variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

evolution of the northern belt southern uplands implications for the southern uplands controversy conodont and graptolite dating provide a high resolution biostratigraphical framework for correlation across the southern upland fault the establishment of an early caradoc age for the red chert and volcanic sequences within the northern belt of the southern uplands confounds the accretionary prism model and our data support the view that following the obduction of the ballantrae ophiolite fan complexes prograded southeastwards across a narrow fault bounded shelf into the deep basin of the northern belt the fan complexes were initiated by uplift in the hinterland caused by the intrusion of plutons into the midland valley terrane sedimentation was controlled by regional extension subsidence and eustasy through the llanvirn and caradoc basic lavas with attenuated within plate geochemical signatures were erupted during the early caradoc peak of extension and may have just post dated the initiation of southwards subduction beneath the lake district

error analysis of paleosalinity calculations a detailed error analysis is performed for the calculation of open ocean salinity changes from carbonate oxygen 18 proxy data measurement errors are generally negligible however errors due to the goodness of fit of various regressions used in the calculation are significant depending on the method used and on the proxies available error bars 1 for the salinity range from 0 6 to 1 8 in particular expected errors for the midlatitude and tropical salinity differences at the last glacial maximum are around 1 1 to 2 5 the largest errors occur because of the differences between temporal and spatial seawater oxygen 18 salinity relationships and through the use of nonconcurrent temperature measurements methods of improving paleosalinity estimates should focus on eliminating these large sources of uncertainty

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

fossil evidence for fault derived stratigraphic repetition in the northeastern newfoundland appalachians two types of bedding parallel faults are common in the dunnage zone of eastern notre dame bay they are i early thrusts which together with bedding were rotated by later folding into steep attitudes and ii postfolding transcurrent faults both types of faults occur at all scales and give rise to repetitions in the stratigraphic sequence a compilation of the ages of various rock types based on fossil evidence indicates a relatively simple stratigraphy for the dunnage zone this interpretation appears to be at variance with many reported stratigraphic successions until repetitions by bedding parallel faulting are taken into account examples are given of sequences in which the repetition of various rock types dated by means of fossils is due to bedding parallel faulting we believe that the simple lithostratigraphy is a reliable aid for structural interpretations in areas where fossils are scarce or absent

evolution of the early paleozoic cordilleran margin of laurentia tectonic and eustatic events interpreted from sequence stratigraphy and conodont community patterns several field seasons in the canadian cordillera have allowed the measurement description and sampling of over 20 000 m of lower paleozoic strata from 26 stratigraphic sections across four platform to basin transects with the recovery of over 100 000 conodonts from more than 1200 4 5 kg samples this work was part of the lithoprobe slave northern cordillera lithospheric evolution snorcle project but is also being extended through a pan lithoprobe project to understand the tectonic and eustatic response of much of the laurentian plate through the early paleozoic based on the abundant field data the complex stratigraphic framework is interpreted in terms of sequence stratigraphy and a derived relative sea level curve using detailed conodont taxonomic and biostratigraphic results cluster analysis of conodont distributional data identified an evolving series of conodont communities through space and time these communities were partitioned across the platform to basin gradient and provide an additional sensitive indicator of relative sea level change these two independent approaches generated comparable eustatic curves for this cordilleran laurentian margin during much of the early paleozoic and identified some global eustatic events noted by earlier workers this part of laurentia was not a simple passive margin during the early paleozoic but rather was affected by four main tectonic events complicated by six principal eustatic changes some success was achieved in filtering the global and regional tectonic eustatic effects and in proposing causes for some of the events

site response in southern california for probabilistic seismic hazard analysis this study determines site response factors that can be applied as cor rections to a rock attenuation relationship for use in probabilistic seismic hazard analysis the site response factors are amplitude and site class dependent these amplification factors are determined by averaging ratios between observed and pre dicted ground motions for peak ground acceleration pga and for 5 damped re sponse spectral acceleration at 0 3 1 0 and 3 0 sec oscillator periods the observa tions come from the strong motion database of the southern california earthquake center scec and the predictions are based on the sadigh 1993 rock attenuation relation when separated and averaged according to surface geology significantly different site response factors are found for quaternary and mesozoic units but a subclassification of quaternary is generally not justified by the data the low input motion amplification factors are consistent with those obtained from independent aftershock studies at the pga and 0 3 second period an observed trend of decreasing quaternary site amplification with higher input motion is consistent with nonlinear soil behavior however the trend exists for mesozoic sites as well implying that this may be an artifact of the sadigh relationship there is a correlation between larger site response factors and lower average shear wave velocity in the upper 30 m for low predicted pga input motions with an increase in the correlation with increasing period the 0 3 sec site response factors for quaternary data in southern california determined in this study are consistent with 0 3 sec nehrp site response correction factors however at 1 0 sec period some inconsistencies remain a trend is also seen with respect to sediment basin depth where deeper sites have higher average site response factors these results constitute a customized attenuation relationship for southern california the implication of these customized attenuation models with respect to probabilistic hazard analysis is examined in field and petersen 2000

a modified ground motion attenuation relationship for southern california that accounts for detailed site classification and a basin depth effect the attenuation relationship presented by boore et al 1997 has been evaluated and customized with respect to southern california strong motion data for peak ground acceleration pga and 0 3 1 0 and 3 0 sec period spectral acceleration this study was motivated by the recent availability of a new site classification map by wills et al 2000 which distinguishes seven different site categories for california based on the 1994 nehrp classification with few exceptions each of the five site types represented in the southern california strong motion database exhibit distinct amplification factors supporting use of the wills et al 2000 map for microzonation purposes following other studies a basin depth term was also found to be significant and therefore added to the relationship sites near the center of the la basin exhibit shaking levels up to a factor of 2 greater on average than otherwise equivalent sites near the edge relative to boore et al 1997 the other primary difference here is that pga exhibits less variation among the wills et al 2000 site types in fact the pga amplification implied by the basin depth effect is greater than that implied by site classification the model does not explicitly account for nonlinear sediment effects which if important will most likely influence rock site pga predictions the most evidence for a magnitude dependent variability or prediction uncertainty is also found and included as an option

holocene variations in asian monsoon moisture a bidecadal sediment record from the south china sea the east asian monsoon system involves extensive transport of sensible latent heat between land and sea and from low to high latitudes our high resolution bidecadal marine records present a first detailed history of monsoon climate change over the holocene the high amplitude perturbation in monsoon moisture centered at 8 150 years ago and the monsoon maximum in the early holocene show inter hemispheric teleconnections to both a cool episode in greenland and to the indian monsoon monitored in the arabian sea periodicities of 84 102 and especially near 775 years in monsoon variation suggest a climatic forcing both by long term oscillations in thermohaline circulation and possibly solar activity cycles

saffordophyllum and evidence for thrusting in the cobbs arm sequence newfoundland a new occurrence of the tabulate coral saffordophyllum is described from turbidites in the cobbs arm sequence of notre dame bay the age of the fossil is interpreted as ashgillian and its presence

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

the scec phase iii strong motion database as part of the southern california earthquake center scec phase iii effort to include site effects in hazard models for southern california a regional database of strong motion observations was developed the observations consist of the peak ground acceleration pga and 5 damped response spectral acceleration sa at 0 3 1 0 and 3 0 sec periods from 28 earthquakes and 281 stations a total of 449 pairs of horizontal pga and sa observations that were taken from the scec strong motion database smdb are presented here the phase iii database includes earthquakes with moment magnitudes larger than 5 0 and stations in southern california with locations between 32 and 36 north latitude observations from buildings with more than two stories and dam abutments or crests are excluded from the database observations with distances of 150 km or greater were also excluded the agencies that provided the data to smdb are the u s geological survey california strong motion instrumentation program university of southern california and the los angeles department of water and power the database also contains site classification information for each station a first general classification is based on the 1 750 000 california map of quaternary tertiary and mesozoic geologic units by jennings 1977 as modified by park and elrick 1998 a second more detailed classification is based on quaternary mapping in the los angeles region by tinsley and fumal 1985 as modified by park and elrick 1998 a third classification is based on the correlation of surface geology with shear wave velocity in the upper 30 m wills et al 2000 an arbitrary depth to basement parameter is assigned to stations that are located within the boundary of the 3d velocity model used by olsen 2000 which is based on the scec 3d velocity model version 1 this parameter is defined as the depth to the 2 5km sec velocity isosurface special parameters associated with particular attenuation relations such as different distance measures a hanging wall flag and fault type flag are also assigned to each observation these data are all presented within the tables and figures of this article and also have been made available via a downloadable file on the internet http smdb crustal ucsb edu phase3

southwest new world island stratigraphy new fossil data new implications for the history of the central mobile belt newfoundland the identification of fossils from 16 new localities on southwestern new world island has resulted in the refinement and simplification of local stratigraphy and in the correlation of rock units across an intensely deformed area complex stratigraphic classifications of earlier workers are replaced by a simpler scheme consisting of four formations the summerford formation oldest rogers cove formation sansom formation and goldson formation mclange units are fault related and cannot be included in the stratigraphy fossil and lithological data provided here confirm previous indications that the rocks of the summerford formation are the remains of a long lived volcanic island complex this complex is overlain by a markedly diachronous coarsening upwards sequence of marine clastic sediments now represented by the rogers cove sansom and goldson formations the new stratigraphic data combined with structural evidence indicate that the stratigraphy is repeated across several bedding parallel faults significant diachroneity of formation boundaries and the absence of syndepositional high angle faults suggest deposition in one large rnid paleozoic basin rather than in a number of small dynamic basins

a test of various site effect parameterizations in probabilistic seismic hazard analyses of southern california we evaluate the implications of several attenuation relationships including three customized for southern california in terms of accounting for site effects in probabilistic seismic hazard studies the analysis is carried out at 43 sites along a profile spanning the los angeles basin with respect to peak acceleration and 0 3 1 0 and 3 0 sec response spectral acceleration values that have a 10 chance of being exceeded in 50 years the variability among currently viable attenuation relationships espistemic uncertainty is an approximate factor of 2 biases between several commonly used attenuation relationships and southern california strong motion data imply hazard differences that exceed 10 however correcting each relationship for the southern california bias does not necessarily bring hazard estimates into better agreement a detailed subclassification of site types beyond rock versus soil is found to be both justified by data and to make important distinctions in terms of hazard levels a basin depth effect is also shown to be important implying a difference of up to a factor of 2 in ground motion between the deepest and shallowest parts of the los angeles basin in fact for peak acceleration the basin depth effect is even more influential than the surface site condition questions remain however whether basin depth is a proxy for some other site attribute such as distance from the basin edge the reduction in prediction error sigma produced by applying detailed site and or basin depth corrections does not have an important influence on the hazard in fact the sigma reduction is less than epistemic uncertainties on sigma itself due to data limitations it is impossible to determine which attenuation relationship is best however our results do indicate which site conditions seem most influential this information should prove useful to those developing or updating attenuation relationships and to those attempting to make more refined estimates of hazard in the near future

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

salinity records for the 1997 98 el nino from western pacific corals 1 seasonal sea surface salinity sss records can be of great value in reconstructing el nino southern oscillation enso variability in the equatorial western and central pacific a region where enso related evaporation and precipitation e p changes are dramatic the 18o values of coral skeleton 18ocoral reflect seawater 18o 18oseawater changes which in tropical oceans are also generally influenced by e p changes therefore 18ocoral is a good indicator of rainfall and enso variability we present biweekly data from palau in the northern part of the western pacific warm pool for the period 1998 2000 which indicate a strong quantitative relationship between 18ocoral sea surface temperature 18oseawater and sss the coral skeletal 18o values documented the sss changes after the 1997 98 el nino therefore 18ocoral can be used to estimate paleosalinity changes however the slope of the 18oseawater sss relationship cannot be assumed to be constant throughout the tropics making site specific calibrations is essential

changes in the indonesian throughflow during the past 2000 yr the indonesian throughflow itf is the only low latitude conduit for exchange of surface and thermocline waters between the indian and pacific oceans 80 of the itf waters pass through the makassar strait the flux of heat and salt through the strait is in part a function of the density difference between its southern and northern ends here the mg ca and stable oxygen isotope compositions of the planktonic foraminifer globigerinoides ruber sampled from two sediment cores collected at the northern and southern ends of the makassar strait are used to reconstruct surface water temperature sst sea surface salinity sss and seawater density variability over the past 2000 yr maximum sst and sss occurred at both sites between 850 and 700 yr ago coinciding with the medieval solar maximum and medieval warm period ca 1000 700 yr ago sst and sss declined at both locations after 700 yr ago and reached minimum values during the little ice age between 300 and 100 yr ago however the magnitude of sst and sss change over the past 2000 yr was distinctly different between the two sites especially during the period between 2000 and 900 yr ago this led to changes in the south to north density gradient within the makassar strait specifically the time interval from ca 2000 to 800 yr ago was marked predominantly by higher densities at the northern end relative to the southern end of the strait suggesting reduced heat flux from the pacific to the indian ocean this is consistent with previous work showing that this time interval was also marked by frequent el nino conditions conversely the period from ca 800 to 300 yr ago including the lia was marked by frequent periods when surface density was higher at the southern end of the strait indicative of enhanced heat flux to the indian ocean

seasonal change in foraminiferal production in the western equatorial pacific warm pool evidence from sediment trap experiments seasonal changes in the flux of individual planktonic foraminifera in the deep ocean have been studied in the western equatorial pacific warm pool using material collected by sediment traps over a period of 1 yr 1991 1992 mean total foraminiferal fluxes tffs were 171 and 97 shells m 2 day 1 at sites n1 2 59 8 n 135 01 5 e and n2 4 07 5 n 136 16 6 e respectively the seasonal change in tffs was much higher than for organic matter om and carbonate fluxes the major species of planktonic foraminifera were pulleniatina obliquiloculata neogloboquadrina dutertrei globigerinoides sacculifer globigerinella aequilateralis and globigerinoides ruber symbiont bearing species and n dutertrei were predominant in the western equatorial pacific warm pool comparison between the warm pool and upwelling deep sea research ii 43 1996 1257 mar micropaleontology 33 1998 157 indicates that the foraminiferal assemblage trapped at the western equatorial pacific warm pool was comparable with the south equatorial and subtropical assemblages during a plankton tow study conducted at 140 w in 1992 it suggests that fairly oligotrophic conditions prevailed in the western equatorial pacific warm pool in association with terrestrial nutrient inputs or temporary mixing by wind bursts the om flux was more positively correlated with the 63 m carbonate fraction mainly composed of coccoliths r 0 87 and biogenic opal which suggests that om fluxes were more affected by phytoplankton productivity although food availability is generally important for foraminiferal production tffs were poorly correlated with om fluxes at sites n1 and n2 which is partly attributed to the significant influence of symbiont photosynthesis the 18o values of p obliquiloculata and n dutertrei showed maxima in association with high om fluxes during period 2 from august to october and period 4 from late december to april at site n1 reflecting thickening of the mixed layer following wind bursts g sacculifer showed a lunar reproduction cycle when between july and october carbonate production was more predominant than biogenic opal production a similar profile was evident for g ruber orbulina universa and g aequilateralis these four species are generally predominant at low latitudes therefore the lunar reproduction cycle may significantly affect the fluctuation in carbonate production in the equatorial ocean

late middle ordovician olistostrome formation and magmatism along the red indian line the laurentian arc gondwanan arc boundary at sops head newfoundland the sops head complex of badger bay central newfoundland includes olistostromal and tectonized melanges and marks the red indian line the boundary between the peri gondwanan exploits and peri laurentian notre dame subzones of the oceanic dunnage zone basalts in the olistostromal melange preserve peperitic contacts with mudstone and limestone within slumped sedimentary units demonstrating that magmatism was coeval with olistostrome formation conodonts from the limestones date these events as late darriwilian llandeilian middle ordovician in age the conodont fauna consists entirely of north atlantic faunal realm elements suggesting a peri gondwanan or mid iapetan provenance for limestone of the sops head complex basalt geochemistry suggests magmatism in a mature volcanic arc to back arc setting the sops head complex shows similarities in age provenance and stratigraphic setting to the dunnage melange suggesting that the two units are correlative

paleoecology of selected conodontophorid species from the cobbs arm formation middle ordovician new world island north central newfoundland the upper chazyan llandeilian cobbs arm formation of new world island north central newfoundland consists of pure limestones and limestones with varying amounts of volcaniclastic admixture inte

calibration of the specific barrier model to earthquakes of different tectonic regions the specific barrier model proposed and developed by papageorgiou and aki 1983a b 1985 provides the most complete yet parsimonious self consis tent description of the faulting process it applies both in the near fault and in the far field region thus allowing for consistent ground motion simulations over the entire frequency range and for all distances of engineering interest the model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions mainly east ern north america events interplate regions and regions of tectonic extension spu dich et al 1999 database the ensemble average value of a key parameter of the specific barrier model the local stress drop dr l i s 161 bars for interplate earth quakes 114 bars for extensional regime earthquakes and 180 bars for intraplate earthquakes the high frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self similar scaling the deviation is most likely caused by the effective source area and or irregularities in the rupture kinematics we account for their overall effects through a high frequency source complexity factor f in the source spectrum of the specific barrier model as a result inter and intraplate source spectra show similar high frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger mag nitudes the interplate soil residuals show clear signs of nonlinear site response whereas only slight signs of such nonlinearity are observed for the extensional data set the regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic yet computationally efficient way to model strong ground motions with implications for seismic hazard and risk analysis online material strong motion station and event station pair information

middle ordovician conodonts from the buchans group central newfoundland and their significance for regional stratigraphy of the central volcanic belt discussion nowlan and thurlow have recently reported a conodont fauna of latest arenig early llanvirn age from the buchans group central newfoundland and have suggested that this demonstrates that all volcanogenic massive sulfide deposits and hence associated volcanism in the canadian appalachians are of caradocian or older ordovician age they go on to state that this requires substantial revisions of tectonic models for the northern appalachians we welcome this important contribution to the knowledge regarding the age of roberts arm volcanic belt which includes the buchans group dean 1977 but find their suggestion that current tectonic models for central newfoundland are inadequate or erroneous to be somewhat misleading perhaps this is the case if the tectonic models they are referring to are those for instance of dean 1977 1978 strong 1977 or dean and kean 1980 however their results strongly support the tectonic models set out by kidd et al 1977

the tectonics and depositional history of the ordovician and silurian rocks of notre dame bay newfoundland reply in the notre dame bay region ophiolitic rocks underlie a thick sequence of lower ordovician volcanic arc rocks to the north of the lobster cove chanceport fault neither this fault nor the lukes arm sops head fault shows evidence of very large strike slip movements as parts of the same arc together with much arc derived detritus straddle both faults towards the east this arc derived detritus becomes more distal in aspect and passes laterally into the dunnage melange during the middle ordovician epoch late llandeilo and early caradoc most areas show a marked decrease in volcanic activity and in the amount of coarse detritus deposited coarse turbidites reappear at different times in different areas during the late ordovician these are related to several fault bounded basins and to movements on the lukes arm sops head fault many of these faults particularly in the east are marked by olistostromes several of which can be dated by fossils as late ordovician and early silurian the whole

evaluation of empirical ground motion relations in southern california regression analysis to develop empirical ground motion relations that predict ground motion characteristics as a function of magnitude and distance are an essential part of seismic design and probabilistic seismic hazard assessment several different ground motion relations have been presented based on different data and assumptions this study evaluates five that were judged likely to be appropriate for southern california we test them against the strong motion data recorded in this region between 1933 and 1994 for magnitudes between 5 0 and 7 5 and for distances up to 150 km the ground motion parameters examined are peak acceleration and response spectral acceleration sa at 0 3 1 0 and 3 0 sec periods some of the ground motion relations are more consistent than others with the limited set of southern california data but none of them stand out as either best or unacceptable residuals from all of these models indicate that as the magnitude increases the standard deviation decreases at high frequencies but increases for sa 3 0 sec among those found to be most consistent significant differences remain with respect to predicting ground motion under conditions not yet sampled by the existing observational data set e g near source shaking for large earthquakes theoretical simulations are used elsewhere in this report ni et al 2000 anderson 2000 to help resolve these ambiguities the implications with respect to probabilistic seismic hazard assessment are explored in field and petersen 2000

deciphering the geology of some darriwilian sandbian ordovician ghost formations in the uk and north america using olistoliths in marine debris flows olistostromes with calcareous olistoliths are rare components in the ordovician successions in nw europe and north america having been described from only a small number of localities one of the best exposed but least known is in the garn formation in coastal outcrops in anglesey in northwestern wales here in the graptolite bearing shales of the garn formation there are numerous limestone olistoliths that are derived from an otherwise unknown ghost formation whose original depositional site remains an enigma these olistoliths contain a baltoscandian type of conodont fauna that is otherwise unknown in wales and england it represents the baltoniodus variabilis subzone of the amorphognathus tvaerensis zone similar but slightly older conodont faunas are recorded from olistoliths in the tweeddale member of the shinnel formation in southern scotland and in probable olistoliths of the cobbs arm limestone in northeasternmost newfoundland approximately coeval conodont faunas are present in calcareous olistoliths in the woods hollow shale of west texas and the womble shale in the ouachita mountains of arkansas usa lithological and conodont evidence indicates that the calcareous olistoliths were derived from carbonate sediments deposited in relatively shallow water it is concluded that the study of ghost formation olistoliths may provide otherwise unavailable but important data bearing on the marine depositional history of a particular region

weaker gulf stream in the florida straits during the last glacial maximum as it passes through the florida straits the gulf stream consists of two main components the western boundary flow of the wind driven subtropical gyre and the northward flowing surface and intermediate waters which are part of the global conveyor belt compensating for the deep water that is exported from the north atlantic ocean1 the mean flow through the straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the straits2 here we use oxygen isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the florida current during the last glacial maximum to determine the density structure in the water and thereby reconstruct transport through the straits using the geostrophic method a technique which has been used successfully for estimating present day flow3 our data suggest that during the last glacial maximum the density contrast across the florida straits was reduced with the geostrophic flow referenced to the bottom of the channel at only about two thirds of the modern value if the wind driven western boundary flow was not lower during the last glacial maximum than today these results indicate a significantly weaker conveyor belt component of the gulf stream compared to present day values whereas previous studies based on tracers suggested that deep waters of north atlantic origin were not widespread during glacial times indicating either a relatively weak or a shallow overturning cell our results provide evidence that the overturning cell was indeed weaker during glacial times

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

sedimentology of upper ordovician silurian sequences on new world island newfoundland separate fault controlled basins remapping of northeast new world island newfoundland demonstrates that two major faults separate three distinct sedimentary sequences paleontology and sedimentology indicate that these sequences are partly equivalent in age but were deposited in separate basins of deposition that were adjacent to each other active silurian faults the boyds island and byrne cove faults new names bounded the margins of these basins and directly influenced sedimentation by uplifting ordovician volcanics limestone and black shale which are found both in situ and as blocks within silurian sediments silurian sediments deposited adjacent to these faults are dominated by pebbly mudstones and chaotic bedding interpreted as debris flow deposits and slumped horizons away from the fault scarps sedimentation was predominantly axial it comprises resedimented conglomerates and thick and thin bedded sandstone turbidites west of new world island similar synsedimentary faults are confined to a narrow belt south of the lukes

the dependence of peak horizontal acceleration on magnitude distance and site effects for small magnitude earthquakes in california and eastern north america abstract one hundred and ninety free field accelerograms recorded on deep soil 10 m deep were used to study the near source scaling characteristics of peak horizontal acceleration for 91 earthquakes 2 5 m l 5 0 located primarily in california of the six attenuation relationships developed in this study the one considered most reliable is given by the expression ln p h a 2 5 0 1 0 6 2 3 m l 1 0 ln r 7 2 8 where pha is the mean of the two horizontal components of peak acceleration in g m l is local magnitude r is epicentral distance in kilometers and is a random error term with mean of zero and standard deviation of 0 506 an analysis of residuals based on an additional 171 near source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower accelerations and that free field accelerograms recorded on shallow soil 10 m deep have 82 per cent higher accelerations than free field accelerograms recorded on deep soil accelerations recorded on rock were found to be similar in amplitude to those recorded on deep soil a separate analysis of site effects for the imperial valley and oroville regions of california indicated that peak accelerations from individual sites can depart significantly from predictions based on broad site classifications an analysis of residuals based on 27 selected strong motion recordings from 19 earthquakes in eastern north america indicated that near source accelerations associated with frequencies less than about 25 hz are consistent with predictions based on attenuation relationships derived for california once site effects and differences in regional magnitude scales are taken into account

the ordovician genus pygodus conodont in the cuyania terrane argentina this contribution deals with the record of the ordovician genus pygodus in cuyania argentina several classical sections have been sampled for conodonts in the precordillera and the san rafael block involving diverse sedimentary deposits coarse clastic rocks with carbonate cement carbonate beds intercalated in fine clastic deposits green shale and black carbonate deposits the recovered species of this genus are pygodus lunnensis zhang p anitae bergstrom p serra hadding p protoanserinus zhang and p anserinus lamont lindstrom these key conodonts indicate middle to upper darriwilian lower sandbian age for the bearing strata the species p protoanserinus is recorded for the first time from the precordillera detailed observations were made on specimens of p anitae p lunnensis and p protoanserinus the two last species are described for the first time from cuyania

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

climate and hydrographic variability in the indo pacific warm pool during the last millennium planktonic foraminiferal mg ca and delta o 18 derived sea surface temperature and salinity records from the makassar strait indonesia show a long term cooling and freshening trend as well as considerable centennial scale variability during the last millennium the warmest temperatures and highest salinities occurred during the medieval warm period mwp while the coolest temperatures and lowest salinities occurred during the little ice age lia these changes in the western pacific along with observations from other high resolution records indicate a regionally coherent southern displacement of the inter tropical convergence zone during the lia with more arid conditions in the northern tropics and wetter conditions in the southern tropics

predictions of shear wave velocities in southern california using surface geology a new model of the average shear wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data several geologic units with similar responses are grouped together the resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier more complicated maps analysis within a geographic information system will permit updates and modification of the map as new velocity data are added