yr b p in southwestern washington may have ruptured as far south as coos bay but probably stopped before it reached the coquille estuary because no buried soil records the event and tidal marsh conditions were set to record an earthquake an earthquake limited to a southern segment of the cascadia margin 1940 2130 cal yr b p probably did not rupture north of the coquille estuary an analysis of relative sea level histories from either side of the coquille fault failed to find conclusive evidence for late holocene vertical deformation however we cannot preclude recent upper plate faulting if the fault is active as geomorphic features suggest then constraints on the highest possible elevation of mean tide level allow a maximum vertical slip rate of 0 2 0 4 mm yr in the past 6200 6310 cal yr b p

tree ring dates on two pre little ice age advances in glacier bay national park and preserve alaska usa abstract two interstadial tree ring width chronologies from geikie inlet glacier bay southeast alaska were built from 40 logs one of these chronologies has been calendar dated to ad 224 999 775 yr crossdating with a living ring width chronology from prince william sound alaska trees in this chronology were likely killed through inundation by sediments and meltwater from the advancing geikie glacier and its tributaries ca ad 850 the earlier tree ring chronology spans 545 yr and is a floating ring width series tied to radiocarbon ages of about 3000 cal yr bp this tree ring work indicates two intervals of glacial expansion by the geikie glacier system toward the main trunk glacier in glacier bay between 3400 and 3000 cal yr bp and again about ad 850 the timing of both expansions is consistent with patterns of ice advance at tidewater glaciers in other parts of alaska and british columbia about the same time and with a relative sea level history from just outside glacier bay in icy strait this emerging tree ring dated history builds on previous radiocarbon based glacial histories and is the first study to use tree ring dating to assign calendar dates to glacial activity for glacier bay

relative sea level response to little ice age ice mass change in south central alaska reconciling model predictions and geological evidence abstract integration of geological data and glacio isostatic adjustment gia modelling shows that it is possible to decouple complex mechanisms of relative sea level rsl change in a tectonically active glacial environment we model a simplest solution in which rsl changes in upper cook inlet alaska are a combination of the interplay of tectonic and isostatic processes driven by the unique rheology of this tectonically active location we calculate interseismic uplift during latter part of the penultimate earthquake cycle to vary from 0 3 to 0 7 mm yr diatom based reconstructions of rsl from tidal marsh sediment sequences coupled with detailed age models from ad 1400 to the ad 1964 great earthquake show deviations from a purely tectonically driven model of regional rsl glacial isostatic modelling constrained by gps data predicts up to 70 cm sea level change due to mountain glacier mass balance changes during the little ice age misfits between the gia model predictions and rsl reconstructions in the 19th and 20th century highlight that the tidal marshes of upper cook inlet potentially record a hemispheric wide acceleration in sea level and that other more complex earth process combinations may contribute to regional rsl change

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

paleomagnetism of the callander complex and the cambrian apparent polar wander path for north america the 7 km2 circular callander alkaline complex was emplaced into anorthositic and granitic gneisses of the grenville province in the canadian shield about 575 5 ma ago at the start of the cambrian the complex has not been subsequently metamorphosed or tilted detailed alternating field and thermal step demagnetization of 252 specimens from 29 sites led to the identification of a characteristic a magnetization component with a direction of d 82 2 i 82 7 95 3 1 k 83 n 26 sites in 5 sites of mesocratic to leucocratic syenite from the core of the complex in 5 sites of fenitized host rock from its aureole and in 16 sites of lamprophyre from radiating dikes isothermal remanent magnetization tests show that the a component is retained by both magnetite and hematite in a complete spectrum of domain sizes a reversals test suggests and a contact test shows the a component to be primary its pole position at 46 3 s 121 4 e dp 5 9 dm 6 1 does not fall on published but poorly defined

nitrogen stable isotope ratio of groundwater n2o 15n of n2o and no3 were measured to determine the mechanisms producing n2o in nitrate contaminated groundwaters these groundwaters contained n2o at concentrations between thirty to one hundred times higher than the atmospheric equilibrium the n2o no3 molar ratios in groundwaters were from 0 2 10 3 to 4 4 10 3 the 15n values of n2o 5 8 to 21 3 permil were much lower than those of coexistent no3 3 6 to 7 3 permil in the light of evidence that 15n in n2o from nitrification is highly depleted the present findings suggest nitrification as a dominant mechanism for the production of n2o in the groundwaters however unlike other aquatic systems where nitrification is a major route of n2o production no clear correlation was observed between n2o and o2 in the groundwater this poor correlation strongly suggests that n2o in the groundwater was predominantly produced in the soil column and or unsaturated zone based on two year observation of n2o flux from a spring a possible charging rate of n2o to the aquifer was estimated as 1 2 2 3 mg n2o n m 2 y 1 the rate is much smaller than the reported soil emission rates suggesting the groundwater n2o to be an insignificant source for atmospheric n2o large discrepancies in 15n of n2o between the groundwaters and the surface airs support this view

tide gage measurements of uplift along the south coast of alaska annual mean sea levels along the south coast of alaska are used to measure uplift along the alaska aleutian subduction zone oceanographic effects are removed from the observed annual mean sea levels by subtracting a correction that is proportional to the sea level fluctuations observed in southeast alaska that correction is effective in reducing fluctuations in the observed annual mean sea level as far west as the tip of alaska peninsula additional corrections to remove the eustatic rise in sea level and the apparent fall in sea level due to postglacial isostatic rebound of the land are introduced this corrected sea level record should provide a measure of tectonic subsidence in the area affected by the 1964 alaska earthquake postseismic uplift occurs where coseismic subsidence was observed and postseismic subsidence occurs where coseismic uplift was observed the immediate postseismic response is damped out within the first decade and the subsequent uplift rates appear to be steady over the 1974 1989 interval however some of those rates seem to be too high to be sustained over the 1000 year earthquake recurrence interval appropriate to this area if the interseismic deformation is only to recover the coseismic displacement thus a long term 100 years relaxation in uplift rates is postulated the immediate time constant 5 years postseismic relaxation is attributed to postseismic slip on the plate interface directly downdip from the coseismic rupture the long term time constant 100 years relaxation is attributed to flow in the asthenosphere

precipitation landsliding and erosion across the olympic mountains washington state usa abstract in the olympic mountains of washington state landsliding is the primary surface process by which bedrock and hillslope regolith are delivered to river networks however the relative importance of large earthquakes versus high magnitude precipitation events to the total volume of landslide material transported to valley bottoms remains unknown in part due to the absence of large historical earthquakes to test the hypothesis that erosion is linked to precipitation approximately 1000 landslides were mapped from google earth imagery between 1990 and 2015 along a 15 km wide 85 km long 1250 km2 swath across the range the volume of hillslope material moved by each slide was calculated using previously published area volume scaling relationships and the spatial distribution of landslide volume was compared to mean annual precipitation data acquired from the prism climate group for the period 1981 2010 statistical analysis reveals a significant correlation r 0 55 p

a paleomagnetic study of the layered mafic intrusion at sept iles quebec a paleomagnetic study of gabbroic and anorthositic members of the sept iles layered mafic intrusion has isolated a remanence with direction d 333 i 29 remanence a and a corresponding pole of 141 e 20 n the rocks are cut by numerous diabase dykes of unknown age the remanence carried by the dykes has direction d 188 i 85 remanence b with a corresponding pole of 116 e 59 s another remanence statistically identical to b d 186 i 85 is found at dyke contacts and in the local host rock its associated pole 115 e 61 s is identical to the one derived from the dykes this overprint is significantly different from remanence a and is obviously related to dyke emplacement the location of the pole derived from remanence a is in excellent agreement with many other cambrian poles from a variety of locations throughout cratonic north america the rocks at sept iles have been previously dated radiometrically at 540 ma thus all evidence indicates that remanence a is an original

phanerozoic hot spot traces and paleogeographic reconstructions of the siberian continent based on interaction with the african large low shear velocity province abstract we review intraplate magmatism in siberia and its folded surroundings from 480 ma to the present we describe several large igneous provinces lips and the intervals in which they were continuously formed within the limits of the siberian continent the altay sayan early paleozoic magmatic area 598 446 ma the altay sayan lip 408 393 ma the viluy lip 380 350 ma the barguzin vitim lip 310 275 ma the late paleozoic rift system of central asia 318 242 ma the siberian traps and west siberian rift system 250 249 ma the east mongolian and west trans baikalian lip 228 195 ma and a number of various aged late mesozoic and cenozoic rift zones and magmatic areas from 160 ma to the present day following lawver and muller 1994 kharin 2000 lawver et al 2002 and chernysheva et al 2005 we accept the position of the icelandic hot spot under the siberian trap area at the permo triassic boundary that enables us to estimate the geographic coordinates of the siberian trap location at 250 ma they are the same as iceland today presently the icelandic hot spot is situated above the african large low shear velocity province llsvp that indicates a hot mantle plume we suggest a set of paleogeographic reconstructions of the siberian continent for which we evaluate the paleolatitude based on the paleomagnetic data and estimate the paleolongitude position by placing siberia above the african llsvp furthermore we estimate the geographic coordinates for other ancient hot spots in the framework of the african llsvp that we consider to be responsible for the intraplate magmatism during different time periods in the phanerozoic eon available rare element and isotopic characteristics of the intraplate magmatic rocks of siberia enable us to determine three primary sources moderately depleted mantle prema enriched mantle em i and em ii of the mantle origin magma we propose that the model explains the interaction of the hot mantle plume including hot spots plume tails with the siberian intraplate magmatism areas throughout the phanerozoic eon

using isotope fractionation of nitrate nitrogen and nitrate oxygen for evaluation of microbial denitrification in a sandy aquifer the nitrate input into the groundwater from forest and agricultural land in the fuhrberger feld catchment area is virtually completely degraded by microbial denitrification in the aquifer five multilevel groundwater sampling wells show characteristic depth functions of nitrate proving the denitrification process a series of 10 samples of arable land groundwater was taken from different depths at these multilevel wells and isotope ratios of 15n14n and 18o16o in the nitrate were measured the sampling was based on the two dimensional vertical plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells high nitrate concentrations are associated with low 15n and low 18o values and vice versa the 15n 18o ratio indicates a linear increase with a slope of 1 2 1 the microbial dentrification accords with a rayleigh process with calculated enrichment factors of e 15 9 for 15n and e 8 0 for 18o three samples taken from groundwater recharged under coniferous forest show deviating characteristics low nitrate concentrations with low 15n values 1 4 but very high 18o values 40 50 using the previously quantified enrichment factors for 15n and 18o an attempt was made to ascertain the significance of denitrification in specific depth sections at two other multilevel wells 7 samples in two cases quantitative assessments on the degree of nitrate concentration decrease owing to denitrification were possible however in other cases the specific nitrate isotope fractionation was masked by the variability of nitrate concentration and of nitrate isotope ratios in the corresponding groundwater recharge preventing definite interpretations

simple models for late holocene and present day patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response summary the late holocene glacial moraine chronology in the southernmost south american andes includes four 14c dated neoglacial advances and retreats these are used as proxy information to characterize mass fluctuation of the patagonian icefields during the last 5000 years modelled ice loads force a phase lagged viscoelastic gravitational deformation of the solid earth the ancient glacier fluctuations may therefore drive present day crustal motion even in the absence of present day ice mass imbalance numerical models show that such rates of present day uplift and subsidence are larger than those driven by the viscous memory of late pleistocene deglaciation both spherical and flat earth models are employed the latter being used to study exhaustively the evects of glacial load history on the predicted vertical crustal velocity recent assessment of net mass balance from 1944 to 1985 indicates that the southern patagonian icefield has significantly deteriorated due to snout retreat and thinning volume loss rates are estimated at about 3 4 9 3 km3 yr 1 the predicted vertical isostatic response to this recession and to the modelled holocene neoglaciations is at a marginally detectable level 1m m yr 1 if the mantle asthenosphere beneath patagonia has a viscosity of about 1021 pa s however for reduced mantle viscosities the younger holocene glacial load histories predict larger signatures in fact if the viscosity is about 2 1020 pa s or lower then geodetically detectable vertical motion may be driven by a regional little ice age lia 1400 1750 ad glacier advance and subsequent 20th century retreat although this value for mantle viscosity is lower than thought typical of continental shield mantle 1021 pa s it is consistent with inversions for post seismic relaxation time constants in island arc environments and in regions with significant neogene continental tectonism in the viscosity regime of 5 1018 2 1019 pa s the predicted rates of vertical crustal motion are similar to those presently occurring in fennoscandia and hudson bay 5 10 mm yr 1 geodetic data may be sensitive to the time integrated growth and subsequent retreat of patagonian glacier ice mass over the last 600 years

radiocarbon evidence for extensive plate boundary rupture about 300 years ago at the cascadia subduction zone the cascadia subduction zone a region of converging tectonic plates along the pacific coast of north america has a geological history of very large plate boundary earthquakes1 2 but no such earthquakes have struck this region since euro american settlement about 150 years ago geophysical estimates of the moment magnitudes mw of the largest such earthquakes range from 8 ref 3 to 9 1 2 ref 4 radiocarbon dating of earthquake killed vegetation can set upper bounds on earthquake size by constraining the length of plate boundary that ruptured in individual earth quakes such dating has shown that the most recent rupture or series of ruptures extended at least 55 km along the washington coast within a period of a few decades about 300 years ago5 here we report 85 new 14c ages which suggest that this most recent rupture or series extended at least 900 km between southern british columbia and northern california by comparing the 14c ages with written records of the past 150 years we conclude that a single magnitude 9 earthquake or a series of lesser earthquakes ruptured most of the length of the cascadia subduction zone between the late 1600s and early 1800s and probably in the early 1700s

comment on new palaeomagnetic result from vendian red sediments in cisbaikalia and the problem of the relationship of siberia and laurentia in the vendian by s a pisarevsky r a komissarova and a n khramov pisarevsky et al 2000 document a poorly dated pole from vendian age sedimentary rocks in siberia and argue for a lowlatitude position of both laurentia and siberia during the interval from 650 to 550 ma their argument is based at least in part on a reinterpretation of palaeomagnetic poles from laurentia because previous studies e g symons chiasson 1991 meert et al 1994 torsvik et al 1996 argued for a high latitude position for laurentia beginning at 580 ma perhaps earlier the new data provided by pisarevsky et al 2000 are a welcome addition to the siberian palaeomagnetic database however given the broad age range of their result we feel that the authors over interpret the extant data in an effort to rescue a controversial positioning of siberia against the northern margin of laurentia sears price 2000 pelechaty 1996 hoffman 1991 dalziel 1997 condie rosen 1994 frost et al 1998 therefore we wish to address the following points in the manuscript that we feel are contentious

crustal earthquake triggering by pre historic great earthquakes on subduction zone thrusts triggering of earthquakes on upper plate faults during and shortly after recent great m 8 0 subduction thrust earthquakes raises concerns about earthquake triggering following cascadia subduction zone earthquakes of particular regard to cascadia was the previously noted but only qualitatively identified clustering of m 6 5 crustal earthquakes in the puget sound region between about 1200 900 cal years b p and the possibility that this was triggered by a great cascadia thrust subduction thrust earthquake and therefore portends future such clusters we confirm quantitatively the extraordinary nature of the puget sound region crustal earthquake clustering between 1200 900 cal years b p at least over the last 16 000 we conclude that this cluster was not triggered by the penultimate and possibly full margin great cascadia subduction thrust earthquake however we also show that the paleoseismic record for cascadia is consistent with conclusions of our companion study of the global modern record outside cascadia that m 8 6 subduction thrust events have a high probability of triggering at least one or more m 6 5 crustal earthquakes

late quaternary fluvial terraces near the daocheng ice cap eastern tibetan plateau the timing of terrace formation relative to the glacial interglacial cycle and what factors control that timing such as changes in climate and or uplift are controversial here we present a study of the terraces along the yazheku river using electron spin resonance esr dating and analysis of the sedimentary characteristics in order to establish the timing of terrace formation and to assess the forcing mechanisms that have been proposed the yazheku river flows in glacial trough leading from the haizi shan on the eastern tibetan plateau the range was uplifted during the quaternary and repeatedly glaciated by ice caps the four highest major terraces t5 t4 t3 and t2 are the result of both climatic and tectonic influences strath terraces t5 t2 were created during haizi shan glacial expansions during mis 16 12 6 and 3 4 respectively the major aggradation phases of the four terraces occurred during the deglaciations at the ends of mis 16 12 6 and 2 down cutting which led to the generation of the four terraces immediately followed the deposition of the t5 t2 gravel units these incisions occurred during the transitions between mis 16 15 mis 12 11 mis 6 5 and mis 2 1

paleomagnetism of the catoctin volcanic province a new vendian cambrian apparent polar wander path for north america the vendian cambrian segment of the lauretian apparent polar wander path apwp has been poorly constrained and the subject of some controversy the catoctin volcanic province in central virginia is well dated at 570 35 ma rb sr and 597 18 ma u pb and therefore presented an excellent paleomagnetic target for resolving the laurentian vendian cambrian apwp a total of 206 samples from 32 sites were collected from the catoctin basalts feeder dikes and sills the study revealed three ancient directions of magnetization the youngest c component fails the fold test and yielded a characteristic in situ direction of d 147 i 44 k 21 95 9 the corresponding paleopole falls along the middle ordovician segment of the laurentian apwp and we consider this component to be the result of a taconic remagnetization the second component the b component is carried by hematite exhibits dual polarities and passes a fold test the tilt corrected b component characteristic direction is d 92 i 17 k 16 95 13 the corresponding paleopole at 4 s 193 e falls near a well established late cambrian 505 ma pole for laurentia and we consider this component to be a remagnetization during a late cambrian tectonic event in the central appalachians the third component isolated in the catoctin basalts the a component yields a tilt corrected mean of d 68 i 84 k 59 95 9 this component passes a fold and reversal test a suite of samples was collected from two catoctin feeder dikes and surrounding country rocks that yield a positive baked contact test the a pole at 43 s 128 e falls significantly away from previously proposed vendian poles for laurentia a reevaluation of previous paleomagnetic studies from coeval rock units reveals similarly steep directions and leads us to propose a new apwp this new apw track indicates that laurentia was located near the pole during the interval 615 580 ma and drifted rapidly 16 cm yr 1 toward its late cambrian equatorial position

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

rapid uplift of southern alaska caused by recent ice loss summary extreme uplift rates and sea level changes in southern alaska have been documented by global positioning system gps surveys tide gauge measurements and studies of raised shorelines the movements detected in a network of 45 gps survey points describe a broad pattern of rapid regional uplift the majority of the study area is uplifting at a rate faster than 10 mm yr 1 with several sites uplifting more rapidly than 25 mm yr 1 new tide gauge data presented here consist of repeat occupations of 18 temporary gauge sites sea level rates at these sites agree with similar measurements in southern alaska taken 50 yr earlier and also with the pattern of uplift derived from the gps data raised shoreline studies at 14 sites document total sea level change with a maximum change in sea level of 5 7 m found in upper lynn canal the start of the ongoing uplift episode that raised these shorelines has been dated with dendrochronology and found to be coincident with the start of the collapse of the glacier bay icefield at ca 1750 ad the pattern of total sea level change is in general agreement with upliftrate measurements with greater sea level change found at the sites closest to the peak uplift rates in upper glacier bay we use a viscoelastic earth model subjected to an ice load history built upon observations of glacial change to predict uplift rates at the tide gauge and gps sites as well as the total uplift at the raised shoreline sites our modelling exercises are limited to an ice load model based on independent studies of the region s glacial history over the past 1 7 kyr to evaluate whether the uplift observations can be explained by simple earth models subjected to this load history two layer earth models consisting of an elastic crust and a low viscosity upper mantle half space can be adjusted to fit either the raised shoreline data or the combined gps and tide gauge uplift rate data but cannot fit all the data with a single set of earth model parameters however all three data sets are consistent with an approximated three layer earth model the combined model is constrained by a total of 77 uplift measurements which at the 95 per cent confidence level require a low viscosity asthenosphere a 1 4 0 3 10 19 pa s and thickness 110 20

great earthquakes and tsunamis of the past 2000 years at the salmon river estuary central oregon coast usa four buried tidal marsh soils at a protected inlet near the mouth of the salmon river yield definitive to equivocal evidence for coseismic subsidence and burial by tsunami deposited sand during great earthquakes at the cascadia subduction zone an extensive landward tapering sheet of sand overlies a peaty tidal marsh soil over much of the lower estuary limited pollen and macrofossil data suggest that the soil suddenly subsided 0 3 1 0 m shortly before burial regional correlation of similar soils at tens of estuaries to the north and south and precise 14c ages from one salmon river site imply that the youngest soil subsided during the great earthquake of 26 january a d 1700 evidence for sudden subsidence of three older soils during great earthquakes is more equivocal because older soil stratigraphy can be explained by local hydrographic changes in the estuary regional 14c correlation of two of the three older soils with soils at sites that better meet criteria for a great earthquake origin is consistent with the older soils recording subsidence and tsunamis during at least two great earthquakes pollen evidence of sudden coseismic subsidence from the older soils is inconclusive probably because the amount of subsidence was small 0 5 m the shallow depths of the older soils yield rates of relative sea level rise substantially less than rates previously calculated for oregon estuaries manuscript received 10 october 2003

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

15n isotope biogeochemistry and natural denitrification process in groundwater application to the chalk aquifer of northern france the use of 15n natural isotope tracing in an aquifer contained within chalk rocks in northern france indicates that under certain hydrogeological conditions major denitrification occurs at the boundary where the aquifer becomes confined the nitrate concentrations decrease in the direction of groundwater flow accompanied by an exponential increase in 15n expressed in 15n of the residual nitrate this is characteristic of kinetic isotope effects which accompany the reduction of the nitrate ion during denitrification hydrogeochemical and bacteriological observations confirm this process natural isotope tracing also permits this process to be distinguished from local dilution with nitrate free surface water which would entail a major drop in nitrate values without 15n isotopic enrichment a model is proposed to explain the relatively small observed magnitude of the isotopic fractionation effect

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

paleomagnetic directions in late precambrian glaciomarine sediments of the mirbat sandstone formation oman abstract a paleomagnetic study has been carried out in the late precambrian glaciomarine mirbat sandstone formation in the sultanate of oman limited availability and geographical distribution of outcrops restricted the sampling to six sites of these three were in laminated fine grained clay to siltstones and three in laminated carbonates one of these sites was rejected the remaining five sites represented by a total of 21 samples displayed a similar magnetic component during progressive thermal demagnetization between 0 and 500 c the site mean pole calculated from this component is at 86 5 n 328 1 e p 11 2 m 19 7 this low temperature component is interpreted as the direction of the average recent geomagnetic field in oman two sites 10 samples revealed a consistent magnetic component above 500 c the sample mean declination of 68 4 and inclination of 18 4 k 46 4 95 7 2 are interpreted as the characteristic remanent magnetization the late precambrian arabian pole position computed from the samples at these two sites lies at 23 3 n 141 8 e p 3 9 m 7 5 rotated into west african coordinates the resulting pole position is at 31 6 n 153 2 e in good agreement with published poles from gondwana of late precambrian age 550 ma the resulting paleolatitude is about 9 4 indicating a low latitude of deposition for the glaciomarine deposits of the mirbat sandstone formation

late holocene great earthquakes and relative sea level change at kenai southern alaska kenai located on the west coast of the kenai peninsula alaska subsided during the great earthquake of ad 1964 regional land subsidence is recorded within the estuarine stratigraphy as peat overlain by tidal silt and clay reconstructions using quantitative diatom transfer functions estimate co seismic subsidence relative sea level rise between 0 28 0 28 m and 0 70 0 28 m followed by rapid post seismic recovery stratigraphy records an earlier co seismic event as a second peat silt couplet dated to 1500 1400 cal yr bp with 1 14 0 28 m subsidence two decimetre scale relative sea level rises are more likely the result of glacio isostatic responses to late holocene and little ice age glacier expansions rather than to co seismic subsidence during great earthquakes comparison with other sites around cook inlet at girdwood and ocean view helps in constructing regional patterns of land level change associated with three great earthquakes ad 1964 950 850 cal yr bp and 1500 1400 cal yr bp each earthquake has a different spatial pattern of co seismic subsidence which indicates that assessment of seismic hazard in southern alaska requires an understanding of multiple great earthquakes not only the most recent all three earthquakes show a pre seismic phase of gradual land subsidence that marked the end of relative land uplift caused by inter seismic strain accumulation copyright 2005 john wiley sons ltd

paleomagnetic correlation of late holocene earthquakes among estuaries in washington and oregon 1 paleomagnetic directions of estuarine mud provide additional evidence that individual earthquakes or rapid series of earthquakes caused widespread coseismic land level changes during the past 2000 years in western washington and oregon most of the paleomagnetic measurements were made on mud dating from the first decades after coseismic subsidence from plate boundary earthquakes at the cascadia subduction zone mud deposited soon after the a d 1700 cascadia earthquake has similar remanent directions among all five sites k 171 sampled along 80 km of pacific coast between grays harbor and the mouth of the columbia river likewise internally consistent directions were obtained along this stretch of coast from mud deposited soon after a plate boundary earthquake or earthquake series in a d 340 410 and soon after another such event in a d 680 720 also analyzed were remanent magnetizations of mud deposited shortly before or shortly after land level changes from seismicity in the north america plate beneath puget sound a mean direction for sites on the snohomish river delta near everett from the time of an earthquake on the seattle fault in a d 900 930 is statistically identical 95 confidence level to a mean direction in mud that was uplifted in a d 800 1000 at potentially correlative sites near tacoma and olympia the paleomagnetic direction from everett for the upper plate earthquake of a d 900 930 differs substantially from that for a plate boundary earthquake in a d 810 1190 this difference implies that the upper plate earthquake preceded the plate boundary earthquake by a century or two on the basis of comparisons of their paleomagnetic poles with a previously reconstructed path of geomagnetic paleosecular variation in western north america

new gps constraints on the motion of the yakutat block global positioning system gps measurements were made at yakutat on the yakutat terrane of southern alaska to investigate the motion of the yakutat block with respect to the north american plate and to help constrain motion along the fairweather fault the velocity of yakutat derived from the gps data is 44 1 1 9 mm yr toward n37 4 w relative to stable north america the magnitude of this velocity is similar to that of the pacific plate predicted by nuvel1a although there is a significant difference in the azimuth of these two vectors the motion of yakutat relative to north america is almost exactly parallel to the strike of the fairweather fault suggesting that most deformation inboard of yakutat is right lateral strike slip on the fairweather fault or faults parallel to it and that significant motion normal to the fairweather fault occurs offshore of yakutat the gps velocity at yakutat is also used to help constrain the slip rate and locking depth of the fairweather fault

tree ring analysis in the reconstruction of slope instabilities associated with earthquakes and precipitation the crimean mountains ukraine the crimean mountains in ukraine constitute a seismically active region that is abundant in various types of mass movement the limestone escarpments that rise above the black sea coast in the vicinity of the town of yalta are particularly subject to considerable rockfall landslide and debris flow processes that often endanger infrastructure and human life one of these very active slopes is the area of the ancient taraktash rockslide characterised by active block type movements lateral spreading toppling and incipient sliding rockfalls ongoing sliding activities and debris flows the aims of this study were i to employ tree ring analysis to reconstruct a record of slope instabilities mainly block type movements rockfalls landslides and debris flows within the taraktash slope deformation over a period of more than two centuries and ii to establish the degree of correlation between periods of enhanced slope activity and both historical earthquakes and climatic data the temporal frequency of significant slope processes was addressed through a tree ring analysis that took 738 increment cores from 255 crimean pine trees pinus nigra ssp pallasiana the tree ring record reveals periods of increased activity of block type movements rockfalls and landslides during the major earthquakes in 1790 1875 1927 and 1986 although the slope processes studied are predominantly driven by seismic activity their intensity and duration are also dependent on climatic factors this is especially true for landslides and debris flows which occurred mainly in years characterised by high precipitation totals

rapid viscoelastic uplift in southeast alaska caused by post little ice age glacial retreat our observations show that extreme uplift in southeast alaska began about 1770 ad with relative sea level rsl change to 5 7 m and current uplift rates to 32 mm yr this region experienced widespread glacial melting following the little ice age lia with the collapse of the glacier bay icefield alone equivalent to 8 mm of global sea level rise geodynamic modelling links the uplift to post lia isostatic rebound with the extreme uplift signal and a priori knowledge of ice load changes requiring the presence of a low viscosity asthenosphere 3 710 18 pa s these crustal deformations are triggered by climate change

downward migration of coastal conifers as a response to recent land emergence in eastern hudson bay quebec abstract postglacial uplift in the eastern hudson bay area is among the most rapid in the world 300 m during the last 8000 yr although emergence curves based on 14 c dated raised shorelines give a consistent basis for modeling relative sea level changes such a low resolution dating method is inappropriate for estimating trends over recent decades a major downward displacement of white spruce picea glauca moench voss and tamarack larix laricina duroi k koch occurred on protected shores as a response to shoreline retreat during this century analysis of the age distribution of trees indicates a progradation of white spruce and tamarack on gently sloping terrain ranging from 1 3 and 2 6 cm yr respectively toward the sea improvement of climatic conditions during the 20th century favored such expansion which was probably faster than the real land emergence rates but recent episodes of high water levels caused regression of forest margins over the highly exposed shores nevertheless the downward trend of the treeline over this century substantiates the projections of 14c dated coastal emergence curves during the modern period 1 0 to 1 3 cm yr by providing an estimate of the maximum rates of shoreline retreat

renewal of tidal forests in washington state after a subduction earthquake in a d 1700 abstract with few exceptions today s tidal trees near washington s pacific coast postdate an earthquake that lowered the region by 1 m or more the earthquake which occurred in a d 1700 is the most recent to have ruptured much of the plate boundary at this central part of the cascadia subduction zone because of the coseismic subsidence lowland forests became tidal flats where thousands of trees died most of the trees killed were sitka spruce picea sitchensis in the centuries since the earthquake tidal deposits have built new land that has been colonized by new sitka spruce all but several tens of the region s tidal spruce consequently postdate 1700 as shown by counts of annual rings in 121 of the largest spruce in tidal forests at copalis river grays harbor and willapa bay forests began to return to each of these estuaries in the early 1700s and spread seaward in the late 1700s and 1800s annual rings in the oldest of the trees thus record a large fraction of the earthquake recurrence interval that began with the 1700 earthquake

petrogenesis of the 723 ma coronation sills amundsen basin arctic canada implications for the break up of rodinia the coronation mafic sills and associated natkusiak flood basalts in arctic canada are part of the 723 ma franklin igneous events a flood basalt and dyke swarm province that extends across the southern arctic of north america and greenland two representative sills 70 and 25 m thick respectively outcrop near coronation gulf in nunavut they are composed of clinopyroxene plagioclase olivine and fe ti oxides and have tholeiitic composition similar to the natkusiak basalts their end values range between 4 2 and 5 9 and have la yb n ratios of 1 5 2 these rocks are mantle derived and were affected by minor crustal contamination compositional variations indicate that the coronation sills have experienced extensive fractionation including flow differentiation during emplacement and show increased differentiation from west to east across the province a feature similar to the mackenzie dyke swarm however the mackenzie dyke swarm and the franklin igneous events have distinct chemical composition the franklin rocks are related to a mantle plume located near victoria island at the center of the dyke swarm and could represent an offshoot from the superplume related to the break up of rodinia the absence of such dykes and sills in siberia argues against locating siberia against northern laurentia in a rodinia reconstruction 2003 elsevier b v all rights reserved

great earthquakes of variable magnitude at the cascadia subduction zone comparison of histories of great earthquakes and accompanying tsunamis at eight coastal sites suggests plate boundary ruptures of varying length implying great earthquakes of variable magnitude at the cascadia subduction zone inference of rupture length relies on degree of overlap on radiocarbon age ranges for earthquakes and tsunamis and relative amounts of coseismic subsidence and heights of tsunamis written records of a tsunami in japan provide the most conclusive evidence for rupture of much of the plate boundary during the earthquake of 26 january 1700 cascadia stratigraphic evidence dating from about 1600 cal yr b p similar to that for the 1700 earthquake implies a similarly long rupture with substantial subsidence and a high tsunami correlations are consistent with other long ruptures about 1350 cal yr b p 2500 cal yr b p 3400 cal yr b p 3800 cal yr b p 4400 cal yr b p and 4900 cal yr b p a rupture about 700 1100 cal yr b p was limited to the northern and central parts of the subduction zone and a northern rupture about 2900 cal yr b p may have been similarly limited times of probable short ruptures in southern cascadia include about 1100 cal yr b p 1700 cal yr b p 3200 cal yr b p 4200 cal yr b p 4600 cal yr b p and 4700 cal yr b p rupture patterns suggest that the plate boundary in northern cascadia usually breaks in long ruptures during the greatest earthquakes ruptures in southernmost cascadia vary in length and recurrence intervals more than ruptures in northern cascadia

detection limits of tidal wetland sequences to identify variable rupture modes of megathrust earthquakes abstract recent paleoseismological studies question whether segment boundaries identified for 20th and 21st century great m8 earthquakes persist through multiple earthquake cycles or whether smaller segments with different boundaries rupture and cause significant hazards the smaller segments may include some currently slipping rather than locked in this review we outline general principles regarding indicators of relative sea level change in tidal wetlands and the conditions in which paleoseismic indicators must be distinct from those resulting from non seismic processes we present new evidence from sites across southcentral alaska to illustrate different detection limits of paleoseismic indicators and consider alternative interpretations for marsh submergence and emergence we compare predictions of coseismic uplift and subsidence derived from geophysical models of earthquakes with different rupture modes the spatial patterns of agreement and misfits between model predictions and quantitative reconstructions of coseismic submergence and emergence suggest that no earthquake within the last 4000 years had a pattern of rupture the same as the mw 9 2 alaska earthquake in 1964 from the alaska examples and research from other subduction zones we suggest that if we want to understand whether a megathrust ruptures in segments of variable length in different earthquakes we need to be site specific as to what sort of geological based criteria eliminate the possibility of a particular rupture mode in different earthquakes we conclude that coastal paleoseismological studies benefit from a methodological framework that employs rigorous evaluation of five essential criteria and a sixth which may be very robust but only occur at some sites 1 lateral extent of peat mud or mud peat couplets with sharp contacts 2 suddenness of submergence or emergence and replicated within each site 3 amount of vertical motion quantified with 95 error terms and replicated within each site 4 syncroneity of submergence and emergence based on statistical age modelling 5 spatial pattern of submergence and emergence 6 possible additional evidence such as evidence of a tsunami or liquefaction concurrent with submergence or emergence we suggest that it is possible to consider detection limits as low as 0 1 0 2 m coseismic vertical change

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

holocene landslides and a 3500 year record of pacific northwest earthquakes from sediments in lake washington lake washington which forms the eastern boundary of seattle is located in a tectonically active area containing several strands of the seattle fault high resolution seismic reflection profiling sidescan swath imagery and sediment coring were used to define deformation of holocene lake sediments and the distribution geometry age and causes of submarine landslides numerous large block slides sediment slumps and debris flows are present throughout the lake and large landslides obscure the surficial structure of seattle fault strands as they pass through the lake in addition most bays along the lake margin are the headwalls of large submarine slides submerged forests show evidence of deep seated block failures that have exposed glacial sediments and tertiary rocks the massive submarine block slides and retrogressive submarine slope failures were triggered most likely by large m b 7 earthquakes on the seattle fault and or large to great m b 8 temblors occurring elsewhere in cascadia buried landslides suggest that submarine slope failures and mass wasting occurred more than once in the last 11 000 yr sediments in lake washington preserve a record of episodic deposition of turbidites possibly caused by seismically induced submarine landslides magnetic susceptibility profiles on 36 gravity cores show a characteristic series of magnetic peaks that can be traced throughout the lake x radiography and grain size analyses suggest that the magnetic peaks represent anomalous detrital layers that in some cases are turbidites the areal extent and magnetic signatures of many of the deposits suggest multiple sources which is consistent with numerous local landslides caused by large earthquakes radiocarbon dating and correlation of the downcore magnetic profiles establish a sediment record in which episodic sedimentary disturbances occurred seven times in the last 3500 yr if these deposits are seismically induced turbidites seismites then large earthquakes have occurred about every 300 500 yr in the puget sound region

the age of the sept iles layered mafic intrusion canada implications for the late neoproterozoic cambrian history of southeastern canada the large sept iles layered mafic intrusion of eastern canada has been precisely dated by u pb zircon methods at 565 4 ma consideration of other magmatic events at that time in southeastern canada reveals three different phases of magmatism the first phase was composed of two tholeiitic dike swarms at 615 ma and 590 ma the second including the sept iles intrusion comprised a widespread series of mostly alkaline intrusions emplaced around 575 565 ma along the rift faults of the st lawrence graben the last phase was composed predominantly of alkali and transitional basalts now exposed in the appalachians erupted during the latest neoproterozoic and early cambrian the second and third phases are best accounted for by the arrival of a major mantle plume near the town of sept iles 565 million years ago the widespread but volumetrically minor alkali magmatism that peaked 10 m y earlier is typical of other plumes elsewhere the plume model is reinforced by sedimentological evidence for a crusta

long term perspectives on giant earthquakes and tsunamis at subduction histories of earthquakes and tsunamis inferred from geological evidence aid in anticipating future catastrophes this natural warning system now influences building codes and tsunami planning in the united states canada and japan particularly where geology demonstrates the past occurrence of earthquakes and tsunamis larger than those known from written and instrumental records under favorable circumstances paleoseismology can thus provide long term advisories of unusually large tsunamis the extraordinary indian ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks such variation in rupture mode known from written history at a few subduction zones is also characteristic of earthquake histories inferred from geology on the pacific rim

paleoseismic signature in late holocene sediment cores from saanich inlet british columbia abstract this paper explores the paleoseismic record potentially preserved in the upper 40 m of hydraulic piston cores collected in 1996 at two sites in saanich inlet british columbia during ocean drilling program odp leg 169s the odp cores are missing 1 2 m of water rich sediment directly underlying the seafloor but this sediment is preserved in shorter piston cores collected in 1989 and 1991 the upper part of the odp cores consists of rhythmically laminated varved marine mud with intercalated massive beds interpreted to be debris flow deposits some of the debris flow deposits are linked to past earthquakes including the 1946 vancouver island earthquake m7 2 a great m8 9 plate boundary earthquake at the cascadia subduction zone in january 1700 and a large crustal or plate boundary earthquake about 1000 yr ago earthquakes may also be responsible for debris flows in about ad 1600 1500 1250 1150 850 450 350 180 and bc 200 220 500 900 and 1050 if so the average recurrence interval for moderate to large earthquakes which trigger debris flows in saanich inlet is about 150 yr this recurrence interval is broadly consistent with the frequency of moderate to large earthquakes in the region during the historical period debris flows however can also be triggered by non seismic processes making it difficult to assemble a complete earthquake record from the saanich inlet cores we propose that extensive debris flow deposits emplaced by single large failures or many smaller coincident failures probably have a seismic origin

variability of near term probability for the next great earthquake on the cascadia subduction zone the threat of a great m 9 earthquake along the cascadia subduction zone is evidenced by both paleoseismology data and current strain accumulation along the fault on the basis of recent information on the characteristics of this subduction system we estimate the conditional probabilities of a great earthquake occurring within the next 50 years and their variabilities the most important vari ation is associated with the existence of episodic slow slip on the deep portion of the subduction interface we show that these events modulate the conditional probability dramatically over their 14 month cycle during the 2 week slow slip events the weekly probability of a great earthquake is about 30 to 100 times as high as it is during any week of the rest of the year near term probabilities also vary significantly with the assumed distribution of earthquake recurrence intervals under a reference scenario of unimodal distribution of recurrence intervals about 500 600 years the 50 year conditional probability is low 0 12 at a 95 confidence interval how ever under a tantalizing bimodal distribution hypothesis this probability could be either four times as high 6 45 or four times as low less than 1 depending on whether the current interval is short 350 years or long 850 years

response of a small oregon estuary to coseismic subsidence and postseismic uplift in the past 300 years the sixes river estuary south coastal oregon sits above the locked portion of the cascadia subduction zone which intermittently releases in subduction zone earthquakes one such cascadia earthquake 300 years ago caused subsidence and a tsunami at the sixes estuary the subsidence raised the river9s base level resulting in an 3 km upstream shift of the head of tide of the estuary at the upper end of the expanded estuary more than 4 m of overbank sediment was deposited in the first decades or century after subsidence subsequent incision through the overbank deposits accompanied the gradual emergence of the estuary and attendant downstream shift of the head of tide as relative sea level fell in response to interseismic uplift

net late holocene emergence despite earthquake induced submergence south central chile abstract intertidal deposits show net late holocene emergence at three sites along the pacific coast near maullin and carelmapu chile latitude 41 6 41 7 s the maximum amount of net emergence is ca 1 m in the past 1500 years and ca 2 1 2 m in the past 4000 years emergence probably would have prevailed at a fourth site near maullin were the site not underlain by easily compacted deposits this site shows slight

post glacial sea level change along the pacific coast of north america abstract sea level history since the last glacial maximum on the pacific margin of north america is complex and heterogeneous owing to regional differences in crustal deformation neotectonics changes in global ocean volumes eustasy and the depression and rebound of the earth s crust in response to ice sheets on land isostasy at the last glacial maximum the cordilleran ice sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore this combined with different tectonic settings along the coast resulted in divergent relative sea level responses during the holocene for example sea level was up to 200 m higher than present in the lower fraser valley region of southwest british columbia due largely to isostatic depression at the same time sea level was 150 m lower than present in haida gwaii on the northern coast of british columbia due to the combined effects of the forebulge raising the land and lower eustatic sea level a forebulge also developed in parts of southeast alaska resulting in post glacial sea levels at least 122 m lower than present and possibly as low as 165 m on the coasts of washington and oregon as well as south central alaska neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea level changes

paleoseismic evidence for late holocene tectonic deformation along the saddle mountain fault zone southeastern olympic peninsula washington abstract trench and wetland coring studies show that northeast striking strands of the saddle mountain fault zone ruptured the ground about 1000 years ago generating prominent scarps three conspicuous subparallel fault scarps can be traced for 15 km on light detection and ranging lidar imagery traversing the foothills of the southeast olympic mountains the saddle mountain east fault the saddle mountain west fault and the newly identified sund creek fault uplift of the saddle mountain east fault scarp impounded stream flow forming price lake and submerging an existing forest thereby leaving drowned stumps still rooted in place stratigraphy mapped in two trenches one across the saddle mountain east fault and the other across the sund creek fault records one and two earthquakes respectively as faulting juxtaposed miocene age bedrock against glacial and postglacial deposits although the stratigraphy demonstrates that reverse motion generated the scarps slip indicators measured on fault surfaces suggest a component of left lateral slip from trench exposures we estimate the postglacial slip rate to be 0 2 mm yr and between 0 7 and 3 2 mm yr during the past 3000 years integrating radiocarbon data from this study with earlier saddle mountain fault studies into an oxcal bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three saddle mountain faults to 1170 970 calibrated years cal b p which overlaps with the nearby m w 7 5 1050 1020 cal b p seattle fault earthquake an earlier earthquake recorded in the sund creek trench exposure dates to around 3500 cal b p the geometry of the saddle mountain faults and their near synchronous rupture to nearby faults 1000 years ago suggest that the saddle mountain fault zone forms a western boundary fault along which the fore arc blocks migrate northward in response to margin parallel shortening across the puget lowland

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

evidence for liquefaction identified in peeled slices of holocene deposits along the lower columbia river washington peels made from 10 geoslices beneath a riverbank at washington9s hunting island 45 km inland from the pacific coast aid in identifying sand that liquefied during prehistoric earthquakes of estimated magnitude 8 9 at the cascadia subduction zone each slice was obtained by driving sheetpile and a shutter plate to depths of 6 8 m the resulting sample as long as 8 m had a trapezoidal cross section 42 55 cm by 8 cm the slicing created few artifacts other than bending and smearing at slice edges each slice is dominated by well stratified sand and mud deposited by the tidal columbia river nearly 90 of the sand is distinctly laminated the sand contains mud beds as thick as 0 5 m and at least 20 m long and it is capped by a mud bed that contains a buried soil that marks the 1700 cascadia earthquake of estimated magnitude 9 every slice intersected sills and dikes of fluidized sand and many slices show folds and faults as well sills which outnumber dikes mostly follow and locally invade the undersides of mud beds the mud beds probably impeded diffuse upward flow of water expelled from liquefied sand trapped beneath mud beds this water flowed laterally destroyed bedding by entraining fluidizing sand and locally scoured the overlying mud horizontal zones of folded sand extend at least 10 or 20 m and some contain low angle faults many of the folds probably formed while sand was weakened by liquefaction the low angle faults may mark the soles of river bottom slumps or lateral spreads as many as four great cascadia earthquakes in the past 2000 yr contributed to the intrusions folds and faults this subsurface evidence for fluid escape and deformation casts doubt on maximum accelerations that were previously inferred from local absence of liquefaction features at the ground surface along the columbia river the geosliced evidence for liquefaction abounds not only beneath banks riddled with dikes but also beneath banks in which dikes are absent such dike free banks of the columbia river if interpreted without study of postdepositional structures in deposits beneath them provide insufficient basis for setting upper bounds on the strength of shaking from great cascadia earthquakes online material data from outcrop surveys vibracores and penetrometer tests tabular summary of depositional and postdepositional features in geoslices

late holocene relative sea level changes and the earthquake deformation cycle around upper cook inlet alaska abstract multiple peat silt couplets preserved in tidal marsh sediment sequences suggest that numerous great plate boundary earthquakes caused the coast around cook inlet alaska to subside over the past 3500 years field and laboratory analyses of the two youngest couplets record the well documented earthquake of ad 1964 and the penultimate one approximately 850 cal yr bp diatom assemblages from a range of modern day estuarine environments from tidal flat through salt marsh to acidic bog produce quantitative diatom transfer function models for elevation reconstructions based on fossil samples only nine out of 124 fossil assemblages analysed including previously published data for the ad 1964 earthquake have a poor modern analogue calibration of fossil samples indicate co seismic subsidence of 1 50 0 32 m for ad 1964 similar to measurements taken after the earthquake and 1 45 0 34 m for the 850 cal yr bp earthquake elevation standard errors for individual fossil samples range from 0 08 m in peat layers to 0 35 m in silt units lack of a chronology within fossil silt units prevents identification of changes in the rate of recovery and land uplift between the post seismic and inter seismic periods however preservation of multiple peat silt couplets indicates no net emergence over multiple earthquake cycles glacio isostatic movements from little ice age glacier advance and retreat explains a 0 15 m relative sea level oscillation recorded within the peat layer subsequently submerged as a result of the ad 1964 earthquake before both this and the 850 cal yr bp earthquake diatom assemblages suggest pre seismic relative sea level rise of 0 12 0 13 m representing possible precursors to great earthquakes

rapid resetting of an estuarine recorder of the 1964 alaska earthquake tides and plants have already restored much of a landscape that the 1964 alaska earthquake destroyed at the head of a macrotidal estuary near anchorage in the vicinity of portage subsidence during the earthquake changed meadows thickets and spruce groves into barren tidal flats tidal flat silt and sand soon buried the pre earthquake landscape while filling intertidal space that the subsidence had made the flats supported new meadows and thickets by 1973 and new spruce by 1980 three new findings confirm that the flats aggraded rapidly and that their vegetation is maturing 1 most of the postearthquake deposits at portage date from the first decade after the 1964 earthquake their thickness of 23 sites in a 0 5 km 2 area was 1 4 0 2 m in 1973 1 6 0 2 m in 1991 and 1 6 0 3 m in 1998 2 many of the deposits probably date from the first months after the earthquake the deposits contain sedimentary couplets in which coarse silt or very fine sand is capped by fine or medium silt about 100 such couplets make up the lowest 0 5 m or more of the postearthquake deposits in two outcrops these couplets thicken and thin rhythmically both as groups of 5 20 couplets and as pairs of successive couplets probably the groups of thick couplets represent the highest tides the groups of thin couplets represent some of the lesser high tides and the pairs record inequality between twice daily high tides 3 in the 1980s and 1990s thickets expanded and spruce multiplied the vegetation now resembles the fossil assemblage rooted in the buried landscape from 1964 had the 1964 alaska earthquake been repeated a decade later the two earthquakes would now be recorded by two superposed buried landscapes near portage much more than a decade is probably needed to reset similar recorders at mesotidal estuaries of the cascadia subduction zone

nitrous oxide production and consumption in british limestone aquifers nitrous oxide and other nitrogen species were measured in groundwater from the most important limestone aquifers in the uk nitrous oxide levels were generally very high with concentrations exceeding the concentration of air equilibrated water by up to 320 times the correlations between n2o no3 and dissolved oxygen as well as the spatial distribution of these chemical parameters were used to identify nitrification as the main n2o production mechanism in the investigated aquifers most of the n2o in groundwater appears to be produced via nitrification in the unsaturated zone which is probably strongly supplemented by nitrogenous compounds from anthropogenic land applications nitrous oxide production in the saturated zone is less substantial and can also be denitrification mediated denitrification under very reducing aquifer conditions can result in nitrous oxide consumption the observed high n2o concentrations in groundwater which are most likely caused by agricultural aquifer pollution can potentially lead to large n2o emissions from aquifers to the atmosphere which will contribute to the climatic forcing induced by higher atmospheric n2o concentrations