new glass fission track ages of middle pleistocene tephras on yakushima island southern japan abstract the ages of two hornblende bearing middle pleistocene rhyolitic tephra beds on yakushima island southern japan have been determined by the glass itpft method koseda pyroclastic flow deposit is 0 58 0 08 ma and anbo tephra an is 0 78 0 09 ma the normal geomagnetic polarity of an demonstrates a stratigraphic position just above the bruhnes matuyama boundary both volcanic units are the result of large magnitude eruptions from a source that is most probably located at one of the calderas south of the central part of the kagoshima graben southern kyushu given the low total alkali content of their glass shards they must have been widely distributed across kyushu and central japan although no other occurrences are presently known new information on their mineralogy glass composition and age will greatly facilitate recognition of their distal correlatives although not explored in this study these two tephra beds will undoubtedly play a useful role in future studies aimed at elucidating the quaternary paleoenvironmental history of yakushima island

rock types and permeability prediction from dipmeter and image logs shuaiba reservoir aptian abu dhabi the shuaiba formation is a complex carbonate reservoir characterized by small scale geological heterogeneity primarily related to rudist macrofauna the textural heterogeneity corresponds to extreme permeability variation that is the controlling factor in reservoir production because of the large vertical resolution contrast between cores actual scale and conventional logs averaged responses over a few feet extrapolation of small scale heterogeneity into uncored wells using a traditional approach is unreliable high resolution log data like dipmeters and image logs are required to characterize small scale heterogeneity that is essential to a good three dimensional 3 d geological model that predicts true reservoir behavior our study illustrates an approach to improve the reservoir characterization of the shuaiba by quantifying small scale heterogeneity using dipmeter and image logs a methodology is proposed to use the existing high resolution high resolution dipmeter tool hdt stratigraphic high resolution dipmeter tool shdt and formation microscanner fms and conventional log data to characterize and extrapolate geological heterogeneity texture and neural network analyses derived from microresistivity variations and a multiregression approach have been used in two wells to demonstrate the methodology both rock types and permeability are estimated for extrapolation into uncored wells although differences between the conductivity of conductive and resistive areas when normalized for background conductivity are an indirect measure of permeability for hdt and shdt the connectivity coefficient of conductive anomalies derived from textural analysis is related to permeability in the case of fms reservoir rock types rrt obtained from the methodology correlate well with rrts derived from the integration of core special core analysis scal and conventional log data in two test wells permeability estimations including small scale extreme variations from less than 1 md in tight mudstones to greater than 1 d in caprinid rudstones are in good agreement with the core plug permeability measurements after a simple calibration in one example permeability trends in rudist rrts which are not discernible using core plugs and minipermeameter data are clearly resolved using shdt data the degree of correlation between estimated and core permeabilities is greater with increased vertical resolution of the tool hdt lowest fms highest distinct rrts resulting from small scale geological heterogeneity can be classified and permeability can be estimated with a high degree of confidence providing a better pathway of extrapolating from core data to conventional logs for 3 d modeling the methodology has potential application to other carbonate and siliciclastic reservoirs with appropriate calibration and scaling underused hdt shdt fms and fullbore formation microimager fmi databases are available in many other areas that could be analyzed an order of magnitude improvement in the ability to characterize small scale heterogeneity has significant implications for future coring logging programs and reservoir characterization efforts duffy russell is a senior carbonate geologist at saudi aramco in the reservoir characterization department southern fields characterization division he received b s and m s degrees in geology from north carolina state university in 1976 and duke university in 1979 and a ph d in geology from the university of aberdeen in 2001 he started his career as a geophysicist with amoco production company in 1979 and has worked nearly 21 years as a geologist for mobil oil corporation and exxonmobil specializing in carbonate reservoir characterization mahmoud akbar is a principal geologist for schlumberger working iran qatar the united arab emirates oman and yemen he started his professional career with schlumberger wireline and testing in 1985 in pakistan he received b sc 1983 and m sc 1985 degrees in applied geology from the university of punjab pakistan he has carried out research in the lower himalayas on factors controlling fractures and their effect on rock strength badarinadh vissapragada is a senior petrophysicist with schlumberger data and consulting services abu dhabi united arab emirates he did his postgraduate study in geophysics at andhra university waltair india he has more than 19 years of petrophysics experience in india and middle east reservoirs from fieldwide petrophysical studies and reservoir characterization his special interests are reservoir rock typing permeability and fracture detection gordon walkden is head of the department of geology and petroleum geology at the university of aberdeen scotland after receiving a degree from quintin school in london he obtained his ph d in carbonate sedimentology from manchester university united kingdom in 1970 gordon was appointed senior lecturer in 1988 and became department head in 1993 he has extensive field experience and supervision of research projects in britain europe north america and the middle east

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

identification and correlation of visible tephras in the lake suigetsu sg06 sedimentary archive japan chronostratigraphic markers for synchronising of east asian west pacific palaeoclimatic records across the last 150 ka abstract the lake suigetsu sg06 sedimentary archive from honshu island central japan provides a high resolution palaeoenvironmental record including a detailed record of explosive volcanism from japan and south korea thirty visible tephra are recorded within the 73 m long sg06 core which spans the last 150 ka here we describe and characterise these tephras based on major element glass composition which is useful for the identification and correlation of these tephras and the age models of the records in which they are found utilising the large number of radiocarbon measurements n 600 from terrestrial plant macrofossils in the lake suigetsu sg06 record we are able to provide precise and accurate ages for the tephras from eruptions within the last 50 ka glass compositional data of some of the largest eruptions from japan k ah at aso 4 aso a aso d and ata sampled at proximal outcrops are also presented these data show that the major element glass chemistry is distinctive for many of the visible sg06 tephra units and allows some of the layers to be correlated to known eruptions from volcanoes in japan and south korea namely k ah sg06 0967 u oki sg06 1288 at sg06 2650 aso 4 sg06 4963 sg06 4979 k tz sg06 5181 aso abcd sg06 5287 and ata sg06 5181 the following ages were obtained for the sg06 tephra units 3 966 4 064 cal ka bp 95 4 probability range for the sg06 0588 tephra 10 242 10 329 cal ka bp 95 4 probability range for sg06 1293 19 487 112 sg06 2012 ka bp 2 for sg06 1965 28 425 194 sg06 2012 ka bp 2 for sg06 2504 28 848 196 sg06 2012 ka bp 2 for sg06 2534 29 765 190 sg06 2012 ka bp 2 for sg06 2601 29 775 191 sg06 2012 ka bp 2 for sg06 2602 43 713 156 sg06 2012 ka bp 2 for sg06 3485 46 364 202 sg06 2012 ka bp 2 for sg06 3668 49 974 337 sg06 2012 ka bp 2 for sg06 3912 50 929 378 sg06 2012 ka bp 2 for sg06 3974 and improved ages for two of the most important tephra markers across japan the k ah 7 165 7 303 cal ka bp at 95 4 probability range sg06 0967 and at tephra 30 009 189 sg06 2012 ka bp at 2 sg06 2650

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

revised age and distribution of ca 87ka aso 4 tephra based on new evidence from the northwest pacific ocean the major element compositions of glass shards of aso 4 tephra can be distinguished from those of other widespread tephras in and around the japanese islands by analysing 325 tephras in 27 sediment cores collected from the northwest pacific ocean and the sea of okhotsk aso 4 tephra was identified at 14 locations on the basis of the glass major element composition and refractive indices of glass shards and phenocrysts similarity coefficients between aso 4 type and its correlatives ranged between 0 92 and 0 99 whereas comparisons between aso 4 tephra and 92 other widespread quaternary tephras were all 0 85 cao feo plots clearly show the bimodal composition of glass shards in aso 4 tephra aso 4 tephra reached the northern part of the shatsky rise 2910 km from its source caldera its thickness and grain size suggest that the axis of fall out zone is oriented to the northeast of the aso caldera a detailed 18o isotopic stratigraphy embracing the last 144 ka has been determined for core md01 2421 collected off central japan aso 4 tephra is present in this core and occurs in zone mis 5b more precisely at 86 8 87 3 ka using this datum the sedimentation rate in the northwest pacific basin to the north of the 37 5 n latitude is greater than that to the south of 35 n latitude this new information on the distribution and age of aso 4 tephra improves our understanding on the magnitude of this eruption and provides a precise chronostratigraphic marker in the late quaternary pelagic sediment of the northwest pacific ocean

dynamics of a zone of four parallel faults a deterministic model we consider a two dimensional model for quasi static evolution of four parallel faults the model is based on the physics of continuum with slips along the faults long range interactions a distribution of barriers and asperities a velocity dependent friction healing and reactivation of cohesive forces and a mutual causality between faulting and tectonic forces all taken into account both the long term time series of seismic activity and details of seismic and aseismic crustal deformations during each phase of the earthquake cycle are produced by the model it is shown that the system whose evolution is described by a set of deterministic differential equations may exhibit periodic or quite irregular despite its assumed symmetry behavior depending on model parameters

developing a holocene tephrostratigraphy for northern japan using the sedimentary record from lake kushu rebun island abstract palaeoclimate records in east asia offer significant potential to further our understanding of monsoon dynamics and can serve as a link between north atlantic and tropical climate systems the sedimentary core from lake kushu rebun island provides the first high resolution palaeoclimate record from northern japan in order for this regionally significant archive to be synchronised to other records and to generate a more detailed holocene tephra lattice for east asia we present the first cryptotephra stratigraphy for northern japan using the kushu rk12 core the detailed rk12 tephrostratigraphy integrates local and far travelled tephras originating from japan russia china north korea and most likely indonesia five key cryptotephra layers have been identified precisely dated and correlated to the specific eruptions or the source region b tm tephra changbaishan volcano sh 12 tephra shiveluch volcano ko g tephra komagatake volcano ma f j tephra mashu volcano and rk12 0819 tephra with possible indonesian origin these tephra horizons are very widely dispersed providing opportunities to synchronise distant palaeoclimate records from the polar region through high northern latitudes to the tropics which facilitate interregional comparison of palaeoclimate and environmental data in addition a number of the geochemically analysed horizons contain other minor numbers of compositionally distinct glass which can also be grouped and correlated to their source volcanoes these minor analyses are of interest since they provide new insight into regional tephra dispersal e g ash dispersal potential of aira and towada and could suggest that there are other potential eruptions that have yet to be identified in the geological record e g potential changbaishan eruptions the integrated lake kushu cryptotephra record extends the ash dispersal of several key tephra horizons in the region the presence of the shiveluch sh 12 tephra in lake kushu ca 1900 km away documents the first example of a russian tephra reaching the japanese archipelago furthermore glass compositions suggest that the core could preserve an eruption event derived from indonesia highlighting the future possibility to significantly extend and interlink the tephra lattice across the entirety of asia this is an essential step for the understanding of how climate changes propagate over large geographical areas indeed several of these tephra markers coincide with significant ecological changes reflected in the pollen proxy record at lake kushu using this high resolution palaeoenvironmental record we however find no significant ecological impact following the large late holocene millennium eruption from changbaishan china north korea

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

evidence for chaotic fault interactions in the seismicity of the san andreas fault and nankai trough interactions between fault segments are one of the main sources of complexity in the seismicity of active tectonic regions such interactions are likely to influence the spatial and temporal patterns of earthquakes here we examine the dynamical behaviour introduced by fault interactions using a simple spring loaded slider block model with velocity weakening friction the model consists of two slider blocks coupled to each other and to a constant velocity driver by elastic springs for an asymmetric system in which the frictional forces on the two blocks are not equal the solutions exhibit chaotic behaviour the system s behaviour over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault we see similarities between our model simulations and observed patterns of seismicity on the south central san andreas fault in california and in the nankai trough along the coast of southwestern japan

patterns of seismic activity preceding large earthquakes we analyze the patterns of seismic activity which precede large events in a mechanical model of a fault the model generates a statistical distribution of events similar to that observed for a single fault with a scaling region consistent with the gutenberg richter law at small and moderate magnitudes and an excess of events at large magnitudes we find only slight variation in the scaling behavior during a loading cycle however we do observe systematic variations in space and time of the overall rate of activity in the model the activity accelerates dramatically preceding a large event and is usually a maximum hi the neighborhood of the future epicenter these results are compared to california seismicity data where we find that activity patterns vary regionally looking at patterns of activity in the san francisco bay area since 1948 we find an increase of activity on the calaveras fault near san jose beginning in the 1980s which if our model is relevant would forecast a large earthquake in that region the 1989 loma prieta earthquake occurred on the san andreas fault within 30 km of the section of the calaveras fault showing increased activity

carbonate rocks and petroleum reservoirs a geological perspective from the industry abstract carbonate oil reservoirs are sometimes regarded with apprehension in the petroleum industry since it can be difficult to predict the quality of and ensure high recovery factors from this rock family particular problems are the complex and heterogeneous nature of porosity in carbonate rocks often leading to large ranges in permeability for any given porosity and the organization of carbonate successions most commonly as vertically heterogeneous but laterally persistent layers important issues that arise time and again in carbonate reservoir description include a predicting reservoir quality at inter well scales and in uncored wells b recognizing problematic high permeability layers c determining the permeability component to allocate to fractures and connected vug systems and d populating reservoir models with representative physical parameters because porosity in carbonate rocks generally presents as diverse and heterogeneous conventional core plugs are seldom representative of large rock volumes and significant issues remain in terms of the scale compatibility of the various datasets for measured physical parameters that are used in carbonate reservoir description many of the world9s largest carbonate reservoirs were discovered and developed shortly after the second world war and are now showing signs of maturity expressed variously as poor pressure support water or gas breakthrough and stranded resources the proportion of the world9s conventional petroleum that is reservoired in carbonate rocks is commonly estimated at around 50 60 and many large carbonate reservoirs are likely to have a production lifetime beyond 50 years it is no coincidence then that the petroleum industry has been the primary source of funding of and promotion of research into carbonate rocks and depositional systems often with impacts extending well beyond oil and gas exploitation

quaternary volcanic front at the junction of the south west japan arc and the ryukyu arc abstract the hohi volcanic zone a 70 by 40 km volcanic graben on kyushu island at the junction of the south west japan arc and the ryukyu arc has been formed since 6 ma to the present quaternary volcanism producing centers along a ne sw trending line the volcanic front started at about 1 5 ma this volcanic front crosses the e w alignment that was built by the pliocene volcanoes of the hohi volcanic zone the quaternary volcanic front is parallel to the depth contours of the present deep seismic plane and is perpendicular to the current direction of subduction of the philippine sea plate the age of formation of the volcanic front coincides with the time when several other tectonic events occurred such as the counter clockwise shift from nnw to wnw in relative convergence direction of the philippine sea plate the volcanic rocks erupted after 1 5 ma are more widely distributed with a larger total volume in the denser seismic zone than in the aseismic zone this suggests that the volcanism on the volcanic front is closely related to seismicity at about 120 km depth the active seismic area may have accelerated to generate a partially molten zone beyond the dragged hydrated peridotite layer above the downgoing slab in comparison to the aseismic area

play analysis and leading edge oil reservoir development methods in the permian basin increased recovery through advanced technologies the permian basin of west texas and southeast new mexico remains an important oil producing province accounting for 17 of united states production 327 million bbl in 2002 with a resource base of such size increased understanding of reservoir geology and improved use of enhanced recovery practices in the basin can have a substantial impact on united states oil production thirty two oil plays covering both the texas and new mexico portions of the permian basin were defined on the basis of reservoir stratigraphy lithology depositional environment and structural and tectonic setting one thousand three hundred and thirty nine significant sized reservoirs cumulative production of 1 million bbl 1 59 105 m3 of oil through 2000 were assigned to a geologic play cumulative production from these reservoirs was 28 9 billion bbl 4 59 109 m3 or 95 of the basin s total examples of successful reservoir development practices are listed by play because methods demonstrated to work well in one reservoir should be applicable to other reservoirs in the play the permian basin is dominantly a carbonate province carbonate reservoirs account for 75 of total oil production clastics 14 mixed clastics and carbonates 8 and chert 3 the plays having the largest cumulative production are the northwest shelf san andres platform carbonate play 4 0 billion bbl 6 31 108 m3 the leonard restricted platform carbonate play 3 3 billion bbl 5 25 108 m3 the pennsylvanian and lower permian horseshoe atoll carbonate play 2 7 billion bbl 4 29 108 m3 and the san andres platform carbonate play 2 2 billion bbl 3 42 108 m3 the permian system dominates production accounting for 73 of cumulative production followed by the pennsylvanian 13 and the ordovician 6 the estimated remaining reserves from that component of the resource base that is already discovered and producing is 3 25 billion bbl 5 17 108 m3

ice age as a trigger of active quaternary volcanism and tectonism abstract the stress accumulation within the crust caused by the surface mass redistribution associated with the glaciation deglaciation cycle during the quaternary was numerically evaluated in order to examine the relationship between active quaternary volcanism and tectonism in island arc areas and ice age the vertical gradient of horizontal stress difference in the lithosphere for a meltwater of 130 m in equivalent sea level reaches a maximum value of 0 8 mpa km which is corresponding to the equivalent buoyancy of about 100 kg m3 for magma filled cracks for an earth model with a lithospheric layer of 20 30 km thickness and with a viscosity greater than 1023 pa s the changes in stress difference during the stages of deglaciation of 10 000 years amount to 13 mpa for both the top and bottom of the thin lithosphere thus the additional stress difference within the crust may be effective for island arc areas with thin lithospheric thickness we therefore speculate that the stress accumulation associated with ice age may be an important trigger and or accelerator on the active quaternary volcanism and tectonism for the areas along the circum pacific

lateral magma intrusion from a caldera forming magma chamber constraints from geochronology and geochemistry of volcanic products from lateral cones around the aso caldera sw japan abstract we investigated the k ar ages and the petrological and geochemical features of lava units from lateral cones and lava distributed around the aso caldera in central kyushu japan in order to constrain the spatial range of lateral magma intrusion during the caldera forming stage the results of the k ar age determination showed that most of the analyzed lava units erupted almost simultaneously with the aso caldera forming pyroclastic eruptions 266 to 89 ka in addition the petrography major and trace element compositions and sr isotope ratios of these lava units are indistinguishable from the caldera forming pyroclastic products the contemporaneous activities of compositionally similar magmas inside and outside of the caldera presumably indicate the occurrence of a lateral intrusion of caldera forming magma which had accumulated in a huge magma chamber beneath the caldera system our results suggest that a total of 6 3 vol of caldera forming magma in the aso volcano migrated more than 20 km along the faults from the center of the caldera

postseismic stress transfer explains time clustering of large earthquakes in mongolia abstract three m 8 earthquakes have occurred in mongolia during a 52 year period 1905 1957 since these earthquakes were well separated in space 400 km the coseismic stress change is far too low 0 001 bar to explain mutual earthquake triggering by contrast postseismic relaxation gradually causes a significant stress change 0 1 0 9 bar over large distances using a spring slider model to simulate earthquake interaction we find that viscoelastic stress transfer may be responsible for the earthquake time clustering observed in active tectonic areas therefore revealing postseismic strain by satellite geodesy and modeling earthquake clusters could improve our understanding of earthquake occurrence especially in zones where large earthquakes have already struck in past decades

geologic investigation of cross well seismic response in a carbonate reservoir mcelroy field west texas cross well seismic data from mcelroy field a permian dolomite reservoir in west texas demonstrate that high resolution velocity and reflection images are obtainable in this carbonate reservoir our geologic ground truthing results suggest that cross well data when integrated with porosity models based on log facies add value to reservoir characterization the cross well data added information at the interwell scale that we could get no other way reservoir quality in the portion of mcelroy field that we investigated does not obviously relate to core based lithofacies due to a complex diagenetic overprint primarily cementation by gypsum and anhydrite the coincidence of s wave reflections on the cross well data with decreases in porosity or gypsum cement from whole core analysis suggests that total porosity and mineralogy dominantly influence velocity overall the vertical location of layers generated by reflection imaging correlates fairly well with major log variations in particular positive events on the s wave images correspond almost exactly with increases in sonic velocity increases in resistivity increases in bulk density and decreases on the neutron porosity log from high porosity or gypsum to low porosity or gypsum both the log and cross well data respond to the same diagenetic overprint and its resulting petrophysical characteristics therefore we group log data into log facies using multivariate statistical techniques such as cluster analysis rather than using core data for correlating reservoir flow units and relating them to the cross well images many of the positive amplitude events on the s wave profiles correspond to transitions in a vertical sense between the best reservoir cluster and less porous reservoir clusters which indicates the strong relationship between velocity and porosity in addition lateral variations in many of the positive amplitude events can be tied to changes in porosity and differences in the clusters between the wells comparing geostatistical porosity models directly to the s wave images suggests that the s wave reflection images appear to be resolving lateral changes in porosity of less than 56 m 185 ft but more than 15 m 50 ft

application of fracture mechanics to the simulation of seismicity and recurrence of characteristic earthquakes on a fault we present a fault model consisting of a large number of collinear cracks and intervening asperities for the simulation of seismicity and recurrence of large earthquakes on a fault we apply fracture mechanics to the analysis of the interaction of cracks and to the consideration of fracture condition our fault model gives rise to a complex frequency distribution of event sizes even if no externally imposed spatial inhomogeneity is assumed for the distribution of cracks and asperities and a homogeneous statistical distribution is assumed for fracture strengths the frequency distribution of event sizes is found to be bimodal with no intermediate size event in all the calculations for the smaller events the frequency distribution shows a power law behavior whereas the larger size events denote ones that rupture the whole fault statistically the same frequency distributions are obtained for inhomogeneous distributions of crack lengths and fracture strengths the occurrence of events that rupture the whole fault is shown to be periodic when the fault is isolated the magnitudes of these large events generally increase with increasing recurrence period for given fault length and rate of remote loading the events having a longer recurrence period have a shorter fault length for given magnitude and rate of remote loading if there are fault interactions the periodicity in the recurrence of the large events that would be observed for the isolated fault disappears and the recurrence of the large events becomes complex

holocene tephrostratigraphic framework and monsoon evolution of east asia key tephra beds for synchronising palaeoclimate records abstract in east asia our understanding of holocene climate change forcing mechanisms and propagation require the precise chronological control of palaeoclimate records to allow robust integration of data sets the existing chronologies predominantly based on 14c method however are not sufficient to constrain key questions about abrupt climate shifts that occur within a century in the transitions between states widely dispersed tephra layers allow precise dating and synchronisation of sedimentary archives providing a chronological framework for integrating records especially where the visible tephra record is complemented by the addition of cryptotephra non visible ash despite significant tephra studies in this region however a comprehensive holocene tephra framework is not available to address this issue we carry out a thorough review on holocene tephra investigations undertaken in japan using widespread tephra beds we present an integrated tephra framework and suggest the way forward for establishing this as a wider approach for east asia the framework is based on twenty two ash layers that are mainly from japan and to a lesser extent china n korea s korea and russia each tephra is assessed in terms of chronology geochemistry and distribution the framework is compared with high resolution palaeoclimate records from east asia using this we demonstrate regional variations in monsoon evolution and more importantly the potential of tephra isochrons in constraining such variations given the scarce identification of tephra layers in those well resolved palaeoclimate records we advocate a more systematic employment of the cryptotephra method which would potentially lead to a significant advance in east asian tephrochronology and the correlation of palaeoclimate archives in the region

model for intermediate term precursory clustering of earthquakes a causal sequence of an earthquake swarm extended quiescence foreshocks and main shock can be understood in terms of an aggregation model of crack growth and ultimate fusion on a multiplanar earthquake fault system the rheological model is one of accelerated crack growth under conditions of slip weakening coupled with a slow recovery of static friction after fracture once a slip feature has been generated that spans a large part of the available geometry a stress shadow is cast on other neighboring cracks that strongly retards and inhibits crack growth thus initiating the quiescent phase abruptly the success of the model depends on the assumption that nonlinear rheology regulates the rate of slip and that earthquake faults are not simply connected surfaces but instead have many strands

a simplified spring block model of earthquakes the time interval between earthquakes is much larger than the actual time involved during slip in an individual event the authors have used this fact to construct a cellular automaton model of earthquakes this model describes the time evolution of a 2 d system of coupled masses and springs sliding on a frictional surface the model exhibits power law frequency size relations and can exhibit large earthquakes with the same scatter in the recurrence time observed for actual earthquakes

integrated characterization of carbonate ramp reservoirs using permian san andres formation outcrop analogs the san andres formation permian guadalupian of the permian basin is representative of carbonate ramp reservoirs in that it has highly stratified character complex facies and permeability structure and generally low recovery efficiencies of 30 of original oil in place the approach used here to describe carbonate ramp reservoirs such as the san andres formation produces detailed reservoir models based on integration of sequence stratigraphic analysis petrophysical quantification through definition of rock fabric flow units and fluid flow simulation synthesis of these subdisciplines clarifies which aspects of the geologic petrophysical model are most significant in predicting reservoir performance and ultimately in understanding the location of remaining oil satur tion the san andres formation crops out along the algerita escarpment a long oblique dip continuous shelf to basin exposure in the central guadalupe mountains these outcrops provide a unique opportunity to study lateral relationships in geologic and petrophysical structure analogous to those occurring between wells in subsurface reservoirs on the basis of sequence stratigraphic analysis three scales of cyclicity are recognized depositional sequences high frequency sequences and cycles examination of the cycles in two detailed window areas provides a practical scale for petrophysical quantification and fluid flow simulation an understanding of cycle position within the high frequency sequence framework also provides predictive information petrophysical analysis revealed six rock fabric groups dominated by intergranular separate vug or dense intercrystalline pore types comparison of these rock fabric groups with facies descriptions produced a rock fabric flow unit model that honors the geologic structure of the cycle and sequence framework permeability data were averaged within rock fabric flow units using a geometric mean approach based on fine scale fluid flow modeling of deterministic and stochastically generated permeability fields two dimensional black oil fluid flow models illustrate that 1 major differences in sweep efficiency and fluid flow performance are predicted when linear interwell interpolations are compared with actual interwell scale geologic structure as determined by outcrop geologic and petrophysical mapping 2 an understanding of static geologic petrophysical conditions provides only a partial understanding of reservoir performance defined by the interaction of these static properties and dynamic properties of fluid flow interaction within the flow unit architecture and 3 because of the orderly distribution of high and low permeability facies within cycle stacks of high frequency sequences this larger scale of geologic description can give a reasonable first order approximation of fluid flow patterns and early breakthrough end page 181

demise of one volcanic zone and birth of another a 12 m y marine record of major rhyolitic eruptions from new zealand ocean drilling program sites 1123 and 1124 provide an unprecedented 12 m y record of major rhyolitic eruptions from the coromandel and taupo volcanic zones of new zealand macroscopic tephras n 197 were dated using magnetostratigraphy supplemented by geochemical correlation with subaerial tephra isothermal plateau fission track ages and orbitally tuned stable isotope data eruptions began in the coromandel volcanic zone ca 12 ma 1 6 1 m y earlier than previously known thereafter volcanism was fairly continuous with a tempo and intensity that increased through the late miocene pliocene and into the quaternary when the taupo volcanic zone formed the transition from the coromandel to the taupo zone previously placed as ca 4 2 ma was seamless without obvious breaks or changes in ash composition this well dated history of long lived and productive volcanism allows for more confident correlation with other circum pacific tephra records thus helping confirm the occurrence of widespread coeval eruptions throughout the region

a diatom record for the past 400 ka from lake biwa in japan correlates with global paleoclimatic trends abstract detailed diatom records from a 140 m sediment core with a time resolution of approximately 1000 1500 yr were obtained from lake biwa to examine possible correlations between diatom concentrations and paleoclimatic changes during the last approximately 400 ka in the sediments the diatom assemblages are generally dominated by planktonic diatoms the diatom stratigraphy is characterized by four zones with distinctly higher concentration values and 12 horizons with low concentration values diatom records from the 140 m core and another core indicate that these changes were not local phenomena but occurred throughout the lake basin comparison of diatom concentration records with pollen records from lake biwa sediments indicates that higher diatom concentrations represent warmer and wetter climatic conditions and that lower concentrations represent colder and drier climatic conditions comparison of diatom records from lake biwa with marine oxygen isotopic records shows that the number of peaks and their relative amplitudes are similar in both profiles therefore peaks and drops in diatom concentration profile might correlate with most oxygen isotopic events this finding indicates that during approximately the last 400 ka the changes in diatom concentration represented as diatom productivity in lake biwa correlate closely with global paleoclimatic changes at the scale of the milankovitch cycle precession cycles of 23 and 19 ka and that diatom concentration was higher during warm events and lower during cold or cooling events

correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential pearce nicholas denton j s perkins w t westgate j a 2007 correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential journal of quaternary science 22 7 pp 721 736 rae2008

interactive dynamics of faults abstract seismic activity may be treated as a process of slip movements along a complex system of interacting faults numerical simulations of quasi static faulting process were carried out by using two dimensional model of four parallel faults we may observe a variety of possible fault zone behaviour which results from the interactive and dynamical nature of the system some preliminary results of three dimensional modelling are also presented

review of methods of estimating rhyolitic tephra volumes applications to the taupo volcanic zone new zealand there have been at least 35 rhyolitic plinian eruptions in the last 50 kyr from 2 volcanic centres in taupo volcanic zone tvz new zealand to determine the total volume of erupted material calculation techniques are reviewed and further developed all involve extrapolation from isopach maps three methods assume an exponential decay of thickness with distance from source and a further two are based on the area enclosed by each isopach comparison of methods shows those based on area to be more accurate except the log log plot of area and thickness which requires excessive extrapolation a log volume vs thickness plot is considered superior because minimal extrapolation is needed for most tephras volumes calculated by the different methods are in reasonable agreement volumes previously calculated by the crystal concentration method are 2 3 times greater than those from the six methods used here total pumice fragmentation is probably not required for the liberation of crystals and this would decrease calculated volumes during the last 50 kyr magma has been erupted at a constant mean rate in the taupo volcanic zone a simple step function shows a strong relationship between deviations from the mean rate and either the next erupted volume or the time to the next eruption extrapolation of these step functions suggests future eruptions in less than 400 years for okataina and about 8000 years for taupo the volume of rhyolitic material erupted from tvz within the last 50 kyr is estimated at 360 km3 of tephra 350 km3 of ignimbrite and 55 km3 of extrusive equivalent to about 350 km3 of magma at an average rate of eruption of 7 km3 year at least 4200 km3 of rhyolitic magma has been erupted since the inception of tvz about 0 6 m y ago if back are spreading of tvz at 7 mm yr is compensated for by dyke intrusion into the upper 10 km of crust 8400 km3 of magma is required the total volume of magma generated by partial melting is estimated at 12 600 km3 removal of this melt would cause subsidence of 2 1 km the present depth to subvolcanic basement in tvz

vertical density currents a review of their potential role in the deposition and interpretation of deep sea ash layers marine tephra layers form important chronostratigraphic markers and may also provide information on eruption dynamics and chronology recent experiments and field data from the 1991 pinatubo eruption challenge tacit assumptions that following atmospheric fallout on the ocean surface marine sedimentation of ash grade material occurs by stokes law settling of individual grains laboratory experiments have demonstrated that vertical density currents can be initiated at representative mass flux rates further experiments described herein involving sustained particle fluxes entering stratified environments demonstrate that ash particles can decouple from the transporting fluid whose vertical motions are limited by the stable density gradient in the ocean vertical density currents generated by ash loading and gravitational destabilization of the water column can overcome the strong stable density gradients in the ocean and transport ash particles vertically 1 3 orders of magnitude faster than possible by stokesian settling greatly reducing their residence time sea bed sedimentation is inferred to involve settling of individual coarse or dense grains through the entire water column plus suspension fallout from the polydisperse turbid layer delivered by convective plumes yielding normal distribution grading the turbid layer may continue laterally as a nepheloid current under the influence of bottom slopes and or geostrophic forces either mechanism possibly modifying the grain size distribution of the suspension and hence the resulting ash layer by transporting selected fractions into different depositional locations consequently and regardless of any subsequent reworking deep sea ash isopachs may not directly reflect an eruptive signal and the ash layers may not directly record the order rate or location of arrival of ash particles at the ocean surface

reconstructing the quaternary evolution of the world s most active silicic volcanic system insights from an 1 65 ma deep ocean tephra record sourced from taupo volcanic zone new zealand abstract the taupo volcanic zone tvz central north island new zealand is the most frequently active quaternary rhyolitic system in the world silicic tephras recovered from ocean drilling programme site 1123 41 47 16 s 171 29 94 w 3290 m water depth in the southwest pacific ocean provide a well dated record of explosive tvz volcanism since 1 65 ma we present major minor and trace element data for 70 quaternary tephra layers from site 1123 determined by electron probe microanalysis 1314 analyses and laser ablation inductively coupled plasma mass spectrometry 654 analyses trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie lines between three sediment cores 1123a 1123b and 1123c recovered from site 1123 these tephra tie lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the site 1123 composite record trace element fingerprinting of tephras identifies 4 5 m and 7 9 m thick sections of repeated sediments in 1123a 49 0 53 5 mbsf metres below seafloor and 1123c 48 1 56 0 mbsf respectively these previously unrecognised repeated sections have resulted in significant errors in the site 1123 composite stratigraphy and age model for the interval 1 15 1 38 ma and can explain the poor correspondence between 18o profiles for site 1123 and site 849 equatorial pacific during this interval the revised composite stratigraphy for site 1123 shows that the 70 tephra layers when correlated between cores correspond to 37 38 individual eruptive events tephras 7 of which can be correlated to onshore tvz deposits the frequency of large volume tvz derived silicic eruptions as recorded by the deposition of tephras at site 1123 has not been uniform through time rather it has been typified by short periods 25 50 ka of intense activity bracketed by longer periods 100 130 ka of quiescence the most active period at least 1 event per 7 ka occurred between 1 53 and 1 66 ma corresponding to the first 130 ka of tvz rhyolitic magmatism since 1 2 ma 80 of tephras preserved at site 1123 and the more proximal site 1124 were erupted and deposited during glacial periods this feature may reflect either enhanced atmospheric transport of volcanic ash to these sites up to 1000 km from source during glacial conditions or more speculatively that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea level changes only 8 of the 37 38 site 1123 tephra units 20 can be found in all three cores and 22 tephra units 60 are only present in one of the three cores whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume instead it is postulated that tephra preservation at site 1123 is patchy and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents at this site at least 5 cores would need to have been drilled within a proximity of 10 s to 100 s of metres of each other to yield a 99 chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1 65 ma

late quaternary oceanic fronts along chatham rise indicated by phytoplankton assemblages and refined calcareous nannofossil stratigraphy for the mid latitude sw pacific abstract a quantitative analysis was carried out of planktonic diatoms biogenic opal and calcareous nannofossils biogenic calcite in late quaternary sediments mis 1 6 from four cores along a n s transect east of new zealand from 39 50 s to 50 04 s across the e w trending submarine ridge the chatham rise this was done to trace movements of oceanic fronts and to improve calcareous nannofossil stratigraphy for the last 130 000 yr in the sw pacific sites odp 1123 and q 858 are below present day subtropical surface waters north of chatham rise site dsdp 594 is below present day mixed temperate subantarctic surface water south of the rise and site odp 1120 is below subantarctic surface water the more diverse and opportunistic planktonic diatoms provided marker species for subtropical surface waters alveus marina fragilariopsis doliolus rhizosolenia bergonii and azpeitia nodulifer and others for subantarctic surface waters nitzschia kerguelensis thalassiosira lentiginosa application of these tracers permits the following conclusions 1 subtropical conditions persisted north of chatham rise throughout the past 130 000 yr in spite of the cooling of surface waters during colder periods 2 during warm times mis 5 and mis 3 and in mis 1 the sporadic occurrence of subtropical species south of chatham rise indicates occasional admixture of subtropical surface waters that far south 3 subantarctic waters extended to the southern slopes of the chatham rise during mis 5b late mis 5a to early mis 4 during the warmer time intervals in early mis 3 and during latest mis 3 to early mis 2 4 subantarctic frontal conditions existed over southern chatham rise during early mis 4 and late mis 3 to early mis 2 and 5 it is probable that during cooler times mis 6 mis 5b and in mis 2 intensified particle transport from the bounty trough to the northern flank of chatham rise occurred by intensified boundary currents the larger abundance fluctuations in both microfossil groups at the sites south of chatham rise than north of chatham rise reflect northward shifts of the circumpolar subantarctic water csw and a contemporaneous disappearance of australasian subantarctic water asw implying an elevated temperature gradient between the surface water masses north and south of the chatham rise at the times of such northward shifts of csw calcareous nannofossils are less diverse than diatoms and are less specialised some calcareous nannofossil species show abundance shifts at the same time at different latitudes two of these abundance shifts can be used for correlation between subtropical and subantarctic sediments in the sw pacific 1 reversal in the relative abundance of calcidiscus leptoporus and coccolithus pelagicus associated with the mis 2 1 boundary and 2 drop in abundance of gephyrocapsa muellerae or medium sized gephyrocapsa at the mis 4 3 boundary an additional abundance shift seems to be restricted to subtropical to mixed temperate subtropical subantarctic surface waters 3 increase in abundance of g muellerae or medium sized gephyrocapsa at the beginning of mis 2 below the okareka tephra

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

a physical basis for time clustering of large earthquakes we develop a theory that links stress interaction between earthquakes and the occurrence of temporal clustering coseismic static stress change in the vicinity 50 km of large earthquakes suggests that perturbations of 0 1 to 1 bars may affect the occurrence of other earthquakes at larger distances interactions also seem to exist four m 8 earthquakes have occurred in mongolia on distant faults 400 km during the last century also paleoseismic observations documenting much longer time periods display a time clustering of major events we demonstrate with simple mechanical concepts that postseismic stress relaxation magnifies the coseismic stress change and has a major effect on fault interaction during the seismic cycle in the simple case where two distant faults are coupled the probabilistic occurrence of triggered earthquakes may increase dramatically due to long range postseismic coupling

regional sediment recycling in the abyssal southwest pacific ocean an active plate boundary with a high sediment output three major submarine channels and the world9s largest deep western boundary current dwbc make up an extensive recycling system along the 4500 km continental margin east of new zealand seismic reflection sedimentary and oceanographic data demonstrate that detritus from the rising mountains of the new zealand plate boundary is transferred to the southwest pacific abyssal floor by turbidity currents flowing along solander 450 km long bounty 950 km and hikurangi 1400 km channels these conduits discharge directly into the dwbc which transports material north to form a series of sediment drifts the northernmost drift containing sediment from hikurangi channel and eroded drifts to the south is now subducting into kermadec trench geochemical data suggest that sediment is recycled through the mantle to re emerge in the arc volcanic rocks thus one cycle is completed and a new one begins

high resolution record of quaternary explosive volcanism recorded in fluvio lacustrine sediments of the uwa basin southwest japan abstract the identification of widespread tephras is important not only for understanding volcanic processes but also for age estimation and establishing stratigraphic relationships many widespread tephras have been erupted from six active and buried caldera volcanoes in the sw japan ryukyu volcanic arcs to reconstruct high resolution tephrostratigraphy we analyzed core ut from the uwa basin on western shikoku island and correlated the tephras in the core with the proximal source deposits that we sampled this 120 m long core composed of fluvio lacustrine deposits spanning the middle pleistocene to holocene we recognized and characterized 52 visible tephra and tephric sediment layers in the core on the basis of their stratigraphy the petrographic features and the major element composition of glass shards we successfully correlated 15 tephras with the following previously identified widespread tephras mainly from volcanoes on kyushu kikai akahoya 7 3 ka aira tn 29 ka aso 4 87 ka kikai tozurahara 95 ka aso abcd 100 ka ata 105 110 ka aso 3 112 7 ka calculated in this study aso 2 140 ka ata toihama 240 ka aso 1 250 270 ka tky ng1 290 300 ka kakuto 330 340 ka oda 420 450 ka hiwaki 570 580 ka and yufugawa 600 ka above 50 m depth all known widespread tephras from kyushu younger than 350 ky were included in the sequence that has a fairly constant sedimentation rate of about 0 14 mm yr this high resolution tephrostratigraphy was correlated with those of regional long core records from the lake biwa in the central japan and offshore of shikoku that contributes to establish onshore onshore and onshore offshore correlations in southwest japan in the sediments each of the following tephras from caldera forming eruptions aso 4 aso abcd ata aso 3 aso 2 and aso 1 occurred above multiple compositionally similar tephra layers erupted from the same volcano over a long time period this high resolution record is therefore an important contribution to the correlation of regional stratigraphy and reconstruction of both the long term eruptive history and the magma evolution of volcanoes in the sw japan and ryukyu volcanic arcs

fluctuations of the campanian explosive volcanic activity south italy during the past 190 000 years as determined by marine tephrochronology abstract a statistical analysis of the time variations of the frequency of explosive events is derived from the detailed record of marine tephra in deep sea sediment cores of the central mediterranean sea the sequence of campanian events south italy shows several volcanic pulses during the past 190 000 years which were compared to the continental data these episodes which match the different phases of the geochemical evolution of magmas in this area occurred with a 23 kyr periodicity this may be related to the life time of the magma chambers involved in this area with such time cycles precessional forcing of the volcanic activity and or glacio eustatic pressure variations may be envisaged as causal phenomena

revision of the marine chronology in the wanganui basin new zealand based on the isothermal plateau fission track dating of tephra horizons abstract the occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies in this study three widespread and stratigraphically important rhyolitic tephra horizons interbedded in plio pleistocene strata of the wanganui basin new zealand are dated by application of the isothermal plateau fission track itpft technique to hydrated glass shards all glass samples were corrected for annealing and consequently yield reliable ages rangitawa tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission track age estimates of ca 0 35 ma itpft ages of 1 05 0 05 and 1 63 0 15 ma for potaka pumice and pakihikura pumice respectively are considerably older than previous ft estimates but consistent with new magnetostratigraphic data that places the potaka within the jaramillo subchron and pakihikura within the matuyama chron between the cobb mountain and olduvai subchrons combining our fission track ages with the magnetostratigraphy the true age of sediments within the wanganui basin is found to be significantly underestimated sedimentation rates of between ca 680 630 m ma from 1 63 ma to 0 35 ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous ft chronology this new itpft age data demonstrates that the existing plio pleistocene marine chronology in new zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern north island that contain the same itpft dated tephra horizons

the temporal distribution of seismic radiation during deep earthquake rupture the time history of energy release during earthquakes illuminates the process of failure which remains enigmatic for events deeper than about 100 kilometers stacks of teleseismic records from regional arrays for 122 intermediate depths of 100 to 350 kilometers and deep depths of 350 to 700 kilometers earthquakes show that the temporal pattern of short period seismic radiation has a systematic variation with depth on average for intermediate depth events more radiation is released toward the beginning of the rupture than near the end whereas for deep events radiation is released symmetrically over the duration of the event with an abrupt beginning and end of rupture these findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level