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

optical dating of deep sea sediments using single grains of quartz a comparison with radiocarbon abstract in this paper we demonstrate that optical dating of single grains of quartz offers an alternative means of dating deep sea sediments the precision and accuracy of the technique which has the potential to date sediments deposited during the last 500 000 years or so is limited by the random and systematic uncertainties associated with producing optical ages these result in total relative age uncertainties of between 10 and 20 at the 68 confidence interval which are similar in size to those associated with late quaternary oxygen isotope chronologies we analysed single grains of quartz from several depth intervals down core fr10 95 gc17 which was collected offshore from cape range peninsula western australia from a water depth of 1093 m in the eastern indian ocean the single grain optical ages are shown to be consistent with ams radiocarbon ages obtained from planktonic foraminifera from the same core we also show that marine sediments are not immune from partial or heterogeneous bleaching incomplete resetting of the optical dating signal where partial or heterogeneous bleaching of the optical dating signal is indicated we recommend that single grain dating be employed and the burial dose estimated from the population of grains with the lowest absorbed radiation dose

historic and ancient tsunamis uncovered on the jalisco colima pacific coast the mexican subduction zone research on extreme wave events such as tsunamis using the geological record in areas of infrequent and or small magnitude earthquakes can aid in extending the long term history and recurrence intervals of large events this information is valuable for risk management and community preparedness in coastal areas here we investigate tsunami deposits on the jalisco coast of mexico that overlies the subducting rivera plate under the north american plate an area due for a large thrust earthquake and potential tsunami here we apply a full battery of rock magnetic analyses that also include a detailed ams study and other typically applied proxies in tsunami deposits research we present evidence to demonstrate that anomalous sand units with sharp basal contacts at la manzanilla tenacatita bay and el tecuan shore sites on the jalisco coast may be the products of tsunamis generated by known historical ms 8 2 earthquake of 3 june 1932 and other earlier tsunamigenic earthquakes a sandy unit with a sharp basal contact flame structures at the base rip up clasts at la manzanilla and four sand units with sharp basal contact overlying buried soils at el tecuan together with other proxies such as magnetic properties and others suggest tsunami deposits 210pb dating of sediments slightly above the upper sand layer indicate an age a d 1935 11 at el tecuan historical accounts of tsunami inundation at both sites provide further evidence that this is most probably the result of the 3 june 1932 tsunami hence this study may provide the first evidence of a tsunami triggered by this earthquake and also of three probable predecessors further evidence of at least three earlier tsunamis that occurred since the fifteenth century is also evident in the stratigraphy these events may correspond to events listed in historical archives namely the 1563 1816 and or the 1818 events

revealing the coastal event history of the andaman islands bay of bengal during the holocene using radiocarbon and osl dating earthquakes that trigger tsunamis are of great geological ecological and socio economic importance the knowledge of the recurrence interval of these events will give information about the hazard for a region coastal sediments on the andaman islands located in the eastern bay of bengal were investigated to find evidence for palaeotsunamis and palaeoearthquakes fieldwork was conducted on red skin island and north cinque island south of south andaman sediment material from event layers was dated by optically stimulated luminescence and radiocarbon dating method the results show evidence possibly for one earthquake at about 1 000 or 3 000 years before the present together with deposits from possible tsunamis and storms the complex pattern of co and post seismic uplift and subsidence of the andaman islands is reflected in the investigated sections and made it possible to reconstruct an event history for the last 3 000 years

optically stimulated luminescence dating of a late quaternary shoreline deposit tunisia abstract quartz optical dates have been measured from high energy shoreline deposits at hergla and chebba tunisia which may be related to a tsunami or severe storm surge preliminary results from two sites place the date of the boulder beds within oxygen isotope stage 5e

optical dating of tsunami laid sand from an oregon coastal lake abstract optical ages for five samples of tsunami laid sand from an oregon coastal lake were determined using an infrared optical dating method on k feldspar separates and as a test of accuracy compared to ages determined by ams 14c dating of detrital plant fragments found in the same beds two optical ages were about 20 younger than calibrated 14c ages of about 3 1 and 4 3 ka correction of the optical ages using measured anomalous fading rates brings them into agreement with the 14c ages the approach used holds significant promise for improving the accuracy of infrared optical dating methods luminescence data for the other three samples result in optical age limits much greater than the 14c ages these data provide a textbook demonstration of the correlation between scatter in the luminescence intensity of individual sample aliquots and their normalization values that is expected when the samples contain sand grains not adequately exposed to daylight just prior to or during deposition and burial thus the data for these three samples suggest that the tsunamis eroded young and old sand deposits before dropping the sand in the lake

sheltered coastal environments as archives of paleo tsunami deposits observations from the 2004 indian ocean tsunami the 2004 earthquake left several traces of coseismic land deformation and tsunami deposits both on the islands along the plate boundary and distant shores of the indian ocean rim countries researchers are now exploring these sites to develop a chronology of past events where the coastal regions are also inundated by storm surges there is an additional challenge to discriminate between the deposits formed by these two processes paleo tsunami research relies largely on finding deposits where preservation potential is high and storm surge origin can be excluded during the past decade of our work along the andaman and nicobar islands and the east coast of india we have observed that the 2004 tsunami deposits are best preserved in lagoons inland streams and also on elevated terraces chronological evidence for older events obtained from such sites is better correlated with those from thailand sri lanka and indonesia reiterating their usefulness in tsunami geology studies c 2014 elsevier ltd all rights reserved

ultralong period seismic study of the december 2004 indian ocean earthquake and implications for regional tectonics and the subduction process analysis of the earth s longest period normal modes shows that the december 2004 sumatra andaman earthquake was much larger mw 9 3 than ini tially inferred from surface wave data and involved slip on a much longer fault than initially inferred from body wave data the seismic moment and relative excitation of the normal modes indicate that the entire aftershock zone ruptured consistent with the large tsunami amplitudes in thailand sri lanka and india an apparent increase in seismic moment with period results from interference between parts of the fault the earthquake resulted from subduction of the indian plate beneath the burma microplate a sliver plate between the indian and sunda plates hence the rate and direction of convergence depends on the motion of the burma plate which is not well known convergence would be highly oblique if the rate of motion between burma and sunda is that inferred from spreading in the andaman sea and less if a slower rate is inferred from the sagaing fault the december earthquake was much larger than expected from a previously proposed relation based on the idea of seismic coupling in which such earthquakes occur only when young lithosphere subducts rapidly moreover a global reanalysis finds little support for this correlation hence we suspect that much of the apparent differences between subduction zones such as some trench segments but not others being prone to m w 8 5 events and hence oceanwide tsunamis may reflect the short earthquake history sampled this possi bility is supported by the variability in rupture mode at individual trench segments

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

the distribution of apparent dose as determined by optically stimulated luminescence in small aliquots of fluvial quartz implications for dating young sediments abstract we noted recently murray et al 1995 that quartz samples taken from in channel fluvial deposits have apparent doses ranging over several orders of magnitude we suggested that these dose distributions are best explained by a mixture of a small number of poorly bleached grains and a larger number of well bleached grains in this paper we examine the distribution of apparent dose in small aliquots each composed of 2000 grains of different particle size fractions 63 90 m 90 125 m 125 180 m 180 212 m 212 250 m diameter from two samples collected from the murrumbidgee river new south wales australia the samples are of known burial age the first being 70 years old and the second being its modern equivalent 0 2 gy the difference in the lowest apparent dose in the two samples is considered to be the result of their different burial times we suggest a method for dating recently deposited

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

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

coseismic slip and afterslip of the great mw 9 15 sumatra andaman earthquake of 2004 we determine coseismic and the first month postseismic deformation associated with the sumatra andaman earthquake of 26 december 2004 from near field global positioning system gps surveys in northwestern sumatra and along the nicobar andaman islands continuous and campaign gps measurements from thailand and malaysia and in situ and remotely sensed observations of the vertical motion of coral reefs the coseismic model shows that the sunda subduction mega thrust ruptured over a distance of about 1500 km and a width of less than 150 km releasing a total moment of 6 7 7 0 10 22 n m equivalent to a magnitude m w 9 15 the latitudinal distribution of released moment in our model has three distinct peaks at about 4 n 7 n and 9 n which compares well to the latitudinal variations seen in the seismic inversion and of the analysis of radiated t waves our coseismic model is also consistent with interpretation of normal modes and with the amplitude of very long period surface waves the tsunami predicted from this model fits rela tively well the altimetric measurements made by the jason and topex satellites neither slow nor delayed slip is needed to explain the normal modes and the tsunami wave the near field geodetic data that encompass both coseismic deformation and up to 40 days of postseismic deformation require that slip must have continued on the plate interface after the 500 sec long seismic rupture the postseismic geodetic moment of about 2 4 10 22 nm mw 8 8 is equal to about 30 5 of the coseismic moment release evolution of postseismic deformation is consistent with rate strengthening frictional afterslip online material summary of geodetic data used in this study

multiple dating approach 14c 230th u and 36cl of tsunami transported reef top boulders on bonaire leeward antilles current achievements and challenges abstract dating the transport deposition time of supratidal coarse clast deposits is difficult limiting their value for inferring frequency magnitude patterns of high energy wave events on bonaire leeward antilles caribbean these deposits form prominent landforms and transport by one or several holocene tsunamis is assumed at least for the largest clasts although a large dataset of 14c and electron spin resonance esr ages is available for major coral rubble ridges and ramparts it is still debated whether these data reflect the timing of major events and how these datasets are biased by the reworking of coral fragments as an attempt to overcome the current challenges for dating the dislocation of singular boulders three distinct dating methods are implemented and compared i 14c dating of boring bivalves attached to the boulders ii 230th u dating of post depositional secondary calcite flowstone and subaerial microbialites at the underside of the boulders and iii surface exposure dating of overturned boulders via 36cl concentration measurements in corals approaches ii and iii have never been applied to coastal boulder deposits so far the three 14c age estimates are older than 40 ka i e most probably beyond the applicability of the method which is attributed to post depositional diagenetic processes shedding doubt on the usefulness of this method in the local context the remarkably convergent 230th u ages all pointing to the late holocene period 1 0 1 6 ka are minimum ages for the transport event s the microbialite sample yields an age of 1 23 0 23 ka and both flowstone samples are in stratigraphic order the older onset of carbonate precipitation and younger flowstone layers yield ages of 1 59 0 03 and 1 23 0 03 ka respectively four coral samples collected from the topside of overturned boulders yielded similar 36cl concentration measurements however the computed ages are affected by large uncertainties mostly due to the high natural chlorine concentration after correction for the inherited component and chemical denudation since platform emergence inducing additional uncertainty the calculated 36cl ages cluster between 2 5 1 3 and 3 0 1 4 ka for three of four boulders whilst the fourth one yields an age of 6 1 1 8 ka probably related to a higher inheritance these 230th u and 36cl age estimates are coherent with a suggested tsunami age of

stratigraphic evidence for pre 2004 tsunamis in southwestern thailand abstract the 2004 sumatra andaman earthquake and the associated indian ocean tsunami vastly exceeded the size of their predecessors from the previous two centuries or more we sought clues on how often large tsunamis occur by taking 9 shallow cores 0 5 2 0 km inland from the modern shore on a holocene beach ridge plain of phra thong island 125 km north of phuket we tentatively correlated one sand sheet among these cores and found a second sand bed beneath in one of the cores we infer that these deposits represent two pre 2004 tsunamis the island s setting precludes river floods and tends to rule out storms as causes of the sand deposition establishment of the beach ridge plain requires that both the inferred tsunamis occurred after holocene sea levels approached their present position radiocarbon ages of bulk soil samples are consistent with this conclusion though root penetration into soil samples probably makes the ages appear younger one inferred tsunami occurred before ad 1300 and the other occurred before ad 1900 based on the age estimates the tsunamis probably originated along the sunda megathrust from where tsunamis can travel directly to the thailand coast

proxy mineral magnetic and elemental analyses for 2004 tsunami impact deposit along the muttukadu backwater east coast of india scope of the palaeotsunami studies abstract following the line of approach enumerated in the tsunami toolkit of chague goff et al 2011 expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami earth sci rev 107 1 2 107 122 measurements of elemental and mineral magnetic properties coupled with textural parameters have been used to evaluate the 2004 indian ocean tsunami iot induced sediments on the muttukadu backwaters east coast of india to investigate the sediment provenance specific fe mn and pb elemental concentrations were measured in surface sediments and compared with the previously published pre tsunami database of backwater inner continental shelf sediments we found the enrichment of fe and pb against depletion of mn concentration in present tsunami sediments as compared with pre tsunami muttukadu sediments reflecting the variation of the sediment source area however the present data of fe and pb enrichment and mn depletion correlates well with continental shelf sediments hinting at sedimentary routes processes of erosion and wave propagation the studied tsunami deposits are characterized by dominant 40 85 coarse sand fractions and higher proportion of detrital low and high coercivity fe ti oxides such as magnetite titanomagnetite and hematite reflected by magnetic concentration magnetic susceptibility anhysteretic remanent magnetization arm and coercivity dependent parameters soft isothermal remanent magnetization soft irm hard irm magnetomineralogical s ratio and saturation irm sirm so it can be shown that the random spatial variability and the inverse relationship between magnetic concentration arm and sirm parameters and grain size arm sirm and arm sirm ratios as diagnostic criteria for the tsunami impacted the distribution of magnetic parameters in coastal backwater environments contrasting mineral magnetic and geochemical properties together with more sand mean 65 when compared with silt mean 25 content in tsunami sediments indicates that the area was affected by high energy tsunami waves the study validates environmental magnetism as a proxy which is fast and robust for identifying the tsunami or palaeotsunami deposits

large scale washover sedimentation in a freshwater lagoon from the southeast australian coast sea level change tsunami or exceptionally large storm a distinct lens of marine sand up to 90 cm thick confined vertically by peat is found in the upper fill of a closed freshwater back barrier lagoon on the southeast australian coast coring of the deposit suggests it extends continuously up to 600 m inland and tapers landward rising to 1 6 m above principle datum in places the sand is overlain by accumulations of organic rich silt that contain charophytes indicating re estab lishment of lagoon conditions hypotheses considered for the deposition of the sandsheet are higher holocene sea level storms and tsunami ground penetrating radar transects of the seaward dune system suggest a penecontemporaneous erosional contact between a series of truncated pre event dunes and several small over lying post event dunes dating the sandsheet was problematic but it is confined to the last 800 years the young age combined with a lack of associated beach deposits and evidence of wave scouring suggest that a higher sea level hypothesis is unlikely this sand lens is attributed to a large scale washover event from the southeast based on comparisons with modern storm deposits from the same coast and sedimentological diagnostic crite ria derived from studies of modern storm and tsunami deposited sandsheets it is concluded that this sand deposit is the product of a short lived large scale overwash event attributed to a late holocene tsunami

optical dating of holocene sediments from a variety of geomorphic settings using single grains of quartz this paper presents an improved method for the optical dating of holocene sediments from a variety of geomorphic settings we have measured the equivalent dose de in individual grains of quartz using green laser light for optical stimulation and have simulated the de distributions for multiple grain synthetic aliquots using the single grain data for 12 samples of known independent age we show that application of a minimum age model to the single grain and small 10 grain aliquot de data provides the most accurate estimate of the burial dose for nine of the samples examined 3 aeolian 5 fluvial and 1 marine the weighted mean de as obtained using the central age model gives rise to burial age overestimates of up to a factor of 10 for these nine samples whether single grains small aliquots or large 100 grain aliquots are used for the other three samples two aeolian and one fluvial application of either the minimum age model or the central age model to the single grain small aliquot and large aliquot de data yields burial ages in accord with the independent age control we infer that these three samples were well bleached at the time of deposition these results show that heterogeneous bleaching of the optical dating signal is commonplace in nature and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition we also show that grains sensitive to infrared ir stimulation can give rise to low de values which will result in significant underestimation of the burial dose and hence of the age of deposition we demonstrate that use of a modified single aliquot regenerative dose protocol incorporating ir stimulation prior to green light stimulation deals effectively with contamination by ir sensitive grains we conclude that application of the modified protocol to single grains or small aliquots of quartz using the lowest de population to estimate the burial dose is the best means of obtaining reliable ages for holocene sediments from a wide range of depositional environments d 2003 elsevier b v all rights reserved

pleistocene and holocene geomorphological development in the algarve southern portugal abstract a detailed chronological framework for pleistocene and holocene geomorphology and landscape evolution in the algarve is proposed with regards to the pleistocene attention has focused on the origin dating and stratigraphy of the ludo formation subsuming the classifications of earlier writers it is now proposed that during the pliocene a marine transgression occurred across a tectonically controlled basin that was constrained by the mountains of the algarve interior to the north fluvial sands were then deposited in a regressive phase during the late pliocene early pleistocene while braided streams operating under semi arid conditions subsequently laid down sands and gravels in the middle and upper pleistocene lying unconformably over the ludo formation is an alluvial deposit odiaxere gravels and loule sands of late pleistocene early holocene date that is found within the river valleys of the algarve in the early holocene ca 10 000 ca 7000 bp and early late holocene ca 5000 ca 3000 bp the situation in the algarve was one of climatic amelioration i e warmer and wetter conditions rising sea levels vegetation colonization soil development and towards the end of this period trenching of the odiaxere gravels and loule sands from ca 3000 bp evidence is abundant that humans became important geomorphological agents either acting on their own or in combination with climatic factors from around 5000 bp conditions became dryer and between ca 3000 bp and ca 700 bp clearance of land by pre roman roman and especially islamic agricultural settlers caused widespread erosion and the deposition of extensive spreads of topsoil dominated sediment within river valleys i e the holocene terrace and in coastal estuaries a period followed up to 1900 ce when agricultural practices were less damaging to the soil erosion was reduced and the holocene terrace together with coastal and estuarine deposits was incised in the past century and under increased human pressure renewed erosion is in evidence in the interior valleys and at the coast

optical dating of tsunami laid sands abstract the ages of some tsunami deposits can be determined by optical dating a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents waves wind or bioturbation during the last years before the tsunami measurements have been made using 1 4 ev infrared excitation of k feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in washington state and british columbia source sands gave equivalent doses indicative of recent exposure to daylight tsunami sand at cultus bay washington yielded an optical age of 1285 95 yr calendric years before a d 1995 1 at 2 this age overlaps the range of from 1030 to 1100 yr determined through a combination of high precision radiocarbon dating and stratigraphic correlation tsunami sands at three sites near tofino and port alberni on vancouver island british columbia have optical ages of 260 20 325 25 and 335 45 yr historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old these optical ages support the hypothesis that the vancouver island sands were deposited by a tsunami generated by a large earthquake on the cascadia subduction zone about 300 yr ago

bayesian probabilities for mw 9 0 earthquakes in the aleutian islands from a regionally scaled global rate we use the global rate of mw 9 0 earthquakes and standard bayesian procedures to estimate the probability of such mega events in the aleutian islands where they pose a significant risk to hawaii we find that the probability of such an earthquake along the aleutians island arc is 6 5 to 12 over the next 50 years 50 credibility interval and that the annualized risk to hawai i is about 30 m our method the regionally scaled global rate method or rsgr is to scale the global rate of mw 9 0 events in proportion to the fraction of global subduction units of area per year that takes place in the aleutians the rsgr method assumes that mw 9 0 events are a poisson process with a rate that is both globally and regionally stationary on the time scale of centuries and it follows the principle of burbidge et al 2008 who used the product of fault length and convergence rate i e the area being subducted per annum to scale the poisson rate for the gss to sections of the indonesian subduction zone before applying rsgr to the aleutians we first apply it to five other regions of the global subduction system where its rate predictions can be compared with those from paleotsunami paleoseismic and geoarcheology data to obtain regional rates from paleodata we give a closed form solution for the probability density function of the poisson rate when event count and observation time are both uncertain

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

osl dating and gpr mapping of palaeotsunami inundation a 4000 year history of indian ocean tsunamis as recorded in sri lanka to evaluate and mitigate tsunami hazard as long as possible records of inundations and dates of past events are needed coastal sediments deposited by tsunamis tsunamites can potentially provide this information however of the three key elements needed for reconstruction of palaeotsunamis identification of sediments dating and finding the inundation distance the latter remains the most difficult the existing methods for estimating the extent of a palaeotsunami inundation rely on extensive excavation which is not always possible here by analysing tsunamites from sri lanka identified using sedimentological and paleontological characteristics we show that their internal dielectric properties differ significantly from surrounding sediments the significant difference in the value of dielectric constant of the otherwise almost indistinguishable sediments is due to higher water content of tsunamites the contrasts were found to be sharp and not to erode over thousands of years they cause sizeable electromagnetic wave reflections from tsunamite sediments which permit the use of ground penetrating radar gpr to trace their extent and morphology in this study of the 2004 boxing day indian ocean tsunami we use gpr in two locations in sri lanka to trace four identified major palaeotsunami deposits for at least 400 m inland investigation inland was constrained by inaccessible security zones the subsurface extent of tsunamites not available without extensive excavation provides a good proxy for inundation the deposits were dated using the established method of optically stimulated luminescence osl this dating partly corroborated by available historical records and independent studies contributes to the global picture of tsunami hazard in the indian ocean the proposed method of combined gpr osl based reconstruction of palaeotsunami deposits enables estimates of inundation recurrence and therefore tsunami hazard for any sandy coast with identifiable tsunamite deposits the method could be also used for anchoring and synchronizing chronologies of ancient civilisations adjacent to the ocean shores

indian ocean tsunami recurrence from optical dating of tsunami sand sheets in thailand abstract sand sheets deposited by the 2004 indian ocean tsunami and three holocene tsunami predecessors in western thailand have been dated by optically stimulated luminescence osl ages from the modern indian ocean tsunami sand sheet allow an assessment of the suitability of osl to date tsunami deposited sediment in tropical beach ridge plain depositional environments they show that provided appropriate precautions are taken to correct for incomplete bleaching of sediments osl can provide a robust chronology of tsunami recurrence ages from the tsunami deposited sand sheets underlying the 2004 tsunami deposits provide a chronology of the largest tsunamis in western thailand over the late holocene three sand sheets likely deposited by tsunamis of similar magnitude to the 2004 event were dated by luminescence to 380 50 990 130 1410 190 and 2100 260 years before ad 1950 at 1 sigma precision the youngest of these compares with previous radiocarbon ages of detrital bark high in buried soils jankaew et al 2008 which suggest that the most recent large scale predecessor to the 2004 tsunami occurred soon after 550 700 cal bp the osl ages from the lower two sand sheets provide constraint on tsunami recurrence that was not previously available from radiocarbon dating the ages imply that between 350 and 1100 years separate successive tsunamis on the andaman coast of thailand with an average tsunami recurrence interval of around 550 years these results contribute to the growing body of research on tsunami recurrence in the indian ocean region and show that osl can provide independent estimates of tsunami recurrence for hazard analysis particularly in areas where suitable material for radiocarbon dating is unavailable

holocene sea levels along the andaman sea coast of thailand for the malay thai peninsula several sea level curves for the younger holocene based on field evidence as well as on hydro isostatic modelling of a far field site have been published the general assumption is a rapid rise to a mid holocene maximum up to 5 m above present sea level followed by a constant or oscillating regression however from the andaman sea coast of thailand which was affected by the 2004 tsunami only isolated observations are available regarding holocene sea levels thus the timing and magnitude of the holocene highstand as well as the course of the regression remain to be defined as several palaeotsunamis could be detected in the meantime it is important to know the related sea levels as exactly as possible to judge the energy inundation width and potential wave height of these events therefore fixed biological indicators from the rocky coasts of the phang nga bay and phuket as well as morphological indicators from beach ridge and swale sequences along the exposed west coast ko phra thong were studied to gain information about the holocene sea level development in this region while oyster and coral data from the phang nga bay and phuket document a holocene maximum of 2 6 m at 5700 cal bp the ridge crests and swale bases in the northwest of the study area point to maximum heights of 1 5 2 0 m above the present level around 5300 years ago during the last 3000 years to when the largest part of the holocene palaeotsunami deposits from thailand was dated relative sea levels rsl in both areas did not exceed 1 5 m

coral evidence for earthquake recurrence and an a d 1390 1455 cluster at the south end of the 2004 aceh andaman rupture coral records of relative sea level change provide a history of vertical interseismic and coseismic deformation along the coast of northern simeulue island sumatra and reveal details about earthquakes in the 10th and 14th 15th centuries a d along the southern end of the december 2004 m w 9 2 sunda megathrust rupture over a 56 year period between a d 1390 and 1455 northern simeulue experienced a cluster of megathrust ruptures associated with total uplift that was considerably more than in 2004 uplifted corals at two sites constrain the first event of the cluster to a d 1393 3 and 1394 2 2 a smaller but well substantiated uplift occurred in northern simeulue in 1430 3 an inferred third uplift in a d 1450 3 killed all corals on the reef flats of northern simeulue the amount of uplift during this third event though confirmed only to have exceeded 28 and 41 cm at two sites probably surpassed the 100 and 44 cm that occurred respectively at those sites in 2004 and it was likely more than in 2004 over all of northern simeulue the evidence for past earthquake clustering combined with the inference of considerably greater uplift in a d 1390 1455 than in 2004 suggests that strain may still be stored along the southernmost part of the 2004 rupture interseismic subsidence rates recorded by northern simeulue coral microatolls have varied by up to a factor of 4 at some sites from one earthquake cycle to another

tectonics arabia s slow dance with india india and arabia collide with eurasia at slightly different velocities detailed mapping of the arabian sea suggests that this motion started between 3 and 8 million years ago possibly with a transfer of an arabian plate wedge to the indian plate

scilly isles uk optical dating of a possible tsunami deposit from the 1755 lisbon earthquake abstract we present the results of optical dating of quartz from marine and aeolian deposits on st agnes island scilly isles uk the single aliquot regenerative dose protocol was used to estimate the equivalent dose in these samples proposed tsunami laid deposits at big pool provided ages of 230 40 and 380 60 years both are consistent with an expected age of 244 years an osl age of 6 3 years was obtained on a modern sub aqueous beach deposit these results suggest that the osl signal in the tsunami laid quartz was completely reset before deposition and that these sediments can be dated accurately by optical dating techniques sand dunes at bergecooth 250 m south of big pool were also dated using osl these ages indicate phases of aeolian activity at 300 a and 1000 a in the scilly isles

luminescence and radiocarbon chronologies of playa sedimentation in the murray basin southeastern australia abstract playa lakes are important palaeoenvironmental repositories in arid landscapes as geochemically open and organically poor systems however accurate dating of playa sequences is often hampered this study paired accelerator mass spectrometry radiocarbon ams 14c and optically stimulated luminescence osl ages from four murray basin playa lakes to assess the accuracy of the chronometric techniques in these environments the osl dating directed the sampling strategy which targeted sandier sections of the playa lacustrine sequences these appear to comprise aeolian derived fine quartzose sand ensuring the effective resetting of the luminescence signals prior to deposition in contrast the 14c ages were on bulk organic carbon and not targeted ages are generally in stratigraphic order and span the middle late last glacial and holocene this accords with models of past groundwater hydrology for the playa basins only half of the paired samples are in agreement at 2 precision however with five of the 14c ages older than their corresponding osl ages low organic contents of playa sediments increases the susceptibility of 14c ages to contamination with the incorporation of small amounts of dead carbon into the dated samples possibly accounting for the apparent discrepancies obtaining valid chronologies from arid settings requires close targeting of dated fractions the application of independent techniques is essential for scrutinizing the dating results

tsunami deposits in a super large wave flume abstract understanding the process of sediment transport under tsunami inundation is essential to providing credible information about potential tsunamis from tsunami deposits in this study a super large wave flume 205 m long and 3 4 m wide was used to investigate the hydraulic process of tsunami inundation and sedimentary features of the resulting tsunami deposit a uniformly sloping topography 1 50 with a sand dune 0 2 m high was built in the flume and the topography change induced by a solitary wave was measured the maximum wave height at the shoreline was 0 6 m and the horizontal velocity reached up to 3 5 m s resulting in a sediment concentration of up to 5 by volume the inundation and return flow completely eroded the dune and caused deposition which showed landward and seaward thinning and fining the vertical distribution of grain size and density in the inundation flow indicated upward fining and an upward decrease in density and the deposits showed inverse grading at the base in addition to normal grading therefore the inverse grading was attributed to the depositional process instead of the vertical distribution of grain size in the flow such as via a traction carpet the inundation flow was classified into two phases the first phase flow which appeared at the front of the inundation flow was governed by the wave speed at the shoreline the second phase flow which occurred near the dune was controlled by the difference in wave levels in front of and behind the dune the deposits caused by the first phase flow near the inundation limit were constant regardless of the presence of the dune indicating that the effect of the dune on the deposits was limited in the nearshore region the deposits near the inundation limit showing rapid fining and different chemical compositions were carried by muddy foam floating on the water surface the sediment supply from offshore to onshore over the dune was small and the erosion of the sand dune accounted for 36 of the onshore deposits the offshore deposits were mainly caused by wave motion and the contribution of the onshore sediment brought by the return flow was small 24 however the return flow had a large effect on the sedimentary structure of the offshore deposits such as seaward fining our results will help to examine the physical processes resulting in the empirically established common sedimentary characteristics of tsunami deposits and will provide a detailed data set to validate sediment transport models used in numerical simulations

age estimates of coastal terraces in the andaman and nicobar islands and their tectonic implications the great indian ocean earthquake of december 26 2004 caused significant vertical changes in its rupture zone about 800 km of the rupture is along the andaman and nicobar islands which forms the outer arc ridge of the subduction zone coseismic deformation along the exposed land could be observed as uplift subsidence here we analyze the morphological features along the coast of the andaman and nicobar islands in an effort to reconstruct the past tectonics taking cues from the coseismic effects we obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates which vary from 1 33 mm yr 1 in the little andaman to 2 80 mm yr 1 in south andaman and 2 45 mm yr 1 in the north andaman our radiocarbon dates converge on sim 600 yr and sim 1000 yr old coastal uplifts which we attribute to the level changes due to two major previous subduction earthquakes in the region

source area and rupture parameters of the 31 december 1881 mw 7 9 car nicobar earthquake estimated from tsunamis recorded in the bay of bengal 1 on the morning of 31 december 1881 a submarine earthquake beneath the andaman islands generated a tsunami with a maximum crest height of 0 8 m that was recorded by eight tide gauges surrounding the bay of bengal since the earthquake occurred 8 years before the construction of the world s first teleseismic recording seismometer little has been known about its rupture parameters or location waveform and amplitude modeling of the tsunami indicate that it was generated by a mw 7 9 0 1 rupture on the india andaman plate boundary resulting in 10 60 cm of uplift of the island of car nicobar the rupture consisted of two segments the northern 40 km long segment is separated from the southern 150 km long segment by a 100 km region corresponding to the westward projection of the west andaman spreading center the main rupture occurred between 8 5 n and 10 n with a total area of 150 km 60 km dipping 20 e with a mean slip of 2 7 m the recurrence time for 1881 type events is estimated to be 114 200 years on the basis of inferred gps convergence rates and inferred plate closure vectors although slip partitioning in the region may extend this estimate by as much as 30

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples