precessional forcing of lacustrine sedimentation in the late cenozoic chemeron basin central kenya rift and calibration of the gauss matuyama boundary the fluviolacustrine sedimentary sequence of the chemeron formation exposed in the barsemoi river drainage tugen hills kenya contains a package of five successive diatomite fluvial cycles that record the periodic development of freshwater lakes within the axial portion of the central kenya rift the overwhelming abundance in the diatomite of planktonic species of the genera aulacoseira and stephanodiscus and the virtual absence of benthic littoral diatoms and detrital material indicate areally extensive deep lake systems a paleomagnetic reversal stratigraphy has been determined and chronostratigraphic tie points established by 40 ar 39 ar dating of intercalated tuffs the sequence spans the interval 3 1 2 35 ma and bears a detailed record of the gauss matuyama paleomagnetic transition the 40 ar 39 ar age for this boundary of 2 589 0 003 ma can be adjusted to concordance with the astronomical polarity time scale apts on the basis of an independent calibration to 2 610 ma 29 kyr older than the previous apts age the diatomites recur at an orbital precessional interval of 23 kyr and are centered on a 400 kyr eccentricity maximum it is concluded that these diatomite fluvial cycles reflect a narrow interval of orbitally forced wet dry climatic conditions that may be expressed regionally across east africa the timing of the lacustrine pulses relative to predicted insolation models favors origination of moisture from the northern africa monsoon rather than local circulation driven by direct equatorial insolation this moisture event at 2 7 2 55 ma and later east african episodes at 1 9 1 7 and 1 1 0 9 ma are approximately coincident with major global climatic and oceanographic events

bone diagenesis and origin of calcium phosphate nodules from a hominid site in the lukeino formation tugen hills kenya the lukeino formation 6 09 5 68 ma kenya is a fossiliferous fluvio lacustrine sedimentary sequence 100 m thick which yielded the fossil remains of the oldest east african bipedal hominid called orrorin tugenensis at one of the hominid sites aragai centimetric to pluri centimetric indurated calcium phosphate nodules occur in a specific sedimentary layer mineralogical and geochemical analyses coupled with sem optical microscopy and cathodoluminescence observations were performed on four calcium phosphate nodules and one bone showing differential alteration with characteristics locally similar to that of the nodules in order to determine the nature and origin of these nodules a crystallinity index ci and histological index hi were also assigned to these samples to characterize their degree of transformation analyses reveal that all nodules and the studied bone have a similar mineralogical and chemical composition nodules show no internal structure and are composed of a carbonate fluorapatite matrix including feldspars clays and spheres of iron and manganese oxides their high ci indicates significant recrystallization compared to modern bone the altered bone shows infilling of the trabecular cavities characterized by a clay deposit along the walls oxide spheres with a silica center and carbonate fluorapatite baguettes in the highly altered area of the bone a phenomenon of dissolution and dismantlement of bone structures adjacent to an area characterized by the presence of a phosphate matrix is observed the genesis of these calcium phosphate nodules seems to result from an advanced stage of transformation of bones due to a combination of physical chemical and biological bacterial processes the different stages of diagenesis are characterized by the incorporation of components from the sedimentary layer including diatoms and by neoformations of clays and oxides in the bone pores the bone structure is affected by fracturing and dissolution of carbonate hydroxylapatite which reprecipitated in bone cavities under the form of carbonate fluorapatite automorphic crystals then the bone structures and mineral neoformations were affected by a dismantlement phenomenon which increased the dissolution of the bone apatite this resulted in a carbonate fluorapatite matrix in which no trace of the initial bone structure is visible this particular mechanism of genesis of calcium phosphate nodules most probably takes place by action of fluid circulation in a confined environment such as a lake edge or marsh

noble gas and carbon isotopic evidence for co2 driven silicate dissolution in a recent natural co2 field secure storage of anthropogenic carbon dioxide co2 in geological reservoirs requires predicting gas water rock interactions over millennial timescales noble gases and carbon isotope measurements can be used to shed light on the nature of competing dissolution precipitation processes over different timescales from the fast dissolution of gaseous co2 in groundwater to more sluggish reactions involving dissolution and precipitation of newly formed minerals in the reservoir here we study a compilation of gas analyses including noble gases and 13c of co2 from nine different natural co2 reservoirs amongst these reservoirs the bravo dome co2 field new mexico usa shows distinct geochemical trends which are explained by degassing of noble gases from groundwater altering the composition of the gas phase this groundwater degassing is synchronous with the dissolution of co2 in groundwater progressive creation of alkalinity via co2 promoted mineral dissolution is required to explain the observed positive correlation between co2 3he and 13c of the gas phase a unique feature of bravo dome the differences between bravo dome and other natural co2 reservoirs are likely explained by the more recent filling of bravo dome reflecting co2 water rock interactions over thousands of years rather than over millions of years in older reservoirs

ground motion characteristics and nonlinear soil response observed by donet1 seafloor observation network during the 2016 southeast off mie japan earthquakeground motion characteristics and nonlinear soil response observed by donet1

scattering of teleseismic p waves by the japan trench a significant effect of reverberation in the seawater column abstract we detected a scattered wave train in data from the high sensitivity seismograph network in japan hi net following the arrival of the near vertically incident p wave generated by the 2009 earthquake mw 7 8 off the south island of new zealand the scattered wave train represented predominantly vertical ground motion at a period of 20 to 50 s and with an apparent velocity of 3 5 km s it propagated cylindrically westward through the kanto area of central japan array analysis showed that the scattered wave train developed beneath the pacific ocean near the boso triple junction southeast of the kanto area a 3d finite difference simulation of seismic wave propagation using a high resolution model incorporating subsurface structure topography and bathymetry revealed that the strong scattered waves that were generated along the japan trench and propagated normal to the trench axis represented multiple reverberations of seismic waves between the seafloor and the pacific plate boundary in addition strong reverberation of acoustic waves in the seawater column above the boso triple junction causes elongated scattered waves which reasonably explains our observations

on the duration of seismic motion incident onto the valley of mexico for subduction zone earthquakes summary we have used finite difference simulations in 2 d models of the lithosphere to estimate the duration of long period 2 s ground motion incident onto the valley of mexico for subduction zone earthquakes our simulations suggest that two heterogeneous structures extend the duration of the ground motion between the subduction zone and mexico city by more than 1 min 1 the mexican volcanic belt and 2 two low velocity layers in the coastal region the accretionary prism and the water layer the duration generated by a crustal model including these structures is similar to that for earthquake records observed in between the coast and mexico city in the valley of mexico our models including only regional scale heterogeneity reproduce approximately one half of the observed duration the results suggest that both the regional and the local scale low velocity structures must be taken into account in order to explain the observed extended signal duration in the valley of mexico

constraining shallow slip and tsunami excitation in megathrust ruptures using seismic and ocean acoustic waves recorded on ocean bottom sensor networks abstract great earthquakes along subduction zone plate boundaries like the 2011 magnitude 9 0 tohoku oki japan event deform the seafloor to generate massive tsunamis tsunami wave heights near shore are greatest when excitation occurs far offshore near the trench where water depths are greatest and fault slip is shallow the tohoku event featuring over 30 m of slip near the trench exemplifies this hazard unfortunately the rupture process that far offshore is poorly constrained with land based geodetic and even most seafloor deformation measurements and seismic inferences of shallow slip are often nonunique here we demonstrate through dynamic rupture simulations of the tohoku event that long period guided waves in the ocean specifically leaking oceanic p wave modes known as pl waves can resolve the shallow rupture process and tsunami excitation near the trench with predicted pressure changes of 0 1 1 mpa along most of the seafloor landward of the trench and periods of several seconds these pl waves should be observable with ocean bottom pressure sensors and or seismometers with cabled sensor networks like those being deployed offshore japan and in other subduction zones these waves could be used to rapidly quantify shallow slip and near trench seafloor uplift and improve local tsunami early warning systems

fdm simulation of seismic wave propagation for an aftershock of the 2009 suruga bay earthquake effects of ocean bottom topography and seawater layer abstract feasibility studies on simulating seismic wave propagation in media for a suboceanic earthquake including both land and ocean bottom topographies and a seawater layer are scarce some of the conventional staggered grid finite difference method fdm simulations use a simplified structure model without a seawater layer and with a flat ocean bottom topography in this study we apply our heterogeneity oceanic layer and topography scheme hot fdm and a 3d structure model including land and ocean bottom topographies a seawater layer and a fluid solid boundary condition to an aftershock m w 5 8 of the 2009 suruga bay earthquake we attempt to reproduce observations at seismic stations near the coast and then simulate waveforms in the ocean bottom stations our results show that a large difference between the cases with and without topographies can be seen in the coda part after the s wave in the simulated waveforms in terms of amplitudes and elongations the synthetic waveforms in the model with topographies are in agreement with the observed waveforms our results also show that a significant difference in the amplification of the coda part between the cases with and without the seawater layer can be found at the ocean bottom stations this coda part is the s and rayleigh wave propagation associated with the ocean and the underlying sediment layers our results show that a realistic model with topographies and a seawater layer is needed in fdm simulations in order to precisely reproduce observed waveforms or predict seismic motion for a suboceanic earthquake

interference of long period seismic wavefield observed by the dense hi net array in japan 1 in order to recover small signals of long period ground motions recorded by a short period seismometer we designed a time domain recursive filter that simulates seismic waves recorded with broadband seismometers we applied the time domain filter to seismograms recorded by the dense hi net array which consists of 800 stations at intervals of approximately 20 km the effectiveness of the time domain filter is demonstrated through the comparison of broadband waveforms obtained by the filter and sts 2 true broadband seismograms from the f net at the same site good agreement is observed between filtered and true broadband waveforms with high correlation coefficients for periods of up to 100 s for waveforms from the 2007 sumatra earthquake m7 9 which occurred approximately 5000 5800 km away from japan the applicability of the time domain filter to the recovery of long period signals from the record of a short period seismometer depends on the signal to noise ratio as a result a limited bandwidth of broadband signal is recovered for smaller earthquake from the spatiotemporal variation of the long period t 20 100 s wavefield obtained by the time domain filter we newly found an anomalous phase pattern of splitting of polarity along the wavefront particularly for the relatively short period band of from 20 50 s array analysis of the dense broadband waveforms revealed multipathing of the rayleigh waves which propagated toward central japan from two directions with slightly different slowness vectors the interference of two rayleigh waves caused such splitting of wavefield

synthesizing ocean bottom pressure records including seismic wave and tsunami contributions toward realistic tests of monitoring systems the present study proposes a method for synthesizing the ocean bottom pressure records during a tsunamigenic earthquake firstly a linear seismic wave simulation is conducted with a kinematic earthquake fault model as a source then a nonlinear tsunami simulation is conducted using the sea bottom movement calculated in the seismic wave simulation by using these simulation results this method can provide realistic ocean bottom pressure change data including both seismic and tsunami contributions a simple theoretical consideration indicates that the dynamic pressure change caused by the sea bottom acceleration can contribute significantly until the duration of 90 s for a depth of 4000 m in the ocean the performance of a tsunami monitoring system was investigated using the synthesized ocean bottom pressure records it indicates that the system based on the hydrostatic approximation could not measure the actual tsunami height when the time does not elapse enough the dynamic pressure change and the permanent sea bottom deformation inside the source region break the condition of a simple hydrostatic approximation a tsunami source estimation method of tfish is also examined even though the synthesized records contain a large dynamic pressure change which is not considered in the algorithm tfish showed a satisfactory performance when 5 min after the earthquake occurrence the pressure records synthesized in this study including both seismic wave and tsunami contributions are more practical for evaluating the performance of our monitoring ability whereas most tsunami monitoring tests neglect the seismic wave contribution

taphonomy of a middle miocene autochthonous forest assemblage ngorora formation central kenya abstract a 12 6 million year old forest assemblage of leaves twigs and rare fruit is preserved in the ngorora formation of central kenya the assemblage is autochtonous preserved in airfall tuff and represents well the diversity heterogeneity and richness of the original forest the herbaceous component not usually preserved in paleobotanical assemblages is present nearest neighbor analysis and mapping of the vertical distribution of plant organs indicates that leaves and twigs are preserved near the parent plant and that there is no apparent size weight or species bias in deposition of these remains leaves occur isolated in clusters or attached to branches and fell directly to the ground as a result of ashfall most falling very soon after ashfall commenced the absence of upright trunks and large stems is probably due to post depositional weathering which may also be responsible for the absence of a leaf litter layer however leaf litter may have been absent at the time of ash deposition

deuterium hydrogen inter diffusion in chlorite abstract interactions between aqueous fluids and rocks occur in a broad range of contexts ranging from hydrothermal alteration veins to regional metamorphism tracking these processes and understanding their reaction kinetics require a precise knowledge of the diffusion of water in rocks and of isotope fractionation in major minerals such as chlorite deuterium hydrogen exchange between mg rich chlorite and water d2o was experimentally investigated using a belt press over the temperature range of 315 650 c at pressures of 1 5 gpa and 3 gpa both chloritite chip and chlorite powder were used d d h ratios in chlorite grains were mapped using raman spectroscopy deuterium hydrogen exchange proceeded by deuterium hydrogen inter diffusion in chlorite lattice diffusion as chlorite is a phyllosilicate i e an anisotropic mineral diffusion coefficients were determined for crystallographic directions parallel and perpendicular to the silicate layers perpendicular and parallel to the c axis respectively arrhenius relations for deuterium hydrogen inter diffusion coefficients were derived from the new dataset activation energy e is comprised between 215 21 1 kj mol perpendicular to the c axis and 194 21 kj mol parallel to the c axis log10 d0 is 2 2 1 3 m2 s for diffusion in the direction perpendicular to the c axis and 4 5 1 3 m2 s for diffusion parallel to it the bulk diffusion law derived from a combination of our data with data from graham et al 1987 yields e 176 8 kj mol and log10 d0 5 1 0 4 m2 s

fault parameters of the 1896 sanriku tsunami earthquake estimated from tsunami numerical modeling the june 15 1896 sanriku earthquake generated devastating tsunamis with the maximum run up of 25 m and caused the worst tsunami disaster in the history of japan despite its moderate surface wave magnitude ms 7 2 and weak seismic intensity this is a typical tsunami earthquake which generates anomalously larger tsunamis than expected from its seismic waves previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments in this paper we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in japan the result indicates that the tsunami source is very close to the japan trench and the fault strike is parallel to the trench axis the fault width is about 50 km suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge

electrical conductivity of the serpentinised mantle and fluid flow in subduction zones in the mantle wedge of subduction zones electromagnetic profiles reveal high electrical conductivity bodies in hot areas 700 degrees c water released by dehydration of the slab induces melting of the mantle under volcanic arcs that can explain the observed high conductivities in the cold 1 m fluids during progressive serpentinisation of the mantle wedge these fluids can mix with arc magmas at depths and account for high chlorine water ratios in arc lavas

modeling of long period ground motions in the nankai subduction zone model simulation using the accretionary prism derived from oceanfloor local s wave velocity structures the accretionary prism in the subduction zone which consists of thick low velocity oceanic sediments significantly affects the propagation of seismic waves for shallow offshore earthquakes including large interplate earthquakes in order to simulate long period 5 s ground motions in the nankai subduction zone we constructed a three dimensional 3d seismic velocity structure model of the accretionary prism by interpolation extrapolation of local s wave velocity structures beneath 46 oceanfloor seismic stations donet which are deployed just above the accretionary prism off the southern kii and eastern shikoku regions we modeled local s wave velocity structures using a simple two parameter depth varying velocity function to investigate the effects of the accretionary prism on ground and seafloor motions we conducted numerical simulations of seismic wave propagation for three local earthquakes that occurred in southwestern japan the simulations reasonably reproduced the observed seismograms not only for the period ranges of the moment tensor inversion 50 s but also for the strong long period ground motions in the sedimentary basins 5 s especially in the region where donet stations are densely deployed since depth varying local s wave structures significantly improve the reproducibility of long period ground motions our modeling procedure is useful for modeling long period ground motions of local and regional offshore subduction zone earthquakes

spatial relationship between shallow very low frequency earthquakes and the subducted kyushu palau ridge in the hyuga nada region of the nankai subduction zone

tufa as a record of perennial fresh water in a semi arid rift basin kapthurin formation kenya lithological and biological features of a fossiliferous tufa in the kapthurin formation baringo kenya reveal the presence of a lush wetland in a semiarid environment during the middle pleistocene ca 500 ka in this portion of the east african rift valley four geological sections each between 3 m and 8 m in thickness exposed over a distance of 0ae5 km reveal a 1 to 2 m thick paludal tufa which is composed of three carbonate beds two dark grey silty claystones and a reddish brown silty palaeosol high resolution stratigraphic analysis carbonate petrography stable isotope and elemental geochemistry clay mineralogy and fossil remains molluscs ostracods diatoms and charophytes reveal a ground water fed system that fluctuated in depth and periodically disappeared altogether oxygen isotope ratios d 18 o of tufa matrix range from 4ae5 to 8ae0 vienna pee dee belemnite and become more positive up section indicating the decreasing influence of fault related fluids and increasing residence time or freshness of wetland water rather than evaporative enrichment this spring was situated on a lake margin during low lake levels thrived during periods of increased ground water input and was ultimately replaced by an alkaline lake the wetland would appear to have existed during a cool interval within the generally warm marine isotope stage 13 or perhaps during the warm second half of marine isotope stage 13 the ground water source of this wetland arose through a fault system thus the position of the tufa deposit is controlled structurally but the timing and duration of the wetland system may have been influenced by both climatic and tectonic factors

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

a deep outer rise reverse fault earthquake immediately triggered a shallow normal fault earthquake the 7 december 2012 off sanriku earthquake mw 7 3 1 teleseismic body wave analysis revealed that the 7 december 2012 off sanriku earthquake mw 7 3 at the outer rise of japan trench consisted of two successive subevents the first subevent with reverse fault mechanism event 1 mw 7 1 at 56 km depth was followed by approximately 20 s later the second subevent with normal fault mechanism event 2 mw 7 2 at 6 km depth finite fault slip models show that the slip of event 1 was concentrated around the initial rupture point with the maximum of 2 7 m and that event 2 had two asperities with the maximum of 4 5 m at both sides of the initial rupture point the static coulomb failure function analyses suggested that event 1 triggered event 2 and that both subevents were promoted by the 2011 tohoku earthquake mw 9 1

fdm simulation of seismic waves ocean acoustic waves and tsunamis based on tsunami coupled equations of motion we have developed a new unified modeling technique for the total simulation of seismic waves ocean acoustic waves and tsunamis resulting from earthquakes based on a finite difference method simulation of the 3d equations of motion using the equilibrium between the pressure gradient and gravity in these equations tsunami propagation is naturally incorporated in the simulation based on the equations of motion the performance of the parallel computation for the newly developed tsunami coupled equations using a domain partitioning procedure shows a high efficiency coefficient with a large number of cpu cores the simulation results show how the near field term associated with seismic waves produced by shallow earthquakes leads to a permanent coseismic deformation of the ground surface which gives rise to the initial tsunami on the sea surface propagation of the tsunami along the sea surface as a gravity wave and ocean acoustic waves in seawater with high frequency multiple p wave reflections between the free surface and sea bottom are also clearly demonstrated by the present simulations we find a good agreement in the tsunami waveform between our results and those obtained by other simulations based on an analytical model and the navier stokes equations demonstrating the effectiveness of the tsunami coupling simulation model based on this simulation we show that the ratio of the amplitude of ocean acoustic waves to the height of the tsunami both of which are produced by the earthquake strongly depends on the rise time of the earthquake rupture this ratio can be used to obtain a more detailed understanding of the source rupture processes of subduction zone earthquakes and for implementing an improved tsunami alert system for slow tsunami earthquakes

a middle pleistocene intense monsoonal episode from the kapthurin formation kenya stable isotopic evidence from bovid teeth and pedogenic carbonates abstract carbon and oxygen isotope values of bovid tooth enamel and pedogenic carbonates were used to reconstruct the paleoenvironments associated with middle pleistocene archeological and paleontological sites from the kapthurin formation kenya fossil teeth and pedogenic carbonates were collected from lacustrine and fluvial facies k3 and k3 of the kapthurin formation 543 509 ka twenty teeth from six bovid tribes and twenty four pedogenic carbonates were sequentially sampled for stable oxygen and carbon analysis the primary aims of this work are to reconstruct the vegetative habitats of bovids and environmental landscapes from the kapthurin formation assessing the presence of c3 c4 or mixed vegetation and foragers we also assess general paleoclimate factors such as overall aridity seasonal shifts in water availability and broad habitat reconstructions carbon isotope values suggest a wide range of foraging strategies were available to bovids and are characterized by both c3 dominated and c4 dominated diets with little evidence for mixed feeders while pedogenic carbonates suggest the landscape combined a mix of c3 and c4 vegetation sources structurally similar to wooded grasslands paleoclimatic conditions based on the reconstructed mean annual water deficit from 18oenamel values suggest a hyper mesic environment most comparable to the modern ituri rainforest indicating a much wetter climate than the modern lake baringo basin this environment coincides with an intensified middle pleistocene african monsoonal system at the onset of marine isotope stage 13 533 ka the middle pleistocene lake baringo regional habitat appears to have been one dominated by woodland areas perennially active streams marsh and sumpland environments and a surrounding grassland ecosystem this lush basin would have provided hominins with a diverse and productive ecosystem perhaps not surprisingly archeological sites are found in all habitats including wet forested and grassland environments

insight into complex rupturing of the immature bending normal fault in the outer slope of the japan trench from aftershocks of the 2005 sanriku earthquake mw 7 0 located by ocean bottom seismometry 1 the distribution of aftershocks of a large mw 7 0 normal faulting earthquake beneath the outer slope of the japan trench in 2005 measured in 2007 using ocean bottom seismographs indicates that the earthquake was involved with a set of conjugate normal faults although the faults reach to the upper mantle the estimated vp and vp vs show no remarkable changes that can be related to extensive hydration in the crust or uppermost mantle the absence of horst graben topographic structure in the rupture area suggests that immaturity of the bending fault system is responsible for the relatively unhydrated lithosphere several earthquakes below the aftershock zone may belong to the lower plane seismicity of the shallow double seismic zone because no earthquakes were recorded in the area for more than 80 years before the 2005 event shallow extensional and deep compressive earthquakes may be activated concurrently in the focal area of this earthquake

environmental significance of upper miocene phosphorites at hominid sites in the lukeino formation tugen hills kenya the lukeino formation contains an important sedimentary and fossiliferous record of the late miocene 6 09 5 68 ma which has in particular yielded the fossil remains of the oldest east african bipedal hominid called orrorin tugenensis this fluvio lacustrine sedimentary succession crops out in the kenyan part of the east african rift it is mainly composed of clay to sandy clay deposits intercalated with volcanic ash horizons and localized layers of carbonates and diatomites a detailed sedimentological and mineralogical study of the lukeino formation was conducted to throw light on the environmental conditions in which the hominids lived several centimetric relatively continuous and indurated phosphatic horizons of sedimentary origin were identified at two sites sunbarua and kapcheberek mineralogical xrd and geochemical analyses as well as observations by sem which was coupled with an energy dispersive spectroscopy eds microprobe indicate that the autochthonous phosphate layers are composed of a micritic matrix of francolite 38 93 with incorporation of silicates in variable proportions from one layer to another the phosphate matrix contains very well preserved and abundant diatom frustules in the basal phosphate layer these diatoms are identified as aulacoseira granulata implying a ph of 7 8 8 2 for freshwaters of the palaeolake lukeino calcitic tubular structures linked to a possible bacterial origin are also observed locally phosphate layers occur abruptly within a thick clay sandy series associated with an intense runoff phase during the deposition of this interval of the lukeino formation the massive and cyclic input of phosphorus to the lake promoted productivity to the stage where it caused a diatom bloom the establishment of several phosphate horizons testifies to successive phases of eutrophication of palaeolake lukeino the diatom cells provided some of the organic matter which was decomposed by bacterial activity at the bottom of the lake in suboxic conditions but in insufficient quantities to fully form the phosphatic materials the rest of the organic matter needed for phosphogenesis came from terrigenous supply plant debris suggesting the presence of dense vegetation in the catchment of the palaeolake lukeino during this well drained interval of deposition of the lukeino formation

determination of trace element partition coefficients between water and minerals by high pressure and high temperature experiments leaching technique a refined approach for the experimental determination of fluid composition at elevated pressure and temperature conditions is developed it effectively determines partition coefficients of trace elements between aqueous fluid and minerals this approach is developed on top of many previously known technical achievements however it differs from the previous ones by the use of calibrated base and acid leaching of quenched samples to strip off the precipitates formed from the fluid during the quench this permits the reconstruction of a fluid composition from an experimental charge that consists of a complete mixture of solid and fluid phases this is a significant difference from the previous analogous studies in which the fluid was separated from the solids all through the experiment mass balance calculations and error propagation assess the merits of the present method applied to a fluid antigorite system

anomalous propagation of long period ground motions recorded in tokyo during the 23 october 2004 mw 6 6 niigata ken chuetsu japan earthquake unusually large 5 cm and prolonged shaking associated with long period ground motions at periods of about 7 sec were observed in central tokyo during the mw 6 6 niigata ken chuetsu earthquake of 23 october 2004 the long period ground motions caused significant resonance in high rise buildings of about 70 floors in height thus it is an urgent matter to understand the development and amplification properties of long period ground motions in tokyo associated with large earthquakes in this study we use numerous waveform records from 585 stations in a nationwide accelerometer network k net kik net and 495 intensity meters in the area around tokyo the data reveal that the long period ground motion is characterized in most part by a surface rayleigh wave generated at the northern edge of kanto basin and the surface wave is developed as propagating through a thick cover of sediments 3000 4000 m that overlies rigid bedrock to complement the observational data we conducted a large scale computer simu lation of seismic wave propagation by employing the earth simulator supercomputer with a detailed source slip model and a high resolution 3d sedimentary structural model of central japan the results of the computer simulation demonstrate that the anomalously prolonged ground shaking of the long period signal recorded in the center of tokyo occurred because of the stagnation of seismic energy resulting from the multipathing and focusing of rayleigh waves toward the bottom of the kanto basin from surrounding mountain regions with interaction to the 3d basin structure

seismic and tsunami wave propagation of the 2011 off the pacific coast of tohoku earthquake as inferred from the tsunami coupled finite difference simulation abstract the 2011 tohoku earthquake m 9 0 caused significant hazards including strong ground motion coseismic ground deformation and tsunamis for a deeper understanding of these phenomena we conducted a large scale parallel computer simulation by means of the finite difference method fdm with newly developed tsunami coupled equations of motion this method is based on the equations of motion for an elastic medium treating seawater as elastic material having zero s wave velocity tsunami waves are included by taking into account gravity and their equilibrium with the pressure gradient an effective method of fdm simulation using the state of the art massively parallelized k computer is also studied with the use of a 3d layered velocity structure that includes topography and bathymetry basement structure moho depth and plate boundaries and use of the appropriate source rupture model based on joint inversion of seismic waves and geodetic observations the simulated seismic waves demonstrate anomalous seismic wave propagation by the thick 3d basin structure inland we also found that the sea column acts as a strong absorber of seismic waves for shallow up dip slip on the ocean side coseismic deformation and tsunamis are dynamically generated in this simulation tsunami attacks on the subsided pacific coast are simulated without any additional assumptions we also modeled the tsunami and seismic records of ocean bottom pressure gauges above the fault because sea bottom tsunami and seismic observation is powerful but very complex recording both seismic and tsunami waves the use of these coupled numerical simulations has great potential for resolving complex source fault rupture processes in a 3d heterogeneous structure online material mpeg movies of fault slip seismic wave propagation seafloor and ground displacement and tsunamic propagation

fdm simulation of an anomalous later phase from the japan trench subduction zone earthquakes we investigated the development of a distinct later phase observed at stations near the japan trench associated with shallow outer rise earthquakes off the coast of sanriku northern japan based on the analysis of three component broadband seismograms and fdm simulations of seismic wave propagation using a heterogeneous structural model of the japan trench subduction zone snapshots of seismic wave propagation obtained through these simulations clearly demonstrate the complicated seismic wavefield constructed by a coupling of the ocean acoustic waves and the rayleigh waves propagating within seawater and below the sea bottom by multiple reflections associated with shallow subduction zone earthquakes we demonstrated that the conversion to the rayleigh wave from the coupled ocean acoustic waves and the rayleigh wave as they propagate upward along the slope of seafloor near the coast is the primary cause of the arrival of the distinct later phase at the station near the coast through a sequence of simulations using different structural models of the japan trench subduction zone we determined that the thick layer of seawater along the trench and the suddenly rising sea bottom onshore of the japanese island are the major causes of the distinct later phase the results of the present study indicate that for realistic modeling of seismic wave propagation from the subduction zone earthquakes a high resolution bathymetry model is very crucial although most current simulations do not include a water column in their simulation models

thermal cracking and the deep hydration of oceanic lithosphere a key to the generation of plate tectonics 1 the development of transient thermal stress in suboceanic mantle is investigated on the basis of two dimensional thermoviscoelastic models incorporating composite rheology appropriate for dry oceanic lithosphere thermal stress is shown to be sufficiently high to deeply fracture the coldest part of lithosphere e g to the depth of at least 30 km and possibly down to 50 km in 100 ma old lithosphere the release of thermal stress by tension cracking is limited to the vicinity of cracks and the cascade crack system is suggested to be required given the finite fracture strength of mantle materials possible physical and chemical consequences of deep thermal cracking are also discussed the rheological evolution of oceanic lithosphere is likely to be affected by thermal cracking and subsequent serpentinization which introduces the localized zones of weakness in the otherwise stiffest part of lithosphere this localized weakening may help to explain why plate tectonic convection not stagnant lid convection operates in earth s mantle

diatom paleolimnology of late pliocene baringo basin kenya paleolakes abstract kenya s baringo tugen hills barsemoi drill site is one of six localities across kenya and ethiopia from which the hominin sites and paleolakes drilling project has obtained sediment cores in an effort to investigate the role of environmental forcing in shaping human evolution the baringo basin site features extensive exposures of the chemeron formation which contains 100 fossil vertebrate localities including five hominin sites the 228 m drill core dating from 3 29 to 2 56 ma is characterized by fluvio lacustrine sediments including multiple diatomites with evidence of variable degrees of later pedogenic modification in the lower part of the core 3 29 3 04 ma diatoms were preserved only in very low abundance consistent with predominantly fluvial or lake marginal environments in contrast five diatomites and two additional diatom rich intervals were deposited after 3 04 ma reflecting a major shift in the basin hydrology planktonic freshwater species dominated these diatom rich intervals whereas periphytic taxa were present in proportions less than 2 suggesting that these intervals represent open water deposition during lake highstands littoral or saline assemblages are largely absent throughout the core instead we observed a pattern of increasing diatom frustule dissolution at the tops and bottoms of diatomite units indicating increased alkalinity during the transgressive regressive phases a na bearing zeolite analcime indicative of saline waters precipitated in clastic dominated intervals between diatomites suggesting extreme environmental variability between lake highstands and lowstands diatom assemblages were consistently dominated by a few species belonging to the genera aulacoseira and stephanodiscus which were at times co dominant we infer that assemblages dominated by aulacoseira represent a well mixed lake with abundant supply of silica when stephanodiscus was dominant which occurred more frequently in the later freshwater phases we infer incomplete mixing and reduced silica flux to the epilimnion upper water layer