importance of small earthquakes for stress transfers and earthquake triggering 1 we estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension d this model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as similar to 10 dm 2 the stronger the spatial clustering the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering if earthquake magnitudes follow the gutenberg richter law with b d 2 small earthquakes collectively dominate stress transfer and earthquake triggering because their greater frequency overcomes their smaller individual triggering potential using a southern california catalog we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 alpha m where alpha 1 05 0 05 we also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake s magnitude m when alpha approximate to b small earthquakes are roughly as important to earthquake triggering as larger ones we evaluate the fractal correlation dimension d of hypocenters using two relocated catalogs for southern california the value of d measured for distances 0 1 r 5 km is d 1 54 for the shearer et al catalog and d 1 73 for the hauksson et al catalog the value of d reflects both the structure of the fault network and the nature of earthquake interactions by considering only those earthquake pairs with interevent times larger than 1000 days we can largely remove the effects of short term clustering then d approximate to 2 close to the value d 2 alpha 2 1 predicted by assuming that earthquake triggering is due to static stress the value d approximate to 2b implies that small earthquakes are as important as larger ones for stress transfers between earthquakes and that considering stress changes induced by small earthquakes should improve models of earthquake interactions

significance of coarse clasts in viscous debris flows abstract debris flows are flowing mixture of water and sediments from clay to boulder sized particles the sediments control both occurrence and characteristics of debris flows however the relevant literature has concentrated mainly on fine debris considering their large fractions in debris flows the significance of coarse clasts 0 005 mm is investigated by comparing the crude debris cd the fractions of aggregation of data collected in 39 tested debris water mixtures leads us to conclude that the coarse clasts can greatly affect the slurrying susceptibility of debris masses and bulk behavior of slurries the debris flow indices id from the cd to rd slurries with maximum grain sizes of 10 and 5 mm decrease by 29 and 17 respectively the cd slurries possess higher yield strength and viscosity than their rd counterparts with the same solid volumetric concentrations cvs the areas inundated by 10 cd slurries with maximum grain sizes of 10 and 5 mm are approximately 17 39 of those of their rd counterparts the excess pore pressures in the rd slurries dissipate more quickly than those in the cd slurries the shape and surface texture of coarse clasts regulate slurrying of debris masses as well as influence their liquefaction potential which in turn has an impact on the mobility and persistence of subsequent slurries the platy flaky debris producing mountain catchments generally experience lower magnitude higher frequency lower cv debris flows of relatively less destructive power and the debris flows dominated by equidimensional clasts are often more powerful and hazardous despite their potentially lower frequency

a common origin for aftershocks foreshocks and multiplets we demonstrate that the statistics of earthquake data in the global cen troid moment tensor cmt and national earthquake information center neic catalogs and local california council of the national seismic system cnss catalog are consistent with the idea that a single physical triggering mechanism is responsible for the occurrence of aftershocks foreshocks and multiplets specifically we test the hypothesis that tectonic earthquakes usually show clustering only as a result of an initial earthquake triggering subsequent ones and that the magnitude of each trig gered earthquake is entirely independent of the magnitude of the triggering earth quake therefore a certain percentage of the time as determined by the gutenberg richter magnitude frequency relationship an earthquake should by chance be larger than or comparable in size to the earthquake that triggered it this hypothesis predicts that the number of times foreshocks or multiplets are observed should be a fixed fraction of the number of aftershock observations we find that this is indeed the case in the global cmt and neic catalogs the average ratios between foreshock aftershock and multiplet rates are consistent with what would be predicted by the gutenberg richter relationship with b 1 we give special attention to the solomon islands where it has been claimed that unique fault structures lead to unusually high numbers of multiplets we use monte carlo trials to demonstrate that the solomon islands multiplets may be explained simply by a high regional aftershock rate and earthquake density we also verify our foreshock results from the more complete recordings of small earthquakes available in the california catalog and find that foreshock rates for a wide range of foreshock and mainshock magnitudes can be projected from aftershock rates using the gutenberg richter relationship with b 1 and the relationship that the number of earthquakes triggered varies with triggering earthquake magnitude m as c10m where c is a productivity constant and is equal to 1 finally we test an alternative model that proposes that foreshocks do not trigger their mainshocks but are instead triggered by the mainshock nucleation phase in this model the nucleation phase varies with mainshock magnitude so we would expect mainshock magnitude to be correlated with the magnitude number or spatial extent of the foreshocks we find no evidence for any of these correlations

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

a case study of two m 5 mainshocks in anza california is the footprint of an aftershock sequence larger than we think it has been traditionally held that aftershocks occur within one to two fault lengths of the mainshock here we demonstrate that this perception has been shaped by the sensitivity of seismic networks the 31 october 2001 mw 5 0 and 12 june 2005 mw 5 2 anza mainshocks in southern california occurred in the middle of the densely instrumented anza seismic network and thus were unusually well recorded for the june 2005 event aftershocks as small as m 0 0 could be observed stretching for at least 50 km along the san jacinto fault even though the mainshock fault was only 4 5 km long it was hypothesized that an observed aseismic slipping patch produced a spatially extended aftershock triggering source presumably slowing the decay of aftershock density with distance and leading to a broader aftershock zone we find however the decay of aftershock density with distance for both anza se quences to be similar to that observed elsewhere in california this indicates there is no need for an additional triggering mechanism and suggests that given widespread dense instrumentation aftershock sequences would routinely have footprints much larger than currently expected despite the large 2005 aftershock zone we find that the probability that the 2005 anza mainshock triggered the m 4 9 yucaipa mainshock which occurred 4 2 days later and 72 km away to be only 14 1 this probability is a strong function of the time delay had the earthquakes been separated by only an hour the probability of triggering would have been 89 online material movies exploring the spatial extent of aftershocks from the 2001 and 2005 anza sequences

secondary aftershocks and their importance for aftershock forecasting the potential locations of aftershocks which can be large and damaging are often forecast by calculating where the mainshock increased stress we find however that the mainshock induced stress field is often rapidly altered by aftershock induced stresses we find that the percentage of aftershocks that are secondary aftershocks or aftershocks triggered by previous aftershocks increases with time after the mainshock if we only consider aftershock sequences in which all aftershocks are smaller than the mainshock the percentage of aftershocks that are secondary also increases with mainshock magnitude using the california earthquake catalog and monte carlo trials we estimate that on average more than 50 of aftershocks produced 8 or more days after m 5 mainshocks and more than 50 of all aftershocks produced by m 7 mainshocks that have aftershock sequences lasting at least 15 days are triggered by previous aftershocks these results suggest that previous aftershock times and locations may be important predictors for new aftershocks we find that for four large aftershock sequences in california an updated forecast method using previous aftershock data and neglecting mainshock induced stress changes can outperform forecasts made by calculating the static coulomb stress change induced solely by the mainshock manuscript received 20 november 2002

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

enigmatic fossils from the upper silurian of bolivia evidence for marine productivity in high latitude gondwana specimens collected recently from the las carmelitas facies of the kirusillas formation exposed in the cochabamba area bolivia and dated as ludlow late silurian by graptolites show bedding surfaces almost completely covered by coalified compressions and impressions the majority comprise mixtures of fragmented amorphous unidentifiable material debris but some horizons are dominated by well defined morphological entities with a particular type or combination of types confined to a particular layer in all five morphotypes have been circumscribed but their affinities based on a comprehensive review of the possibilities remain conjectural algal affinities are suggested tentatively for abundant unbranched narrow strap shaped fossils lacking any further diagnostic features and the numerous coalified discs or three dimensionally preserved spheres leiosphaerid acritarchs occurring isolated in the matrix or less often in clusters following a discussion on the recognition of faecal pellets in the fossil record it is postulated that elliptical spiral or simply segmented structures may be the excreta of planktonic or benthic metazoans although the latter seems less likely in view of the proposed anoxic depositional environment of the shales that lack any bioturbation such coalified remains whether from primary producers or grazers indicate high productivity at high palaeolatitudes in the late silurian continental seas in this region of peri gondwana

the influence of organic matter addition by caulescent andean rosettes on surficial soil properties abstract this report examines the effects of addition of organic matter to soils below caulescent andean rosettes in the paramo de piedras blancas venezuelan andes at 4260 4300 m altitude two plant species coespeletia timotensis forma lutescens and espeletia semiglobulata were investigated in an area occupied by a series of small hills the soils here were lithic and typic cryochrepts developed on pegmatitic granite and mica schist paired surface soil samples were obtained beneath plant canopies and in bare areas outside of these 106 samples were gathered organic matter content was 36 to 52 higher under rosettes than in adjacent bare areas soils below plants were also finer but these differences were not as pronounced due to the variation in organic matter physical and chemical soil properties differed sharply between rosette and control areas soils were darker below plants bulk density decreased and porosity and water content at field capacity increased under rosettes cation exchange capacity total n content and exchangeable bases ca mg k and p levels were considerably higher beneath rosettes there soil acidity decreased and percentage base saturation and c n ratios increased simple and multiple regressions indicated that soil properties were closely dependent on organic matter content the percentage of fines 0 05 mm was also correlated with physical soil properties and cation exchange capacity but its effect on property variance was considerably less pronounced than that of organic matter the results indicate that pedogenesis in this harsh periglacial paramo is significantly affected by the addition of plant litter thus andean rosettes appear to exert considerable influence on the evolution of the coarse high altitude soils

a new estimation of the decay of aftershock density with distance to the mainshock we investigate how aftershocks are spatially distributed relative to the mainshock compared to previous studies ours focuses on earthquakes causally related to the mainshock rather than on aftershocks of previous aftershocks we show that this distinction can be made objectively but becomes uncertain at long time scales and large distances analyzing a regional earthquake data set it is found that at time t following a mainshock of magnitude m the probability of finding an aftershock at distance r relative to the mainshock fault decays as r where is typically between 1 7 and 2 1 for 3 m 6 and is independent of m for r less than 10 to 20 km and t less than 1 day uncertainties on this probability at larger r and t do not allow for a correct estimation of this spatial decay we further show that a static stress model coupled with a rate and state friction model predicts a similar decay with an exponent 2 2 in the same space and time intervals this suggests that static stress changes could explain the repartition of aftershocks around the mainshock even at distances larger than 10 times the rupture length

comment on a model of earthquake triggering probabilities and application to dynamic deformations constrained by ground motion observations by joan gomberg and karen felzer

predictive models to estimate sediment volumes deposited by debris flows vargas state venezuela an adjustment of multivariate statistical techniques debris flows are a moving mass composed from water and solids mixture mainly in form of sediments with a high destructive power the debris volume that is transported and deposited outside the drainage system of a watershed has a great importance in the definition of its hydrological response the objective of this work was to propose predictive models generated through the adjustment of multivariate statistical techniques to estimate the sediment volumes deposited by debris flows measurements and calculations of the morphometric parameters of the watersheds and drainage networks have been performed with the support of gis software and spreadsheets the relationships between morphometric parameters and sediment volumes have been analyzed by applying multivariate statistical techniques such as linear correlation analysis the principal component analysis and multiple linear regression analysis have been performed with principal components which allowed the generation of predictive models from the predictive models generated for the sediment volumes deposited by the debris flow event of december 1999 raised results closer to reality with better pearson s correlation coefficients from those related to the gradient and shape of the watershed relief and extension of the drainage network morphometric variables for the estimation of deposited sediment volumes due pre and post 1999 event conditions only the predictive models generated with the gradient and shape of the watershed relief variable have had good results

bed scour by debris flows experimental investigation of effects of debris flow composition debris flows can grow greatly in size by entrainment of bed material enhancing their runout and hazardous impact here we experimentally investigate the effects of debris flow composition on the amount and spatial patterns of bed scour and erosion downstream of a fixed to erodible bed transition the experimental debris flows were observed to entrain bed particles both grain by grain and en masse and the majority of entrainment was observed to occur during passage of the flow front the spatial bed scour patterns are highly variable but large scale patterns are largely similar over 22 5 35 channel slopes for debris flows of similar composition scour depth is generally largest slightly downstream of the fixed to erodible bed transition except for clay rich debris flows which cause a relatively uniform scour pattern the spatial variability in the scour depth decreases with increasing water gravel grain size and clay fraction basal scour depth increases with channel slope flow velocity flow depth discharge and shear stress in our experiments whereas there is no correlation with grain collisional stress the strongest correlation is between basal scour and shear stress and discharge there are substantial differences in the scour caused by different types of debris flows in general mean and maximum scour depths become larger with increasing water fraction and grain size and decrease with increasing clay content however the erodibility of coarse grained experimental debris flows gravel fraction 0 64 is similar on a wide range of channel slopes flow depths flow velocities discharges and shear stresses this probably relates to the relatively large influence of grain collisional stress to the total bed stress in these flows 30 50 the relative effect of grain collisional stress is low in the other experimental debris flows 5 causing erosion to be largely controlled by basal shear stress

the processes and mechanism of failure and debris flow initiation for gravel soil with different clay content clay content can influence gravel soil mass failure and debris flow initiation significantly but quantification of the clay content influence in the published literature is lacking this paper describes the experiments carried out to explore soil mass failure and debris flow initiation with different clay contents the whole process of gravel soil mass failure and debris flow initiation can be grouped into five phases i infiltration excess runoff ii fracture extending iii initial slip iv large scale slip v debris flow triggering in the experiments when the clay content of soil mass is lower than 2 5 no soil failure and debris flow are triggered only the soil masses with moderate clay contents 5 10 show the clear processes of the five phases that need the shortest rainfall duration among different clay contents soil masses with high clay content 10 and low clay content 2 5 5 need longer rainfall duration to cover the five phases for partially triggering soil failure and debris flows clay content is closely linked with the soil failure and debris flow initiation under rainfall the key mechanism can be grouped into two reasons i the clay particles absorb the moisture and dilate to fill the soil pores and the content of the clay has a direct link with the filled pores ii the gravel soil masses with different clay content differ in their structure for the low clay content soil mass group 2 5 5 the coarse grains of the gravel soil form large pores and saturated clay particles are too few to block most soil pores as a result pore water pressure of soil mass is released easily in the raining process therefore inner friction holds strong and soil mass is hard to mobilize into slip and debris flows on the other hand for soil masses with high 10 clay contents soil failure and debris flow are triggered under the aid of surface runoff flux to reduce the cohesion of the soil whereas only for the soil masses with moderate clay contents 5 10 large scale soil failure and debris flow can be triggered within the shortest duration in this case the debris flow is of the form of soil mechanics which is triggered after soil masses slip and liquefaction the others are of the form of hydraulic mechanics the experiments provide valuable evidence for quantifying clay content impact on gravel soil failure and debris flow initiation because they were carried out in a flume the research results are applicable to the soil failure and debris flow initiation in bedrock gully situations

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

matrix granulometry of catastrophic debris flows december 1999 in central coastal venezuela abstract after 2 days of intense precipitation devastating flooding and debris flows affected the central coast of venezuela on december 15 16 1999 these events killed nearly 30 000 people and destroyed or damaged 126 000 homes i visited the disaster area in march 2000 coastal valleys affected by debris flows were extensively covered by an interstitial matrix that included large amounts of often impressive boulders up to 35 40 tons in weight granulometric analyses of four matrix samples from the naiguata valley showed they were all similarly coarse their main constituent was sand and grains data suggest the following events must have taken place in coastal venezuela torrential rains quickly caused flooding along creeks and rivers which must have rapidly attained hyperconcentrated streamflow bulking of stream alluvium in flood surges may also have taken place however the storm triggered widespread landsliding along the steep unstable flanks of the coastal cordillera many slides started in upper basin areas underlain by gneiss bedrock pena de mora such slides released vast amounts of coarse sandy debris which mixed with turbulent floodwaters to produce numerous granular noncohesive debris flows these flows despite their coarse matrix exhibited intense particle collisions and interactions thus were able to effectively mobilize vast masses of large boulders

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

experimental study of bedrock erosion by granular flows 1 field studies suggest that bedrock incision by granular flows may be the primary process cutting valleys in steep unglaciated landscapes an expression has been proposed for debris flow incision into bedrock which posits that erosion rate depends on stresses due to granular interactions at the snout of debris flows here we explore this idea by conducting laboratory experiments to test the hypothesis that bedrock erosion is related to grain collisional stresses which scale with shear rate and particle size we placed granular material in a 56 cm diameter rotating drum to explore the relationship between erosion of a synthetic bedrock sample and variables such as grain size shear rate water content and bed strength grain collisional stresses are estimated as the inertial stress using the product of the squares of particle size and vertical shear rate our uniform granular material consisted of 1 mm sand and quartzite river gravel with means of 4 6 or 10 mm in 67 experimental runs the eroded depth of the bed sample varied with inertial stresses in the granular flow to a power less than 1 0 and inversely with the bed strength the flows tended to slip on smooth boundaries resulting in higher erosion rates than no slip cases we found that lateral wall resistance generated shear across the channel producing two cells whose widths depended on wall roughness while the hypothesized inertial stress dependency is supported with these data wear mechanics needs to account for grain dynamics specifically at the snout and possibly to include lateral shear effects

fossil and recent debris flows in medium high mountains moravskoslezske beskydy mts czech republic abstract the significance of debris flows for the morphogenesis of the medium high mountains of central europe has long been neglected herein we provide evidence from the moravskoslezske beskydy mountains flysch western carpathians czech republic where fossil pleistocene debris flow events in spite of their low recent activity were important erosion and accumulation agents in shaping the mountainous terrain geomorphological and sedimentological analyses helped to differentiate between two classes of debris flow deposits deposits of the 1st class are relatively voluminous contemporary terraced landforms which originated in the pleistocene transport limited conditions recent activity of debris flows presented by the 2nd class accumulations is characterized by the presence of low magnitude events mostly originated during the reworking of older diamictons the inheritance of large volumes of old debris flow diamictons in steep mountainous terrain is the evidence of slow erosional transformation of the last glacial landforms pointing to the fact that recent topography of the mountains is not in full equilibrium with contemporary climatic and environmental conditions

neoproterozoic tsunamiite upper bhander sandstone central india abstract this paper addresses a distinctive event bedset encased by coastal erg margin deposits at a preferred stratigraphic level near the base of the neoproterozoic upper bhander sandstone in central india the bedset is composed of couplets of sandstone beds that exhibit incisive amalgamation although they differ in geometry structures at soles within and at tops of beds vertical grain size variation as well as palaeocurrent pattern and direction the wide extent of the bedset is evident from several exposures spread over a distance of more than 50 km roughly in strike parallel direction flow and depositional dynamics interpreted from the coupled event beds are more consistent with a tsunami origin than alternative palaeogeography compatible models of climate induced storm flash flood or accentuated tide deposits a palaeotsunamiite model is thus discussed with separate incoming and outgoing components considering the overall depositional setting to be an epeiric sea coast in an intracratonic sag basin the relevant bedset is inferred to reflect the record of a teletsunamiite it would also be one of the very few precambrian tsunamiites known so far exceptional preservation of this possible tsunamiite was facilitated by sheltered deposition behind the backshore zone and the berm as well as by rapid burial by wind deflated sands and advancing aeolian dunes