on the use of multiple site estimations in probabilistic seismic hazard assessment abstract we analyze specific features of multiple site ms probabilistic seismic hazard assessment psha that is the annual rate of ground motion level exceedance in at least one of several sites of interest located within a defined area or along a linear extended object the relation between ms hazard estimates and strong ground motion data obtained during large earthquakes is discussed in the cases of the 1999 chi chi m w 7 6 and the 2008 wenchuan m w 7 9 earthquakes the strong motion records obtained in the epicentral zones may be considered as examples of the ground motion exceeding the design level estimated using the conventional pointwise pw psha we show that the ms psha when being performed for the 475 yr standard return period provides reasonable estimations of the intensity level that may occur during the earthquakes parameters of which are close to the parameters of events with maximum possible magnitude accepted in psha for the regions the ms psha efficiency is discussed with respect to 1 evaluation of the performance of probabilistic seismic hazard maps and 2 application of the ms hazard estimates as a basis for design loads based on the results of this work we propose a multilevel approach to psha considering the fixed reference probability of exceedance e g 10 in 50 yrs 1 a standard pw psha to be performed in a seismic prone region first level and 2 this analysis should be supplemented by an ms psha for urban and industrial areas or for zones of a particular economic and social importance second level

testing probabilistic seismic hazard estimates by comparison with observations an example in italy summary an evaluation of the actual reliability of probabilistic seismic hazard psh assessments provided by existing numerical techniques is mandatory to orientate new researches and improvements two procedures devoted to this task are proposed which are based on the comparison of the hazard estimates with empirical observations e g strong motion data these procedures have been applied to the estimates provided by the methodology adopted for most recent seismic hazard evaluations in italy the analysis shows that a significant mismatch exists between peak ground acceleration values characterized by an exceedence probability of 10 per cent in 30 yr and what has actually been observed at 68 accelerometric stations located on stiff soil where continuous seismicity monitoring has been performed in the last 30 yr although this finding should be considered with caution it suggests that a future re examination of the adopted psh computational model could be useful to avoid possible underestimates of seismic hazard in italy

a reappraisal of the 1835 eruption of cosiguina and its atmospheric impact in the great january 1835 eruption of cosiguina volcano nicaragua andesitic magma and lithic material were erupted over a period of at least three days proximal facies consist of clastogenic lava scoria fall and lithic ash fall produced by phreatomagmatic to vulcanian or plinian activity together with surge deposits and lithic block falls pyroclastic flow deposits covered some flanks of the volcano and entered the sea in the gulf of fonseca little record exists of the distal ash fall thus the total bulk volume erupted can only be roughly constrained to 2 9 5 6 km3 furthermore the amount of juvenile material is thought to be small a recent study of volatiles in 1835 scoria suggests sulfur release from the magma was negligible this reappraisal indicates that the cosiguina eruption probably had little global climatic impact despite its violent nature the magnitude of the eruption was modest the eruption occurred too late to initiate the northern hemisphere cooling trend form 1828 1836 dry fogs and other atmospheric optical phenomena usually observed after eruptions that contribute significantly to the stratospheric aerosol burden were not recorded after 1835

ignimbrites of basaltic andesite and andesite compositions from tanna new hebrides arc tanna island is part of a large volcanic complex mainly subsided below sea level on land two series of hydroclastic deposits and ignimbrites overlie the subaerial remains of a basal mainly effusive volcano the older tanna ignimbrite series oti late pliocene or pleistocene in age consists of ash flows and ash and scoria flow deposits associated with fallout tephra layers overlain by indurated pumice flow deposits phreatomagmatic features are a constant characteristic of these tuffs the younger late pleistocene pyroclastics the siwi sequence show basal phreatomagmatic deposits overlain by two successive flow units each comprising a densely welded layer and a nonwelded ash flow deposit whole rock analyses of 17 juvenile clasts from the two sequences vitric blocks from the phreatomagmatic deposits welded blocks scoriaceous bombs and pumices from the ignimbrites show basaltic andesite and andesite compositions sio2 53 60 in addition 296 microprobe analyses of glasses in these clasts show a wide compositional range from 51 to 69 sio2 dominant compositions at 54 56 58 5 and 61 62 sio2 characterize the glass from the oti glass compositions in the lower phreatomagmatic deposits from the siwi sequence also show multimodal distribution with peaks at sio2 55 57 5 61 62 and 64 whereas the upper ignimbrite has a predominant composition at 61 62 sio2 in both cases mineralogical data and crystal fractionation models suggest that these compositions represent the magmatic signature of a voluminous layered chamber the compositional gradient of which is the result of fractional crystallization during two major eruptive stages probably related to two caldera collapses the oti and siwi ignimbrites represent large outpourings from these magmatic reservoirs the successive eruptive dynamics from phreatomagmatic to plinian emphasize the role of water in initiating the eruptions without which the mafic and intermediate magmas probably would not have erupted

frost rings in trees as records of major volcanic eruptions new data about climatically effective volcanic eruptions during the past several thousand years may be contained in frost damage zones in the annual rings of trees there is good agreement in the timing of frost events and recent eruptions and the damage can be plausibly linked to climatic effects of stratospheric aerosol veils on hemispheric and global scales the cataclysmic proto historic eruption of santorini thera in the aegean is tentatively dated to 1628 26 bc from frost ring evidence

sulfur budget and global climate impact of the a d 1835 eruption of cosiguina volcano nicaragua large explosive volcanic eruptions can inject massive amounts of sulfuric gases into the earth s atmosphere and in so doing affect global climate the january 1835 eruption of cosiguina volcano nicaragua ranks among the americas largest and most explosive historical eruptions but whether it had effects on global climate remains ambiguous new petrologic analyses of the cosiguina deposits reveal that the eruption released enough sulfur to explain a prominent ca ad 1835 sulfate anomaly in ice cores from both the arctic and antarctic a compilation of temperature sensitive tree ring chronologies indicates appreciable cooling of the earth s surface in response to the eruption consistent with instrumental temperature records we conclude that this eruption represents one of the most important sulfur producing events of the last few centuries and had a sizable climate impact rivaling that of the 1991 eruption of mount pinatubo

test of seismic hazard map from 500 years of recorded intensity data in japan abstract maximum seismic intensity maps for japan are constructed using the recorded intensity data from 1498 to 2007 and are used to test the probabilistic seismic hazard map pshm by the headquarters for earthquake research promotion japan the historical intensity maps are compared with the hazard maps of probable maximum seismic intensity for a 475 yr return period assuming a poisson distribution 10 in 50 yrs we look at cases that include all events only subduction zone earthquakes and all events excluding subduction zone earthquakes the megathrust earthquakes in the subduction zones produce large bands of high intensities along the pacific coast side while onshore crustal earthquakes create a patchy distribution of large intensities over all of japan the maximum recorded intensity map for the past 500 yrs and the maximum predicted intensity map for the return period from the pshm are very similar for the cases including all events and the subduction zone earthquakes while there is poor correlation for the third category that includes mostly onshore crustal earthquakes if we consider only the amount of area not the specific locations the recorded intensity map and the pshm using the maximum case have a high degree of correlation for japanese meteorological agency jma intensity higher than 4 for all of the cases statistically the present hazard maps for japan seem to agree with the past intensity distributions and can be regarded as appropriate hazard maps even though there may be strong dependencies on uncertain model parameters for the pshms

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

estimated seismic intensity distributions for earthquakes in taiwan from 1900 to 2008 in this study we recreated peak ground accelerations pga and peak ground velocity pgv distributions for taiwan by applying the attenuation relations of liu and tsai 2005 to calculate the pga and pgv values for 1989 mw 5 0 earthquakes in a catalog of earthquakes from 1900 to 2008 with homogenized magnitude mw chen and tsai 2008 we further combined the pga and pgv values to obtain corresponding modified mercalli intensity mmi values wald quitoriano heaton kanamori et al 1999 and their spatial distributions and recurrence intervals we adopted a logarithmic functional form analogous to the gutenberg richter relation for seismicity to represent the annual frequency of seismic intensity parameters log10n a blog10pga log10n a blog10pgv and log10n a bi the regions with high pga and pgv values are often associated with low b values in these equations as it is well known that the mw 7 45 chi chi earthquake of 21 september 1999 had produced high pga values in excess of 0 9g and pgv values in excess of 300 cm s we used these relations to estimate the poisson probability distributions in taiwan for mmi viii i e pga 485g for recurrence intervals of 30 50 and 100 years the results show a wide range of differences in the poisson probability of mmi viii among different areas of taiwan for example for a 50 year interval this probability at 10 major cities in taiwan is as follows taipei 0 67 hsinchu 2 15 taichung 5 24 chiayi 24 35 tainan 1 61 kaohsiung 0 04 hengchun 4 94 ilan 17 67 hualien 37 04 and taitung 9 82 these esti mates should be of interest to city planners especially for earthquake preparedness planning

light rings in subarctic conifers as a dendrochronological tool abstract light rings are characterized by one or a very few latewood cell layers an indication of shortened growing seasons and are particularly frequent in black spruce picea mariana mill bsp at the treeline in quebec the construction of a light ring chronology spanning the period ad 1398 1982 showed that the highest frequency 25 of light rings among 160 trees and krummholz occurred in 1593 1620 1634 1784 1816 1817 1853 1969 and 1972 these diagnostic rings be a useful cross dating tool for dendroecologists working with living and dead krummholz with a low growth variability about two thirds of the 65 light ring years coincide with years or triads of major volcanic eruptions the climatic conditions low temperature occurring at the end of the growing season in part induced by the climatic effect of volcanism seem to initiate light rings

pacific offshore record of plinian arc volcanism in central america 2 tephra volumes and erupted masses 1 sediment gravity cores collected from the pacific seafloor offshore central america contain numerous distal ash layers from plinian type eruptions at the central american volcanic arc dating back to more than 200 ka in part 1 of this contribution we have correlated many of those ash layers between cores and with 26 tephras on land the marine ash layers cover areas of up to 106 km2 in the pacific ocean and represent a major fraction 60 90 of the erupted tephra volumes because the pacific coast lies within a few tens of kilometers downwind from the volcanic arc combining our own mapping efforts on land and published mapping results with our marine data yields erupted volumes of all major tephras along the arc that range from 1 to 420 km3 recalculated to erupted magma mass the widespread tephras account for 65 of the total magma output at the arc complementing our tephra data with published volumes of the arc volcanic edifices and volcano ages we calculate the long term average magma eruption rates for each volcano moreover we use incompatible element variations to calculate the cumulate masses that were fractionated during variable degrees of differentiation this yields a minimum estimate of long term average magma production rate at each volcano because intrusives without surface expression and losses by erosion are not accounted for peak magma production rates increase from costa rica to guatemala but there is considerable scatter within each region and large differences even between neighboring volcanoes

multidisciplinary observations of the 2011 explosive eruption of telica volcano nicaragua implications for the dynamics of low explosivity ash eruptions we present multidisciplinary observations of the march june 2011 vei 2 eruptive episode of the basalticandesite telica volcano nicaragua which allow for a comprehensive study of the eruption mechanics of low explosivity eruptions at persistently active volcanoes the observations are from a dense network of seismic and gps instrumentation augmented by visual observations of the eruptive episode geochemical and petrologic analysis of eruptive products plume so2 measurements and temperature measurements of fumaroles inside and outside the active vent the 2011 eruptive episode was telica s most explosive since 1999 and consisted of numerous vulcanian explosions with maximum column heights of 1 5 2 km above the crater rim depositing a low volume of dominantly hydrothermally altered ash based on observed variations in seismicity temperature and so2 flux the lack of deformation of the edifice the non juvenile origin of and predominance of accretionary lapilli in the ash we propose that temporary sealing of the hydrothermal system between similar to 0 5 and 2 km depth allowed pressure to build up prior to vulcanian explosions making this a phreatic eruptive episode

correlations between eruption magnitude so2 yield and surface cooling about the book humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

summer temperature patterns over europe a reconstruction from 1750 a d based on maximum latewood density indices of conifers abstract temperature variations over europe are reconstructed for a 6 month summer season from april to september for the period 1750 1850 using a network of maximum latewood density chronologies of coniferous trees around 44 of the variance of the whole temperature grid was explained in calibration independent verification indicates that over the reconstruction period the explained variance averaged over the whole grid should lie in the range 30 to 35 the reconstructions are better in the north of the region about 50 explained temperature variance based on comparison with independent climate data than in the south below 20 the temperature recontructions indicate cooler summers over europe from 1812 to 1816 and during the 1830s the summers of the 1820s were the warmest reconstructed decadal variations occur on a regional scale but no similar periods of anomalously cooler or warmer summers occurred between 1750 and 1810 throughout europe

assessment of the record of the 1982 el chichon eruption as preserved in greenland snow variability in the so42 and cl time series for the 1980s from 12 shallow snow pits across the greenland ice sheet is used to evaluate the record of the 1982 el chichon eruption and the potential for recording a moderate northern equatorial eruption in a single greenland ice core composition of volcanic glass found in spring 1983 snow in one of the pits in the summit region matches that from el chichon glass thereby verifying the deposition of material from the eruption high na and cl concentrations in this same layer probably represent deposition of the reaction products of halite and h2so4 as observed in the stratosphere following the eruption these findings and the presence of a cl signal in five of the other pits indicate that the cl aerosol component of some eruptions has the potential to remain aloft for at least 1 year after the eruption some of these aerosols may be adsorbed onto tephra particles distinct so42 peaks that can be confidently linked to el chichon were found in only 50 of the records developed through subseasonal sampling however in several other pits an elevated baseline thought to represent more lengthy periods of el chichon aerosol deposition as opposed to deposition from a single snowfall event were observed smoothing of the original data by the calculation of annual so42 flux resulted in the presence of high flux values between 1982 and 1984 years thought to be affected by el chichon aerosol deposition in 9 of the 12 pits these results suggest that a single ice core from anywhere in greenland may record a signal from a northern equatorial eruption of magnitude similar to that of el chichon about 75 of the time this is despite the overall high levels of so2 4 deposition from anthropogenic sources that now make identification and quantification of the volcanic so2 portion of the record more difficult than obtaining the same data for preindustrial volcanism nevertheless composite records from all the pits sampled yielded stratospheric loading 20 mt and optical depth 0 13 estimates similar to stratospheric and satellite based measurements following the eruption equally high so42 concentration and flux values in snow from 1980 to 1982 reflect deposition from the series of middle to high northern latitude volcanic eruptions 1979 1981

comparison of probabilistic seismic hazard estimates in italy abstract macroseismic intensity has recently attracted attention as a tool for validating probabilistic seismic hazard assessment psha studies or as an alternative method for psha in countries where the historical catalog is much longer than the instrumental one in italy the new seismic hazard map was recently produced using the cornell mcguire approach in terms of the peak ground acceleration characterized by a 10 exceedance probability for an exposure time of 50 yr a max we compare this map with an alternative one produced using a different approach based on a nonparametric and zonation free statistical analysis of local seismic histories in this case results are expressed in terms of the maximum intensity corresponding to an exceedance probability of not less than 10 for an exposure time of 50 yr i ref in order to compare the two maps we selected 1401 control sites where local seismic history includes at least 10 intensity values relative to felt effects documented during past earthquakes the values of a max and i ref at these sites have been ranked in the respective domains the spatial distribution of rank differences of a max and i ref values shows a strong correlation with the seismogenic zoning used in the calculation of psha following the cornell mcguire approach this suggests that the adopted zoning could be incomplete some further hidden sources may exist and too rough to capture actual seismogenic sources because more detailed zoning is prevented by the amount of data available the results obtained suggest the preference of zonation free approaches for seismic hazard assessment in italy furthermore among the possible zonation free approaches those that offer better exploitation of local information about the effects of past earthquakes would be preferred

volcanic eruptions cool summers and famines in the northeastern part of japan abstract during the last 300 years most of the poor rice harvests caused by unusual cool summers and leading to famine conditions in the tohoku district the northeastern part of japan took place just after the great volcanic eruptions an analysis of instrumental observations in the past century on the kinkasan island indicates that though the standard deviation in the summer air temperature is 1 1 c for 1882 1985 the summer air temperature averages 1 3 0 5 c lower than normal during the summer following the great volcanic eruptions the mid latitudinal mean surface air temperature in the northern hemisphere decreased only about 0 2 c this result indicates that the summer air temperature in tohoku district tends to be particularly sensitive to such eruptions in all the cool summers a blocking high persisted over the ocean northeast of japan and impeded the northward movement of the raiu front the stagnating polar front during the early summer exceptionally cool summers occurred frequently w

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

radiative forcing and climate impact resulting from so2 injections based on a 200 000 year record of plinian eruptions along the central american volcanic arc we present for the first time a self consistent methodology connecting volcanological field data to global climate model estimates for a regional time series of explosive volcanic events using the petrologic method we estimated so2 emissions from 36 detected plinian volcanic eruptions occurring at the central american volcanic arc cava during the past 200 000 years together with simple parametrized relationships collected from past studies we derive estimates of global maximum volcanic aerosol optical depth aod and radiative forcing rf describing the effect of each eruption on radiation reaching the earth s surface in parallel aod and rf time series for selected cava eruptions are simulated with the global aerosol model maecham5 ham which shows a relationship between stratospheric so2 injection and maximum global mean aod that is linear for smaller volcanic eruptions 5 mt so2 and nonlinear for larger ones 5 mt so2 and is qualitatively and quantitatively consistent with the relationship used in the simple parametrized approximation potential climate impacts of the selected cava eruptions are estimated using an earth system model of intermediate complexity by rf time series derived by 1 directly from the global aerosol model and 2 from the simple parametrized approximation assuming a 12 month exponential decay of global aod we find that while the maximum aod and rf values are consistent between the two methods their temporal evolutions are significantly different as a result simulated global maximum temperature anomalies and the duration of the temperature response depend on which rf time series is used varying between 2 and 3 k and 60 and 90 years for the largest eruption of the cava dataset comparing the recurrence time of eruptions based on the cava dataset with the duration of climate impacts based on the model results we conclude that cumulative impacts due to successive eruptions are unlikely the methodology and results presented here can be used to calculate approximate volcanic forcings and potential climate impacts from sulfur emissions sulfate aerosol or aod data for any eruption that injects sulfur into the tropical stratosphere

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

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

the last deglaciation absolute and radiocarbon chronologies e bard and w s broecker publisher springer verlag berlin heidelberg new york 1992 344 pp isbn 3 540 53123 8 dm 228

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

comment on test of seismic hazard map from 500 years of recorded intensity data in japan by masatoshi miyazawa and jim mori miyazawa and mori 2009 propose testing probabilistic seismic hazard assessments pshas for japan in terms of predicted macroseismic intensities against those observed over the past 500 yrs while the comparison presents a real interest to the seismological and engineering communities their reasoning is based on an incorrect hypothesis and leads to several problems comparing probabilistic estimates and observations is an important topic any available observations should be used to infer constraints on the probabilistic estimates testing long term earthquake hazard predictions is currently one of the biggest challenges in the area of engineering seismology several current large scale seismic hazard projects have work packages dedicated to developing so called validation techniques e g the european commission funded seismic hazard harmonization in europe share project and the global earthquake model obviously this task should be performed with great caution as such validation studies have a direct impact on for example estimates of seismic risk and building regulations

mafic pyroclastic flows at santa maria gaua volcano vanuatu the caldera formation problem in mainly mafic island arc volcanoes at santa maria volcano new hebrides island arc extensive ash and scoria flow deposits overlie the mainly effusive pre caldera cone hydromagmatic features characterize these deposits the composition of juvenile clasts ranges from basalt to acid andesite dacite sio2 51 63 6 with a dominant basaltic composition the stratigraphic position of this pyroclastic series and its spatial distribution around a 8 5 km 6 km wide caldera provide evidence of a relationship between this series and the caldera formation in addition these pyroclastic deposits are co genetic to parasitic cones and lava flows developed along faults concentric to the caldera both series result from a compositionally layered magma reservoir the subordinate differentiated magmas being the result of fractional crystallization from the basalts a model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed this model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence a process often proposed for the formation of calderas in island are volcanoes of mainly mafic composition

probabilistic seismic hazard estimation in low seismicity regions considering non poissonian seismic occurrence summary in low seismicity regions such as france or germany the estimation of probabilistic seismic hazard must cope with the difficult identification of active faults and with the low amount of seismic data available since the probabilistic hazard method was initiated most studies assume a poissonian occurrence of earthquakes here we propose a method that enables the inclusion of time and space dependences between earthquakes into the probabilistic estimation of hazard combining the seismicity model epidemic type aftershocks sequence etas with a monte carlo technique aftershocks are naturally accounted for in the hazard determination the method is applied to the pyrenees region in southern france the impact on hazard of declustering and of the usual assumption that earthquakes occur according to a poisson process is quantified showing that aftershocks contribute on average less than 5 per cent to the probabilistic hazard with an upper bound around 18 per cent

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

seismic hazard from instrumentally recorded historical and simulated earthquakes application to the tibet himalayan region abstract we present a new approach to assessment of regional seismic hazard which accounts for observed instrumentally recorded and historic earthquakes as well as for seismic events simulated for a significantly longer period of time than that of observations we apply this approach to probabilistic seismic hazard analysis psha for the tibet himalayan region the large magnitude synthetic events which are consistent with the geophysical and geodetic data together with the observed earthquakes are employed for the monte carlo psha earthquake scenarios for hazard assessment are generated stochastically to sample the magnitude and spatial distribution of seismicity as well as the distribution of ground motion for each seismic event the peak ground acceleration values which are estimated for the return period of 475 yr show that the hazard level associated with large events in the tibet himalayan region significantly increases if the long record of simulated seismicity is considered in the psha the magnitude and the source location of the 2008 wenchuan m 7 9 earthquake are among the range of those described by the seismic source model accepted in our analysis we analyze the relationship between the ground motion data obtained in the earthquake s epicentral area and the obtained psha estimations using a deaggregation technique the proposed approach provides a better understanding of ground shaking due to possible large magnitude events and could be useful for risk assessment earthquake engineering purposes and emergency planning

late cenozoic tephrostratigraphy offshore the southern central american volcanic arc 1 tephra ages and provenance we studied the tephra inventory of 18 deep sea drill sites from six dsdp odp legs legs 84 138 170 202 205 206 and two iodp legs legs 334 and 344 offshore the southern central american volcanic arc cava eight drill sites are located on the incoming cocos plate and ten drill sites on the continental slope of the caribbean plate in total we examined 840 ash bearing horizons and identified 650 of these as primary ash beds of which 430 originated from the cava correlations of ash beds were established between marine cores and with terrestrial tephra deposits using major and trace element glass compositions with respect to relative stratigraphic order as a prerequisite for marine terrestrial correlations we present a new geochemical data set for significant neogene and quaternary costa rican tephras moreover new ar ar ages for marine tephras have been determined and marine ash beds are also dated using the pelagic sedimentation rates the resulting correlations and provenance analyses build a tephrochronostratigraphic framework for costa rica and nicaragua that covers the last 8 myr we define 39 correlations of marine ash beds to specific tephra formations in costa rica and nicaragua from the 4 15 ma lower sandillal ignimbrite to the 3 5 ka rincon de la vieja tephra from costa rica as well as another 32 widely distributed tephra layers for which their specific region of origin along costa rica and nicaragua can be constrained this article is protected by copyright all rights reserved

a 2680 year volcanic record from the dt 401 east antarctic ice core 1 volcanic signals recorded in the antarctic and greenland ice cores can provide useful information on past explosive volcanism and its impact in this study we carried out a continuous sulfate analysis of a 102 65 m east antarctic ice core dt 401 dated as 2682 years and identified 36 extensive volcanic eruption signals using cole dai s method which gives an average of 1 4 eruptions per century consistent with the results from the plateau remote pr b ice core when the record is divided into three parts the latest millennium 1999 1000 a d the middle millennium 999 1 a d and the earliest 682 years 0 a d to 682 b c it is found that there were more volcanic eruptions that occurred during the latest millennium 19 eruptions than during the middle millennium 10 eruptions of the record and that the intensities of the eruptions in the latest millennium are markedly larger than those in the middle one there were only seven events recorded in the earliest 682 years but their intensities were greater and nearly half of the eruptions had a similar intensity to tambora s 1815 a d which differs from the pr b record it is also found that volcanism and its average accumulation rate were lower during the little ice age than during the medieval warm period comparison of volcanic records between dt 401 and other antarctica ice cores pr b dome c dt 263 and byrd show that in the east antarctica area with its lower accumulation rates postdepositional effects may play an important role in the deposition of the sulfate

a 400 ka tephrochronological framework for central america from lake peten itza guatemala sediments highlights dating 400 ka paleoclimate record of neotropics revision and new eruptive volumes for large central american eruptions age models for peten itza sediments linking lacustrine ash inventory to eruptions from central america and mexico abstract lake peten itza northern guatemala lies within a hydrologically closed basin in the south central area of the yucatan peninsula and was drilled under the auspices of the international continental scientific drilling program icdp in 2006 at 16 55 n latitude the lake is ideally located for study of past climate and environmental conditions in the neotropical lowlands because of its great depth 160 m lake peten itza has a record of continuous sediment accumulation that extends well into the late pleistocene a key obstacle to obtaining long climate records from the region is the difficulty of establishing a robust chronology beyond 40 ka the limit of 14c dating tephra layers within the lake peten itza sediments however enable development of age depth relations beyond 40 ka ash beds from large magnitude pleistocene to holocene silicic eruptions of caldera volcanoes along the central american volcanic arc cava were found throughout drill cores collected from lake peten itza these ash beds were used to establish a robust chronology extending back 400 ka we used major and trace element glass composition to establish 12 well constrained correlations between the lacustrine tephra layers in lake peten itza sediments and dated deposits at the cava source volcanoes and with their marine equivalents in eastern pacific ocean sediments the data also enabled revision of eight previous determinations of erupted volumes and masses and initial estimates for another four eruptions as well as the designation of source areas for 14 previously unknown eruptions the new and revised sedimentation rates for the older sediment successions identify the interglacial of mis5a between 84 and 72 ka followed by a stadial between 72 and 59 ka that corresponds to mis4 we modified the age models for the lake peten itza sediment sequences extended the paleoclimate and paleoecological record for this neotropical region to 400 ka and determined the magnitude and timing of cava eruptions

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

can strong motion observations be used to constrain probabilistic seismic hazard estimates abstract because of the new regulatory requirements that hazards have to be estimated in probabilistic terms the number of probabilistic hazard studies conducted has recently been increasing the present study aims at defining the possibilities and limits for comparing predictions from these studies and observations comparison tests based directly on the rate of ground motion occurrences are favored over the rate of earthquake occurrences based on the properties of poisson processes the minimum time window ensuring reliable occurrence rate estimates at a site is computed and evaluated for example for ground motions with a 475 yr return period at a site a minimal 12 000 yr observation time window is required for estimating the rate with a 20 uncertainty coefficient of variation standard deviation divided by the mean these values are not dependent on the seismicity level of the regions under study an analysis of recorded ground motions at the stations of the permanent french accelerometer network shows that at best the occurrence rates can be estimated with an accuracy of 30 for very low acceleration levels 0 0001 0 001 g for the station stet the same analysis carried out at two stations with longer recording histories and located in higher seismicity regions greece and california provides ground motion levels up to 0 1 g therefore the question posed is can the results of a comparison test at low acceleration levels be generalized to higher acceleration levels even if using a ground motion prediction equation uniformly valid for a wide range of accelerations

comment on why earthquake hazard maps often fail and what to do about it by s stein r geller and m liu stein et al 2012 contends that the occurrence of some recent destructive earthquakes in areas mapped as low hazard in some probabilistic seismic hazard maps illustrates limitations of earthquake hazard mapping this statement is fundamentally incorrect these instances illustrate that short term observations such as recent seismicity do not characterize the hazard from faults with long recurrence time earthquakes this is not an inherent limitation in the methodology of probabilistic seismic hazard assessment psha they repeat arguments made in their previous articles one of them recent stein et al 2011 and others on the new madrid region of the central united states that were published and commented on several years ago e g frankel 2003 2004 stein et al 2003 stein et al 2012 makes three major points 1 the inputs to seismic hazard maps should include long term geologic data in addition to historical and instrumental seismicity 2 uncertainties in hazard values should be estimated and communicated to users and 3 seismic hazard maps need to be objectively tested the first two points have long been recognized and practiced in the seismic hazard mapping community in the united states and elsewhere the third point has also been the subject of substantial work e g stirling and petersen 2006 this comment points out problems

a comparison between the forecast by the united states national seismic hazard maps with recent ground motion records confidence in scientific models accumulates by continuously validating the model s predictions by observations we compared the seismic hazard forecasts of the four published versions of the u s geological survey national seismic hazard maps with observed ground motions a large dataset is necessary for a statistically meaningful comparison and so our comparison was based on an aggregated approach such that the observations and the forecast in a region california and the central and eastern united states ceus were combined and compared as a whole we used instrumental records in california and macroseismic intensity in the ceus since 2000 as the observation which was largely prospective to the hazard maps we verified that the observed seismic hazard based on macroseismic intensity was consistent with that based on instrumental records making model evaluation in the ceus for which instrumental records were almost nonexistent viable the observed hazard was found to be generally consistent with the forecasted one for peak ground acceleration pga in california and for both pga and spectral acceleration at 1 s sa1 in the ceus forecasted hazard for sa1 for california appeared to be conservative recent versions of the hazard map were in better agreement with observations in california small earthquakes as expected were found to have insignificant impact on sa1 induced earthquakes in the ceus have increased the observed seismic hazard but did not invalidate the hazard model as a whole we examined the resolving power of the test by computing its statistical power

british shore platforms and ice sheets during the past few years views about the relative ages and modes of formation of fossil rock platforms and cliffs in scotland have changed considerably1 3 i suggest further changes here and present a model of rock platform relationships which involves an interglacial set of platforms a glacial set and a late glacial feature interpretations of the glaciation of the outer hebrides have recently been completely revised this revision has major implications for the glaciation of the inner hebrides which in turn has wider implications

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

near surface weakening in japan after the 2011 tohoku oki earthquake 1 the magnitude mw 9 0 tohoku oki earthquake on 11 march 2011 was one of the largest in recent history ground motion caused by the seismicity around the time of the main shock was recorded by kik net the strong motion network that covers most of japan by deconvolving waveforms generated by earthquakes that are recorded at the surface and in a borehole at kik net station fksh18 we detect a reduction of shear wave velocity in the upper 100 m of about 10 and a subsequent healing that varies logarithmically with time using all available borehole and surface records of more than 300 earthquakes that occurred between 1 january 2011 and 26 may 2011 we observe a reduction in the shear wave velocity of about 5 in the upper few hundred meters after the tohoku oki earthquake throughout northeastern japan the area of the velocity reduction is about 1 200 km wide which is much wider than earlier studies reporting velocity reductions following other larger earthquakes the reduction of the shear wave velocity is an indication that the shear modulus and hence the shear strength is reduced over a large part of japan

reply to comment on test of seismic hazard map from 500 years of recorded intensity data in japan by masatoshi miyazawa and jim mori by celine beauval pierre yves bard and john douglas miyazawa and mori 2009 focused on obtaining the recorded maximum seismic intensity in japan over the last 500 years and made comparisons to the corresponding japanese probabilistic seismic hazard map pshm by the headquarters for earthquake research promotion 2005 the comments by beauval et al 2010 state that this comparison is not correct in this reply we try to further justify the validity of the comparison by clarifying that 1 many stations over japan are used to test the pshms on average and 2 the pshm assumes both a time dependent model and a time independent model for the probability of earthquake occurrences the present pshms in japan use both time dependent and time independent models it is well known that large earthquakes with magnitude larger than 7 repeatedly occur in subduction zones at intervals on the order of 100 years or less and with similar mechanisms also the recurrences of onshore earthquakes on major active faults have been investigated geologically though their uncertainties are much larger compared to the subduction zone earthquakes the recurrences of these earthquakes are modeled in the pshm as a brownian passage time distribution fujiwara et al 2006 and miyazawa and mori 2009 p 3124 say that the present pshm is a time dependent hazard map for some onshore earthquakes with unclear return periods and earthquakes with nonspecified source faults the occurrence probability is modeled as a poisson process which is time independent for details see national research institute for earth science and disaster prevention 2009 and the japan seismic hazard information station web site national research institute for earth science and disaster prevention nied 2010 beauval et al 2010 point out

radiocarbon redating of contaminated samples from a tropical volcano the mansion series of st kitts west indies heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits in addition to easy contamination of this wood by root systems and soluble humic material because the physical nature of the charcoal varies some samples are more prone to contamination two independent studies of the same volcano mt liamuiga on st kitts in the lesser antilles sometimes using samples from the same carbonized tree yielded a systematic difference in radiocarbon ages an exchange of samples and a re investigation of three physically distinct types of charcoal yielded the following results rare hard dense charcoal lacking contamination which had yielded a spurious age of 2860 years bp was redated at 1845 58 years bp common soft friable charcoal with good cellular structure proved to be susceptible to contamination a field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre treatment was used indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets a previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the mansion series contradicted ages older than 41000 years bp from common friable charcoal in the lower mansion series the soft powdery charcoal was re investigated using a sample collected a few centimeters from the original although field decontamination of this sample was not possible more extensive laboratory treatment yielded an age of ca 43000 years bp again proving that routine laboratory pretreatments are inadequate a revised geochronology for the mansion series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits

the possible effects of large 19th and 20th century volcanic eruptions on zonal and hemispheric surface temperatures abstract the contribution of volcanic material to the stratosphere from major eruptions within the last two centuries has been estimated using volcanological criteria including eruption type eruption column height volume and duration of eruption and composition and degree of fragmentation of magma the chronology of major explosive volcanic eruptions is compared with a record of mean surface temperature deviation t for the same interval constructed from all available temperature data the temperature records are divided into 6 latitudinal zones allowing analysis for individual zones where temperature changes induced by aerosol perturbation might be intensified we focus on the explosive volcanic events which by our estimates injected the most material into the stratosphere these include tambora 1815 krakatau 1883 santa maria 1902 katmai 1912 and quizapu 1932 such eruptions appear to have produced a consistent but small temperature decrease on the order of 0 2 to 0 5 c on a hemispheric scale for periods ranging from one to five years although these changes are similar to background temperature variations the maximum change in t after some of these explosions appears to lag by up to three years in going from equatorial to polar latitudes somewhat smaller eruptions e g agung 1963 and possibly cosiguina 1835 seem to have produced about the same perturbation in t as the larger eruptions this suggests either a limiting mechanism on loading of the aerosol layer after a volcanic eruption or that the composition of injected material i e the ratio of silicate dust to volatiles and composition of the volatiles may significantly effect stratospheric optical depth perturbation temperatures do not remain depressed for a longer period after a series of closely timed eruptions e g the 1881 1889 or the 1902 1903 sequences than after single events

formation of the mid fifteenth century kuwae caldera vanuatu by an initial hydroclastic and subsequent ignimbritic eruption in the mid fifteenth century one of the largest eruptions of the last 10 000 years occurred in the central new hebrides arc forming the kuwae caldera 12x6 km this eruption followed a late maar phase in the pre caldera edifice responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers tuffs related to caldera formation 120 m of deposits on a composite section from the caldera wall were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes the lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition but clasts show compositions ranging from 48 to 60 sio2 the unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range 60 73 sio2 but are dominantly dacitic this broad compositional range is thought to be due to crystal fractionation the striking evolution from one eruptive style hydromagmatic to the other magmatic with emission of a large volume of ignimbrites which occurred either over the tuff series as a whole or at the beginning of each ignimbritic phase is the most impressive characteristic of the caldera forming event this strongly suggests triggering of the main eruptive phases by magma water interaction a three step model of caldera formation is presented 1 moderate hydromagmatic sequences hd 1 4 and magmatic fallout deposits activity from a central vent probably over a period of months or years affected an area slightly wider than the present caldera at the end of this stage intense seismic activity and extrusion of differentiated magma outside the caldera area occurred 2 unhomogenized dacite was released during a hydromagmatic episode hd 5 this was immediately followed by two major pyroclastic flows pfd 1 and 2 the vents spread and intense magma water interaction at the beginning of this stage decreased rapidly as magma discharge increased subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera 3 dacitic welded tuffs were emplaced during a second main phase wfd 1 5 at the beginning of this phase magma water interaction continued producing typical hydromagmatic deposits hd 6 caldera collapse extended to the northern part of the caldera previous c14 dates and records of explosive volcanism in ice from the south pole show that the climactic phase of this event occurred in 1452 a d