spatial distribution of intermediate depth earthquakes with horizontal or vertical nodal planes beneath northeastern japan abstract the 1993 kushiro oki off kushiro earthquake m jma 7 8 is one of the largest intermediate depth earthquakes that have occurred in northeastern japan this earthquake is a notable event that has a nearly horizontal fault plane extended from the lower seismic plane of the double planed seismic zone toward the upper seismic plane we have examined the spatial distribution of focal mechanism solutions of deep and intermediate depth earthquakes beneath northeastern japan concerning this peculiar event analyses of 127 new solutions along with existing solutions confirm the previous results on essential features of their spatial distribution the predominant types of solutions are down dip compression in the upper plane except beneath eastern hokkaido and down dip extension in the lower plane p axes in the upper seismic plane and t axes in the lower plane are in the direction of plate convergence beneath hokkaido however t axes show significant deviation from the direction of plate convergence the stress axes beneath the junction between the northeastern japan arc and the kuril arc exhibit slight deviation from those in the adjacent areas suggesting slab distortion beneath the junction we next investigate the spatial distribution of events with horizontal nodal planes as candidates for events with similar focal mechanisms to the kushiro oki earthquake the activity of earthquakes with horizontal nodal planes is definitely high in the lower plane especially beneath hokkaido many of them have similar focal mechanisms to the kushiro oki earthquake indicating that the kushiro oki earthquake is not exceptional but is a typical event in the region however the fault planes of these events are variable in space some events are known to have vertical fault planes there are shallow and deep depth bounds and a southwestern boundary for the events with horizontal fault planes these facts suggest that the horizontal faulting is probably caused by some regional stress concentration owing to the unbending and the distortion of the segmented slab at the junction

spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

coupled micromorphological and stable isotope analysis of quaternary calcrete development pedogenic calcretes are widespread in arid and semi arid regions using calcrete profiles from four river terraces of the rio alias in southeast spain this study explores the potential of using detailed micromorphological and stable isotopic analysis to more fully understand the impacts of quaternary environmental change on calcrete development the four profiles increase in carbonate complexity with progressive age reflecting calcretisation over multiple glacial interglacial cycles since mis 9 c 300 ka calcrete profiles contain a mixture of alpha non biogenic and beta biogenic microfabrics alpha fabrics have higher 13c and 18o values the profiles contain a range of crystal textures but there is little difference between the 13c and 18o values of spar microspar and micrite cements strong positive covariance between 13c and 18o suggests that both isotopes are responding to the same environmental parameter which is inferred to be relative aridity the study reveals that the detailed co analysis of calcrete micromorphology and stable isotope signatures can allow patterns of calcrete formation to be placed into a wider palaeoclimatic context this demonstrates the potential of this technique to more reliably constrain the palaeoenvironmental significance of secondary carbonates in dryland settings where other proxy records may be poorly preserved

plate coupling in the northern south island and southernmost north island new zealand as illuminated by earthquake focal mechanisms subduction of the pacific plate in the northern south island and southernmost north island of new zealand is transitional insofar as the crustal thickness of the pacific plate increases significantly along strike in the northern south island focal mechanisms of 145 events shallower than 100 km in this region have been determined using both first motion polarity data and amplitudes of seismogram envelopes the stress regime in the subducted plate appears to be dominated by slab pull t axes in both the upper and lower planes of the dipping seismic zone generally parallel the local dip of the zone and the average azimuth of these t axes is rotated some 25 clockwise out of the direction of dip of the subducted plate this can be related to the asymmetrical shape of the subducted slab in contrast the stress regime in the overlying plate appears to be dominated by subhorizontal compression low angle thrust events near the plate interface in cook strait and the southernmost north island concentrate in two areas which may mark the updip and downdip edges of a locked region identified from global positioning system gps observations an absence of low angle thrust events near the plate interface in the northern south island and the tendency of p axes of events in the subducted plate to become more horizontal suggest that plate coupling there is stronger than in the southernmost north island differential coupling at the plate interface provides a viable mechanism for producing the large tectonic rotations seen in the northern south island

rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

pleistocene paleosol development and paleoenvironmental dynamics in east africa a multiproxy record from the homo bearing aalat pedostratigraphic succession dandiero basin eritrea abstract the climatic changes during the early middle pleistocene transition are a key to understand the ecosystem dynamics that involved the homo erectus ergaster distribution the aalat pedostratigraphic succession represents a continental archive in the african rift valley eritrea where remains of homo around 1 ma were identified high resolution magnetostratigraphy dated this succession between the base of the jaramillo subchron and the lower brunhes chron despite the present arid desert climate the aalat section records a persistence of water driven fluvio lacustrine environments which suggests a major tectonic control on sedimentation although climate changes are clearly overprinted macro and micromorphological physico chemical mineralogical and geochemical features up to now poorly available for pleistocene paleosols in east africa depict a poor to moderate degree of development although calcic and petrocalcic petrogypsic horizons at different stratigraphic heights indicate phases of geomorphic stability the concurrent alternation of these horizons with iron stained layers suggests cyclical changes from dry to wet conditions which fit well with aeolian dust fluxes and marine isotope stages of glacials and interglacials at higher latitudes stable isotope data are consistent with these climatic cycles and suggest a succession of monsoonal and non monsoonal conditions the homo erectus settlement lasted apparently for a short time span because a long high discharge fluvial sedimentation and or an aridity phase at the base of the fluvial facies could have made the area less suitable for human settling and could have hindered preservation of fossils and artifacts

joint focal mechanism determination with source region station corrections using short period body wave amplitude data abstract we have developed a method that simultaneously determines focal mechanism solutions of many small earthquakes and source region station corrections for short period body wave amplitudes by inverting amplitude data of p sh and sv waves together with p wave polarity data the observed seismic waveform includes the effects of site amplification and attenuation along its ray path in addition to the radiation pattern of earthquake source the amplitude of seismograms at frequencies higher than a few hertz is extremely sensitive to heterogeneous structure near the ground surface consequently we need to know in detail the effects of site amplification and attenuation in order to estimate focal mechanisms by using short period waveforms however at present we do not know the detailed crustal structure with a resolution necessary for this estimation in the present study we assume that p and s wave attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance backazimuth and incident angle based on this assumption we determined focal mechanism solutions of many earthquakes and the coefficients in the function for each station simultaneously by using p sh and sv wave amplitudes and p wave polarities we applied the present method to 170 aftershocks of the 1996 onikobe earthquake m 5 9 which occurred in the central part of northeastern japan we obtained focal mechanism solutions of many microearthquakes whose mechanism solutions could not be determined by using p wave polarity data alone p axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east west direction t axes are on average near vertical at the shallowest depth as the depth approaches 5 km the t axes become horizontal and then gradually become near vertical again

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

do stable isotope data from calcrete record late pleistocene monsoonal climate variation in the thar desert of india late pleistocene terrestrial climate records in india may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete petrography shows that calcrete nodules in quaternary sediments of the thar desert in rajasthan are pedogenic with little evidence for postpedogenic alteration the calcrete occurs in four laterally persistent and one nonpersistent eolian units separated by colluvial gravel thermoluminescence and infrared and green light stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units i iv of ca 70 000 60 000 ca 60 000 55 000 ca 55 000 43 000 and ca 43 000 25 000 yr respectively the youngest eolian unit v is 10 000 yr old and contains no calcrete stable oxygen isotope compositions of calcretes in most of eolian unit i in the upper part of eolian unit iv and in the nonpersistent eolian unit range between 4 6 and 2 1 pdb these values up to 4 4 greater than values from eolian units ii and iii are interpreted as representing nonmonsoonal18o enriched normal continental waters during climatic phases when the monsoon weakened or failed conversely 25 000 60 000 yr old calcretes eolian units ii and iii probably formed under monsoonal conditions the two periods of weakened monsoon are consistent with other paleoclimatic data from india and may represent widespread aridity on the indian subcontinent during isotope stages 2 and 4 the total variation in 13c is 1 7 0 0 1 7 and 13c covaries positively and linearly with 18o 13c values are highest when 18o values indicate the most arid climatic conditions this is best explained by expansion of c4grasses at the expense of c3plants at low latitudes during glacial periods when atmosphericpco2was lowered c4dominance was overridingly influenced by global change in atmosphericpco2despite the lowered summer rainfall

late holocene climate in the lower narmada valley gujarat western india inferred using sedimentary carbon and oxygen isotope ratios we report the late holocene climate and vegetation of the lower narmada valley gujarat western india as inferred from the stable carbon and oxygen isotopic composition 13c and 18o of sediment

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

procedures for computing focal mechanisms from local sv p z data abstract a procedure for calculating the focal mechanism of an earthquake from the distribution of the ratio of the amplitudes of sv to p waves has been developed and tested the input consists of information taken from the hypocenter solution for the earthquake a factor for each station that corrects for the effect of the free surface on the observed wave amplitudes and the observed values of the ratio of the vertical component of p to the vertical component of sv the procedure starts with the selection of a slip direction the program then finds the best fault strike and dip corresponding to that slip direction with best measured by the smallest scatter of the dip for any strike all three fault parameters are then adjusted by an iterative least squares adjustment sv p z is a strongly nonlinear function of the fault parameters so the solution found by the procedure is inherently nonunique the acceptable solutions can be quite well constrained if the slip direction can be estimated initially on the basis of independent information a variety of tests of the procedure have been carried out on real and synthetic data given a set of amplitude data for an earthquake in bear valley california and told only that the mode of slip was predominantly strike slip the program found the san andreas fault i e converged to a fault with strike and dip close to the known values further work on a german earthquake served to bring out some of the ambiguities of the solutions analysis of data from a brief swarm of earthquakes in southwest germany showed that the method yields useful mechanisms for small events and revealed a rotation of the focal mechanisms during the swarm processing of amplitudes from synthetic seismograms gave a fault plane close to the known input but marked disagreement between the sv amplitudes on the synthetic seismograms and the amplitudes predicted by simple dislocation theory is unresolved

depth dependent stress field in and around the atotsugawa fault central japan deduced from microearthquake focal mechanisms evidence for localized aseismic deformation in the downward extension of the fault 1 focal mechanisms have been determined from p wave polarity data as well as body wave amplitudes for 154 microearthquakes that occurred around the atotsugawa fault in central japan between 2002 and 2004 while we found many microearthquakes with a pure strike slip mechanism that is similar to the faulting style of the atotsugawa fault a considerable number of microearthquakes with reverse faulting components are also occurring most of the p axes are horizontal and oriented in the wnw ese direction which conforms to the general tectonic trend in this area in contrast the t axes have a wide range of plunge suggesting that reverse faulting type earthquakes as well as strike slip ones are occurring the most conspicuous feature in the focal mechanism distribution is the depth dependence where shallow earthquakes are primarily reverse faulting and strike slip earthquakes become predominant with depth a stress tensor inversion reveals that the shallower part is characterized by a mixture of reverse and strike slip faulting regimes and that a pure strike slip faulting regime appears only around the bottom of the seismogenic zone together with other geophysical observational evidence for the fault we suggest that the existence of a localized aseismic deformation below the atotsugawa fault is the simplest scenario that can explain the observed stress fields this scenario provides a stress accumulation mechanism of disastrous shallow inland earthquakes in which the localized aseismic deformation accumulates stress onto the fault plane in the seismogenic zone during an earthquake cycle and the main shock would occur when the failure stress is reached on the fault

distinct s wave reflector in the midcrust beneath nikko shirane volcano in the northeastern japan arc distinct s waves reflected from a midcrustal seismic velocity discontinuity are detected beneath nikko shirane volcano in the southernmost part of the northeastern japan arc a detailed travel time analysis of the reflected s waves by using data acquired through a dense seismic network temporarily set up in this region shows that this unusual s wave reflector is distributed over an area of 15 15 km2 at depths ranging from 8 to 15 km the reflector has a conical shape becoming shallow toward the summit of nikko shirane volcano observed amplitude spectral ratios of reflected s waves to direct s waves show that the reflector body has a strong velocity contrast to the surrounding medium and its thickness is of the order of 100 m at most the reflector body is approximated by two thin layers probably filled with partially molten materials cutoff depth for shallow seismicity in this area is 3 5 km above the reflector and becomes shallow toward nikko shirane volcano nearly parallel to the reflector the depth to brittle ductile transition zone seems to be prescribed by the existence of the reflector body which is perhaps a thin magma body

geochemistry of calcretes calcic palaeosols and hardpan coimbatore southern india formation and paleoenvironment abstract there is no major chemical variation in the late quaternary calcic nodules formed within vertisols in the foot hill regions and hardpan calcretes greater than 200 ka formed over the precambrian substrate that occur as duricrust horizons in the plains around coimbatore region tamil nadu india the bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in cao sio2 al2o3 and fe2o3 content the trend of trace metal content in calcic nodules and in the hardpan calcrete is mn zn ni cr pb co cu and zn mn ni co pb cu cr respectively paas normalised ree data of the calcretes calcic nodules and the hardpan demonstrate a positive euanomaly this could be attributed to feldspar apatite mineral alteration and soil digenetic processes differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in eu the stable isotope values of the calcic nodules do not exhibit a wide range 18o 3 39 to 5 84 and 13c 3 01 to 6 64 compared to the hardpan calcretes 18o 2 91 to 12 98 and 13c 0 05 to 7 4 the palaeoenvironment during the formation of the calcretes nodules was dominated by the c4 plants with sparse vegetation cover and that the parent material bedrock supported a thin veneer of soil column with sparse vegetation cover as present day calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical groundwater processes in arid semi arid conditions over along geological period during the late mis3 to the lgm period the south west monsoon was weak with mean annual rainfall mar between 300 and 500 mm yr the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments

biogenic β fabric features in the hard laminated crusts of the mersin and adana regions southern turkey and the role of soil organisms in the formation of the calcrete profiles abstract this paper describes fabric features and their distribution in the calcretes and emphasizes the role of soil organisms in the formation of the calcrete profiles quaternary calcretes are common in the mersin and adana provinces occurring as powdery nodular tubular fracture infill and various forms of crusts the stable isotope values indicate calcrete development under semi arid climatic conditions and a pedogenic origin biogenic or fabric constituents are abundant in the hard laminated crust these are the rhizoliths alveolar septal structures needle fiber calcites calcified filaments spherical calcite bodies microcodium and vadose calcrete pisoliths rhizoliths have mainly formed by the petrification of roots and often contain cellular cortex structures the alveolar septal structure comprises root voids separated by a micritic wall or a bundle of tangentially oriented calcite needles needle fiber calcite is common in the hard laminated crust as monocrystalline rods and polycrystalline needles monocrystalline rods are smooth and small

depth dependent change in the focal mechanism of shallow earthquakes implications for brittle plastic transition in a seismogenic region an analysis is conducted of the focal mechanism solutions of 2150 shallow earthquakes that have occurred in the central part in the kinki district japan it is found that in regions shallower than the characteristic depth the depth at which the frequency depth distribution of earthquakes is maximum t axis plunges are widely distributed in the horizontal and vertical directions furthermore the distribution of the plunges does not change with depth in the region in regions deeper than the characteristic depth the plunges are concentrated horizontally that is both strike slip and reverse fault events are found in regions shallower than the characteristic depth while strike slip events dominate in the deeper region it is inferred from the above results that the minimum horizontal stress has almost the same magnitude as the vertical stress in regions shallower than the characteristic depth while in the deeper regions the minimum horizontal stress is less than the vertical stress this conclusion implies that the minimum horizontal stress increases proportional to the depth in regions shallower than the characteristic depth but does not increase in proportion to depth in the deeper regions it was also concluded that the brittle semibrittle transition could possibly occur at the characteristic depth

northeast monsoon variations during the holocene inferred from palaeochannels and active channels of the palar river basin southern peninsular india the present day palar river and its palaeochannel located in the southern peninsular india were investigated with a multidisciplinary approach the main aim of the study was to reconstruct the palaeoenvironment history of the palar river basin and to delineate the role of holocene fluctuations that played a major role in the geomorphological evolution of the region since the holocene period the results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence osl dates reveal distinct seven climatic phases since the past 10 ka phase 1 signifies a very high precipitation as attested by the low cwi with high rb sr ratio subsequent to phase 1 a decreasing trend in the northeast monsoon rainfall nemr is observed phase 2 phase 3 4 83 3 59 ka reflects a decrease in nemr further supported by low mn al mg al and chemical index of alteration cia values phase 4 3 59 ka is marked by high sand flux higher k al ti al rb sr and ba

uranium series dated authigenic carbonates and acheulian sites in southern egypt field investigations in southern egypt have yielded acheulian artifacts in situ in authigenic carbonate deposits caco 3 cemented alluvium along the edges of nowaggraded paleovalleys wadi arid and wadi safsaf uranium series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45 141 and 212 ka thousand years ago most of the carbonate appears to have been precipitated from groundwater which suggests that these three episodes of deposition may be related to late pleistocene humid climates that facilitated human settlement in this now hyperarid region carbonate cements from sediments containing acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys

a 300 kyr record of upwelling off oman during the late quaternary evidence of the asian southwest monsoon in the northwest arabian sea upwelling occurs each summer driven by the strong sw monsoon winds upwelling results in high biological productivity and a distinctive assemblage of plankton species in the surface waters off oman that are preserved in the sediments along the oman continental margin creating a geologic record of monsoon driven upwelling sediments recovered from the oman continental margin during ocean drilling program leg 117 provide an opportunity to examine how upwelling has varied during the late quaternary spanning a longer interval than piston cores recovered prior to the odp cruise variations in foraminifer shell accumulation and in the relative abundance of globigerina bulloides indicate dominant cycles of variation at 1 100 kyr the dominant frequency of glacial interglacial variations and at 1 23 kyr the frequency of precessionally driven cycles in seasonal insolation the strongest monsoon winds indicated by increased upwelling occurred during interglacial times when perihelion was aligned with the summer solstice an orbital change that increased the insolation received during summer in the northern hemisphere during glacial times upwelling was reduced and although the precessional cycles were still present their amplitude was smaller at both frequencies the upwelling cycles are in phase with minimum ice volume evidence that glacial interglacial climate changes also include changes to the climate system that influence the low latitude monsoon we attribute the decrease in the monsoon winds observed during glacial times to changes in bare land albedo over asia and or to changes in the areal extent and seasonal cycle in asian snow cover that decrease the summer land sea temperature contrast other mechanisms may also be involved these new upwelling time series differ substantially from previous results however the previous work relied on cores located farther offshore where upwelling is less intense and other physical mechanisms become important our results support the observations derived from atmospheric general circulation models of the atmosphere that indicate that both glacial boundary conditions and the strength of summer insolation are important variables contributing to cycles in the monsoon winds during the late quaternary

the toba volcanic super eruption environmental change and hominin occupation history in india over the last 140 000 years a prolonged interdisciplinary fieldwork program was initiated in india to investigate the impact of the toba super eruption on terrestrial ecosystems and hominins fieldwork was centered on the jurreru river valley and the middle son river valley in southern and northern india archaeological sites span from 140 000 years ago through to the holocene providing a long term view about hominin occupation history primary air fall deposits of the young toba tuff ytt were identified and changes in terrestrial environments prior to and after the super eruption are indicated prior to the toba eruption drying of local ecological settings was underway the emplacement of ash on landscapes and its subsequent erosion had local ecological and hydrological effects although drier conditions are indicated after the deposition of the ash deposits a mosaic of environments was present in india indicating that animals and hominins could have survived the volcanic event evidence indicates that middle paleolithic industries in stratified contexts are present in india prior to and after the toba super eruption middle paleolithic hominins appear to have survived the negative effects of the volcanic eruption and climatic fluctuations in the late pleistocene middle paleolithic industries produced from ca 77e38 000 years ago in india were probably manufactured by homo sapiens

automated near realtime cmt inversion the earthquake research institute eri of the university of tokyo has completely automated the process of determining source mechanisms of earthquakes using waveform data the solutions are automatically distributed using the internet without being checked the process is initiated by receipt of e mail giving the origin time and location of an earthquake to determine the source mechanism we apply the harvard centroid moment tensor cmt inversion method to long period body wave data the portion of the seismogram from the first arrival to the initial surface wave the method has been successfully applied since october 1993 to all of the major earthquakes in the world for which we received event e mail 108 of the 242 cmt solutions in 1994 were determined within 6 hours of the event with an average delay of 3 8 hours for local events e g events around japan it is also possible to determine cmt solutions within 30 minutes from the occurrence of the earthquakes using an efficient dialup data retrieval system operated by eri

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

petrologic analysis and geochemistry of the late neogene early quaternary hardpan calcretes of western rajasthan india abstract calcretes formed over bedrock such as precambrian hornblende chlorite schist rhyolite and carbonaceous phyllites in western rajasthan india were studied for their mineralogical composition and geochemistry they form a distinct element of the quaternary landscape of western rajasthan india the study area is located within the nagaur churu jaipur tract of western rajasthan the purpose of this study was to determine the processes governing the development of hardpan calcretes and to evaluate the local and regional controls on their formation micromorphology included pedogenetic and groundwater features within the hardpan calcretes thickening of calcite laminae downward and tapering at the sideward edges around the unweathered minerals of quartz and feldspars indicated cumulative and compound pedogenesis which probably occurred locally and downward movement of carbonate solution and pore water carbonate solutions were probably derived from the upper horizons or surfaces bringing about the process of dissolution and recementation of individual laminae occurrence of fibrous palygorskite as coatings around the detrital grains and siderite oolitic and pisolitic in shape points to a subalkaline subacidic process of pedogenesis in a semi arid to arid climate stable 13c and 18o isotope data of the hardpan calcrete laminae vary between 0 3 to 1 5 and 5 9 and 1 5 respectively indicating their formation at or near surface capillary fringe probably supporting a thin column of soil the source of most of the calcite is groundwater however calcite nodule formation was largely dependent on pedogenic processes associated with evaporation evapotranspiration and or microenvironmental changes in ph and co2 partial pressure dust is also a major source for carbonate precipitation although it is commonly assumed that the powdery calcretes are younger in age compared to the more complex forms the occurrence of middle palaeolithic tools below the hardpan calcrete at roopangarh and dayalpura and above the hardpan calcretes at mitri genana and rol indicates that the morphology of calcretes is not a reliable indicator of age

a new synthesis of evidence for the upper pleistocene occupation of 16r dune and its southern asian context the site of 16r dune located at the eastern edge of the thar desert provides a key benchmark for palaeolithic studies in southern asia application of chronometric dating of the excavated sequence at 16r in the 1980 s has permitted significant insights into the timing and nature of cultural evolution in the indian subcontinent recent studies of the 16r dune sedimentary section have presented a revised chronology for the cultural horizons although the impact of this upon the timing of occupation of the site and technological development in the region has not been discussed critically the largest artefact assemblage from the site originally dated by traditional radiocarbon dating to 26 ka and labelled upper palaeolithic is bracketed by recent luminescence dates of 40 80 ka and can better be described as middle palaeolithic the sedimentary and chronological context for the cultural assemblages at 16r dune is reviewed and the resulting synthesis is discussed within its regional context and with respect to contemporary debates regarding the dispersal of modern humans

origin of red pelagic carbonates as an interplay of global climate and local basin factors insight from the lower devonian of the prague basin czech republic abstract red pelagic sediments are relatively common in the phanerozoic they are often interpreted as products of sea bottom oxidation during greenhouse climate showing a conspicuous alternation with black shales and thus carrying important palaeoceanographic information the lower devonian pragian carbonate strata of the prague basin czech republic praha formation contain a marked band of red pelagic carbonate up to 15 m thick which can be correlated for several tens of km we investigated seven sections 17 to 255 m thick of the prague basin using the methods of facies analysis outcrop gamma ray logging diffuse reflectance spectroscopy optical microscopy element geochemistry magneto mineralogy and electron microprobe analysis the aim was to find the mineral carriers of the red colour investigate the stratigraphic context of the red carbonates and evaluate the local and global prerequisites for their formation the red pigmentation represents enrichment by hematite with respect to goethite approximately 31 of the total reflectance falling in the red colour band represents a threshold for red coloration the red pigmentation is carried by submicronic hematite dispersed in argillaceous pelagic calcilutite and or inside skeletal allochems gamma ray log correlation indicates that the red carbonate band developed in stratigraphic levels with low sedimentation rates typically from 1 to 7 1 mm kyr which are comparable to the mesozoic rosso ammonitico facies the red beds and the whole praha formation pragian to early emsian are characterized by low toc values

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

mapping of a magma reservoir beneath nikko shirane volcano in northern kanto japan from travel time and seismogram shape anomalies since ray paths of direct p and s waves are largely distorted in a magma body a seismic shadow zone is created however scattered or diffracted waves with very small amplitudes can arrive in the shadow zone because their ray paths are different from those of the direct waves they become the first arrival in the shadow zone more than 100 seismologists from many institutions in japan joined together to perform an intensified seismic study in the nikko ashio area northern kanto japan it was suggested that there is a magma body beneath mount nikko shirane an active volcano that causes a seismic shadow zone because p waves recorded by the joint observation are anomalously attenuated in cases when they propagate through a zone beneath the eastern part of the volcano we developed a new method to estimate the shape of the anomalous attenuation zone by proposing the use of a new parameter the energy ratio between directp or s waves and their coda waves to discriminate whether or not each observation station is located inside or outside the shadow zone we estimated the shape of the anomalous attenuation zone by dividing the study area into blocks with dimensions of 2 km 2 km 1 km and using the energy ratio data of p waves for local events the obtained result shows the existence of an anomalous attenuation zone in the area east of nikko shirane volcano with a diameter of about 10 km at depths greater than 3 km it was also found from plots of deep event seismograms recorded by the same observation that travel times are delayed by about 0 7 s for ray paths crossing the anomalous attenuation zone obtained by the energy ratio data this value requires the p wave velocity in the anomalous zone to be less than that of the surrounding crustal material by at least about 30 suggesting the existence of a huge magma reservoir in this area

case 23 nomination of precursory seismic quiescence as a significant precursor several cases of extremely strong quiescences have been investigated in great detail and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity several additional cases of quantitatively measured quiescence have been documented the method of measuring quiescence has progressed from using visual means to using a quantitative approach and the understanding of the noise sources has significantly advanced during the last few years therefore i feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the list of significant precursors although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process

pedogenic carbonates in texas stable isotope distributions and their implications for reconstructing region wide paleoenvironments abstract pedogenic carbonates are ubiquitous in paleosols through geologic history and have been widely used to speculate on paleoclimatic conditions during their formation they are widespread and well developed in large areas of texas a majority are of late quaternary age and have formed across a range of climatic conditions on various types of substrates to evaluate the usefulness of pedogenic carbonates as environmental indicators this study investigates regional scale trends in stable isotope compositions of pedogenic carbonates across approximately 900 km of texas the 13c values of 49 pedogenic carbonate profiles 182 analyses on various host strata e g limestone igneous rocks range from 10 6 to 0 7 v pdb most 13c values are evenly distributed between 9 and 1 and the 18o values range from 9 1 to 0 2 v pdb mainly between 6 and 2 there is no correlation between carbon and oxygen isotopic values r2 0 0002 pedogenic carbonates in the texas gulf coastal plains southern high plains and west texas exhibit higher 13c values than those in south and central texas which corresponds to the spatial change in vegetation between c4 dominated and c3 dominated plants the marked increase in 13c values of the pedogenic carbonates from the tertiary strata into the overlying quaternary strata confirms the invasion of a c4 biomass into the southern high plains since the early pliocene from east to west the 18o values of late quaternary pedogenic carbonates decrease gradually a trend that mimics the spatial variation of 18o values of modern meteoric water primarily due to the increased distance from the gulf of mexico source of most of the meteoric water in contrast to the regional trends the stable isotope values of some pedogenic carbonates developed on marine limestone and calcareous alluvium in central texas and south texas have isotopic signatures inherited from the host strata in addition some of the 13c values of pedogenic carbonate nodules in the gulf coastal plains have been affected by saline groundwater soil carbonates formed in the shallow parts of the profile such as petrocalcic horizons may have also been influenced by the atmospheric co2 nevertheless climatic trends are readily apparent in the isotopic data thus demonstrating their potential value in region wide paleoclimatic analyses

paleoenvironments of the earliest stone toolmakers gona ethiopia fluvio lacustrine sediments of the hadar and busidima formations along the northern awash river ethiopia archive almost three million years 3 4 to 0 6 ma of human evolution including the earliest documented record of stone toolmaking at 2 5 2 6 ma this paper brings together sedimentologic and isotopic evidence for the paleoenvironmental context of early hominids from both formations but with particular emphasis on the setting for the early toolmakers the pre 2 92 ma record hadar formation is characterized by low gradient fl uvial paludal and lacustrine deposition in an undissected topography most analogous to reaches of the modern middle awash river near gewane the gona area experienced repeated deep dissection and aggradation by the awash river starting between 2 92 and ca 2 7 ma and continuing through the top of the record at 0 6 ma busidima formation each aggradational succession is 10 20 m in thickness and fi nes upward from wellrounded conglomerates at the base to capping paleosols at the top during this period the ancestral awash represented by these fi ning upward sequences was dominantly meandering and fl owed northeast as it does today smaller channels tributary to the axial awash system are also extensively exposed in the busidima formation compared to the axial system conglomerates the tributary channels transported fi ner less mature volcanic clasts mixed with abundant carbonate nodules reworked from adjacent badlands stone artifacts oldowan 2 6 2 0 ma at the oldest archaeological sites are only associated with the axial awash system in the bedded silts or capping paleosols of the fi ning upward sequences the implements were made from rounded cobbles from the channels but manufacture and use of the tools was always away from the channel bars on the nearby sandy banks and silt dominated fl oodplains archaeological sites higher in the record acheulian 1 7 ma occur in similar axial river contexts as well as along tributary channels further removed from artifact raw material sources mature paleosols in the hadar and busidima formations are mostly pale to darkbrown vertisols typifi ed by abundant clay slickensides pseudo anticlinal and vertical fracturing and carbonate nodules such calcic vertisols are common in the region today demonstrating that the paleoclimate over the past 3 4 m y has been semi arid and strongly seasonal carbon isotopic results from pedogenic carbonates in the vertisols allow reconstruction of the proportion of c 3 plants trees and shrubs to c 4 plants grasses through time the 13

a new late pleistocene fauna from arid coastal india implications for inundated coastal refugia and human dispersals abstract a diverse late pleistocene fossil assemblage was recovered from a sea cliff locality near gopnath in gujarat northwestern india these remains are the first large sample of pleistocene faunal materials from arid northwestern india several taxa known primarily from coarse alluvial deposits of central india are documented for the first time from an undisturbed open air site adjoining the great indian desert the sample includes a new species of antelope from a lineage considered extinct outside of africa since the early pleistocene the paleoenvironmental context faunal composition and type of fossil preservation reported here is unique the gopnath fauna accumulated in a pond within a carbonate dune field that formed part of a larger coastal oasis ecosystem this paleoscape occupied the cambay gulf during hyper arid glacial low stands the gopnath fossils are correlated to late acheulean lithics from a coastal cliff locality

palaeoenvironmental dynamics and palaeolithic occupation at katoati thar desert india late pleistocene palaeoenvironments in the thar desert india located at the eastern extent of the saharo arabian desert belt have fluctuated considerably as a result of the varying range and intensity of the indian summer monsoon phases of widespread pleistocene aridity are well documented in the thar desert but research focusing on humid proxies is critical to examine how the region may have facilitated population expansions across southern asia at katoati located on the northeast margin of the thar desert the combination of field recording of sediment sections with detailed analyses micromorphology stable isotope loss on ignition magnetic susceptibility and x ray fluorescence from an archaeological site identify a series of hominin occupations during phases of enhanced humidity between 96 and 60 ka a gradient of humidity on the eastern margin of the thar desert during the late pleistocene is identified with the periodic humidity evident at katoati occurring more frequently and with longer duration towards the southern margin this uneven distribution of humidity in the thar desert is likely to have strongly influenced when and where hominin populations could expand into and across the region

earthquake mechanisms from linear programming inversion of seismic wave amplitude ratios the amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first motion polarities but amplitudes are severely distorted by the effects of heterogeneity in the earth this distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases rather than simple amplitudes but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal searching methods are particularly costly if general moment tensor mechanisms are allowed efficient linear programming methods which do not suffer from these problems have previously been applied to inverting polarities and wave amplitudes we extend these methods to amplitude ratios in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation three component digital data for an earthquake at the hengill grensdalur geothermal area in southwestern iceland illustrate the power of the method polarities of p sh and sv waves unusually well distributed on the focal sphere cannot distinguish between diverse mechanisms including a double couple amplitude ratios on the other hand clearly rule out the double couple solution and require a large explosive isotropic component

environmental change in the great plains an isotopic record from fossil horses abstract carbon and oxygen isotope ratios of fossil horse tooth enamel from nebraska and texas show evidence for late neogene environmental changes in the great plains the earliest unambiguous c4 dietary signal among texas equids coincides with the age of the classic late hemphillian age coffee ranch fauna which we suggest is 6 6 ma based on volcanic ash correlations c4 vegetation was present in the diets of a small fraction of late hemphillian equids in nebraska and was thereafter ordinary in the diets of both nebraska and texas equids there is no unequivocal evidence for abundant c4 vegetation in the diets of pre late hemphillian equids and we suggest that the ensuing dietary change reflects c4 biomass expansion in the latest miocene carbon isotope ratios of post hemphillian horses in nebraska can be divided into two statistically distinct populations on the basis of whether tortoise remains co occur with horse remains indicating that the two proxies carbon isotopes and presence absence of tort

late quaternary climatic reconstruction for the maghreb north africa abstract the paleoclimatic evolution of the maghreb since 40 000 yr b p is not yet known in great detail for that purpose data from more than 35 sites have been collected although only about 11014c dates and a few prehistoric remains can be used to correlate these data however the sites are well distributed over the maghreb and the convergent results from paleosoils paleolakes alluvian or eolian deposits pollen analysis etc induce one to draw up a certain pattern in climatic evolution for the period between 40 000 and 20 000 yr b p the data are still fragmentary but are concordant in indicating wetter environments generalized as far as the northern sahara the effect of dropping temperatures on the increasing water budget and soil moisture is not yet clear but rainfall could have been more regular and more abundant as a consequence of the shifting of middle latitude cyclone paths towards the south in both summer and winter the environmental indicators show that between about 20 and 18 000 yr b p rainfall progressively became more irregular however proofs of aridity in the south maghreb and the northern sahara is evident only for the period between 12 10 000 yr b p at that time the saharan high pressure belt was reinforced and well established at higher latitudes than at present this dry climate lasted more or less until the thermal optimum after 6000 yr b p there is some evidence that the climate became wetter again but the environmental conditions were rather different from those of before 20 000 yr b p for instance the middle holocene dark humic sois are the result of a pedogenesis different from that of the late pleistocene reddish paleosoils for the last two millennia it is not easy to distinguish between a natural trend towards aridification and desertification through man s intervention

multiple episodes of aggradation and calcrete formation in late quaternary aeolian sands central thar desert rajasthan india abstract a 12 m thick section in a dune sandy plain terrain of the central thar in rajasthan has provided a near continuous record of environmental change for the past 160 ka the site presently receives 280 mm rainfall almost entirely from the summer monsoon the base of this section comprises a gravel bed of an ephemeral stream and the overlying six litho units each with discrete boundaries comprise a succession of aeolian sands luminescence dating provided an estimate of the timing of the sand aggradation periods to 160 90 60 27 and 17 14 ka and helped constrain the timing of calcrete formation periods in each aggradation unit discrete nodular calcretes formed by the leaching of carbonate from the overlying solum this is analogous to present day conditions in sandy plains during periods of increased rainfall and landscape stability several of these calcretes are however devoid of their donor solum suggesting solum removal during a subsequent period of decreased rainfall and resultant surface instability this is supported by the presence of reworked nodules on the surfaces of some calcretes a prominent phase of calcrete development followed the aeolian sand aggradation at 60 ka suggesting climate amelioration that also caused the formation of groundwater related calcrete and mottling the study suggests that stage ii calcrete nodules form in a time frame of 10 20 ka and confirms limited data on the duration and stage of calcrete development in the literature the 13c values of calcrete carbonate lie in a narrow range 0 5 to 1 1 suggesting formation under soils with c4 vegetation this implies that even during phases of climatic amelioration the high temperatures and increased seasonality of rainfall did not permit significant development of c3 plants in the central thar

fluvial response to climate change inferred from sediment cores from the ghaggar hakra paleochannel in nw indo gangetic plains abstract in the indo gangetic plains igp the inter basinal area between the ganga in east and the indus in west is currently devoid of any major drainage a wide paleochannel belt the ghaggar hakra channel has been mapped in this region our previous studies along with others established that a large himalayan river flowed through this paleochannel and a large scale drainage reorganisation occurred during the last 10 ka this follow up study presents sedimentary facies and chrono stratigraphy of the alluvial deposits from the ghaggar hakra paleochannel 1 to understand the depositional environments of the river system 2 to reconstruct aggradation incision history and stratigraphic development and 3 to understand fluvial response to climate change at a regional scale sediment cores 35 50 m across the length and width of the paleochannel and optically stimulated luminescence osl based chronology are used to reconstruct alluvial stratigraphy developed during marine isotope stage mis 5 1 twelve sedimentary facies identified in the cores characterize floodplain channel and aeolian depositional settings four stratigraphic units were identified the oldest unit 1 150 ka representing aeolian deposition disconformably underlies the younger units 2 to 4 that represent four periods of fluvial aggradation and incision period i 86 64 ka comprises coarse grained grey micaceous channel sand and period ii 62 30 ka shows transition to fine to medium channel sand interlayered with yellow mud of floodplain deposition period iii 25 12 ka comprised of fine grained grey micaceous channel sand and very fine deposits of channel margin settings period iv 11 4 0 ka marks the termination of flow from the large himalayan river the sutlej into the ghaggar hakra system and fluvial sequence in this period red brown silty clay represents modern ghaggar deposits we suggest a strong climatic control on the stratigraphic development in this region based on the available proxy records we further compare our stratigraphic data with that of the igp and the adjoining western indian rivers for understanding the regional scale fluvial response to monsoonal fluctuations

stable isotopic composition of carbonate pedofeatures in soils along a transect in the southern part of european russia abstract stable isotopic analysis of carbonates is widely used for paleoreconstructions in various regions of the world only few and sparse information on stable isotopic composition of soil components are available for russia the aim of this research was to obtain for the first time systematic data on stable isotopic compositions of c and o in carbonate pedofeatures in modern soils of the european part of russia this territory is known as a classical example of natural bioclimatic zonation with an increasing of mat from 4 5 to 9 4 c and variation of map from 300 to 600 mm we also aimed to compare the isotopic values of hard carbonate nodules with soft carbonates key sites were located in lipetsk kursk voronezh rostov manych and stavropol regions in russia samara key site was studied in ukraine c and o isotopic compositions of soil carbonates vary depending upon geographical position carbonate morphologies and age the overall range of isotopic compositions varies by approximately 5 7 from 12 6 to 5 2 for and 10 8 to 5 6 for o the isotopic compositions of c and o in pedogenic carbonates indicate that carbonates were formed under various environments the general trend of c isotopic compositions correlates with map and mat i e show the climatology gradient similar to latitudinal gradient described for other regions the most complicated isotopic pictures were described in voronezh kursk stavropol and samara key sites which may be explained by the recent or past climatic changes ground or perched water or shallow paleosols containing old carbonates isotopic composition of soft carbonates is usually slightly different from those of hard nodules which may reflect the different mechanism rate of formation for nodules and soft masses and reveal several generations of carbonates carbonates with younger and older radiocarbon age were identified meanwhile the carbonates with older radiocarbon age generally have similar stable isotopic compositions as the carbonates with younger 14c age three bioclimatic types of environment were identified according to the stable isotopic compositions of carbonates wetter and warmer mat 5 4 9 c map 550 600 mm wetter and cooler mat 5 2 5 4 c map 600 mm and drier and warmer mat 8 5 9 4 c map 300 500 mm this information may be used for the future paleoreconstructions in paleosols of the central southern parts of european russia

palaeoenvironments and palaeohydrology of a tropical closed lake lake asal djibouti since 10 000 yr b p in eastern africa republic of djibouti the hypersaline lake asal occupies an exceptional geological topographical and hydrological situation at 155 m below sea level and at 12 km from the sea it lies in the youngest and the deepest basin in a chain of closed depressions of central afar decreasing in elevation from west to east and represents the hydrogeological low of the whole system presently infiltration of marine water represents the major water input to the lake due to high evaporation conditions halite precipitates halocene water level fluctuations 315 m sedimentary conditions from fresh oligosaline waters to heavy brines and palaeohydrology are reconstructed field observations are supported by 85 14c dates on inorganic carbonates mollusc shells stromatolites and hydrothermal travertines stable isotope analyses on carbonates and sulphates mineralogy geochemistry and studies of biological remains discussion of the water balance for the major stages is based on reasonable assumptions about holocene conditions of precipitation and evaporation after an arid terminal pleistocene phase marked by coarse deposits due to exceptional floods the holocene cycle begins with complex strontium rich carbonate phases aragonite high and low mg calcites and dolomite these carbonates could reflect the first underground marine supply and waters concentrated through evaporation a high lake level ca 160 m a s l from ca 8600 to 6000 yr b p corresponds to the deposition of high mg calcite precipitated in a deep fresh water lake lake asal was draining the awash river system ethiopian plateau and escarpment through groundwater circulations the terminal basin of the system was probably the present day marine gulf of ghoubbat al kharab hydrologically separated from the open ocean by a sill at 4 m below sea level possibly due to fracture opening a dramatic regression in the lake level from 160 to 150 m occurred between ca 6000 and 5000 yr b p the inputs of continental water were consequently overwhelmed by marine infiltrations the carbonate phase exhibits clear resemblance with that of the transgressive episode from 5000 yr b p lake asal experienced minor water level fluctuations aragonite rich carbonates precipitated followed by calcium sulphates and halite stable isotopes of gypsum reflect its marine origin and various diagenetic processes the holocene evolution of asal which clearly differs from that of the neighbouring closed basins is due to both its specific geological and hydrological setting and to the regional climatic changes

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

focal mechanisms and the state of stress on the san andreas fault in southern california focal mechanisms have been determined from p wave first motion polarities for 138 small to moderate 2 6 m 4 3 earthquakes that occurred within 10 km of the surface trace of the san andreas fault in southern california between 1978 and 1985 on the basis of these mechanisms the southern san andreas fault has been divided into five segments with different stress regimes earthquakes in the fort tejon segment show oblique reverse sup on east west and northwest striking faults the mojave segment has earthquakes with oblique reverse and right lateral strikesup motion on northwest strikes the san bernardino segment has normal faulting earthquakes on north south striking planes while the banning segment has reverse strike sup and normal faulting events all occurring in the same area the earthquakes in the indio segment show strike slip and oblique normal faulting on northwest to north south striking planes these focal mechanism data have been inverted to determine how the stresses acting on the san andreas fault in southern california vary with position along strike of the fault one of the principal stresses is vertical in all of the regions the vertical stress is the minimum principal stress in fort tejon and mojave the intermediate principal stress in banning and indio and the maximum principal stress in san bernardino the orientations of the horizontal principal stresses also vary between the regions the trend of the maximum horizontal stress rotates over 35 from n15 w at fort tejon to n20 at indio except for the san bernardino segment the trend of the maximum horizontal stress is at a constant angle of about 65 to the local strike of the san andreas fault implying a weak fault the largest change in the present stress state occurs at the end of the rupture zone of the 1857 fort tejon earthquake it appears that the 1857 rupture ended when it propagated into an area of low stress amplitude possibly caused by the 15 angle between the strikes of the san jacinto and san andreas faults the strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation

stable isotopic composition of pedogenic carbonates from the eastern margin of the thar desert rajasthan india pedogenic carbonates in a 19 m thick dune section 16r at didwana and several shorter profiles from the eastern margin of the thar desert rajasthan were studied for their stable isotope composition carbon isotope results show the c4 biomass grasses has dominated local vegetation for most of the 250 000 years represented by the 16r section our results display a decrease in 18o and 13c values during the last interglacial and early glacial periods the higher 13c values in our dune records correlate to episodes in the strong upwelling and decreased sedimentation rates in indian ocean cores probably the result of a strong asian monsoon the high 13c values may therefore denote the expansion of c4 vegetation in response to warm wetter monsoon circulation conversely low 18o and 13c values mark the expansion of c3 vegetation probably caused by enhanced winter rains and lower temperatures

paleoclimate and paleovegetation of lower narmada basin gujarat western india inferred from stable carbon and oxygen isotopes abstract surface sediment samples depth 0 160 cm and a paleosol depth 10 15 m both part of a sediment profile exposed in a cliff section of narmada river western india were analyzed for stable isotopes 13 c and 18 o three organic carbon samples from top 160 cm and two paleosol samples from top and bottom of the paleosol were dated by the radiocarbon method 13 c of both soil carbonates and soil organic carbon fall in the range of mixed c3 and c4 vegetation except for the paleosol which shows differences attributable to the contribution of bedrock carbonate during calcite formation the vegetation was dominantly c3 in the late pleistocene from 15 10 ka bp which shifted to mixed c3 c4 during the holocene enhanced monsoon was observed at 12 5 and 1 6 ka bp the presence of c4 grasses in the late holocene is detectable the present day vegetation is dominantly c3 type 13 c 25 4 probably due to anthropogenic activity where grasslands c4 have been replaced by c3 vegetation recently last 50 years the enhanced atmospheric co 2 concentration in recent times could be a probable agent for the current dominance of c3 vegetation

segmentation of the aleutian plate boundary derived from stress direction estimates based on fault plane solutions we propose a new method to investigate stress homogeneity along plate boundaries based on the cumulative misfit of individual fault plane solutions calculated using assumed stress tensors using this method some segments of faults can be defined without the time consuming inversions for stress directions from earthquake fault plane solutions we assume that the misfits are relatively constant within segments of uniform stress orientation but that they change abruptly at boundaries of segments this assumption is supported by the pattern of misfits observed for about 400 earthquakes located along the aleutian subduction zone from 170 e to 145 w which occurred between 1964 and 1993 the efficacy of the approach is confirmed by stress inversion analysis of moving windows the cumulative misfit as a function of strike along the aleutian arc shows there are five first order boundaries where the stress directions change significantly the first one is near 177 5 e which corresponds to the northward projection of the rat fracture zone the second one falls on the adak fracture zone the third is near the locus where the amlia fracture zone intersects the trench the fourth lies on the easternmost end of the 1957 aftershock zone the last is located where the two major asperities of the 1964 rupture are separated the segmentation boundaries found in our analysis may be controlled by the fracture zones in the subducted plate this observation may be interpreted as due to decoupling within the underthrusting plate along the zones of weakness the fracture zones across which stress may not be transmitted fully the boundaries defined by our method may also be related to the asperity and aftershock distributions of great earthquakes the focal mechanism data in the segments defined as stress homogeneous by our method are then used to invert for the principal stress orientations by employing the focal mechanism stress inversion fmsi computer programs of gephart we find that the stress directions within these segments are different from each other where they can be defined well and the average misfits in these volumes are very small 2 8 and 5 5 the method is not robust enough to detect all the stress segmentation boundaries based on only one reference stress tensor analyses with different reference stress models help to define most or all the stress segmentation boundaries

discrimination of fault planes from auxiliary planes based on simultaneous determination of stress tensor and a large number of fault plane solutions it is well known that there is a large difference in focal mechanism solutions of events even if they occur within a certain small area considering earthquake generating stress to be uniform in a studied area we developed a new method for simultaneously determining the stress tensor and the orientation of fault planes for many events by the use of polarity data of p waves first the number of inconsistent stations is calculated for various values of three parameters in the focal mechanism solution with intervals of 10 this calculation is made for all the events used then four parameters defining the stress tensor are determined by a grid search using the data calculated above with the assumption that the slip direction in the fault plane should be parallel to the direction where the shear stress on the plane becomes maximum a numerical test is made by applying the present method to an artificial data set composed of 25 events with 25 25 readings it is found that a stable solution of the stress tensor is determined by the inversion and about 60 of fault planes are distinguished from auxiliary planes there are no events whose auxiliary planes are incorrectly determined as fault planes this method is used to estimate the earthquake generating stress in the aftershock area of the 1984 western nagano prefecture earthquake central japan the results obtained show that the maximum principal stress is horizontal in the direction of n80 w s80 e there are strike slip events having fault planes almost perpendicular to the fault plane of the main shock

carbon isotopic composition of lignin biomarkers evidence of grassland over the gangetic plain during lgm abstract carbon isotope 13 c compositions of total organic carbon toc as well as several extracted higher plant derived lignin biomarkers along with the recovery of grass phytoliths provide the first direct evidence of existence of extensive grass land c4 vegetation over the ganges deltaic plain during the last glacial maximum lgm the earliest holocene 9 ka is marked by pronounced 13 c depletion in the lignin phenols coinciding with rapid sea level rise intensified monsoon and replacement of grassland vegetation by mangroves another c4 invasion phase is identified during the late holocene 6 2 ka both the lgm and late holocene c4 phases coincide with the well known monsoon minima the study suggests that change in pco 2 might not be the singular driver of vegetation change as proposed recently and the climate models must take the monsoon like mega climate processes into account for reconstructing the glacial biomes

structural control on late miocene to quaternary volcanism in the ne honshu arc japan 1 volcanological and structural field data are used to define the tectonic control on the n s volcanic arc of ne honshu japan since late miocene during late miocene pliocene bimodal products were mainly erupted from along arc and ne sw aligned and elongated calderas the deformation pattern mostly consisted of n s dextral faults and subordinate ne sw extensional structures produced by ne sw compression this pattern because of the indentation of the kuril sliver is similar to that of oblique convergence settings magma rose and extruded along ne sw areas of localized extension created by the dextral faults these extensional areas were uncoupled with regard to those e w trending inferred to have focused the rise of melts from the subducting slab in the mantle during quaternary a larger amount of andesite was mainly erupted from along arc and e w aligned and elongated stratovolcanoes the deformation pattern mostly consisted of n s thrust faults and subordinate e w extensional structures produced by e w compression resulting from orthogonal convergence due to the variation in the absolute motion of the pacific plate the e w extensional structures are the shallowest expression of e w trending hot mantle fingers suggesting mantle crust coupling for the rise of magma such a coupling ensures 1 higher extrusion and 2 mixing between a deeper mafic and a shallower felsic magma generating the andesites the significantly larger volumes ma 1 200 km 1 of length of the arc of magma erupted during quaternary show that pure convergence conditions do not necessarily hinder the rise and extrusion of magma

soils at the hyperarid margin the isotopic composition of soil carbonate from the atacama desert northern chile we evaluate the impact of exceptionally sparse plant cover 0 20 and rainfall 2 114 mm yr on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet the atacama desert in northern chile d 13 c and d 18 o values of carbonates from the atacama are the highest of any desert in the world d 13 c vpdb values from soil carbonate range from 8 2 at the wettest sites to 7 9 at the driest we measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of cerling 1984 earth planet sci lett 71 229 240 in which we assumed an exponential form of the soil co2 production function and relatively shallow 20 30 cm average production depths overall we find that respiration rates are the main predictor of the d 13 c value of soil carbonate in the atacama whereas the fraction c3 to c4 biomass at individual sites has a subordinate influence the high average d 13 c value 4 1 of carbonate from the driest study sites indicates it formed perhaps abiotically in the presence of pure atmospheric co2 d 18 o vpdb values from soil carbonate range from 5 9 at the wettest sites to 7 3 at the driest and show much less regular variation with elevation change than d 13 c values d 18 o values for soil carbonate predicted from local temperature and d 18 o values of rainfall values suggest that extreme 80 in some cases soil dewatering by evaporation occurs at most sites prior to carbonate formation the effects of evaporation compromise the use of d 18 o values from ancient soil carbonate to

a leaf wax biomarker record of early pleistocene hydroclimate from west turkana kenya abstract climate is thought to play a critical role in human evolution however this hypothesis is difficult to test due to a lack of long high quality paleoclimate records from key hominin fossil locales to address this issue we analyzed organic geochemical indicators of climate in a drill core from west turkana kenya that spans 1 9 1 4 ma an interval that includes several important hominin evolutionary transitions we analyzed the hydrogen isotopic composition of terrestrial plant waxes dwax to reconstruct orbital timescale changes in regional hydrology and their relationship with global climate forcings and the hominin fossil record our data indicate little change in the long term mean hydroclimate during this interval in contrast to inferred changes in the level of lake turkana suggesting that lake level may be responding dominantly to deltaic progradation or tectonically driven changes in basin configuration as opposed to hydroclimate time series spectral analyses of the isotopic data reveal strong precession band 21 kyr periodicity indicating that regional hydroclimate was strongly affected by changes in insolation we observe an interval of particularly high amplitude hydrologic variation at 1 7 ma which occurs during a time of high orbital eccentricity hence large changes in processionally driven insolation amplitude this interval overlaps with multiple hominin species turnovers the appearance of new stone tool technology and hominin dispersal out of africa supporting the notion that climate variability played an important role in hominin evolution

geochemistry of buried river sediments from ghaggar plains nw india multi proxy records of variations in provenance paleoclimate and paleovegetation patterns in the late quaternary abstract we report the first geochemical record in two drill sediment cores from a buried channel in the ghaggar plains of nw india which are used to infer variations in provenance paleoclimate and paleovegetation in the locality during the late quaternary aeolian sediments 150 ka in both the cores are overlain by fluvial sediments 75 ka recent major oxide compositions of the core sediments n 35 generally vary between that observed for the modern day ghaggar sutlej and yamuna river sand the isotopic composition 87sr 86sr 0 7365 to 0 7783 and end 14 6 to 19 0 of core sediments n 18 suggest binary mixing of sediments from compositionally distinct higher himalaya hh and lesser himalaya lh endmembers in the catchment and support involvement of a river system originating in the himalayan hinterland distinctly higher 87sr 86sr and lower end in the core sediments during glacial periods can be explained by increasing sediment contribution from lh high 87sr 86sr and low end due to an increase in glacial cover over hh whereas relatively less glacial cover over hh during interglacial periods resulted in more erosion and sediment contribution from hh the down core sr nd isotopic variability clearly reflects climate controlled sediment erosion in the himalayan catchment temporal variations in 18o and 13c of carbonate nodules n 27 are consistent with that reported from the ganga interfluves the 13c variability 4 1 to 1 2 in carbonates is mainly controlled by the extent of silicate hh versus carbonate lh source weathering due to significant climatic shifts the 13c of sediment organic matter 27 4 to 23 2 n 24 suggests dominantly c3 plants in the catchment during the last 75 ka more negative 13c values in sediments during glacial periods relative to those during interglacial periods can be explained by increasing c4 abundance during interglacial periods characterized with both higher summer rainfall and mean annual temperature

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

late middle palaeolithic surface sites occurring on dated sediment formations in the thar desert abstract the dominance of erosional sedimentary processes in desert regions results in palaeolithic records rich in surface scatters engaging with this abundant archaeological resource including incorporating them within absolute chronologies or schemes of environmental variability is critical to understanding hominin habitation in arid landscapes extensive archaeological surveys in the thar desert of india and pakistan over the past 60 years have identified a large number of palaeolithic surface sites in a diverse range of geographic contexts in the past twenty years a rich upper pleistocene palaeoenvironmental record has been developed within the region due to the application of chronometric dating techniques however as yet there have been few attempts by archaeologists to survey previously dated sediment formations in the thar desert and capitalise upon the potential to attribute preliminary terminus post quem dates to surface sites surface survey has been undertaken targeting sediment deposits that may preserve evidence for hominin behaviour between marine isotope stage 5 and 3 a period in which technological and demographic overhauls in hominin populations appear to occur in south asia following brief review of the palaeolithic archaeology and palaeoenvironmental history of the thar desert the results of recent archaeological survey of dated sediments at chamu karna and shergarh tri junction are presented the results offer tentative evidence for the presence of late middle palaeolithic populations in the region which are evaluated and discussed within the context of contemporary occupations across southern asia

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

simultaneous estimation of attenuation structure source parameters and site response spectra application to the northeastern part of honshu japan abstract we have developed an inversion method for estimating q structure by the use of a large number of waveform data from earthquakes we divide an area to be analyzed into small blocks and simultaneously estimate the q value in each block source parameters for each event and site response spectrum for each station the source spectrum is assumed to be expressed by the 2 model and values of corner frequencies and low frequency levels of source spectra are estimated amplitudes are calculated by taking the orientation of focal mechanism solutions into account a trade off among estimated parameters is tested by numerical experiments using three sets of artificial data in a case when artificial data include error of 15 in the orientation of the p axis of focal mechanism solutions the inverted result shows that the original checkerboard pattern of q structure is well reconstructed although estimated q 1 values are about 10 higher than those of the original one the result without the corrections for radiation effect shows that the checkerboard pattern is only reconstructed in the blocks having a sufficient number of ray paths we applied this inversion method to a real data set in the northeastern part of honshu japan estimated q p structure shows that low q p regions are distributed beneath the volcanic front and they move towards the west with increasing depth previous studies of three dimensional seismic velocity structure in this area show that p wave low velocity regions exist in the crust beneath the volcanic front and they are inclined towards the west in the mantle wedge the low q p regions estimated in this study coincide in general with the p wave low velocity regions

temporal change of interplate coupling in northeastern japan during 1995 2002 estimated from continuous gps observations summary temporal change of deformation in northeastern japan is clarified by continuous global positioning system gps observations from 1995 april to 2002 march the observed gps velocity is approximately parallel to the direction of plate convergence on east and west plate boundaries of northeastern japan and shows post seismic transient deformation around source regions of the mw 7 8 1993 hokkaido nansei oki and the mw 7 7 1994 sanriku haruka oki earthquakes we interpret the source of the observed deformation as contemporary interplate coupling on the east subducting boundary to the pacific plate and the west collision boundary to the amurian plate using elastic dislocation theory we inverted horizontal and vertical velocities of 212 gps stations to estimate interplate coupling on both boundaries the estimated coupling during 1995 2002 is spatially heterogeneous however it is temporally almost constant except for the region around the 1993 and 1994 earthquakes after slip of the 1994 earthquake occurred over the coseismic rupture area and its downdip extension on the plate boundary for 0 3 1 3 yr after the earthquake after slip continued only in the downdip extension for later periods and decayed with time weak coupling was recovered in the eastern part of the coseismic rupture area 3 3 yr after the earthquake interplate coupling on the pacific plate was strong in two regions miyagi oki and tokachi oki the west plate boundary is tightly coupled except for the source areas of three large earthquakes that occurred in 1964 1983 and 1993 the apparent decoupling of the source areas of these earthquakes implies long term post seismic deformation as a result of viscoelastic relaxation in the subseismogenic lithosphere

plio pleistocene vegetation changes in the north china plain magnetostratigraphy oxygen and carbon isotopic composition of pedogenic carbonates abstract the plio pleistocene history of c4 plant biomass in northwestern china has been documented from the loess soil sequences of the loess plateau region however how c4 plants evolved in the warmer and low elevation eastern china monsoon zone is still poorly known mainly because of the unavailability of well dated geological records in this study a 203 6 m core of floodplain deposits was recovered from the north china plain near tianjin and dated magnetostratigraphically the results define a chronosequence for the last 3 3 ma the late quaternary portion of the core consists of fluvio marine sediments while the rest of the section 3 3 0 6 ma contains abundant paleosols formed on the floodplain as confirmed by soil micromorphological evidence the stable carbon and oxygen isotopic composition of pedogenic carbonates was measured to document vegetation and climate changes the results reveal mixed c3 and c4 vegetation with an estimated c4 abundance of 40 60 from 3 1 to 2 2 ma and a subsequent gradual decline to 25 until 0 6 ma this trend is consistent with the data from the loess soil sequences further west on the loess plateau suggesting they are regionally significant changes the lowering of growing season temperature and or drier conditions induced by global cooling would explain this overall decline

holocene variations of monsoon rainfall in rajasthan two reconstructed histories of the monsoon rainfall in rajasthan show that the monsoon was weak or absent in latest glacial time with the advent of holocene climatic patterns fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history the two reconstructions separated by only 150 km have some features in common and some striking differences both show maximum monsoon amounts in the early holocene with a roughly two thirds decrease to the present both show salinization in sub boreal time both show long intervals of near complete desiccation in the last four millennia the shorter term variations however are not closely parallel these shorter term variations may be explained in terms of the behavior of the present day interannual variability

early holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments kukkal lake southern india geochemistry and palynology the kukkal basin tamil nadu india receives most of its rain from the southwest monsoon swm a sediment core from kukkal lake preserves a continuous sediment record from the early holocene to p

geomorphic context of two acheulian sites in semi arid peninsular india inferring palaeoenvironment and chronology abstract over the last 30 years research in acheulian culture in india has undergone drastic changes to incorporate an understanding of chronological and environmental aspects this is largely attributed to the increasing role of multi disciplinary approaches at excavated sites like singi talav didwana in thar desert morgaon in western upland maharashtra isampur in northern karnataka and attirampakkam in coastal tamilnadu of these attirampakkam is the only site firmly dated to 1 5ma despite attempts to date these sites to the early pleistocene older than 0 8 ma the application of absolute dating techniques in the indian sub continent has proved challenging due to inherent technical problems climatically the early pleistocene appears to be wetter than the middle pleistocene while the late pleistocene was distinctly arid against this chronological and palaeoclimatic backdrop an attempt has been made to reinvestigate acheulian sites at gangapur in upland maharashtra deccan trap formation and anagwadi in northern karnataka kaladgi formation by using two important geomorphic proxies namely ferricrete and calcrete associated with acheulian artefacts these studies show that both sites are connected with palaeochannels flowing close to modern channels of the godavari and the ghataprabha ferricritised acheulian artefact bearing conglomerate is totally relict in the present semi arid climate which has prevailed since the early middle pleistocene in peninsular india the acheulian site at anagwadi therefore appears to belong to the early pleistocene the site of gangapur is in conformity with a semi arid climate and therefore belongs to the middle pleistocene these sites represent an adaptation of acheulian hominin groups to humid at anagwadi and semi arid environments at gangapur during the early and middle pleistocene age the acheulian artefacts are made on locally available quartzite at anagwadi and basalt at gangapur