environmental impact assessment of the 2011 tohoku oki tsunami on the sendai plain abstract large areas of farmland in the sendai plain japan were inundated by the 11 march 2011 tohoku oki tsunami and covered by a discontinuous 30 0 2 cm thick sediment layer consisting of sand and or mud and generally thinning and fining inland two months after the tsunami numerous rice paddy fields and depressions remained ponded with brackish or saline water a series of field surveys in may august and october 2011 were carried out north of sendai airport in order to assess the environmental impact of the tsunami while evaporation had resulted in elevated conductivity in ponded water in may up to 68 2 ms cm 1 rainfall over the next five months led to dilution although brackish water was still recorded in depressions and on paddy fields tsunami sediments underlying soil and soil beyond the tsunami inundation limit were collected at 43 sites along and near a transect extending over 5 km inland and analysed for grain size organic content water leachable ions acid leachable metals and exchangeable metalloids water leachable anion and cation concentrations were elevated in sandy and muddy tsunami deposits and soils particularly in areas where seawater had stagnated for a longer period of time after the tsunami with up to 10 5 cl 6 6 na 2 8 so 4 440 mg kg 1 br measured in surface sediments the impact of saltwater inundation was documented in the chemistry of soils underlying tsunami sediments which were affected by salt contamination down to 15 cm depth and soils not covered by tsunami deposits the latter implies that the extent of tsunami inundation may successfully be determined using geochemical markers in absence of any sedimentological evidence water leachable ions mostly decreased over time however they remained high enough to impact on rice farming which was completely halted in 2011 although further work is required to assess the longer term impact of tsunami inundation flushing of salt with freshwater as well as the possible removal of sandy muddy sediments and underlying soil are recommended to allow crop production to resume

tracing tsunami signatures of the ad 551 and ad 1303 tsunamis at the gulf of kyparissia peloponnese greece using direct push in situ sensing techniques combined with geophysical studies

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

a record of local storms and trans pacific tsunamis eastern banks peninsula new zealand this study of five sand units at lavericks bay new zealand reports on the sedimentary evidence for three trans pacific tsunamis and two local storms the 1868 arica 1877 iquique and 1960 valdivia tsunamis from chile were the largest distantly generated events in new zealand s history but have never before been identified at the same location it is also the first time that the 1877 iquique tsunami deposit has been found in new zealand two further sand units were identified as local storm deposits laid down in 1869 1870 and 1929 the identification and chronology of these events were established through the use of geochemistry palynology diatoms charcoal abundance and historical documents their relative magnitudes were estimated through the use of grain size parameters and lateral extent of the recognisable sand layers the recognisable sandy tsunami deposits extend about 60 of the inundation distance while the storm sediments are finer and less extensive there were two notable geochemical diffe

reexamination of the a d 869 jogan earthquake size from tsunami deposit distribution simulated flow depth and velocity the rupture parameters and magnitude of the a d 869 jogan earthquake a predecessor of the 2011 tohoku earthquake were previously estimated by matching tsunami deposit distributions with simulated inundation areas the tsunami inundation associated with the 2011 tohoku earthquake however extended farther inland than the sandy tsunami deposits numerical simulation of the 2011 tsunami indicated that flow depths and velocities were approximately 1 m and 0 6 m s respectively at the most inland sand deposit sites on the ishinomaki and sendai plains while these values depend on the assumed bottom roughness we used these values to compare tsunami deposits and inundation simulation of the 869 jogan earthquake from both uniform slip and 2011 type variable slip fault models the results showed that the rupture length of the 869 jogan earthquake was at least 200 km and its minimum moment magnitude was 8 6

deposits flow characteristics and landscape change resulting from the september 2009 south pacific tsunami in the samoan islands the september 29th 2009 tsunami caused widespread coastal modification within the islands of samoa and northern tonga in the south pacific preliminary measurements indicate maximum runup values of around 17 m okal et al 2010 and shore normal inundation distances of up to 620 m jaffe et al 2010 geological field reconnaissance studies were conducted as part of an unesco ioc international tsunami survey team survey within three weeks of the event in order to document the erosion transport and deposition of sediment by the tsunami data collected included a general morphology and geological characteristics of the coast b evidence of tsunami flow inundation flow depth and direction wave height and runup c surficial and subsurface sediment samples including deposit thickness and extent d topographic mapping and e boulder size and location measurements four main types of sedimentary deposits were identified a gravel fields consisting mostly of isolated cobbles and boulders b sand sheets from a few to 25 cm thick c piles of organic mostly vegetation and man made material forming debris ramparts and d surface mud deposits that settled from suspension from standing water in the tsunami aftermath tsunami deposits within the reef system were not widespread however surficial changes to the reefs were observed

geological effects and implications of the 2010 tsunami along the central coast of chile abstract geological effects of the 2010 chilean tsunami were quantified at five near field sites along a 200 km segment of coast located between the two zones of predominant fault slip field measurements including topography flow depths flow directions scour depths and deposit thicknesses provide insights into the processes and morphological changes associated with tsunami inundation and return flow the superposition of downed trees recorded multiple strong onshore and alongshore flows that arrived at different times and from different directions the most likely explanation for the diverse directions and timing of coastal inundation combines 1 variable fault rupture and asymmetrical slip displacement of the seafloor away from the epicenter with 2 resonant amplification of coastal edge waves other possible contributing factors include local interaction of incoming flow and return flow and delayed wave reflection by the southern coast of peru coastal embayments amplified the maximum inundation distances at two sites 2 4 and 2 6 km respectively tsunami vertical erosion included scour and planation of the land surface inundation scour around the bases of trees and channel incision from return flow sheets and wedges of sand and gravel were deposited at all of the sites locally derived boulders up to 1 m in diameter were transported as much as 400 m inland and deposited as fields of dispersed clasts the presence of lobate bedforms at one site indicates that at least some of the late stage sediment transport was as bed load and not as suspended load most of the tsunami deposits were less than 25 cm thick exceptions were thick deposits near open ocean river mouths where sediment supply was abundant human alterations of the land surface at most of the sites provided opportunities to examine some tsunami effects that otherwise would not have been possible including flow histories boulder dispersion and vegetation controls on deposit thickness

signatures of natural catastrophic events and anthropogenic impact in an estuarine environment new zealand the sedimentary record of known natural catastrophic events and anthropogenic activity in an estuarine environment is assessed using sedimentological chemical and geochronological techniques shallow cores collected from intertidal and salt marsh sediments in ahuriri estuary hawke s bay reveal a variety of signatures of natural and human disturbance evidence for the 1931 hawke s bay earthquake which resulted in an uplift of one to two metres in the napier area is given by a change from silt to sand dominated sediment in the lower estuary which is consistent with a shift toward higher energy depositional conditions following uplift however based on physical properties of sediments the 1931 uplift event does not appear to have caused major changes in depositional conditions in the upper estuary similarly no changes were recorded at one site in the lower estuary which seems to represent an area of low energy depositional environment although the 1960 chilean tsunami resulted in structural damage in napier it did not produce any recognisable sedimentological and geochemical signature in the sedimentary record suggesting that the study sites were possibly beyond the limit of sedimentation of the tsunami post european settlement impact is mainly restricted to the lower estuary where increased concentrations of zn cr pb and cu are attributed to industrial discharges evidence of agricultural runoff is shown by an increase in cu concentrations within a fine grained depositional environment that is distal from industrial sources in the town of napier chemical data cl and s suggest a change in the depositional environment in the upper estuary due to increased freshwater influx and or decrease in seawater influence dating by 210pb suggests that this occurred around the middle part of the 19th century and might be attributed to river flooding in the region at that time

sedimentology and paleontology of a tsunami deposit accompanying the great chilean earthquake of february 2010 abstract at pichilemu in the northern third of the rupture area of the moment magnitude scale mw 8 8 2010 chile earthquake deposits of the tsunami accompanying the earthquake consist of a lower layer of medium to fine sand mean grain size of 200 m containing rock clasts overlain by a thin silty very fine sand mean grain size of 125 m layer based on a sedimentological model most 90 of the deposit is finer than 401 408 m suggesting tsunami flow velocities were between 7 m s and 13 5 m s ostracods were common in the upper layer along with a small number of broken benthic foraminifera and a single planktonic foraminifera diatoms were abundant throughout species assemblages represent a mixture of diatoms from differing environments life forms and substrate preferences we attribute the mixed assemblages to turbulence within the water column during tsunami inundation with erosion of beaches and salt marshes followed by redeposition of sand and mud inland breakage of fragile diatom valves in the lower layer may also support transport by turbulent flow a higher abundance of diatom species with mud substrate preferences in the upper layer implies a decrease in flow velocity from lower to upper layers

relationship between the maximum extent of tsunami sand and the inundation limit of the 2011 tohoku oki tsunami on the sendai plain japan abstract this paper focuses on the relationship between the maximum extent of sandy tsunami deposits and inundation distance of the 2011 tohoku oki tsunami inundation limits of the tohoku oki tsunami were assessed over seven shore normal transects along the sendai coastal plain inundation distances were found to range from 0 6 to 4 0 km at the maximum extent of the tsunami deposit the sand unit ranged in thicknesses from 0 1 to 4 0 cm the maximum limit of the 0 5 cm thick sand layer extended to over 90 of the inundation distance where the inundation distance was less than 2 5 km this observation is consistent with previous studies that examined characteristics of recent tsunami events that had inundation distances of at least 2 km the maximum limit of the 0 5 cm thick sand layer extended to 3 km 57 76 of the inundation distance where the inundation distance was more than 2 5 km our results are important for estimating paleo tsunami inundation distances based on the landward extent of sand deposits and valuable for the assessment of future tsunami risks in other coastal areas in the world which have been devastated by huge tsunamis in the past

are inundation limit and maximum extent of sand useful for differentiating tsunamis and storms an example from sediment transport simulations on the sendai plain japan we examined the quantitative difference in the distribution of tsunami and storm deposits based on numerical simulations of inundation and sediment transport due to tsunami and storm events on the sendai plain japan the calculated distance from the shoreline inundated by the 2011 tohoku oki tsunami was smaller than that inundated by storm surges from hypothetical typhoon events previous studies have assumed that deposits observed farther inland than the possible inundation limit of storm waves and storm surge were tsunami deposits however confirming only the extent of inundation is insufficient to distinguish tsunami and storm deposits because the inundation limit of storm surges may be farther inland than that of tsunamis in the case of gently sloping coastal topography such as on the sendai plain in other locations where coastal topography is steep the maximum inland inundation extent of storm surges may be only several hundred meters so marine sourced deposits that are distributed several km inland can be identified as tsunami deposits by default over both gentle and steep slopes another difference between tsunami and storm deposits is the total volume deposited as flow speed over land during a tsunami is faster than during a storm surge therefore the total deposit volume could also be a useful proxy to differentiate tsunami and storm deposits

mixed diatom floras in sedimentary deposits from the 2016 kaikōura tsunami at little pigeon bay aotearoa new zealand abstract this study records the diatom flora from sedimentary deposits found within a coastal cottage following the november 2016 kaik ura earthquake and tsunami at little pigeon bay banks peninsula aotearoa new zealand unlike previous studies of diatoms from modern tsunami deposits the sediments in this study were isolated from any previous and subsequent reworking of sediments the diatom flora n 117 taxa are dominated by benthic and planktonic lifeforms with preferences for marine 28 brackish marine 25 fresh brackish 19 and fresh water 17 conditions the higher abundances of benthic marine and brackish marine diatoms are attributed to direct in washing and reworking of open ocean water with sandy marine sediments from the sub tidal and inter tidal zones comparatively high percentage counts of benthic fresh brackish and freshwater diatom taxa also indicate significant freshwater sources and sediments from the stream and land adjacent to the cottage fractured and damaged diatom frustules within the flora including broken sponge spicules emphasise dynamic processes of reworking abrasion and erosion during incoming and outgoing tsunami waves likelihood based ordination analysis of the diatom flora indicates statistical differences between the flora in the back area of the cottage and the centre and front areas which we attribute primarily to the influence of different waves that inundated the cottage from the seaward and landward directions such a record affirms a highly mixed diatom flora from multiple sources and habitats it also offers a first modern analogue from aotearoa new zealand to assist future assessments of multi proxy based records of past tsunami events preserved in the geological record

elemental and mineralogical analysis of marine and coastal sediments from phra thong island thailand insights into the provenance of coastal hazard deposits abstract sediment records left by coastal hazards e g tsunami and or storms may shed light on the sedimentary and hydrodynamic processes happening during such events modern onshore and offshore sediment samples were compared with the 2004 indian ocean tsunami three palaeotsunami and a 2007 storm deposit from phra thong island thailand to determine provenance relationships between these coastal overwash deposits sedimentological and stratigraphic characteristics are generally inadequate to discriminate tsunami and storm deposits so a statistical approach including cluster analysis principal component analysis and discriminant function analysis was used based on grain size mineralogy and trace element geochemistry the mineral content and trace element geochemistry are statistically inadequate to distinguish the provenance of the modern storm and tsunami deposits at this site but the mean grain size can potentially discriminate these overwash deposits the 2007 storm surge deposits were most likely sourced from the onshore sediment environment whereas all four tsunami units statistically differ from each other indicating diverse sediment sources our statistical analyses suggest that the 2004 tsunami deposit was mainly derived from nearshore marine sediments the uppermost palaeotsunami deposit was possibly derived from both onshore and nearshore materials while the lower palaeotsunami deposits showed no clear evidence of their sediment sources such complexity raises questions about the origin of the sediments in the tsunami and storm deposits and strongly suggests that local context and palaeogeography are important aspects that cannot be ignored in tsunami provenance studies

a 7300 year record of environmental changes in a coastal wetland moawhitu new zealand and evidence for catastrophic overwash tsunami abstract three sedimentary sequences from a coastal wetland behind a sand barrier on the west coast of d urville island new zealand were examined using a multi proxy approach including sedimentological geochemical and microfossil diatom analyses with the chronology established using radiocarbon and 210pb dating data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in moawhitu this was followed by periods of alternating wetland encroachment and open water displaying spatial variations until a peatland was established about 1300 cal yr bp the wetland was then partially drained in the early 1900s leading to compaction of the peat near the surface a coarse layer containing gravel sand and shells with a sharp lower contact in the northern area of the wetland is attributed to an overwash about 2500 3000 yr bp most probably a tsunami generated by the rupture of a local or regional fault the high resolution continuous record obtained with xrf core scanning revealed a geochemical signature ca and s for the overwash 600 m inland in the middle area of the wetland while it was absent from the southern site 1 1 km from the shore this suggests that except at the northern end of moawhitu the sand dune acted as an effective barrier preventing any sediment from overtopping 2500 3000 yr bp with only a geochemical evidence marking the extent of seawater inundation no sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in moawhitu as recounted in m ori oral tradition p r kau although pebbles at the surface of the dune are likely to be linked to this event thus the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century however our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years it also shows that a high resolution continuous xrf record can provide the evidence for short term changes catastrophic or not that did not leave any clear sedimentological signature thus providing a better insight of environmental changes in any depositional environment

multi proxy evidence for trans pacific tsunamis in the hawai ian islands abstract the origin of two sand layers buried in polol wetland on the northeast coast of the island of hawai i was investigated using a multi proxy approach including radiometric dating sedimentology geochemistry micropalaeontology palynology and historical records based on 210 pb 137 cs and pollen data the lower sand unit extending 250 to 350 m inland is attributed to the 1946 aleutian tsunami while the upper sand unit was laid down by the 1957 aleutian tsunami chronological information does not appear to support any link between these deposits and historical storm events furthermore sedimentological geochemical diatom and pollen results suggest deposition of marine and near beach sediments under high energy conditions typically associated with tsunami inundation this work presents the first conclusive sedimentary evidence for distantly generated tsunamis on the hawai ian islands opening the way for more comprehensive historical and palaeotsunami studies indeed a brief review of archaeological data suggests that the hawai ian coast may have experienced similar large magnitude events in the past from both local and distant sources

tsunami geomorphology erosion and deposition from the 15 november 2006 kuril island tsunami the 15 november 2006 kuril earthquake mw 8 1 8 4 and tsunami enabled us to collect a compelling data set of coastal geomorphic change in the kuril islands from 3 months before to 9 and 21 months after the tsunami our pre tsunami and post tsunami surveys of the islands including four topographic profi les measured in 2006 and reoccupied in 2007 allow us the confi dence to attribute many changes to the tsunami in spite of an absence of eyewitness accounts in the central islands areas with low runup 15 m underwent massive erosion that dramatically altered the coastline tsunami deposits roughly corresponded with the extent of tsunami runup and inundation the amount of sediment eroded by the tsunami far outweighed the amount deposited on land in all cases studied the tsunami was dominantly erosive in the kuril islands because the high relief topography of the coastline accelerated tsunami outfl ow

sequence stratigraphy and onlap history of the donets basin ukraine insight into carboniferous icehouse dynamics abstract the degree to which permo carboniferous cyclothemic successions archive evidence for long term variations in ice volume during the late paleozoic ice age is insufficiently resolved here we develop the sequence stratigraphy and onlap offlap history for a 33 my interval of the carboniferous using the u pb calibrated succession of the donets basin ukraine in order to assess the relationship between sea level high latitude changes in glacial extent and climate integrated subsurface and outcrop data permit meter scale correlation of 242 biostratigraphically constrained limestones and coals and in turn individual cyclothems across 250 km of the donets basin rapid uniform subsidence and basinwide continuity of marker beds indicate pennsylvanian deposition under relatively stable tectonic conditions three scales of sequences avg durations of 140 ky 480 ky and 1 6 my are recognized on the basis of stratigraphic stacking patterns and basinwide architecture of marine to terrestrial facies assemblages the hierarchy of sequences and the geographic and stratigraphic positions of shifts in base level sensitive facies across the donets ramp permit the construction of an onlap offlap history at a sub 400 ky scale major sea level lowstands occur across the mid carboniferous boundary and during the early moscovian these lowstands coincide with glacial maxima inferred from high latitude glacigenic deposits the middle to late pennsylvanian is characterized by a stepwise onlap culminating in an earliest gzhelian highstand suggesting contraction of carboniferous ice sheets prior to the initiation of early permian glaciation the stratigraphic position of climate sensitive facies within individual donets cyclothems indicates a turnover from seasonal sub humid or semi arid climate to everwet conditions during the late lowstand and maximum ice sheet accumulation comparison of the stratigraphic and aerial distribution of coals and evaporites in the donets basin with the onlap offlap history further indicates everwet conditions during lowstands and inferred glacial maxima and drier climate during onlap and inferred ice sheet contraction at the intermediate 0 8 to 1 6 my and long 106 yr time scales taken together the relationship between inferred climate and glacioeustasy suggests a likely teleconnection between high latitude ice sheet behavior and low latitude atmospheric dynamics

geological evidence and sediment transport modelling for the 1946 and 1960 tsunamis in shinmachi hilo hawaii abstract the japanese community of shinmachi established on low lying land between downtown hilo and waiakea hawaii was obliterated by the 1946 aleutian tsunami but was rebuilt only to be destroyed again by the 1960 chilean tsunami the aim of this study was to find out if any geological evidence of these well documented events had been preserved in the sedimentary record in wailoa river state park which replaced shinmachi after the 1960 tsunami this was achieved by collecting cores in the park and performing sedimentological chronological and geochemical analyses the latter also processed by principal component analysis sediment transport modelling was carried out for both tsunamis to infer the source of the sediment and areas of deposition on land the field survey revealed two distinct units within peat and soil a thin lower unit composed of weathered basalt fragments within mud unit 1 and an upper unit dominated by fine volcanic sand within fine silt exhibiting subtle upward fining and coarsening unit 2 consisting of unit 2a and unit 2b although these two anomalous units only occur on the western shore of waiakea mill pond analysis with an itrax core scanner shows that unit 1 is characterised by high mn fe rb la and ce counts combined with elevated magnetic susceptibility based on its chemical and sedimentological characteristics unit 1 is attributed to a flood event in wailoa river that occurred around 1520 1660 ce most probably as a result of a tropical storm the sharp lower contact of unit 2 coincides with the appearance of arsenic contemporaneous with an increase in ca sr si ti k zr mn fe la and ce in this study as is used as a chronological and source material marker as it is known to have been released into wailoa river estuary and waiakea mill pond by the canec factory between 1932 and 1963 thus not only the chemical and sedimentological evidence but also sediment transport modelling corroborating the historical record suggest that unit 2a was deposited by the 1946 tsunami and the sediment most likely originated from wailoa river estuary beach and nearshore seafloor the upper part of this unit unit 2b is believed to have been deposited by the 1960 tsunami as suggested by sediment transport modelling although limited accommodation space is likely to have resulted in the thin deposit 3 cm thickness present at that site limited accommodation space on the island of hawaii has led to only rare locations where tsunami deposits are preserved despite the repeated occurrence of tsunamis affecting the island

chemical signatures of palaeotsunamis a forgotten proxy article i nfo article history a range of diagnostic criteria are required to help identify palaeotsunami deposits although chemical signatures have long been used as indicators of palaeosalinity in sedimentary sequences their use in the studies of palaeotsunami deposits is rarely applied and is yet to be widely recognised the chemical composition of interstitial water in coastal ponds and sedimentary sequences in coastal marshes and lagoons has been used successfullyasanindicatoroftsunamiinundation chemicalsignaturescanalsoprovidecluesaboutthelandward limit of runup of a tsunami beyond the area of sediment deposition like most palaeotsunami proxies however the preservation of chemical signatures varies with environmental conditions

evaluation of the use of paleotsunami deposits to reconstruct inundation distance and runup heights associated with prehistoric inundation events crescent city southern cascadia margin historic and prehistoric tsunami sand deposits are used to independently establish runup records for tsunami hazard mitigation and modeled runup verification in crescent city california located in the southern cascadia subduction zone inundation from historic 1964 farfield tsunami 5 6 m runup height left sand sheet deposits 100 200 m width in wetlands located behind a low beach ridge 3 4 m elevation of the national geodetic vertical datum of 1988 navd88 the most landward flooding lines 4 5 5 m elevation in high gradient alluvial wetlands exceed the 1964 sand sheet records of inundation by 1 2 m in elevation the most landward flooding in low gradient alluvial wetlands exceed the corresponding sand sheet record of inundation distance by 1000 m nevertheless the sand sheet record is an important proxy for high velocity inundation sand sheet deposition from the 1964 historic tsunami closely corresponds to the landward extent of large debris transport and structural damage in the crescent city waterfront the sand sheet deposits provide a proxy for maximum hazard or kill zone in the study area six paleotsunami sand sheets 0 3 3 ka are recorded in the back ridge marshes in crescent city yielding a 450 year mean recurrence interval for nearfield cascadia tsunami two paleotsunami sand deposit records likely correlated to cascadia ruptures between 1 0 and 1 5 ka are traced to 1 2 km distance and 9 10 m elevation as adjusted for paleo sea level the paleotsunami sand deposits demonstrate at least twice the runup height and four times the inundation distance of the farfield 1964 tsunami sand sheet in the same marsh system the preserved paleotsunami deposits in crescent city are compared to the most landward flooding as modeled by other investigators from a predicted cascadia mw 9 rupture the short geologic record 1 5 ka yields slightly lower runup records than those predicted for the modeled mw 9 rupture scenario in the same marsh but it generally verifies predicted maximum tsunami runup for use in the planning of emergency response and rapid evacuation copyright 2011 john wiley sons ltd

salinity in soils and tsunami deposits in areas affected by the 2010 chile and 2011 japan tsunamis the accumulation of data sets of past tsunamis is the most basic but reliable way to prepare for future tsunamis because the frequency of tsunami occurrence and their magnitude can be estimated by historical records of tsunamis investigation of tsunami deposits preserved in geological layers is an effective measure to understand ancient tsunamis that occurred before historical records began however the areas containing tsunami deposits can be narrower than the area of tsunami inundation thus resulting in underestimation of the magnitude of past tsunamis a field survey was conducted after the 2010 chile tsunami and 2011 japan tsunami to investigate the chemical properties of the tsunami inundated soil to examine the applicability of tsunami inundation surveys considering water soluble salts in soil the soil and tsunami deposits collected in the tsunami inundated areas are rich in water soluble ions na mg2 cl br and so42 compared with the samples collected in the non inundated areas the analytical result that the ratios of na mg2 br and so42 to cl are nearly the same in the tsunami deposits and in the tsunami inundated soil suggests that the deposition of these ions resulting from the tsunami inundation does not depend on whether or not tsunami deposits exist discriminant analysis of the tsunami inundated areas using the ion contents shows the high applicability of these ions to the detection of tsunami inundation during periods when the amount of rainfall is limited to examine the applicability of this method to palaeotsunamis the continuous monitoring of water soluble ions in tsunami inundated soil is needed as a future study

geomorphology and accommodation space as limiting factors on tsunami deposition chatham island southwest pacific ocean abstract chatham island in the southwest pacific ocean is exposed on all sides to potential tsunami impact in historical time tsunamis are known to have inundated the coast on several occasions with the largest event in 1868 coastal dunes along the northeast coast of chatham island preserve sedimentary evidence of this and possibly earlier tsunami events as localised gravel lags however these deposits lack a clear stratigraphic context and establishing their age is difficult this study examines the sediment record in a freshwater wetland at okawa point located directly landward of the dunes where apparent tsunami gravels occur sediment descriptions pollen foraminifera chemical data and radiocarbon dates from cores are used to reconstruct the environmental history of the wetland the record extends from ca 43 ka to the present and incorporates glacial post glacial and human influenced phases throughout this time the wetland appears to have remained isolated from catastrophic marine inundation the only evidence for saltwater intrusion is observed in the historic period via geochemical grain size and pollen data which record a marine inundation event that forced the transport of a thin cm thick deposit of dune and beach sand into the seaward edge of the wetland this is interpreted as the signature of the 1868 tsunami the lack of more widespread physical evidence for this and other tsunami events in the wetland is attributed to the morphological roughness afforded by coastal dunes and limited accommodation space for holocene deposits

benchmarks and sediment source s of the 1755 lisbon tsunami deposit at boca do rio estuary article standardizing the signature of tsunami deposits has been identified as a major limitation for the identifica tion of paleo tsunami deposits this limitation mostly arises from the strongly source dependent nature of these deposits which in turn determines their composition and depositional architecture and from the effect of the local morphology of the corresponding depositional environment here we provide new high resolution mineralogical geochemical and micro macrofauna data of the 1755 tsunami layer of boca do rio estuary algarve portugal with the aim of unraveling the signatures of estuarine tsunami deposits and linking them to possible sediment sources we also apply for the first time diffuse reflectance spectropho tometry drs analysis our results show that the 1755 tsunami deposit of the boca do rio estuary is featured by an enhancement in sr and ca which are linked to the input of biogenic and detrital carbonates shell frag ments and limestone clasts from the beach foreshore and a strong depletion in most terrestrial and marine sensitive indicators the latter is interpreted as resulting from the reworking of the estuarine clays and subsequent dilution within a huge volume of sand eroded from the coastal barrier it confirms that in the case of the boca do rio estuary the sediment source is essentially proximal and coastal textural and min eralogical features between the base and the top of the tsunami layer suggest the imprint of run up and back wash currents derived from a unique wave micro and macrofauna analysis and drs data of the siliciclastic fraction show slight but significant environmental changes occurring just after the tsunami which could be provoked by an eventual closure of the estuary mouth

diatom assemblages in tsunami deposits associated with the 2004 indian ocean tsunami at phra thong island thailand abstract diatom assemblages in sandy deposits of the 2004 tsunami at phra thong island thailand may provide clues to flow conditions during the tsunami the tsunami deposits contain one or more beds that fine upward commonly from medium sand to silty very fine sand diatom assemblages of the lowermost portion of the deposit predominantly comprise unbroken beach and subtidal species that live attached to sand grains the dominant taxa shift to marine plankton species in the middle of the bed and to a mix of freshwater brackish and marine species near the top these trends are consistent with expected changes in current velocities of tsunami through time during high current velocities medium sand is deposited only beach and subtidal benthic diatoms attached to sediment can be incorporated into the tsunami deposit high shear velocity keeps finer material including planktonic diatoms in suspension with decreasing current velocities finer material including marine plankton can be deposited finally during the lull between tsunami waves the entrained freshwater brackish and marine species settle out with mud and plant trash low numbers of broken diatoms in the lower medium sand implies rapid entrainment and deposition whilst selective breakage of marine plankton thalassionema nitzschioides and thalassiosira and coscinodiscus spp in the middle portion of the deposit probably results from abrasion in the turbulent current before deposition

quaternary stratigraphy and trace element indices of the yangtze delta eastern china with special reference to marine transgressions the quaternary stratigraphy of the yangtze delta has been revealed by a deep 344 64 m continuous borehole the sediments of which are divided into four sections the early q1 middle q2 and late pleistocene q3 and the holocene q4 six lithofacies include lacustrine fluvial coastal drowned river channel deltaic and shallow marine in these time periods the fluvial and lacustrine lithofacies prevailed during q1and q2 coastal and drowned river channel lithofacies periodically appeared in q1 q2 and q3 shallow marine lithofacies dominated q3 and deltaic lithofacies occurred in q4 based on stratigraphy four transgressive events are inferred trace element sr ba b ga v content and ratios of sr ba and b ga are considered with regard to their distribution in the various lithofacies geochemical facies criteria are established based on combined diagnostic indices sr 160 ppm b 90 ppm sr ba 0 35 b ga 4 0 for the shallow marine lithofacies sr 90 ppm b 50 ppm sr ba 0 2 b ga 2 5 for the terrigenous lithofacies these indices correspond well to paleosalinity data obtained using the sedimentary phosphate method ca ca fe transgressive events identified by the geochemical indices are mostly the same as reflected by marine fossils nevertheless geochemical indices can indicate the occurrence of a weak transgression where marine fossils are rare

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

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

extreme wave deposits on the pacific coast of mexico tsunamis or storms a multi proxy approach abstract historical and instrumental data show that the pacific coast of mexico has been exposed to destructive tsunamis over at least the past 500 years this coast is also affected by hurricanes generated in the eastern pacific the great 1985 mexico earthquake and its aftershock generated tsunamis that affected the ixtapa zihuatanejo and michoacan coast the purpose of our study was two fold a to determine whether storm and tsunami deposits could be distinguished and b whether tsunami deposits from historical events are preserved in the tropical environments of the ixtapa zihuatanejo coast two anomalous sand units in the ixtapa estuary are interpreted to be the result of high energy marine inundation events that occurred in the last century several lines of evidence using a multi proxy approach historical studies interviews with local witnesses geomorphological and geological surveys coring and trenching laboratory analyses including grain size micropaleontology geochemistry magnetic susceptibility and radiometric dating and numerical modeling indicate the occurrence of two tsunamis that we link to local events the 21st september 1985 mexico and possibly the 14th march 1979 petatlan earthquakes we thereby provide the first onshore geological evidence of historical tsunamis on the pacific coast of mexico

lagoon subsidence and tsunami on the west coast of new zealand abstract sediment core and trench data from a coastal lagoon on the west coast of the south island new zealand are used to investigate evidence for co seismic subsidence and associated tsunami inundation physical data are used to document a salt marsh soil buried 80 cm below the modern sediment surface that is locally covered by a gravelly sand bed the sediment record also contains geochemical and biological diatom and foram evidence for abrupt changes in salinity of lagoon waters that link to subsidence tsunami flooding and to the open versus closed state of the lagoon tidal entrance at the local scale these relationships allow for separation of tsunami evidence from other agents of environmental change in the lagoon we also propose a conceptual connection between these local changes and regional drivers of landscape development most notably major earthquakes and resultant pulses in sediment supply to the coast

diatom assemblages within tsunami deposit from the 2011 tohoku oki earthquake along the misawa coast aomori prefecture northern japan abstract this paper reports variations in the diatom assemblages within the deposit from the 2011 tohoku oki tsunami along the misawa coast aomori prefecture northern japan the landward extent of the tsunami deposit was as much as 400 m inland the deposit contained mixed assemblages of marine brackish and freshwater diatoms the mixed assemblages indicated that the tsunami deposit was composed of not only beach and dune sand but also soil from the coastal forest marine brackish species were predominant in the seaward tsunami deposit however the relative abundance of marine brackish species rapidly decreased in the samples about 150 to 250 m inland from the shoreline a decrease in marine brackish diatoms at inland locations suggests that the eroded terrestrial soil was incorporated into the tsunami deposit the composition of marine brackish species in the tsunami deposit was different from that of modern inter to supra tidal sediments one possible interpretation for this discrepancy is that the 2011 tsunami deposit were sourced from multiple environments including supra inter and sub tidal locations

mid holocene tectonic geomorphology of northern crete deduced from a coastal sedimentary archive near rethymnon and a late bronze age santorini tsunamite candidate abstract the late bronze age lba tsunami and the a d 365 tsunami are supposed to have affected the northern coasts of crete however near coast sedimentary archives have been rarely investigated in this area and sedimentary archives including palaeotsunami fingerprints are still unknown the main objective of our research was to search for appropriate tsunami sediment traps in order to gain detailed insights into the holocene palaeotsunami history of northern crete we found an excellent fine sediment archive near pirgos located to the west of rethymnon based on a multi electrode geoelectrical survey and an 11 m deep sediment core we analysed the event geochronostratigraphical record by means of sedimentological geochemical geochronological geomorphological and microfossil investigations the pirgos record revealed a thick unit of homogeneous mud of a lagoonal environment starting 6000 years ago the lagoon was affected by five high energy events leaving layers of allochthonous sand microfossil analyses of these layers revealed a mixed foraminiferal assemblage including species from brackish habitats but also displaced and transported species from open marine and deep water environments considering sedimentary characteristics the local wave climate of the cretan sea and the overall geomorphological setting we interpret these layers as related to extreme wave events ewe based on a local radiocarbon age depth model we identified one ewe layer as a reliable candidate for the lba santorini tsunami another ewe layer is most probably associated with the a d 365 tsunami this ewe ended abruptly the lagoonal conditions at pirgos because of to the 1 64 m coseismic uplift at the site the pirgos lagoon existed between the first half of the 6th mill b c and at least the end of the 2nd mill b c we found that the area around pirgos has continuously subsided over 3000 or so years reflecting constant tectonogeomorphological conditions dominated by the nearby subduction zone between the aegean and african plates

sheet gravel evidence for a late holocene tsunami run up on beach dunes great barrier island new zealand abstract a semi continuous sheet of granule to cobble size clasts forms a distinctive deposit on sand dunes located on a coastal barrier in whangapoua bay great barrier island new zealand the gravel sheet extends from the toe of the foredune to 14 3 m above mean sea level and 200 m landward from the beach clasts are rounded to sub rounded and comprise lithologies consistent with local bedrock terrestrial sources for the gravel are considered highly unlikely due to the isolation of the dunes from hillslopes and streams the only source for the clasts is the nearshore to inner shelf of whangapoua bay where gravel sediments have been previously documented the mechanism for transport of the gravel is unlikely to be storm surge due to the elevation of the deposit maximum recorded storm surge on this coast is 0 8 m above mean high water spring tide aeolian processes are also discounted due to the size of clasts and the elevation at which they occur tsunami is therefore considered the most probable mechanism for gravel transport minimum run up height of the tsunami was 14 3 m based on maximum elevation of gravel deposits optical ages on dune sands beneath and covering the gravel allow age bracketing to 0 4 7 ka within this time frame numerous documented regional seismic and volcanic events could have generated the tsunami notably submarine volcanism along the southern kermadec arc to the east southeast of great barrier island where large magnitude events are documented for the late holocene radiocarbon ages on shell from maori middens that appear to have been reworked by tsunami run up constrain the age of this event to post ca 1400 ad regardless of the precise age of this event the well preserved nature of the whangapoua gravel deposit provides for an improved understanding of the high degree of spatial variability in tsunami run up

cosmogenic 36cl accumulation in unstable landforms 2 simulations and measurements on eroding moraines cosmogenic 36cl surface exposure ages obtained for multiple boulders from single landforms are usually characterized by a variance larger than that of the analytical methods employed this excessive boulder to boulder variability progressively more profound with increasing age of landforms is due to removal of soil and gradual exposure of boulders at the surface in our gradual exposure model boulders are initially buried in moraine matrix with time erosion lowers the moraine surface and the boulders are gradually exposed to cosmic rays because the cosmic ray intensity changes with depth the boulders are subjected to variable production rates of the cosmogenic 36cl initial depth of boulders and their chemical composition are variable which results in different amounts of the accumulated cosmogenic 36cl and thus different apparent ages of boulders the shape of the resulting distribution of the apparent ages and the coefficient of variation depend on the erosion depth while the first moment is a function of the true surface age and the erosion depth these properties of the apparent age distributions permit calculation of the surface age the erosion depth and also the average erosion rate we tested the model calculations using 26 boulders from a late pleistocene moraine at bishop creek sierra nevada california the set exhibited a bimodal distribution of the 36cl surface exposure ages we interpreted the older mode as the result of gradual exposure and the younger one as the result of surficial processes other than soil removal the 10 samples that constitute the older mode produced a distribution which closely matches the modeled distribution calculated using an age of 85 kyr and erosion depth of 570 g cm 2 this age is the same as an independent estimate obtained from cation ratio studies and the calculated erosion depth is very close to the erosion depth of 600 g cm 2 based on a simple analytical model of soil erosion these results indicate that our statistical model adequately describes effects of soil erosion on accumulation of cosmogenic 36cl the approach can be used to simultaneously obtain the true landform age and the erosion rate from apparent 36cl ages and thereifore may help in evaluation of surface exposure ages of eroding landforms

geochemical signatures up to the maximum inundation of the 2011 tohoku oki tsunami implications for the 869 ad jogan and other palaeotsunamis abstract the geochemical signature of the tohoku oki tsunami deposit and underlying soil was assessed two months five months and seven months after the 11 march 2011 tsunami inundated the sendai plain the extent of the recognisable sand deposit was traced up to 2 9 km inland while a mud deposit was found up to 4 65 km inland representing 60 and nearly 95 of the maximum tsunami inundation respectively the limit of tsunami inundation was identified 4 85 km from the shore using geochemical marine markers s and cl two months after the tsunami in the absence of any sedimentological evidence concentrations of other geochemical markers k ca sr indicative of the marine incursion and associated minerals were found to decrease landward 13 c and 15 n and c n ratios suggested a mixture of terrestrial and marine organic sources in the sediment while 34 s of sulphate reflected the marine source of water soluble salts the chemical composition of the 869 ad jogan tsunami sand deposit was characterised by high sr and rb concentrations and was comparable to that of the tohoku oki tsunami deposit suggesting that the sources of sediment may be similar marked decreases in s and cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments however both s and cl markers as well as sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami this suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition in particular when marine microfossils are sparse or lacking as is the case on the sendai plain this would allow researchers to redraw palaeotsunami inundation maps and re assess the magnitude of events such as the jogan tsunami and other palaeotsunamis not only on the sendai plain but also elsewhere around the world this has important implications for tsunami risk assessment hazard mitigation and preparedness

traces of tsunami preserved in inter tidal lacustrine and marsh deposits some examples from northeast japan the japan sea earthquake of may 26 1983 triggered a large scale tsunami that surged over the coast of ne japan and caused considerable damage the tsunami resulted in peculiar sedimentary processes on the coast depending on the hydraulic scale of the tsunami three kinds of sedimentary processes were recognized each of which left unique deposits such deposits are expected to remain in sedimentary sequences preserving remarkable sedimentary facies borehole samples drilled at different localities in coastal regions have been examined to detect traces of ancient tsunamis sedimentological and geochemical studies of the samples reveal that layered deposits similar to those developed by the tsunami of the japan sea earthquake are common in the drilled cores estimated ages of these deposits are exactly equivalent to the dates of ancient tsunamis documented in historical records these results show that the invasion of tsunamis is recorded in coastal depositional sequences from analyses of long borehol

seismic signals in coastal dune systems abstract coastal dune ridge systems throughout the world form initially in response to phases of abundant sand supply and yet researchers rarely consider the importance of seismic related activity to dune formation or destruction new zealand examples of seismic related coastal dune formation and their occasional remobilisation are discussed pulses of sand sized sediment produced by large earthquakes and transported to the coast by geomorphic processes can generate new dune ridges tsunami inundation can modify existing dunes producing features such as relict dune pedestals landward sand sheets hummocky topography and parabolic dunes the case is put forward for the need to consider evidence for catastrophic events in coastal dune systems particularly when working in tectonically active areas of the world recognition of some of the effects of seismic related processes on coastal dunes however does not mean that these are easily identified in the field or even present in the existing landscape it does however mean that they should not be ignored

impact of holocene tsunamis detected in lagoonal environments on corfu ionian islands greece geomorphological sedimentary and microfaunal evidence abstract in this paper we present for the first time geomorphological sedimentary and microfaunal evidence of palaeotsunami impact on corfu ionian islands greece the island of corfu is located in an area of exceptional tectonic stress towards the south the african oceanic plate is being subducted underneath the aegean plate whereas towards the north the adriatic and european plates form a continental collision zone recent publications provide evidence of earthquake related co seismic movements that potentially trigger extreme wave events as well as relative sea level fluctuations in this context we investigated two selected near coast geological archives the chalikiopoulou lagoon in the east and the korission lagoon in the southwest of corfu island our results clearly document that the eastern as well as the southwestern coasts of corfu were repeatedly affected by palaeotsunami impact during the holocene with regard to the local topographical constellation and the recent geomorphodynamic potential of each study area evidence of high energy wave impact is based on the stratigraphical and microfaunal record of selected vibracoring sites as well as on numerical modelling results it is concluded that the eastern coast of corfu is preferably affected by high energy wave impacts from a southern direction such impacts are most likely related to teletsunamis from the major seismical zone of the hellenic trench in contrast the southwestern coast of corfu is endangered by impacts from both western and southern directions such impacts may comprise teletsunamis triggered in the hellenic trench or the etna regions but may also be caused by local submarine landslides at the steeply sloping continental shelf directly west of corfu our study builds a bridge between palaeotsunami research conducted in the southern ionian sea and the adriatic sea and allows to better discriminate between the effects of teletsunamis and locally triggered events within one of the seismically most active regions in the eastern mediterranean

insights from geochemistry and diatoms to characterise a tsunami s deposit and maximum inundation limit abstract geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 february 2010 maule tsunami at las canas maule region chile but also to trace the maximum inundation limit of the event the sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60 of the total tsunami inundation distance of 380 m which was marked by organic debris pumice clasts and wooden logs it consisted of coarse to medium sand that thinned and fined inland at the most seaward point the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening fining upward units suggesting deposition by at least two waves while farther inland the fining upward deposit was probably left behind by only one wave chemical proxies ca ti vs sr ba allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and or dune area with diatom assemblages confirming the marine origin of the deposit saltwater indicators e g cl s provide evidence for the maximum inundation limit beyond the extent of the sandy deposit despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami marine and marine brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond suggesting the effect of diatom bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind while the latter might result in a slight over estimation of the inundation distance they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis thus allowing for a better estimation of the magnitude of past events post depositional processes were found to have affected the thinner sandy deposits

sediment sources and sedimentation processes of 2011 tohoku oki tsunami deposits on the sendai plain japan insights from diatoms nannoliths and grain size distribution abstract the 11th march 2011 tohoku oki tsunami inundated the low lying sendai plain japan more than 5 km inland leaving sand and mud deposits over most of the area in order to establish the sources of the tsunami deposits and interpret processes of their sedimentation samples were collected from the deposits underlying soils and the beach along a shore perpendicular transect and analysed for grain size diatom assemblages and nannoliths the fining inland tsunami deposits consisted of poorly to moderately sorted medium to coarse sand within 2 km of the coastline and very poorly to poorly sorted mud farther inland more specifically there was a slight fining of the coarse to medium sand mode within the sandy deposits and an increased contribution of the coarse and very coarse silt fraction in the mud deposits the tsunami deposits also exhibited vertical changes including fining upward and coupled coarsening fining upward trends few diatoms were present in beach sediments soils and tsunami deposits within 1 km of the coastline while diatoms were more abundant farther inland diatom assemblages in the soil and tsunami deposits were similar and dominated by species typical of freshwater brackish habitats while no typically marine species were encountered nannoliths were generally absent in the studied sediments except for few specimens our data indicate that there was probably no or only a very minor component of marine sediments transported onland by the tsunami the sandy tsunami deposits within 1 km of the coastline were mostly derived from beach and dune erosion from 1 to 2 km landward the contribution of these sources decreased while sources comprising local soil erosion and the entrainment of sediments from the teizan bori canal increased farther inland local soil erosion was the major sediment source for the mud deposits the tsunami deposits were most likely deposited during at least two inundations mostly out from suspension resulting in an upward grain size fining trend however bed load deposition was also important in the sandy deposits as suggested by a common grain size upward coarsening position on c m diagrams and frequent horizontal lamination the present study reveals that even very large tsunamis may not transport marine sediments onland and thus many commonly applied indicators of tsunami deposits based on the assumption of their offshore origin marine diatoms foraminifera nannoliths marine sediments may be of limited use

experimental diatom dissolution and the quantification of microfossil preservation in sediments abstract four laboratory experiments on fresh modern diatoms collected from lakes in the northern great plains of north america were carried out to assess the effects of dissolution on diatom abundance and composition marked differences in mean dissolution susceptibility exist between species despite sometimes significant intra specific variation between heterovalves twenty four taxa were ranked according to susceptibility to dissolution using an exponential decay model of valve abundance this dissolution ranking was used to derive two weighted indices of sample preservation a third index f was based on a simple binary classification of valve morphology into dissolved and pristine categories as distinguished by light microscopy lm when compared against rank indices and a measure of species diversity this diatom dissolution index was found to be the best predictor of the progress of dissolution as estimated by total valve abundance or biogenic silica bisi loss strong empirical relationships between f index values and diatom abundance r2 0 84 n 32 and bisi r2 0 89 n 32 were developed and applied to a diatom sequence from a short core from devils lake north dakota and compared to diatom inferred and observed salinity at this site the f index is a simple effective diagnostic tool to assess important aspects of diatom preservation the index can provide insight into si cycling and record changes in conditions pertinent to diatom dissolution and has a role in validation of transfer functions or other inferences derived from compositional data

a geochemical approach for identifying marine incursions implications for tsunami geology on the pacific coast of northeast japan abstract potential tsunami inundation areas can be predicted by the distribution of paleo tsunami deposits on land which are mainly composed of marine derived sands and muds these exotic sandy and muddy layers have been identified by multiple approaches however there still remain uncertainties regarding the sources and weathering trends over the long term and other useful proxies need to be investigated to identify of tsunami deposits we examined the geochemical signatures of modern tsunami deposits from the pacific coast of northeast japan 2011 tohoku tsunami and those paleo tsunami deposits taken from the tohoku district jogan 1080 calibrated ages before present cal bp and yayoi ca 2000 cal bp a geochemical ternary diagram seawater rock as metals showed the weathering trends of tsunami deposits over approximately 2000 years in the sendai plain in the tohoku in the tsunami layers from the tohoku the na ti atomic ratios markedly increased to 23 4 with an average value of 19 3 3 0 jogan and yayoi tsunami deposits which was clearly higher than those of other layers soil deposits 10 3 3 5 on average these results show that na ti ratios and other geochemical proxies are useful indicators of marine incursions in our case and may contribute to the detection of muddy tsunami deposits close to the limit of inundation

preservation potential of tsunami deposits on arid siliciclastic coasts abstract numerous post tsunami surveys have been conducted in the last two decades especially since the 2004 indian ocean tsunami these studies have documented a variety of characteristic sedimentary and erosional features that can be ascribed to known events nevertheless the question arises whether these structures are just ephemeral or have a potential to be preserved in the geological record this review describes the changes that have affected muddy to sandy siliciclastic tsunami deposits in peru each of these was surveyed in the first months after the tsunami chimbote 1996 camana 2001 and pisco paracas 2007 here we describe the changes we observed during re surveys in 2007 and 2008 it has long been recognized that onshore tsunami deposits may suffer from surficial processes tectonic movements and anthropogenic alteration earthquake induced uplift or subsidence may subject a tsunami deposit to erosion or burial respectively quick burial in rapidly subsiding coastal areas may enhance preservation deposits of the last or most landward reaching wave may be preferentially preserved if they escape erosion by subsequent tsunami waves however inland areas are also vulnerable to subaerial reworking including by wind and by humans the peruvian examples reviewed here show that the preservation of arid coast tsunami deposits depends on interactions that are more complex that hitherto perceived these involve sediment type grain size depositional setting co seismic movement bioturbation winds and anthropogenic modification in one example all traces of the tsunami have been removed or reworked by flash floods and ocean waves in another example clasts on a coastal plain from tsunami backwash began to be rounded and abraded by eolian sands immediately after the event eolian processes also smoothed and filled tsunami scours by contrast muddy tsunami deposits in certain areas escaped erosion by wind probably because of their greater cohesion in still another example 0 5 m of co seismic uplift was not enough to prevent ocean waves from removing a tsunami sand sheet that had mantled a coastal marsh the buried record of tsunami deposits on modern coasts may therefore not fully represent the vulnerability of these regions to tsunamigenic hazards

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

geochemical and petrographical characteristics of a domed bog nova scotia a modern analogue for temperate coal deposits a freshwater domed bog in nova scotia canada was investigated for its petrographic mineralogical and geochemical characteristics three cores were taken from the lagg zone margin and centre to examine different stages of evolution in a fen to domed bog sequence based on this study a model was developed which shows the relationship between factors controlling peat geochemistry and petrography all of them being dependent on trophic conditions the bog may represent a modern analogue for temperate coal deposits and thus can be used to help understand spatial variability within coal beds rheotrophic conditions in the early stages of mire development result in the formation of high ash highly humified carex dominated peat while the evolution toward ombrotrophic conditions is reflected in a progressive replacement by low ash and well preserved sphagnum dominated peat the associated decrease in ph reflects a decrease of groundwater influence which is also supported by the mineralogical assemblage and petrographic data decrease in reflectance and change in maceral composition except for cl br i and se which are associated with the organic fraction variations in elemental composition can be explained in terms of mineral matter abundance i e decrease upward and with increasing distance from the margin sea spray is the most probable origin for halogen enrichment in the peat

the sedimentary record of the 1960 tsunami in two coastal lakes on isla de chiloe south central chile abstract this study describes sediments deposited by the tsunami following the 1960 great chilean earthquake mw 9 5 in two coastal lakes lakes cucao and huelde on the west coast of isla de chiloe south central chile 42 6 s sub bottom profiles and side scan sonar mosaics illustrate the sedimentary context of transects of gravity cores the stratigraphy of both lakes features gyttja sedimentation interrupted by the abrupt emplacement of a sandy layer with mud rip up clasts and a mud cap this sandy layer reflects a sudden change in sedimentary environment most probably caused by a high energy inundation radionuclide analyses 137cs and 210pb date the inundation deposit to shortly before the mid 1960s the only known event that matches the sedimentological and chronological criteria is the ad 1960 tsunami using grain size analysis and comparisons with samples from modern environments we demonstrate that the proximal seaward part of the deposit consists of a mixture of sand derived from subaerial sources and reworked gyttja lake sediment in the distal landward part of lake cucao the sand component is lost and the deposit consists entirely of remobilised lake sediments the repetition of tsunami deposit sequences in lake huelde suggests a minimum of three inundating waves sub bottom profiles and side scan sonar mosaics reveal tsunami inundation over the barrier and more prominently through the outlet river channel the dominant role of the river channel as a pathway for sediment transport is also described in core samples by tsunami deposits that fine away from the channel mouth the identification and description of the deposit left by a known tsunami provide important insights into tsunami sedimentation in coastal lakes and have the potential to help in the search for paleotsunami evidence

a seismological study of the 1835 seismic gap in south central chile we study the possible seismic gap in the concepcion constitucion region of south central chile and the nature of the m 7 8 earthquake of january 1939 from 1 march to 31 may 1996 a seismic network of 26 short period digital instruments was deployed in this area we located 379 hypocenters with rms travel time residuals of less than 0 50 s using an approximate velocity distribution using the velest program we improved the velocity model and located 240 high precision hypocenters with residuals less than 0 2 s the large majority of earthquakes occurred along the wadati benioff zone along the upper part of the downgoing slab under central chile a few shallow events were recorded near the chain of active volcanos on the andes these events are similar to those of las melozas near santiago a few events took place at the boundary between the coastal ranges and the central valley well constrained fault plane solutions could be computed for 32 of the 240 well located events most of the earthquakes located on the wadati benioff zone had slab pull fault mechanism due to tensional stresses sub parallel to the downgoing slab this slab pull mechanism is the same as that of eight earthquakes of magnitude around 6 that are listed in the cmt catalog of harvard university for the period 1980 1998 this is also the mechanism inferred for the large 1939 chilean earthquake a very small number of events in the benioff zone had slab push mechanisms that is events whose pressureaxis is aligned with the slab these events are found in double layered wadati benioff zones such as in northern chile or japan our spatial resolution is not good enough to detect the presence of a double layer but we suspect there may be one 2002 elsevier science b v all rights reserved

high resolution geochemical and grain size analysis of the ad 1755 tsunami deposit insights into the inland extent and inundation phases abstract in the study of palaeotsunamis it is crucial to decipher the sedimentological record to derive intensity of past events and to infer different inundation phases to achieve this goal it is important to apply high resolution techniques that allow magnifying intra deposit details at a sub centimetric scale that otherwise would not be perceived consequently valuable information could be overlooked in this work we applied successfully high resolution geochemical and grain size analyses xrf core scanning and image analysis respectively to the ad 1755 tsunami deposit this quartz sand enriched in bioclast deposit exhibiting high si al and ca ti was recognized in the coastal stratigraphic sequence of salgados lagoon due to its contrasting composition when compared with the under and overlying mud layers with scarce bioclasts exhibiting low si al and ca ti in the absence of textural evidence the identification of peaking concentrations of cl s and br all major constituents of sea salt in a continuous muddy sequence allowed slightly extending farther inland the limit of inundation in addition grain size analysis data attested the fining inland of the deposit furthermore despite the macroscopic massive structure of the tsunami deposit throughout the lagoon grain size results revealed more complexity and allowed inferring up to four depositional sequences directly associated with the ad 1755 tsunami inundation

tsunami runup and tide gauge observations from the 14 november 2016 m7 8 kaikōura earthquake new zealand the 2016 m w 7 8 kaik ura earthquake was one of the largest earthquakes in new zealand s historical record and it generated the most significant local source tsunami to affect new zealand since 1947 there are many unusual features of this earthquake from a tsunami perspective the epicentre was well inland of the coast multiple faults were involved in the rupture and the greatest tsunami damage to residential property was far from the source in this paper we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast then present tsunami tide gauge and runup field observations of the tsunami that followed the kaik ura earthquake for the size of the tsunami as inferred from the measured heights the impact of this event was relatively modest and we discuss the reasons for this which include the state of the tide at the time of the earthquake the degree of co seismic uplift and the nature of the coastal environment in the tsunami source region

determining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure in the absence of eyewitness reports or clear sedimentary structures it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns the emplacement dynamics of two historical tsunami deposits were investigated at seven transects in okains bay new zealand using a combined geospatial geomagnetic and sedimentological approach the tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland the deposits are attributed to the 1960 and possibly the 1868 tsunamis based on radiometric dating and correlation with historical records measurements of magnetic fabric mf anisotropy of magnetic susceptibility and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically a combination of statistical methods including spatial autocorrelation testing spearman s rank order correlation principal component analysis pca and k means cluster analysis was applied to examine relationships between mf parameters and sediment texture and infer depositional hydrodynamics flow patterns deduced from mf show the estuary channel acted as a conduit for inundation with flow commonly aligned sub perpendicular to the estuary bed mf and sediment data suggest deposition occurred from settling during laminar flow evidence of both uprush and backwash deposition as well as wave reflection from infrastructure was found statistical analysis of data showed significant relationships between grain size parameters and mf parameters associated with flow speed and magnetic fabric type pca and cluster analysis differentiated samples into two primary hydrodynamic groups 1 samples deposited from laminar flow and 2 samples deposited close to the limit of inundation which includes samples deposited further inland those affected by flow convergence and those in the upper part of tsunami deposits this approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses large scale investigations can be more easily performed this article is protected by copyright all rights reserved

boron beryllium and sulfur in holocene sediments and peats of the nile delta egypt their use as indicators of salinity and climate abstract the concentrations of 14 major and trace elements b ba be co cr cu fe mn ni p s v zn and organic c in bulk sediment samples of holocene age from bore holes in the nile delta egypt are considered in terms of sediment grain size and depositional setting using this background information an attempt is made to evaluate paleosalinity and paleoclimatic change by geochemical analyses of peats in every sediment facies examined we find that grain size is a major controlling factor of geochemical composition but the b be ratio is helpful in paleoenvironmental interpretations organic matter content is the major factor affecting element concentrations in peats zn cr fe be cu mn concentrations on an organic matter free basis are lower in these organic rich layers than in other nile delta sediment facies the sulfur content of the peats indicates a decreased importance of freshwater input to holocene lagoons from about 8000 to 3400 years bp high boron beryllium ratios and the presence of gypsum in peats deposited between 6300 and 4900 years bp record the most evaporitic phase affecting this region this geochemical finding is in close agreement with results of other independent paleoclimatic studies which indicate the onset of arid conditions in northeast africa at about 5000 years bp

new insights of tsunami hazard from the 2011 tohoku oki event we report initial results from our recent field survey documenting the inundation and resultant deposits of the 2011 tohoku oki tsunami from sendai plain japan the tsunami inundated up to 4 5 km inland but the 0 5 cm thick sand deposit extended only 2 8 km 62 of the inundation distance the deposit however continued as a mud layer to the inundation limit the mud deposit contained high concentrations of water leachable chloride and we conclude that geochemical markers and microfossil data may prove to be useful in identifying the maximum inundation limit of paleotsunamis that could extend well beyond any preserved sand layer our newly acquired data on the 2011 event suggest that previous estimates of paleotsunamis e g 869 ad j gan earthquake and tsunami in this area have probably been underestimated if the 2011 and 869 ad events are indeed comparable the risk from these natural hazards in japan is much greater than previously recognized

effects of rainy season on mobilization of contaminants from tsunami deposits left in a coastal zone of thailand by the 26 december 2004 tsunami study on contamination of tsunami sediments deposited on 26 december 2004 conducted shortly after the tsunami in coastal zone of thailand revealed elevated contents of salts in water soluble and some heavy metals and arsenic in bioavailable fractions szczucinski et al in env geol 49 321 331 2005 few months later rainy season started and effected in total rainfall of over 3 300 mm this paper presents results of survey repeated 1 year after the tsunami to assess the effects of rainy season on mobilization of previously determined potential contaminants the same locations were sampled again and analysed with the same methods the tsunami deposit layer was well preserved but in many locations the sediments were coarser than just after tsunami due to washing out of finer fractions the water soluble salts contents were strongly reduced after the rainy season however the concentrations of acid leachable heavy metals and metalloids were still elevated in comparison to reference sample from an area not impacted by tsunami it is possible that the metals and metalloids are successively moved to more bioavailable fraction from forms which were more resistant to mobilization

high resolution analysis of a tsunami deposit case study from the 1755 lisbon tsunami in southwestern spain abstract a multi proxy approach using trench sediment analysis on the southwestern coast of spain los lances bay andalusia provides a high resolution record of the 1755 lisbon tsunami and offers new means to interpret tsunami deposits a combination of sedimentological grain size sorting ams micromorphological x ray tomography and radiography thin sections and geochemical analyses x ray microfluorescence icp aes combines to provide a comprehensive reconstruction of the different phases of tsunami deposition and flow dynamics vertical variations in sediment texture fabric and composition of the 1755 tsunami deposits in los lances are then discussed with reference to existing literature on diagnostic criteria commonly used for identifying and interpreting tsunami deposits finally possible leads for future investigation are proposed

a tsunami ca 6300 years bp and other holocene environmental changes northern hawke s bay new zealand abstract sediment cores collected in a coastal lagoon a few kilometres east of wairoa northern hawke s bay new zealand were examined using sedimentological geochemical palynological and micropaleontological analyses a distinct short lived catastrophic saltwater inundation csi about 6300 years bp and possibly other minor marine incursions are preserved in the coastal estuarine to lagoonal freshwater sedimentary sequences which have been deposited in the last 6500 years the csi is characterised by a gravel unit that thins landward and decreases in particle size to sand within a sequence consisting mainly of brackish estuarine muds diatom assemblages indicate a marked change from the shallow brackish estuarine muds to marine gravels and sands to brackish estuarine muds the marine influence in the gravel and sand is also shown by the presence of marine dinoflagellates and a peak in na rb sedimentological chemical and paleontological in particular diatoms evidence indicates it is a csi we conclude that this was a tsunami and propose the most likely propagating mechanisms marine influence decreases upcore and totally freshwater conditions are evident in the upper section of the cores the geochemistry of the sediments mainly reflects the change in stratigraphy with distinct signatures for tephra na fe cr organic rich and peat units as br and the coarse gravel sand csi unit na rb cr fe but it is also indicative of changes in depositional environment the change in chemistry na rb in the csi event is indicative of a saltwater influence whereas a marked change in s content suggests a sudden change from brackish to freshwater conditions shortly after 4800 years bp another peak in s and br content about 3200 years bp may indicate another temporary change to brackish conditions

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

reciting the layers evidence for past tsunamis at mataora wairau lagoon aotearoa new zealand abstract sedimentary geochemical microfossil and geochronological analyses were carried out on 10 sediment cores across the south eastern corner of mataora wairau lagoon m wl south island aotearoa new zealand this multi proxy approach provides strong evidence for three late holocene palaeotsunamis two previously unreported and a historical tsunami generated by rupture of the wairarapa fault in 1855 ce the main scientific evidence for these events consists of anomalous high energy marine sediment layers that overlie material of contrasting composition these layers coincide with peaks in planktonic and benthic marine to brackish marine diatoms and geochemical signatures indicative of sudden changes in environmental conditions palaeotsunami i maximum date 2095 cal bp and palaeotsunami ii maximum date 915 cal bp previously identified by clark et al 2015 appear to represent large events contemporaneous with major earthquakes inducing tectonic uplift and coseismic subsidence around the cook strait region palaeotsunami ii is close to the date of the earliest settlement of the m wl area by m ori and a traditional narrative that references loss of life following waves over washing the wairau boulder bank given the boulder bank was likely to have been seaward of its current position during events i and ii we surmise that the inundation distances would have been greater than the most landward extent 340 m inferred from the deposits found in this study palaeotsunami iii maximum date 525 cal bp was associated with tectonic subsidence across the study site most likely associated with rupture of the southern hikurangi subduction zone we expect the ongoing refinement of the methods used in this study and the results from future studies of analogue sites and offshore fault systems will improve our understanding of the significant tsunami hazard facing this region

sedimentary deposits from the 17 july 2006 western java tsunami indonesia use of grain size analyses to assess tsunami flow depth speed and traction carpet characteristics the 2006 western java tsunami deposited a discontinuous sheet of sand up to 20 cm thick flooded coastal southern java to a depth of at least 8 m and inundated up to 1 km inland in most places the primarily heavy mineral sand sheet is normally graded and in some it contains complex internal stratigraphy structures within the sand sheet probably record the passage of up to two individual waves a point noted in eyewitness accounts we studied the 2006 tsunami deposits in detail along a flow parallel transect about 750 m long 15 km east of cilacap the tsunami deposit first becomes discernable from the underlying sediment 70 m from the shoreline from 75 to 300 m inland the deposit has been laid down in rice paddies and maintains a thickness of 10 20 cm landward of 300 m the deposit thins dramatically reaching 1 mm by 450 m inland from 450 m to the edge of deposition around 700 m inland the deposit remains 1 mm thick deposition generally attended inundation along the transect the tsunami deposited sand to within about 40 m of the inundation limit the thicker part of the deposit contains primarily sand indistinguishable from that found on the beach 3 weeks after the event but after about 450 m and roughly coinciding with the decrease in thickness the tsunami sediment shifts to become more like the underlying paddy soil than the beach sand grain sizes within the deposit tend to fine upward and landward although overall upward fining takes place in two discrete pulses with an initial section of inverse grading followed by a section of normal grading the two inversely graded sections are also density graded with denser grains at the base and less dense grains at the top the two normally graded sections show no trends in density the inversely graded sections show high density sediment to the base and become less dense upward and represents traction carpet flows at the base of the tsunami these are suggestive of high shear rates in the flow because of the grain sorting in the traction carpet the landward fining trends usually seen in tsunami deposits are masked although lateral changes of mean sediment grain size along the transect do show overall landward fining with more variation as the deposit tapers off the deposit is also thicker in the more seaward portions than would be produced by tsunamis lacking traction carpets

central chile finally breaks chile is the site of some of the largest earthquakes in the world on average a magnitude 8 earthquake occurs there every 10 years or so these earthquakes take place in the subduction zone either as interplate ruptures at the interface between the south american and nazca plates or as intraplate events within the subducted nazca plate a few times in every century massive plate interface earthquakes break several hundred kilometers in a single shock this is what happened on 27 february 2010 when a major earthquake magnitude 8 8 occurred in the maule and biobio regions in central chile see the first figure this region had last experienced a major subduction earthquake in 1835 when darwin 1 visited the area as part of his voyage on the beagle his description of the earthquake inspired many seismologists and historians of chilean earthquakes 2 3

diatom biostratigraphy of tsunami deposits examples from the 1998 papua new guinea tsunami abstract distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment sediments associated with the 1998 tsunami that destroyed much of the sissano lagoon area in northern papua new guinea have been investigated surface sediments from three transects across the sediment spit near warapu have been examined for diatom content and preservation the preservation is variable and the data show an often chaotic assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash the diatoms identified within the warapu sediments indicate an origin from within the inter tidal and offshore area rather than from the beach sand spit complex the sand deposits disclose a high percentage in excess of 75 of broken diatom valves and a predominance of centric circular species due to preferential preservation the study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo tsunami deposits