large bedform generated by the 2011 tohoku oki tsunami at kesennuma bay japan abstract the 11 march 2011 m w 9 0 tohoku megathrust earthquake off the pacific coast of japan was a salient event in the history of japan the resultant huge tsunami the 2011 tohoku oki tsunami inundated a vast coastal area of northeastern japan causing widespread devastation twenty days after the tsunami we analyzed the impact of the tsunami on the sea bottom of the kesennuma inner bay using side scan sonar to explore the damage and bathymetric change in the harbor herein we present the first direct evidence that the sea bottom sediments of around 10 15 m were largely reworked by the tsunami to thickness of a few meters and that large dunes were formed by the tsunami considering that the sea wave influence is as weak as it is inside the inner bay the potential exists that even meter thick paleo tsunami deposits are preserved in shallow sea bottoms with large bedforms this finding will be a stepping stone to future geological studies of tsunami effects in shallow sea regions

identification of tsunami deposits considering the tsunami waveform an example of subaqueous tsunami deposits in holocene shallow bay on southern boso peninsula central japan abstract this study proposes a tsunami depositional model based on observations of emerged holocene tsunami deposits in outcrops located in eastern japan the model is also applicable to the identification of other deposits such as those laid down by storms the tsunami deposits described were formed in a small bay of 10 20 m water depth and are mainly composed of sand and gravel they show various sedimentary structures including hummocky cross stratification hcs and inverse and normal grading although individually the sedimentary structures are similar to those commonly found in storm deposits the combination of vertical stacking in the tsunami deposits makes a unique pattern this vertical stacking of internal structures is due to the waveform of the source tsunamis reflecting 1 extremely long wavelengths and wave period and 2 temporal changes of wave sizes from the beginning to end of the tsunamis the tsunami deposits display many sub layers with scoured and graded structures each sub layer especially in sandy facies is characterized by hcs and inverse and normal grading that are the result of deposition from prolonged high energy sediment flows the vertical stack of sub layers shows incremental deposition from the repeated sediment flows mud drapes cover the sub layers and indicate the existence of flow velocity stagnant stages between each sediment flow current reversals within the sub layers indicate the repeated occurrence of the up and return flows the tsunami deposits are vertically divided into four depositional units tna to tnd in ascending order reflecting the temporal change of wave sizes in the tsunami wave trains unit tna is relatively fine grained and indicative of small tsunami waves during the early stage of the tsunami unit tnb is a protruding coarse grained and thickest stratified division and is the result of a relatively large wave group during the middle stage of the tsunami unit tnc is a fine alternation of thin sand sheets and mud drapes deposited from waning waves during the later stage of the tsunami unit tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout cyclic build up of these sub layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays

effect of predeformational basin geometry in the kinematic evolution of a thin skinned orogenic wedge insights from three dimensional finite element modeling of the provo salient sevier fold thrust belt utah 1 in fold thrust belts sedimentary cover rocks are detached from undeformed basement and undergo crustal scale shortening and internal deformation we have investigated a three dimensional 3 d nonlinear elastic plastic finite element model using the restored provo salient of the sevier belt as our initial configuration in the model the deformed sedimentary prism displays large scale geometries that are seen in many natural fold thrust belts e g arcuate salient wedge shaped cross section and kinematics that are compatible with observations in the internal and external portions of the provo salient these suggest that the model can be used to predict geologic information that is generally not available from detailed observational studies in natural fold thrust belts e g strain history material displacements stress conditions the model results indicate symmetric noncoaxial plane strain paths with consistent stress and strain orientations and material displacement directions in the middle of the 3 d wedge and fully 3 d nonsymmetric noncoaxial nonplane strain paths with out of transport material displacements over the lateral boundaries the results from test runs further suggest that oblique ramps with strike direction less than 20 from the regional transport direction behave like lateral ramps and those with strike direction greater than 80 from the regional transport direction behave similar to frontal ramps oblique ramps with dips greater than 60 behave like tear faults these variations in different parts of the wedge are caused mainly by interaction between the transport parallel motion of the moving wedge and the preexisting footwall template of ramps and flats that the wedge has to ride over during its evolution

tsunami deposits refine great earthquake rupture extent and recurrence over the past 1300 years along the nankai and tokai fault segments of the nankai trough japan abstract study of prehistoric to medieval age tsunami deposits along a riverbank site near the eastern nankai trough central japan show that not only did tokai earthquakes occur with a higher frequency than previously thought but that contemporaneous ruptures of the tokai and nankai fault segments were also more common the site revealed a 1 km long coast normal cross section of the strand plain and exposed four sandy tsunami deposits each of which indicates inundation over 2 km inland of the coast radiocarbon dating of previously studied and newly discovered deposits in the region indicates a shorter recurrence time for tokai earthquakes and clarifies their linkage with nankai earthquakes we attribute the younger two tsunami deposits to the 1498 and 1096 ce tokai earthquakes the older two deposits confirm the occurrence of the tokai earthquakes in 887 ce and in the latest 7th century these events are not reliably recorded in historical documents in the tokai region but were noted in the nankai area the 887 ce earthquake likely represents a full length rupture of the tokai and nankai segments as was the case for the 1707 ce earthquake integrated with the previous studies these new results show that nine tokai earthquakes occurred over the last 1300 years the oldest in the latest 7th century and in 887 1096 1361 1498 1614 1707 1854 and 1944 ce recalculated recurrence intervals range from 90 to 265 years except for the 1498 meio tokai earthquake the tokai earthquakes occurred simultaneously with nankai earthquakes

new bedform phase diagrams and discriminant functions for formative conditions of bedforms in open channel flows understanding of the formative conditions of fluvial bedforms is significant for both river management and geological studies diagrams showing bedform stability conditions have been widely used for the analyses of sedimentary structures however the use of discriminants to determine the boundaries of different bedforms regimes has not yet been explored in this study we use discriminant functions to describe formative conditions for a range of fluvial bedforms in a 3d dimensionless parametric space we do this by means of discriminant analysis using the mahalanobis distance we analyzed 3793 available laboratory and field data and used these to produce new bedform phase diagrams these diagrams employ three dimensionless parameters representing properties of flow hydraulics and sediment particles as their axes the discriminant functions for bedform regimes proposed herein are quadratic functions of three dimensionless parameters and are expressed as curved surfaces in 3d space these empirical functions can be used to estimate paleoflow velocities from sedimentary structures as an example of the reconstruction of hydraulic conditions we calculated the paleoflow velocity of the 2011 tohoku oki tsunami backwash flow from the sedimentary structures of the tsunami deposit in so doing we successfully reconstructed reasonable values of the paleoflow velocities

bed forms in bimodal sand gravel sediments laboratory and field analysis bed forms were studied in goodwin creek and a laboratory flume channel the bed sediment of the field site and flume had median diameters of 8ae3 modes of 0ae4 22ae6 mm and 1ae82 mm modes of 0ae5 5ae6 mm respectively the laboratory andfieldchannelshadsimilarvaluesofbimodalparameters ratiosofflowdepth to median bed material diameter and ratios of shear stress to critical shear stress and were judged to be comparable in the transport of bed load sediment and the resulting bed forms three groupings of bed forms from the laboratory flume experiments ripple like bed forms bed load sheets low relief bed waves were identified using the height and period of the bed forms for the range of flow depths and discharges investigated in the flume bed forms became higher and longer with increasing bed shear stress bed forms from goodwin creek were similar to those from theflume with comparable ratios between bed form length height and flow depth the bed forms in the flume provide a positive link between rate and size fluctuations measured in the field and the bed forms the smaller bed forms identified were sediment starved and are not considered to be dunes while the largest bed forms in which all of the bed material sizes were mobilized in the field and laboratory were judged to be dunes

sedimentary processes and the distribution of tsunami deposits on a narrow coastal lowland backed by a cliff in flume experiments abstract we performed flume experiments to examine tsunami flow conditions sedimentary processes and the distribution of tsunami deposits on a narrow coastal lowland backed by a cliff the experiments directed tsunamis of eight magnitudes onto a terrestrial model of a narrow coastal plain backed by a cliff and the results were compared with those of similar previously conducted experiments without a cliff in the experimental series with the cliff the tsunami flow was blocked and pooled and as a consequence the flow changed from supercritical to subcritical with a hydraulic jump the flow transformation forced the suspended sediment in the subsequent flow to stall and deposit as a result the distribution of deposits show a local maximum at a short distance from the cliff in particular in the case of larger tsunami flows this result suggests that an impeder such as a cliff can cause transformation of a tsunami flow and locally thick deposits

three dimensional kinematic history at an oblique ramp leamington zone sevier belt utah abstract differences in kinematics in adjoining salients in fold thrust belts are typically accommodated along bounding transverse zones the leamington zone is an oblique ramp that accommodates slip between structures in the provo salient and the central utah segment of the sevier fold thrust belt the leamington zone consists of the leamington canyon thrust associated second order asymmetric folds and an out of syncline reverse fault the leamington canyon thrust is a rotated se dipping thrust fault with top to southeast motion it represents an oblique ramp of the folded canyon range thrust fold tightening of the syncline se of the folded leamington canyon thrust trace during later emplacement of underlying structures caused out of syncline reverse faulting in the fold core analysis of the finite strain minor fault populations and conjugate fracture sets were used in interpreting the 3 d kinematic history along the leamington zone restored maximum stretching directions of finite strain ellipsoids trend eastward overall inferred motion planes from populations of slickenlines on minor faults are consistent with overall southeastward motion acute bisectors of conjugate fracture sets may reflect more southward directions later in the deformation history these superimposed deformations with local relative chronologies of plastic and brittle structures using cross cutting relationships indicate that the leamington zone area shows overall clockwise changes in kinematic directions from e to ese to sse during successive pulses of deformation the temporal changes in kinematic directions along the leamington zone most likely reflect variations in kinematics over the oblique ramp as the overall easterly displaced 3 d fold thrust belt wedge interacted with the pre existing oblique ramp structure with small magnitudes of superimposed local vertical axis rotations during later folding and fold tightening of the leamington canyon thrust

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

horizontal and vertical variation of 2004 indian tsunami deposits an example of two transects along the western coast of thailand abstract we investigated horizontal and vertical variations in modern tsunami deposits along two transects at nam khem and khao lak western coast of thailand deposited by the large tsunami associated with the earthquake magnitude 9 0 of 26 december 2004 off sumatra indonesia tsunami waves 6 10 m high struck the area approximately 2 h after the earthquake tsunami deposits cover the low lying coastal plains and extend more than 1 km inland from the shoreline no landward decrease in sediment thicknesses was found clearly at either transect terrace scarps and a steep slope behind the coastal plain probably stopped tsunami deposition further inland causing substantial sediments to be deposited in front of these features very clear vertical variations in grain size and multiple layers are found in the deposits to about 600 m inland at nam khem fine grained sediments overlie the coarse grained sediments of the basal layer of the tsunami deposits at some sites the fine grained sediments are overlain by another layer of coarse grained sediments suggesting deposits laid down in succession by multiple waves the basal coarse grained sediments at nam khem fine landward the up flow waned inland based on the assumption that the grain size of the basal deposits relates to the strength of the up flow these results are potentially useful in disaster prevention and coastal environmental change management as well as for interpreting paleotsunami deposits in geological records

x ray tomography of tsunami deposits towards a new depositional model of tsunami deposits x ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in andalusia spain 1755 lisbon tsunami the technique allows characterization of grain size distribution structures component analysis and sedimentary fabric of fine grained unconsolidated tsunami deposits at resolutions down to particle scale the results are validated by comparing to data obtained using other techniques such as laser diffraction anisotropy of magnetic susceptibility and x ray microfluorescence on the same deposits specific technical details such as sampling scanning and image processing methods and further improvements are addressed the use of x ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines rip up clasts crude laminations convolutions floating outsized clasts and contacts between successive units this analysis of the 1755 tsunami deposits using x ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets with laminated mudlines corresponding to the basal frictional region of these carpets the onset of the tsunami backwash is marked by a micro vortex resembling kelvin helmoltz instabilities

δ13c and δ18o variations in primary and secondary carbonate phases several contrasting examples from palaeoproterozoic 13c rich metamorphosed dolostones abstract the palaeoproterozoic kuetsjarvi sedimentary formation from the pechenga greenstone belt nw russia has been studied with the purpose of determining 13ccarb and 18ocarb values in various carbonate phases from genetically different 13c rich dolostones sampled by micro coring techniques samples were collected from quarries and drillholes this avoids the influence of recent weathering on isotopic composition and allows rocks from different metamorphic facies intersected by deep drillholes to be sampled in the low grade greenschist facies conditions distinct textural components from the same parental impure dolostones have yielded 13c values ranging within 1 and showing no statistical differences between early dolomicrite and late void and fenestra filling dolospar no significant differences have been observed between analyses of the whole rock and microcored samples genetically different dolomites however retain their primary isotopic peculiarities and show 13c differences exceeding 30 no external isotopically light carbon has been introduced during diagenesis and therefore there is no evidence of soil derived co2 which commonly shifts 13c to more negative values 18o values show 2 6 fluctuations in distinct textural components from the same parental dolostones which were caused by syn depositional early diagenetic processes genetically different dolomites largely retain their syn depositional early diagenetic 18o values ranging from 9 mantle influenced to 30 evaporation induced the high grade greenschist facies metamorphism marked by the reaction dolomite quartz h2o tremolite calcite2 co2 significantly reset 13c by 3 in the metamorphic calcite2 and 18o by 6 in all carbonate components in such cases the best proxy for depositional 13c values of impure dolostones can only be provided by microcored samples of the dolomite phase

historical tsunami and storm deposits during the last five centuries on the sanriku coast japan abstract nine event deposits in a small alluvial valley along the sanriku coast japan were correlated with historical tsunamis and storms that have been recorded in this region since the 15th century we identified nine sandy layers in 15 geo slices collected at distances ranging from 140 to 260 m from the coast in a lowland back marsh protected from the sea by a high sandy ridge based on their sedimentary characteristics grain size distribution and marine microfossil assemblages namely coccoliths these event layers which were well preserved in their order of deposition were probably either tsunami or storm deposits diatom analysis revealed four stages of paleo environmental change from tidal marsh to wetland the uppermost event layer covering the ground surface is probably the deposit from the 2011 tohoku oki tsunami ages for other event deposits were radiometrically dated using 14 c 137 cs and 210 pb with bayesian estimation the second event layers can be correlated with the 1960 chilean or 1968 aomori oki earthquake tsunamis the candidates for the third event layer are the 1947 catherine and 1948 ione typhoons as well as the candidates for the second event layer the fourth and fifth event layers are likely associated with the 1933 and 1896 sanriku oki earthquake tsunamis four lower event layers can be correlated with historical tsunamis and storms that occurred during the 15th to 18th centuries such as the 1611 sanriku oki earthquake tsunami

reducing the age range of tsunami deposits by 14 c dating of rip up clasts abstract erosion by tsunami waves represents an important issue when determining the age of a tsunami deposit because the age is usually estimated using dating of sediments above and below the deposit dating of material within the tsunami deposit if suitable material is obtainable can be used to further constrain its age eroded sediments are sometimes incorporated within the tsunami deposits as rip up clasts which might therefore be used as minimum age dating material however the single calibrated 14 c age often shows a wide age range because of fluctuations in the calibration curve therefore it remains uncertain whether rip up clast measurements are useful to constrain the depositional age of tsunami deposits or not in this study we carried out high resolution 14 c dating of tsunami deposits including rip up clasts of peat in rikuzentakata northeastern japan where numerous rip up clasts were observed within a tsunami deposit sediments above and below the tsunami deposit and a 5 cm large rip up clast were dated sequentially comparison of these dating results with the calibration curve revealed that the clast was inverted its age was better constrained based on the stratigraphic order and we infer that the clast corresponds to approximately 100 years of sedimentation the oldest age of the clast was consistent with the age of the peat immediately below the tsunami deposit suggesting that surface sediments probably formed the rip up clast at the time of the tsunami thus the dating of the rip up clast was useful to further constrain the depositional age of the tsunami deposit as we narrowed the tsunami deposit age range by approximately 100 years results show that ignoring tsunami related erosion might lead to overestimation of the tsunami deposit age for this reason an appropriate dating site which is less affected by minor tsunami related erosion with regards to the paleo topography should be explored we therefore propose a more effective sampling strategy for better age estimation of tsunami deposits

interpreting flash flood palaeoflow parameters from antidunes and gravel lenses an example from montserrat west indies the wavelength of stationary water surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow in sand bed flume experiments alexander et al 2001 found that lens structures were preserved during antidune growth and change and the dimension of the lenses were empirically related to antidune wavelength and thus could be used to estimate flow velocity and depth this study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting testing the alexander et al 2001 relationship at a field scale trains of stationary and upstream migrating water surface waves were prevalent during the flash flood in october 2012 in the belham valley montserrat west indies wave positions and wavelengths were assessed at 900 s intervals through the daylight hours of the event within a monitored reach the wave data indicate flow depths up to 1 3 m and velocity up to 3 6 m s 1 sedimentary structures formed by antidune growth and change were preserved in the event deposit these structures include lenses of clast supported gravel and massive sand with varying internal architecture the lenses and associated low angle strata are comparable to sand bed structures formed from stationary and upstream migrating waves in flume experiments confirming the diagnostic value of these structures using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

magnetic fabric evidence for rapid characteristic changes in the dynamics of the 2011 tohoku oki tsunami abstract low field anisotropy of magnetic susceptibility ams and rock magnetic measurements were applied to sediments deposited by the 2011 tohoku oki tsunami to reveal the dynamic of the tsunami run up and the character of the sedimentation along the misawa coast aomori prefecture northern japan in the tsunami deposits studied elongated coarse grained multi domain titanomagnetite and magnetite minerals were the carriers of the ams signal two main types of sedimentary environment are described a higher energy tangential stress dominated environment with imbrication and traction rolling transportation and a calmer post peak wave environment ruled by gravitational stress rapid characteristic changes in the tsunami dynamics are also described the tsunami began with erosion of the pre tsunami surface caused by rapidly increasing energy bedload features such as ripple stratification were developed by the repeated accelerations and decelerations of the tsunami wave during run up the arrival of the peak wave was indicated by high density flow slurry like sediments following the peak wave the decreasing energy was marked by a change in magnetic fabric mf the study showed that quite similar tendencies in the character of tsunami dynamics can be identified in tsunami deposits despite their materials being deposited in currents with quite different energy levels

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

subaerial exposure surfaces in a palaeoproterozoic 13c rich dolostone sequence from the pechenga greenstone belt palaeoenvironmental and isotopic implications for the 2330 2060 ma global isotope excursion of 13c 12c abstract this article reports the discovery of numerous subaerial exposure surfaces which occur in the ca 2200 ma kuetsjarvi sedimentary formation ksf from the pechenga greenstone belt ne fennoscandian shield russia the formation was accumulated within an intraplate rift and is composed of fluviatile deltaic siliciclastic deposits and lacustrine dolostones the dolostones are enriched in 13 c 13 c 6 6 to 7 6 v pdb 18 o 16 7 to 21 5 v smow which is in general assigned to a global perturbation of the carbon cycle the lacustrine dolostone unit contains desiccated and in situ brecciated carbonate beds subaerial erosion and dissolution surfaces epikarst surficial silicification silcretes and hot water spring travertines the dissolution surfaces marked by formation of a few centimetre thick vuggy non laminated dolomicrite capped by silicified nodular zone resemble modern calcretes which formed by capillary rise of surface waters per ascensum calcrete following saturation of the regolith zone under arid or semi arid conditions abundant red iron stained superficial dolocrete implies the existence of an o 2 rich atmosphere rezolith black pebbles alveolar septal structures microcodium and other fabrics associated with plant roots and input of terrestrial organic matter which are typical for post cretaceous pedogenic calcretes have not been identified alfa fabrics can be applied to describe dolocretes though rhombic calcite crystals are lacking neither 13 c depletion nor 13 c enrichment has been documented in the dolocrete which suggests no contribution of co 2 derived from soil or from any other c org rich sources enriched in 12 c and apparent lack of biological uptake of 12 c during formation of the dolocrete both petrographic and carbon isotope data do not support earlier assertions that palaeoproterozoic subaerial surface was colonised by microbial mats a few samples have high 18 o values up to 30 despite diagenetic and metamorphic resetting of the oxygen isotope system suggesting evaporation during formation of the superficial dolocrete such documented episodes of subaerial exposure formation of hot water travertines superficial dolocrete and silcrete suggest that there must have been frequent decoupling between the kuetsjarvi depositional system and the bordering sea this imposes an additional restriction on the use of the isotopic composition of the ksf dolostones for reconstruction of the 13 c carb global secular curve

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

2004 indian ocean tsunami inflow and outflow at phuket thailand at bangtao beach phuket the 2004 indian ocean tsunami produced a repeated sequence in which rapid inflow of turbulent water was followed by ponding and then by gradual outflow photographs and eyewitness accounts show an initial withdrawal followed by series of inflows the tsunami left behind a sand sheet as much as 25 cm thick that contains parallel inclined landward and seaward lamina in addition to the normal grading commonly reported from tsunami deposits the sheet contains evidence for two times of vigorous inflow each of these is marked by mud rip ups medium to coarse sand that grades upward to fine landward inclined laminae and a sharp basal contact the top of the sand sheet when observed in the first days after the tsunami abounded in current dune and ripple bedforms of mostly landward orientation the tsunami s first positive wave left noonshore sedimentary record in this pitting area the second wave deposited sand that is much less extensive and slightly finer than that of the third wave the deposit of both these waves contains multiple fining upward sequences possibly due to multiple surges in one wave train the depth averaged flow velocity estimated from thickness and grain size are in the range 7 21 m s whereas a near bottom threshold velocity calculated from bedforms reveals the order of magnitude difference from 1 74 to 1 03 m s 2007 elsevier b v all rights reserved

a spatial statistics approach to the quantification of finite strain variation in penetratively deformed thrust sheets an example from the sheeprock thrust sheet sevier fold and thrust belt utah abstract strain is an important component of the total displacement field in the emplacement of a thrust sheet the finite strain tensor in a penetratively deformed thrust sheet is a spatial variable i describe a method for quantitative estimation of the finite strain variation in thrust sheets by applying spatial statistics analysis on strain data collected from a part of the sheeprock thrust sheet in the southern sheeprock mountains and the west tintic mountains north central utah strain was measured in the quartzites of the sheeprock thrust sheet and the spatial statistics method is illustrated using the x z strain axial ratios the sheeprock thrust sheet was penetratively deformed during sevier age fault propagation folding i quantified finite strain from quartzites using the modified normalized fry method and calculated the three dimensional strain ellipsoid from the quartzites using three orthogonal thin sections from each oriented field sample the variation of finite strain in the sheeprock thrust sheet was best represented by an exponential semivariogram model which i used to predict values of strain from unsampled locations by ordinary kriging cross validation showed that in general the predicted and measured values show good agreement within 1 of each other the sampled space was contoured using the measured and predicted strain values to obtain a detailed finite strain variation pattern in a part of the sheeprock thrust sheet

finite strain and strain variation analysis in the sheeprock thrust sheet an internal thrust sheet in the provo salient of the sevier fold and thrust belt central utah abstract the sheeprock thrust sheet in west central utah is an internal thrust sheet in the provo salient of the sevier fold and thrust belt we have measured finite strain in quartzites the dominant lithology sampled along a square grid within the thrust sheet using the modified normalized fry method mcnaught m a 1994 modifying the normalized fry method for aggregates of non elliptical grains journal of structural geology16 493 503 the x y and x z axial ratios from unsampled locations within the sample area were estimated using the spatial statistics approach the strain ellipsoids exhibit a variable three dimensional orientation pattern resulting from modification of the initial layer parallel shortening lps strain ellipsoid by fault parallel shear in conjunction with vertical flattening and or horizontal stretching indicating that the thrust sheet did not undergo plane strain deformation in the transport plane this suggests that the plane strain assumption used in drawing restorable balanced cross sections breaks down for internal thrust sheets with more than one penetrative strain producing deformation event the x z strain axial ratios decrease away from the thrust towards the middle of the sheet the x y strain axial ratios from interpolated image diagrams indicate transport parallel stretching at the front end of the sheet and strike parallel stretching at the back end of the sheet the footwall and hanging wall finite strain patterns are similar indicating that most of the strain in the sheeprock thrust sheet developed early in the deformation history of the thrust sheet before and perhaps during the growth of a large fault propagation fold pair

the 2011 tohoku oki tsunami three years on abstract the 2011 tohoku oki tsunami that devastated the pacific coast of tohoku japan was a turning point for modern research as a result of this event it was recognized that paleotsunami research is vital to help understand the size and recurrence interval of low frequency large tsunamis this paper reviews the progress of geological research on the 2011 tohoku oki tsunami and summarizes new questions that are arising out of this work for example recent work suggests that the landward extent and thickness of the sandy deposit as well as the presence or absence of marine microfossils in the sediment are most likely to be mainly controlled by the initial wave properties sediment source offshore bathymetry and onshore topography this in turn implies that there are certain relationships between the characteristics of a tsunami deposit and the wave properties and it may be possible to reconstruct the latter from the deposits offshore tsunami deposits related to the 2011 tohoku oki tsunami have also been well described this recent research indicates that sedimentation and erosion in inner bay and open ocean 20 m water depth locations can be in the order of several meters suggesting that the tsunami shear force was strong in the nearshore zone on the other hand sandy to muddy deposits a few centimeters thick were observed at about 100 to 6000 m water depth it is likely that the tsunami resulted in resuspension of sea bottom sediments and that suspended material flowed downslope as a turbidity current or suspended flow although many authors recognize the possibility that strong earthquake groundshaking might have also generated turbidity currents studies of the 2011 tohoku oki event have led researchers back to two of the fundamental issues of tsunami geology understanding the linkage between onshore and offshore sedimentation and erosion and establishing identification criteria for tsunami deposits moreover though beyond the issue of simple tsunami geology it is important for all researchers to communicate with governments and the general public in order to reduce future casualties by using risk assessments based on our understanding of infrequent large tsunamis

effects of topography on particle composition of 2011 tsunami deposits on the ria type sanriku coast japan abstract a geological survey was conducted in a small valley along the sanriku coast and the grain compositions of both autochthonous gravels and the 2011 tsunami deposit from the tohoku oki earthquake were investigated to reveal the depositional form of the tsunami deposits on the ria type coast the features of autochthonous gravels in the beach riverbed and slope areas are characterized by a combination of their rock type and roundness the roundness values of the beach and slope gravels are large 0 8 0 9 and small 0 1 0 2 respectively regardless of rock type and the riverbed gravels are typically granite rocks with an intermediate roundness 0 4 0 5 the 2011 tsunami deposits along the survey transect include the above autochthonous gravels and show several characteristic features such as a sharp erosional contact with the underlying peaty soil normal and or inverse grading structures mud sheets and richness in gravels in the lower unit while the thickness shows no systematic changes with the distance from the coast the presence of slope gravels suggests high tsunami inundation and flux which eroded bare rock and talus and transported them to the valley plain by backwash current the mixture of beach and riverbed deposits implies the formation of both an upstream current from the beach which transported beach pebbles inland and a backwash current along the channel which accumulated sub angular riverbed gravels around the river mouth the characteristics of the 2011 tsunami deposit on the sanriku coast where narrow valleys are surrounded by high cliffs with steep slopes are significantly different from those of sandy tsunami deposits in sendai plain where a flat plain develops within several kilometers of the coastline the differences among sedimentary facies are affected by the topography and autochthonous deposits

palaeoproterozoic travertines of volcanic affiliation from a 13c rich rift lake environment abstract the ca 2 2 ga kuetsjarvi sedimentary formation ksf of the pechenga greenstone belt the north east fennoscandian shield contains the oldest travertines so far reported in the literature the travertine hosting succession is composed of flat laminated dolomitic stromatolites micritic and allochemical dolostones all formed in coastal plains of a rift related playa lake system in an arid semiarid climate the travertines are categorised as thermal autochtonous spring travertine crust and spring orifice travertine mounds formed from hot water springs issuing at the playa lakeshore the travertines are represented by crusts and small scale mounds both composed of a series of 1 5 mm thick dark light couplets of fibrous dolomite crystals with compromise boundaries and radiating dolomite crystals travertines are composed of dolomite mg ca 0 42 0 47 exhibiting a general lack of replacement textures travertines exhibit several phases of growth separated by dissolution processes and accompanied by precipitation of sio 2 the upper surface of crusts and mounds are often affected by desiccation joints and covered with thicker sio 2 veneer 18 o 18 6 the host dolostones are characterised by 13 c carb of 6 1 8 8 v pdb and 18 o values ranging from 11 to 19 v smow microcored samples of travertine dolomite exhibit 13 c and 18 o values ranging from 6 1 to 7 7 and from 12 0 to 21 5 respectively the 13 c rich nature of the background stratified dolostones is caused by the 2 4 2 06 ga global shift in 13 c 12 c carbonate carbon associated with enhanced accumulation of c org and perturbation of the global carbon cycle the source of co 2 for the travertines is considered to be of volcanogenic origin with an initial 13 c value of ca 6 0 several processes contributed to carbon and oxygen isotope composition of travertine dolomite i an initial co 2 loss at the spring orifice ii water cooling and rapid co 2 loss during water transit iii persistent evaporation from thermal water ponds pools and iv mixing with co 2 of ambient lake water enriched in 13 c silica is thought to have been dissolved by groundwater from underlying sediments and been transported upwards by a mechanism of capillary rise due to dry climatic condition

tsunami history over the past 2000 years on the sanriku coast japan determined using gravel deposits to estimate tsunami inundation behavior abstract at numanohama marsh on the rocky sanriku coast in northeast japan we identified 17 sand layers with sedimentary structures characteristic of event deposits i e a sharp erosional contact with the underlying unit a normal and or inverse grading structure parallel cross lamination mud clasts and or a thin mud layer abundant marine nannofossils coccoliths and the small catchment area in the narrow valley suggest that these event layers were likely formed by inundations during tsunamis or storms among the 17 sand layers nine contained gravels derived from the beach riverbed or slope areas six event layers contained all three of these gravels suggesting a strong inflow current that transported round pebbles from the beach erosion of wall rock in the valley during the inflow and outflow phases and a backwash current that caused sub angular riverbed gravel to accumulate in lowland areas these six layers were traced up to 490 m inland from the coastline present elevation 7 m above mean sea level and were several cm thick at almost every survey point we concluded that these six event layers are tsunami deposits and dating results revealed that they correlate with the 2011 tohoku oki earthquake the 1933 and 1896 sanriku oki earthquakes any of the 1763 aomori oki 1793 miyagi oki and 1856 aomori oki earthquakes the 1611 tohoku oki earthquake and the 869 tohoku oki jogan earthquake in addition changes in the sedimentary environment inferred from diatom assemblages were well correlated with the deposition of three of the event layers two historical earthquakes the 1454 and 1611 tohoku oki earthquakes have been previously suggested as being the immediate predecessors of the 2011 tohoku oki earthquake and our dating results favor the 1611 earthquake although the source region of the 869 tohoku oki jogan earthquake has been estimated to have been off the fukushima and miyagi prefectures our results suggest that the source region extended further north along the japan trench

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

a simple model for calculating tsunami flow speed from tsunami deposits abstract this paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit the inverse problem for sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport tsunami sediment transport is modeled as a steady spatially uniform process the amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period slowing varying uprush portion of the tsunami spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation there is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness the model is tested using field data collected at arop papua new guinea soon after the 1998 tsunami speed estimates of 14 m s at 200 m inland from the shoreline compare favorably with those from a 1 d inundation model and from application of bernoulli s principle to water levels on buildings left standing after the tsunami as evidence that the model is applicable to some sandy tsunami deposits the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami

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

geochemical and micropaleontological impacts caused by the 2011 tohoku oki tsunami in matsushima bay northeastern japan abstract we present stratigraphic geochemical cns elemental analysis and micropaleontological ostracode assemblages evidence for the 2011 tohoku oki tsunami impact in matsushima bay northeastern japan and examine the recovery process after the impact to the bay environment using short sediment cores from two different topographic settings at a water depth of approximately 4 m at both sites tsunami deposits are composed of two sedimentary layers that recorded the first tsunami run up and backwash at the western site near the channel that connects the bay with the pacific ocean the first tsunami wave eroded the bay floor sediments and left the tsunami deposits composed of medium sand rich in shell fragments but with sparse numbers of meiobenthic ostracodes by contrast at the eastern site which is surrounded by many small islands the first wave eroded very little of the bay floor sediments and left tsunami deposits consisting of sandy mud rich in exotic ostracodes such as phytal species shallow marine sand dwelling species and brackish water species overlying post tsunami deposits are composed mainly of organic rich mud in which organic matter was derived primarily from marine plankton ostracode assemblages in the tsunami deposits lack the offshore species that live in water depths 50 m and are dominated by the species from matsushima bay and its adjacent nearshore upper sublittoral areas and brackish water environments the distance from deep water offshore areas to the core sites is too far to transport ostracode valves by tsunami waves

effects of longitudinal valley slopes on runup of the 2011 tohoku tsunami on the sanriku coast northeastern japan abstract the 2011 tohoku earthquake and tsunami caused heavy damage in low lying river valleys of the sanriku coast northeastern japan the landward extent of inundation by the tsunami varied considerably among the valleys indicating that tsunami runups were strongly affected by the subaerial fluvial morphology of the valleys we used detailed tsunami inundation maps to investigate tsunami runups along river valleys along the sanriku coast considering both the protected areas landward of coastal seawalls and levees protected zone and areas on the river side of levees channel zone we determined the mean longitudinal slopes of all river valleys and used them in conjunction with published tsunami inundation maps to determine the distances and heights of tsunami runups in 68 valleys along the sanriku coast runup heights tended to be higher and inundation distances longer in the channel zone than in the protected zone comparisons of runups among valleys with different longitudinal valley slopes showed that inundation distance decreased with increasing valley slope and that runup height increased with increasing slope during runup some of the kinetic energy of a tsunami is consumed as frictional work and some is transformed upslope to potential energy the steeper the longitudinal slope the greater the amount of energy transformed and stored as potential energy and consequently the amount of energy consumed by frictional work declines and inundation distance shortens in the protected zone more energy is consumed by frictional work during destruction of artificial structures such as houses and inundation distance is shorter than in the channel zone our analysis of 2011 tsunami data clarified relationship among tsunami runups shoreline tsunami heights geometry of the coastline and longitudinal valley slopes among sanriku ria coast coastline geometry appears to be a secondary influence on the shoreline tsunami height and runup that the shoreline tsunami height was not the dominant influence on tsunami runup emphasizes the importance of subaerial topography on tsunami runup especially in narrow steep valleys which are often of the topography along coasts that face plate margins

flow speed estimated by inverse modeling of sandy tsunami deposits results from the 11 march 2011 tsunami on the coastal plain near the sendai airport honshu japan abstract tsunami deposits contain information about the flow that created them which can be interpreted to estimate tsunami magnitude sandy deposits near sendai airport are modeled using an inverse sediment transport model to explore the spatial and temporal variation of tsunami flow speed in the 11 march 2011 tohoku oki tsunami the 2011 deposits contain grain size signatures of both sediment transport convergences and sediment settling out of suspension sediment transport convergences form massive or inversely graded intervals sediment falling out of suspension forms a specific type of normal grading termed suspension grading the jaffe and gelfenbaum 2007 inverse sediment transport model which relates the thickness and bulk grain size of suspension graded intervals to tsunami flow speed was applied to 24 suspension graded intervals ranging in thickness from 2 to 4 cm at 7 trenches located from about 250 to 1350 m inland from the shoreline modeled tsunami flow speeds range from 2 2 to 9 0 m s and were strongly dependent on the choice of manning s n roughness parameterization flow speeds were highest from about 75 300 m landward of the forested sand dunes where the tsunami encountered lower roughness in a low lying area as it traveled downslope and decreased by 16 as the tsunami moved inland over the subsequent 596 m as many as 5 suspension graded intervals interpreted as forming during the onshore flow of up to 5 waves were identified at each location with a tendency for an inland decrease in the number of suspension graded intervals suggesting fewer waves inland tsunami flows tended to be fastest in the lower two intervals earlier waves and slowest in the uppermost interval last wave of the deposits modeled reconstructions of the suspension graded intervals at a vertical resolution of 1 cm reproduced observed upward fining of the distributions reasonably well supporting the use of the inverse model estimates of the time required to form 99 of the thickness of the suspension graded intervals ranged 2 to 5 min allowing that sediment falling from suspension could have formed these portions of the deposits in the time between waves application of the inverse model to determine paleotsunami flow speeds from deposits although now possible is complicated by uncertainty in roughness as inverse approaches to estimating roughness and tsunami flow speed improve the magnitude of paleotsunamis will be better understood and the ability to assess tsunami hazard from paleotsunami deposits will improve

fractionation of carbon and oxygen isotopes in 13c rich palaeoproterozoic dolostones in the transition from medium grade to high grade greenschist facies a case study from the kola superdeep drillhole samples from the kola superdeep drillhole 12 262 m a deep drillhole 1060 m and from the surface seaprated by only around 10 km provided a unique opportunity for direct tracing of 13 c and 18 o changes through a low to high grade greenschist facies transition within impure 13 c rich palaeoproterozoic dolostones the least altered dolostones have 13 c of 9 and 18 o of 22 the metamorphic transition is expressed by dolomite calcite 1 quartz k feldspar tremolite calcite 2 dolomite calcite 1 and defined by 13 c depletion of calcite 2 c 3 0 calcite 1 1 0 2 0 and dolomite 18 o shows a considerable resetting in all carbonate components by around 6 caused by a rayleigh distillation process coupled with isotopic exchange between the carbonates and fluids with an external source of oxygen the retrograde alteration is expressed by the formation of quartz chlorite veinlets within tectonically bound zones of brecciated and sheared dolostones the maximum 18 o depletion in dolomite 9 and calcite 1 c 4 were probably controlled by infiltration into permeable zones of external fluids associated with retrograde alteration 13 c remains largely unaffected

an experimental study into the geometry of supply limited dunes the relationship between dune geometry and the volume of mobile sediment was studied in flume experiments in these flume experiments the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed a strong relationship was found between the volume that is mobile and therefore available for bedform formation and the dune dimensions and regularity if the sediment supply is limited dunes are smaller and more regular series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths the relationship between the dune dimensions and the available volume is different for each series the observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship

the future of tsunami research following the 2011 tohoku oki event abstract in this paper we summarize the regional setting our previous understanding of historical and pre historical tsunamis on the pacific coast of tohoku japan prior to the 2011 tohoku oki tsunami and our current understanding of the sedimentological geochemical and paleontological features of the onshore and offshore deposits of the event post tsunami surveys revealed many new insights such as 1 the maximum extent of the sand deposit is sometimes only 60 of the inundation distance 2 the inundation limit can be estimated by geochemical analysis even a few months after the event 3 a minor amount of marine sediment was transported inland by the tsunami on the sendai and adjacent plains with the major sediment sources being from beach and dune erosion or vented sediments from liquefaction although nearshore and offshore surveys revealed that there was a significant amount of sediment transport on the seafloor 4 coarse gravel deposits 1 m in thickness were usually thicker than the sand ones 30 cm in thickness and 5 beach erosion was minimal in some places while severe in others another important aspect of this event is that it was a large infrequent tsunami that took place where possible predecessors e g ad869 j gan were already known to have occurred based on historical and geological evidence the ad869 j gan tsunami deposits are noticeably similar to the 2011 tohoku oki sands therefore suggesting that the j gan and its source mechanism may have been larger than previously thought while we have learned many lessons from the 2011 tohoku oki event more research is needed to provide reliable tsunami risk assessments around the world

bedforms record the flow conditions of the 2011 tohoku oki tsunami on the sendai plain northeast japan abstract this article describes the bedforms formed by the 2011 tohoku oki tsunami on the southern sendai plain ne japan integrated analyses of satellite images field survey data and x ray radiographs revealed the natural shapes of these bedforms the dominant bedforms are dunes and antidunes about 20 cm thick high and relatively flat because of their meter scale wavelengths their morphologies reflect mainly the tsunami run up flow on the flat lowland and the return flow in a narrow steep valley flow depth changed at sites where the level of the ground surface changed along the tsunami flow path causing the flow velocity to fluctuate flow velocity decreased in depressed deep water sections and increased in raised shallow water sections the types and positions of the tsunami deposit bedforms were thus strongly controlled by local ground surface roughness such as raised roadbeds and levees as a result the observed thickness distribution of the tsunami deposits fluctuates it is important to consider the possible existence of bedforms in paleotsunami surveys especially for accurate determination of the thickness distribution of the tsunami deposits because thickness data are essential information for reconstruction of the tsunami inundation limit as well as its flow speed