tsunami deposits in a lacustrine sequence of the sanriku coast northeast japan abstract lacustrine deposits of the pacific coast of northeast japan consisting mostly of black organic mud contain intercalated thin beds of well sorted medium sand examination of the deposits from a coastal site of sanriku has revealed that sand grains are of marine origin and are fractions of deposits in marshy ponds transported from the littoral environment by a great flooding of seawater the mode of sedimentation shown in the thin beds of sand implies that they were deposited by tsunamis each with a maximum rise of 1 m or more above sea level

holocene evolution of phra thong s beach ridge plain thailand chronology processes and driving factors abstract beach ridge plains are a common morphological element of coastal areas all over the world while morphological depressions of beach ridge plains swales may function as archives for deposits of extreme wave events the ridges are not only used as an indicator for coastal evolution but also to reconstruct the processes that are responsible for their formation in this study the morphological sedimentary and chronological structure of the beach ridge plain on phra thong island was used as an archive for the temporally and spatially complex pattern of shoreline changes during the holocene the presence of three spatio temporal ridge plain units separated by episodes of shoreline erosion and characterised by varying directions and rates of shoreline progradation reveals six distinct phases of island evolution within the last 6000 years unit i was deposited during phase 1 5500 4000 years ago with high progradation rates of 2 1 2 5 m year subsequent to a short episode of erosion during phase 2 4000 3800 years ago fast shoreline progradation at a rate of 2 7 m year unit iia occurred once again in phase 3 3800 3300 years ago after 3300 years ago the sedimentation rate decreased to less than 1 m year resulting in the formation of unit iib during phase 4 3300 1500 years ago in phase 5 between 1500 and 800 years ago ridge plain formation was once more interrupted by significant shoreline erosion finally over most of the last 800 years during phase 6 slow shoreline progradation led to the formation of unit iii this evolution is best explained by the interaction of long term sea level change wave climate episodic events tsunamis and storms and local sediment supply however the linkage of successive ridge and swale formation changing progradation rates and switch over between phases of erosion and deposition with its trigger mechanisms remains speculative since i the processes involved vary locally and are poorly understood for phra thong island and ii even our comparably large dataset cannot reconstruct the complex spatial and temporal pattern of shoreline evolution without significant uncertainties this implies that interpretations of ridge plains based on small datasets might be too generalised to capture the real complexity of the system and as a consequence might lead to incorrect conclusions about palaeoenvironmental conditions

determining the burial time of single grains of quartz using optically stimulated luminescence abstract in the optical dating of sediments it is usually assumed that the optically stimulated luminescence osl signal has been completely reset by light exposure prior to burial this assumption is often not valid one approach to testing and perhaps circumventing this assumption is to examine the apparent date of last exposure to daylight of individual sediment grains this paper reports on the application for the first time of 2 new measurement protocols to the estimation of the radiation dose received during burial for individual quartz grains from an aeolian deposit of known age 10 000 year old which is considered likely to have been completely reset by sunlight at deposition additive dose laboratory doses added to the burial dose before osl measurement and regenerative dose doses added after measurement of osl from burial dose single aliquot protocols are applied to 28 and 25 individual grains respectively each grain provides an independent estimate d e of the burial dose the average d e from the additive dose protocol 21 8 1 1 gy is in good agreement with the average from the regenerative dose protocol 23 8 1 0 gy both agree well with 1 13 multiple grain regenerative dose single aliquot measurements each on 1 mg sub samples of 23 9 0 3 gy 2 9 multiple grain additive dose single aliquot measurements also on 1 mg sub samples of 22 4 0 7 gy and 3 one previously published multiple aliquot additive dose estimate of 23 5 0 6 gy using 52 sub samples each of 5 mg the resulting optical ages are in good accord with 14 c and thermoluminescence age determinations the distribution of equivalent doses in the single grains is however unexpectedly large 23 of mean d e given the very likely complete resetting of the osl signal at deposition possible reasons are discussed and it is concluded that heterogeneity in beta dosimetry is the most likely explanation the single grain optical dating protocols reported here allow a detailed examination of the dose distribution in very small samples thus they should enable accurate dates to be obtained for sediments and soils that contain poorly bleached or mixed age components as well as deposits in which quartz grains are present in extremely low abundance

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

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

erosion of a paleo tsunami record by the 2011 tohoku oki tsunami along the southern sendai plain abstract erosion of sediment beneath a coastal lake by the 2011 tohoku oki tsunami largely removed up to 1100 years of the geologic record of tsunami and tephra deposition that lost geologic record included the 1611 keicho tsunami deposit and the 915 to a tephra amounting to ca 1 4 m of lake bottom sediment as judged from comparison of stratigraphy at four locations examined before and after the 2011 tsunami the tsunami replaced the eroded sediment with a 7 15 cm thick sand sheet and an overlying 20 60 cm thick layer of black mud both 2011 deposit components were likely derived from sediment eroded along the tsunami flow path including granite rock fragments downstream of the lake basin and mainly reworked lake floor sediment erosion and redeposition of lake floor sediment by tsunami inundation can introduce uncertainty to sandy tsunami deposit age estimation the 2011 tsunami sand might be dated a few hundred years older than the actual age if one overlooks the reworked muddy tsunami deposit in its facies the mud closely resembles mud deposited from the usual environment but is mixed with sediments of various ages therefore it is important to identify the reworked muddy tsunami deposit based on geochemistry and micropaleontology to avoid misinterpretation of the depositional age of tsunami deposits erosion of deposits beneath the lake floor also erases evidence leaving an incomplete paleo tsunami history reconstructing geological records of tsunamis in coastal lakes requires careful evaluation of the possible effects of tsunami erosion identifying sediment sources mapping stratigraphic unconformities and constructing detailed age depth models to test for gaps in sedimentation can produce important insights

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

nine unusually large tsunami deposits from the past 4000 years at kiritappu marsh along the southern kuril trench abstract large earthquakes along the kuril subduction zone in northern japan are known to have caused damaging tsunami although there is a little information on historical earthquakes and tsunami in this area because no documents exist before the 19th century that might refer to tsunami events to determine the likely timing and size of future events we need information on their recurrence intervals and to do this for the prehistoric past we have investigated sediments located in the kiritappu marsh in eastern hokaido that we interpret as laid down by tsunami using reliable multiple lines of evidence from sedimentological geomorphological micropaleontological and chronological results we identify 13 tsunami sands two of these lie within a peat bed above a historical tephra ta a ad 1739 the upper one probably corresponds to the ad 1843 tempo tokachi oki earthquake m 8 2 tsunami and the lower to either the ad 1952 tokachi oki earthquake m 8 2 tsunami or the ad 1960 chilean earthquake m 9 5 tsunami underlying are 11 prehistoric tsunami sand beds nine large sand beds and two smaller sand beds deposited during the past 4000 years because of the wide spatial distribution of the large sand beds and inundation distances inland of between 1200 to 3000 m we suggest that they record unusually large tsunamis along the kuril subduction zone according to our analyses these tsunami sands were derived from the coastal area and although they do not show clear graded bedding they commonly have gradational upper boundaries and erosional bases and include internal sedimentary structures such as plane beds dunes and current ripples reflecting bedload transportation based on our results we calculate the recurrence interval of unusually large earthquakes probably m 8 6 along the kuril subduction zone as about 365 553 years and estimate the youngest large event to have occurred in the 17th century

erosion deposition and landscape change on the sendai coastal plain japan resulting from the march 11 2011 tohoku oki tsunami case studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow and refining the criteria used to identify paleotsunami deposits in the geologic record here we report on erosion deposition and associated landscape change resulting from the march 11 2011 tohoku oki tsunami along a nearly 4 5 km shore normal transect on the coastal plain near sendai japan the study area on the broad low relief prograding coastal sendai plain comprised a sand beach backed by 3 m high sand dunes and a forest a wetland the teizan canal agricultural rice fields buildings and roads field observations focused on measurements of tsunami flow characteristics height and direction mapping of erosion features and assessing sediment deposition based on shallow trenches at 50 100 m spacing recorded tsunami inundation heights reached up to about 11 m above mean sea level within the first 500 m from the shoreline and then ranged between 3 and 5 m for the next 2 km gradually decreasing to about 3 m close to the inundation limit the tsunami deposit generally thinned landward from an average maximum 30 cm thick sand deposit in the coastal forest to a thin mud drape several mm thick near the inundation limit a discontinuous sand dominated sheet was prevalent to about 2800 m from the shoreline where mud content then gradually increased further landward eventually resulting in a mud dominated deposit ranging from 3 5 cm to a few mm thickness the overall thinning and fining of the deposit was often interrupted by localized features that led to complex sedimentological relationships over short distances satellite imagery taken on 14 march 2011 3 days after the tohoku oki tsunami shows prominent foreshore incisions with 100 s meters spacing alongshore a foredune ridge that underwent severe erosion and development of a prominent shore parallel elongated scour depression our field survey in early may 2011 revealed that the foreshore recovered quickly with rapid post tsunami sediment deposition from incident waves whereas the dune ridge complex had undergone only minor re working from eolian processes

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

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

the reliability of uranium series mollusc dates from the western mediterranean basin abstract fossil mollusc shells from western mediterranean raised beach deposits have been dated using u series techniques sub sampling has allowed intra shell isotopic variability to be assessed although most of the calculated ages appear plausible and some internal consistency exists closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect some previously published u series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells

elemental signature of terrigenous sediment runoff as recorded in coastal salt ponds us virgin islands abstract a high resolution multi proxy approach is utilized on mm to cm scale laminated coastal salt pond sediments from st john u s virgin islands to determine 1 the sedimentological signature of depositional events processes 2 link this sedimentological signature with known depositional events processes in the historical past 100 years record and 3 project back into the recent geologic past past 1400 years to investigate the natural variability of depositional events processes high resolution short lived radioisotope geochronology 210pb 137cs 7be combined with high resolution elemental scanning techniques scanning xrf and scanning la icp ms allows for the direct comparison of well preserved salt pond deposits to historical records of depositional events e g runoff rainfall tropical cyclones tsunamis to identify the sedimentary signature of each type of event there is a robust sedimentary record of terrigenous sediment runoff linked to the frequency of rainfall events that exceed a threshold of 12 mm day minimum to mobilize and transport sediment for study sites this is manifested in the sedimentary record as increases in terrigenous indicator elements al fe ti si which agree well with rainfall records over the past 50 years variability in the sedimentary record over the past 100 years reflects decadal scale fluctuations between periods of increased frequency of rainfall events and decreased frequency of rainfall events dm scale variability in terrigenous indicator elements over the past 1400 years represents the natural system variability on a decadal centennial scale and provides a high resolution long term baseline of natural variability of rainfall runoff events a period of increased terrigenous sediment delivery during the 1700s and 1800s likely indicates increased erosion in response to anthropogenic activities associated with the island s plantation era and perhaps increased frequency of rainfall events

surface wave tomography from ambient seismic noise of accelerograph networks in southern korea 1 an efficient and robust cross correlation technique for estimation of surface wave green s function between two locations is applied to a set of ambient noise data recorded by accelerograph networks in the southern korea we have estimated 1843 group velocities of rayleigh waves in the period band of 2 4 seconds from correlation pairs of 91 accelerograph stations relatively dense and uniform coverage of the pairs provides us with high resolution tomographic image of surface wave group velocities in the region the resulting group velocity distribution correlates well with the characteristic features of geological map of the region displaying low velocities for the sedimentary basins and regions of volcanic and metasedimentary rocks and high velocities for the regions where granitoid basement rocks outcrop the short period information from the accelerograph network can enhance resolution of the subsurface structures at depths within a few kilometers which may be predominantly responsible for simulation results of strong ground motions

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

geotectonic setting of hydrothermal activity on the summit of lucky strike seamount 37 17 n mid atlantic ridge we have investigated the relations between volcanic tectonic and hydrothermal activity on lucky strike seamount 37 17 n mid atlantic ridge using a nested survey strategy involving collection of data from different deep sea mapping systems the highly tectonized seamount summit consists of three volcanic cones surrounding a relatively flat depression with a young lava lake in its center hydrothermal activity is focused mainly within the summit depression with most of the vents located proximal to the lava lake isolated active and inactive chimneys and mounds are widespread throughout the summit depression and occur on both volcanic pillow lava and hydrothermal sulfide rubble and hydrothermally cemented breccias substrates the large volume of sulfide rubble together with the nature of the sulfide structures indicates that hydrothermal activity has been episodic but ongoing for a long period of time hundreds to thousands of years on the basis of the distribution of hydrothermal deposits we propose a model of alternation between tectonic and volcanic control on hydrothermalism at lucky strike seamount midsegment melt focusing produces a spatially and temporally stable heat source that sustains focused high temperature hydrothermal activity over long time periods during periods of amagmatic extension active faulting within the summit depression provides multiple near surface fluid flow pathways for discharge of high temperature fluids and widespread deposition of massive sulfides during eruptive events rapid effusion of very hot lava creates a lava lake and hyaloclastite deposits the new sheet flows form a cap on the hydrothermal system and fluid upflow is reorganized discharge of high temperature fluids is restricted to isolated sites with relatively high permeability for example the edges of the lava lake much of the upwelling hydrothermal fluid pools in the subsurface conductively cools and mixes with entrained seawater before discharging as widespread low temperature diffuse flow hyaloclastites become cemented further augmenting the sealing of the system present day activity at lucky strike seamount represents this locally volcanically controlled phase of activity despite the segment as a whole being dominantly amagmatic

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

a new flow cytometry method enabling rapid purification of fossil pollen from terrestrial sediments for ams radiocarbon dating radiocarbon 14c accelerator mass spectrometry ams dating has played a significant role towards improving our understanding of the timing of events and rates of change in archaeological and environmental records over the last 50 000 years although it is not always possible to find suitable macrofossils for 14c dating microfossils notably plant pollen are a viable alternative obtaining preserved pollen samples of known provenance and of sufficient quantity for dating by 14c ams is however challenging because of time consuming methods of extraction and purification and possible contamination from other organic material here we report a new rapid and straightforward method using flow cytometry fcm to distinguish sort and collect sufficient quantities of fossil pollen with minimal contamination from lake sediments for radiocarbon dating using this approach we demonstrate 14c ams ages that date back to at least 40 ka bp while future work may be required to refine purification methodologies for different sample types and to precisely quantify the dating limit of this approach fcm dating of microfossils shows considerable promise in generating robust geochronological frameworks for sequences that have previously proved problematic copyright 2013 john wiley sons ltd

multi proxy records of regionally sourced tsunamis new zealand abstract a multi proxy study of sediment cores from kaituna bay mimiwhangata in northern new zealand has produced a record of three palaeotsunamis dated to around 6500 cal yr bp 2800 cal yr bp and 1450 ad these events punctuate a coastal palaeoenvironmental history spanning the last 8000 years or more in which the site progressed from a semi open lagoon to a freshwater swamp proxies used included stratigraphy geochemistry palynology diatoms foraminifera geomorphology and a regional palaeotsunami synthesis the identification of tsunamigenic sources for these events is tentative we propose that the two oldest events are associated with a source in the tonga kermadec trench region with the most recent possibly associated with the kuwae caldera collapse in 1452 1453 ad palaeotsunami deposits contemporaneous with the estimated age of the three events identified in this study were used to assist in identifying possible source regions the development of regional and national palaeotsunami databases is in its infancy but as more data become available the ability to determine the source magnitude and frequency of past events will improve this will greatly enhance our understanding of the regional risk from tsunamis