new inferences of mantle viscosity from joint inversion of long wavelength mantle convection and post glacial rebound data we perform joint inversions for mantle viscosity of geophysical observables associated with both mantle convection and glacial isostatic adjustment gia our data include coefficients of the non hydrostatic geoid up to degree 8 and decay times associated with post glacial relative sea level rsl variations in hudson bay and fennoscandia we find that both data sets may be reconciled using a single profile of mantle viscosity which is characterized by a significant increase with depth across this region this result weakens previous arguments that the mantle rheology has significant transient effects the viscosity profiles we obtain are found to reconcile the observed free air gravity anomaly over hudson bay

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

the largest local tsunami in 20th century hawaii abstract the 1975 kalapana tsunami had waves that ran up to 14 6 m high it deposited a discontinuous basalt boulder and carbonate sand veneer on the halape apua point coast of the island of hawaii these deposits fine up to 320 m inland and 10 4 masl the deposit is an unusual sedimentary association in which sand sized material is a minor component both boulders and sand fine inland over the same distance not in a continuum and they terminate at approximately the same point boulders were transported and deposited by only one wave the second whereas the sand deposit was in part reworked by subsequent smaller waves boulder transport by one wave in association with a relative paucity of finer sediment reduced internal clast interference and helped to impart a marked fining inland sequence this fining inland sequence is at odds with work that proposes a chaotic or random nature of boulder emplacement by tsunamis where there is abundant sediment clast interference during entrainment will impede the fining inland of larger material in cases where it is difficult to determine the nature of inundation or the number of tsunamis a chaotic pattern may simply reflect deposition by storm tsunami or a combination of the two

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

sea level changes in the tectonically stable malay thai peninsula abstract the malay thai peninsula is part of sundaland a geological region of relative crustal stability therefore the positions of old shorelines of the past 20 000 years or so can be considered to indicate positions of actual past sea levels over 200 shoreline indicators at positions below as well as above present sea level have been radiocarbon dated these dated positions indicate that prior to 6 ka the sea rose from at least 90 m below present sea level at rates that initially amounted to 15 mm year and later became 6 mm year at ca 6 ka the rising sea surpassed its current position and at ca 5 ka it reached 5 m during this maximum marine inundation the peninsula was narrower since the low coastal plains did not yet exist in the period following this maximum transgression the available shoreline data indicate that regional sea level subsided through a series of fluctuations that were characterized by amplitudes of 2 m and periods of about 2000 years the peaks and troughs of the fluctuations became progressively lower the latest peak was at about 1 7 m or 0 7 m above present high tide a few hundred years ago the cause of these fluctuations is not yet known but the trend suggests that in the near future regional sea level may subside at annual rates between 1 5 mm and 2 mm this rate of descent is 25 to 30 of the estimated rate of sea level rise that may result from global warming in other words for the malay thai peninsula the effect of sea level rise on account of manmade greenhouse gases will be partly compensated by actual subsidence of regional sea level

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

tsunami sedimentation associated with the lisbon earthquake of 1 november ad 1755 boca do rio algarve portugal a description is given of a distinctive marine deposit at boca do rio on the algarve coast of portugal it is proposed here that the sediment accumulation was deposited by the tsunami generated by the lisbon earthquake of 1 november ad 1755 the deposit exhibits sedimentary characteristics quite unlike other coastal sediment accumulations that are deposited by more moderate wave regimes these include laterally continuous sand layers chaotic pebble horizons large amounts of gravel sized shell debris and distinctive assemblages of marine microfossils a preliminary attempt is made here to use the empirical field and laboratory data to define more clearly the processes of coastal sedimentation that characterize tsunami runup the use of tsunami sediments as time synchronous marker horizons is also discussed

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

sediments deposited by the 2004 indian ocean tsunami along the malaysia thailand peninsula stratigraphy grain size distribution and foraminiferal assemblages of pre tsunami and tsunami sediment from the indian ocean tsunami at five sites along the malaysia thailand peninsula were analyzed to gain information on tsunami sediment source and deposition style between three and five stratigraphic units were identified at each site and contained between one and three fining upward sequences reflecting waning flow or pre backwash deposition coarser sand layers reflecting uprush high energy flow separated the fining upward sequences with the exception of one site sungai burong which contained a coarsening upward sequence all contacts between the pre tsunami and tsunami sediment were sharp or erosional medium and coarse sand dominated all of the tsunami sediment deposits and often contained shell fragments foraminiferal assemblages were able to differentiate pre tsunami sediment from tsunami sediment where no lithological or grain size distribution change was evident between two and four foraminiferal zones were identified at each of the five sites and provided estimates of sediment source and wave characteristics

contemporary foraminiferal distributions of a mangrove environment great barrier reef coastline australia implications for sea level reconstructions abstract contemporary foraminiferal samples and associated environmental information were collected from cocoa creek a mesotidal fringing mangrove environment on the great barrier reef gbr coastline australia to elucidate the relationship of the foraminiferal assemblages with elevation and environment there is a strong and highly significant relationship between elevation and the foraminiferal assemblages supporting the intertidal vertical zonation concept which suggests that the distribution of foraminifera in the intertidal zone is usually a direct function of elevation with the most important controlling factors being the duration and frequency of subaerial exposure multivariate analyses separate the intertidal foraminiferal assemblages into three elevational zones with zone i the highest and zone iii the lowest zones i and ii are dominated by agglutinated species trochammina inflata and miliammina fusca respectively and zone iii is dominated by calcareous species notably ammonia tepida and elphidium discoidale multiloculum these assemblage zones are similar to those found in both tropical and temperate intertidal environments a predictive transfer function has been developed to allow reconstruction of former sea levels for tropical environments based upon the relationship between foraminiferal assemblage and elevation results suggest that a precision of 0 07 m should be attainable superior to most similar studies from temperate mid latitude environments our work has produced the first foraminifera based transfer function for environmental interpretations for tropical australia and allows the potential development of a new generation of high resolution sea level reconstructions for the post glacial sequences of the gbr shelf

field survey and numerical simulations a review of the 1998 papua new guinea tsunami the papua new guinea png tsunami of 1998 is re examined through a detailed review of the field survey as well as numerous numerical computations the discussion of the field survey explores a number of possible misinterpretations of the recorded data the survey data are then employed by a numerical model as a validation tool a boussinesq model and a nonlinear shallow water wave nlsw model are compared in order to quantify the effect of frequency dispersion on the landslide generated tsunami the numerical comparisons indicate that the nlsw model is a poor estimator of offshore wave heights however due to what appears to be depth limited breaking seaward of sissano spit both numerical models are in agreement in the prediction of maximum water elevations at the overtopped spit by comparing three different hot start initial profiles of the tsunami wave it is shown that the initial shape and orientation of the tsunami wave is secondary to the initial displaced water mass in regard to prediction of water elevations on the spit these numerical results indicate that agreement between numerical prediction of runup values with field recorded values at png cannot be used to validate either a nlsw tsunami propagation model or a specific landslide tsunami hot start initial condition finally with the use of traditional tsunami codes a new interpretation of the png runup measurements is presented

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

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

micropaleontological evidence of large earthquakes in the past 7200 years in southern hawke s bay new zealand abstract foraminiferal and diatom assemblages in 11 cores 3 7 5 m deep of holocene sediment from brackish marine ahuriri inlet in southern hawke s bay new zealand provide a record of 8 5 m of subsidence followed by 1 5 m of uplift in the last 7200 cal years in a region overlying the subduction zone between the australian and pacific plates modern analogue technique was used to estimate paleotidal elevation of the 97 richest foraminiferal assemblages the most precise estimates are for high tidal salt marsh assemblages cored in marginal settings in the north and south of the former inlet the least precise estimates are from low tidal and subtidal assemblages from cores in the middle of the inlet these paleoelevation estimates combined with sediment thicknesses age determinations from tephrostratigraphy and radiocarbon dates the new zealand holocene sea level curve and estimates of compaction identify the holocene land elevation changes and earthquake displacement events in each core the following major earthquake related displacements are inferred ca 7000 cal yr bp 0 6 m displacement ca 5800 cal yr bp 0 5 m ca 4200 cal yr bp ca 1 5 m ca 3000 cal yr bp 1 4 to 1 8 m ca 1600 cal yr bp ca 1 7 m ca 600 cal yr bp ca 1 m 1931ad napier earthquake 1 5 m further smaller events involving regional subsidence or earthquake shake compaction are indicated during the 7000 3000 yr bp interval but cannot be identified precisely the six possibly subduction interface subsidence events in the last 7000 years have had a return time of 1000 1400 years identified displacement events have a range of sedimentary expressions from an eroded and burrowed hiatus surface to an abrupt lithologic switch from mud to sand or peat to shelly mud or in some places no change in sediment character whatsoever

inflow and outflow facies from the 1993 tsunami in southwest hokkaido abstract we describe in detail the sedimentary facies provenance and grain size distributions of the 1993 tsunami deposits in the lower reaches of usubetsu river only two lithofacies were recognized a gravel lobe facies glf and a sand sheet facies ssf the gravel lobe facies was deposited rapidly by a hydraulic jump in contrast the sand sheet facies which contains both current ripples and dunes was deposited by a traction current under subcritical flow conditions we identified four stratigraphic units unit 1 unit 2 unit 3 and unit 4 in ascending order we interpreted units 1 and 2 as having been deposited by the inflow and outflow events of the first run up and units 3 and 4 by the inflow and outflow events of the second run up respectively units 3 and 4 were more widely distributed and coarser grained than units 1 and 2 because the second run up was larger than the first run up furthermore unit 4 was more widely distributed than unit 3 because the outflow eroded the inflow deposits grain size distributions of the inflow and outflow deposits were clearly different unit 4 deposits had a peak at 2 5 phi p 1 population in contrast unit 3 deposits had a bimodal distribution with peaks at 0 5 1 5 phi p 2 population and at 2 5 phi p 1 population a comparison of the tsunami deposits with other sedimentary deposits near the study area showed that the tsunami deposits were mainly derived from the seabed at depths below 5 5 m in the offshore area where the marine sands are about 2 2 5 phi in size and thus are the source of the p 1 population the p 2 population is derived from coarse 0 5 2 phi fluvial materials eroded during the tsunami run up according to our calculations benthic foraminiferal tests were entrained from the comparatively deep seabed at depths up to 100 m during the tsunami run up and included in the tsunami deposits

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

diatoms as an aid in identifying late holocene tsunami deposits diatoms bacillariophyta help identify the onshore deposits of tsunamis from earthquakes on the cascadia subduction zone along the pacific coast of oregon washington and british columbia and on faults high in the north american plate in the puget sound area of washington at the copalis river washington diatom analyses suggest that a tsunami deposit about 300 calendric years old 300 yr bp originated from sandy shoals of the lower estuary rather than nearby beaches or coastal dunes at cultus bay and west point washington well preserved benthic estuarine diatoms in sand sheets overlying tidal marsh peat indicate that the deposits came from intertidal or nearshore areas of puget sound on an abruptly uplifted mudflat at the landward end of hood canal at lynch cove washington tidal flat diatoms refute the possibility of a terrestrial source for the sand diatoms in 300 yr bp tsunami deposits on the niawiakum river washington confirm that the sand in these deposits had a marine source and help

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

an earthquake history derived from stratigraphic and microfossil evidence of relative sea level change at coos bay southern coastal oregon much of the uncertainty in determining the number and magnitude of past great earthquakes in the cascadia subduction zone of western north america stems from difficulties in using estuarine stratigraphy to infer the size and rate of late holocene relative sea level changes a sequence of interbedded peaty and muddy intertidal sediment beneath a small protected tidal marsh in a narrow inlet of coos bay oregon records ten rapid to instantaneous rises in relative sea level each rise is marked by a contact that records an upward transition from peaty to muddy sediment but only two contacts dating from about 1700 and 2300 yr ago show the site wide extent and abrupt changes in lithology and foraminiferal and diatom assemblages that can be used to infer at least half a meter of sudden coseismic subsidence although the characteristics of a third gradual contact do not differ from those of some contacts produced by nonseismic processes regional correlation with other similar sequences and high precision 14 c dating suggest that the third contact records a great plate boundary earthquake about 300 yr ago a fourth contact formed too slowly to have been caused by coseismic subsidence because lithologic and microfossil data are not sufficient to distinguish a coseismic from a nonseismic origin for the other six peat mud contacts we cannot determine earthquake recurrence intervals at this site similar uncertainties in great earthquake recurrence and magnitude prevail at similar sites elsewhere in the cascadia subduction zone except those with sequences showing changes in fossils indicative of 1 m of sudden subsidence sand sheets deposited by tsunamis or liquefaction features

the development of a diatom based transfer function along the pacific coast of eastern hokkaido northern japan an aid in paleoseismic studies of the kuril subduction zone abstract this paper provides a dataset to develop a diatom based transfer function which is applicable to paleoseismic studies at southwestern kuril subduction zone northern japan modern diatom samples were collected from five transects from saltmarshes of lakes akkeshi and onnetoh along the pacific coast of eastern hokkaido the relationships between diatom species and environmental variables were elucidated by canonical correspondence analysis cca and partial ccas partial ccas associated with monte carlo permutation tests show that elevation accounts for a significant portion of the total variance in the diatom data therefore statistically significant transfer functions quantifying the relationship between modern diatom assemblages and elevation were developed using weighted averaging partial least squares and applied to fossil diatom assemblages from lake onnetoh the reconstructed curve of elevations contains five emergence and four submergence events and the transfer functions calculated the amplitude of four of the emergence events to be at least 1 m the results are consistent with paleoecological data produced by previous studies if these events represent uplift associated with interplate earthquake and subsidence during an interseismic period along the kuril subduction zone transfer functions of eastern hokkaido can contribute to reconstruction of the recurrence intervals and the amplitude of earthquakes

foraminiferal evidence for the amount of coseismic subsidence during a late holocene earthquake on vancouver island west coast of canada abstract foraminiferal data from two sites 6 km apart on the shores of an inlet near tofino on the west coast of vancouver island british columbia allow estimates to be made of the amount of coseismic subsidence during a large earthquake 100 400 years ago the sampled sediment succession at the two sites is similar peat representing a former marsh surface is abruptly overlain by intertidal mud grading upward into peat of the present marsh at one of the sites a layer of sand interpreted to be a tsunami deposit locally separates the buried peat from the overlying intertidal mud the abrupt peat mud contact records sudden crustal subsidence during the earthquake the paleoelevation of each fossil sample was estimated by comparing its foraminiferal assemblage with modern assemblages of known elevation the modern assemblages were obtained from surface samples collected along transects across the marsh near the fossil sample sites comparisons were made statistically using transfer functions estimates of coseismic subsidence based on differences in paleoelevations just above and below the top of the buried peat range from 20 cm to 1 m with the most likely value in the 55 70 cm range post seismic crustal rebound began soon after the earthquake and may have been largely complete a few decades later

coastal sedimentation associated with the june 2nd and 3rd 1994 tsunami in rajegwesi java abstract this paper presents the second detailed study of sediments deposited by modern tusnamis the first being that of the flores indonesia tsunami of december 1992 shi et al 1995 sediment cores were collected from areas in which eyewitnesses reported sediment deposition grain size analysis shows pronounced vertical variations in grain size as well as changes in standard deviation skewness and kurtosis that appear to be indicative of complex tsunami flooding vertical variations in grain size in individual cores are greater than spatial variations between cores taken along a transect completed perpendicular to the coastline the java tsunami deposited sediments do not show unequivocal evidence of local erosion but instead evidence for sediment transport and deposition is clear and is characterised by dominantly unimodal sediments with fine tailed distributions

megatsunami deposits on kohala volcano hawaii from flank collapse of mauna loa the origin of coastal and high elevation marine gravels on the hawaiian islands of lanai and molokai is controversial because the vertical tectonics of these islands is poorly constrained the gravels are either from eustatic highstands or were left by massive tsunamis from offshore giant landslides in contrast at kohala on the island of hawaii where continuous subsidence is well established lithofacies analysis and dating of a fossiliferous marine conglomerate 1 5 61 m above present sea level support a tsunami origin and indicate a runup of 400 m 6 km inland the conglomerate age 110 10 ka suggests a tsunami caused by the ca 120 ka giant alika 2 landslide from nearby mauna loa volcano

holocene sea levels and palaeoenvironments malay thai peninsula southeast asia sedimentological and palynological investigations of great songkhla lakes east coast of the malay thai peninsula southeast asia reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps compared with other regions in southeast asia the assemblages are of relatively low diversity geochronological data indicate that the great songkhla lakes record one of the earliest mangrove environments in southeast asia 8420 8190 cal yr bp which are subsequently replaced by a freshwater swamp at 7880 7680 cal yr bp owing to the decline of marine influence sea level observations from great songkhla lakes and other areas of the malay thai peninsula reveal an upward trend of holocene relative sea level from a minimum of 22 m at 9700 9250 cal yr bp to a mid holocene high stand of 4850 4450 cal yr bp which equates to a rise of c 5 5 mm yr the sea level fall from the high stand is steady at c 1 1 mm yr geophysical modelling shows that hydroisostasy

stratigraphic and microfossil evidence for late holocene tsunamis at swantown marsh whidbey island washington abstract four muddy sand sheets occur within a tidal marsh peat at swantown on the west coast of whidbey island washington the two largest sand sheets pinch out about 100 m inland and became thinner and finer grained landward all four sand sheets contain marine microfossils and have internal stratification they record repeated inundation of the marsh over a short time period by distinct pulses of sediment laden ocean water consistent with deposition by a tsunami wave train the layers have been radiocarbon dated to 1160 1350 1400 1700 1810 2060 and 1830 2120 cal yr b p the overlap in age between the two youngest layers and inferred great earthquake events at the cascadia plate boundary some 250 km to the west suggests they were emplaced by tsunamis from this source area the two older layers do not correlate with plate boundary events they may be products of tsunamis caused by earthquakes on local faults in the strait of juan de fuca or by submarine landslides in this area

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

mapping lateral variations in upper mantle attenuation by stacking p and pp spectra 1 we study the lateral variations in p wave attenuation in the upper mantle at frequencies between 0 16 and 0 86 hz by analyzing the spectra from 18 000 p and 14 000 pp arrivals we select seismograms from shallow earthquakes at epicentral distances of 40 80 for p waves and 80 160 for pp waves each spectrum is the product of source receiver and propagation response functions as well as local source and receiver side effects we correct each spectrum for average source and attenuation models since there are multiple receivers for each source and multiple sources for each receiver we can approximate the source and receiver side terms by stacking the appropriate p log spectra the resulting source specific response functions include any remaining source spectrum and near source q structure the receiver stacks include the site response and near receiver q structure we correct the pp log spectra for the appropriate source and receiver side stacks since attenuation in the lower mantle is small the residual log spectrum approximates attenuation in the upper mantle near the pp bounce point and is used to estimate we constrain the anomalies to the top 220 km of the mantle as suggested by previous q studies and translate the measurements to variations in 1000 q the patterns of more and less attenuating regions generally correlate with previously published shear attenuation models and surface tectonics continents are usually less attenuating than the global average whereas oceanic regions tend to be more attenuating there are interesting exceptions to this tectonic pattern such as an attenuating region beneath southern africa

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

amount of subsidence during a late holocene earthquake evidence from fossil tidal marsh foraminifera at vancouver island west coast of canada abstract fossil foraminifera in intertidal deposits beneath a marsh near tofino on west central vancouver island british columbia provide a basis for estimating the amount of subsidence during a large earthquake less than 400 years ago we compared the fossil foraminiferal assemblages with present day assemblages along a surveyed transect across the marsh and we estimated paleo elevation by means of both subjective and quantitative methods the comparisons suggest that the site subsided at least 0 2 m and perhaps more than 1 m during the earthquake most of the subsidence was tectonic for the deposits rest on a pleistocene substrate unlikely to have compacted much when shaken soon after the earthquake the land began to rebound tectonically most of the 0 2 1 m of recorded subsidence was recovered during deposition of the first 6 cm of sediment above the buried marsh surface probably within a few decades after the earthquake because of the speed at which the land rebounded some recovery may have occurred before the first post earthquake sediments were deposited if so the actual amount of subsidence is larger than the foraminiferal data indicate

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

the global reach of the 26 december 2004 sumatra tsunami numerical model simulations combined with tide gauge and satellite altimetry data reveal that wave amplitudes directionality and global propagation patterns of the 26 december 2004 sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid ocean ridge topographic waveguides

linking tsunami deposits submarine slides and offshore earthquakes abstract the recognition that many tsunamis are associated with coastal sedimentation has been of great value in the study of tsunamis prehistorically geological investigation of such sediments has resulted in the identification of a series of palaeotsunamis that appear to have taken place in different areas of the world in most cases however it has proved difficult to link former tsunamis to specific source mechanisms studies of modern tsunamis have also faced difficulties in the recognition of the specific source mechanisms for example offshore earthquakes may trigger submarine slides that combine to produce complex patterns of tsunami flooding at the coast

the 17 july 1998 tsunami papua new guinea evidence and initial interpretation abstract a m w 7 1 earthquake that occurred at 08 49 hours 17 july 1998 utc 6 49 pm local time off the north coast of papua new guinea generated a locally destructive tsunami more than 2189 people died and virtually no structures were left standing along 19 km of coast a fast moving wall of sand laden water left fishing nets and other detritus in trees up to 17 5 m above sea level concrete was stripped to the reinforcing metal and some trees were ripped out and carried more than a kilometre back into sissano lagoon the site is in an active sedimentary basin the aitape trough with 4500 m thickness of neogene sediments between the bewani fault zone and the wewak trench there is some debate about the form of tsunami propagation for this event however we present evidence for subsidence of 30 40 cm on the landward side of the spit fronting sissano lagoon furthermore the area may have subsided up to three times this century in situ stumps of drowned trees in the lagoon record at least one earlier event the low angle harvard university cmt solution m w 7 1 depth 6 0 km 10 landward dip on fault with northward displacement is consistent with the tectonic setting and pattern of aftershocks elastic modelling of the energy release suggests 2 m horizontal displacement over 600 km 2 40 cm subsidence landward and 60 cm uplift seaward convergent flow of the displaced water into the area of subsidence focused wave energy on the coast and generated the locally high wave the record of tsunami at sissano lagoon indicates that the spit fronting the lagoon is unsafe for habitation there is potential for similar coseismic coastal subsidence to focus tsunami in other areas with similar tectonic settings

palaeotsunami deposits a new zealand perspective abstract over the past few years geological investigations of coastal sediments in new zealand have provided evidence of past tsunami the identification of palaeotsunami deposits is helping to increase our knowledge about the sources magnitude and frequency of these events this paper briefly outlines both the key diagnostic characteristics used in new zealand to identify palaeotsunami deposits and the emerging findings related to recent research