geochemical variability in distal and proximal glass from the youngest toba tuff eruption the youngest toba tuff ytt erupted at ca 74 ka is a distinctive and widespread tephra marker across south and southeast asia the climatic human and environmental consequences of the ytt eruption are widely debated although a considerable body of geochemical data is available for this unit there has not been a systematic study of the variability of the ash geochemistry intrinsic magmatic and extrinsic post depositional chemical variations bring fundamental information regarding the petrogenesis of the magma the distribution of the tephra and the interaction between the ash and the receiving environment considering the importance of the geochemistry of the ytt for stratigraphic correlations and eruptive models it is central to the ytt debate to quantify and interpret such variations here we collate all published geochemical data on the ytt glass including analyses from 67 sites described in the literature and three new samples two principal sources of chemical variation are investigated i compositional zonation of the magma reservoir and ii post depositional alteration post depositional leaching is responsible for up to ca 11 differences in na2o k2o and ca 1 differences in sio2 al2o3 ratios in ytt glass from marine sites continental tephras are 2 higher in na2o k2o and 3 higher in sio2 al2o3 with respect to the marine tephra we interpret such post depositional glass alteration as related to seawater induced alkali migration in marine environments crystal fractionation and consequential magmatic differentiation which produced order of magnitude variations in trace element concentrations reported in the literature also produced major element differences in the ytt glass feo al2o3 ratios vary by about 50 which is analytically significant these variations represent magmatic fractionation involving fe bearing phases we also compared major element concentrations in ytt and oldest toba tuff ott ash samples to identify potential compositional differences that could constrain the stratigraphic identity of the morgaon ash western india no differences between the ott and ytt samples were observed

eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

climate volcanism feedback and the toba eruption of 74 000 years ago abstract a general feedback between volcanism and climate at times of transition in the quaternary climate record is suggested exemplified by events accompanying the toba eruption 74 000 yr ago the largest known late quaternary explosive volcanic eruption the toba paroxysm occurred during the 18o stage 5a 4 transition a period of rapid ice growth and falling global sea level which may have been a factor in creating stresses that triggered the volcanic event toba is estimated to have produced between 1015 and 1016 g of fine ash and sulfur gases lofted in co ignimbrite ash clouds to heights of at least 32 5 km which may have led to dense stratospheric dust and sulfuric acid aerosol clouds these conditions could have created a brief dramatic cooling or volcanic winter followed by estimated annual northern hemisphere surface temperature decreases of 3 to 5 c caused by the longer lived aerosols summer temperature decreases of 10 c at high northern latitudes adjacent to regions already covered by snow and ice might have increased snow cover and sea ice extent accelerating the global cooling already in progress evidence for such climate volcanic feedback following milankovitch periodicities is found at several climatic transitions

contribution of grain size and compositional data from the bengal fan sediment to the understanding of toba volcanic event abstract toba tephra layers in cores from the bengal fan have been studied to characterize their granulometric mineralogic and geochemical features the layers are silt sized sediments with no significant non volcanic contamination the samples are very homogeneous glass shards have moderate hydration about 6 water a calc alkaline character and a rhyolitic composition the major and trace element compositions indicate an orogenic affinity and coincide with literature data for the youngest toba tephra level ytt 75 ka x ray diffraction xrd data indicate that the glass is the dominant phase with minor feldspar biotite and quartz the grain size analyses of the beds show discontinuous vertical variation and no linear trends from south to north over about 1500 km the vertical granulometric gap of the layers probably represents a single pyroclastic emplacement unit subjected to pre depositional particle aggregation

erosional history of the eastern tibetan plateau since 190 kyr ago clay mineralogical and geochemical investigations from the southwestern south china sea a high resolution study of clay mineralogy and major element geochemistry has been conducted on high sedimentation rate cores md01 2393 and md97 2150 collected off the mekong river mouth in the southwestern south china sea in order to reconstruct the erosional and weathering history of the mekong basin the chronology is based upon planktonic foraminiferal oxygen isotope records combined with carbonate stratigraphy clay minerals and major element results suggest that the mekong river is the major sedimentary source over the past 190 kyr for both cores illite and chlorite were derived mainly from the eastern tibetan plateau kaolinite was derived mainly from active erosion of inherited clays from reworked sediments in the middle part of the mekong basin smectites originated mainly through chemical weathering of parent aluminosilicate and ferromagnesian silicate under warm and humid conditions in the middle to lower parts of the mekong basin smectites illite chlorite and smectites kaolinite ratios coupled to k2o sio2 and al2o3 sio2 ratios allow us to reconstruct a history of chemical weathering versus physical erosion good correlations between those ratios suggest monsoon controlled weathering and erosion over the eastern tibetan plateau and the mekong basin variations with time scales of 0 3 0 6 kyr for the last 70 kyr and 1 2 kyr for 70 190 kyr ago in the chemical weathering erosional history are strongly related to the east asian monsoon evolution which is itself related to the summer solar radiation calculated for the northern hemisphere d 2004 elsevier b v all rights reserved

newly discovered eastern dispersal of the youngest toba tuff volcanic glasses with minor mafic mineral fragments such as biotite and hornblende found in deep sea sediments of the south china sea basin scsb have been clearly identified as eruptive products of the youngest toba tuff ytt northern sumatra indonesia the tephra layer occurs between marine oxygen isotopic event 5 1 79 3 ka and event 4 22 64 1 ka with an interpolated age of 74 0 ka which is in good consistence with previous radiometric dating 73 75 ka and ice core dating 71 5 ka of the ytt the tephra consists predominantly of bubble wall shards with minor elongated vesicles of pumice fragments geochemical characteristics of the tephra such as high total alkali content high 87 sr 86 sr ratio and uniformity of their compositions all suggest that the recovered tephra is of the youngest toba tuff this finding supports an extended dispersal of coarse 63 mm glass shards over 1500 km northeast of the toba caldera a direction opposite to what previously conceived while providing a better documentation of the distribution extent of the toba ash this report points to the need to reestimating the eruptive volume of the ytt and re evaluating its environmental impact q 2000 elsevier science b v all rights reserved

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

precise u pb ages and geochemistry of palaeoproterozoic mafic dykes from southern west greenland linking the north atlantic and the dharwar cratons palaeoproterozoic magmatism throughout the north atlantic craton nac has produced dyke swarms of diverse orientations and emplacement ages in southern west greenland previously identified swarms include the ca 2500 ma kilarsaarfik dykes ca 2215 ma boninitic norite bn dykes and the abundant ca 2040 ma kangamiut and coeval 2050 2030 ma md3 dykes additional insight into the distribution of swarms is provided by new baddeleyite u pb id tims dates interpreted as emplacement ages for six dykes the geochemistry for a total of 42 samples on 40 dykes including the dated dykes provides some constraints on their petrogenesis two e w trending dykes yield ages of 2365 2 ma and 2374 4 ma representing a hitherto unknown magmatic event we propose the name graedefjord dykes for dykes of this age in southern west greenland one ne sw trending dyke is dated at 2209 5 ma close to a previously published 2214 10 ma age for a n s trending dyke member of bn dykes three dykes yield md3 ages of 2053 2 ma e w trending 2049 6 ma n s trending and 2042 2 ma wnw ese trending ca 2 21 ga old and predominantly ne se and nne sse trending dolerites some of which are high al basalts were derived from a relatively depleted mantle and injected during a boninite dolerite magmatic event together with nearby bn dykes derived from a harzburgitic yet highly lree and lile enriched subcontinental lithospheric mantle sclm ca 2 05 ga kangamiut md3 dolerites were derived from a similar ambient asthenospheric mantle and subsequently experienced crustal assimilation during fractional crystallisation the ca 2370 ma dykes in the nac are coeval with the dharwar giant dyke swarm of the dharwar craton dc and based on this unique age match it is proposed that the dharwar and nac were neighbours in the palaeoproterozoic furthermore both blocks share 222 2 21 ga dykes and matching the trends of 2 2 2 1 and 2 37 ga swarms between the two blocks allows several plausible reconstructions c 2012 published by elsevier b v

comment on environmental impact of the 73ka toba super eruption in south asia by m a j williams s h ambrose s van der kaars c ruehlemann u chattopadhyaya j pal and p r chauhan palaeogeography palaeoclimatology palaeoecology 284 2009 295 314 abstract williams et al williams m ambrose s h van der kaars s ruehlemann c chattopadhyaya u pal j n chauhan p 2009 environmental impact of the 73 ka toba super eruption in south asia palaeogeography palaeoclimatology palaeoecology 284 295 314 recently reported late pleistocene palaeoenvironment indicators from terrestrial sites in central india and a marine core from the bay of bengal they correlate isotopic data from soil carbonates and pollen from the marine core using occurrences of the youngest toba tuff ytt a widespread tephra erupted from the sumatran toba caldera 74 000 years ago they conclude that the toba eruption caused both climatic cooling and prolonged deforestation in south asia however consideration of the bases for these claims reveals that the ytt eruption is used as a chronological marker of cooling at the end of dansgaard oeschger interstadial 20 and no evidence is provided that the eruption caused or prolonged this process furthermore while the presented data add to the south asian palaeoenvironmental literature the applicability of the results to questions of impact on human and other populations is overstated

geochemical constraints on the late stage evolution of basaltic magma as revealed by composite dikes within the kangâmiut dike swarm west greenland abstract the kang miut dike swarm in west greenland contains numerous composite dikes with mafic margins and andesitic centers internal chilled margins show that the andesitic centers intruded into the middle of the mafic dikes major element systematics indicate that the fractionation of olivine clinopyroxene plagioclase and fe ti oxides drove the evolution of the kang miut parental magma during its transition from mafic to andesitic compositions incompatible trace elements show a marked relative decrease in middle and heavy rare earth elements ree between the mafic margins and the andesitic centers the decrease in the ree is not explicable by olivine clinopyroxene plagioclase and fe ti oxide fractionation or by the fractionation of the accessory phases apatite zircon or garnet rb sr and sm nd isotopes from margin and center pairs from these composite dikes are nearly identical indicating that crustal contamination had little to no affect on their evolution trace element modeling utilizing the mixing of evolved kang miut magmas and low degree melts derived from partial melting of garnet lherzolite produce excellent fits with the trace element patterns for the andesitic centers these models suggest that the late stage evolution of the kang miut dikes included input of mantle melts produced during the end stages of rifting

broadband waveform modeling of moderate earthquakes in the san francisco bay area and preliminary assessment of the usgs 3d seismic velocity model abstract recently the united states geologic survey earthquake hazards program developed a 3d seismic velocity model of northern california based on geology including a detailed model of the urbanized san francisco bay area in this study we report comparisons of observed three component broadband 0 03 0 25 hz waveforms with synthetic seismograms computed with the new 3d model using an elastic finite difference method we selected a set of 12 moderate earthquakes m w 4 0 5 1 that occurred within the greater san francisco bay area having well constrained source parameters and broadband recordings with high signal to noise ratios the objective of this study was to investigate how well the 3d velocity model predicts observed waveforms and to identify features of the model that may require revision to improve the waveform fits and predictions of ground motions for future events we show for the 3 september 2000 yountville earthquake that reported source parameters accurately predict waveforms at two close strong motion stations approximately 10 km from the epicenter by comparing synthetics for the average 1d model gil7 stidham et al 1999 and the 3d structures we show that the effects of seismic wave propagation in the 3d model become important for frequencies at and above 0 1 hz periods less than 10 sec comparison of observed and synthetic seismograms for the 3d model consistently shows that the model predicts energy arriving earlier than is observed particularly for the surface waves indicating that the shear velocities in the upper crust must be reduced we cross correlated the observed and synthetic waveforms and recorded the delay time and linear correlation for best alignment of the data and delayed synthetic the results indicate that generally the 3d model predicts the observed waveforms well mean linear correlations 0 41 and includes features that arise from the interaction of the wave field with 3d structure especially the major sedimentary basins in san pablo bay san francisco bay santa clara valley and livermore valley simple conversion of the observed delay times for optimal alignment suggests shear velocities should be reduced by 4 5 on average based on these findings we conclude that the model is an excellent first step suggesting that the overall structure of the model is accurate i e the basin and discontinuity geometry however the velocities must be reduced to improve the observed timing of surface wave arrivals

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

possible source dichotomy of contemporaneous post collisional barren i type versus tin bearing a type granites lying on opposite sides of the south tien shan suture abstract two granitoid complexes in the eastern kyrgyz tien shan situated north and south of the southern tien shan suture were studied the suture formed as a result of the closure of the turkestan ocean and collision of the tarim microcontinent in the south with the middle tien shan in the north the timing of collision is still disputed the deformed calc alkaline terektinsky complex situated immediately north of the suture represents one of the largest shear zone related intrusions in the tien shan 130 5 15 km in size small stocks of evolved a type granites of the inylchek complex hosting economic tin mineralization were emplaced immediately south of the suture opposite the terektinsky complex two samples from the terektinsky complex and 3 samples from three a type stocks were collected for u pb zircon shrimp ii geochronology the ages at 2 level obtained for the terektinsky complex north of the suture 294 5 ma and 291 5 ma and ages of the small granite bodies south of the suture 299 4 ma 295 4 ma 289 6 ma tashkoro inylchek and maida adir intrusions respectively are nearly identical within error limits they show that the southern tien shan suture in the eastern kyrgyz tien shan had already formed by 295 ma and had evolved into a transcrustal mega shear zone controlling emplacement of granitoids geochemical distinction between the two magmatic systems is based on 10 original bulk and trace analyses of rocks from this study and on a large dataset extracted from previously published research and unpublished reports geochemically the rocks of the terektinsky complex comprise calc alkaline high potassium i type series while the granites of the inylchek complex are typical a type granites with an elevated alumina saturation index and higher boron contents compared to a standard a type rapakivi granite contrasting metallogenic features of the two granitoid complexes south and north of the southern tien shan suture are defined by their sources a fertile fore arc complex and or passive margin sediments of tarim to the south and barren metamorphic precambrian basement of the middle tien shan to the north

local and regional scale impacts of the 74 ka toba supervolcanic eruption on hominin populations and habitats in india abstract the toba supervolcanic eruption of 74 000 years ago is argued to have devastated homo sapiens populations causing a human population bottleneck through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash fall this dramatic eruption the largest in at least the last 2 million years is hypothesized to have shaped the genetic structure and diversity of human populations today past assessments of toba s human impacts however have been predominantly theoretical using archaeological and geological evidence from sites in india this study addresses toba s local scale impacts on hominin technology behavior demography and habitats in two valleys in india the jurreru and middle son valleys using paleoclimatological and volcanological data regional scale impacts throughout india are inferred a refugia hypothesis is presented that argues for variation in the scale of toba s impact throughout india driven by regional differences in monsoonal dynamics geography and topography areas of north west india the indo gangetic plain and parts of the deccan to the east of the western ghats are argued to have been the most affected whereas areas of southern and eastern india may have preserved the largest refugia for hominin populations

mafic dike swarms as absolute time markers in high grade terranes 40ar 39ar geochronological constraints on the kangâmiut dikes west greenland the paleoproterozoic kang miut dikes are valuable time markers in the complex high grade terranes of west greenland they are used to separate the archean basement from areas affected by the proterozoic nagssugtoqidian orogen it is shown here that both unmetamorphosed and metamorphosed kang miut dikes exposed in the foreland of the orogen preserve pre nagssugtoqidian 40ar 39ar ages two suites of kang miut dikes have been identified ca 2530 ma and ca 2040 ma metamorphism of the dikes in the foreland occurred shortly after their emplacement within the resolution of the argon system we suggest that crustal heating during dike emplacement or heat derived from the individual dikes caused the development of metamorphic minerals and textures internal shearing of the dikes in the foreland occurred as late as 1740 ma contemporaneous with closure of the argon system in hornblende inside the orogen following peak nagssugtoqidian metamorphism ca 1850 ma inside the orogen reworked equivalents of the kang miut dikes record parts of the post nagssugtoqidian cooling path thermotectonic activity during the nagssugtoqidian orogeny is bracketed between intrusion of the youngest kang miut dikes ca 2040 ma and post peak metamorphic cooling of the orogen to 500 c at 1740 ma

depth calculation for the january 06 2016 the september 09 2016 and the september 03 2017 nuclear tests of north korea from detailed depth phases using regional and teleseismic arrays north korea has conducted six underground nuclear explosions so far in this study we determined source depth and characterization for the 2016j 2016s and 2017s tests which were conducted on january 6 2016 2016j september 9 2016 2016s and september 3 2017 2017s respectively it has been difficult to ascertain the accurate depth of north korean nuclear explosions due to paucity of data and information we explore the depth calculation for the north korean nuclear tests based on the detailed depth phases using teleseismic and regional arrays we present the coherent spectral nulls from the average spectra of pp p sp p and ppn pn spn pn which correlate with the depth phases showing 180 phase reversals with the p wave arrivals we estimated the burial depths at 2 12 2 10 1 98 km for the 2016j 2016s and 2017s nuclear tests respectively we anticipate our absolute findings to be significant since in the past depth estimates for north korean nuclear tests have been inconclusive and unclear owing to not only paucity of data but also trade offs of the relative assessment based on the satellite images between the true source location and the tunnel entrance for the 2006 nuclear test used as a reference event

event discrimination using regional moment tensors with teleseismic p constraints determining whether a seismic event is an earthquake explosion collapse or something more complex can be done using regional 10 s full waveform moment tensors down to low magnitudes m 3 5 the moment tensor results can be improved for sparse station configurations when teleseismic 30 array based short period t 1 s p constraints are added the inclusion of teleseismic p aids in event discrimination because it samples the lower region of the focal sphere a region where intermediate period waveforms recorded at the surface have low sensitivity for shallow event depths the teleseismic p constraint is particularly useful in reducing the trade off between a shallow explosion and a shallow volume compensated linear vector dipole with a vertical axis in compression this trade off can complicate discrimination the teleseismic p constraint is applied to the source type analysis of the announced nuclear test of the democratic people s republic of korea on 25 may 2009 resulting in greater confidence in a dominantly explosive solution

volcanic sulfate deposition to greenland and antarctica a modeling sensitivity study reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional we test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the maecham5 ham aerosol climate model an ensemble of 70 simulations is analyzed with so2 injections ranging from 8 5 to 700 tg with eruptions in january and july modeled sulfate deposition flux to antarctica shows excellent spatial correlation with ice core derived estimates for pinatubo and tambora although the comparison suggests the modeled flux to the ice sheets is 4 5 times too large we find that greenland and antarctic deposition efficiencies the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden vary as a function of the magnitude and season of stratospheric sulfur injection changes in simulated sulfate deposition for large so2 injections are connected to increases in aerosol particle size which impact aerosol sedimentation velocity and radiative properties the latter leading to strong dynamical changes including strengthening of the winter polar vortices which inhibits the transport of stratospheric aerosols to high latitudes the resulting relationship between antarctic and greenland volcanic sulfate deposition is nonlinear for very large eruptions with significantly less sulfate deposition to antarctica than to greenland these model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of tambora magnitude and larger

moderate earthquake ground motion validation in the san francisco bay area abstract we performed 3d ground motion simulations for 10 recent small to moderate earthquakes m w 4 1 5 4 in the san francisco bay area to evaluate two versions of the usgs3d velocity model brocher 2005 jachens et al 2006 brocher 2008 comparisons were made in terms of modeling phase arrival timing peak ground motion amplitudes and the seismic waveforms in the simulations we assumed the source parameters reported in the berkeley seismological laboratory bsl moment tensor catalog broadband seismic data from the berkeley digital seismic network bdsn and strong motion data from the usgs and the california geological survey cgs strong motion arrays were used in the analysis the comparison of peak ground velocity pgv for both models reveals that both 3d models predict the observed pgv well over four orders of magnitude and p and s wave timing and pseudospectral acceleration psa are well modeled by the 3d structure while the revised model model 8 3 0 significantly improved the timing of the first arrival and the waveform fit is generally good there remain discrepancies in estimated amplitudes and durations that require improvements to the structure nevertheless from our low frequency 0 5 hz analysis we found that the 3d model is suitable for the simulation of pgv to assess the strong shaking hazard of future large earthquakes because earthquakes larger than m 6 have pgv carried by waves of 1 to several seconds period

major element geochemistry of glass shards and minerals of the youngest toba tephra in the southwestern south china sea an ash layer newly discovered in core md01 2393 from the southwestern south china sea has been studied in order to characterize its major element features the layer 4 0 cm thick light grayish and silt size occurs right at the marine isotope stage 4 5 transition ca 74 kyr ago the morphology and geochemistry of glass shards combined with oxygen isotope and carbonate stratigraphy confirm the youngest toba eruption in northern sumatra as the origin of the ash layer major element data on mineral crystals i e biotite plagioclase and hornblende from the ash layer suggest that biotite is phenocrystic while hornblende and some plagioclase are xenocrystic implying that these xenocrysts were incorporated into the youngest toba magma before the eruption q 2005 elsevier ltd all rights reserved

simulation of topographic effects on seismic waves from shallow explosions near the north korean nuclear test site with emphasis on shear wave generation 1 we performed high resolution 8 hz three dimensional simulations of ground motions from shallow explosions in the presence of rough surface topography near the north korean nuclear test site to study elastic propagation effects with emphasis on theoretical aspects of shear wave generation interaction with rough topography causes significant p to rg scattering along the surface with amplification of high frequency 2 8 hz shear waves relative to the flat earth case shear waves of different polarizations are coupled by topographic scattering rg precursors composed of p to rg conversions traveling as surface waves have the spectral amplitudes comparable to the p wave while the rg phase has the low frequency 0 5 3 hz spectral shape of the rg from the flat case plus the high frequency 3 8 hz p wave spectra motions at near vertical takeoff angles corresponding to teleseismic propagation are increased or decreased indicating that waves are focused or defocused by topographic features above the source topographic roughness has a dramatic effect as short wavelength features 2 5 km are included higher frequencies are amplified by topography including frequencies corresponding to wavelengths shorter than the shortest topographic scale length overall topography enhances energy propagating along the surface near the source amplifies surface waves and tends to balance sv and sh polarized motions all of which impact shear wave observations used for nuclear explosion monitoring further simulation studies could elucidate how the wavefield emerging from a topographically rough area ultimately propagates to regional and or teleseismic distances

the rise collapse and compaction of mt mantap from the 3 september 2017 north korean nuclear test surveillance of clandestine nuclear tests relies on a global seismic network but the potential of spaceborne monitoring has been underexploited we used satellite radar imagery to determine the complete surface displacement field of up to 3 5 meters of divergent horizontal motion with 0 5 meters of subsidence associated with north korea s largest underground nuclear test combining insight from geodetic and seismological remote sensing we found that the aftermath of the initial explosive deformation involved subsidence associated with subsurface collapse and aseismic compaction of the damaged rocks of the test site the explosive yield from the nuclear detonation with best fitting source parameters for 450 meter depth was 191 kilotonnes of tnt equivalent our results demonstrate the capability of spaceborne remote sensing to help characterize large underground nuclear tests

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

regional seismic observations of the 9 october 2006 underground nuclear explosion in north korea and the influence of crustal structure on regional phases 1 the crustally guided shear wave lg is typically the most prominent phase of a nuclear explosion at regional distance this lg phase is analyzed often to discriminate a nuclear explosion from a natural earthquake in addition the lg phase allows us to determine the size of the detonation a nuclear explosion test in north korea was conducted on 9 october 2006 the epicenter was located close to the eastern shore of the korean peninsula resulting in raypaths that vary significantly according to the azimuths in particular rays radiated in the southern direction experience lateral variation of crustal structures at the continental margin we examine the influence of raypaths on regional seismic phases by comparing the spectra and waveforms from different raypaths three natural earthquakes in north korea are also examined to determine the raypath effect we find that the lg from the nuclear explosion dissipated significantly as result of energy leakage into the mantle resulting from variations in crustal thickness along the portion of the raypath traversing the western tip of the sea of japan east sea some of the leaked energy develops into mantle lid waves sn causing a large energy increase to sn a similar feature is observed in the records of natural earthquakes this feature is confirmed by seismic waveform modeling the raypath effect also causes underestimation of magnitude the lg body wave magnitude mb lg is estimated to be 3 8 4 2 for records from pure continental paths and 2 6 3 4 for records from paths crossing continental margins this result illustrates the need to consider raypath effects for the correct estimation of magnitudes of regional events including a nuclear explosion

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

influence of continental margin on regional seismic wavefield abstract regional seismic analysis is an only way to investigate the source properties of small or moderate sized seismic events that occur in physically unaccessible regions such as oceanic regions and politically prohibited regions the ground motions by earthquakes need to be understood for better mitigation of seismic hazards particularly in continental margins that often incorporate high seismicity it has not been fully understood how seismic waves interact with complex crustal structures in continental margins responses of regional waves to complex crustal structures need to be quantified analysis of regional waveforms from controlled sources is desirable for investigation of influence of crustal structures the influence of continental margin around the korean peninsula is investigated in terms of spectral contents horizontal to vertical h v spectral ratios and quality factors using regional waveforms for the 2009 north korean underground nuclear explosion test that was well recorded by stations in the southern korean peninsula regional waveforms and spectral amplitudes vary significantly by path spectral contents of regional phases are different among stations in common great circle directions all regional phases modulate highly in continental margins path dependent seismic attenuation is strong in low frequencies 3 hz and weak in high frequencies 3 hz continental margins cause directional energy partition of regional waves depending on the path regional waves attenuate highly in passage across continental margin and then regrow on continental paths the growth rate is stronger than inherent attenuation rate causing seismic amplification the shapes of h v ratios are similar among various regional phases at common stations on the other hand the h v ratios for common phases vary by station in the same azimuths characteristic differences in h v ratios between two horizontal components suggest directional partition of seismic energy by crustal structures in the paths

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

early proterozoic geomagnetic field in western laurentia implications for paleolatitudes local rotations and stratigraphy abstract the east west trending post orogenic subvertical cleaver dykes from the great bear magmatic arc are dated by the u pb baddeleyite method to be 1740 5 4 ma they have a mean direction of magnetization of d i 136 5 and 57 4 k 64 95 4 5 based on samples from 17 diabase dykes a mean location 65 7 n 118 03 w and a corresponding paleopole at 19 4 n 83 3 w a95 6 1 studies of baked contacts country rocks distant from dykes and later intrusions that cut them show that the dykes became magnetized soon after intrusion the paleopole is not significantly different from that obtained from the 1759 1 ma post orogenic jan lake granite from the hudsonian orogen in southeast saskatchewan these paleopoles fall among a cluster previously determined from post orogenic overprints in a wide variety of rocks and geological settings across laurentia their mean is 20 8 n 94 5 w a95 5 2 collectively they record a widespread remagnetization episode following the hudsonian orogeny during which the polarity of the field remained constant this single polarity interval the cleaver superchron has a mean age of approximately 1747 ma and its duration is at least 13 million years but is probably much longer with further refinement it could become a global statigraphical marker there are 18 paleopoles from red beds and igneous rocks which record the paleofield in western laurentia mainly over an extended interval we estimate to be at least 100 million years between about 1960 and 1830 ma during the hudsonian orogeny over this interval western laurentia remained at a low and essentially constant latitude reversals of the geomagnetic field occurred opposed magnetizations being of approximately equal frequency there are numerous magnetochrons which could in future assist in regional stratigraphic correlations on the basis of six studies we estimate that the reference paleopole for this interval is at 1 1 s 71 7 w a95 12 1 n 6 paleopoles from the other 12 studies are spread over a 100 arc indicating large variable rotations about local vertical axes which probably resulted from transcurrent faulting caused by indentation of the bordering archean slave and superior cratons during the hudsonian orogeny these reference paleopoles show that during the hudsonian orogeny western laurentia was in paleolatitudes of 15 30 during post hudsonian time ca 1750 ma paleolatitudes were about 20 higher paleowind directions inferred by others indicate that laurentia during these intervals was in the northern hemisphere

a 135 000 year vostok specmap common temporal framework the object of the present study is to introduce a means of comparing the vostok and marine chronologies our strategy has been to use the 18o of atmospheric o2 denoted 18oatm from the vostok ice core as a proxy for the 18o of seawater denoted 18osw our underlying premise in using 18oatm as a proxy for 18osw is that past variations in 18osw an indicator of continental ice volume have been transmitted to the atmospheric o2 reservoir by photosynthesizing organisms in the surface waters of the world s oceans we compare our record of 18oatm to the 18osw record which has been developed from studies of the isotopic composition of biogenic calcite 18oforam in deep sea cores we have tied our 18oatm record from vostok to the specmap timescale throughout the last 135 kyr by correlating 18oatm with a 18osw record from v19 30 results of the correlation indicate that 77 of the variance is shared between these two records we observed differences between the 18oatm and the 18osw records during the coldest periods which indicate that there have been subtle changes in the factors which regulate 18oatm other than 18osw our use of 18oatm as a proxy for 18osw must therefore be considered tentative especially during these periods by correlating 18oatm with 18osw we provide a common temporal framework for comparing phase relationships between atmospheric records from ice cores and oceanographic records constructed from deep sea cores our correlated age depth relation for the vostok core should not be considered an absolute vostok timescale we consider it to be the preferred timescale for comparing vostok climate records with marine climate records which have been placed on the specmap timescale we have examined the fidelity of this common temporal framework by comparing sea surface temperature sst records from sediment cores with an antarctic temperature record from the vostok ice core we have demonstrated that when the southern ocean sst and antarctic temperature records are compared on this common temporal framework they show a high degree of similarity we interpret this result as supporting our use of the common temporal framework for comparing other climate records from the vostok ice core with any climate record that has been correlated into the specmap chronology

a millennial scale u37k sea surface temperature record from the south china sea 8 n over the last 150 kyr monsoon and sea level influence we report 150 kyr records of u37 sea surface temperature sst and carbonate content with 150 200 year sampling resolution from the southern south china sea scs in the northern margin of the western pacific warm pool wpwp using images core md972151 the glacial interglacial sst change is about 5 c for termination ii 23 5 to 28 5 c and 4 c for termination i 24 to 28 c the simultaneous rise of sea level and u37 sst during termination i suggests that sea level change has played an important role in the scs sst variability by influencing the exchange of tropical ocean warm surface water with the scs through the sunda shelf region sill depth 30 50 m when sea level drop was less than 30 m relative to today s md972151 sst was constantly above 27 c a situation which occurred during mis 5e part of mis5c and 5a and over the last 11 kyr sea level change was also the main control on carbonate content in the scs this was lower during low sea level stands due to the dilution effect of enhanced terrigenous inputs within the limitations of our age model millennial scale sst oscillations 1 5 c over a few hundred years occurred frequently during the entire glacial period correlating reasonably well with the hulu monsoon record from eastern china and the dansgaard oeschger d o cycles recorded for high latitude regions in the northern hemisphere such correlations suggest a possible teleconnection between higher latitude atmospheric forcing and low latitude climate oscillations in the western pacific tropical region via the asian monsoon system carbonate content also reveals millennial scale oscillations during the glacial period with higher content correlated with higher sst millennial scale fluctuations of sst and carbonate contents at this low latitude scs provide additional evidence that high frequency climate changes are global phenomena

constraints of crustal heterogeneity and q f from regional 4 hz wave propagation for the 2009 north korea nuclear testconstraints of crustal heterogeneity and q f from regional 4 hz wave propagation

nonisotropic radiation of the 2013 north korean nuclear explosion on 12 february 2013 north korea conducted an underground nuclear test in the northeastern mountainous part of the country the explosion reached magnitude mb 5 1 being recorded at most of seismic stations around the world and becoming one of the best ever recorded nuclear explosions in history similarly as other nuclear explosions buried in nevada kazakhstan or china the 2013 north korean explosion is characterized by a significant nonisotropic radiation this radiation is manifested by distinct sh and love waves in the wave field and is inconsistent with the model of a spherically symmetric source we show that the love waves are not generated by a tectonic earthquake triggered on a nearby fault structures but produced by asymmetry of the explosive source caused by presence of deviatoric stress in the surrounding rock the retrieved moment tensor of the 2013 explosion is characterized by the isotropic component of 57 5 the double couple component of 17 9 and the compensated linear vector dipole component of 24 7 the p t and n axes of the moment tensor are consistent with the principal axes of the regional tectonic stress in the korean peninsula a comparison of waveforms and particle motions of the 2013 explosion and the previous north korean nuclear explosion buried in 2009 indicates that the 2013 explosion was slightly more nonisotropic

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

aerosol size confines climate response to volcanic super eruptions extremely large volcanic eruptions have been linked to global climate change biotic turnover and for the younger toba tuff ytt eruption 74 000 years ago near extinction of modern humans one of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles a huge atmospheric concentration of sulfate causes higher collision rates larger particle sizes and rapid fall out which in turn greatly affects radiative feedbacks we address this key process by incorporating the effects of aerosol microphysical processes into an earth system model the temperature response is shorter 9 10 years and three times weaker 3 5 k at maximum globally than estimated before although cooling could still have reached 12 k in some midlatitude continental regions after one year the smaller response plus its geographic patchiness suggests that most biota may have escaped threshold extinction pressures from the eruption

ultra distal tephra deposits from super eruptions examples from toba indonesia and taupo volcanic zone new zealand abstract voluminous rhyolitic eruptions from toba indonesia and taupo volcanic zone tvz new zealand have dispersed volcanic ash over vast areas in the late quaternary the 74 ka youngest toba tuff ytt eruption deposited ash over the bay of bengal and the indian subcontinent to the west the 340 ka whakamaru eruption tvz deposited the widespread rangitawa tephra dominantly to the southeast in addition to occurrences northwest of vent extending across the landmass of new zealand and the south pacific ocean and tasman sea with distal terrestrial exposures on the chatham islands these super eruptions involved 2500 km 3 and 1500 km 3 of magma dense rock equivalent dre respectively ultra distal terrestrial exposures of ytt at two localities in india middle son valley madhya pradesh and jurreru river valley andhra pradesh at distances of 2000 km from the source caldera show a basal primary ashfall unit 4 cm thick although deposits containing reworked ash are up to 3 m in total thickness exposures of rangitawa tephra on the chatham islands 900 km from the source caldera are 15 30 cm thick at more proximal localities 200 km from source rangitawa tephra is 55 70 cm thick and characterized by a crystal rich basal layer and normal grading both distal tephra deposits are characterized by very fine ash with high pm 10 fractions and are crystal poor glass chemistry stratigraphy and grain size data for these distal tephra deposits are presented with comparisons of their correlation dispersal and preservation using field observations ash transport and deposition were modeled for both eruptions using a semi analytical model hazmap with assumptions concerning average wind direction and strength during eruption column shape and vent size model outputs provide new insights into eruption dynamics and better estimates of eruption volumes associated with tephra fallout modeling based on observed ytt distal tephra thicknesses indicate a relatively low

north korea s 2017 test and its nontectonic aftershock seismology illuminates physical processes occurring during underground explosions not all yet fully understood the thus far strongest north korean test of 3rd september 2017 was followed by a moderate seismic event ml 4 1 after 8 5 minutes here we provide evidence that this aftershock was a non tectonic event which radiated seismic waves as a buried horizontal closing crack this vigorous crack closure occurring shortly after the blast is studied in the north korea test site for the first time the event can be qualitatively explained as rapid destruction of an explosion generated cracked rock chimney due to cavity collapse although other compaction processes cannot be ruled out

a detailed framework of marine isotope stages 4 and 5 volcanic events recorded in two greenland ice cores sulphate records from greenland ice cores indicate that marine isotope stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial

quantitative assessment to the impact of insar ionospheric and tropospheric corrections on source parameter modelling application to the 4th nuclear test north korea

advanced seismic analyses of the source characteristics of the 2006 and 2009 north korean nuclear tests in 2006 and 2009 north korea conducted underground nuclear tests at a remote mountainous site in the northeastern part of the country both events were small leading to uncertainties for location yield estimation and discrimination based on seismic observations the objectives of the studies described in this paper have been to more fully exploit data from the international monitoring system ims network and other unclassified sources e g incorporated research institutions for seismology iris japanese national research institute for earth science and disaster prevention nied to analyze these nuclear tests we have used differential waveform interferometry dwif to refine relative locations for the tests and extended the methodology using observations from regional stations to estimate relative emplacement depths which are consistent with explosion source model predictions for broadband regional p wave spectral ratios topographic data from the test site were analyzed to constrain relative locations and depths needed for containment of the two tests based on normal testing practice network averaged teleseismic p wave spectra were inverted using a model based approach and provide explosion yield estimates in the range 0 6 1 0 kt for the 2006 test and 2 0 4 8 kt for the 2009 test depending on assumed emplacement depth detailed spectral analysis of broadband regional p observations are most consistent with theoretical explosion models with yields of 0 9 and 4 6 kt for the 2006 and 2009 tests respectively with associated source depths of 200 and 550 m consistent with previous studies the surface wave m s magnitudes for the 2006 and 2009 tests provide anomalously large m s yield estimates and problematic m s m b identification characteristics finite difference simulations of long period surface wave signals incorporating tensile prestress consistent with the regional tectonics lead to predicted m s values that agree much better with the observed values

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

new geochemical evidence for the youngest toba tuff in india abstract new geochemical data on tephra samples from a layer present at several archeological sites in india support correlation of this layer to the youngest toba tuff erupted from northern sumatra about 74 000 yr ago the data show that the indian tephra layer is not a correlative of older tephra erupted from toba as has been suggested on the basis of artifact assemblages previously published geochemical data on the indian tephra beds was based on bulk ash samples containing mineral and clay contaminants and the resulting variability in analyses did not allow identification or discrimination of individual eruptive events our new data were collected on individual glass shards and small purified glass separates which have greater resolving power in fingerprinting acheulian and paleolithic artifacts found at some of the indian tephra sites do not reflect the antiquity of the tephra bed as they occur in fluvial sediments and may be reworked

ytt ash from quaternary sediments of kapileshwar area purna alluvial basin central india abstract a thick pocket of volcanic ash 2 5 m represented by various shades of gray powdery massive to laminated in nature hosted in yellowish brown thinly bedded laminated silty clay lithocolumn has been studied for its preservational and geochemical aspects the ash column shows preservations of both primary and reworked ashes which are distinguishable on the basis of their field criteria including colors bedding geometries and thicknesses petrological study of the same reveals high representation of glass shards with bubble wall blocky and pumice morphologies minor occurrences of light and heavy minerals and unidentifiable admixture of fine grained sediments geochemistry of both bulk ash and glass shards through icp aes and epma respectively suggest high percentages of sio2 al2o3 na2o and k2o ree data generated through icp ms show strong negative eu anomaly the effects of weathering or aqueous solution on the geochemistry are also noticeable as evident by the variations in the values of both mobile and immobile elements however the data obtained from both bulk ash and glass shards are within the limits of ytt composition calm to very low energy environment of deposition is suggested for their deposition paleoclimatic proxies represented by rhizoliths rhizospheres rhizolith balls ant traces and vertebrate remains preserved in the pre tephra succession have also been commented

new occurrence of youngest toba tuff in abyssal sediments of the central indian basin abstract volcanic glass and pumice found in siliceous abyssal sediments of the central indian basin south of the equator have previously been assigned various origins including intra basin volcanism indonesian arc and krakatau rhyolitic glass shards dispersed in sediments from 8 cores that we have examined are compositionally identical to those of fallout deposits of the youngest toba tuff erupted at 74 ka from northern sumatra the correlation extends the distribution of coarse 63 m glass shards some 1500 km south of the previously known fallout zone and into the southern hemisphere reaching latitudes of ca 14 s this provides evidence for bi hemispheric dispersal of the ash cloud and supports global dispersal of gas and aerosols from the eruption such dispersal could have facilitated the global impact of the eruption

use of amphibole chemistry for detecting tephras in deep sea sequences chikyu c9001c cores and developing a middle pleistocene tephrochronology for ne japan abstract using amphibole crystals we detected tephras in deep sea sequences chikyu c9001c cores and correlated marine and terrestrial tephras in ne japan then we reconsidered some previously reported tephra ages by using the age model of the cores we identified 50 spikes in amphibole grains numbered a1 a50 from top to bottom among these 12 spikes a38 49 corresponded to a thick non tephric sand layer we selected 20 spikes containing amphibole grains with glass coatings as likely primary tephras and analyzed their chemistry for tephra characterization on the basis of its amphibole chemistry we correlated spike a34 with the tn cii ciii layers of the tanabu c tephra tn c which erupted from osore volcano on shimokita peninsula we then showed that spike a34 represents primary tephra deposition not secondary deposition through bioturbation or bottom current reworking because amphibole grains with homogeneous chemistry were accumulated only in sediment near the spike within 10 cm we also showed that the chemical variation within each amphibole grain was not as great as the variation between grains which further supports the correlation between spike a34 and tn cii ciii these findings show that amphibole grains which are resistant to weathering can be used for characterization and correlation of weathered tephras from which glass shards have been removed by dissolution the glass shard chemistry of the 16h6a 60 80 tephra at 4 58 m below spike a34 which does not correspond to an amphibole spike suggests that this tephra likely correlates with the amphibole free tn ci layer in the terrestrial sequences non tephric sediments marine sand and lahar deposits occur between tn ci and tn cii ciii suggesting that some time elapsed after the deposition of tn ci before tn cii ciii were deposited by using the stratigraphic information of the 16h6a 60 80 tephra and spike a34 together with the 18o stratigraphy of the deep sea sequence we re assigned the eruptive age of tn c from the previously reported zircon fission track age of 180 40 ka to mis 8 257 263 ka

characterization and correlation of cryptotephras using major element analyses of melt inclusions preserved in quartz in last interglacial marine sediments southeastern shikoku japan although sediments underlying marine terraces in se shikoku southwest japan contain no visible tephra layers late pleistocene cryptotephras were detected in a paleosol within the sediments the cryptotephras contained little or no glass but they were characterized through major element analyses of glass preserved as melt inclusions in quartz grains extracted from the paleosol the analyses enabled correlation of the cryptotephras with known eruptives from volcanoes on kyushu namely the kikai tozurahara tephra mis 5 2 5 3 the aira tn tephra 28 6 cal ka and the kikai akahoya tephra 7 5 cal ka these correlations enabled dating of the marine terrace surface known as the murotomisaki 1 surface in se shikoku as being older than mis 5 2 5 3 probably mis 5 5 in age in the absence of glass or mafic minerals because of weathering the analysis of melt inclusions in resistant quartz grains demonstrably provides a powerful method for characterizing cryptotephras to facilitate their correlation and thus their application as a linking and dating tool

source analysis of the memorial day explosion kimchaek north korea 1 a series of source inversions are performed for the 25 may 2009 memorial day north korean seismic event using intermediate period 10 50 s complete waveform modeling an earthquake source is inconsistent with the data and the best fit full seismic moment tensor is dominantly explosive 60 with a moment magnitude mw of 4 5 a pure explosion solution yields a scalar seismic moment of 1 8 1022 dyne cm mw4 1 and fits the data almost as well as the full solution the difference between the full and explosion solutions is the predicted fit to observed tangential displacement which requires some type of non isotropic non explosive radiation possible causes of the tangential displacement are additional tectonic sources tensile failure at depth and anisotropic wave propagation similar displacements may be hidden in the noise of the 2006 event future analyses of this type could be used to identify and characterize non earthquake events such as explosions and mine collapses

moment tensor analysis of very shallow sources an issue for moment tensor mt inversion of shallow seismic sources is that some components of the green s functions have vanishing amplitudes at the free surface which can result in bias in the mt solution the effects of the free surface on the stability of the mt method become important as we continue to investigate and improve the capabilities of regional full mt inversion for source type identification and discrimination it is important to understand free surface effects on discriminating shallow explosive sources for nuclear monitoring purposes it may also be important in natural systems that have very shallow seismicity such as volcanic and geothermal systems we examine the effects of the free surface on the mt via synthetic testing and apply the mt based discrimination method to three quarry blasts from the humming albatross experiment these shallow chemical explosions at 10 m depth and recorded up to several kilometers distance represent rather severe source station geometry in terms of free surface effects we show that the method is capable of recovering a predominantly explosive source mechanism and the combined waveform and first motion method enables the unique discrimination of these events recovering the design yield using seismic moment estimates from mt inversion remains challenging but we can begin to put error bounds on our moment estimates using the network sensitivity solution technique ford et al 2010 online material figures showing synthetic tests for a pure explosion and a composite source at local distances and table of moment tensor components

toward the snowball earth deglaciation the current state of knowledge suggests that the neoproterozoic snowball earth is far from deglaciation even at 0 2 bars of co2 since understanding the termination of the fully ice covered state is essential to sustain or not the snowball earth theory we used an atmospheric general climate model agcm to explore some key factors which could induce deglaciation after testing the models sensitivity to their parameterizations of clouds co2 and snow we investigated the warming effect caused by a dusty surface associated with ash release during a mega volcanic eruption we found that the snow aging process its dirtiness and the ash deposition on the snow free ice are key factors for deglaciation our modelling study suggests that under a co2 enriched atmosphere a dusty snowball earth could reach the deglaciation threshold

the toba volcanic event and interstadial stadial climates at the marine isotopic stage 5 to 4 transition in the northern indian ocean abstract the toba volcanic event one of the largest eruptions during the quaternary is documented in marine sediment cores from the northeastern arabian sea on the crest of the murray ridge and along the western indian continental margin we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5 4 boundary with the chemical composition of the youngest toba tuff time series of the uk 37 alkenone index planktic foraminiferal species magnetic susceptibility and sediment accumulation rates from this interval show that the toba event occurred between two warm periods lasting a few millennia using toba as an instantaneous stratigraphic marker for correlation between the marine and ice core chronostratigraphies these two arabian sea climatic events correspond to greenland interstadials 20 and 19 respectively our data sets thus depict substantial interstadial stadial fluctuations in sea surface temperature and surface water productivity we show that variable terrigenous eolian sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record within the provided stratigraphic resolution of several decades to centennials none of these proxies shows a particular impact of the toba eruption however our results are additional support that toba despite its exceptional magnitude had only a minor impact on the evolution of low latitude monsoonal climate on centennial to millennial time scales

reply to the comment on environmental impact of the 73 ka toba super eruption in south asia by m a j williams s h ambrose s van der kaars c ruehlemann u chattopadhyaya j pal p r chauhan palaeogeography palaeoclimatology palaeoecology 284 2009 295 314 abstract haslam and petraglia raise three broad questions concerning our paper environmental impact of the 73 ka toba super eruption in south asia by martin a j williams stanley h ambrose sander van der kaars carsten ruehlemann umesh chattopadhyaya jagannath pal parth r chauhan palaeogeography palaeoclimatology palaeoecology 284 2009 295 314 a what was the relationship between the 73 ka toba eruption and the cold stade between the dansgaard oeschger interstades 20 and 19 b what was the regional impact of the eruption on vegetation c what was the possible effect of the eruption upon humans and mammals in response to questions a and b we note that the 73 ka toba eruption was followed by several centuries of intense cooling and wind blown dust accession in the greenland gisp2 ice core by a change from forest to grassland or open woodland in central india carbon isotopic analysis and in the wider region pollen analysis of a marine sediment core in the bay of bengal in regard to c the genetic evidence is as yet too imprecisely dated to demonstrate causality as is the archaeological evidence cited by haslam and petraglia in favour of minimal impact future work supported by higher resolution chronologies than are presently available is needed to provide a less equivocal picture of the environmental impact of the 73 ka toba eruption

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

tropical rainforest vegetation climate and sea level during the pleistocene in kerala india abstract the southwestern ghats region of the indian peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year the record of tropical rainforest corresponding to the dynamic series of pleistocene interglacial glacial cycles is poorly known from peninsular india this communication discusses the palynological study of organic matter om deposits 40 ka bp in two well sections chaganachery kerala from the indian peninsula west coast a rich archive of tropical rainforest pollen spores and marine dinoflagellate cysts indicates anoxic fluvio marine estuarine depositional environments during warmer climates with an intensified asian monsoon the geochemical fingerprinting of glass shards indicates the presence of youngest toba ash of 74 ka from northern sumatra and therefore establishes a time controlled stratigraphy thus the depositional time period of the om is related to the sea level highstand of marine isotopic stage 5 1 80 ka which was the host to the ytt shards the late quaternary pollen spores diversity suggests that the modern climatic conditions in the southwestern ghats have facilitated the conservation of moist evergreen rainforest and dry moist deciduous forest the pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic tertiary period from the indian peninsula thus it appears that the tropical rainforest survived here as plant refugia in xeric glacial quaternary periods perhaps as riparian vegetation and was rejuvenated during the holocene as modern extant flora

did the 73 ka toba super eruption have an enduring effect insights from genetics prehistoric archaeology pollen analysis stable isotope geochemistry geomorphology ice cores and climate models abstract the potential impact of the 73 ka toba super eruption upon global and regional climate terrestrial ecosystems and prehistoric human populations remains unclear evidence from genetics prehistoric archaeology pollen analysis stable isotope geochemistry geomorphology ice cores and climate models has provided some useful working hypotheses further progress requires a substantial improvement in the accuracy precision and resolution of the chronologies of each of the marine and terrestrial proxy records used to reconstruct the environmental impact of this extreme event

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

relative surface wave amplitude and phase anomalies from the democratic people s republic of korea announced nuclear tests relative amplitude and phase anomalies we performed relative locations of six event pairs based on surface wave sw and body wave bw differential travel times of the 2016 09 09 2016 01 06 2013 02 12 and 2009 05 25 announced north korea nuclear explosions the sw relative locations for the 2009 05 25 and 2013 02 12 events were inconsistent with the bws when paired with other events and only the 2016 01 06 2016 09 09 pair was consistent apparent sw phase shift is investigated with respect to the bw relative locations the pairs formed with the 2009 05 25 and 2013 02 12 events beneath the southeast slope of mount mant ap have the largest phase shifts and amplitude ratio deviations whereas the least deviation was from the 2016 01 06 and 2016 09 09 event pair beneath the mountain peak regional moment tensors mts predict the amplitude ratios but do not resolve the relative phase we find mts with 10 difference in isotropic and rotated clvd can fit both relative phase and amplitude ratios sw relative locations of highly isotropic and correlated explosion clusters can be affected by topography and small differences in mt

environmental impact of the 73 ka toba super eruption in south asia abstract the cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery the eruption of toba volcano in northern sumatra some 73 000 years ago was the largest explosive eruption of the past two million years with a volcanic explosivity index of magnitude 8 but its impact on climate has been controversial in order to resolve this issue we have analysed pollen from a marine core in the bay of bengal with stratified toba ash and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central india pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation reflected in a decline in tree cover in india and the adjacent region carbon isotopes show that c 3 forest was replaced by wooded to open c 4 grassland in central india our results demonstrate that the toba eruption caused climatic cooling and prolonged deforestation in south asia and challenge claims of minimal impact on tropical ecosystems and human populations

cooling of the south china sea by the toba eruption and correlation with other climate proxies 71 000 years ago the toba tephra layer has been identified in core md972151 in the southern south china sea scs northeast of the indonesia toba caldera this affords us an opportunity to directly determine a 1 c cooling for ca 1 kyr on the scs following the toba eruption 71 ka during the marine isotope stage 5a 4 transition using century scale sea surface temperature records this cooling event in the scs is well correlated with several coeval proxies such as increased east asia winter monsoon intensity increased ice rafted detritus in the north pacific ocean sediments and decreased 18 o in greenland ice core such correlation suggests a climate change where cold climate signals originated in the northern hemisphere ice sheets transferred southward by the winter monsoon and cooled the scs

limited global change due to the largest known quaternary eruption toba 74 kyr bp abstract the 74 kyr bp super eruption of toba volcano in sumatra is the largest known quaternary eruption on the basis of preserved deposits the eruption magnitude has been estimated at 7 10 15 kg 2800 km 3 of dense magma the largest sulphate anomaly in the greenland ice sheet project 2 core has been identified as fallout from toba s stratospheric aerosol veil correlation of the sulphate and oxygen isotope stratigraphy of the ice core suggests that the toba eruption might have played a role in triggering a millennium of cool climate prior to dansgaard oeschger event 19 although a comparable stadial preceded event 20 a possible 6 yr duration volcanic winter immediately following the eruption has also been proposed as the cause of a putative bottleneck in human population supporting in a general way the garden of eden model for the origin of modern humans however along with counter arguments regarding the timing of any demographic crash there remain major gaps in our understanding of the 74 kyr bp toba eruption that hinder attempts to model its global atmospheric and climatic and hence human consequences the tephra record reveals basic aspects of the eruption style but calculations of the duration and hence intensity and plume height of the event are poorly constrained furthermore estimates of the sulphur yield of the erupting magma central to predictions of its atmospheric and climatic impacts vary by two orders of magnitude 3 5 330 10 10 kg previous estimates of globally averaged surface cooling of 3 5 c after the eruption are probably too high a figure closer to 1 c appears more realistic the volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the toba super eruption

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

toba ash layers in the south china sea evidence of contrasting wind directions during eruption ca 74 ka two cores from the southern south china sea contain discrete ash layers that mainly consist of rhyolithic glass shards on the basis of the specmap time scale the ash layers were dated to ca 74 ka the age of the youngest toba eruption in northern sumatra this link is supported by the chemical composition of the glass which is distinct from volcanic glass supplied from the philippines and the northern south china sea but is almost identical with the chemistry of the toba ash the youngest toba ash layers in the south china sea expand the previously known ash fall zone over more than 1800 km to the east the dispersal of ashes from sumatra in both western and eastern directions indicates two contrasting wind directions and suggests that 1 the toba eruption probably happened during the southeast asian summer monsoon season and 2 the volume of erupted magma was larger than previously interpreted

precise u pb baddeleyite ages of mafic dykes and intrusions in southern west greenland and implications for a possible reconstruction with the superior craton the archaean block of southern greenland constitutes the core of the north atlantic craton nac and is host to a large number of precambrian mafic intrusions and dyke swarms many of which are regionally extensive but poorly dated for southern west greenland we present a u pb zircon age of 2990 13 ma for the amikoq mafic ultramafic layered intrusion fiskefjord area and four baddeleyite u pb ages of precambrian dolerite dykes specifically a dyke located se of ameralik fjord is dated at 2499 2 ma similar to a previously reported ar 40 ar 39 age of a dyke in the kangamiut area for these and related intrusions of ca 2 5 ga age in southern west greenland we propose the name kilaarsarfik dykes three wnw trending dykes of the md3 swarm yield ages of 2050 2 ma 2041 3 ma and 2029 3 ma a similar u pb baddeleyite age of 2045 2 ma is also presented for a se trending dolerite iglusuataliksuak dyke in the nain province the rifted western block of the nac in labrador we speculate that the md3 dykes and age equivalent nne trending kangamiut dykes of southern west greenland together with the iglusuataliksuak dyke after closure of the labrador sea represent components of a single areally extensive radiating swarm that signaled the arrival of a mantle plume centred on what is presently the western margin of the north atlantic craton comparison of the magmatic barcodes from the nain and greenland portions of the north atlantic craton with the established record from the north eastern superior craton shows matches at 2500 ma 2214 ma 2050 2030 ma and 1960 1950 ma we use these new age constraints together with orientations of the dyke swarms to offer a preliminary reconstruction of the north atlantic craton near the north eastern margin of the superior craton during the latest archaean and early palaeoproterozoic possibly with the core zone craton of eastern canada intervening c 2010 elsevier b v all rights reserved less

depth estimate of the dprk s 2006 10 09 2009 05 25 and 2013 02 12 underground nuclear tests using local and teleseismic arrays abstract the democratic people s republic of korea dprk aka north korea conducted underground nuclear explosions on october 9 2006 m 4 3 may 25 2009 m 4 7 and february 12 2013 m 5 1 we expanded standard depth calculation methods to encompass full depth utilizing spectral nulls of spectra using body waves and rayleigh waves from local and teleseismic arrays the depths of burial were calculated from the fundamental mode rayleigh wave spectra as well as the average spectra of depth phase pp p sp p ppn pn spn pn considering take off angles based on the flat earth model the average depths of the 2006 2009 and 2013 nuclear tests were thus estimated at 2 12 km 2 06 km and 2 05 km respectively it should be noted that those depths are significantly greater than expected from the standard experiment practice the possibility of the over buried nuclear tests would affect the interpretation of ms mb discriminants as well as the estimation of the yield

toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium the toba ash occurs extensively in the indian subcontinent and marks a ca 74 000 yr old event in the bay of bengal and indian ocean it is about 10 cm thick whereas in several alluvial basins it is usually 1 3 m thick the latter occurs in a partly reworked state but as nearly chemically pure first cycle sediments the ash has a broad northwesterly dispersal pattern samples of ash from the indian subcontinent compare closely with the youngest 74 000 yr b p toba tuff and the deep sea toba ash in bulk chemical composition ree signature and bubble wall shard morphology however a more proximally located and thicker 2 5 m ash bed from the alluvial basins in the gneissic area and close to east coast has a lower magnitude negative eu anomaly possibly because of minor contamination by feldspathic silt quaternary sediments in the central narmada and middle son basins contain rich late and middle pleistocene mammalian and cultural records based on the presence of the ash layer marker and stratigraphic relations late pleistocene sediments within the subcontinent can be correlated with those from central india and the deep sea

the 73 ka toba super eruption and its impact history of a debate abstract toba volcano in northern sumatra is located at the intersection of two major tectonic lineaments in one of the most seismically active regions in the world and its caldera is considered the largest quaternary caldera on earth the most recent toba explosive eruption at 73 ka was an order of magnitude larger than that of tambora in 1815 and has a volcanic explosivity index of 8 the exceptional magnitude of this super eruption and the widespread distribution of the younger toba tuff ytt in marine cores in the indian ocean the arabian sea and the south china sea have prompted sustained debate as to its global and regional impact on climate ecosystems and prehistoric human populations however despite climate modelling and appeals to a variety of proxy climatic data including geochemistry pollen analysis archaeology and stable isotopes the extent of the impact remains unclear in order to achieve better progress in the future greater care is needed to obtain higher resolution and more precise chronologies from the marine and terrestrial proxy records used to test whether or not the 73 ka toba super eruption had a significant environmental impact records from speleothems and ice cores have much to offer in this regard

phenocrysts versus xenocrysts in the youngest toba tuff implications for the petrogenesis of 2800 km3 of magma the petrogenesis of the 2800 km 3 of magma erupted as the youngest toba tuff has been investigated using experimental petrology and 40 ar 39 ar dating of biotite sanidine hornblende and plagioclase from the tuff we find that hornblende does not crystallize experimentally from the magma at temperatures and pressures indicated by the natural mineral assemblage hornblende is also not in isotopic equilibrium with biotite and sanidine both of which grew experimentally hornblende thus appears xenocrystic despite being a major phase in the tuff some plagioclase is also xenocrystic on the basis of ar isotopes but others are probably phenocrystic because plagioclase grew experimentally crystal clots of hornblende plagioclase observed in the tuff suggest that the xenocrysts came from a common source which was at least 1 5 ma the oldest hornblende 40 ar 39 ar age our results suggest that the toba tuff magma resided at nearly water saturated pressures of 100 150 mpa and that xenocrysts were entrained as recently as 10 yr before the eruption the ubiquitous presence of hornblende in the tuff indicates that entrainment occurred throughout the 2800 km 3 of magma