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

remarkable bathymetric change in the nearshore zone by the 2004 indian ocean tsunami kirinda harbor sri lanka we investigated bathymetric data obtained at kirinda harbor sri lanka one month before and 2 and 11 months after the 2004 indian ocean tsunami our bathymetric surveyed data and numerical modeling results suggest that the first run up tsunami wave transported huge amounts of offshore sea bottom sediment and deposited it in a layer up to 4 m thick along the shoreface slope in some places this accreted sediment was not eroded by the backwash because of the particular arrangement of artificial structures and sand dunes especially the sedimentation process and the volume of the sediment transported by the run up waves can be examined where the influence of the backwash flow was very minor remarkable sedimentation attributable to the run up wave would have occurred mainly by the deposition of the sediment particles along the slope by the run up waves the slope was developed toward the stoss side rather than by the settlement of the sediment from the suspension load we estimated that considerable amounts of sediment were transported by the tsunami from the offshore sea bottom but most were deposited not on land but in the sea eleven months after the tsunami the harbor bathymetry had almost undergone complete reversion to its pre tsunami condition implying that the tsunami impact on permanent geomorphological landforms was limited at this harbor

spatial thickness variability of the 2011 tohoku oki tsunami deposits along the coastline of sendai bay abstract soon after the 2011 tohoku oki event approximately 1300 tsunami deposit thickness data were collected spatially by the governors to cover the entire tsunami affected area sendai plain along the sendai bay coastline this dataset along with high resolution and high precision data of flow depth and pre tsunami and post tsunami elevation enables us first to conduct a direct comparison of the sedimentation and erosion volumes as well as the tsunami hydrodynamic features e g flow depth and sediment thickness the total balance of sedimentation and erosion volumes revealed that the volume of tsunami deposited sediments can be explained roughly using the erosion volumes at the beach and sand dunes for sandy deposits and at rice paddy fields for muddy deposits both the flow depth and sediment thickness showed positive correlations with the distance from the shoreline while sediment thickness is no correlation to the elevation except in the zone closest to the shoreline where erosion is present in addition a statistical relation was found between the flow depth and sediment thickness in fact the frequency distribution of sediment concentration defined here as the sediment thickness divided by the maximum flow depth at each survey site fits well with the logarithmic normal distribution with geometric average of about 2 this fit indicates that the tsunami deposits on the sendai plain can be explained generally if we simply assume that the saturated level of the sediment concentration in the flow is limited to about 2 on average irrespective of the grain size such a simple explanation might be applicable only for the tsunami deposits on the sendai plain because the topography is remarkably flat and low therefore the tsunami inundation process is relatively simple nevertheless a possible relation between tsunami flow depth and sediment thickness suggested here would be very useful to consider the ideal sedimentary process of the tsunami deposits and to improve forward and inverse modelings

progressive mitigation method of rock bursts under complicated geological conditions abstract jingxi coalfield which is called china s geological encyclopedia has a complicated geological condition as one its representative mines muchengjian mine has witnessed nearly thirty rock bursts in the past decade considering geological structures the in situ stress state and the burst proneness of coal one typical mining area in muchengjian mine is selected for analysis where nearly one third of rock bursts occurred this analysis lays the foundation for selecting mitigation strategies results indicate that the blasting disturbance plays an important role in the intensity and the scale of these rock bursts jingxi coalfield has three types of rock burst mechanisms i high in situ stress rock burst ii high mining induced stress rock burst and iii high in situ stress plus high mining induced stress rock burst therefore we follow two guidelines for rock burst control one is to mitigate the high stress concentration and the second is to control the disturbance stress on the basis of these two guidelines we designed a progressive mitigation method of rock bursts pmmrb first the weak disturbance destress techniques e g large diameter drilling water infusion are applied to weaken the strength and the burst proneness of coal and to expand crack zones to reduce the stress concentration and second the strong disturbance destress blasting is applied if the release of stress concentration is not sufficient pmmrb is adopted in a similar mining area with a higher in situ stress which indicates that pmmrb is applicable to the control of rock bursts and the reduction of rock burst intensity

sedimentary fabric characterized by x ray tomography a case study from tsunami deposits on the marquesas islands french polynesia x ray tomography is used to analyse the grain size and sedimentary fabric of two tsunami deposits in the marquesas islands french polynesia pacific ocean which are particularly exposed to trans pacific tsunamis one site is located on the southern coast of nuku hiva island hooumi and the other one is on the southern coast of hiva oa island tahauku results are compared with other techniques such as two dimensional image analysis on bulk samples particle analyser and anisotropy of magnetic susceptibility the sedimentary fabric is characterized through three dimensional stacks of horizontal slices following a vertical step of 2 5 mm along the cores while grain size distribution is estimated from two dimensional vertical slices following a step of 2 mm four types of fabric are distinguished a moderate to high angle 15 to 75 b bimodal low angle 15 c low to high angle with at least two different orientations and d dispersed fabric the fabric geometry in a tsunami deposit is not only controlled by the characteristics of the flow itself current strength flow regime etc but also sediment concentration deposition rate and grain size distribution there is a notable correlation between unimodal high angle fabric type a and finely skewed grain size distribution the two tsunami deposits studied represent two different scenarios of inundation as demonstrated here x ray tomography is an essential method for characterizing past tsunamis from their deposits the method can be applied to many other types of sediments and sedimentary rocks

the preservation potential of coastal coseismic and tsunami evidence observed following the 2012 mw 7 8 haida gwaii thrust earthquake abstract we describe near field coseismic and tsunami evidence collected following the 28 october 2012 m w 7 8 thrust earthquake that occurred offshore western haida gwaii british columbia and discuss factors that influence its extent and preservation potential observations indicate minor geomorphic and sedimentological impacts on the rugged and unpopulated west coast of the islands despite widespread coastal coseismic subsidence 0 5 m triggered landslides and tsunami waves exceeding 3 m in runup maximum 13 m along 230 km of coastline evidence left by the tsunami was minimal likely because it occurred during a low tide that restricted its onshore reach its flow depth and its capacity to entrain and transport significant amounts of clastic sediment sources of which are minimal or absent on the dominantly steep rocky coastline it is unlikely that subaerial evidence of coseismic subsidence and tsunami inundation will be recognizably recorded in the coastal stratigraphy of western haida gwaii due to the relatively small magnitude of subsidence a lack of suitable coastal environments such as tidal marshes to record paleoelevation differences sedimentation rates that are too low to bury a paleoseismic or paleotsunami record and long term relative sea level fall leading to erosion and bioturbation a higher preservation potential is likely for tsunami deposits in coastal lakes ponds and bogs as well as coseismic slope failure deposits offshore in lakes and in sheltered fjords our findings imply that large tsunamigenic earthquakes are likely undersampled in the paleoseismic record of haida gwaii and of other plate margins with similar characteristics

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

numerical assessment of bathymetric changes caused by the 2004 indian ocean tsunami at kirinda fishery harbor sri lanka abstract thus far various numerical models have been developed and improved to aid understanding of the sediment transport process due to tsunamis however the applicability of these models for the field scale bathymetric change remains a major issue due to the scarcity of measured bathymetric data immediately before and after tsunamis this study focuses on assessing the applicability of the sediment transport model by comparing the model results with measured bathymetry data obtained one month before and two months after the 2004 indian ocean tsunami at kirinda fishery harbor sri lanka obtained model results were compared with measured data along four different transects in particular similar to the measured data the model reproduced the bed level change at the harbor mouth well although it shows some discrepancy on bathymetric change along the shoreline which is directly affected by littoral drift therefore it is noted that the divergence of reproducing the local bathymetry change is due to the normal wind wave effect on measured data and the model limitations hence we included the wind wave effect in modeled data and the discrepancy between measured and modeled data was reduced furthermore the modeled bed level change indicates a dynamic behavior in terms of the net variation during the tsunami flow such that deposition dominates in the inflow and erosion dominates in the backflow both bed level variation and the suspended load concentration reveal that the large amount of eroded sediment attributable to tsunami waves was in suspended form and was deposited in the nearshore area after the water fluctuation had abated the model results further indicate that eroded sediment at the initial depth deeper than 11 m might be brought by the incoming tsunami waves and deposited in the nearshore area where the depth is shallower than 7 m

dual porosity fractured miocene syn rift dolomite reservoir in the issaran field gulf of suez egypt a case history of the zonal isolation of highly fractured water carrier bed

ostracodes reveal the sea bed origin of tsunami deposits 1 in rikuzentakata city ostracode assemblages in sediment deposited by the tohoku oki earthquake and tsunami of 11 march 2011 revealed that the sediment was derived from the seafloor from at least 9 m water depth and was transported inland more than 1 km the tsunami wave height at this location was higher than 10 m four hundred fifty seven modern ostracode assemblages were used in the modern analogue technique to estimate the depth source of the tsunami deposited assemblages the application of this method to paleo tsunami deposits may provide insight into past tsunami wave height and potentially earthquake slip and magnitude

sedimentary and foraminiferal evidence of the 2011 tōhoku oki tsunami on the sendai coastal plain japan abstract the 2011 t hoku oki megathrust earthquake mw 9 0 generated a tsunami that reached the sendai coastal plain with flow heights of 2 to 11 m above tp tokyo peil we examined the tsunami deposit exposed in 14 shallow trenches along a 4 5 km transect perpendicular to the coast we primarily document the stratigraphical sedimentological foraminiferal and geochemical characteristics of the t hoku oki tsunami deposit and perform a preliminary comparison with sediments deposited by the j gan tsunami of a d 869 in the coastal forest and rice fields inundated by the t hoku oki tsunami a poorly sorted dark brown soil is buried by a poorly sorted brown medium grained sand deposit in some trenches located more than 1 2 km inland the sand is capped by a thin muddy sand layer the tsunami deposit although highly variable in thickness is generally thickest 25 cm near the coastal dune and thins to less than 5 mm at 4 5 km inland the tsunami deposit was discriminated from the underlying soil by the appearance of recent and fossil foraminifera and a pronounced increase in grain size that fined upward and landward the recent foraminifera preserved in the sandy facies of the deposit are rare and showed evidence of prolonged subaerial exposure e g pitting corrosion fragmentation recent foraminifera likely originated from coastal dune and beach sediments that were breached by the tsunami calcified and sediment in filled fossil foraminifera are abundant and were eroded from sedimentary units and transported by fluvial or wave activity to sendai bay trends associated with test size e g decreasing concentration of large test sizes with distance inland are in agreement with grain size data at two locations a decrease in total organic carbon and an increase in 13c were found in the tsunami sand compared with the underlying soil supporting a beach to intertidal origin for the upper unit

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

liquefaction as an important source of the a d 2011 tohoku oki tsunami deposits at sendai plain japan this paper describes the topographic change and the recovery process as well as the sediment sources for tsunami deposits based on field surveys and analysis of digital elevation model data before and after the a d 2011 tohoku oki tsunami at the sendai plain japan we found that the amount of sediment deposited on land was approximately four times greater than the eroded volume of sediment at the beach large amounts of the sediments deposited at the studied transect probably originated from liquefaction this result suggests that the vented sediments might have been an important source of the tsunami deposits if liquefaction is generated by the strong ground motion of a near field earthquake in contrast minor erosion was observed at the beach and the beach berm was rebuilt within three months after the tsunami moreover the erosional channel that had cut into the beach had been filled by sand within 13 days after the tsunami therefore it is not expected that a sedimentary record of the tsunami will be preserved in the nearshore zone along the sendai coast although remnants of small scours on land might remain long after the tsunami

heavy minerals in the 2011 tohoku oki tsunami deposits insights into sediment sources and hydrodynamics abstract the 2011 tohoku oki tsunami left sand and mud deposits more than 4 km inland on the coastal plain of sendai japan the tsunami deposits pre tsunami soils and beach sediments were analysed for grain size and heavy mineral content and assemblages to test the applicability of heavy mineral analyses in the identification of tsunami deposits and interpretation of associated sedimentation processes heavy minerals comprised on average 35 of the tsunami deposit in the 0 125 0 25 mm grain size fraction the most common were orthopyroxenes clinopyroxenes amphiboles limonites and opaque minerals heavy mineral concentrations and assemblages were similar in the tsunami deposits beach and pre tsunami soils and sediments and thus tsunami deposits could not simply be identified based on their heavy minerals sediment provenance analysis revealed that tsunami deposits left within 1 5 km of the shoreline were mostly eroded from the beach dune and local soils while deposits farther inland 1 5 km were mostly derived from local soil erosion no evidence was found for a significant contribution of offshore sediments detailed analyses revealed that the lowermost portion of tsunami deposits was mostly of local origin while the sediment source of the upper portion was variable a comparison with a previous study of heavy minerals in 2004 iot deposits confirms that heavy minerals in tsunami deposits are mostly source dependent and may represent a useful supplementary tool in studies of tsunami deposits however the interpretation must always be placed in the local geological context and corroborated with other tsunami proxies

sedimentary features observed in the tsunami deposits at rikuzentakata city abstract the march 11 2011 tohoku oki tsunami triggered by an earthquake off the east coast of northeastern honshu island tohoku region japan deposited large amounts of sediment on land including the sendai plain and sanriku coast this study reports on the characteristics of the tsunami deposits in rikuzentakata city southeastern iwate prefecture northeastern japan a field survey identified the inundation pattern of the tsunami in this region and the facies model of the tsunami deposits at the bay head deltas of estuarine systems the tsunami deposits in rikuzentakata city generally consist of one to four units that represent a discrete runup or backwash flow each unit is characterized by initial inverse grading and successive normal grading that correspond to the accelerating and decelerating stages of the flow respectively an internal erosional surface often developed between the inverse graded and normal graded units it corresponds to the maximum shear velocity of the flow and truncates the underlying inverse graded unit in the case of the runup unit silty fine grained drapes overlay the graded sandy interval a correlation of the sedimentary structures and grain fabric analysis revealed that the tohoku oki tsunami inundated rikuzentakata city at least twice and that the flow velocity exceeded 2 4 m s paleontological analysis of the sediment and kriging estimation of the total volume of the tsunami deposit implied that the sediments were sourced not only from eroded beach sands but also from the seafloor of hirota bay or more offshore regions

local variation of inundation sedimentary characteristics and mineral assemblages of the 2011 tohoku oki tsunami on the misawa coast aomori japan abstract the 2011 tohoku oki tsunami caused severe damage to the coastal regions of eastern japan and left a sediment veneer over affected areas we discuss differences in depositional characteristics of the 2011 tohoku oki tsunami from the viewpoint of the sediment source coastal topography and flow height the study area on the misawa coast northern tohoku includes a 20 km long coastline with sandy beaches coastal dunes and a gently sloping lowland this landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit during field surveys conducted from april 10 to may 2 2011 we described the thickness facies and structure of the tsunami deposit we also collected sand samples at approximately 20 m intervals along 13 shore perpendicular transects extending up to 550 m inland for grain size and mineral assemblage analysis the tsunami flow height was estimated by measuring the elevation of debris found in trees broken tree limbs or water marks on buildings the nature of the coastal lowland affected the flow height and inundation distance in the southern part of the study area where there is a narrow 100 m wide low lying coastal strip the run up height reached 10 m on the landward terrace slopes to the north the maximum inundation reached 550 m with a run up height of 3 2 m on the wider low lying coastal topography the average flow height was 4 5 m the tsunami eroded coastal dunes and formed small scarps along the coast immediately landward of the coastal dunes the tsunami deposit was more than 20 cm thick but thinned markedly inland from this point close to the dunes the deposit was composed largely of medium sand 1 2 with planar and parallel bedding but with no apparent upward fining or coarsening the grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point the mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand at sites more than half the inundation distance inland the thinner tsunami deposit consisted mainly of fine sand 2 375 with some upward fining the difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes we infer that the well sorted finer sediments were deposited out of suspension whereas the relatively coarse sands were laid down from traction flows the depositional characteristics of the 2011 tohoku oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point as opposed to flow height

assessing the magnitude of the 869 jogan tsunami using sedimentary deposits prediction and consequence of the 2011 tohoku oki tsunami article i nfo in this paper the spatial distribution and sedimentological features of the 869 jogan tsunami deposit along the pacific coast of japan are reviewed to evaluate deposit based estimates of the magnitude of the jogan tsunami and the use of tsunami deposits in the prediction of the 2011 tohoku oki earthquake and tsunami inundation of the sendai plain and the offshore wave sources of both tsunamis are compared the jogan tsunami deposit is ubiquitous on the coastal plains of sendai bay whereas to date it is only identified in a few locations along the sanriku and joban coasts this resulted in an underprediction of the size of the wave source of the tohoku oki tsunami the inland boundary of the inundation area of the tohoku oki tsunami on the sendai plain is approximately equivalent to that of the jogan tsunami although many sedimentological and geomorphologic factors make a direct comparison of the tsunamis complicated and difficult the magnitude of the jogan earthquake mw 8 4 which was derived from the tsunami deposit inland extent and numerical inundation modeling was too small to predict the magnitude of the tohoku oki earthquake mw 9 0 9 1 and tsunami additional research is needed to improve deposit based estimates of the magnitudes of past tsunamis and to increase the ability to use tsunami deposits in conjunction with inundation modeling to assess future tsunami hazards

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

flow speed estimated by inverse modeling of sandy sediment deposited by the 29 september 2009 tsunami near satitoa east upolu samoa abstract sandy deposits from the 29 september 2009 tsunami on the east coast of upolu samoa were investigated to document their characteristics and used to apply an inverse sediment transport model to estimate tsunami flow speed sandy deposits 6 to 15 cm thick formed from 25 to 250 m inland sedimentary layers in the deposits that are defined by vertical grain size variation and contacts are interpreted to have formed during onshore runup of two waves deposits at 3 locations 100 170 and 240 m inland contained two layers that are predominately normally graded 80 but contained massive sections 15 and inversely graded sections 5 at their bases about 75 of the total thickness of normally graded intervals exhibits a signature of sediment falling out of suspension at their top this type of grading termed suspension grading here was first recognized in turbidity current deposits and is characterized by the entire distribution shifting finer upwards in a layer as high settling velocity coarser material deposits first and low settling velocity finer material deposits last the jaffe and gelfenbaum 2007 inverse sediment transport model was applied to intervals within layers that exhibited suspension grading to estimate tsunami flow speed and was able to reproduce the general trends of the observed suspension grading a key unknown input in the modeling is the bottom roughness for a bottom roughness parameterization using a manning s n of 0 03 equivalent to a z0 0 006 m for the observed flow depths of 2 3 m flow speeds calculated for the 2 layers at the 3 locations were 3 8 3 6 and 3 7 m s bottom layer earlier wave and 4 4 4 4 and 4 1 m s top layer later wave at 100 170 and 240 m inland respectively these estimates are consistent with the 3 8 m s tsunami flow speed from boulder transport calculations and result in froude numbers of 0 7 1 0 when maximum measured flow depths are used because the inverse model assumes the deposit was formed by sediment falling out of suspension care must be taken to model only intervals of the deposit exhibiting suspension grading including intervals deposited by either bedload or suspended load transport convergences result in higher and sometimes unrealistic tsunami flow speed estimates

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

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

sources and transportation modes of the 2011 tohoku oki tsunami deposits on the central east japan coast abstract we evaluated sediment sources of the 2011 tohoku oki tsunami deposits along a 4500 m inland transect from the central east japan coast using grain size mineralogy and foraminifera analyses the tsunami run up height in our study area was 13 to 20 m near the coastline 1 4 to 2 8 m in the middle of the valley and 1 3 m around the inundation limit the inundation distance was around 4800 m the deposits are composed of sand and mud and show a fining and thinning trend mineral composition of the tsunami deposits was similar to that of coastal dune and beach deposits indicating that most of the tsunami sediment originated from there a minor foraminifera population in the deposit 15 specimens per 5 g of sample compared with 100 specimens per 1 g for typical marine sediment indicates that marine sediment source was not dominant topography played an important role in sediment transport process and deposit distribution the run up wave accelerated faster in concave topography became more erosive and resulted in a thin deposit in topographic lows we infer that the deposits up to 2300 m from the coastline were deposited by bedload and suspension whereas suspension was responsible for deposits farther inland

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

onshore tsunami deposits caused by the 1993 southwest hokkaido and 1983 japan sea earthquakes onshore tsunami deposits resulting from the 1993 southwest hokkaido and 1983 japan sea earthquakes were described to evaluate the feasibility of tsunami deposits for inferring paleoseismic events along submarine faults tsunami deposits were divided into three types based on their composition and aerial distribution a deposits consisting only of floating materials b locally distributed siliclastic deposits and c widespread siliclastic deposits the most widely distributed tsunami deposits consist of the first two types type c deposits are mostly limited to areas where the higher tsunami runup was observed the scale of tsunami represented by vertical tsunami runup is an important factor controlling the volume of tsunami deposits the thickest deposits about 10 cm occur behind coastal dunes to produce thick siliclastic tsunami deposits a suitable source area such as sand bar or dune must be available in addition to sufficient vertical tsunami runup estimation of the amounts of erosion and deposition indicates that tsunami deposits were derived from both onshore and shoreface regions the composition and grain size of the tsunami deposits strongly reflect the nature of the sedimentary materials of their source area sedimentary structures of the tsunami deposits suggest both low and high flow regimes consequently it seems very difficult to identify tsunami deposits based only on grain size distribution or sedimentary structure of a single site in ancient successions

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

numerical modeling of the 2011 tohoku oki tsunami in the offshore and onshore of sendai plain japan abstract this paper examines the results of a numerical modeling of the 2011 tohoku oki earthquake tsunami to investigate its offshore propagation and inundation along a shore normal transect located in the center of the sendai plain the inundation distance flow depth and flow speed were compared with the available data measured during a post tsunami field survey and estimated from the video records the calculated inundation distance reached 4 5 5 5 km from the coastline which is comparable to the actual inundation distance the variation of tsunami heights from 2 4 6 m and flow speeds from 3 4 6 2 m s along the transect is generally consistent with the measured heights and estimated speeds the waveform on the beach showed that the wave train was composed of a high 10 11 m first wave followed by low 4 m waves considering the waveform and the topographic change the erosion of the beach and the sedimentation inland are explained mainly by the first wave in addition the calculated flow speed and friction velocities in the offshore may account for the formation of the possible tsunami deposits which were reported recently by a sea bottom survey the modeling results are generally consistent with the available data and are considered to be useful for understanding the inundation pattern and sedimentation process of the tohoku oki tsunami on the sendai plain

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

long term perspectives on giant earthquakes and tsunamis at subduction histories of earthquakes and tsunamis inferred from geological evidence aid in anticipating future catastrophes this natural warning system now influences building codes and tsunami planning in the united states canada and japan particularly where geology demonstrates the past occurrence of earthquakes and tsunamis larger than those known from written and instrumental records under favorable circumstances paleoseismology can thus provide long term advisories of unusually large tsunamis the extraordinary indian ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks such variation in rupture mode known from written history at a few subduction zones is also characteristic of earthquake histories inferred from geology on the pacific rim

coastal changes in the sendai area from the impact of the 2011 tōhoku oki tsunami interpretations of time series satellite images helicopter borne video footage and field observations a combination of time series satellite imagery helicopter borne video footage and field observation is used to identify the impact of a major tsunami on a low lying coastal zone located in eastern japan a comparison is made between the coast protected by armoured engineered sea walls and the coast without changes are mapped from before and after imagery and sedimentary processes identified from the video footage the results are validated by field observations the impact along a natural coast with minimal defences is erosion focussed on the back beach along coasts with hard engineered protection constructed to defend against erosion the presence of three to six metre high concrete faced embankments results in severe erosion on their landward faces the erosion is due to the tsunami wave accelerating through a hydraulic jump as it passes over the embankment resulting in the formation of a ditch into which the foundations collapse engineered coastal defences are thus found to be small defence against highly energetic tsunami waves that overtop them there is little erosion or sedimentation of the whole beach and where active it mainly forms v shaped channels these channels are probably initiated during tsunami inflow and then further developed during tsunami backflow tsunami backflow on such a low lying area takes place energetically as sheet flow immediately after tsunami flooding has ceased subsequently when the water level landward of the coastal dune ridges falls below their elevation flow becomes confined to rivers and breaches in the coast formed during tsunami inflow enigmatic short lived strand lines are attributed to the slow fall of sea level after such a major tsunami immediately after the tsunami coastal reconstruction begins sourced from the sediment recently flushed into the sea by tsunami backflow

tsunami earthquake can occur elsewhere along the japan trench historical and geological evidence for the 1677 earthquake and tsunami since the 11 march 2011 tohoku earthquake the mechanisms of large earthquakes along the japan trench have been intensely investigated however characteristics of tsunami earthquakes which trigger unusually large tsunami remain unknown the earthquake of 4 november 1677 was a tsunami earthquake striking the southern part of the japan trench its source mechanism remains unclear this study elucidates the fault slip and moment magnitude of the 1677 earthquake and tsunami based on integrated analyses of historical documents tsunami deposits and numerical simulation geological survey results the analytical results of thickness and grain size distributions and diatoms revealed that tsunami deposits in a small pond at 11 m elevation were probably formed by the 1677 event this finding and historical descriptions are useful as important constraint conditions to estimate unusually large fault slips and moment magnitude of the 1677 earthquake numerical simulation results reveal that 8 34 8 63 moment magnitude with the large 11 16 m slip area is necessary to satisfy the constraint conditions this fault slip and magnitude are equivalent to those of the 1896 sanriku earthquake a well known tsunami earthquake in the northern part of the japan trench we therefore conclude that a tsunami earthquake of moment magnitude 8 3 8 6 with unusually large slip can occur elsewhere along the japan trench this point should be considered for future tsunami risk assessment along the japan trench and along any trench having similar tectonic settings to those of the japan trench

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

sedimentological and geophysical properties of a ca 4000 year old tsunami deposit in southern spain abstract the coastlines around the gulf of cadiz were affected by numerous tsunami events damaging infrastructure and causing countless human losses a tsunami deposit at barbate zahara de los atunes spain is located at various heights above mean sea level and shows several characteristics indicative of high energy event deposition this study uses sedimentology foraminifera assemblage magnetic susceptibility x ray fluorescence analysis ground penetrating radar gpr to support an interpretation of high energy deposition and determine the deposit s transport mechanisms and sediment source radiocarbon and optically stimulated luminescence dating of the tsunami deposit reveals ages of 4000 bp and does not support the ad 1755 lisbon event as suggested in former publications

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

sedimentary processes associated with sand and boulder deposits formed by the 2011 tohoku oki tsunami at sabusawa island japan abstract this paper reports on the sedimentary processes of sand and boulder deposition at sabusawa island japan as a result of the 2011 tohoku oki tsunami boulders were composed of tuffaceous rocks and sourced from an earthquake triggered slope failure as well as concrete fragments of seawall they were scattered over the ground surface and did not form boulder ridges although there was some local imbrication the boulders were deposited on top of a sand layer indicating that the latter possibly deposited from bed load covered the ground surface first this sand layer probably reduced friction allowing boulders to be transported more easily than might be expected across a hard ground with a high bottom friction sand deposits showed landward thinning and fining features while the boulders showed a landward coarsening tuffaceous boulders or a landward fining concrete boulders indicating that large clasts were not necessarily scattered randomly but rather might have a clast size gradient with distance inland these features are explained by the local topographic setting that constrained the directions of incoming and returning tsunami flows some clasts at the inland extent of the boulder field were covered by an upward fining sand layer this feature suggests that the boulders were deposited prior to the suspended sands with the latter subsequently laid down before the water level dropped below the top of the boulders such modern investigations of the sedimentary features of various sizes of grains and clasts immediately after a tsunami provide invaluable data for the reconstruction of inundation processes

effects of tsunami magnitude and terrestrial topography on sedimentary processes and distribution of tsunami deposits in flume experiments abstract to identify and interpret tsunami deposits correctly a better understanding of the effects of both tsunami magnitude and topographic setting are required in the present study laboratory experiments were performed to model these effects on sedimentary processes and the distribution of tsunami deposits on coastal lowlands the experiments directed tsunamis of eight different magnitudes on to three different models of terrestrial topography one with flat topography one with a shallow water filled pool and one with a deep water filled pool the results suggested a relationship between the distribution of tsunami deposits and the hydraulic condition of the tsunami flow onto the terrestrial topography in particular the tsunami deposits in the pools were spatially more variable than those on land because of the variation in flow intensity associated with transformation of the flow from supercritical to subcritical with a hydraulic jump we observed a gap between the landward extent of deposits and the tsunami inundation distance particularly in the experiments with a pool the total amount of sediment in tsunami deposits on the terrestrial area was found to depend on the magnitude of the tsunami but the thickness of the deposits at any one given spot did not always depend on the tsunami magnitude even in the same topographic these results show that terrestrial topography has significant effects on the spatial distribution of tsunami deposits that must be taken into consideration when interpreting the history and magnitude of paleotsunami events from tsunami deposits

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