regional moment tensor inversion for strong aftershocks of the august 17 1999 izmit earthquake mw 7 4 we analyzed the source mechanisms of the thirty largest aftershocks 4 0 ml 6 2 of the august 17 1999 izmit earthquake mw 7 4 by applying the regional moment tensor inversion method using data from near regional broadband stations the inversion solutions were compared to 17 well constrained first motion solutions and were seen to be in good agreement we found that the dominance of strike slip motion is the main characteristic of the izmit earthquake sequence significant aftershock activity was recorded to the west and east of the un ruptured extremities in the east the aftershocks located near the town of duzce represent an early replica of the november 12 1999 duzce earthquake mw 7 2 in terms of locations and source mechanisms in the marmara sea where the fault geometry is still very poorly resolved most aftershocks have right lateral strike slip solutions with strike direction parallel to the submerged branches of the north anatolian fault

modeling of 3d basin structures for seismic wave simulations based on available information on the target area case study of the osaka basin japan practical procedures for modeling basin structure are proposed one is to construct a smooth 3d basin structure model under and around the target site for low frequency strong motion simulation the other is to make a 1d velocity structure model just under the target site for high frequencies these procedures were applied to the osaka basin japan in which numerous exploration studies were conducted before and after the 1995 hyogoken nanbu kobe earthquake the published results of those explorations in addition to those from our several investigations were compiled to construct the model a two dimensional third order b spline function was used to establish a smooth structure model from available depth data microtremor array observations were used to model the velocities and densities of the sedimentary layer structures a four layer model well explains the dispersion characteristics of rayleigh waves that make up the microtremors by adding a detailed shallow velocity structure to the top of the deeper four layer model adequate site responses for a wide frequency range of ground motions can be obtained this proposed procedure can be used to determine the basement geometry of other sedimentary basins

the pleistocene glaciolacustrine sediments in the belchatow mine central poland endogenic and exogenic controls abstract the quaternary overburden of belchatow outcrop contains five glaciolacustrine units the three most widespread are presented they originated during the advance of the sanian elsterian odranian drenthian and wartanian warthian ice sheets the following lake environments are distinguished lake bottom plain tectonically active subaqueous slope subaqueous fan terminoglacial subaqueous fan and prodelta fan the lakes formed under changing conditions the most significant tectonic activity of the graben took place during the odranian and the lake deposits from this glaciation represent terminoglacial conditions the wartanian lake deposits are the only ones that show a shallow water facies that has not been eroded because it has not been overridden by an ice sheet sedimentation conditions changed during the succeeding glaciations endogenic factors affecting sedimentation i e tectonic activity of the graben complemented some exogenic controls such as the distance from the ice sheet the thermal conditions of the lake and the type of sediment supply tectonics changed the style of deposition so much that the lakes although situated in a lowland area displayed characteristics of deep valleys

intensified monsoon and spatiotemporal changes in precipitation patterns in the nw himalaya during the early mid holocene we have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the spiti valley nw himalaya this site lies in the climatically sensitive winter westerlies and indian summer monsoon ism transitional regime and provides an opportunity to reconstruct the precipitation seasonality and extreme precipitation events that are characterised by intensified erosion the lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid holocene 8 7 6 1 cal ka bp we have identified three stages during the period of lake s existence the stage i 8 7 7 6 cal ka bp is marked by lake establishment stage ii 7 6 6 8 cal ka bp by sustained cooler periods and weakened summer monsoon and stage iii 6 8 6 1 cal ka bp by a shift from colder to warmer climate with stronger ism we have identified several short term cooler periods at ca 8 7 8 5 8 3 and 7 2 6 9 cal ka bp based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca 6 8 cal ka bp that is followed by the onset of the intensified monsoon in the nw himalaya

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

intertropical latitudes and precessional and half precessional cycles a mcintyre and b molfino in their report about the forcing of atlantic equatorial and subpolar millennial cycles by precession suggest that climatic changes in high polar latitudes which are related to heinrich iceberg surges may be caused by events that occur in low latitudes 1 1 this

glacial interglacial variations in carbon cycling revealed by molecular and isotope stratigraphy of lake nkunga mt kenya east africa abstract the lipid content n alkanes n alkanols n alkanoic acids and the 13c values of these lipids were measured in nineteen sediment samples taken from a 21 18 m long core from lake nkunga a high altitude 1820 m a s l freshwater lake situated in the montane rain forest on mt kenya the record spans the early last glacial marine isotope stages 5a to 4 and the late holocene 1030 45 14c yr bp to the present day the intervening hiatus spans the last glacial maximum and the early to mid holocene the molecular biogeochemical results are interpreted in terms of past changes in climate vegetation and atmospheric co2 concentration three different sources of organic matter input were identified from the n alkyl lipids namely terrestrial plants aquatic plants and algae unusual distribution patterns of dominant mid chain length n alkanes c23 25 n alkanols c22 24 and n alkanoic acids c22 24 are attributed to aquatic macrophytes an 11 decrease in bulk carbon isotope values between the sediments of early glacial 17 and late holocene age 28 is also apparent in the individual homologues of the n alkyl lipids the observed isotopic shift in terrestrial higher plant biomarkers is similar to that observed in nearby sacred lake and is consistent with an expansion of c4 grasses or sedges during the early glacial the corresponding vegetation was a dry montane juniper olive forest with a grassy understorey representing cold dry conditions with lower co2

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

tropical sea surface temperatures during the last glacial period a view based on alkenones in indian ocean sediments abstract the quantification of tropical temperatures during the last glacial cycle 0 150 kyr bp is a controversial issue since different proxies seem to provide conflicting informations to obtain a complementary point of view we use the alkenone method to estimate sea surface temperatures and focus our work on deep sea sediments recovered from the tropical indian ocean we present alkenone data obtained in two cores which cover in detail the last deglaciation and in about twenty cores distributed between 20 s and 20 n that were chosen to evaluate the temperature contrast of the last glacial interglacial transition our results indicate that indian ocean tropical temperatures remained an average within 1 5 2 5 c of their present values during the last glaciation at 10 n the last deglaciation is characterized by two warming steps which is similar to the classical deglacial chronology observed in the north atlantic area at 20 s the deglacial warming occurred at ca 15 cal kyr bp lagging significantly 5 4 kyr behind the antarctic warming but in phase with northern hemisphere time series

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

three dimensional topography of the sediment basement interface in the tokyo metropolitan area central japan abstract an extensive seismic refraction experiment was conducted in the tokyo metropolitan area central japan to reveal the three dimensional basin structure in this area sixty three explosions were fired over 14 years and more than 2000 travel times were picked for several phases for our inversion the basement is divided into two homogeneous regions where the sediment is assumed to be of uniform velocity the interface separating the sediment and basement is then parameterized by bi cubic b splines and a smoothness constraint is imposed to avoid oscillatory artifacts in the solution the relative weight of the constraint to data residuals is determined by minimizing akaike9s bayesian information criterion about 1500 travel times of refracted p waves are inverted tomographically and the interface shape determined agrees well with the results of other geophysical surveys such as borehole measurements and gravimetric observations the basement velocities in the northern and southern regions are 5 7 and 5 4 km sec respectively previous two dimensional analyses suggested there is a 4 5 km sec layer in the uppermost part of the southern basement but we ignore it for simplicity so that estimated depths are likely underestimated by 1 2 km in the southern region nevertheless this study provides the first detailed image of the basin structure in the area which will help strong motion and earthquake hazard studies as additional constraints

reconstruction of a subalpine grass dominated ecosystem lake rutundu mount kenya a novel multi proxy approach palaeoecological reconstructions based on a single proxy are limited but by combining pollen biogeochemistry and grass cuticle analysis ecosystem structure and function can be better understood lake rutundu is a small subalpine lake on the northeast flank of mt kenya during the last glacial pollen evidence suggests a shrub grassland dominated by afroalpine taxa and poaceae representing a dry cold open environment the 13c values of terrestrial biomarkers imply a high proportion of c4 plants grass cuticle analysis allows resolution of the different c4 subtypes and shows that the vegetation was dominated by tall c4 panicoid grasses prone to frequent fires during the holocene poaceae pollen declined while subalpine shrubs increased the 13c values of terrestrial biomarkers imply a c3 dominated vegetation together with an expansion of rainforest at lower altitudes this suggests wetter conditions more favourable to c3 plants increased percentages of c3 pooid grass cuticles confirm a reduction in moisture stress

ams 14c chronology of 40 0 cal ka bp continuous deposits from a crater lake lake massoko tanzania abstract lake massoko tanzania 8 20 s 33 45 e 870 m a s l is a freshwater maar lake belonging to the rungwe volcanic area 15 km northwest of the livingstone mountains and lake malawi the rainfall regime is driven by the yearly oscillation of the intertropical convergence zone which determines a wet summer and a dry and windy winter the presence of lake malawi to the south and high ranges to the north result in a higher annual precipitation than that observed at a regional scale air masses overloaded with humidity bypassing lake malawi are submitted to ascending currents producing rainfall up to 2400 mm yr 1 in the lake massoko area important exchanges between the lake and groundwater reservoirs have been demonstrated from hydrological and isotopic balances of lake massoko on a regional scale these exchanges are superimposed on groundwater circulation the hydrological setting of lake massoko is also influenced by the tectonics of the region dominated by the northwest southeast tilt of tectonic blocks the sedimentary sequences of lake massoko cored in 1995 and 1996 under the eec project rukwa rukwa project final report 1997 likely register the palaeoenvironmental changes on the catchment the sediment record is nearly continuous due to the near constant high water level of the lake in contrast with many other lacustrine sequences in which reduced deposition rates discrepancies and or gaps characterise arid periods such as the last glacial maximum and the younger dryas event all the ams 14c dates on authigenic organic samples fit with the stratigraphy and the palaoenvironmental record of lake massoko exhibits a constant mean sedimentation rate of 0 628 mm yr 1 for the last ca 40 cal ka bp

water level fluctuations of lake tanganyika in phase with oceanic changes during the last glaciation and deglaciation there has been considerable controversy about the magnitude of fluctuations of the levels of lake tanganyika the earth s second deepest lake 1 470 m following the discovery of submerged valleys extending down to 550 m below present lake levels1 these fluctuations register changes in the precipitation evaporation evapotranspiration ratio in a large equatorial tropical area of catchment south of the equator here we report new palaeohydrological data back to 40 kyr bp from carbon dating of the total organic matter in two diatomaceous cores the results constrain the vertical lake level fluctuations more than has hitherto been possible2 5 and show that the fluctuations from 26 kyr bp are correlated with changes in global sea level and ice volume surpris ingly fluctuations seem to be in phase with those of the african lakes north of the equator which are clearly linked to the milankovitch mechanisms

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

timing of the younger dryas event in east africa from lake level changes the last deglaciation was interrupted by an abrupt cooling event the younger dryas at 11 000 ndash 10 000 yr bp uncalibrated radiocarbon timescale 1 originally recognized in climate records from northwest europe the younger dryas has now been identified in marine and ice core records worldwide2 6 in the tropics a broadly contemporaneous change in climate is recorded by decreases in water levels and increased salinity of lakes7 9 14 indicating a period of arid climate caused by a reduction in ocean to land moisture flux the exact timing of these changes in relation to the younger dryas event in high latitude records has remained unclear however here we present climate records based on analyses of diatom assemblages geochemistry and magnetic mineralogy of radiocarbon dated sequences of laminated lake sediments from lake magadi in the east african rift these records provide a detailed record of climate change in lowland equatorial africa throughout the last deglaciation 12 800 ndash 10 000 14c yr bp we find that lake level and humidity maxima coincide with the most rapid phases of ice melting in the northern hemisphere and that the climate changes including the younger dryas event were synchronous at low and high latitudes thus the effects of abrupt climate change appear to be felt at both high and low latitudes without a significant time lag

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

seasonal controls on sediment transport and deposition in lake ohau south island new zealand implications for a high resolution holocene palaeoclimate reconstruction laminated sediments in lake ohau mackenzie basin new zealand offer a potential high resolution climate record for the past 17 kyr such records are particularly important due to the relative paucity of detailed palaeoclimate data from the southern hemisphere mid latitudes this paper presents outcomes of a study of the sedimentation processes of this temperate lake setting hydrometeorological limnological and sedimentological data were collected over a 14 month period between 2011 and 2013 these data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin wide scale sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy in contrast seasonal change in the lake system controls accumulation of light winter and dark summer laminations at the distal end of the lake resulting in the preservation of varves this study documents the key processes influencing sediment deposition throughout lake ohau and provides fundamental data for generating a high resolution palaeoclimate record from this temperate lake

the palaeolimnology of northern lake malawi over the last 25 ka based upon the elemental and stable isotopic composition of sedimentary organic matter abstract sediments accumulating in offshore areas of northern lake malawi typically contain 1 4 organic carbon this organic matter om is of mainly phytoplankton origin with varying mixtures of terrestrial and degraded reworked material high resolution stable carbon and nitrogen isotopic elemental and rock eval pyrolysis analyses of the bulk om contained in three cores have been used to characterise the om and provide detailed insights into the palaeolimnology and palaeoclimatology of northern lake malawi over the last 25 ka preservation of the om as reflected by its rock eval hydrogen index hi is highly variable periods characterised by notably low hi 15 n during the mid and late holocene suggest intervals of stable stratification due to significantly reduced wind driven mixing in the northern part of the lake when n fixing cyanophytes formed a major component of the phytoplankton the geochemical data support recent suggestions of lowstand conditions in lake malawi at the time of the lgm and provide additional evidence of periods of intense but localised aridity in the terminal pleistocene earliest holocene and at the time of the little ice age the change in mixing regime at ca 11 8 ka seems to have been the result of a radical reorganisation of the dominant surface wind flow over south eastern africa the transition was within the resolution of currently available chronologies apparently contemporaneous with marked changes in the circulation patterns of adjacent oceans and the climate of more distant parts of the northern hemisphere

the sensitivity of a tanzanian crater lake to catastrophic tephra input and four millennia of climate change diatom genera in many large east african lakes change little throughout the holocene period suggesting relatively stable ecological conditions and some resilience to environmental change ecosystem stability is less common in smaller more sensitive lakes such as those within volcanic craters where external impacts can cause abrupt and rapid fluctuations a 4100 year diatom and cyanobacteria pigment record from lake massoko a volcanic crater lake in southern tanzania is used to illustrate important switches in resource ratios following tephra deposition 1190 years ago it is hypothesized that the tephra reduced the rate of p diffusion from the sediments and increased the si p ratio in the lake a period of acute change in planktonic diatom communities resulted from the tephra impact and lasted c 110 years the magnitude of the change shown by the diatoms and their slow recovery from the tephra may be due in part to a coincident fall in lake level caused by a reduction in regional rainfall the statistical significance of the tephra impact relative to that of catchment and climate change has been tested using variance partitioning and rate of change analysis multiproxy indicators show an important period of positive water balance 1700 ago and a relatively dry episode persisting between 1000 and 400 years ago the lake ecosystem is shown to be highly sensitive to both climate change and tephra deposition

sedimentation in chilko lake a record of the geomorphic environment of the eastern coast mountains of british columbia canada abstract chilko lake is the largest and deepest lake draining the coast mountains of british columbia a sedimentary record from the 60 km long lake was constructed by using 3 5 khz subbottom acoustic profiles and short cores of surface sediments sediment accumulation since deglaciation is remarkably thin averaging less than 10 m except in the central deep part of the lake despite extensive activity of holocene and modern glaciers in the 1960 km 2 contributing watershed sediment focusing of silts and clays in the main part of the lake occurs mainly by overflow interflow processes from the edmond and nine mile deschamps drainages sandy turbidites from these drainages and other smaller streams however extend for several kilometers into the lake basin distinct laminae in short cores from the central lake suggest that modern rates of deposition reach a maximum of 2 2 mm a 1 210 pb dating and inferences from the acoustic results however indicate a lake wide long term average rate of less than 1 mm a 1 which is equivalent to a specific sediment yield of about 80 t km 2 a 1 this specific yield is amongst the lowest for glacier fed lakes of the southern canadian cordillera a low sediment supply can be related to three factors 1 a much drier climate on the leeward side of the coast mountains producing lower specific discharges 2 fewer autumn rainstorms that affect mainly lakes west of the coast mountains and 3 opportunities for storage of sediment in the lower 20 km of edmond river which drains the most heavily glacierized portion of the watershed

lacustrine sedimentation in a monsoon environment the record from phewa tal middle mountain region of nepal abstract a watershed scale approach to the sedimentary environment of the phewa tal drainage basin is used to assess rates and patterns of sediment accumulation within phewa tal reservoir the susceptibility of surficial materials to erosion and transportation is highest in the early part of the monsoon season but major erosional events also occur during the monsoon proper thus sediment delivery to the reservoir is at least two orders of magnitude higher during the monsoon than the dry season in the reservoir suspended sediment is distributed mainly by interflows at 4 to 6 m and 8 to 12 m depth phewa tal has four distinct sedimentary environments as interpreted from the sedimentary record in cores 1 the deltaic environment which receives sediment directly from the main inflowing stream the harpan khola and from up valley wetlands and agricultural fields experiences rates of sedimentation of up to 1 m a 1 2 the delta proximal region where clearly varved sediments are deposited in response to the annual monsoon has a mean rate of sedimentation is 23 5 mm a 1 3 the distal environment is beyond the influence of sediment charged interflows and is characterised by accumulation from suspension to form largely massive deposits so that annual rates of sedimentation cannot be determined stratigraphically 4 the region near the pardi dam is dominated by seasonal flushing and erosion of fine sediments during the monsoon the sedimentary record documents the geomorphic processes of the drainage basin especially as controlled by the monsoon and indicates the impact of human occupance in the drainage basin in the twentieth century the useable life of the reservoir is estimated as 360 years

a revised 30 000 year paleoclimatic and paleohydrologic history of lake albert east africa abstract new geochemical and palynological data and a sedimentological reinterpretation of two cores from lake albert allow a revision of the paleoclimatic and paleohydrologic history of northwest uganda over the last 30 000 14 c yr bp our findings document one and possibly three periods of significantly reduced inflow to the nile river system from the white nile based on sediment fabric and mineralogy shifts in percentages of total organic carbon toc and total organic nitrogen ton hydrogen index hi and 13 c and 15 n as well as poor preservation of sporopollenin and siliceous microfossils we recognize two mature paleosols that formed between 18 000 and 12 500 14 c yr bp at the surface of exposed lacustrine muds a thin fossiliferous zone between the two soils documents a brief period of flooding lake albert was below the level of the coring site and thus a closed basin for several thousand years during the late pleistocene around 12 500 14 c yr bp the younger vertisol was flooded by a major rise in lake level relatively deep water conditions were established soon after this transgression but an apparent change in sedimentation rate sometime between 8 000 and 3 400 14 c yr bp may reflect another briefer period of low water which resulted in interruption of sedimentation at the coring site palynological data document a rapid and abrupt shift to drier conditions around lake albert from 11 400 to 9 900 14 c yr bp coincident with the cool younger dryas event of the northern hemisphere geochemical evidence suggests that throughout the terminal pleistocene and early holocene and again in the late holocene the water column was relatively well mixed with little tendency to persistent anoxia

an overview of local site effects and the associated building damage in adapazari during the 17 august 1999 izmit earthquake two major earthquakes occurred in turkey along the north anatolian fault in 1999 the first one which occurred on 17 august 1999 had a moment magnitude of 7 4 and ruptured the 140 km segment of the fault in the marmara region adapazari a city with a population of 190 000 which is mostly located on a deep alluvial basin in the near field of the ruptured fault was among the worst affected urban areas in the earthquake affected region the distribution of damage over the city was highly nonuniform indicating the variability of the ground response to the strong motion five to six story buildings located over deep alluvial soils were most adversely affected by the earthquake geotechnical characteristics of the alluvial basin of adapazari are evaluated using the deep and shallow borehole logs and the measured parameters from the field and laboratory this data is used for developing representative one dimensional site response models for various depths of alluvium and for liquefaction assessment in saturated surface soils recorded data from several aftershocks are utilized for model calibration the results of soil response studies are found to be highly correlated with the general trends in the intensity and distribution of building damage based on in situ tests soil liquefaction is determined to have occurred extensively in adapazari which is in conformity with the postearthquake observations of widespread liquefaction induced foundation displacements evidently liquefied soil layers served as passive isolation mechanism for numerous buildings some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage manuscript received 30 august 2000

late pleistocene desiccation of lake victoria and rapid evolution of cichlid fishes lake victoria is the largest lake in africa and harbors more than 300 endemic species of haplochromine cichlid fish seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the late pleistocene before 12 400 carbon 14 years before the present these results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid

a high resolution paleoclimate record spanning the past 25 000 years in southern east africa high resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern lake malawi provide a climate signal for this part of tropical africa spanning the past 25 000 years the biogenic silica mass accumulation rate was low during the relatively dry late pleistocene when the river flux of silica to the lake was suppressed millennial scale fluctuations due to upwelling intensity in the late pleistocene climate of the lake malawi basin appear to have been closely linked to the northern hemisphere climate until 11 thousand years ago relatively cold conditions in the northern hemisphere coincided with more frequent north winds over the malawi basin perhaps resulting from a more southward migration of the intertropical convergence zone

sediment budget to assess the geomorphic effect of a cyclonic storm new zealand abstract a short term sediment budget was constructed to assess the erosion response of a soft rock hill country watershed to an intense rainstorm event the watershed is located in a landslide prone area on the east coast of the north island new zealand during march 1988 753 mm of rain was recorded over a four day period with 320 mm and 329 mm on successive days known as cyclone bola this was the largest rainstorm event in the tutira watershed in the 93 year rainfall record the budget quantifies the total sediment generated during the storm the relative contribution of erosion processes involved the amount of sediment held in storage and the amount discharged into two lakes within the watershed a landform map of the watershed was constructed and the contribution of each landform type to the total budget was calculated a total of 1 35 0 13 million m3 of sediment was generated during the storm at an average of 420 m3 ha this is equivalent to a denudation value of 42 mm for the total watershed 3208 ha and 83 mm for the landforms severely affected by landsliding 1427 ha of the sediment generated 21 remained on hillslopes 22 was deposited on valley floors 51 was deposited on the lakebeds and the remaining 6 was discharged from the watershed via the lake outlet most of the sediment generated during the storm was from primary source areas on hill slopes with sediment in secondary storage providing only a small contribution landslide erosion was the main process accounting for 89 of the sediment generated channel tunnel gully and sheet erosion were only minor contributors to the budget six hillslope landforms which occupy only 44 of the watershed generated 90 of the sediment the results of this sediment budget when put in context with the storm magnitude frequency history being analysed from lake cores contribute to the identification of sustainable land use and management of soft rock hill country

palaeomagnetic study of the holocene and upper pleistocene sediments from lake barombi mbo cameroun first results abstract the analyses of the stable deposition and post depositional remanent magnetization carried by the lacustrine sediments contained in a 24 m sequence collected from the bottom of the maar lake barombi mbo cameroun yield well defined declination and inclination oscillations which can be attributed to palaeosecular variations of the local geomagnetic field the transformation to a time scale based on the interpolation and extrapolation of 14 c ages allows comparison of this record with contemporaneous records obtained in other parts of the world the successive inclination peaks can be individually identified with those found in western europe in spite of small chronological discrepancies which are in the range of the standard deviation of the ages normalization of the nrms by anhysteretic magnetization provides a profile of relative palaeointensities which shows similarities with that reconstructed from the same time interval in a sequence from western europe although an important phase shift appears

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

site specific issues for strong ground motions during the kocaeli turkey earthquake of 17 august 1999 as inferred from array observations of microtremors and aftershocks array observations of microtremors and aftershocks were carried out near the permanent strong motion observation sites and the damaged areas after the kocaeli turkey earthquake of 17 august 1999 the major objectives were to determine s wave velocity structures at the sites and to understand the site effects on strong motion or damage array observation of microtremors is a useful method for determining the s wave velocity structures in a sedimentary basin with less practical restriction than the other geotechnical methods the spatial autocorrelation method spac was applied to array data of microtremors for determining s wave velocity structures the spac method generally provides an equivalent result with that of the frequency wavenumber method using fewer array sites and a smaller array size most strong motion sites near the fault are classified into stiff and or very hard soils the records cannot directly be used for interpreting damage to buildings in the sedimentary basin records of long durations of strong motion at ats near avcilar west of istanbul are closely related to the low velocity v s 200 m sec of the surface layers the s wave velocity structure at avcilar where there was severe damage during the mainshock is similar to that of the lowland ats and it differs significantly from that of cna located 4 km northeast of avcilar where the strong motion record was obtained from the mainshock the strong ground motion at avcilar during the mainshock is estimated to be similar to that at ats of the strong motion sites sakarya skr is located on very hard soil whereas thick and soft sediments cover downtown adapazari it is plausible that strong ground motions during the mainshock in the damaged area adc were significantly different from those of skr a large difference between the strong motions of a hillside and the lzmit bay area in and around golcuk is also indicated by a comparison of aftershock records

nonlinear site response at kik net kmmh16 mashiki and heavily damaged sites during the 2016 mw 7 1 kumamoto earthquake japan abstract damage from severe ground motion occurred in the downtown area of mashiki in the kumamoto prefecture during the 2016 kumamoto earthquake japan such damage was heavy in the center of the downtown area nonlinear site responses for the first shock and mainshock which occurred on 14 and 16 april 2016 respectively are important factors that explain why the area was heavily damaged we analyzed soil nonlinearity using surface and borehole records obtained from the kik net kmmh16 mashiki station from our analysis we found that s wave velocity models clearly depended on the amplitude of input ground motion we estimated the strain dependent shear stiffness and damping ratio to explain this s wave velocity dependence we conducted equivalent linear analyses at the kmmh16 site based on a nonlinear model from these analyses we concluded that our synthetic surface ground motions agreed well with the observed ones especially for the s wave amplitudes and phases of the first shock and mainshock noted above in addition we performed the same analyses at the tmp3 site which was actually located within one of the heavily damaged zones the synthetic motions here also agreed with the observed ones with differences in spectral accelerations being well explained by our analyses our results indicated that soil nonlinearity played a major role in causing the difference of ground motions thus leading to the heavily damaged zone in the downtown area of mashiki

field dependence of ac susceptibility in titanomagnetites abstract ac susceptibility measurements as a function of field amplitude hac and of frequency show a strong field dependence for a set of synthetic titanomagnetites fe3 xtixo4 and for certain basalts from the soh 1 hawaiian drill hole and from iceland in phase susceptibility is constant below fields of about 10 100 a m and then increases by as much as a factor of two as hac is increased to 2000 a m both the initial field independent susceptibilities and the field dependence of susceptibility are systematically related to composition initial susceptibility is 3 si for a single crystal sphere of tm0 x 0 and decreases with increasing titanium content field dependence is nearly zero for tm0 and increases systematically to a maximum near tm60 x 0 6 this field dependence can in some cases be mistaken for frequency dependence and lead to incorrect interpretations of magnetic grain size and composition when titanomagnetite is present

climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania the interactions between climatic and volcanic forcing on diatom communities contained in a 50 000 year sedimentary sequence from lake massoko tanzania were examined at the century scale 19 discrete tephra inputs to the lake isolated the sedimentary nutrient supply and shifted the diatom communities to those tolerant of low phosphorus levels whereas at the millennial scale diatom inferred shifts in precipitation evaporation based on conductivity optima and diatom life form ratios were broadly similar to lake level reconstructions from lake rukwa lake malawi and others in the region some fluctuations of lake massoko are consistent with the precession driven changes in insolation but the major climate shifts do not relate directly to orbital forcing of summer insolation south of the equator and show more consistency with records from the equatorial and northern tropics that receive rainfall from the passing of the intertropical convergence zone sea surface temperatures are strongly correlated to multimillennial scale climate patterns over this region of africa

a biomass burning record from the west equatorial pacific over the last 360 ky methodological climatic and anthropic implications abstract to reconstruct past fire activity in the west pacific east asian region we investigate a 360 ky pelagic sedimentary record from the caroline basin in the western pacific warm pool wpwp core md97 2140 2547 m water depth in the lack of standard protocol and terminology for the determination of combustion derived products in sedimentary archives three proxies were compared with other paleoceanographic proxies oxidation resistant elemental carbon orec black carbon bc and microcharcoal the mineral caco3 and organic carbon corg records of core md97 2140 generally covary with the oxygen isotope record suggesting that glacial interglacial changes in ice volume and sea level control the preservation of caco3 and terrigeneous inputs of corg in the deep sea sediments of the caroline basin the changes in orec are primarily connected to the changes in corg record in contrast the bc and charcoal records which better reflect the input of biomass burning products are tightly connected with changes in the precession band 23 ky likely through low latitude atmospheric circulation patterns a peculiar control by the competing influence of the long term el nino southern oscillation enso like forcing and the glacial interglacial cycle on the east asian summer monsoon 30 19 11 and 6 ky periods is suggested in addition large increases in bc and charcoal are observed between ca 53 43 and 12 10 ky bp these events strikingly correspond to the main late pleistocene and early holocene periods of human colonization in the region likely suggesting an additional anthropic impact on the fire activity

sediments of ice dammed self draining ape lake british columbia the glacier damming ape lake has withdrawn from its neoglacial terminal moraines in the lake since early in this century at an average rate of 15 m a as a result the first known drainings of ape lake occurred in october 1984 and august 1986 in each event about 54 of the volume of the lake was lost through a tunnel in the damming glacier most of the remaining water was held in the deep basin of the lake behind partially breached neoglacial terminal moraines as the glaciers have withdrawn the character of the sediments has changed sediments in the deep basin of the lake are varved but the grain size especially of the summer deposits has decreased and rates of sedimentation have decreased from about 4 mm a to less than 2 mm a in shallow water deposition of varved sediments has given way to the deposition of massive sediments at rates of less than 1 mm a ice rafted debris is rare in deep water despite the presence of calving bergs during and following the first draining significant subaerial

rupture process of the 1999 kocaeli turkey earthquake estimated from strong motion waveforms the multiple time window linear waveform inversion is applied to study the source process of the 1999 kocaeli turkey earthquake using strong motion data two peculiar observations characterize this event the first one is a conflicting observation of the long surface ruptures and short source duration resulting from the observed strong motion waveforms the second is an anomalously short s p time observed at a station skr considering its hypocentral distance a supershear rupture propagation ellsworth and celebi 1999 and the p wave triggering of an asperity anderson et al 2000 were both proposed to explain the record at skr our waveform inversion study is aimed to examine these possibilities in order to clarify the relation between the spatial distribution of the surface ruptures and coseismic slips we divide the assumed fault plane into three parts and look for the first time window front propagation velocity propagation velocity of triggering front of the first time window at each subfault in each part by performing numerous inversions changing the first time window front propagation velocity separately in each part and selecting the best first time window propagation velocities that give largest variance reduction at the same time appropriate smoothness of spatiotemporal slip distribution is searched for by performing inversions with different strength of smoothing constraints against the observational equations and judging the relative appropriateness of inversion results in terms of the akaike s bayesian information criterion the best source model is characterized by an asperity that is about 35 km east of the epicenter and near a segment boundary at sapanca lake triggered by the first time window front with 5 8 km sec close to p wave velocity the time progression of the rupture suggests a scenario where a p wave arriving from the hypocenter or somewhere around the hypocenter triggered the second largest asperity near the junction of the segments at sapanca lake which is a preferable interpretation the first time window propagation velocities west of the hypocenter and east of skr are expected to be 3 0 km sec manuscript received 20 august 2000

environmental assessment from the sedimentary record of high latitude fiords the sedimentary record of fiords at high latitude where global change may be occurring earliest and will be greatest has the potential for assessment of environmental change at both low resolution the scale of millennia and high resolution decadal to less than daily unlike the lacustrine record which has been used very successfully in these studies the sedimentary processes and thus the sedimentary deposits of fiords differ 1 in the role of salt water in inhibiting mixing and promoting flocculation and through the role of sea ice 2 in the exchange of mass and energy with the much larger ocean beyond and 3 in the role of benthic biota in the sedimentary environment the work reviewed in this paper shows that fiord sediments are being used to assess sedimentary and oceanic processes as well as glacial periglacial and geomorphic history and that they are important proxies for long term climate and hydrology recommendations for advancing this work include long term monitoring of conditions in fiords and their drainage basins so that the transfer relations can be more solidly constructed from the proxy of fiord sediment integration of results from fiords in opposite polar latitudes and among proxies especially from lacustrine and ice core records will produce valuable insights assessment of the range of conditions in fiords from the most polar to temperate regions is important to building models of their processes and understanding of the paleoenvironmental signals that can be interpreted from each type

sedimentation in a deep glacier fed lake lake tekapo new zealand surface sediments cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in lake tekapo sedimentation is dominated by the godley river which forms an extensive delta in the northern third of the lake delta growth accounts for 55 of annual sediment deposition in winter sandy muds are deposited at the top of the delta slope where they may move under gravity as a surficial slide oversteepening of the upper slope also generates deep seated failures the entire 20 km2 of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment down the delta slope sedimentation rates decrease surface sediments get finer and varves become better developed in the lake basin sediments are parallel bedded varves which contain typical winter summer annual cycles as well as minor non annual flood varves annual varve thickness and semi annual varve frequency are determined by variations in the discharge of the godley river sedimentation in the basin accounts for 40 of the budget and sedimentation rates decrease with distance from the delta except at the distal end of the basin where turbid underflows are stopped by the rising lake floor beyond the basin sedimentation rates decrease abruptly coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore the remaining 5 of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement which occasionally slumps to the basin floor

modeling of 3d subsurface structure and numerical simulation of strong ground motion in the adapazari basin during the 1999 kocaeli earthquake turkey the 1999 kocaeli izmit earthquake seriously damaged the downtown area of adapazari turkey the wavefield of the strong ground motions is considered to have been affected by the deep ground structure a refraction and reflection seismic survey was made to obtain the velocity structure of the profile in the north south direction across the basin a 3d subsurface model is presented based on results of the refraction and reflection survey on data obtained from a gravity survey and on observations of microseisms and aftershocks the proposed model shows deep sediment with a steep slope beneath downtown adapazari strong ground motions in the frequency range of 0 1 1 0 hz propagating in the subsurface model during the kocaeli earthquake also were simulated numerically by the 3d finite difference method the simulated results show that ground motions in downtown adapazari were larger than those in the area between downtown and the source fault because the former were significantly amplified by the basin edge effect

relative timing of deglacial climate events in antarctica and greenland the last deglaciation was marked by large hemispheric millennial scale climate variations the bolling allerod and younger dryas periods in the north and the antarctic cold reversal in the south a chronology from the high accumulation law dome east antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the antarctic cold reversal did not follow the abrupt warming during the northern bolling transition around 14 500 years ago this result suggests that southern changes are not a direct response to abrupt changes in north atlantic thermohaline circulation as is assumed in the conventional picture of a hemispheric temperature seesaw

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

east african climate change and orbital forcing during the last 175 kyr bp abstract variations in the temporal and spatial distribution of solar radiation caused by orbital changes provide a partial explanation for the observed long term fluctuations in african lake levels the understanding of such relationships is essential for designing climate prediction models for the tropics our assessment of the nature and timing of east african climate change is based on lake level fluctuations of lake naivasha in the central kenya rift 0 55 s 36 20 e inferred from sediment characteristics diatoms authigenic mineral assemblages and 17 single crystal 40ar 39ar age determinations assuming that these fluctuations reflect climate changes the lake naivasha record demonstrates that periods of increased humidity in east africa mainly followed maximum equatorial solar radiation in march or september interestingly the most dramatic change in the naivasha basin occurred as early as 146 kyr bp and the highest lake level was recorded at about 139 133 kyr bp this is consistent with other well dated low latitude climate records but does not correspond to peaks in northern hemisphere summer insolation as the trigger for the ice age cycles the naivasha record therefore provides evidence for low latitude forcing of the ice age climate cycles

catastrophic valley fills record large himalayan earthquakes pokhara nepal abstract uncertain timing and magnitudes of past mega earthquakes continue to confound seismic risk appraisals in the himalayas telltale traces of surface ruptures are rare while fault trenches document several events at best so that additional proxies of strong ground motion are needed to complement the paleoseismological record we study nepal s pokhara basin which has the largest and most extensively dated archive of earthquake triggered valley fills in the himalayas these sediments form a 148 km2 fan that issues from the steep seti khola gorge in the annapurna massif invading and plugging 15 tributary valleys with tens of meters of debris and impounding several lakes nearly a dozen new radiocarbon ages corroborate at least three episodes of catastrophic sedimentation on the fan between 700 and 1700 ad coinciding with great earthquakes in 1100 1255 and 1344 ad and emplacing roughly 5 km3 of debris that forms the pokhara formation we offer a first systematic sedimentological study of this formation revealing four lithofacies characterized by thick sequences of mid fan fluvial conglomerates debris flow beds and fan marginal slackwater deposits new geochemical provenance analyses reveal that these upstream dipping deposits of higher himalayan origin contain lenses of locally derived river clasts that mark time gaps between at least three major sediment pulses that buried different parts of the fan the spatial pattern of 14c dates across the fan and the provenance data are key to distinguishing these individual sediment pulses as these are not evident from their sedimentology alone our study demonstrates how geomorphic and sedimentary evidence of catastrophic valley infill can help to independently verify and augment paleoseismological fault trench records of great himalayan earthquakes while offering unparalleled insights into their long term geomorphic impacts on major drainage basins

solar modulation of cosmogenic nuclide production over the last millennium comparison between 14c and 10be records for about the last 30 years it has been recognized that the high frequency component of the tree rings 14c 12c record is dominated by the modulation of the cosmic ray flux by the solar wind in particular it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric 14c 12c during the last millennium other periods of high 14c 12c values were observed but their solar origin is still debatable in the present work we compare these fluctuations with an independent record of cosmogenic 10be measured in ice from the south pole to check the solar origin of the observed 14c 12c variations in order to compare quantitatively the results obtained on 10be and 14c it is necessary to take into account the different behaviour of these two cosmogenic isotopes and especially the damping effect of the carbon cycle in the case of 14c as an input to a 12 box numerical model we used the relative fluctuations of the 10be concentrations record measured in south pole ice and converted it into a synthetic 14c record we took into account the fact that 10be modulation is enhanced in polar regions due to the orientation of the geomagnetic field as expected the fluctuations of the modelled 14c record are much smaller a factor of 20 than those observed for the raw 10be record in addition the variations are smoother and shifted in time by a few decades the 10be based 14c variations closely resemble the 14c measurements obtained on tree rings r 0 81 in particular it is easy to identify periods of maximal 14c 12c which correspond to solar activity minima centred at about 1060 1320 wolf 1500 sporer 1690 maunder and 1820 dalton yr a d cross correlation calculations suggest that there is no significant lag between the 10be based 14c and the tree ring 14c records our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium

millennial scale dynamics of the east asian winter monsoon during the last 200 000 years the primary productivity dynamics of the last 200 000 years in the sulu sea was reconstructed using the abundance of the coccolithophore florisphaera profunda in the images md97 2141 core we find that primary productivity was enhanced during glacial periods which we suggest is due to a stronger east asian winter monsoon during the last 80 kyr eight significant increases in primary productivity pp in the sulu sea are similar to east asian winter monsoon changes recorded in chinese loess the pp maxima are not linked with heinrich events he in the north atlantic although four pp peaks are synchronous with he the pp oscillations have frequencies near those of the dansgaard oeschger cycles in northern hemisphere ice records and indicate a teleconnection of the east asian winter monsoon with greenland climate in this sulu sea record the east asian winter monsoon oscillates with periodicities of6 4 2 3 4 2 3 and 1 5 kyr in particular the 1 5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the holocene without any ice volume modulation this stationarity suggests that the 1 5 kyr cycle is not driven by some high latitude forcing

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

possible connection between surface winds solar activity and the earth s magnetic field records of 14c in tree rings provide a proxy for changes in solar activity on timescales of decades to centuries1 2 here i report an association between maunder type solar cycles recorded in tree rings and fluctuations in surface wind intensity on a roughly 200 year timescale over a period of about 2 000 years in the mid holocene the wind record is preserved as changes in the thickness of varved sediments in elk lake minnesota which contain a large aeolian component changes in cyclonic activity and tropospheric winds have been reported1 5 to occur in this region a few days after strong coronal mass ejections cmes increases of up to 7 in zonal flow have been reported5 at an altitude of 300 m after strong cmes in winter the implication of this association is that century scale changes in surface winds over minnesota were the long term maunder scale counterpart of short term daily changes in winds after cmes the weak magnetic field strength of the earth at this time6 7 might be relevant to a possible mechanism for the association

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

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

shear wave velocity structure of the izmit bay area turkey estimated from active passive array surface wave and single station microtremor methods summary to provide quantitative information on the shear wave velocity structure of the izmit bay area we conduct active passive array surface wave and single station microtremor measurements at 60 sites we process these array measurements to produce combined rayleigh wave dispersion curves that span a broad frequency range 0 5 20 hz we also make use of horizontal to vertical spectral ratio hvsr curves obtained from the single station microtremor measurements to benefit from their close relation to the ellipticity of rayleigh waves using the dispersion curve sensitivity to the absolute velocities and the shape of the hvsr curve sensitivity to the velocity contrasts of the velocity depth model we have applied a combined inversion technique to derive better constrained shear velocity models at each site the derived shear velocity models are used to provide a vs30 site classification map and information on the sediment bedrock structure for the izmit bay area the vs30 map shows that the entire shoreline regions including artificial infill areas of the izmit bay have vs30 values less than 200 m s 1 locally as low as 80 m s 1 the older sediment areas of the izmit basin have vs30 values ranging between 250 and 350 m s 1 the highest vs30 values are associated with rock sites reaching about 950 1300 m s 1 we also present a high correlation between the vs30 values and the phase velocity of rayleigh wave corresponding to the 40 m wavelength c40 the important implication of this correlation is that vs30 may be estimated from c40 without inverting the dispersion curve the inferred sediment bedrock interface along a cross section shows an antisymmetric v shaped basin with a sedimentary cover thickness reaching about 1200 m at the deepest part of the izmit basin this deepest part coincides in the map view where the north anatolian fault zone crosses the basin in the east west direction the sedimentary cover thickness is found to be 750 m in the golcuk derince basin

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

centennial to millennial changes in maar lake deposition during the last 45 000 years in tropical southern africa lake masoko tanzania abstract the masoko maar southern tanzania provides one of the most continuous late quaternary lacustrine sedimentary records from africa a detailed chronostratigraphic framework coupled with sedimentological and magnetic measurements allows us to construct a 30 year resolution continuous sedimentary sequence covering the last 45 000 years and to address local depositional environment and climate variability in the tropical southern africa based on present day observations and measurements our results indicate that the low field magnetic susceptibility of the sediment is highly controlled by climate driven processes wind stress and or lake level amplitude changes acting on the titanomagnetite rich shoreline reservoir the tephra and turbidite free magnetic susceptibility record is strongly modulated by a persistent multi decadal to centennial variability 80 to 200 years probably linked to the gleissberg and suess cycles of solar activity at lower frequency the variability of deposition is controlled by the precessional cycle and its harmonics suggesting a dominant multi millennial forcing of low latitude insolation on climatic changes in tropical southern africa inferred wetter conditions during the last glacial maximum and the younger dryas at masoko 9 s indicate southward shifts of the intertropical convergence zone associated with the north atlantic glacial dynamics and or contrasted hydrological changes in the rungwe highlands compared to the neighbouring areas finally former regional transfer function between diatom assemblages and water chemistry suggested drier conditions during the last glacial maximum at lake masoko barker p williamson d gasse f gibert e 2003 climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania quaternary research 60 368 376 in this context further climate proxy data such as pollen and hydrobiological studies in small deep lakes are needed to support our alternative interpretation of the masoko record

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

development and testing of a 3d seismic velocity model of the po plain sedimentary basin italy abstract we built a 3d seismic model of the po plain and neighboring regions of northern italy covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid we started by collecting an extensive and diverse set of geological and geophysical data including seismic reflection and refraction profiles borehole logs and available geological information major geological boundaries and discontinuities have thus been identified and mapped into the model we used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness seismic wave properties have been assigned to each unit using a rule based system and v p v s and derived from other studies sedimentary strata although with varying levels of compaction and hence material properties may locally reach a thickness of 15 km and give rise to significant effects in seismic wave propagation we have used our new model to compute the seismic response for two recent earthquakes to test its performance results show that the 3d model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments whereas paths outside the basin may be well fit by more homogeneous 1d hard rock structure we conclude that the new model is suited for simulation of wave propagation mostly for t 3 s and may serve well as a constraint for earthquake location and further improvements via body or surface wave inversion

tectonic controls on rift basin morphology evolution of the northern malawi nyasa rift radiometric k ar and ar 40 ar 39 age determinations of volcanic and volcaniclastic rocks combined with structural gravity and seismic reflection data are used to constrain the age of sedimentary strata contained within the seismically and volcanically active northern malawi nyasa rift and to characterize changes in basin and flank morphologies with time faulting and volcanism within the tukuyu karonga basin began at approximately 8 6 ma when sediments were deposited in abroad initially asymmetric lake basin bounded on its northeastern side by a border fault system with minor topographic relief extensions primarily by a slip along the border fault and subsequent regional isostatic compensation led to the development of a 5 km deep basin bounded by broad uplifted flanks along the low relief basin margin opposite border fault younger stratigraphic sequences commonly onlap older wedge shaped sequences although their internal geometry is often progradational intrabasinal faulting flankuplift and basaltic and felsic volcanism from centers at the northern end of the basin became more important at about 2 5 ma when cross rift transfer faults developed to link the tukuyu karonga basin to the rukwa basin local uplift and volcanic construction at the northern end of the basin led to a southeastward shift in the basin s depocenter sequence boundaries are commonly erosional along this low relief hanging wall margin and conformable in the deep lake basin the geometry of stratigraphic sequences and the distribution of the erosion indicate that horizontal and vertical crustal movements both across and along the length of the rift basin led to changes in levels of the lake irrespective of paleoclimatic fluctuations

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas