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

palaeotsunamis along canada s pacific coast abstract to fully understand tsunami hazards along canada s pacific coast we must consider all potential sources including local and region wide earthquakes volcanic activity slope failure events and bolide impacts furthermore as climate changes future extreme meteorological conditions will exacerbate slope failures on steep and over steepened slopes and potentially augment the magnitude and frequency of earthquake generated tsunamis there have been numerous reviews of the geological records of palaeotsunamis along the cascadia margin but as yet there has been no attempt made to pull together all data related to palaeotsunamis along the pacific coast of canada we summarise all geological data related to palaeotsunamis reported in the region all relevant non geological data and other information concerning potential tsunamigenic sources evidence for between 10 and 22 palaeotsunamis prior to european arrival have been documented with the cascadia subduction zone y event ad1700 being the most widely recognised geological archaeological and anthropological data all indicate a complex multi sourced prehistory of seismic tsunami activity that is poorly understood a clustering of potential activity off the se coast of vancouver island suggests that we should also attempt to better understand locally generated events along canada s pacific coast

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

great earthquakes on canada s west coast a review this article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geological survey of canada contribution 20090196 the first lithoprobe transect in 1984 across vancouver island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes

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

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

a review of geological records of large tsunamis at vancouver island british columbia and implications for hazard abstract large tsunamis strike the british columbia coast an average of once every several hundred years some of the tsunamis including one from alaska in 1964 are the result of distant great earthquakes most however are triggered by earthquakes at the cascadia subduction zone which extends along the pacific coast from vancouver island to northern california evidence of these tsunamis has been found in tidal marshes and low elevation coastal lakes on western vancouver island the tsunamis deposited sheets of sand and gravel now preserved in sequences of peat and mud these sheets commonly contain marine fossils and they thin and fine landward consistent with deposition by landward surges of water they occur in low energy settings where other possible depositional processes such as stream flooding and storm surges can be ruled out the most recent large tsunami generated by an earthquake at the cascadia subduction zone has been dated in washington and japan to ad 1700 the spatial distribution of the deposits of the 1700 tsunami together with theoretical numerical modelling indicate wave run ups of up to 5 m asl along the outer coast of vancouver island and up to 15 20 m asl at the heads of some inlets the waves attenuated as they moved eastward along juan de fuca strait and into puget sound and the strait of georgia no deposits of the 1700 event or for that matter any other tsunami have yet been found in the strait of georgia suggesting that waves were probably no more than 1 m high in this area if a tsunami like the 1700 event were to occur today communities along the outer pacific coast from southern british columbia to northern california would be severely damaged there would be little time to evacuate these communities because the tsunami would strike the outer coast within minutes of the first ground shaking fortunately such tsunamis are infrequent perhaps as few as seven have occurred in the last 3500 yr other tsunamis that are much smaller and more localized although probably more frequent are caused by local crustal earthquakes and landslides along the british columbia coast two such tsunamis have occurred in british columbia in recent years one in 1946 in the strait of georgia and another in 1975 at the head of a fiord on the northern mainland coast

west coast tides during cascadia subduction zone tsunamis low neap tides occurred along the west coast of the united states and canada around 0500 ut january 27 1700 a time for the last major cascadia earthquake tsunami based on teletsunami arrival times in japan satake et al 1996 however high range perigean spring tides occurred only a week later illustrating how accurately occurrence times must be known to constrain the region s background water levels during such events the ranges of background water levels increase northward from 3 m at monterey to 8 5 m at queen charlotte as estimated from the amplitudes of perigean spring tides and subtidal winter fluctuations

tsunamis and tectonic deformation at the northern cascadia margin a 3000 year record from deserted lake vancouver island british columbia canada three layers of sand occur within a sequence of muddy gyttja in a 3 m core recovered from deserted lake which lies at the head of a fjord on the central west coast of vancouver island british columbia canada the sedimentology and microfossil assemblages of these layers are consistent with deposition by tsunamis radiocarbon ages suggest that the tsunamis were generated by plate boundary earthquakes at the cascadia subduction zone about 2600 1600 and 300 years ago diatom and protozoan contents of the gyttja layers indicate that relative sea level fell in the periods between tsunamis the sea level changes are probably a product of interseismic uplift of the north america plate margin post tsunami diatom and protozoan assemblages are generally more marine than their pre tsunami counterparts suggesting that the study site subsided during earth quakes estimates of interseismic and coseismic deformation during one earthquake cycle indicate that less than half of the interseismic uplift was recovered during the earthquake leading to cumulative or permanent uplift of the area

linear and nonlinear computations of the 1992 nicaragua earthquake tsunami numerical computations of tsunamis are made for the 1992 nicaragua earthquake using different governing equations bottom frictional values and bathymetry data the results are compared with each other as well as with the observations both tide gauge records and runup heights comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a small grid size is more effective than to include nonlinear terms in tsunami computation linear computation overestimates the amplitude for the later phase than the first arrival particularly when the amplitude becomes large the computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights the average ratio or the amplification factor is estimated to be 3 in the present case when the grid size of 1 minute is used the factor however may depend on the grid size for the computation

numerical simulations of tsunami waves and currents for southern vancouver island from a cascadia megathrust earthquake the 1700 great cascadia earthquake m 9 generated widespread tsunami waves that affected the entire pacific ocean and caused damage as distant as japan similar catastrophic waves may be generated by a future cascadia megathrust earthquake we use three rupture scenarios for this earthquake in numerical experiments to study propagation of tsunami waves off the west coast of north america and to predict tsunami heights and currents in several bays and harbours on southern vancouver island british columbia including ucluelet located on the west coast of the island and victoria and esquimalt harbours inside juan de fuca strait the earthquake scenarios are an 1100 km long rupture over the entire length of the subduction zone and separate ruptures of its northern or southern segments as expected the southern earthquake scenario has a limited effect over most of the vancouver island coast with waves in the harbours not exceeding 1 m the other two scenarios produce large tsunami waves higher than 16 m at one location near ucluelet and over 4 m inside esquimalt and victoria harbours and very strong currents that reach 17 m s in narrow channels and near headlands because the assumed rupture scenarios are based on a previous earthquake direct use of the model results to estimate the effect of a future earthquake requires appropriate qualification

high resolution climate signals in the bolling allerod interstadial greenland interstadial 1 as reflected in european tree ring chronologies compared to marine varves and ice core records abstract lateglacial and holocene tree ring chronologies are unique archives which provide various information on past environments on a true annual time scale changes in ring width can be related to past climate anomalies and dendrodated wood provides an ideal source for radiocarbon calibration we present a 1051 year tree ring chronology from the late glacial built from subfossil scots pines pinus sylvestris that grew in different regions of central and southern europe through a series of high precision radiocarbon measurements we obtained a floating radiocarbon chronology which allowed accurate wiggle matching to the intcal98 calibration curve the trees show a coherent pattern in ring width variations throughout central europe and extending into the mediterranean which indicates a strong external climatic factor most probably temperature during the growing season we identified major growth events which appear synchronous with events seen in isotopic and tracer signals in the greenland ice cores and with changes in the strength of upwelling in the cariaco basin

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

extreme inundation flows during the hokkaido nansei oki tsunami the tsunami generated by the july 12 1993 hokkaido nansei oki mw 7 8 earthquake produced in japan the worst local tsunami related death toll in fifty years with estimated 10 18m sec overland flow velocities and 30m runup these extreme values are the largest recorded in japan this century and are among the highest ever documented for non landslide generated tsunamis we model this event to confirm the estimated overland flow velocities and we find that given reasonable ground deformation data current state of the art shallow water wave models can predict tsunami inundation correctly including extreme runup current velocities and overland flow we find that even small local topographic structures affect the runup to first order and that the resolution of the bathymetric data is more important than the grid resolution our results qualitatively suggest that for this event coastal inundation is more correlated with inundation velocities than with inundation heights explaining also why threshold type modeling has substantially underpredicted coastal inundation for this and other recent events

a revised dislocation model of interseismic deformation of the cascadia subduction zone 1 cas3d 2 a new three dimensional 3 d dislocation model is developed to model interseismic deformation rates at the cascadia subduction zone the model is considered a snapshot description of the deformation field that changes with time the effect of northward secular motion of the central and southern cascadia forearc sliver is subtracted to obtain the effective convergence between the subducting plate and the forearc horizontal deformation data including strain rates and surface velocities from global positioning system gps measurements provide primary geodetic constraints but uplift rate data from tide gauges and leveling also provide important validations for the model a locked zone based on the results of previous thermal models constrained by heat flow observations is located entirely offshore beneath the continental slope similar to previous dislocation models an effective zone of downdip transition from locking to full slip is used but the slip deficit rate is assumed to decrease exponentially with downdip distance the exponential function resolves the problem of overpredicting coastal gps velocities and underpredicting inland velocities by previous models that used a linear downdip transition a wide effective transition zone etz partially accounts for stress relaxation in the mantle wedge that cannot be simulated by the elastic model the pattern of coseismic deformation is expected to be different from that of interseismic deformation at present 300 years after the last great subduction earthquake the downdip transition from full rupture to no slip should take place over a much narrower zone

edge wave and non trapped modes of the 25 april 1992 cape mendocino tsunami the 25 april 1992 cape mendocino earthquake generated a tsunami characterized by both coastal trapped edge wave and non trapped tsunami modes that propagated north and south along the u s west coast both observed and synthetic time series at crescent city and north spit are consistent with the zero order edge wave mode solution for a semi infinite sloping beach depth profile wave amplitudes at crescent city were about twice that observed at north spit in spite of the fact that the source region was three times farther from crescent city than north spit the largest observed amplitude was due to an edge wave which arrived almost three hours after the initial onset of the tsunami since such waves are highly localized nearshore this suggests that the enhanced responsiveness at crescent city is at least partly due to local dynamic processes furthermore the substantially delayed arrival of this wave which was generated at the southern end of the cascadia subduction zone has significant implications for hazard mitigation efforts along the entire u s west coast specifically this study demonstrates that slow moving but very energetic edge wave modes could be generated by future large tsunamigenic earthquakes in the csz and that these might arrive unexpectedly at coastal communities several hours after the initial tsunami waves have subsided

multiple sources for late holocene tsunamis at discovery bay washington state usa nine muddy sand beds interrupt a 2500 yr old sequence of peat deposits beneath a tidal marsh at the head of discovery bay on the south shore of the strait of juan de fuca washington an inferred tsunami origin for the sand beds is assessed by means of six criteria although all the sand beds contain marine diatoms and almost all the beds display internal stratification the areal extent of the oldest beds is too limited to confirm their origin as tsunami deposits the ages of four beds overlap with known late holocene tsunamis generated by plate boundary earthquakes at the cascadia subduction zone diatom assemblages in peat deposits bracketing these four beds do not indicate concurrent change in elevation at discovery bay diatoms in the peat bracketing a tsunami bed deposited about 1000 cal yr bp indicate a few decimeters of submergence suggesting deformation on a nearby upper plate fault other beds may mark tsunamis caused by more distant upper plate earthquakes or local submarine landslides trigg

evaluation of tsunami amplitudes for the pacific coast of canada abstract maximum tsunami water levels and currents along the british columbia outer coast have been computed for waves originating from alaska chile the aleutian islands shumagin gap and kamchatka three computer models have been developed to generate and propagate a tsunami from each of these source regions in the pacific ocean to the continental shelf off canada s west coast and into 20 separate inlet systems the model predictions have been verified against water level measurements made at tide gauges after the march 28 1964 alaska earthquake simulated seabed motions giving rise to the alaskan and chilean tsunamis have been based on surveys of vertical displacements made after the great earthquakes of 1964 alaska and 1960 chile hypothetical bottom motions have been used for the shumagin gap and kamachatka simulations these simulations represent the largest tsunamigenic events to be expected from these areas maximum wave and current amplitudes have been tabulated for each simulated tsunami in 185 key locations along the british columbia coast on the north coast of british columbia the alaska tsunami generated the largest amplitudes in all other regions of the west coast the largest amplitudes were generated by the shumagin gap simulation wave amplitudes in excess of 9 m were predicted at several locations along the coast and current speeds of 3 to 4 m s were produced the most vulnerable regions are the outer coast of vancouver island the west coast of graham island and the central coast of the mainland some areas such as the north central coast are sheltered enough to limit expected maximum water levels to less than 3 m the computer models developed in this study are sufficiently general to be applicable to other tsunami affected regions on the globe

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

element and sr isotope signatures of titanite as indicator of variable fluid composition in hydrated eclogite abstract the trace element signature sr common pb u th ree and hfse of titanite gives important information about the formation process of metamorphic titanite we investigated titanite from different textural positions of a strongly retrogressed eclogite from the tromso norway high p area it shows characteristic titanite rims around partially absorbed rutile interpreted as grown during retrogression and hydration of the high p assemblage the titanite rims around rutile are polycrystalline and in contact with the plagioclase amphibole matrix large idioblastic single crystal titanite grew in veins without relics of precursor rutile compositional zoning of al ti f in titanite of both textural positions is irregular and not related to core or rim position in the crystals there is no evidence for systematic growth sequences or diffusion reflecting changing p t conditions or systematic changes of fluid composition trace element patterns of titanite la icp ms data however show systematic variations in the coupling and decoupling behaviour of strongly fluid mobile sr u moderately fluid mobile ree and little fluid mobile nb ta zr hf elements the trace element signatures of titanite from the two different fabric positions reflect contrasting characteristic fluid compositions single crystal titanite equilibrated with fluid that was channelled in the vein polycrystalline titanite on rutile records the composition of a fluid that had migrated along grain boundaries in the amphibole plagioclase matrix fluid from the matrix also contributed to the geochemical signature of vein titanite whereas influence of fluid from the vein on the composition of polycrystalline titanite in the matrix is not evident 87sr 86sr isotope ratios of the different titanite types support the inference from trace elements of spatially and temporally variable fluid sources