sedimentary record of recent tsunamis in the huelva estuary southwestern spain abstract the coast of the gulf of cadiz has been repeatedly struck by tsunamis during the late holocene and the historic period historical documents record at least seven catastrophic tsunamis affecting this coast while others have been detected by oceanic instruments nevertheless very few studies have documented the sedimentary record of these tsunamis in the low energy coastal environments of the gulf of cadiz the huelva estuary is located at the central sector of the gulf of cadiz and is a mesotidal estuary fed by the tinto and odiel rivers the mean tidal range of the huelva estuary is ca 2 m and the mean significant wave height is ca 0 5 m the outer part of the estuary is characterized by extensive sand rich sedimentary bodies of marine origin whereas the central and inner parts are infilled by muddy tidally deposited sediment bodies recorded within these estuarine sediment bodies are five laterally continuous shelly units these units display many of the typical characteristics of tsunami deposits each typically comprises an erosional base followed by a fining upwards sequence that begins with the shell accumulation and ends with bioturbated muddy sand the results of 14 c ages and recent radionuclides accumulation rates in this study illustrate that these five tsunami deposits correspond with known events that occurred in ad 1755 1531 949 1033 881 and 395 381 all of which are documented in historical sources

age and significance of earthquake induced liquefaction near vancouver british columbia canada in late 1994 sand dykes large sand blows and deformed strata were exposed in the walls of an excavation at annacis island on the fraser river delta near vancouver british columbia the features record liquefaction during a large earthquake about 1700 years ago this was perhaps the largest earthquake to affect the vancouver area in the last 3500 years similar less well dated features have been reported from several other sites on the fraser delta and may be products of the same earthquake three radiocarbon ages that closely delimit the time of liquefaction on annacis island are similar to the most precise radiocarbon ages on coseismically subsided marsh soils at estuaries in southern washington and oregon both the liquefaction and the subsidence may have been produced by a single great plate boundary earthquake at the cascadia subduction zone alternatively liquefaction at annacis island may have been caused by a large crustal or subcrustal earthquake of about the same age as a plate boundary earthquake farther west the data from annacis island and other sites on the fraser delta suggest that earthquakes capable of producing extensive liquefaction in this area are rare events further liquefaction analysis using historical seismicity suggests that current assessment procedures may overestimate liquefaction risk

rethinking turbidite paleoseismology along the cascadia subduction zone a stratigraphic synthesis of dozens of deep sea cores most of them overlooked in recent decades provides new insights into deepsea turbidites as guides to earthquake and tsunami hazards along the cascadia subduction zone which extends 1100 km along the pacific coast of north america the synthesis shows greater variability in holocene stratigraphy and facies off the washington coast than was recognized a quarter century ago in a confluence test for seismic triggering of sediment gravity flows that test compared counts of holocene turbidites upstream and downstream of a deep sea channel junction similarity in the turbidite counts among seven core sites provided evidence that turbidity currents from different submarine canyons usually reached the junction around the same time as expected of widespread seismic triggering the fuller synthesis however shows distinct differences between tributaries and these differences suggest sediment routing for which the confluence test was not designed the synthesis also bears on recent estimates of cascadia earthquake magnitudes and recurrence intervals the magnitude estimates hinge on stratigraphic correlations that discount variability in turbidite facies the recurrence estimates require turbidites to represent megathrust earthquakes more dependably than they do along a flow path where turbidite frequency appears limited less by seismic shaking than by sediment supply these concerns underscore the complexity of extracting earthquake history from deep sea turbidites at cascadia

green mosses date the storegga tsunami to the chilliest decades of the 8 2 ka cold event abstract chlorophyll in dead plants ordinarily decomposes completely before permanent burial through exposure to light water and oxygen here we describe 8000 year old terrestrial mosses that retain several percent of its original chlorophyll the mosses were ripped of the land surface carried 50 100 m off the norwegian coast of the time and deposited in depressions on the sea floor by the storegga tsunami a little of the chlorophyll survived because within hours after entraining it the tsunami buried the mosses in shell rich sediments these sediments preserved the chlorophyll by keeping out light and oxygen and by keeping the ph above 7 three factors known to favour chlorophyll s stability because the green mosses were buried alive their radiocarbon clock started ticking within hours after the storegga slide had set off the tsunami radiocarbon measurement of the mosses therefore give slide ages of uncommon geological precision and these together with a sequence of ages above and below the boundary date the storegga slide to the chilliest decades of the 8 2 ka cold event at 8120 8175 years before ad 1950 north atlantic coastal and fjord climatic records claimed to show evidence of the 8 2 cold event should be carefully examined for possible contamination and disturbance from the storegga tsunami

estimating tectonic uplift of the cape fear arch south eastern united states using reconstructions of holocene relative sea level we use relative sea level rsl reconstructions and a spatiotemporal statistical model to estimate the rate of uplift of the cape fear arch a mesozoic structural high during the last 4000 years we reconstructed rsl using 12 radiocarbon dated samples of basal salt marsh sediment preserved at elizabeth creek marsh on the cape fear river the new data show that rsl rose by 3m during the past 4 6 ka at an average rate of 0 67 0 12mm a 1 rsl reconstructions from other sites in southern north carolina which have rates of 0 91 0 10 to 0 84 0 24mm a 1 probably show p 0 9 higher rates of regional rsl rise for the same period while sites from northern south carolina which have rates of 0 72 0 17 to 0 80 0 21mm a 1 probably p 0 67 show the same we attribute the differences between elizabeth creek marsh and neighboring regions to uplift of the cape fear arch which we estimate to be 0 24 0 15mm a 1 uplift of the arch may be responsible for lower rates of 20 th century rsl rise recorded by the wilmington tide gauge relative to rates measured elsewhere along the us mid atlantic coast copyright 2014 john wiley sons ltd

diatom evidence for earthquake induced subsidence and tsunami 300 yr ago in southern coastal washington fossil diatoms from four stratigraphic sections along the tidal niawiakum river southwestern washington provide an independent paleoecological test of a relative sea level rise that has been attributed to subsidence during an inferred earthquake in the cascadia subduction zone about 300 yr ago diatom assemblages in a buried soil and overlying mud indicate a sudden and lasting shift from marshes and forests near or above highest tides to mud flats and incipient tidal marshes with a progressive return to high level tidal marshes by sediment aggradation and perhaps gradual tectonic uplift the amount of coseismic submergence required to generate the paleoecological changes observed at these sites could have ranged from a minimum of 0 8 1 0 m to a maximum of 3 0 m fossil diatoms also provide an independent test of previous inferences that the subsidence was shortly followed by a tsunami the inferred tsunami deposit is a distinct sandy interval that widely overlies the buried marsh and forest soil diatoms from this interval consist of species observed on modern sand flats of the open bay identifying a bayward source for the sand occurrences of the same sand flat species above the buried soil in the farthest up valley outcrop where a sandy interval is not recognizable suggest that the tsunami extended farther landward than was previously inferred from the stratigraphy these data rule out proposed alternatives to the coseismic subsidence model that is climatically induced sea level rise temporary submergence caused by storms and support the hypothesis that a great earthquake struck southwestern washington 300 yr ago

evidence for earthquake triggering of large landslides in coastal oregon usa abstract landslides are ubiquitous along the oregon coast many are large deep slides in sedimentary rock and are dormant or active only during the rainy season morphology observed movement rates and total movement suggest that many are at least several hundreds of years old the offshore cascadia subduction zone produces great earthquakes every 300 500 years that generate tsunami that inundate the coast within minutes many slides and slide prone areas underlie tsunami evacuation and emergency response routes we evaluated the likelihood of existing and future large rockslides being triggered by pore water pressure increase or earthquake induced ground motion using field observations and modeling of three typical slides monitoring for 2 9 years indicated that the rockslides reactivate when pore pressures exceed readily identifiable levels measurements of total movement and observed movement rates suggest that two of the rockslides are 296 336 years old the third could not be dated the most recent great cascadia earthquake was m 9 0 and occurred during january 1700 while regional climatological conditions have been stable for at least the past 600 years hence the estimated ages of the slides support earthquake ground motion as their triggering mechanism limit equilibrium slope stability modeling suggests that increased pore water pressures could not trigger formation of the observed slides even when accompanied by progressive strength loss modeling suggests that ground accelerations comparable to those recorded at geologically similar sites during the m 9 0 11 march 2011 japan trench subduction zone earthquake would trigger formation of the rockslides displacement modeling following the newmark approach suggests that the rockslides would move only centimeters upon coseismic formation however coseismic reactivation of existing rockslides would involve meters of displacement our findings provide better understanding of the dynamic coastal bluff environment and hazards from future subduction zone earthquakes

paleoseismicity of the southern end of the cascadia subduction zone northwestern california the southern end of the cascadia subduction zone csz in northwestern california poses a high seismic hazard this study uses the quaternary stratigraphy of the bays and estuaries to reconstruct coseismic subsidence caused by strong to great earthquakes we used lithology macrofossils and microfossils to estimate the amount of relative sea level change at contacts caused by coseismic subsidence our paleoseismic record contains evidence of four to six earthquakes over the past 2000 years using the pattern and magnitude of submergence and other paleoseismic information trenches and other sites we determine whether the earthquakes were local or regional we found that the record contained evidence for both smaller strong to major earthquakes on local structures m w 6 5 7 2 and larger regional subduction zone related great earthquakes m w 8 2 we compared our record to other records from oregon and washington and found three earthquakes likely caused by the rupture of the entire csz around approximately 230 270 the a d 1700 event 1150 1400 and 1750 1900 cal b p in addition two other local earthquakes likely occurred around 500 600 1000 1250 and possibly 1500 1650 cal b p online material table of radiocarbon ages obtained in the study

characterizing structural and lithologic controls on deep seated landsliding implications for topographic relief and landscape evolution in the oregon coast range usa in mountainous areas landslides regulate temporal variations in sediment production and may suppress simple linkages between topographic development and tectonic forcing rates and mechanisms of mass wasting depend on lithology bedrock structure and climatic and tectonic setting these factors tend to vary signifi cantly in active tectonic regions thus clouding our ability to predict how landsliding modulates topographic development over human and geological time scales here we use a novel dem based technique to document the distribution of large landslides in the oregon coast range ocr and quantify how they affect topographic relief we developed an automated algorithm that exploits the distinctive topographic signature specifi cally the relationship between curvature and gradient of large landslides to map their distribution within the gently folded tyee formation eocene deltaicsubmarine ramp sediments in contrast to steep and highly dissected terrain frequently identifi ed as characteristic of the ocr which exhibits steep planar sideslopes and highly curved low gradient ridgetops and valleys terrain prone to large landslides tends to have low values of both drainage density and curvature and gradient values that cluster between 0 16 and 0 44 the distribution of failure dominated terrain in our 10 000 km2 study area is infl uenced by systematic variations in sedimentary facies and bedrock structure the fraction of terrain altered by large landslides 0 1 km2 varies from 5 in the sand rich delta slope and proximal ramp facies southern section of our study area to 25 in the north distal ramp facies coincident with an increase in the thickness of siltstone beds and a decrease in the sandstone siltstone ratio local relief declines progressively northward suggesting that deep seated landsliding is sensitive to the thickness and frequency of low shearstrength siltstone beds and may serve to limit topographic development in the ocr structural controls are superimposed on facies related variations as deep seated landslides are frequently found on slopes whose downslope aspect corresponds to the bedrock dip direction for 1516 strike and dip measurements in our study area we calculated the fraction of proximal terrain 2 5 km altered by deep seated landsliding in the sand rich southern region the proportion of proximal slide dominated terrain increases modestly with bedrock dip in the silt rich northern region terrain altered by deep seated landsliding is pervasive and an increase in dip from 0 to 16 corresponds to a change in the fraction of slide prone terrain from 10 to 28 our technique for mapping large landslides has utility for hazard analysis and land management over million year time scales the progradational character of the tyee formation suggests that continued uplift and exhumation of the ocr should result in a southward propagation of slide prone silt rich distal facies as a result deep seated landsliding will become increasingly prominent and topographic relief in the central and southern ocr will progressively decline whereas spatial variability in climatic or tectonic forcing is often invoked to explain systematic variations in topographic development our results emphasize the importance of structural and intraformation lithologic controls on landsliding as such analyses linking surface processes climate tectonics and landscapes should be couched in the context of diverse geologic and topographic data

late holocene tectonics and paleoseismicity southern cascadia subduction zone holocene deformation indicative of large subduction zone earthquakes has occurred on two large thrust fault systems in the humboldt bay region of northern california displaced stratigraphic markers record three offsets of 5 to 7 meters each on the little salmon fault during the past 1700 years smaller and less frequent holocene displacements have occurred in the mad river fault zone elsewhere as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded carbon 14 dates suggest that the faulting subsidence and uplift events were synchronous relations between magnitude and various fault offset parameters indicate that earthquakes accompanying displacements on the little salmon fault had magnitudes of at least 7 6 to 7 8 more likely this faulting accompanied rupture of the boundary between the gorda and north american plates and magnitudes were about 8 4 or greater

differences in coastal subsidence in southern oregon usa during at least six prehistoric megathrust earthquakes abstract stratigraphic sedimentologic including ct 3d x ray tomography scans foraminiferal and radiocarbon analyses show that at least six of seven abrupt peat to mud contacts in cores from a tidal marsh at talbot creek south slough coos bay record sudden subsidence relative sea level rise during great megathrust earthquakes at the cascadia subduction zone data for one contact are insufficient to infer whether or not it records a great earthquake it may also have formed through local non seismic hydrographic processes to estimate the amount of subsidence marked by each contact we expanded a previous regional modern foraminiferal dataset to 174 samples from six oregon estuaries using a transfer function derived from the new dataset estimates of coseismic subsidence across the six earthquake contacts vary from 0 31 m to 0 75 m comparison of subsidence estimates for three contacts in adjacent cores shows within site differences of 0 10 m about half the 0 22 m error although some estimates may be minimums due to uncertain ecological preferences for balticammina pseudomacrescens in brackish environments and almost monospecific assemblages of miliammina fusca on tidal flats we also account for the influence of taphonomic processes such as infiltration of mud with mixed foraminiferal assemblages into peat on subsidence estimates comparisons of our subsidence estimates with values for correlative contacts at other oregon sites suggest that some of our estimates are minimums and that cascadia s megathrust earthquake ruptures have been heterogeneous over the past 3500 years

can turbidites be used to reconstruct a paleoearthquake record for the central sumatran margin turbidite paleoseismology aims to use submarine gravity flow deposits turbidites as proxies for large earthquakes a critical assumption being that large earthquakes generate turbidity currents synchronously over a wide area we test whether all large earthquakes generate synchronous turbidites and if not investigate where large earthquakes fail to do this the sumatran margin has a well characterized earthquake record spanning the past 200 yr including the large magnitude earthquakes in 2004 mw 9 1 and 2005 mw 8 7 sediment cores collected from the central sumatran margin in 2009 reveal that surprisingly few turbidites were emplaced in the past 100 150 yr and those that were deposited are not widespread importantly slope basin deposits preserve no evidence of turbidites that correlate with the earthquakes in 2004 and 2005 although recent flow deposits are seen in the trench adjacent slope basins and adjacent pairs of slope basin and trench sites commonly have different sedimentary records and cannot be correlated these core sites from the central sumatran margin do not support the assumption that all large earthquakes generate the widespread synchronous turbidites necessary for reconstructing an accurate paleoearthquake record

evidence for possible precursor events of megathrust earthquakes on the west coast of north america megathrust earthquakes in western north america may be preceded by a precursor phase several years prior to megathrust induced earthquakes for example on 27 march 1964 a 9 2 magnitude on the richter scale earthquake occurred on the coast of alaska changes in foraminifera and diatom assemblages at girdwood flats alaska provide evidence of a precursor to this earthquake thereby detailing a previously unknown sequence of events we describe further evidence of precursor phases from marshes in turnagain arm alaska united states and farther south in netarts bay oregon united states this is the first time that two widely spaced locations have been examined for earthquake related precursor stages the alaska earthquake offers the possibility to compare a modern sequence a d 1964 of events with the geologic record the netarts bay marsh has experienced no modern earthquake that could be used for comparison but the nature of megathrust zones implies that the modern and ancient events should be physically similar new cores examined from turnagain arm include both the 1964 earthquake and an event identified and dated at 1800 yr b p prior to the 1964 event the foraminifera and thecamoebian assemblages changed from a forest phase to a mildly brackish stage this sequence was dated as being 15 yr or less in length using pb210 and cs137 dating techniques the event at 1800 yr b p was also associated with a similar precursor stage indicating a small subsidence prior to the megathrust earthquake related subsidence event in netarts bay a new core was taken at a previously cored site to make use of carbon 14 dates and the assurance that at least four events were known to have occurred over the past 3000 yr the new core contains four transitions each identified by a mineralic deposit often sharply bounded below and gradationally overlain by marsh peat transition in this context refers to the section of core analyzed 15 cm above and below each of the four sand layers foraminiferal assemblage analyses indicate that these units represented a high marsh prequake phase followed by a lower marsh precursor stage the earthquake related deposition sand layer and then a rebound back into postquake marsh deposits sand deposits with either no or few foraminifera are inferred as tsunami earthquake related deposition stages these transitions in two widely separated geographic areas alaska and oregon indicate that similar mechanisms operate for large megathrust earthquakes at subduction zones from alaska to northern california in the cascadia subduction zone thus implying that precursor events also occur and can be detected by foraminiferal zonation all along this area in a recent article dragert et al 2001 1 scientists from the west coast suggested that slow or silent earthquakes they measured with continuous geographical positioning systems might be indicators of megathrust earthquakes the transitions we document may be the prehistoric representations of these silent quakes foraminiferal evidence may help by allowing more accurate positioning of seismometers along the west coast of north america and thereby lead to more precise and timely earthquake prediction methods 1 ref 14

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

microfossil analysis of sediments representing the 1964 earthquake exposed at girdwood flats alaska usa abstract diatom pollen foraminifera and thecamoebian assemblages from an outcrop of peat and silt at girdwood flats in the upper turnagain arm of the cook inlet alaska record four phases of relative land and sea level changes the first phase is the development of freshwater swamp above high marsh sediments during relative land uplift caused by strain accumulation along the locked portion of the alaska aleutian subduction zone in second phase the top 2 cm of the peat all microfossil groups record pre seismic relative sea level rise relative land subsidence the third phase is rapid land subsidence 1 7 m during the earthquake of march 1964 that initiated intertidal silt accumulation above the peat the final phase is the colonisation of mudflat by salt marsh communities during post seismic land uplift the microfossil data compare favourably with sequences from washington oregon and british columbia that record late holocene submergence events caused by earthquakes the comparable changes in microfossil assemblages record the different phases of relative land and sea level changes and the magnitude of land subsidence caused by each earthquake expressed relative to the tidal range at the site these results raise the question whether preseismic sea level rise represents any kind of warning of large 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

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

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

liquefaction evidence for the strength of ground motions resulting from late holocene cascadia subduction earthquakes with emphasis on the event of 1700 a d during the past decade paleoseismic studies done by many researchers in the coastal regions of the pacific northwest have shown that regional downdropping and subsequent tsunami inundation occurred in response to a major earthquake along the cascadia subduction zone this earthquake occurred almost certainly in 1700 a d and is believed by many to have been of m 8 5 9 or perhaps larger in order to characterize the severity of ground motions from this earthquake we report on a field search and analysis of seismically induced liquefaction features the search was conducted chiefly along the banks of islands in the lowermost columbia river of oregon and washington and in stream banks along smaller rivers throughout southwestern washington to a lesser extent the investigation included rivers in central oregon numerous small to moderate sized liquefaction features from the earthquake of 1700 a d were found in some regions but there was a notable lack of liquefaction features in others the regional distribution of liquefaction features is evaluated as a function of geologic and geotechnical factors in different field settings near the coast our use of widely different field settings each in which we independently assess the strength of shaking and arrive at the same conclusion enhances the credibility of our interpretations our regional inventory of liquefaction features and preliminary geotechnical analysis of liquefaction potential provide substantial evidence for only moderate levels of ground shaking in coastal washington and oregon during the subduction earthquake of 1700 a d additionally it appears that a similar conclusion can be reached for an earlier subduction earthquake that occurred within the past 1100 years which also has been characterized by others as being m 8 or greater on the basis of more limited data for older events collected in our regional study it appears that seismic shaking has been no stronger throughout holocene time our interpreted levels of shaking are considerably lower than current estimates in the technical literature that use theoretical and statistical models to predict ground motions of subduction earthquakes in the cascadia region because of the influence of estimated ground motions from cascadia subduction zone earthquakes on seismic hazard evaluations more paleoliquefaction and geotechnical field studies are needed to definitively bracket the strength of shaking with further work it should be possible to extend the record of seismic shaking through much of holocene time in large portions of washington and oregon

sudden probably coseismic submergence of holocene trees and grass in coastal washington state growth position plant fossils in coastal washington state imply a suddenness of holocene submergence that is better explained coseismic lowering of the land than be decade or century long rise of the sea these fossils include western red cedar and sitka spruce whose death probably resulted from estuarine submergence close to 300 years ago rings in eroded bark free trunks of the red cedar show that growth remained normal within decades of death rings in buried bark bearing stumps of the spruce further show normal growth continuing until the year of death other growth position fossils implying sudden submergence include the stems and leaves of salt marsh grass entombed in tide flat mud close to 300 years ago and roughly 1 700 and 3 100 years ago the preservation of these stems and leaves shows that submergence and initial burial outpaced decomposition which appears to take just a few years in modern salt marshes in some places the stems and leaves close to 300 year old are surrounded by sand left by an extraordinary landward directed surge probably a tsunami from a great thrust earthquake on the cascadia subduction zone

micromorphological analysis of coastal sediments from willapa bay washington usa a technique for analysing inferred tsunami deposits tsunami deposits are provisionally distinguished in the field on the basis of anomalous sand horizons fining up and fining landward coupled with organic rich fragmented backwash sediments in this paper micromorphological features of a sediment sequence previously interpreted as being of tsunami origin are described these characteristics are shown to be consistent with the macro scale features used elsewhere but show additional details not seen in standard stratigraphies including possible evidence for individual waves possibly wave magnitude progression organic fragment alignment and intraclast microstructures although replication and more complete studies are needed this analysis confirms the identification of a tsunami in willapa bay in ca 1700 ad while demonstrating a widely applicable technique for confirming or refuting possible tsunami deposits

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

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

sedimentology of seismo turbidites off the cascadia and northern california active tectonic continental margins northwest pacific ocean abstract holocene turbidites from turbidite channel systems along the active tectonic continental margins of the cascadia subduction zone offshore vancouver island to mendocino triple junction and the northern san andreas transform fault the triple junction to san francisco bay have been analyzed for sedimentologic features related to their seismic origin centimeter thick silt sand beds turbidite base capped by mud layers turbidite tail and interbedded with hemipelagic silty clay intervals with high biogenic content have been characterized by visual core descriptions grain size analysis x ray radiographs and physical properties along the northern california margin in upstream single tributary canyons and channels most turbidites are uni pulsed classic fining up whereas downstream below multiple tributary canyon and channel confluences most deposits are stacked turbidites because each set of stacked turbidites has no hemipelagic sediment between each turbidite unit and each unit has a distinct mineralogy from a different tributary canyon we interpret that a stacked turbidite is deposited by several coeval turbidity currents fed by multiple tributary canyons and channels with synchronous triggering from a single san andreas fault earthquake the cascadia margin is characterized by individual multi pulsed turbidites that contain multiple coarse grained sub units without hemipelagic sediment between pulses because the number and character of multiple coarse grained pulses for each correlative multi pulsed turbidite is almost always constant both upstream and downstream in different channel systems for 600 km along the margin we interpret that the earthquake shaking or aftershock signature is usually preserved for the much stronger cascadia 9 mw compared to weaker california 8 mw earthquakes which result in upstream uni pulsed turbidites and downstream stacked turbidites consequently both the strongest 9 mw great earthquakes and downstream confluences cause multi pulsed and stacked turbidites that are typical for seismo turbidites generated by a single great earthquake along both margins earthquake triggering and multi pulsed or stacked turbidites become an alternative explanation for amalgamated turbidite beds in active tectonic margins and show that multiple grain size pulses and reverse grading are not unique criteria for hyperpycnites thalweg levee turbidites or mini basin margin turbidites the analyses of the turbidites along the cascadia and northern california margins reveal common sedimentologic characteristics of turbidites triggered by great earthquakes that can be used to distinguish seismo turbidites in other active tectonic margins around the world

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

coastal evidence for holocene subduction zone earthquakes and tsunamis in central chile abstract the 500 year historical record of seismicity along the central chile coast 30 34 s is characterized by a series of m 8 0 8 5 earthquakes followed by low tsunamis 10 m but the frequency of such large events is unknown we extend the seismic history of central chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of valparaiso 33 s at this site higher relative sea level during the mid holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence within this 2600 yr long sequence we traced six laterally continuous sand beds probably deposited by high tsunamis plant remains that underlie the sand beds were radiocarbon dated to 6200 5600 5000 4400 3800 and 3700 cal yr bp sediment properties and diatom assemblages of the sand beds for example anomalous marine planktonic diatoms and upward fining of silt sized diatom valves point to a marine sediment source and high energy deposition grain size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment upward fining sequences characteristic of suspension deposition are present in five of the six sand beds despite the lack of significant lithologic changes between the sedimentary units under and overlying tsunami deposits we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds during our mid holocene window of evidence preservation the mean recurrence interval of earthquakes and tsunamis is 500 years our findings imply that the frequency of historical earthquakes in central chile is not representative of the greatest earthquakes and tsunamis that the central chilean subduction zone has produced

challenges of anticipating the 2011 tohoku earthquake and tsunami using coastal geology 1 can the magnitude of a giant earthquake be estimated from paleoseismological data alone attempts to estimate the size of the jogan earthquake of ad 869 whose tsunami affected much of the same coast as the 2011 tohoku tsunami offers an excellent opportunity to address this question which is fundamental to assessing earthquake and tsunami hazards at subduction zones between 2004 and 2010 examining stratigraphy at 399 locations beneath paddy fields along 180 km of coast mainly south of sendai we learned that a tsunami deposit associated with the ad 869 jogan earthquake had run inland at least 1 5 km across multiple coastal lowlands and that one of the lowlands had subsided during the jogan earthquake and an earlier earthquake as well radiocarbon ages just below above sand deposits left by the pre jogan tsunamis suggested recurrence intervals in the range of 500 to 800 years modeling inundation and subsidence we estimated size of the jogan earthquake as moment magnitude 8 4 or larger and a fault rupture area 200 km long we did not consider a longer rupture like the one in 2011 because coastal landform and absence of a volcanic ash layer make any jogan layer difficult to identify along the sanriku coast still sendai tsunami geology might have reduced casualties by improving evacuation maps and informing public awareness campaigns

tidal marsh stratigraphy sea level change and large earthquakes i a 5000 year record in washington u s a abstract many of the estuaries of the pacific northwest of the u s a and canada contain stratigraphic sequences typified by alternating peat mud couplets recent studies in this region interpret such couplets as the product of repeated large magnitude s or 9 earthquakes on the cascadia subduction zone the resultant pattern of land level movements is described by a model the earthquake deformation cycle of coseismic land subsidence followed by land uplift during interseismic strain accumulation however peat mud couplets similar to those recorded in the pacific northwest are found on other less tectonically active temperate latitude coasts such as northwest europe and the atlantic coast of the u s a where they have been interpreted as the product of non seismic coastal processes in this paper we apply the methods and scientific framework common to sea level investigations in northwest europe to a sequence of peat mud couplets recorded in the lower johns river an estuary in southern washington to provide a test of the earthquake deformation cycle stratigraphic investigations of the intertidal sediments along the lower johns river using lithological pollen diatom and foraminiferal data show evidence for eight coastal submergence events during the last 5000 years to evaluate the earthquake deformation cycle we assess the lateral extent of peat mud couplets the synchroneity of submergence the presence of tsunami deposits accompanying submergence and the suddenness and amount of submergence each submergence is shown to be accompanied by changes in coastal sedimentation broadly commensurate with those predicted by the earthquake deformation cycle demonstrating the continued intermittent seismic activity of the cascadia subduction zone throughout the mid and late holocene quantitative analyses of contemporary and fossil biostratigraphic data using twinspan and detrended correspondence analysis enable us to estimate the magnitude of submergence accompanying each peat mud couplet one event was accompanied by submergence of about 1 5 m or more four events by intermediate submergence of about 1 0 5 m and a further three events by submergence of

modern foraminifera δ13c and bulk geochemistry of central oregon tidal marshes and their application in paleoseismology we assessed the utility of 13c and bulk geochemistry total organic content and c n to reconstruct relative sea level changes on the cascadia subduction zone through comparison with an established sea level indicator benthic foraminifera four modern transects collected from three tidal environments at siletz bay oregon usa produced three elevation dependent groups in both the foraminiferal and 13c bulk geochemistry datasets foraminiferal samples from the tidal flat and low marsh are identified by miliammina fusca abundances of 45 middle and high marsh by m fusca abundances of 25 the 13c values from the groups defined with 13c bulk geochemistry analyses decrease with an increasing elevation 24 1 1 7 in the tidal flat and low marsh 27 3 1 4 in the middle and high marsh and 29 6 0 8 in the highest marsh samples we applied the modern foraminiferal and 13c distributions to a core that contained a stratigraphic contact marking the great cascadia earthquake of ad 1700 both techniques gave similar values for coseismic subsidence across the contact 0 88 0 39 m and 0 71 0 56 m suggesting that 13c has potential for identifying amounts of relative sea level change due to tectonics

stratigraphic record of holocene coseismic subsidence padang west sumatra 1 stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of padang west sumatra along the mentawai segment 0 5 s 0 3 s of the sunda subduction zone each earthquake is marked by a sharp soil mud contact that represents a sudden change from mangrove to tidal flat the earthquakes occurred about 4000 and 3000 cal years b p based on radiocarbon ages of detrital plant fragments and seeds the absence of younger paleoseismic evidence suggests that late holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone our results point to a brief few thousand year window of preservation of subsidence events in tidal wetland stratigraphic sequences a result that is generally applicable to other emergent coastlines of west sumatra

forcing of large scale cycles of coastal change at the entrance to willapa bay washington abstract anomalous morphological features within large estuaries may be 1 recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes and 2 possible predictors of cycles of future coastal change at the entrance to willapa bay washington chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of cape shoalwater northward channel migration since the late 1800s conforms to the long term net sediment transport direction what requires explanation is periodic southward relocation of the trunk channel by as much as 5 km and attendant construction of moderately large sand spits on the north side of the bay such as kindred island tokeland peninsula and cape shoalwater both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of el nino winter storms however co seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition unless external forcing changes sand supply and predominant sediment transport directions in the future the relative rise in sea level frequent winter storms and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary

the 1992 cape mendocino earthquake broadband determination of source parameters the april 25 1992 cape mendocino earthquake ms 7 1 has renewed speculation about the nature of subduction along the cascadia subduction zone and the associated seismic hazard this event may represent the first large m 6 thrust event along the entire cascadia subduction zone in historic times last 200 years we analyze long period surface waves and broadband body waves in order to estimate the mainshock source parameters we also examine broadband body waves from the nearby 1991 honeydew earthquake m 6 in order to assess the contributions of both rupture complexity and unmodeled source and receiver structure in the cape mendocino waveforms from both body and surface wave inversions as well as forward modeling of body waves we estimate a best double couple mechanism for the cape mendocino earthquake strike 330 10 dip 12 2 rake 75 15 seismic moment 1 93 1019 n m and mw 6 8 this mechanism contains a significant component of slip in the estimated direction of gorda north america plate convergence although this earthquake had suitable geometry for relieving strain accumulated by gorda north america plate convergence we cannot resolve whether it occurred on the interplate megathrust or on a fault within the overriding accretionary prism we find evidence for southwest offshore rupture toward an azimuth of 240 in addition we find evidence for early aftershocks in both the teleseismically recorded body waves and in locally recorded strong motions we model one aftershock delayed 13 s from the mainshock with a mechanism that is different from the mainshock mechanism but is consistent with the north south trending horizontal compression found offshore within the gorda plate we postulate that this aftershock and two additional large strike slip aftershocks that ruptured the gorda plate within 24 hours of the mainshock were caused by the transfer of stress accumulated across the cascadia subduction zone and accretionary prism far offshore to the gorda plate where it reduced the normal stress across nw se oriented faults triggering failure the complexity of fault interactions near the mendocino triple junction needs to be understood before potential seismic hazards of the southern cascadia subduction zone can be quantified

crustal structure beneath the central oregon convergent margin from potential field modeling evidence for a buried basement ridge in local contact with a seaward dipping backstop models of magnetic and gravity anomalies along two e w transects offshore central oregon one of which is coincident with a detailed velocity model provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop the models indicate that the backstop forming western edge of the siletz terrane an oceanic plateau that was accreted to north america 50 million years ago has a seaward dip of less than 60o3 seismic magnetic and gravity data are compatible with no more than 2 km of subducted sediments between the siletz terrane and the underlying crystalline crust of the juan de fuca plate the data also suggest the presence of a n s trending 200 km long basaltic ridge buried beneath the accretionary com plex from about 43on to 45on although the height and width of this ridge probably vary along strike it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the siletz terrane beneath heceta bank several models for the origin of this ridge are discussed these include a sliver of siletz terrane detached from the main siletz terrane dur ing a late eocene episode of strike slip faulting imbrication and thickening of subducted oceanic crust in place an aseismic ridge rafted in on the subducting oceanic crust during the past 1 2 mil lion years and a series of ridges and or seamounts rafted in over a longer period of time and trans ferred from the subducting plate to the overlying plate the last model is the most consistent with the complicated history of local uplift subsidence and slope instability recorded in the ridges basins and banks of this part of the margin we speculate that the massive seaward dip ping western edge of the siletz terrane in this region inhibits subduction of seamounts and sedi ments resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction this process may also be responsible for thickening of lower accretionary complex material over steepening of slopes leading to massive slumping and north south extension through strike slip faulting in the accretionary complex to the west of the buried ridge regardless of its origin the ridge may currently be acting as an asperity inhibiting subduction

oblique strike slip faulting of the central cascadia submarine forearc at least nine wnw trending left lateral strike slip faults have been mapped on the oregon washington continental margin using sidescan sonar seismic reflection and bathymetric data augmented by submersible observations the faults range in length from 33 to 115 km and cross much of the continental slope five faults offset both the juan de fuca plate and north american plates and cross the plate boundary with little or no offset by the frontal thrust left lateral separation of channels folds and holocene sediments indicate active slip during the holocene and late pleistocene offset of surficial features ranges from 120 to 900 m and displaced subsurface piercing points at the seaward ends of the faults indicate a minimum of 2 2 to 5 5 km of total slip near their western tips fault ages range from 300 ka to 650 ka yielding late pleistocene holocene slip rates of 5 5 2 to 8 5 2 mm yr the geometry and slip direction of these faults implies clockwise rotation of fault bounded blocks about vertical axes within the cascadia forearc structural relationships indicate that some of the faults probably originate in the juan de fuca plate and propagate into the overlying forearc the basement involved faults may originate as shears antithetic to a dextral shear couple within the slab as plate coupling forces are probably insufficient to rupture the oceanic lithosphere the set of sinistral faults is consistent with a model of regional deformation of the submarine forearc defined to include the deforming slab by right simple shear driven by oblique subduction of the juan de fuca plate

variable rupture mode of the subduction zone along the ecuador colombia coast three large earthquakes occurred within the rupture zone of the 1906 colombia ecuador earthquake m w 8 8 in 1942 m s 7 9 1958 ms 7 8 and 1979 m s 7 7 we compared the size and mechanism of these earthquakes by using long period surface waves tsunami data and macroseismic data the 1979 event is a thrust event with a seismic moment of 2 9 10 28 dyne cm and represents subduction of the nazca plate beneath south america the rupture length and direction are 230 km and n40 e respectively examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction the seismic moment estimated from the tsunami data and the size of the rupture zone is 2 10 29 dyne cm the 1942 and 1958 events are much smaller about 1 5 to 1 10 of the 1979 event in the seismic moment than the 1979 event we conclude that the sum of the seismic moments of the 1942 1958 and 1979 events is only formula of that of the 1906 event despite the fact that the sequence of the 1942 1958 and 1979 events ruptured approximately the same segment as the 1906 event this difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between the weak zone normally behaves aseismically but slips abruptly only when it is driven by failure of the asperities a small earthquake represents failure of one asperity and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small a great earthquake represents failure of more than one asperity and consequently involves much larger width and slip

tsunamigenic earthquakes past and present milestones we review a number of events which taken individually have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards notably through the development of warning algorithms starting with the 1700 cascadia earthquake we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics the diversity of earthquake cycles the development of warning algorithms the response of communities at risk to warnings and their education the latter being either formal or rooted in ancestral heritage we discuss in detail lessons from the 2004 sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004

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

reexamination of the magnitudes for the 1906 and 1922 chilean earthquakes using japanese tsunami amplitudes implications for source depth constraints far field tsunami records from the japanese tide gauge network allow the reexamination of the moment magnitudes mw for the 1906 and 1922 chilean earthquakes which to date rely on limited information mainly from seismological observations alone tide gauges along the japanese coast provide extensive records of tsunamis triggered by six great mw 8 chilean earthquakes with instrumentally determined moment magnitudes these tsunami records are used to explore the dependence of tsunami amplitudes in japan on the parent earthquake magnitude of chilean origin using the resulting regression parameters together with tide gauge amplitudes measured in japan we estimate apparent moment magnitudes of mw 8 0 8 2 and mw 8 5 8 6 for the 1906 central and 1922 north central chile earthquakes the large discrepancy of the 1906 magnitude estimated from the tsunami observed in japan as compared with those previously determined from seismic waves ms 8 4 suggests a deeper than average source with reduced tsunami excitation a deep dislocation along the chilean megathrust would favor uplift of the coast rather than beneath the sea giving rise to a smaller tsunami and producing effects consistent with those observed in 1906 the 1922 magnitude inferred from far field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes ms 8 3 that were likely affected by the well known saturation effects thus a repeat of the large 1922 earthquake poses seismic and tsunami hazards in a region identified as a mature seismic gap

non destructive analyses to determine appropriate stratigraphic level for dating of tsunami deposits abstract the upper boundary of a tsunami deposit often comprises a mud dominated layer called a mud cap resulting from the different settling times of various grain sizes in the suspended sediment this mud cap is often visibly indistinguishable from muds that can be deposited under normal circumstances following a tsunami in fact dating organic material immediately above the sandy tsunami deposit often produces significantly older ages than the actual age of the event because of the mud cap contains a wide variety of entrained material herein we present several analytical results related to mud caps our results indicate that mud caps are difficult to recognize visually whereas ct and xrf analyses enable us to recognize them in a non destructive way for the dating of tsunami deposits it is crucially important to conduct such non destructive analyses before sampling to recognize unfavorable stratigraphic components for dating such careful sampling is extremely important for accurate dating of tsunami deposit which is essential for reconstruction of paleotsunami size and its frequency therefore our finding will also contribute to tsunami hazard assessment

ambiguous correlation of precisely dated coral detritus with the tsunamis of 1861 and 1907 at simeulue island aceh province indonesia precise u th dates from coral detritus in two pre 2004 tsunami deposits on simeulue island in aceh province allow us to correlate the deposits with historically documented tsunamis in the recent few centuries but because of potential discordance between the death dates of the corals and deposition of the sand layers ambiguity in this correlation remains pits at coastal lowland sites exposed sand layers beneath the 2004 tsunami deposit at busung and naibos on southern simeulue island the layers share sedimentological characteristics with the deposit of the 2004 tsunami and are interpreted as pre 2004 tsunami deposits historical accounts document earthquakes and tsunamis in 1907 and 1861 and suggest that the 1907 tsunami was larger locally than any others historically nonetheless u th analyses of coral boulders in the younger of two pre 2004 deposits at busung and in the lone deposit at naibos yielded dates of death that overlap with 1861 but there were no tsunami layers that could be directly dated to 1907 the younger pre 2004 sand deposit can be attributed to both the 1861 and 1907 events if the dated corals were killed by uplift in 1861 and subsequently entrained and deposited by the 1907 tsunami a piece of coral in the older of the two pre 2004 sand layers at busung dated to around ad 1783 and was deposited by an unknown tsunami that occurred after ad 1783 or possibly by the 1861 tsunami the nearly equatorial latitude of the study sites minimizes potential for geological confusion between tsunami and storm our results show the difficulty in matching known events and geological records when using limiting maximum ages from allochthonous fossils even with high precision radiometric dates

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

tree ring evidence for an a d 1700 cascadia earthquake in washington and northern oregon geologic evidence and radiocarbon dating indicate that a subduction earthquake or series of earthquakes occurred about 300 yr ago along the pacific northwest coast of the united states some radiocarbon dates come from remnants of the myriad trees drowned by coincident subsidence at several coastal lowland locations in washington and northern oregon we located two or more trees that survived partial submergence and lived to the 1990s many of them were damaged by shaking and or inundation some survivors recorded the event s by anomalous changes in ring width or anatomy of their annual rings the disturbance initiating the changes can be dated to between the growing seasons of a d 1699 and 1700 one killed tree has a last ring of a d 1699 tree ring dated evidence of disturbance extends along about 100 km of coastal washington and northern oregon these results support the inference that a great m w 8 earthquake or larger at the cascadia subduction zone generated the historical tsunami that struck japan in january 1700

durability assessments of rare green andesites widely used as building stones in buca izmir turkey miocene volcanism was active in the city area of izmir turkey where volcanic deposits formed predominantly made of gray and pinkish colored andesite these rocks have been widely used in the construction of many buildings in the region in the northern part of izmir known as the buca region there is an area where andesite presents green color the occurrence of the green andesite is rather rare and historically this rock type has been used in the construction of ancient valuable architectonic structures including aqueducts historical buildings and mosques some of these structures date back to the beginning of the first century ad when the region was under the control of the roman empire interestingly the recent survey of these structures showed that after all of these years the green andesite still appears pretty much well preserved only showing slight deterioration in the form of limited crumbling although these rocks were used in this particular region in the past their material properties have not been investigated so far the purpose of this study was therefore to identify mineralogical chemical physical and mechanical properties of these rocks which eventually determine their durability the first phase of the research focused on detailed site investigation which resulted in the definition of the geological extent of the green andesite and the identification of two historical quarries from one of which representative samples was collected for laboratory investigation which was the main task of the second phase of the research the main cause for the green color of the andesite resulted the presence of celadonite which is also accompanied by cristobalite the presence of cristobalite in the pores as a secondary mineral appears to have contributed to the increased strength and durability of buca andesite laboratory evaluation of the durability was in general agreement with field observations although some test gave ambiguous results this discrepancy revealed some weakness of laboratory tests to precisely assess durability of building stones

pollen analysis of coprolites from a late pleistocene holocene cave deposit wezmeh cave west iran insights into the late pleistocene and late holocene vegetation and flora of the central zagros mountains abstract coprolite pollen analysis is increasingly used by palynologists to reconstruct the palaeovegetation especially in the arid to semi arid regions where lakes and peat bogs are scarce this study is the first palynological analysis of coprolites in iran to examine their potential in palaeoenvironmental reconstructions four pollen rich coprolite samples were studied from the wezmeh cave in western iran with a recently discovered late quaternary 70 ka to sub recent faunal assemblage dominated by carnivore remains pollen analysis of coprolites shows that a mountain steppe dominated the glacial landscapes of the area only one sub recent sample indicates the presence of dispersed tree stands one sample was rich in tulipa pollen suggesting that tulips were relatively abundant during the glacial periods cousinia asteraceae pollen was found in all samples with considerable values in one sample indicating its importance in the glacial landscapes of the zagros mountains this study revealed that coprolite pollen analysis can provide an invaluable source of information to understand the floristic composition of palaeolandscapes of the irano turanian region

order and diversity in the modes of circum pacific earthquake recurrence recurrence characteristics of great circum pacific earthquakes and determinations of spatial distribution of seismic moment release are surveyed in order to delineate their general features and relate earthquake slip distribution to models of recurrent rupture as noted by others the pattern of moment release is typically very irregular with strong concentrations in a few isolated regions of a much larger aftershock zone despite this complexity rupture nucleation is notably systematic with mainshock epicenter showing a strong tendency to locate in or immediately adjacent to identified regions of high moment release this generalization suggests that earthquake recurrence is more likely to be controlled by maximum rather than average fault slip well documented case histories from twelve plate boundary regions demonstrate that seismic strain release tends to be temporally well ordered while source dimensions slip and cumulative moment release vary considerably from cycle to cycle on none of the segments studied do earthquakes consistently recur in nearly identical events instead individual great earthquakes differ significantly from cycle to cycle or rerupture takes place in a sequence of two or more smaller events despite these differences the duration of the seismic cycle is approximately uniform furthermore when strain release occurs in a sequence of large earthquakes these events take place towards the end of the cycle and occur with increasing rupture length and magnitude these ordered and irregular features of earthquake recurrence argue for the existence of corresponding elements on plate boundary faults the ordered characteristics are identified with zones of concentrated moment release that slip comparable amounts in each cycle and have high shear strength the irregular features are associated with intervening weaker regions that move in response to the stress concentration of dynamic rupture and slip by differing amounts in each event although these mechanistic associations are indirect and tentative the features of recurrent behavior documented here have implications for long term earthquake hazard assessment that are not dependent on the models proposed to explain them chief among these are the cycle to cycle differences among gap filling events and the absence of shocks that fill major slip deficient regions early in the seismic cycle

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

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

great earthquake paleogeodesy and tsunamis of the past 2000 years at alsea bay central oregon coast usa the width of plate boundary fault rupture at the cascadia subduction zone a dimension related to earthquake magnitude remains uncertain because of the lack of quantitative information about land level movements during past great earthquake deformation cycles beneath a marsh at alsea bay on the central oregon coast four sheets of tsunami deposited sand blanket contacts between tidal mud and peat radiocarbon ages for the sheets match ages for similar evidence of regional coseismic subsidence and tsunamis during four of cascadia s great earthquakes barring rapid unrecorded postseismic uplift reconstruction of changes in land level from core samples using diatom and foraminiferal transfer functions includes modest coseismic subsidence 0 470 2 m during the four earthquakes interpretation is complicated however by the 30 38 of potentially unreliable transfer function values from samples with poor analogs in modern diatom and foraminiferal assemblages reconstructions of coseismic subsidence using good analog samples range from 0 4670 12 to 0 0970 20 m showing greater variability than implied by sample specific errors from apparent high rates of land uplift following subsidence and tsunamis we infer that postseismic rebound caused by slip on deep parts of the plate boundary and or viscoelastic stress relaxation in the upper plate may be almost as large as coseismic subsidence modest coseismic subsidence 100 km landward of the deformation front implies that plate boundary ruptures in central oregon were largely offshore ruptures may have been long and narrow during earthquakes near magnitude 9 as suggested for the ad 1700 earthquake or of smaller and more variable dimensions and magnitudes r 2008 elsevier ltd all rights reserved

geologic evidence for earthquakes during the past 2000 years along the copalis river southern coastal washington evidence for several prehistoric earthquakes is present in deposits less than 2000 years old that crop out at the copalis river estuary 47 07 2 n 124 09 7 w the deposits show that land subsided decimeters into the intertidal zone on as many as three occasions and that sand vented while the land underwent little or no subsidence on another occasion the evidence for earthquake induced subsidence consists of buried marsh and forest soils that evince sudden estuarine submergence attended on at least one occasion by a landward directed surge of sandy water this combination of submergence and surge implies subsidence and tsunami exposed evidence for subsidence and tsunami along the copalis river is strong for a time within a few decades of 300 years ago moderate for a time 1400 1900 years ago and weak subsidence or lacking tsunami for an intermediate time also about 1400 1900 years ago the history of sudden submergence and tsunami in the past 2000 years at the copalis river estuary resembles that shown by buried soils farther south in coastal washington at grays harbor and willapa bay the history can be explained most simply by great mw of 8 or 9 thrust earthquakes at the boundary between the juan de fuca and north america plates with one or two earthquakes occurring 1400 1900 years ago and another close to 300 years ago the evidence for earthquake induced venting along the copalis river consists of sand intrusions and vented sand volcanoes the sand rose through muddy estuarine deposits at least 3 m thick entraining these deposits in fragments as much as 0 3 m long intrusion occurred at one or more times in the past 2000 years and at least some of the venting occurred 900 1300 years ago the sand bodies do not imply artesian flow of flood pressured groundwater because the sand vented forcefully and infrequently through a lowland that probably lacked natural levees the earthquake implied by the venting of sand 900 1300 years ago could have come from a source below above or at the boundary between the juan de fuca and north america plates if from the subducted juan de fuca plate the implied earthquake was farther west or larger than the largest earthquakes within that plate during the past 100 years evidence permitting a source within the north america plate includes a fault scarp an uplifted tideflat and landslides near puget sound dating from the interval 700 1700 years ago a plate boundary source would explain buried soils whose estuarine submergence and burial imply coseismic subsidence for parts of coastal washington in the interval 600 1300 years ago however stratigraphy shows that little or no coseismic subsidence occurred along the copalis river during the venting 900 1300 years ago if a plate boundary earthquake struck coastal washington 900 1300 years ago the earthquake produced a different distribution of land level change than did the plate boundary earthquakes inferred for 1400 1900 and 300 years ago

detection of large prehistoric earthquakes in the pacific northwest by microfossil analysis geologic and palynological evidence for rapid sea level change 3400 and 2000 carbon 14 years ago 3600 and 1900 calendar years ago has been found at sites up to 110 kilometers apart in southwestern british columbia submergence on southern vancouver island and slight emergence on the mainland during the older event are consistent with a great magnitude m 8 earthquake on the cascadia subduction zone the younger event is characterized by submergence throughout the region and may also record a plate boundary earthquake or a very large crustal or intraplate earthquake microfossil analysis can detect small amounts of coseismic uplift and subsidence that leave little or no lithostratigraphic signature

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

trees and herbs killed by an earthquake 300 yr ago at humboldt bay california evidence of rapid seismic induced subsidence at humboldt bay california is produced by analyses of annual growth rings of relict sitka spruce picea sitchensis bong carr roots and entombed herbaceous plants these results add to previously reported evidence that an earthquake caused subsidence 300 yr ago at mad river slough california both types of remains are rooted in buried soils that stood at or above the high tide level until the area subsided at least 0 5 m into the intertidal zone burial by intertidal muds took place quickly enough to preserve the herbs in the growth position analysis of the annual growth rings of the tree roots shows that all died within four growing seasons but the time of root death varies even among roots of the same tree with no central nervous system tree cells do not die simultaneously throughout the organism the 0 5 to 1 5 m of subsidence as evidenced by stratigraphy and sedimentology was not enough to kill all the trees even in one season although such gradual death could be due to rapid aseismic subsidence the tree deaths and preserved herbs are much better explained by sudden coseismic subsidence

stratigraphic and microfossil evidence for a 4500 year history of cascadia subduction zone earthquakes and tsunamis at yaquina river estuary oregon usa we infer that each buried soil represents a cascadia subduction zone earthquake because the soils are laterally extensive and abruptly overlain by sandy deposits and mud preservation of coseismically buried soils occurred from 4500 yr ago until 500 600 yr ago after which preservation was compromised by cessation of gradual relative sea level rise which in turn precluded drowning of marsh soils during instances of coseismic subsidence based on grain size and microfossil data sandy deposits overlying buried soils accumulated immediately after a subduction zone earthquake during tsunami incursion into sallys bend the possibility that the sandy deposits were sourced directly from landslides triggered upstream in the yaquina river basin by seismic shaking was discounted based on sedimentologic microfossil and depositional site characteristics of the sandy deposits which were inconsistent with a fluvial origin biostratigraphic analyses of sediment above two buried soils in the case of two earthquakes one occurring shortly before 1541 1708 cal yr b p and the other occurring shortly before 3227 3444 cal yr b p provide estimates that coseismic subsidence was a minimum of 0 4 m the average recurrence interval of subduction zone earthquakes is 420 580 yr based on an 3750 4050 yr long record and seven to nine interearthquake intervals

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

evidence for a large earthquake and tsunami 100 400 years ago on western vancouver island british columbia abstract a peaty marsh soil is sharply overlain by a sand sheet and intertidal mud at tidal marshes near tofino and ucluelet vancouver island british columbia foraminifera and vascular plant fossils show that the buried soil was submerged suddenly and was covered quickly by sand radiocarbon ages place this event between 100 and 400 yr ago the coastal subsidence suggested by the submergence occurred in an area of net late holocene emergence perhaps during the most recent great earthquake on the northern part of the cascadia subduction zone the sand sheet overlying the peaty soil records the tsunami triggered by this earthquake similar stratigraphic sequences of about the same age have been reported from estuaries along the outer coasts of washington and northern oregon suggesting that hundreds of kilometers of the cascadia subduction zone may have ruptured during one or a series of plate boundary earthquakes less than 400 yr ago

a systematic review of geological evidence for holocene earthquakes and tsunamis along the nankai suruga trough japan the nankai suruga trough the subduction zone that lies immediately south of japan s densely populated southern coastline generates devastating great earthquakes magnitude 8 characterised by intense shaking crustal deformation and tsunami generation forecasting the hazards associated with future earthquakes along this 700 km long fault requires a comprehensive understanding of past fault behaviour while the region benefits from a long and detailed historical record palaeoseismology has the potential to provide a longer term perspective and additional crucial insights in this paper we summarise the current state of knowledge regarding geological evidence for past earthquakes and tsunamis along the nankai suruga trough incorporating literature originally published in both japanese and english and enhancing available results with new age modelling approaches we summarise and critically evaluate evidence from a wide variety of sources palaeoseismic evidence includes uplifted marine terraces and biota marine and lacustrine turbidites liquefaction features subsided marshes and tsunami deposits in coastal lakes and lowlands while 75 publications describe proposed evidence from 70 sites only a limited number provide compelling well dated evidence the best available records enable us to map the most likely rupture zones of twelve earthquakes that occurred during the historical period this spatiotemporal compilation suggests that the 1707 ce earthquake ruptured almost the full length of the subduction zone and that earthquakes in 1361 ce and 684 ce may have been predecessors of similar magnitude intervening earthquakes were of lesser magnitude highlighting the variability in rupture mode that characterises the nankai suruga trough intervals between ruptures of the same seismic segment range from 450 years during the historical period over longer timescales palaeoseismic evidence suggests intervals between earthquakes ranging from 100 to 700 years however these figures reflect a range of thresholds controlling the creation and preservation of evidence at any given site as well as the genuine intervals between earthquakes at present there is no geological data that suggest the occurrence of a larger magnitude earthquake than that experienced in 1707 ce however few studies have sought to establish the relative magnitudes of different earthquake and tsunami events along the nankai suruga trough alongside the lack of research designed to quantify the maximum magnitude of past earthquakes we emphasise issues over alternative hypotheses for proposed palaeoseismic evidence the paucity of robust chronological frameworks and insufficient appreciation of changing thresholds of evidence creation and preservation over time as key issues that must be addressed by future research

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

geologic evidence of earthquakes at the snohomish delta washington in the past 1200 yr exposed channel banks along distributaries of the lower snohomish delta in the puget lowland of washington reveal evidence of at least three episodes of liquefaction at least one event of abrupt subsidence and at least one tsunami since ca a d 800 the 45 measured stratigraphic sections consist mostly of 2 4 m of olivegray intertidal mud containing abundant marsh plant rhizomes the most distinctive stratigraphic unit is a couplet comprising a 0 523 cm thick laminated fining upward tsunami laid sand bed overlain by 2210 cm of gray clay we correlated the couplet which is generally 2 m below the modern marsh surface across an 20 km2 area sand dikes and sand filled cracks to 1 m wide which terminate upward at the couplet and sand volcanoes preserved at the level of the sand bed record liquefaction at the same time as couplet deposition differences in the type and abundance of marsh plant rhizomes across the couplet horizon as well as the gray clay layer suggest that compaction during this liquefaction led to abrupt local lowering of the marsh surface by as much as 50 75 cm radiocarbon ages show that the tsunami and liquefaction date from ca a d 800 to 980 similar to the age of a large earthquake on the seattle fault 50 km to the south we have found evidence for at least two and possibly as many as five other earthquakes in the measured sections at two or more stratigraphic levels above the couplet sand dikes locally feed sand volcanoes radiocarbon ages and stratigraphic position gov suggest that one set of these dikes formed ca a d 910 990 radiocarbon ages on a younger set indicate a limiting maximum age of a d 1400 1640 we also interpret a sharp lithologic change from olive gray rhizome rich mud to grayer rhizome poor mud 1 m above the couplet to indicate a second abrupt lowering of the marsh surface during an earthquake ca a d 1040 1400 but no conclusive liquefaction structures have been identified at this horizon two distinctive coarse sand laminae 30 80 cm below the couplet may record tsunamis older than a d 800 thus study shows that in the past 1200 yr this part of washington s puget lowland has been subjected to stronger ground shaking than in historic times since ca 1870

current deformation and the width of the seismogenic zone of the northern cascadia subduction thrust evidence has been obtained for the accumulation of elastic strain across the northern cascadia subduction zone that may be released in a future very large subduction thrust earthquake vertical and horizontal strain rates across the southern vancouver island region have been determined through 1 long term trends in tide gauge data 2 changes in repeated accurate leveling surveys 3 changes in repeated high accuracy gravity profiles and 4 horizontal shortening observed in repeated precise positioning surveys the outer coast is uplifting at a rate of a few millimeters per year decreasing landward and shortening is occurring across the 100 km wide coastal region at a rate of about 0 1 microstrain per year mm km 1yr 1 the results are compared with the distribution of strain accumulation predicted from elastic dislocation and viscoelastic models for a subduction thrust fault the location of the fault as used in the models is well defined by multichannel seismic reflection and other geophysical data most of the observed current deformation can be explained by interseismic strain accumulation associated with the subduction thrust of southern vancouver island and northern washington provided the locked portion is restricted to a 60 km wide band offshore beneath the continental shelf and slope this conclusion also results from modeling the coseismic subsidence on the outer coast of vancouver island about 300 years ago deduced from paleoseismicity data the unusually narrow downdip extent of the subduction thrust seismogenic zone that extends little if at all beneath the coast is a consequence of high temperatures associated with the young age of the subducted oceanic lithosphere and the thick blanket of insulating sediments the high temperatures limit brittle seismogenic behavior downdip to where the thrust fault is at a depth of less than 15 km the distance from the seismic portion of the megathrust limits the estimated ground motion at the major centers of vancouver and victoria from this source the narrow width may also limit the earthquake size however events of magnitude well over 8 are possible

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

tsunami deposits beneath tidal marshes on vancouver island british columbia thin sheets of sand occur within holocene mud and peat deposits beneath tidal marshes at tofino ucluelet and port alberni on vancouver island british columbia the sand sheets are extensive and have sharp upper and lower contacts in most cases they consist of moderately sorted massive sand and silty sand with abundant wood and other plant detritus at port alberni the thickest sheet has gravel and is graded the upper two sand sheets in the tofino ucluelet area and possibly the third are also present at port alberni eyewitness accounts and 137 cs analysis suggest that the uppermost thinnest sand was deposited by the tsunami triggered by the great alaska earthquake in 1964 the next oldest sand sheet has been radiocarbon dated at our data suggest that large tsunamis have struck the southern british columbia coast several times during the late holocene and that some were much larger than the 1964 tsunami which caused about 10 million damage 1964 canadian dollars to communities on vancouver island because such tsunamis can be expected in the future they pose a hazard to people and property in some coastal areas

microfossils from coastal environments as indicators of paleo earthquakes tsunamis and storms abstract coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest but least frequent events coastal sediments from low energy depositional environments archive geologic evidence of paleo earthquakes tsunamis and storms many of the best reconstructions of these events are derived from changes in microfossil diatoms foraminifera and pollen assemblages in this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines examples from the united states alaska and the pacific northwest japan and chile show that microfossil based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles we discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance e g beach nearshore or offshore sources and identify overwash deposits and how this information can be used to reconstruct the recurrence of tsunamis and storms analysis of overwash deposits from thailand and malaysia indicates the ability of microfossils to resolve individual waves within tsunami sediments and an example from the sendai coastal plain in japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 tohoku tsunami deposit finally we present recent examples from the gulf of mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes

seismic or hydrodynamic control of rapid late holocene sea level rises in southern coastal oregon usa intertidal stratigraphy has been instrumental in demonstrating the hazard posed by great earthquakes at the cascadia subduction zone but inferring an earthquake history from interbedded sequences of peat and mud is complicated by many factors that influence sedimentation and relative sea level change on both tectonic and nontectonic coasts rapid to sudden rises in relative sea level marked by sharp contacts between intertidal peat and overlying mud or sand may reflect coseismic coastal subsidence and tsunami deposition or alterna tively nonseismic hydrodynamic changes in estuaries reconnaissance coring at 16 sites in the marshes fringing a narrow protected tidal inlet of coos bay supplemented by diatom and 14c analyses at four sites reveals a stratigraphic record too fragmentary and ambiguous to distinguish seismic from hydrodynamic causes for more than three of the 10 rises in relative sea level identified only three sharp contacts have the wide extent and evidence of substantial 0 5 m submergence that distinguish them from similar contacts produced by nonseis mic processes correlation with stratigraphic sequences at other estuaries shows that the fringing marshes suddenly subsided and were partially buried by tsunami sand during a great plate boundary earthquake about 300 years ago similar contacts were produced by earthquakes about 1500 1800 years ago and perhaps about 2400 2700 years ago other earthquakes with substantially less subsidence may also have occurred but evi dence is too ambiguous to reconstruct a more complete history

microfossil evidence for land movements associated with the ad 1964 alaska earthquake microfossil diatom and pollen data from a number of cores at coastal marshes at girdwood flats and kenai flats in cook inlet alaska suggest that there was a phase of gradual land subsidence prior to the main shock of the ad 1964 earthquake this phase followed a long period of gradual land uplift since the last large earthquake which occurred about 730 900 years ago caesium 137cs records indicate that subsidence started approximately 15 years before the 1964 earthquake this pre seismic subsidence is evident in the coastal marsh sediment sequences in changes in diatom and pollen assemblages that indicate changes in tidal marsh environments or a change from raised bog to marsh conditions the microfossil evidence indicates 0 15 m pre seismic land subsidence at both girdwood flats and kenai flats and co seismic subsidence of 1 8 m and 0 2 m respectively

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

influences of recurrence times and fault zone temperatures on the age rate dependence of subduction zone seismicity correlations among subduction zone seismicity convergence rate and subducting plate age are reassessed considering the possible roles of both recurrence times and fault zone temperatures distributions of earthquakes with respect to subducting lithosphere age and convergence rate are grossly explained by a recurrence relation when ages and rates at the world s trenches are taken into account correlations between maximum earthquake size m w max and convergence rate occur because faster subduction lowers the average recurrence time so that at random within a limited sampling time faster subduction zones have larger earthquakes published empirical slopes of an assumed linear relationship between m w max and convergence rate are predicted to within 1 standard deviation by such a recurrence model recurrence predicts that m w max should be related to the logarithm of convergence rate and revised age rate m w max data agree with such a relationship no resolvable global correlation between age and m w max is found hence mechanical explanations of subduction zone seismicity based on such correlations are not required predicted average steady state temperatures based on age and dip of the subducting lithosphere and convergence rate at most subduction zone thrust faults are within a small range of values 50 c the few warm outliers that is cascadia mexico and southernmost chile south of chile rise that subduct very young lithosphere also have low seismic coupling coefficients suggesting that high temperature may inhibit seismicity fault zone temperatures can explain global variations in seismic coupling coefficients as well as the slab anchor model of scholz and campos 1995 applying this to the cascadia subduction zone in contrast to conclusions drawn from mechanical models of subduction and consistent with many other observations due to its extremely high temperature cascadia may be a region where aseismic subduction predominates

rupture lengths and temporal history of significant earthquakes on the offshore and north coast segments of the northern san andreas fault based on turbidite stratigraphy piston gravity and jumbo kasten cores were collected from channel and canyon systems draining the northern california continentalmargintoinvestigatetherecordofperiodicholoceneturbiditesforpossibleconnectiontolargemagnitudeearthquakeson the adjacent northern san andreas fault poorly known channel systems were mapped with multibeam sonar to define pathways and channel confluences cores sampled all major and many minor channel systems extending from cape mendocino to just north of monterey bay sampling both along and across channels was done and particular attention was paid to channel confluences as these areas afford opportunities to test for synchronous triggering of turbidity currents while at sea all cores were scanned using a geotek multisensor core logger mscl which collects high resolution photography p wave velocity gamma ray density and magnetic susceptibility data from the unsplit cores lithology was logged visually and cores were later imaged with x radiography we use 14 c ages relative dating tests at channel confluences and stratigraphic correlation using physical properties to determine

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