estimating s wave attenuation in sediments by deconvolution analysis of kik net borehole seismograms abstract s wave attenuation characteristics of sediments are important for accurate prediction of ground motion high quality borehole seismic observation data have been accumulated in japan since the construction of kik net a nationwide network in the early 2000s we estimated s wave attenuation values in sediments by applying a new deconvolution method to kik net data first incident and surface reflected waves from local earthquakes are separated by deconvolving the seismogram from the bottom of the borehole with the seismogram from the ground surface then values of sediments are estimated from transfer functions or system functions between incident and surface reflected waves that are stacked with respect to available earthquakes applying the deconvolution method to the records from kik net stations having boreholes deeper than 300 m we obtained stable estimates of values in the 0 5 10 hz range at 16 stations the values decrease with frequency up to about 2 3 hz but become nearly constant at higher frequencies by fitting a power law function to the values at frequencies lower than 2 hz values at 1 hz ranged from 0 02 to 0 2 and the exponent of the power law ranged from 0 12 to 1 00 the obtained values show clear depth dependence our results are consistent with values estimated by previous studies which supports the usefulness of our new method

tephrochronology and absolute centennial scale synchronisation of european and greenland records for the last glacial to interglacial transition a case study of soppensee and ngrip the tephrostratigraphy of soppensee switzerland is presented here for the first time with new geochemical data for four tephra layers derived from three volcanic centres the best available age estimates for the laacher see tephra and vedde ash layers are incorporated into a revision of the radiocarbon based bayesian age model for the last glacial to interglacial transition at soppensee which is used to explore synchronicity of climatic events between europe and the north atlantic local temperature changes recorded by biotic and abiotic proxies in soppensee appear to shift in phase with the oxygen isotope signal in greenland at the onset of the younger dryas however with the clarity of improved precision an apparent offset that likely results from a dating artefact is seen between records at the termination of the stadial event from a methodological standpoint the results clearly show that only by establishing detailed and independent chronological frameworks can abrupt climatic variability be compared between different regions with sufficiently high temporal precision to addresses the notion of hemispheric climatic synchronicity at the centennial scale in the late quaternary continuing to develop such approaches is therefore essential in order to understand how far in time and space the climate has behaved in such a way

ludlow and pridoli upper silurian graptolite biostratigraphy of the central arctic islands a preliminary report a fauna comprising slightly more than 30 species of upper silurian graptolites has been recognized from the arctic islands the following preliminary biostratigraphic biozones are recognizable l

ages of 24 widespread tephras erupted since 30 000 years ago in new zealand with re evaluation of the timing and palaeoclimatic implications of the lateglacial cool episode recorded at kaipo bog abstract tephras are important for the nz intimate project because they link all three records comprising the composite inter regional stratotype developed for the new zealand climate event stratigraphy nz ces here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30 000 calendar cal years ago in new zealand to help facilitate their use as chronostratigraphic dating tools for the nz ces and for other palaeoenvironmental and geological applications the selected tephras comprise 12 rhyolitic tephras from taupo nine rhyolitic tephras from okataina one peralkaline rhyolitic tephra from tuhua and one andesitic tephra each from tongariro and egmont taranaki volcanic centres age models for the tephras were obtained using three methods i 14 c based wiggle match dating of wood from trees killed by volcanic eruptions these dates published previously ii flexible depositional modelling of a high resolution 14 c dated age depth sequence at kaipo bog using two bayesian based modelling programs bacon and oxcal s p sequence function and the intcal09 data set with sh offset correction 44 17 yr and iii calibration of 14 c ages using oxcal s tau boundary function and the shcal04 and intcal09 data sets our preferred dates or calibrated ages for the 24 tephras are as follows youngest to oldest all mid point or mean ages of 95 probability ranges kaharoa ad 1314 12 taupo unit y ad 232 10 mapara unit x 2059 118 cal yr bp whakaipo unit v 2800 60 cal yr bp waimihia unit s 3401 108 cal yr bp stent unit q 4322 112 cal yr bp unit k 5111 210 cal yr bp whakatane 5526 145 cal yr bp tuhua 6577 547 cal yr bp mamaku 7940 257 cal yr bp rotoma 9423 120 cal yr bp opepe unit e 9991 160 cal yr bp poronui unit c 11 170 115 cal yr bp karapiti unit b 11 460 172 cal yr bp okupata 11 767 192 cal yr bp konini bed b 11 880 183 cal yr bp waiohau 14 009 155 cal yr bp rotorua 15 635 412 cal yr bp rerewhakaaitu 17 496 462 cal yr bp okareka 21 858 290 cal yr bp te rere 25 171 964 cal yr bp kawakawa oruanui 25 358 162 cal yr bp poihipi 28 446 670 cal yr bp and okaia 28 621 1428 cal yr bp secondly we have re dated the start and end of the lateglacial cool episode climate event nzce 3 in the nz ces previously referred to as the lateglacial climate reversal as defined at kaipo bog in eastern north island new zealand using both bacon and oxcal p sequence modelling with the intcal09 data set the ca 1200 yr long cool episode indicated by a lithostratigraphic change in the kaipo peat sequence to grey mud with lowered carbon content and a high resolution pollen derived cooling signal began 13 739 125 cal yr bp and ended 12 550 140 cal yr bp mid point ages of the 95 highest posterior density regions bacon modelling the oxcal modelling generating almost identical ages confirmed these ages the lateglacial cool episode ca 13 8 12 6 cal ka bp thus overlaps a large part of the entire antarctic cold reversal chronozone ca 14 1 12 4 cal ka bp or ca 14 6 12 8 cal ka bp and an early part of the greenland stadial 1 younger dryas chronozone ca 12 9 11 7 cal ka bp the timing of the lateglacial cool episode at kaipo is broadly consistent with the latitudinal patterns in the antarctic cold reversal signal suggested for the new zealand archipelago from marine and terrestrial records and with records from southern south america

holocene vegetation and volcanic activity auckland isthmus new zealand a 12 000 to 4000 yr bp pollen and tephra bearing profile from auckland new zealand provides insights into the vegetation history and evidence for early holocene volcanic activity in this area centred on the mount wellington basaltic volcano possibly 500 yr separated initial scoriaceous ash deposition ca 9500 yr ago and subsequent major lava flows ca 9000 yr ago from mount wellington the local vegelation topography and drainage patterns were substantially modified during this time and damming by the lava flows resulted in the formation of lake waiatarua in a shallow valley head ca 9000 yr ago diatom evidence indicates that this lake was initially deep 5 m but was shallowing around 4000 yr ago in contrast to the mount wellington eruptions tephra deposition resulting from distant rhyolitic volcanic activity of the central north island and mayor island has had little effect on the auckland vegetation during this time interval 12 000 4000 yr ago between ca 12 000 and 10 000 yr ago conifer angiosperm forest was the predominant vegetation cover on auckland isthmus but during the early holocene forest dominated by metrosideros expanded probably on to fresh volcanic surfaces resulting from the mount wellington eruptions at this time swamp forest communities developed in waiatarua valley basin and included species indicative of moist mild relatively frost free climates some taxa show histories consistent with other records from the northern new zealand region including the rise of ascarina lucida ca 11 000 to 9000 yr ago and its subsequent decline and the expansion of agathis australis kauri forest communities from ca 6000 yr ago taken together the history of local and regional vegetation points to a mild moist and weakly seasonal early holocene climate which subsequently became drier with greater seasonal temperature extremes

toward a comprehensive upper quaternary tephra and ignimbrite stratigraphy in new zealand using electron microprobe analysis of glass shards abstract new zealand quaternary marine and terrestrial sequences contain numerous tephras or volcanic ash horizons that are the distal correlatives of voluminous welded ignimbrite sheets erupted from central north island electron microprobe analyses of glass shards from the distal tephras demonstrate their homogeneity and are shown to identify each tephra examined by matching tephras from stratigraphically controlled sequences the first comprehensive tephra stratigraphy spanning from 50 000 to 700 000 yr ago and covering the new zealand region is advanced analyses on glass shards from the unwelded base of ignimbrite sheets are comparable to the distal tephra analyses and allow correlation between ignimbrites and to the distal tephras the better exposed tephra record constrains the number of separate eruptive events and the stratigraphy of the ignimbrites both of which were previously confused by lack of outcrop samples from pumiceous marine sediments were found to contain two or more chemically distinct populations of glass the pumice is in cross bedded sands or sand lenses within conglomerate attesting to a shallow high energy environment where reworking could occur however each glass population could be matched to older known tephras

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

the seismic response of two dimensional sedimentary deposits with large vertical velocity gradients an extension of the aki larner technique to vertically inhomogeneous media is presented so that vertical velocity gradients may be taken into account in two dimensional models only sh waves are considered here but the theory is valid for p and sv waves as well this method is applied to investigate the seismic response of two dimensional sedimentary deposits with large velocity gradients three different cases are considered a shallow high contrast valley a deep high contrast valley and a deep low contrast valley in each case a comparison is performed with the results of a two dimensional model taking into account only homogeneous sediments and a one dimensional model taking into account the vertical inhomogeneity of sediments the presence of a large velocity gradient does not change a lot the qualitative behavior of a two dimensional deposit local surface waves and or two dimensional resonance patterns are observed as in the case of homogeneous sediments nevertheless the surface waves are much more dispersive with lower phase and group velocities and larger amplitudes only very deep valleys give rise to the development of two dimensional resonance on the other hand the amplifications obtained in such deposits may reach much larger values than those predicted with either two dimensional homogeneous models or one dimensional inhomogeneous models since these results have been obtained for realistic values of valley geometrical and mechanical considerations they should find some application in earthquake engineering or seismic microzonation studies

distal volcanic ash layers in the lateglacial interstadial gi 1 problems of stratigraphic discrimination abstract a new icelandic ash layer has been detected in mid interstadial sediments in a number of scottish lateglacial sequences and has been named the penifiler tephra it is rhyolitic in composition and possesses a chemistry which is similar to the borrobol tephra of early lateglacial interstadial age which also occurs in a number of these same sequences where the borrobol tephra has been identified in these sequences it consistently exhibits a diffuse distribution accompanied in some cases by stratigraphic bimodality a number of sedimentological and taphonomic factors are considered in order to account for this distribution one possibility is that these distributions are produced by taphonomic factors another possibility is that the borrobol tephra may not be the product of a single icelandic eruption but of two events closely spaced in time in at least two of the sequences investigated in this study basaltic shards were found in association with the penifiler and borrobol tephras suggesting either a basaltic phase associated with these eruptions or coincident eruptions from a separate basaltic volcanic centre the discovery of the new penifiler tephra makes a contribution to the regional tephrostratigraphic framework and provides an additional isochron for assessing the synchroneity of palaeoenvironmental changes during the interstadial the true stratigraphic nature and age of the borrobol tephra however remains unresolved and therefore its use as an isochron is more problematic the possible occurrence of basaltic populations may strengthen correlations with basaltic tephras recently detected in the ngrip ice core

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

time lapse changes of seismic velocity in the shallow ground caused by strong ground motion shock of the 2000 western tottori earthquake japan as revealed from coda deconvolution analysis abstract a large earthquake shock often drops the seismic velocity of the shallow ground however it is not clear whether the dropped velocity recovers shortly after the earthquake shock or not the purpose of this article is to report the time lapse changes of seismic velocity in the shallow ground after the 2000 western tottori earthquake japan we deconvolve the coda record of small earthquakes registered on the ground surface by that registered at the 100 m depth in a borehole at a station that experienced a strong shock from the mainshock because coda waves are mostly composed of randomly scattered s waves deconvolution of the two coda records enables us to obtain a robust image of the ground structure assuming that the shear modulus was reduced at the depth of 0 11 m we estimate the shear modulus change in each time period after the mainshock by fitting synthetic coda deconvolution to the observed one from 1 to 16 hz as a result the shear modulus dropped to 52 of the value obtained before the mainshock a few minutes after the strong earthquake shock this caused a decrease in the s wave velocity of 30 and an increase in s wave travel time of 17 msec the shear modulus continued to recover for over 1 yr following the logarithm of the lapse time it recovered to 69 83 87 and 97 of the value obtained before the mainshock in the periods of 0 to 1 week 1 week to 1 month 1 month to 1 yr and 1 to 4 yr after the mainshock respectively

multi proxy evidence of late holocene human induced environmental changes at lake pupuke auckland new zealand abstract new zealand was the last major landmass in the world to be colonised by people despite the short time depth of human presence in the country there is ongoing debate about the date of earliest arrival of people that resulted in the emergence of two contrasting colonisation hypotheses the early hypothesis and the short prehistory to decide between both hypotheses we employed a range of multi proxy investigations geochemistry stable isotopes and mineral magnetism on a lacustrine sequence from lake pupuke a maar lake in the city of auckland and an area potentially among the first places in new zealand to have been colonised by early people the environmental history reconstructed from the multi proxy evidence identified a clear lack of catchment disturbance from c 2000 b p until several decades before the eruption of the rangitoto volcano the nature and abruptness of disturbance unambiguously point to anthropogenic forcings and are likely to mark the onset of prehistoric human colonisation at the site linear interpolation between independently dated tephrochronostratigraphic marker beds present in the sediments allowed to date this event to c 610 cal yr b p this date is in compliance with the short prehistory for this region

the atakoy vertical array turkey insights into seismic wave propagation in the shallow most crustal layers by waveform deconvolution summary a vertical array of accelerometers was installed in atak oy western istanbul with the longterm aim of improving our understanding of in situ soil behaviour to assess the modelling and parametric uncertainties associated with the employed methodologies for strong motion site response analysis and for shallow geological investigations geotechnical and geophysical investigations were carried out to define the subsoil structure at the selected site data associated with 10 earthquakes 2 7 m 4 3 collected during the first months of operation of the array were used to image the upgoing and downgoing waves by deconvolution of waveforms recorded at different depths results have shown that the velocity of propagation of the imaged upgoing and downgoing waves in the borehole is consistent with that of s or p waves depending on the component of ground acceleration analysed but independent of the chosen signal window in particular an excellent agreement was found between the observed upgoing and downgoing wave traveltimes and the ones calculated using a model derived by seismic noise analysis of array data the presence of a smaller pulse on the waveforms obtained by deconvolution of the horizontal components suggests both internal s wave reflection and s to p mode conversion as well as a not normal incidence of the wavefield the presence of a pulse propagating with s wave velocity in the uppermost 25 m in the waveforms obtained by the deconvolution of the vertical components suggests p to s mode conversion these evidences imply that even when site amplification is mainly related to 1 d effects the standard practice in engineering seismology of deconvolving the surface recording down to the bedrock using an approximate s wave transfer function generally valid for vertical incidence of sh waves might lead to errors in the estimation of the input ground motion required in engineering calculations finally downgoing waves with significant amplitudes were found down to 70 m and even to 140 m depth this result provides a warning about the use of shallow borehole recordings as input for the numerical simulation of ground motion and for the derivation of ground motion prediction relationships

towards a late quaternary tephrochronological framework for the southernmost part of south america the laguna potrok aike tephra record abstract a total of 18 tephra samples have been analysed from the composite sediment sequence from site 2 of the laguna potrok aike icdp expedition 5022 from southern patagonia argentina which extends back to ca 51 ka cal bp analyses of the volcanic glass show that all layers but one are rhyolitic in composition with sio2 contents ranging between ca 74 5 and 78 wt and suggest an origin in the austral andean volcanic zone avz 49 55 s nonetheless two main data clusters occur one group with k2o contents between ca 1 5 and 2 0 wt indicating an origin in the mt burney volcanic area and one group with k2o contents between ca 2 7 and 3 9 wt tentatively correlated with viedma lautaro and the aguilera volcanoes in the northern part of the avz the early holocene tephra mb1 and the late pleistocene reclus r1 tephra occur in the upper part of the sequence periods with significant tephra deposition occurred between ca 51 44 ka cal bp and ca 31 25 ka cal bp with a decrease in tephra layer frequency between these two periods

3d viscoelastic wave propagation in the upper borrego valley california constrained by borehole and surface data we have simulated 2 hz wave propagation in a three dimensional model of the upper borrego valley southern california for a m 4 9 earthquake with epicenter 5 km north of the valley a 4th order staggered grid finite difference method was used to calculate viscoelastic ground motion in a basin model 9 km by 5 km by 0 4 km consisting of heterogeneous sediments surrounded by bedrock we simulated the earthquake as a double couple point source and computed the ground motions in the valley separately for the parts of the source incident from below and from the north the earthquake was recorded by a surface array as well as a deep downhole array 0 238 m depth in the center of the valley all equipped with digital three component seismic instruments the simulation reproduces the overall pattern of ground motions at basin and borehole sites and shows a good correlation of observed to synthetic waveforms in particular the 3d simulation reproduces the recorded peak motions cumulative kinetic energies and fourier spectral amplitudes within a factor of 2 for most components at the individual sites the correlation between data and simulation allows us to identify the secondary arrivals in the records as love and rayleigh waves generated at the edges of the valley and the troughs of the basin the peak velocities for the waves incident into the valley from below are generally more than an order of magnitude larger than those for the waves incident from the north the success of the prediction requires the inclusion of anelastic attenuation in the simulation with q values for p and s waves in the alluvium of about 30 we also used a profile of the 3d model and the soil parameters at the deep borehole to examine the ability of 2 5d and 1d model approximations to predict the data the maximum peak velocities and total cumulative kinetic energies are reproduced at the recording sites within a factor of 2 for both 2 5d and 1d model approximations but are underpredicted by up to an order of magnitude at some depths for individual components in particular the 2 5d and 1d simulations tend to underpredict the duration

distal record of multi sourced tephra in onepoto basin auckland new zealand implications for volcanic chronology frequency and hazards we have documented 80 tephra beds dating from ca 9 5 to 50 ka contained within continuously deposited palaeolake sediments from onepoto basin a volcanic explosion crater in auckland new zealand the known sources for distal 190 km from vent tephra include the rhyolitic taupo volcanic centre 4 and okataina volcanic centre 14 and the andesitic taranaki volcano 40 and tongariro volcanic centre 3 the record provides evidence for four new events between ca 50 and 28 ka mangaone subgroup suggesting okataina was more active than previously known the tephra record also greatly extends the known northern dispersal of other mangaone subgroup tephra ten rhyolitic tephra pre date the rotoehu eruption ca 50 ka and some are chemically dissimilar to post 50 ka rhyolites some of these older tephra were produced by large magnitude events however their source remains uncertain eight tephra from the local basaltic auckland volcanic field avf are also identified interpolation of sedimentation rates allow us to estimate the timing of 12 major explosive eruptions from taranaki volcano in the 27 5 9 5 ka period in addition 28 older events are recognised the tephra are trachytic to rhyolitic in composition all have high k2o contents 3 wt and there are no temporal trends this contrasts with the proximal lava record that shows a trend of increasing k2o with time by combining the onepoto tephra record with that of the previously documented pukaki crater 15 avf basaltic fall events are constrained at 34 6 30 9 29 6 29 6 25 7 25 2 24 2 23 8 19 4 19 4 15 8 and 14 5 ka and three pre 50 ka events this provides some of the best age constraints for the avf and the only reliable data for hazard recurrence calculations the minimum event frequency of both distal and local fall events can be estimated and demonstrates the auckland city region is frequently impacted by ash fall from many volcanoes

tools and techniques for developing tephra stratigraphies in lake cores a case study from the basaltic auckland volcanic field new zealand abstract probabilistic hazard forecasting for a volcanic region relies on understanding and reconstructing the eruptive record derived potentially from proximal as well as distal volcanoes tephrostratigraphy is commonly used as a reconstructive tool by cross correlating tephra deposits to create a stratigraphic framework that can be used to assess magnitude frequency relationships for eruptive histories when applied to widespread rhyolitic deposits tephra identifications and correlations have been successful however the identification and correlation of basaltic tephras are more problematic here using tephras in drill cores from six maars in the auckland volcanic field avf new zealand we show how x ray density scanning coupled with magnetic susceptibility analysis can be used to accurately and reliably identify basaltic glass shard bearing horizons in lacustrine sediments and which when combined with the major and trace element signatures of the tephras can be used to distinguish primary from reworked layers after reliably identifying primary vs reworked basaltic horizons within the cores we detail an improved method for cross core correlation based on stratigraphy and geochemical fingerprinting we present major and trace element data for individual glass shards from 57 separate basaltic horizons identified within the cores our results suggest that in cases where major element compositions sio2 cao al2o3 feo mgo do not provide unambiguous correlations trace elements e g la gd yb zr nb nd and trace element ratios e g la yb n gd yb n zr yb n are successful in improving the compositional distinction between the avf basaltic tephra horizons thereby allowing an improved eruptive history of the avf to be reconstructed

sourcing and identifying andesitic tephras using major oxide titanomagnetite and hornblende chemistry egmont volcano and tongariro volcanic centre new zealand canonical discriminant function analysis was employed to discriminate between electron microprobe determined titanomagnetite and hornblende analyses from egmont volcano and tongariro volcanic centre data sets of 436 titanomagnetite and 206 hornblende analyses from the two sources were used for the study titanomagnetite chemistry provided the best discrimination between these two sources with classification efficiencies of 99 for sample averages and 95 for individual analyses the difference between sources for hornblende chemistry was less marked but classification efficiencies of 100 for sample averages and 87 for individual analyses were achieved using the same methods a preliminary discrimination of individual egmont volcano sourced tephras was attempted titanomagnetite chemistry enabled the discrimination of several individual tephras or at least pairs of tephra units but hornblende chemistry provided little discrimination this technique provides an improvement on previous methods for chemically distinguishing distal tephra from the two sources as well as potentially identifying individual tephras from a particular source a major advantage over previous discrimination techniques is that individual analyses can be classified with a known probability of group membership with groups such as volcano source or an individual tephra unit tephras in a depositional environment where mixing is common such as within soil loess and marine sequences can be sourced or identified more easily with classification of individual grains

rapid change in early holocene environments inferred from lake pupuke auckland city new zealand sediment cores from lake pupuke in auckland city new zealand contain a high resolution millennial to centennial scale record of changing climate and catchment hydrology spanning the past ca 10 000 years here we focus on the period between 9500 25 and 7000 155 cal yr bp during which grain size diatom palaeoecology biogenic silica concentrations sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions with a significant event commencing at ca 8240 cal yr bp commensurate with a lowering of lake level faster erosion rates and increased sediment influx with a duration of ca 360 yrs however the changes in the lake are not reflected in the terrestrial vegetation where the pollen record indicates that podocarp forest dominated the auckland region with apparent environmental stability during this part of the early holocene the synchronous change in most of the proxies between ca 8240 and 7880 cal yr bp at lake pupuke indicates the presence of a sustained episode of relatively low lake level and concomitant increased rate of erosion in the early holocene that appears to be at least partly coeval with the 8200 cal yr bp meltwater event proposed for the north atlantic region copyright 2008 john wiley sons ltd

identification of cryptotephra horizons in a north east atlantic marine record spanning marine isotope stages 4 and 5a 60 000 82 000 a b2k abstract tephrochronology is one of the few techniques that offer considerable but as yet largely unrealised potential for the correlation of north atlantic palaeoclimatic archives spanning the mis 4 and 5a substage period a phase of pronounced global cooling during the initiation of the last glacial period in this investigation two previously unidentified rhyolitic tephra horizons believed to be sourced from iceland were isolated within the giant piston core md04 2822 retrieved from the rockall trough north east atlantic one horizon was deposited at the beginning of greenland stadial 19 70 150 a b2k and the other around the cooling transition at the end of greenland interstadial 20 75 320 a b2k density separation epma and la icp ms techniques were utilised for the identification of these cryptotephra within the fine fraction sediment

extracting a primary holocene crytoptephra record from pupuke maar sediments auckland new zealand post depositional reworking of volcanic glass shards is a common problem in tephrochronological studies distinguishing between primary and reworked tephra is challenging particularly in cryptotephra investigations that depend on identifying peaks of glass shard concentrations in sediment sequences rather than discrete macroscopic tephra layers here we investigated macro and cryptotephra in sediments of lake pupuke new zealand to identify primary from reworked tephra and thus refine the record of tephra fall events in the region over the last ca 9 cal ka geochemical fingerprinting stratigraphic correlation 14c ages and x ray fluorescence and magnetic susceptibility core scanning were employed to filter out reworked tephra and thus establish a new holocene tephrochronological framework for the region five primary macrotephra layers and 18 primary cryptotephra were identified confidence levels are attached to the newly identified cryptotephra and geochemical characterization of well dated rhyolite tephra was used to establish an associated age model our results suggest that holocene tephra fall from both local and distal volcanoes affected auckland more frequently than previously documented with a possible average frequency of at least once every 424 years furthermore the study demonstrates the importance of identifying the extent of post depositional reworking to establish the veracity of the cryptotephra record

attenuation and velocity structure for site response analyses via downhole seismogram inversion a seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude downhole array recordings based on a global optimization scheme in the wavelet domain complemented by a local least square s fit operator in the frequency domain the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space whereas the best fit model detection is substantially accelerated through the local deterministic inversion results presented for selected aftershocks of the mw 7 0 sanriku minami earthquake in japan recorded by the kik net strong motion network illustrate robustness of the impedance structure estimation by contrast the attenuation structure is shown to be sensitive to the frequency content of seismic input data attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple scattered energy sensitivity analyses illustrate that for the same forward model results can be substantially different based on the definition of the objective function it is concluded that even for engineering purposes inversion should aim to decouple intrinsic and scattering attenuation mechanisms

assessing the applicability of deconvolution of borehole records for determining near surface shear wave attenuationassessing the applicability of deconvolution of borehole records

a summary of attenuation measurements from borehole recordings of earthquakes the 10 hz transition problem earthquake seismograms recorded by instruments in deep boreholes have low levels of background noise and wide signal bandwidth they have been used to extend our knowledge of crustal attenuation both in the near surface and at seismogenic depths site effects are of major importance to seismic hazard estimation and the comparison of surface shallow and deep recordings allows direct determination of the attenuation in the near surface all studies to date have found that q is very low in the near surface 10 in the upper 100 m and increases rapidly with depth unlike site amplification attenuation at shallow depths exhibits little dependence on rock type these observations are consistent with the opening of fractures under decreasing lithostatic pressure being the principal cause of the severe near surface attenuation seismograms recorded in deep boreholes are relatively unaffected by near surface effects and thus can be used to measure crustal attenuation to higher frequencies 100 hz than surface recordings studies using both direct and coda waves recorded at over 2 km depth find q to be high 1000 at seismogenic depths in california increasing only weakly with frequency between 10 and 100 hz intrinsic attenuation appears to be the dominant mechanism these observations contrast with those of the rapidly increasing q with frequency determined from surface studies in the frequency range 1 to 10 hz further work is necessary to constrain the factors responsible for this apparent change in the frequency dependence of q but it is clearly unwise to extrapolate q estimates made below about 10 hz to higher frequencies

stratigraphy chronology styles and dynamics of late quaternary eruptions from taupo volcano new zealand taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite dominated central portion of the taupo volcanic zone in the north island of new zealand taupo has an average magma output rate of 0 2 m 3 s 1 over the past 65 000 years and is one of the most frequently active and productive rhyolite volcanoes known the structure of the modern inverse volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 c years bp oruanui eruption and has been little modified since except for collapse following the 1850 14 c years bp eruption the products of 28 eruptions labelled psi omega a ldots z all of which post date the oruanui eruption are defined and described here twenty seven of these eruptions are represented by pyroclastic deposits of which three were accompanied by a mappable lava extrusion and one eruption z solely by evidence for a lava extrusion the deposits of seven eruptions b c e s v x and y largely correspond to previously defined tephra formations karapiti poronui opepe waimihia whakaipo mapara and taupo respectively the previously defined motutere and hinemaiaia tephras are reinterpreted to represent the products of 12 eruptions g to r while the remaining eight deposits and one eruption are newly recognized eruption psi occurred at ca 17 200 14 c or 20 500 calibrated years bp and eruption z about 1740 calibrated years bp eruption volumes vary by more than three orders of magnitude between 0 01 and more than 44 km 3 and repose periods by more than two orders of magnitude from ca 20 to 6000 years the eruption deposits reflect great variations in parameters such as volume the dispersal characteristics of the fall deposits the presence or absence of intraeruptive time breaks the formation of pyroclastic flows the degree of magma water interaction the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions all but seven fall deposits are plinian in dispersal two y1 and probably w are sub plinian one y5 has been termed ultraplinian while psi and a are too poorly preserved for their dispersal to be assessed the lengths of repose periods in the post oruanui sequence range are not randomly distributed but show self similar properties fractal dimensionality repose intervals r in years of not more than 350 years follow n 53 5r 0 21 and those of not less than 350 years follow n 2096r 0 83 where n is the number of eruptions the shorter repose periods may reflect triggering processes such as regional extension affecting magma bodies during their viable lifetimes while longer repose intervals i e not less than 350 years may reflect an episodicity of major rifting events or the production of magma bodies below the volcano bulk volumes v in km 3 of the eruption products also show self similar properties fractal dimensionality with n 6 17v 0 46 however there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible the post oruanui activity at taupo represents noise superimposed on the more uniform longer term activity in the central taupo volcanic zone where large greater than 100 km 3 eruptions such as the oruanui occur at more evenly spaced intervals of one per 40 60 000 years

earthquake ground motion in the mygdonian basin greece the e2vp verification and validation of 3d numerical simulation up to 4 hz n a low seismicity context the use of numerical simulations becomes essential due to the lack of representative earthquakes for empirical approaches the goals of the euroseistest verification and validation project e2vp are to provide 1 a quantitative analysis of accuracy of the current most advanced numerical methods applied to realistic 3d models of sedimentary basins verification and 2 a quantitative comparison of the recorded ground motions with their numerical predictions validation the target is the euroseistest site located within the mygdonian basin greece the site is instrumented with surface and borehole accelerometers and a 3d model of the medium is available the simulations are performed up to 4 hz beyond the 0 7 hz fundamental frequency thus covering a frequency range at which ground motion undergoes significant amplification the discrete representation of material heterogeneities the attenuation model the approximation of the free surface and nonreflecting boundaries are identified as the main sources of differences among the numerical predictions the predictions well reproduce some but not all features of the actual site effect the differences between real and predicted ground motions have multiple origins the accuracy of source parameters location hypocentral depth and focal mechanism the uncertainties in the description of the geological medium damping internal sediment layering structure and shape of the sediment basement interface overall the agreement reached among synthetics up to 4 hz despite the complexity of the basin model with code to code differences much smaller than predictions to observations differences makes it possible to include the numerical simulations in site specific analysis in the 3d linear case and low to intermediate frequency range

longevity of a small shield volcano revealed by crypto tephra studies rangitoto volcano new zealand change in eruptive behavior of a basaltic field abstract the life span of small volcanoes in terrestrial basaltic fields commonly considered monogenetic can be difficult to assess due to a paucity of datable materials capable of providing a 102 103 year age resolution we have used microscopic tephra layers crypto tephra in lake sediments to determine the longevity of rangitoto volcano a small shield that represents the most recent volcanism in the auckland volcanic field avf new zealand previous studies suggested construction in a relatively short interval at 550 500 cal yrs bp in contrast the tephra record shows evidence of intermittent activity from 1498 140 to at least 504 6 cal yrs bp a longevity of 1000 years rangitoto volcano is thought to represent about half the magma erupted in the 250 ka history of avf thus the avf has experienced a dramatic shift to prolonged and voluminous central vent volcanism in its most recent history this demonstrates the difficulty in determining time erupted volume relationships in such fields previous avf hazard risk modeling based on isolated short lived

a continuous 5300 yr holocene cryptotephrostratigraphic record from northern new zealand and implications for tephrochronology and volcanic hazard assessment a continuous 5280 calendar cal yr long cryptotephrostratigraphic record of a peat core from northern new zealand demonstrates that cryptotephra studies can enhance conventional tephra records by extending the known distribution of ash fall and enabling re assessment of volcanic hazards a systematic sampling strategy was used to locate peaks in glass shard concentrations and to determine loci of individual geochemical populations and a palynological method involving spiking samples with lycopodium spores was adapted to facilitate accurate counting of glass shard concentrations using glass shard major element compositions and a core chronology based on eight ams 14c ages and two visible macroscopic tephra layers taupo tephra unit y 1688 1748 cal bp and tuhua tephra 6800 7230 cal bp 2cr age ranges four cryptotephras were correlated with known eruptions whakaipo unit v 2743 2782 cal bp stent unit q 4240 4510 cal bp and unit k 4970 5290 cal bp erupted from taupo volcanic ce

using cryptotephras to extend regional tephrochronologies an example from southeast alaska and implications for hazard assessment abstract cryptotephrochronology the use of hidden diminutive volcanic ash layers to date sediments has rarely been applied outside western europe but has the potential to improve the tephrochronology of other regions of the world here we present the first comprehensive cryptotephra study in alaska cores were extracted from five peatland sites with cryptotephras located by ashing and microscopy and their glass geochemistry examined using electron probe microanalysis glass geochemical data from nine tephras were compared between sites and with data from previous alaskan tephra studies one tephra present in all the cores is believed to represent a previously unidentified eruption of mt churchill and is named here as the lena tephra a mid holocene tephra in one site is very similar to aniakchak tephra and most likely represents a previously unidentified aniakchak eruption ca 5300 5030 cal yr bp other tephras are from the late holocene white river eruption a mid holocene mt churchill eruption and possibly eruptions of redoubt and augustine volcanoes these results show the potential of cryptotephras to expand the geographic limits of tephrochronology and demonstrate that mt churchill has been more active in the holocene than previously appreciated this finding may necessitate reassessment of volcanic hazards in the region

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi

eruption recurrence rates in a basaltic volcanic field based on tephra layers in maar sediments implications for hazards in the auckland volcanic field long term eruption recurrence rates in monogenetic basaltic volcanic fields are difficult to assess because of low eruption frequencies but they are important because of the spread of human infrastructure into such fields auckland city new zealand is built on the auckland volcanic field a young 250 ka basaltic volcanic field in the absence of abundant material for radiocarbon and isotopic dating an eruptive chronology based on basalt tephra layers deposited in maar lakes was developed interbedded well dated tephra layers from silicic volcanoes some 220 270 km to the south were used as age constraints the basalt tephra layers reveal a pattern of activity not evident from the temporal spatial distribution of volcanic landforms twenty four basalt tephra layers over the last 80 k y represent an average frequency of one per 3 5 k y recurrence times vary from 0 5 k y to 20 k y and show no temporal trend the tephra record shows a major flare up in explosive activity at 32 2 ka during heightened activity at 34 24 ka this was related to a period of simultaneous eruptions from several volcanoes across the field revealed by paleomagnetic and isotopic ages in contrast the field has been relative quiet during the last 20 k y punctuated by the construction of a shield volcano at 0 7 ka thus the surface manifestation of magmatism varies greatly with time complicating long term volcanic hazard forecasting despite the high risk from future basalt activity because of proximity ash fall from distant andesite volcanoes is the most frequently occurring volcanic hazard in auckland city

unravelling a complex volcanic history from fine grained intricate holocene ash sequences at the tongariro volcanic centre new zealand abstract holocene volcanism at the tongariro volcanic centre tgvc at the south western end of the taupo volcanic zone tvz new zealand involved eruptions from at least three centres and was dominated by numerous small eruptions of vei 1 4 these produced very thin grey to black fine to coarse ash deposits of basaltic andesite to andesitic composition being unable to uniquely recognise and correlate these deposits presented a challenge in documenting the complete eruption record from the tgvc and to distinguish the periods of activity associated with each centre previous studies combined fine and poorly distinguishable tephras into mappable formations comprising many tens of units bracketed by rhyolitic marker tephras derived from the tvz caldera centres to the north very fine scaled mapping and analysis of glass of holocene tephras in the tgvc were used to document the comprehensive explosive eruption record over the last 12 000 cal years glass compositional analyses distinguished the tephras from the three main centres of the tgvc mt ruapehu mt ngauruhoe and red crater the latter two being part of the mt tongariro complex the three vents are sufficiently distinctive to be defined by ratios of major element oxides in the glasses with the oxide pair k 2 o feo being the most diagnostic ruapehu sourced tephras are generally higher in k 2 o 1 4 4 wt and lower in feo 3 7 8 3 wt than tongariro derived units red crater and ngauruhoe the diagnostic analyses provided the basis for correlating multiple tephra packages on the ring plains surrounding the tgvc and for establishing a revised eruption frequency for each of the volcanoes the new data show that ngauruhoe began erupting about 7000 cal years ago up to 4500 cal years earlier than previously thought

towards rapid assay of cryptotephra in peat cores review and evaluation of various methods abstract peat bogs are highly effective archives for the preservation and detection of cryptotephra but the conventional methods used to detect these hidden diminutive layers are destructive and can be time consuming we briefly review methods that have been used for cryptotephra detection and evaluate the potential of a range of alternative reconnaissance methods both non destructive and destructive to provide for more rapid examination of continuous cryptotephra content in peat cores the techniques evaluated magnetic susceptibility ms spectrophotometry and x ray fluorescence are used to pick out compositional contrasts between tephra deposits and peat measurements of organic content are also evaluated as a potential guide to tephra content based on an inverse relationship although we find limitations to each method particularly where deployed at the distal most end of tephra dispersal there is potential for all methods to be used in the detection of cryptotephra where time or material is limited these methods can also provide additional sedimentological and stratigraphic information for studies of peat cores however where a reliable cryptotephra profile is required we conclude that there is no quick or easy substitute for the conventional extraction microscopy method

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects