hydroacoustic events located at the intersection of the atlantis 30 n and kane 23 40 n transform faults with the mid atlantic ridge we investigate the characteristics of t phase events located at the ends of two segments of the mid atlantic ridge our motivations for the study were to understand whether t phase locations represent earthquake epicenters and thus whether accurate geological inferences can be made from their spatial patterns and to understand further the relationship between t phase event characteristics and earthquake properties we examine the characteristics of 158 t phase events with respect to both event location water depth and source to receiver distance the propagation paths of the t phases are also modeled to study the effects of encountering seafloor topography we find that existing models for t phase excitation and propagation cannot explain adequately all of our observations the amplitudes received levels of t phases at the hydrophones show no dependence on event water depths in contrast to current excitation models which predict a decrease in event magnitude with increasing water depth the received levels are observed to decrease with increasing source to receiver distance and events from the two study areas exhibit different trends in relative received levels between hydrophones once attenuation is taken into account our acoustic ray trace model is able to reproduce similar trends in relative amplitudes at the hydrophones based on 1 d topography between the event and each hydrophone but the variances in both the observed data and model are high we observe a pattern of short t phase onset times for shallow water events and long onset times for deep water events where onset time is defined as the time interval between the appearance of the t phase envelope above the ambient noise and its first peak this suggests that the onset time may be a function of several variables including efficiency of energy conversion based on local topography efficiency of propagation based on event water depth and hypocentral depth in the crust the results of this study underscore the complexity of t phase excitation and propagation and argue that current models of t phase excitation and propagation need to be improved to explain the observed characteristics of t phase data

t phase spectra seismic moments and tsunamigenesis t phase spectrograms and spectra derived from deep ocean hydrophones for tsunamigenic and non tsunamigenic earthquakes in the pacific reveal the following 1 substantial amounts of t phase energy at high frequencies i e 1 hz to at least 35 hz 2 strong correlations of spectral strengths in the 10 hz to 35 hz frequency range to seismic moments and 3 large spectral strengths at high frequencies for tsunamigenic earthquakes these findings are consistent with the low attenuation of the so und fixing and ranging sofar channel which permits efficient propagation of high frequencies to great distances and with the perception that large earthquakes may generate high frequency signals at the water sediment interface which can best be observed by hydroacoustic sensors in the low noise environment of the deep oceans in addition these studies confirm that 1 source bathymetry can strongly influence the character of t phases 2 islands or seamounts near the source area can act as secondary radiators of energy which add to the complexity and duration of the coda 3 there appears to be no significant dependence of t phase strength on earthquake source mechanism and 4 the strength of the t phase is dependent on the purity of its oceanic travel path the strong correlation of t phase spectral strengths to seismic moments suggests that substantial improvements in the reliability of tsunami warnings may be possible by using t phases as an additional independent single station method for estimating seismic moments finally the high frequencies observed in the t phase may be associated with important alternate mechanisms for tsunamigenesis other than faulting i e slumpage compaction or liquefaction

reverse propagation of t waves from the emperor seamount chain 1 analysis of seismo acoustic t waves associated with an intermediate depth earthquake beneath northern japan reveals that the detected t waves are secondary waves scattered by distant seamounts the timing of t wave onset 3000 s after occurrence of the earthquake indicates that the detected t waves did not follow a direct path from the solid liquid conversion point near the japan trench to the observation stations in northeast japan it is hypothesized that the original t waves were reverse scattered back toward japan by peaks of the emperor seamount chain after propagation in the northern pacific ocean the synthesized envelope patterns for acoustics scattered at the seamounts considering this multi path effect reproduce the travel time and amplitude pattern of the observed t waves well with each seamount group producing a discrete amplitude peak of the scattered wave these observations suggest that topographical obstructions act as a secondary source for t wave propagation in the ocean

late pleistocene and holocene palaeohydrology of lake rukwa tanzania inferred from diatom analysis diatom analysis has been used to provide information on the lake level fluctuations of lake rukwa during the last 21 7 ka diatom inferred chemical variables conductivity ph anion and cation ratios indicate that at the lgm lake level was low probably driven by a low p e ratio but with sufficient water to avoid desiccation following the lgm deep water conditions were obtained through a series of steps until maximum water depth was reached by at least 13 5 ka the high lake level phase lasted through the early holocene until after 6 7 ka a shallow saline lake has occupied the basin from ca 5 5 ka until the present day the pattern of reconstructed lake level fluctuation in lake rukwa is similar to that from lake tanganyika and other lakes from the equatorial and northern tropical zone we can confirm that the n tropical mode of millennial scale lake level change since the lgm extended to at least 8 s

constraining the hydration of the subducting nazca plate beneath northern chile using subduction zone guided waves abstract guided wave dispersion is observed from earthquakes at 180 280 km depth recorded at stations in the fore arc of northern chile where the 44 ma nazca plate subducts beneath south america characteristic p wave dispersion is observed at several stations in the chilean fore arc with high frequency energy 5 hz arriving up to 3 s after low frequency

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

on the mechanism of conversion of seismic waves to and from t waves in the vicinity of island shores high frequency seismic records from the polynesian seismic network are used to investigate in detail the processes of conversion of acoustic t wave energy from and to seismic waves at island shores on the source side we study the seismic to acoustic conversion based on t phases from hawaiian events recorded at polynesian stations located on the coral platter on the receiver side we study the acoustic to seismic conversion based on t phases from marine sources recorded across the polynesian islands in both instances our results underline the importance of steep slopes typically 50 in allowing an efficient conversion between p waves in the island structure and t waves in the water column these slopes can be coral reefs or the heads of young presumably unconsolidated basalt flows under this geometry modeling based on raytracing indicates that the seismic record of the t phase consists of a p wave at distances from the conversion point greater than 9 km at shorter distances s waves and surface waves are generated in the absence of a steep slope only surface waves are present these models can be used to compute precise and predictable travel time station corrections allowing the use of seismometers located inland to exploit the superb detection and location capabilities of t waves

nearshore carbonate deposits in lake tanganyika an exceptionally wide variety of carbonate fades dominated by high magnesian calcite occurs along the littoral and shallow sublittoral zones 50 m of lake tanganyika in central africa these facies include exposed and submerged calcite cemented ridges of nearshore terrigenous sand ooid sand shoals and lithified oolite ridges chara meadows of bioturbated calcareous silts gastropod shell blankets and related coquinas and extensive thrombolitic microbial reefs though texturally and compositionally similar to many modern and ancient shallow water marine facies these deposits record carbonate deposition and cementation in a large tropical deep water lake of tectonic origin lithofacies along lake tanganyika represent the broadest spectrum of carbonate deposits yet reported from any modern lake and serve as important analogues for lacustrine carbonate sequences in the stratigraphic record

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

assessment of peat quality by molecular and bulk geochemical analysis application to the holocene record of the chautagne marsh haute savoie france although it is primarily constituted in general from a limited variety of local plants peat is however sensitive to physicochemical changes in the medium in particular those induced by hydrological fluctuations the present study aims at confronting the information on peat quality provided by various families of biochemical components lipids lignin sugars especially in order to check the validity of a new organic matter om quality indicator the r400 index directly drawn from rock eval pyrolysis this parameter which is deduced from the sole s2 pyrolysis peak is extremely robust the chautagne marsh located between the le bourget lake and the rhone river lies in a key situation for recording lake level variations and rhone river floods all along its holocene filling the study was conducted on a 6 m long core which comprises 4 m of peat under 66 cm of pedogenetically altered om rich sediment classical rock eval pyrolysis revealed few qualitative and quantitative om changes with total organic carbon toc values close to 50 and hydrogen index values around 300 350 mg hc g 1toc in the peat the r400 parameter remains practically unchanged in the upper unit affected by pedogenesis it fluctuates however all along the peaty unit together with a progressive downward decrease ascribable to diagenesis molecular analyses show that samples with high r400 values are richer in sugars and in slightly oxidized lignin these results support the idea that the r400 parameter can be used as an indicator of om preservation since om preservation is mostly controlled by the water table in peat the chautagne marsh records hydrological fluctuations such as those of the le bourget lake water level all along the holocene

localization of t wave energy on land revealed by a dense seismic network in japan summary we have investigated the wave propagation characteristics of a seismic t wave on land in northeastern japan using the seismograms recorded by a dense seismic network the analysed t wave is a unique one that was generated by a large intermediate depth earthquake beneath the network that backpropagated from the emperor seamount chain in the northern pacific the t wave has a predominant frequency of 1 5 hz which is lower than the previously reported values spatiotemporal variation of an rms envelope bandpass filtered with a passband of 1 2 hz demonstrates multiple arrivals of the t wave and inhomogeneous distribution of amplitude judging from the spatial pattern of first arrival times and the polarization characteristics such as the relatively large dip angle and high planarity we regard the seismic t wave as a rayleigh wave a possible conversion area estimated by a method similar to the source scanning algorithm is located to the northeast of honshu island and may have a dimension of 100 km the most prominent feature of the spatiotemporal variation of the rms amplitude is the localization of t wave energy in the northeastern part of honshu island this localization can be attributed either to the close proximity of the conversion area to land or to the large extent of the area however these factors are only supplementary because they cannot explain a sharp contrast in amplitude between the two areas with comparable distance but different azimuth from the conversion point an additional and essential factor in explaining the observation is the non isotropic radiation from the conversion points since the conversion occurred on the continental slope the maximum amplitude of converted energy is expected to appear either in the propagation direction of incoming acoustic waves or in the steepest direction of the local topography these factors in particular a convex shape of bathymetry probably caused the focusing of converted energy into the northeastern part of honshu island

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

dynamics of abundance of the mid to late pridoli conodonts from the eastern part of the silurian baltic basin multifractals state shifts and oscillations

δ18o composition of conodont apatite indicates climatic cooling during the middle pridoli phosphatic microfossils such as conodonts and fish microremains dermal scales from the upper silurian pridoli of lithuania have been studied for their oxygen isotope composition the conodont c

carbon isotope stratigraphy across the silurian devonian transition in podolia ukraine evidence for a global biogeochemical perturbation the carbon and oxygen isotope composition of marine carbonates 13 c and 18 o respectively are studied in the fossiliferous stratigraphically well constrained and remarkably expanded successions of podolia sw ukraine spanning the silurian devonian transition significant isotopic shifts are directly comparable to previously published global secular trends in well preserved brachiopod calcite isotopic ratios from this region and therefore may be taken as a reliable primary record of seawater 13 c changes the sections reveal a major positive 13 c excursion with an amplitude above 6 beginning in the upper pridoli and reaching peak values as heavy as 4 2 in the lowermost lochkovian this turnover in carbon cycling is followed by a general trend toward more negative 13 c values in the upper lochkovian the podolian isotopic signals provide strong support for the previously inferred global biogeochemical perturbation across the silurian devonian transition reflecting a complex combination of palaeogeographical biogeochemical and evolutionary processes in the late caledonian geodynamic setting with a likely undervalued role of the expanding vegetation in vast near coastal shallows and deltas

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

the deficient t waves of tsunami earthquakes summary we develop an algorithm quantifying the energy flux of t phases recorded at island stations following major teleseismic events which we further scale by the seismic moment m0 of the earthquake to define a t phase efficiency we apply this concept to a set of six recognized tsunami earthquakes which generated tsunamis larger than expected from their conventional seismic waves through comparison with nearby reference events the t waves of which were recorded at the same sites we find that the tsunami earthquakes exhibit a deficiency in ranging from 1 5 to 2 5 orders of magnitude this result settles a 50 yr old controversy on the possible correlation between t wave generation and tsunami genesis the deficient character of the t waves from tsunami earthquakes readily supports the proposed model of an exceedingly slow rupture velocity for this class of events and the close examination of t wave trains supports the concept of a jerky rupture in at least two cases the computation of is straightforward in real time and could become a valuable contribution to real time tsunami warning in the far field

reconstruction of the dynamics of the climatic system from time series data abstract the oxygen isotope record of the last million years as provided by a deep sea core sediment is analyzed by a method recently developed in the theory of dynamical systems the analysis suggests that climatic variability is the manifestation of a chaotic dynamics described by an attractor of fractal dimensionality a quantitative measure of the limited predictability of the climatic system is provided by the evaluation of the time correlation function and the largest positive lyapounov exponent of the system

high resolution late silurian correlations between gotland sweden and the broken river region ne australia lithologies conodonts and isotopes high resolution correlations partly with a precision better than 10 ka are achieved between late ludfordian sequences on gotland sweden on baltica and a section cog through the coral gardens formation along the broken river northeastern australia on gondwana despite these sections having been on different palaeocontinents facing different oceans the interval is characterised by rapid very large faunal isotopic and lithologic changes lithologies are remarkably similar in the two areas consisting of in order from below marls with thin limestone beds flaggy limestones oncoidal crinoidal limestone oncoidal marls terrigenous clastics silty clay mudstone sandstone oolite and cliff gorge forming limestones further independent correlation dates several of the lithological changes as coeval the 813 c excursion in whole rock carbonates is one of the three largest ones known during the phanerozoic the increase in delta c 13 is very similar in the two areas from below 1 parts per thousand to c 9 parts per thousand vpdb though two gotland samples yielded 9 71 parts per thousand and 10 54 parts per thousand the corresponding cog interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling compared with the lithologies and the delta c 13 curves the conodont faunas display some divergence but key taxa permit precise correlations for much of the studied interval the conodont assemblages change stepwise from very diverse in the polygnathoides siluricus zone to a low diversity fauna dominated markedly by a single taxon upper icriodontid subzone returning abruptly to a comparatively diverse ozarkodina snajdri zone fauna a method resembling graphic correlation in some respects is used to propose a similarly high resolution correlation through a longer interval for future testing c 2006 elsevier b v all rights reserved less

the deep peru 2015 doublet earthquakes abstract on 24 november 2015 two events of magnitude mw 7 5 and mw 7 6 occurred at 600 km depth under the peru brazil boundary these two events were separated in time by 300 s deep event doublets occur often under south america the characteristics that control these events and the dynamic interaction between them are an unresolved problem we used teleseismic and regional data situated above the doublet to perform source inversion in order to characterize their ruptures the overall resemblance between these two events suggests that they share similar rupture process they are not identical but occur on the same fault surface dipping westward using a p wave stripping and stretching method we determine rupture speed of 2 25 km s from regional body wave inversion we find that stress drop is similar for both events they differ by a factor of two the similarity in geometry rupture velocity stress drop and radiated energy suggests that these two events looked like simple elliptical ruptures that propagated like classical sub shear brittle cracks

multifractal and white noise evolutionary dynamics in jurassic cretaceous ammonoidea for more than a decade there has been interdisciplinary debate on whether fossil origination and extinction time series show evidence of self organized criticality soc or some other more complex hierarchical structure analyses of a new data set of jurassic and cretaceous ammonoid genera demonstrate that these taxonomic subgroups do not reproduce the patterns seen in larger data sets that pool disparate taxa rather originations and extinctions in these ammonoids show no evidence of soc limited evidence for a hierarchical multifractal pattern and at least within the suborder ammonitina evidence consistent with a white noise signal although a white noise pattern has been identified previously in an ammonoid family diversity time series the significance of such a result for ammonoid genus originations and extinctions is discussed here for the first time this white noise pattern indicates that processes acting on short time scales less than a few million years dominate the ammonitina origination and extinction records producing a nonhierarchical diversity dynamic because origination events in one interval do not appear to trigger originations in subsequent intervals ammonite evolutionary radiations were likely to be extremely rapid and driven by physical rather than biological opportunities for diversification

nonlinearity and multifractality of climate change in the past 420 000 years 1 evidence of past climate variations are stored in polar ice caps and indicate glacial interglacial cycles of 100 kyr using advanced scaling techniques we study the long range correlation properties of temperature proxy records of four ice cores from antarctica and greenland these series are long range correlated in the time scales of 1 100 kyr we show that these time series are nonlinear for time scales of 1 100 kyr as expressed by temporal long range correlations of magnitudes of temperature increments and by a broad multifractal spectrum our results suggest that temperature increments appear in clusters of big and small increments a big positive or negative climate change is most likely followed by a big positive or negative climate change and a small climate change is most likely followed by a small climate change

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

quantifying the community turnover of the uppermost wenlock and ludlow silurian conodonts in the baltic basin abstract the homerian to ludfordian interval of the mid to late silurian period was a time of significant changes in conodont communities global climate oceanographic patterns and biogeochemical cycles the mulde and the lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in earth s history the silurian baltic basin is the most suitable locality globally for studying these perturbations to the ocean atmosphere system since there is an extensive record of conodont taxa occurrences their communities and their environments spanning across shore face to open ocean settings in this study we present new conodont and 13c data from the upper homerian to ludlow interval from two core sections g luva 99 and g luva 118 representing shelfal environments and the numerical conodont data from the vidukl 61 section from deep water settings and compare them with patterns of conodont diversity change as revealed in the data rich milaiciai 103 core section for this purpose we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross recurrence plots the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns the cross recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms the results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records moreover the sudden state transitions detected in the cross recurrence plots suggest that the lau event was of great importance for conodont community evolution in the studied time slice

t phase observations in global seismogram stacks the t phase conversion of acoustic to seismic energy is typically observed as a high frequency wave train at hydrophones or coastal seismic stations here we show that the t phase can be observed in broadband waveform stacks of 5200 earthquakes recorded by the global seismic network to enhance the phase arrivals in stacks we apply short time window average over long time window average filtering to individual traces before stacking although the t phase arrival is visible in stacks from seismograms filtered at 0 5 5 hz it appears much stronger at higher frequencies 2 8 hz and is further enhanced by only stacking seismograms from oceanic paths stacking only subsets of the data depending on continental path lengths on the receiver side shows that the t phase can be observed at stations up to 4 inland from the coast and changes in the t phase arrival time correspond to reasonable crustal velocities

seismic structure of the north central chilean convergent margin subduction erosion of a paleomagmatic arc we study the erosive convergent margin of north central chile at similar to 31 degrees s by using high resolution bathymetric wide angle refraction and multichannel seismic reflection data to derive a detailed tomographic 2 d velocity depth model in the overriding plate our velocity model shows that the lowermost crustal velocities beneath the upper continental slope are 6 0 6 5km s which are interpreted as the continental basement composed by characteristic metamorphic and igneous rocks of the coastal cordillera beneath the lower and middle continental slope however the presence of a zone of reduced velocities 3 5 5 0km s is interpreted as the outermost fore arc composed of volcanic rocks hydrofractured as a result of frontal and basal erosion at the landward edge of the outermost fore arc the bathymetric and seismic data provide evidence for the presence of a prominent trenchward dipping normal scarp similar to 1km offset which overlies a strong lateral velocity contrast from similar to 5 0 to similar to 6 0km s this pronounced velocity contrast propagates deep into the continental crust and it resembles a major normal listric fault we interpret this seismic discontinuity as the volcanic continental basement contact of the submerged coastal cordillera characterized by a gravitational collapse of the outermost fore arc subduction erosion has most likely caused large scale crustal thinning and long term subsidence of the outermost fore arc

environmental changes at lake cheshi zambia since 40 000 years b p abstract sediment and microfossil analyses of a 7 5 m core from lake cheshi suggest that south central africa experienced late quaternary climate changes similar to those in east africa the lake formed around 34 000 yr b p after a prelacustrine phase of at least 6000 yr from climatic or tectonic causes ratios of precipitation to evaporation were probably similar to those of today until a decline about 15 000 13 000 yr b p when the lake shrank and became chemically concentrated maximal lake levels occurred between 8000 and 4000 yr b p and were followed by a low stand under presumably arid conditions about 3500 yr b p encroachment of sudd vegetation contributed to shallowing during the last 3000 yr a phase of microfossil dilution may reflect human activity in the basin or climatic or hydrological changes melosira valve morphology seems to reflect mixing regimes sponge and testate amoeba remains were most numerous relative to diatoms during low water phases

a 22 kyr bp sedimentological record of lake rukwa 8 s sw tanzania environmental chronostratigraphic and climatic implications abstract the sedimentological study of a 12 8 m long core r96 i from lake rukwa tanzania 8 s provides a new record of past lake level fluctuations that took place in response to changes of the regional climate since the last glacial period from 21 to 15 cal kyr bp nearshore and swamp marsh environments are evidenced from clastic deposition macrophytes debris and ca mg carbonate enrichments a transgressive sequence starting around 15 cal kyr bp lead to the humid lacustrine optimum between 15 and 7 cal kyr bp from 12 to 10 cal kyr bp anoxic lake bottom environments were favored by the concomitant effects of high primary productivity increased subsidence and inputs of volcanic ash in the lake the middle holocene 7 3 cal kyr bp is characterized by high concentrations of silt carbonates and low organic content which indicate the occurrence of relatively oxic shallow and saline depositional environments especially around 7 and 3 4 cal kyr bp although grainsize and toc profiles suggest that shallow environments likely persisted in the upper holocene low mg concentration values for the last 3 kyr may indicate a trend toward relatively more dilute environments the two main lake rukwa low stand periods at 21 15 and 7 3 cal kyr bp correspond remarkably well with the insolation maximum at the equator which occurred at 17 kyr bp for the spring equinox and at 6 kyr bp for the autumn equinox respectively we suggest that during these periods of minimum inter hemispheric insolation gradients monsoon circulation weakened in south equatorial regions and the itcz was located north of 8 s in east africa

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

orbital forcing of glacial interglacial variations in chemical weathering and silicon cycling within the upper white nile basin east africa stable isotope and biomarker evidence from lakes victoria and edward on quaternary time scales the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae notably diatoms for which si is an essential nutrient large tropical river systems dominate the export of si from the continents to the oceans here we investigate variations in si cycling in the upper white nile basin over the last 15 ka using sediment cores from lakes victoria and edward coupled measurements of stable o and si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and si cycling while the abundances of lipid biomarkers characteristic of terrestrial emergent higher plants submerged floating aquatic macrophytes and freshwater algae document past ecosystem changes during the late glacial to mid holocene 15 5 5 ka bp orbital forcing greatly enhanced monsoon rainfall forest cover and chemical weathering riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower si isotope values since 5 5 ka bp increasingly dry climates and more open vegetation reinforced by the spread of agricultural cropland over the last 3 4 ka have reduced dissolved silica inputs into the lakes centennial to millennial scale dry episodes are also evident in the isotopic records and merit further investigation

guided waves propagating in subducted oceanic crust 1 we use guided waves traveling updip along the surface of the nazca slab to image subducted oceanic crust at the chile peru subduction zone observed p onsets of intermediate depth events near 21 s in northern chile reveal waveguide behavior with growing focal depth low frequency energy 2 hz becomes more and more dominant and higher frequencies arrive delayed sometimes resembling two distinct phases to explain the observations we employ two dimensional finite difference fd simulations of complete p sv wave propagation along an updip profile of the subduction zone the fd calculations shed some light on several basic issues regarding crustal waveguides the development of guided waves dependent on event focal depth is simulated further we show that the observed guided wave energy must decouple from the waveguide near 100 km depth to reach the deployed stations and that the decoupling process is related to variations in subduction angle simulations also yield constraints on source locations relative to the low velocity structure finally the frequency content of p onsets is used to constrain the thickness of the waveguide the results indicate that a structure of 4 5 km average width and 7 low velocity remains seismically slow compared to the surrounding mantle down to a depth of at least 160 km the layer is interpreted as the unaltered lower part of the subducted oceanic crust suggesting that complete eclogite transformation in the chile peru subduction zone is unlikely to take place until beyond the volcanic front

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

abrupt change in the dip of the subducting plate beneath north chile no large tsunamigenic earthquake has occurred in north chile since 1877 and the region has been largely recognized as a mature seismic gap1 2 3 4 5 6 7 8 9 at the southern end of the seismic gap the 2007 mw 7 7 tocopilla earthquake ruptured the deeper seismogenic interface whereas the coupled upper interface remained unbroken4 6 7 seismological studies onshore show a gently varying dip of 20 to 30 of the downgoing nazca plate3 6 which extends from the trench down to depths of 40 50 km here we study the lithospheric structure of the subduction zone of north chile at about 22 s using wide angle seismic refraction and reflection data from land and sea complemented by hypocentre data recorded during the 2007 tocopilla aftershocks7 our data document an abrupt increase in the dip of the subducting plate from less than 10 to about 22 at a depth of approximately 20 km the distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench which in turn indicates that the subduction megathrust is not only segmented along the trench but also in the direction of the dip we propose that large magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone

quaternary ostracodes and molluscs from the rukwa basin tanzania and their evolutionary and paleobiogeographic implications abstract much of the spectacular biodiversity of the african great lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries longstanding debate surrounds the evolution of these endemic species the stability of bioprovinces and the exchange of faunas between them over geologic time as the rift developed because these debates are currently unsettled we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history this study reports on late quaternary fossils from the rukwa basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces in particular with lake tanganyika lake rukwa s water level showed large fluctuations over the last 25 ky and for most of this period the lake contained large habitat diversity with different species assemblages and taphonomic controls along its northern and southern shores comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the last glacial maximum but with an extirpation event that occurred in the last 5 ky some of the molluscs and ostracodes studied here are closely related to taxa or part of clades that are currently endemic to lake tanganyika but others testify to wider and perhaps older faunal exchanges between the rukwa bioprovince and those of lake malawi and the upper congo in particular lake mweru the rukwa basin has a long history of rifting and lacustrine conditions and at least temporarily its ecosystems appear to have functioned as satellites to lake tanganyika in which intralacustrine speciation occurred paleontological studies of the rukwa faunas are particularly relevant because of the basin s important role in the late cenozoic biogeography of tropical africa and because many of the molecular traces potentially revealing this history would have been erased in the late holocene extirpation

estimating the age of formation of lakes an example from lake tanganyika east african rift system age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution in the absence of dated core material from the lake s sedimentary basement several techniques have been used to generate such age estimates the most common of these herein called the reflection seismic radiocarbon method rsrm combines estimates of short term sediment accumulation rates derived from radiocarbon dated cores and depth to basement estimates derived from reflection seismic data at or near the same locality to estimate an age to basement age estimates form the rsrm suggest that the structural basins of central lake tanganyika began to form between 9 and 12 ma estimates for the northern and southern basins are younger 7 to 8 ma and 2 to 4 ma respectively the diachroneity of estimates for different segments of the lake is equivocal and may be due to erosional loss of record in the northern and southern structural basins or to progressive opening of the rift the rsrm age estimates for lake tanganyika are considerably younger than most prior estimates and clarify the extensional history of the western branch of the east african rift system 31 refs 3 figs 1 tab

t waves from the great 1994 bolivian deep earthquake in relation to channeling of s wave energy up the slab we report the observation of t phases recorded at a number of pacific island sites following the great bolivian deep earthquake of june 9 1994 by studying their arrival times at the various stations we unravel the process of conversion from seismic to acoustic energy at the south american coastline we find that the maxima of amplitude of the phase are incompatible with propagation along the great circle from source to receiver but rather require the generation of the acoustic wave at a common point at the arica bight for all stations in the south pacific and even farther south for stations in hawaii and the bonin islands the timing of these conversions corresponds to the arrival of regional s waves at the conversion points the high frequency nature of the t phase requires the channeling of the s wave from the seismic source to conversion point through low attenuation material which in turns adds supportive evidence for the mechanical continuity of the downgoing slab under that section of south america despite the observed gap in seismicity between 300 and 600 km

late ordovician early silurian ashgillian llandovery sea level curve derived from conodont community analysis anticosti island quebec abstract earlier workers have established sea level curves for the ashgillian llandovery sequence on anticosti island quebec canada based on sedimentology and on brachiopod and reef communities the complete anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800 1100 m sequence this paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths this allows the establishment of a eustatic sea level curve for the sequence this curve is in general agreement with those of the earlier workers but is more detailed and better constrained stratigraphically given the large sampling program the curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier and different water depths for certain intervals from those established earlier the curve is valuable given that the anticosti sequence is one of the most complete in the world for this interval and its divergence from global eustatic curves for this interval is noted

stable carbon isotopes of amorphous kerogens from phanerozoic sedimentary rocks amorphous kerogens from phanerozoic sedimentary rocks may be divided into two groups on the basis of their 13c values h amorphous kerogens have isotopic values in the range of 24 to 20 per mil and l amorphous kerogens have isotopic values in the range of 35 to 26 per mil the occurrence of amorphous kerogens in the intermediate isotopic range from one rock unit in the data set suggests a weak continuum may exist between these two groups phytoplankton and to a lesser extent zooplankton and bacteria are considered to be the precursors for both kerogen types a plausible explanation for this dichotomy may be found in the source of co2 utilized by phytoplankton which is considered to be controlled by environmental factors h amorphous kerogens are expected to occur in silled basins that are overlain by expansive well circulated deep 500 m water where the prevailing source of carbon in the photic zone is atmospheric derived co2 conversely l amorphous kerogens are expected to occur in restricted basins that are overlain by stratified shallow 200 m water where the prevailing source of carbon in the photic zone may be organic derived co2

interplay of structural climatic and volcanic controls on late quaternary lacustrine deltaic sedimentation patterns in the western branch of the east african rift system rukwa rift basin tanzania abstract this paper presents the first detailed outcrop based sedimentologic investigation of the pleistocene holocene upper lake beds succession in the rukwa rift basin located in the western branch of the east african rift system southwestern tanzania the goal of this investigation is to examine the sedimentary facies and reconstruct the depositional environments of this important archive of quaternary climate and environmental change eleven diagnostic facies associations comprising 24 facies were identified and provide the basis for recognition of three key deposystems 1 alluvial to fluvial channel system 2 lake delta system and 3 profundal lacustrine system analysis of paleocurrent indicators and sandstone provenance indicate widely dispersed source regions and drainage patterns that were strongly influenced by major border fault systems and episodic volcanism six stratigraphic sequences a f ranging from 2 to 17 m thick were identified based on stratal stacking patterns and the development of sequence bounding unconformities and lacustrine flooding surfaces sedimentation processes facies architecture and stratigraphic packaging record a complex interplay between quaternary climate fluctuations and intense episodic volcanism in the nearby rungwe volcanic province set against large scale tectonic controls associated with synchronous development of the east african rift system sequence stratigraphic analysis reveals that the rukwa rift basin episodically shifted between a balanced fill lake basin and an overfilled lake basin deep water basin wide lake expansion occurred at different times during the late quaternary the final depositional sequence preserved in the basin a fluvial underfilled lake basin initiated 7 9 ka and has persisted to the present day high frequency climate change played the key role in sequence development in the upper lake beds however voluminous rift related volcanism and erosion of abundant labile volcanic materials from the rungwe volcanic province as well as syntectonic evolution of the rift led to high sedimentation rates and transformation of flash floods and debris flows in the hinterlands rift margin to hyperpycnal flows towards the basin depocenter

controls on the t phase energy fluxes recorded on juan fernandez island by continental seismic wave paths and nazca bathymetry conicyt pcha doctorado nacional 2017 21171480 prs programa de riesgo sismico universidad de chile fondecyt 1170430

spectral analysis of the middle triassic latemar limestone abstract the middle triassic latemar limestone in the dolomites region northern italy consists of hundreds of vertically stacked meter scale platform carbonate cycles each cycle is composed of a shallow marine subtidal carbonate unit with a thin centimeter scale vadose diagenetic dolomite cap these latemar couplets are the products of repeated episodes of submergence emergence with durations estimated at 20 000 yr the couplets are arranged in upward thinning bundles of five indicating the presence of a 100 000 year modulating component we examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques we found si nificant evidence for the presence of a milankovitch forcing signal in this cycling we also present evidence that the adjacent coeval basinal facies the livinallongo formation exhibits a similar bundling pattern in its cm scale hemipelagic carbonate shale alternations we conclude that milankovitch forced small amplitude sea level oscillations were the most likely cause of these middle triassic carbonate rhythms

generation of hydroacoustic signals by oceanic subseafloor earthquakes a mechanical model summary for more than 15 yr the recording of hydroacoustic signals with hydrophones moored in a minimum sound velocity channel called the sofar sound fixing and ranging channel has allowed for detection and localization of many small magnitude earthquakes in oceanic areas however the interpretation of these hydroacoustic signals fails to provide direct information on the magnitudes focal mechanisms or focal depths of the causative earthquakes these limitations result in part from an incomplete understanding of the physics of the conversion across the seafloor interface from seismic waves generated by subseafloor earthquakes to hydroacoustic t waves to try and overcome some of these limitations we have developed a 2 d finite element mechanical model of the conversion process by computing an exact solution of the velocity field of the waterborne t waves our model shows that a double couple source mechanism of a subseafloor earthquake generates t waves whose take off angles are adequate to allow penetration into the sofar channel and efficient trapping by this waveguide furthermore our model confirms that a double couple source with a high s wave content produces higher amplitude t waves than a simple explosive source which only generates p waves

nucleation phase and dynamic inversion of the mw 6 9 valparaiso 2017 earthquake in central chile the valparaiso 2017 sequence occurred in the central chile mega thrust an active zone where the last mega earthquake occurred in 1730 intense seismicity started 2 days before the mw 6 9 main shock a slow trench ward movement was observed in the coastal gps antennas and was accompanied by foreshocks and repeater type seismicity to characterize the rupture process of the main shock we perform a dynamic inversion using the strong motion records and an elliptical patch approach we suggest that a slow slip event preceded and triggered the mw 6 9 earthquake which ruptured an elliptical asperity semi axis of 10 km and 5 km with a sub shear rupture stress drop of 11 71 mpa yield stress of 17 21 mpa slip weakening of 0 65 m and kappa value of 1 98 this earthquake could be the beginning of a long term nucleation phase to a major rupture within the highly coupled central chile zone where a mega thrust earthquake like 1730 is expected

evidence for periodicity and nonlinearity in a high resolution fossil record of long term evolution the application of new signal analysis techniques provides increased insight into the study of the fossil record and processes of evolution the fossil record of 622 planktic foraminifera contains data from 200 stratigraphic stages of the past 127 m y time series analyses wavelet and fourier transform of the planktic foraminifera fossil record were used to discern periodic components in long term evolution the correlation function analysis was used to distinguish between random and deterministic behavior of the fossil record the analyses show that stationary 30 m y periodicity and complex deterministic patterns occur in the long term planktic foraminifera evolution in particular in the extinction record our results suggest that the occurrence of intense diversity fluctuations with 3 10 m y periodicity after major extinction events may be attributed to nonlinear self organized evolutionary response to the availability of new ecospace this coupled nonlinear periodic scenario may explain the repetitive appearance of similar morphotypes in 30 m y intervals

integrated record of ludlow upper silurian oceanic geobioevents coordination of changes in conodont and brachiopod faunas and stable isotopes abstract the ludlow epoch silurian was marked by several globally recognized but mechanistically poorly understood biotic events the most pronounced of them was the lau event which strongly decimated conodont graptolite and brachiopod faunas additionally this event coincides with the largest positive stable carbon isotopic anomaly in the whole phanerozoic as well as the resurgence of the so called anachronistic microbial facies that were frequently encountered during survival episodes of the major mass extinction events in this contribution based on the analysis of the outer shelf facies succession milaiciai 103 core from the lithuanian part of the silurian baltic basin as integrated quantitative record of conodont brachiopod and 13 c changes across most of the ludlow is presented the succession was subdivided into four conodont zones that served as a stratigraphic framework for analyzing the 13 c and palaeoecological trends the depth constrained cluster analysis revealed successions of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each other near the change points in the stable carbon isotopic curve the application of a newly developed mathematical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts and brachiopods are represented by highly time specific assemblages in the aftermath of the lau event o snajdri interval zone the anomalous interval is confined to the transgressive and highstand phases of the 3rd order post lau transgression the discussed interval is coeval with the extensive development of stromatolitic communities in the nearshore environments around the world the results allow for the first time to quantify the profound ecosystem wide geobiological impact of the mid ludfordian event that lasted up to the latest ludfordian

subduction zone guided waves and the heterogeneity structure of the subducted plate intensity anomalies in northern japan 1 the subducting pacific plate acts an efficient waveguide for high frequency signals and often produces anomalously large intensity on the eastern seaboard of northern japan during deep earthquakes the waveform records in the region of high intensity show a low frequency f 2 hz later arrivals with a long coda this behavior is not explained by a simple subduction zone model comprising a high velocity plate with low attenuation from the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the pacific subduction zone we demonstrate that the high frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0 5 km in thickness the standard deviation of wave speed fluctuations from the averaged background model is about 2 this new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness but low frequency waves with long wavelengths can easy tunnel through such lamina structure the result is frequency selective propagation characteristics with a faster low frequency phase followed by large and high frequency signals with very long coda a low wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high frequency coda three dimensional simulations using the earth simulator supercomputer for modeling of high frequency seismic wave propagation in the pacific subduction zone including plate heterogeneity clearly demonstrate the scattering waveguide effects for high frequency seismic waves traveling in the plate the region of large intensity for the heterogeneous model migrates away from the hypocenter into northern japan with an elongated zone along the pacific coast almost comparable to the observations from deep events in the pacific plate

new evidence for a reduced water balance in east africa during the last glacial maximum implication for model data comparison some syntheses of lake level data for the last glacial maximum lgm in east africa 10 n and 30 s east of 25 e show apparently wetter conditions than present for some basins whereas palaeovegetation reconstruction indicates a generally dry climate pmip gcm simulations for the lgm support both scenarios for this region when run under different boundary conditions here we compare three new records from lakes in the data poor southern part of east africa lake malawi lake massoko and lake rukwa we also re assess previously published lake level data and apply a salinity transfer function to the diatom record from lake manyara our results show that in contrast to previous interpretations these lakes were at least as low as today at the lgm and are thus in agreement with the palaeovegetation data relative drought across east africa is best simulated by gcms that use computed ssts rather than the higher climap values lower ssts and the presence of the northern hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern african tropics

seismic ocean thermometry more than 90 of the energy trapped on earth by increasingly abundant greenhouse gases is absorbed by the ocean monitoring the resulting ocean warming remains a challenging sampling problem to complement existing point measurements we introduce a method that infers basin scale deep ocean temperature changes from the travel times of sound waves that are generated by repeating earthquakes a first implementation of this seismic ocean thermometry constrains temperature anomalies averaged across a 3000 kilometer long section in the equatorial east indian ocean with a standard error of 0 0060 kelvin between 2005 and 2016 we find temperature fluctuations on time scales of 12 months 6 months and 10 days and we infer a decadal warming trend that substantially exceeds previous estimates

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back