factors controlling the burial of organic carbon in laminated and bioturbated sediments off nw mexico implications for hydrocarbon preservation factors controlling the burial of organic carbon oc in late quaternary sediments on the nw mexican continental margin are assessed using a suite of box and piston cores strategically located on the shelf slope rise with respect to the intense oxygen minimum in this region an oc concentration maximum occurs on the mid slope below the core of an intense water column o2 minimum due to current winnowing on the outer shelf the preferential accumulation of organic matter in fine grained deposits and the offshore decrease in the settling flux of organic detritus the organic matter at all water depths is overwhelmingly marine hydrogen indices hi are higher on the slope 300 mg hc g toc than on the shelf 300 mg hc g toc where current winnowing has promoted organic matter degradation but there is no difference in hi in slope sediments accumulating under well oxygenated and o2 deficient conditions the degree of winnowing appears to be the primary factor affecting the preservational quality of organic matter deposited on this margin rates of accumulation of oc and opal are all higher in the interglacial intervals when compared with the glacial deposits over the last 140 000 yr however matrix corrected hi values in the mid and lower slope cores are invariant and are similar to values in the laminated intervals from the oxygen minimum site thus cyclic changes in organic carbon accumulation on this margin have been controlled by production variations rather than differential preservation hi values in late quaternary sediments from several continental margins including nw mexico and euxinic basins correspond to type ii kerogen irrespective of bottom water o2 concentrations therefore the preservation of oil prone kerogen in productive margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water o2 concentrations as envisioned in models of petroleum source rock deposition

broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

upper crustal low frequency seismicity at mount st helens detected with a dense geophone array abstract mount st helens has been closely monitored by a permanent network including 16 seismometers located within a 15 km radius yet some of its diverse seismic signals remain challenging to detect and relate to deformation processes data from a dense array of 904 geophones within 15 km of mount st helens provide novel constraints on weak seismic signals observed during a two week deployment in 2014 here we report on the identification of weak low frequency lf events that were either not detected by the permanent network or were misclassified as likely rockfalls we refer to the signals as lf earthquakes because they have less power above 10 hz and longer durations compared to similar magnitude volcano tectonic vt events reverse time imaging with the entire geophone array indicates that the lf hypocenters overlap with the frequent vt seismicity in a sub vertical column beneath the summit crater at 6 km below sea level beamforming of p wave arrivals with an exceptionally dense sub array yields slowness estimates that confirm a subsurface origin for 16 lf events occurrence of vt and lf events in approximately the same volume suggests distinct source processes rather than path effects as the primary explanation for their different signals some of the lf and vt events have multiple spectral peaks that may be consistent with source mechanisms involving resonance in fluid filled cavities however the majority of lf and vt event spectra exhibit smooth amplitude decay with increasing frequency consistent with shear failure sources the depletion of high frequencies for lf events could be caused by unusually low rupture velocities or stress drops our results indicate a variety of earthquake source processes occur in a sub vertical column at 6 km depth which is thought to overly the primary upper crustal magma reservoir lf events are typically associated with eruptive or near eruptive activity and are generally not reported at depths greater than 1 km at mount st helens but based on our short duration high density experiment we suggest that upper crustal lf events may be more common than previously recognized and occur across a broader depth range

the physical basis of mb ms and variable frequency magnitude methods for earthquake explosion discrimination we use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake explosion discrimination we use six three dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials four factors contribute to the success of the mb ms discriminant source spectra focal mechanism near source elastic properties and interference of p spectral differences contribute about 0 5 magnitude unit to the separation between earthquake and explosion populations for large events but this difference vanishes for events with mb 4 0 using a frequency band of 0 5 3 0 hz for small events the vfm discriminant is complementary to mb ms in several ways vfm is improved by p interference while mb ms is degraded vfm is more effective for hard rock explosions while mb ms will preferentially discriminate explosions in low velocity materials and vfm is insensitive to fault orientation vfm is more sensitive to noise and regional attenuation differences than mb ms simultaneous use of both methods should allow improved discrimination of small events

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

the δ15n of nitrate in the southern ocean consumption of nitrate in surface waters we report nitrogen isotope data for nitrate from transects of hydrocast and surface samples collected in the eastern indian and pacific sectors of the southern ocean focusing here on the data from the upper water column to study the effect of nitrate consumption by phytoplankton the 15n of nitrate increases by 1 2 from deep water into the antarctic summertime surface layer due to kinetic isotopic fractionation during nitrate uptake estimation of the nitrate uptake isotope effect from antarctic depth profiles yields values in the range of 5 6 in east indian sector and 4 5 in the east pacific sector surface transect data from the pacific sector also yield values of 4 5 the major uncertainty in the profile based estimation of the isotope effect involves the 15n of nitrate from the temperature minimum layer below the summertime antarctic surface layer which deviates significantly from the predictions of simple models of isotope fractionation for the subantarctic surface it is possible to distinguish between nitrate supplied laterally from the surface antarctic and nitrate supplied vertically from the subantarctic thermocline because of the distinctive relationships between the 15n and concentration of nitrate in these two potential sources our subantarctic samples collected during the summer and fall indicate that nitrate is supplied to the subantarctic surface largely by northward transport of antarctic surface water isotopic data from the pacific sector of the subantarctic suggest an isotope effect of 4 5 indistinguishable from the antarctic estimates in this sector

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

dynamics of seasonal and interannual variability of the peru chile undercurrent 1 coastal sea level current satellite altimeter data and an equatorial kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the peru chile undercurrent satellite altimetry shows that low frequency sea level anomalies near 30 s propagate offshore as expected from rossby wave theory those anomalies are related to disturbances of equatorial origin observed near the coast of south america with a wind forced equatorial kelvin wave model and simple rossby wave dynamics we show that much of the sea level anomalies and more than 50 of the observed undercurrent variability near 30 s at seasonal and interannual periods can be explained by long rossby waves forced by the equatorial kelvin waves the amplitude of the equatorial kelvin wave can be used to estimate the amplitude of the rossby wave near the south american coast and thus to monitor low frequency changes in the peru chile undercurrent

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

source effects on regional seismic discriminant measurements source effects on high frequency regional seismic discriminant measurements involving p s type ratios pn lg pg lg are isolated for earthquakes in southern california and southern nevada the scatter in earthquake population discriminant measurements for fixed propagation paths is statistically analyzed to assess the spatial and frequency dependent contributions from source radiation pattern and source depth variations along with variable near source scattering this is useful because procedures for reducing the variance caused by propagation effects must be constrained by knowledge of the intrinsic scatter resulting from independent source effects for which corrections are not available without a priori knowledge of the source type and depth broadband waveforms for earthquakes near the nevada test site nts and in southern california recorded at stations of the livermore nts network lnn the caltech terrascope network and the berkeley digital seismic network bdsn are used to obtain pg lg and pn lg measurements and to assess source depth and mechanism contributions to measurement variance pn lg and pg lg spectral amplitude ratios for several frequency bands between 0 5 and 10 hz from vertical velocity waveforms are computed for a total of 18 tightly located clusters of earthquakes for each cluster we examine the correlations between observed pn lg and pg lg ratios and estimated source depths or predictions based on previously determined source mechanisms focal mechanism predictions do not match the observations well likely due to strong near source scattering and directivity effects that overwhelm the point source radiation pattern however the data do show significant scatter even for sources only a few kilometers apart source depth produces some coherent trends which can be emphasized by averaging results from multiple stations these trends vary from region to region presumably due to specific local crustal layering but most of the variance is not deterministically predictable and appears to arise from strong variations in near source scattering variance estimates for logarithmic amplitude ratios normalized by mean amplitude ratios vary from 0 01 to 0 05 for different phase pairs frequency dependent variations of the mean variance minimum and maximum amplitude ratio parameters show strong distance dependence out to about 300 km and then appear to become independent of event station distance these variance parameters appear to be suitable for use in spatial interpolations of observed p s type ratios for a specific unidentified event path as needed for nuclear test monitoring

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

diatom bound 15n 14n new support for enhanced nutrient consumption in the ice age subantarctic 1 diatom bound 15n 14n was used to reconstruct the glacial nutrient status of the subantarctic zone in the southern ocean down core records from both the pacific and indian sectors show 15n of 5 to 6 during the last glacial maximum and a decrease coincident with the glacial termination to values as low as 2 the effect of either diatom assemblage or physiological change on the diatom bound 15n 14n is unknown and cannot yet be ruled out as a possible explanation for the observed change however the consistency between indian and pacific sector records and with other paleoceanographic data suggests that the glacial interglacial difference in diatom bound 15n 14n was driven by higher consumption of nitrate in the subantarctic surface during the last ice age such a change in nutrient consumption may have resulted from atmospheric iron fertilization and or decreased glacial mixed layer depths associated with sea ice melting enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of co2 in the ice age atmosphere it also would have reduced the preformed nutrient content of the low latitude thermocline leading to decreases in low latitude productivity suboxia and denitrification

magma reservoirs from the upper crust to the moho inferred from high resolution vp and vs models beneath mount st helens washington state usa the size frequency and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath mount st helens washington state usa currently the most active volcano in the cascade range data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir as well as its connection to deeper zones of magma accumulation in the crust the inversion of p and s wave traveltime data collected during the active source component of the imush imaging magma under st helens project reveals a high p wave vp s wave vs velocity anomaly beneath mount st helens between depths of 4 and 13 km which we interpret as the primary upper middle crustal magma reservoir beneath and southeast of this shallow reservoir a low vp velocity column extends from 15 km depth to the moho deep long period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids southeast of mount st helens an upper middle crustal high vp vs body beneath the indian heaven volcanic field may also have a magmatic origin both of these high vp vs bodies are at the boundaries of the low vp middle lower crustal column and both are directly above high vp middle lower crustal regions that may represent cumulates associated with recent quaternary or paleogene neogene cascade magmatism seismicity immediately following the 18 may 1980 eruption terminates near the top of the inferred middle lower crustal cumulates and directly adjacent to the inferred middle lower crustal magma reservoir these spatial relationships suggest that the boundaries of these high density cumulates play an important role in both vertical and lateral transport of magma through the crust

changing marine productivity off northern chile during the past 19 000 years a multivariable approach a multivariable approach utilising bulk sediment planktonic foraminifera and siliceous phytoplankton has been used to reconstruct rapid variations in palaeoproductivity in the peru chile current system off northern chile for the past 19 000 cal yr during the early deglaciation 19 000 16 000 cal yr bp our data point to strongest upwelling intensity and highest productivity of the past 19 000 cal yr the late deglaciation 16 000 13 000 cal yr bp is characterised by a major change in the oceanographic setting warmer water masses and weaker upwelling at the study site lowest productivity and weakest upwelling intensity are observed from the early to the middle holocene 13 000 4000 cal yr bp and the beginning of the late holocene 4000 cal yr bp is marked by increasing productivity mainly driven by silicate producing organisms changes in the productivity and upwelling intensity in our record may have resulted from a large scale compression and or displacement of the south pacific subtropical gyre during more productive periods in line with a northward extension of the antarctic circumpolar current and increased advection of antarctic water masses with the peru chile current the corresponding increase in hemispheric thermal gradient and wind stress induced stronger upwelling during the periods of lower productivity this scenario probably reversed copyright 2004 john wiley sons ltd

glacial interglacial changes in subarctic north pacific stratification since the first evidence of low algal productivity during ice ages in the antarctic zone of the southern ocean was discovered there has been debate as to whether it was associated with increased polar ocean stratification or with sea ice cover shortening the productive season the sediment concentration of biogenic barium at ocean drilling program site 882 indicates low algal productivity during ice ages in the subarctic north pacific as well site 882 is located southeast of the summer sea ice extent even during glacial maxima ruling out sea ice driven light limitation and supporting stratification as the explanation with implications for the glacial cycles of atmospheric carbon dioxide concentration

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

glacial interglacial modulation of the marine nitrogen cycle by high latitude o2 supply to the global thermocline 1 an analysis of sedimentary nitrogen isotope records compiled from widely distributed marine environments emphasizes the global synchrony of denitrification changes and provides evidence for a strong temporal coupling of these variations to changes in nitrogen fixation as previously inferred we explain the global coherence of these records by a simple physical control on the flux of dissolved oxygen to suboxic zones and the coupling to fixation via the supply of phosphorus to diazotrophs in suitable environments according to our hypothesis lower glacial stage sea surface temperature increased oxygen solubility while stronger winds in high latitude regions enhanced the rate of thermocline ventilation the resultant colder rapidly flushed thermocline lessened the spatial extent of denitrification and consequently n fixation during warm periods sluggish circulation of warmer less oxygen rich thermocline waters caused expansion of denitrification zones and a concomitant increase in n fixation local fluctuations in export productivity would have modulated this global signal

initial test of the silicic acid leakage hypothesis using sedimentary biomarkers 1 several mechanisms have been proposed for large co2 changes at glacial terminations including shifting the caco3 corg rain ratio by changing surface water nutrient supply altering the balance between diatom and coccolithophore production diatom si n is highest in fe stressed high latitude waters southern ocean fe enrichment studies suggest diatom si demands reduced under fe replete glacial conditions allowing increased silicic acid to leak northward in subducted intermediate water and upwell at lower latitudes we test this silicic acid leakage hypothesis using relative abundances of phytoplankton specific biomarkers in peru margin sediments spanning 0 20 ka results indicate increased coccolithophorid diatom production from 0 5 to 3 between 18 0 15 5 ka temporal correlation with the initial pco2 rise and early deglacial shift in mode water ventilation implicates a coincidental possibly causative reorganization of sub antarctic mode water formation and reduced fe abundance however coccolithophorid production subsequently declined suggesting rain ratio changes were only partly responsible for the co2 deglacial transition

chlorine 36 evidence for the mono lake event in the summit grip ice core abstract a distinct peak has been discovered in the 36 cl data from the grip ice core between the dansgaard oeschger d o events 6 and 7 at approximately 32 kyr bp this peak can be attributed to a minimum of the geomagnetic dipole field associated with the mono lake event since the 36 cl peak reflects a higher production rate of all cosmogenic radionuclides it has an impact on the 14 c dating of the last ice age furthermore it provides an additional time marker similar to a peak found earlier corresponding to the laschamp event at approximately 39 kyr bp

southern ocean contributions to glacial interglacial changes of atmospheric pco2 an assessment of carbon isotope records in diatoms eleven new antarctic records of diatom bound 13corg show significantly lighter values during the last glacial maximum than during the holocene with a general trend of increasing depletions southward of the modern antarctic polar front mapf in contrast glacial diatoms from cores farther north of the mapf show 13corg values which are 1 heavier than during the holocene likely causes for the low glacial 13corg in antarctic diatoms are higher co2 aq lower growth rates and changes in diatom abundance or size taken at face value the glacial depletions of 13corg suggest that antarctic surface waters south of the mapf might have been a source of atmospheric pco2 during the glacial period alternatively the glacial depletions might have been caused by either a relatively small decrease in growth rates or changes in the abundance of the two dominant diatom species or their average cell size interpretations of the subantarctic records are complicated by similar uncertainties

highlights from a seismic broadband array on stromboli volcano an array of nine three component broadband seismometers was deployed in two different configurations on stromboli volcano the analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano these new observations are restricted to the low frequency range below 1 hz and underline therefore the superiority of broadband recordings over conventional short period observations surprisingly simple wavelets indicate an initially contracting source mechanism gas jets that could not be seen in a short period seismic record at all generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism the analysis of particle motion and seismic array techniques permits a location of the seismic source we find low frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption related events a video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals

calibration of regional s p amplitude ratio discriminants s p amplitude ratios have proven to be a valuable discriminant in support of monitoring a comprehensive nuclear test ban treaty regional s and p phases attenuate at different rates and the attenuation can vary geographically therefore calibration is needed to apply the s p discriminant in new regions calibration includes application of frequency dependent source and distance corrections for regional pn pg sn and lg phases jenkins et al 1998 developed pn pg sn and lg amplitude models for nine geographic regions and two global composite models stable and tectonic they determined frequency dependent source and attenuation corrections from a large data set obtained from the prototype international data center pidc we use their corrections to evaluate calibrated s p discriminants our discrimination data set includes 1000 amplitude ratios from earthquakes industrial explosions chemical explosions and nuclear explosions from lop nor india and pakistan we find that the calibrated s p ratio is largest for earthquakes and smallest for the nuclear explosions as expected however the discriminant is not universally valid in particular the s p ratio for the pakistan nuclear explosion fell within the normal range for the earthquakes this event was recorded by only a few stations at far regional distances and appears to have an anomalously high sn amplitude the industrial explosions overlap with the earthquake population however the buried chemical explosions generally register lower s p ratio than earthquakes

denitrification under glacial and interglacial conditions a physical approach 1 recent analysis of sedimentary 15n records over the last 200 000 years has shown an expansion of water column denitrification zones during warmer periods and a shrinkage of these oxygen poor regions during glacial periods two different mechanisms could be responsible for driving the changes in the denitrification records variations in local productivity leading to a change in remineralization rates and or changes in the ocean circulation and ocean temperature resulting in variations of the physical supply of dissolved oxygen here we focus on the supply mechanism by using a fully coupled atmosphere ocean sea ice land surface scheme model the university of victoria earth system climate model to examine oxygen supply under varying physical conditions while maintaining an invariant biological oxygen utilization scheme we show that circulation changes can be the cause for the observed changes in dissolved oxygen in the glacial ocean lower temperatures and enhanced formation of antarctic intermediate water and north pacific intermediate water during glacial periods increase the physical supply of oxygen and therefore decrease water column denitrification in our last glacial maximum simulations the change in water characteristics in the eastern tropical pacific is important enough to reduce denitrification by 46 to 65 compared to present day conditions depending on the wind fields used as boundary conditions the consequences of our findings could be substantial for the near future with a warming climate denitrification zones could expand leading to changes in the biological pump and the flux of n2o into the atmosphere

can the fisk conjecture be explained by rock damage around explosions we investigate the possibility that rock damage ashby and sammis 1990 johnson and sammis 2001 can explain recent observations of fisk 2006 2007 that p and s wave corner frequencies from explosions differ by a factor approximately related to the ratio of near source compressional and shear velocities the fisk conjecture the observation of differing p and s wave corner frequencies from explosions forms the basis for the success of the high frequency p s discriminant using first order considerations we find that the damage mechanics model can indeed explain the fisk conjecture although this is certainly not a unique explanation the key to our argument is that although the radius of rock damage is less than that of the so called elastic radius the slow velocity of the outward propagating damage front can reduce shear wave corner frequencies this explanation differs slightly from that of fisk 2006 2007 who states that s waves from explosions occur at a similar length scale comparable to the elastic radius as for p waves because of the significant reduction in v s caused by rock damage we suggest that the shear waves generated within the damage region can have a radius significantly less than the elastic radius for a p wave additionally because rock damage is controlled by the difference of the maximum and minimum principal stress first order considerations suggest that lithospheric overburden does not shut off rock damage until scaled depths of burial of up to graphic 1 thus effects due to rock damage may be an important source of shear waves for nearly all tamped nuclear explosions for which we have experience 1 embed inline graphic 1 gif

the termination of the equatorial undercurrent in the eastern pacific abstract the termination of the equatorial undercurrent euc in the eastern tropical pacific has been studied through analysis of the historical hydrographic station data in the region bounded by 5 n 10 s 80 w and 100 w three distinctive hydrographic features associated with the euc are used along with dynamic topography to trace the mean path of the euc and to investigate aspects of its seasonal variation these features are 1 the 13 c thermostad 2 the high salinity core and 3 the high dissolved oxygen concentration tongue the thermostad is thickest just south of the equator to the west of the galapagos islands with a decreasing maximum extending southeast to the coast of south america near 7 s the thermostad is poorly developed in the mean near the equator east of the galapagos islands this pattern appears to be produced by convergence of eastward flow in the euc and in the southern subsurface countercurrent as the euc flows southeastward from the galapagos this interpretation is supported by the geostrophic flow calculated from the mean dynamic topography the isolated high salinity core is found to the south of the equator and is traced all the way to the coast of south america the high oxygen tongue associated with the euc splits at the galapagos with the southward projecting branch disappearing rapidly as an identifiable feature the other branch of the tongue continues around the islands to the north and along the equator to the coast of ecuador some evidence of recirculation of euc water in the south equatorial current is seen to the northwest of the galapagos a strong seasonal pulsation of the euc affects these features in a consistent way with the pulse occurring first west of the galapagos and later along the coast the thermostad first reaches maximum development and then a pronounced downwelling of the thermocline occurs rapidly leading to minimum thermostad extent associated wtih this downwelling is an eastward protruding high salinity tongue near the equator which is later seen as an isolated core along the coast at 4 s and 6 s pressure gradients along the equator and the coast inferred from dynamic topography suggest that this pulse is associated with an increase in the flow of the euc and ultimately the peru chile undercurrent the pressure gradient reversal along the equator occurs prior to the annual wind reversal suggesting that remote forcing plays a role in the seasonal pulse of the euc in the eastern pacific

atypical δ 15 n variations at the southern boundary of the east pacific oxygen minimum zone over the last 50 ka abstract we report a nitrogen isotope record odp site 1233 from the southern chile margin at 41 s the site is located slightly south of the southern boundary of the peru chile upwelling system and the associated oxygen minimum zone off peru and northern chile we show that our nitrogen isotope record from the time interval 0 50 calendar kiloyears before present ka b p bears an atypical pattern both in shape and timing when compared with records obtained from either the continental margin of the eastern pacific or the subantarctic zone saz of the southern ocean the 15 n values at site 1233 are relatively high throughout the record varying between 9 and 13 the major features are a pronounced 15 n increase at the beginning of the deglaciation a maximum from 19 to 10 ka b p thereafter a large decrease during the early holocene and millenial scale oscillations showing an antarctic timing we propose that the record results from an amalgam of low latitude and high latitude processes low latitude processes including a stronger advection signal of heavy nitrates from the denitrifying zones off peru and northern chile would explain the timing of the deglaciation rise and the heaviest values found over this interval excluding the antarctic cold reversal period the overall differences between site 1233 and records from peru and northwest american margins suggest however that the origin of the 15 n signal off chile is largely controlled by hydrologic and climatic changes in the southern ocean we propose that the interplay between nutrient demand in the saz and latitudinal shifts of hydrologic fronts controlled both the concentrations and the isotopic signature of the remaining nitrate delivered to the chile margin then the glacial surface waters of the southern chile margin were likely lower in nitrate concentration and bear a higher 15 n than during interglacial periods

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

intermittent existence of a southern californian upwelling cell during submillennial climate change of the last 60 kyr 1 application of a high resolution multiproxy approach to a sedimentary section drilled at ocean drilling program site 1017 located under a highly active upwelling cell off point conception california provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr the proxies include bulk sediment major and minor elements organic carbon and carbonate concentrations 15n and planktonic foraminiferal species assemblage and carbon isotope determinations the collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial scale climate oscillations of marine isotope stage mis 3 during that interval the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events however the last glacial maximum was also relatively productive productivity increased dramatically during the bolling warm interval while the allerod and younger dryas were much less productive high coccolithophorid abundance commenced during the earliest holocene after 10 ka the complexity of the productivity response was probably related to interplay between local winds as well as california undercurrent strength

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

active earth pressure in cohesive soils with an inclined ground surface an analytical solution is developed to determine the active lateral earth pressure distribution on a retaining structure when it consists of a cohesive backfill internal friction angle 0 cohesion c 0 with an inclined ground surface the solution derived encompasses both bell s equation for cohesive or cohesionless backfill with a horizontal ground surface and rankine s solution for cohesionless backfill with an inclined ground surface the orientation of the failure surface is also determined results indicate that unlike the soil wall scenarios of bell and rankine where the failure planes are parallel with a fixed orientation independent of the overburden pressure for sloping cohesive backfill 0 c 0 the slope of the failure surface is a function of the overburden pressure and becomes shallower with depth thus forming a curvilinear failure surface the solution developed can also be used to check the sustainability of a slope the analytical solution can be programmed conveniently

radiolaria and pollen records from 0 to 50 ka at odp site 1233 continental and marine climate records from the southeast pacific abstract site 1233 drilled during leg 202 of the ocean drilling program provides a detailed record of marine and continental climate change in the southeast pacific and south american continent splits from over 500 samples taken at 20 cm intervals for quantitative analysis of radiolarian and pollen populations yield a temporal resolution of 200 400 years in each sample 39 pollen taxa and 40 radiolarian species and genera were evaluated age control is provided by 25 ams 14c dates lamy f kaiser j ninnemann u hebbeln d arz h w stoner j 2004 science 304 1959 1962 multivariate statistical analyses of these data allow us to conclude the following 1 during the past 50 ka the region of the central chile coast is not directly influenced by polar water from the antarctic region 2 changes in ocean conditions off central chile during this time interval primarily reflect north south shifts in the position of the south pacific transition zone 3 changes in chilean vegetation reflect comparable latitudinal shifts in precipitation and the position of the southern westerlies 4 the first canonical variate of radiolarian and pollen records extracted from site 1233 are remarkably similar to each other as well as to temperature records from the antarctic which suggests that marine and continental climate variability in the region is tightly coupled at periods longer than 3000 years 5 the phase coupling of these climate records which lead variations of continental erosion based on iron abundance at the same site are consistent with a hypothesis that erosion is linked to relatively long i e few thousand years response times of the patagonian ice sheet and thus is not a direct indicator of regional climate

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

millennial scale instability of the antarctic ice sheet during the last glaciation records of ice rafted detritus ird concentration in deep sea cores from the southeast atlantic ocean reveal millennial scale pulses of ird delivery between 20 000 and 74 000 years ago prominent ird layers correlate across the polar frontal zone suggesting episodes of antarctic ice sheet instability carbon isotopes 13 c of benthic foraminifers a proxy of deepwater circulation reveal that south atlantic ird events coincided with strong increases in north atlantic deep water nadw production and inferred warming interstadials in the high latitude north atlantic sea level rise or increased nadw production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the weddell sea region of west antarctica

seismic discrimination of controlled explosions and earthquakes near mount st helens using p s ratios explosions and earthquakes are effectively discriminated by p s amplitude ratios for moderate magnitude events m 4 observed at regional to teleseismic distances 200 km it is less clear if p s

developing local to near regional explosion and earthquake discriminants abstract we develop local to near regional 0 200 km amplitude discriminants using earthquakes single fired explosions and delayed fired explosions we use the source phenomenology experiment spe broadband data collected across the colorado plateau during the summer of 2003 which recorded explosions in hard and soft rock mines we optimized a local surface wave magnitude scale derived from a stable regional surface wave magnitude russell 2006 for the sources however the magnitude of the source and the distance to the station limit the surface wave energy which can cause instability in the surface wave magnitudes magnitude scales for the local phases pg lg sg and rg were also tested and compared when an azimuthal station correction was applied to each magnitude scale there was an average reduction of standard deviation by 16 58 regional and teleseismic discrimination techniques were optimized for local distance and our results show that lithology of the source is a critical component in discriminating events at local distances we also found that magnitude and amplitude ratios are effectively used to discriminate between small earthquakes and explosions at local distances with each performing the best in the hard rock lithology furthermore the ratio techniques perform equally in both lithologies if multiple stations are used to establish the ratio values we find that an average of four or five stations will generally have a 90 or better correct identification for both types of ratios finally we find that the source lithology local site effects and large scale geologic features control most of the variability in the amplitude measurements

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

comparison of ice rafted debris and physical properties in odp site 1094 south atlantic with the vostok ice core over the last four climatic cycles abstract visual counts of ice rafted debris ird foraminifera and radiolaria were made for 1500 samples in site 1094 spanning the last four climatic cycles marine isotope stages 1 11 most but not all of the ird variability is captured by whole core physical properties including magnetic susceptibility and ray attenuation bulk density glacial periods are marked by high ird abundance and millennial scale variability which may reflect instability of ice shelves in the weddell sea region each interglacial period exhibits low ird and high foraminiferal abundance during the early part of the interglacial indicating relatively warm sea surface temperatures and reduced influence of sea ice ird increases and foraminiferal abundances decrease during the latter part of each interglacial indicating a return to more glacial like conditions glacial terminations i and v are each characterized by a step wise reduction in ice rafting punctuated by a brief pulse in ird delivery and reversal in 18o the coarse fraction of the sediment is dominated by ash and radiolaria and the relative abundance of these components is remarkably similar to the concentration of na in vostok each of these variables is believed to be controlled mainly by sea ice cover thereby providing a means for sediment ice core correlation

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

new insights into quaternary glacial dynamic changes on the george v land continental margin east antarctica abstract the continental margin of the george v land represents the seaward termination of one of the largest sub glacial basins the wilkes basin of the east antarctic ice sheet eais and hence is a potentially useful site for the investigation of the cenozoic glacial history of antarctica because the seafloor morphology relates strictly to recent glacial marine sedimentary processes we have compiled all available echo soundings data collected until the year 2001 and integrated the data set with satellite altimetry data as a result we have produced a new bathymetric map of the margin covering an area of more than 80 000 km 2 with a spatial resolution of about 1 km the bathymetric data have been integrated with sub bottom profiler data with the purpose of defining sedimentary processes and their variations during the quaternary the continental shelf of the wilkes land margin is characterised by alternating banks and glacial troughs connected to sub marine canyons that cut into the continental slope our study focussed on the continental rise where asymmetrical ridges alternate with large deep sea channels the ridges have a long gentle eastern side and short steep western side with axis elongated approximately in north south direction perpendicular to the margin the channels represent the main sediment drainage pattern feeding the ridge depositional system found along the continental rise the sediment is supplied to the continental shelf edge by ice sheets and sediment gravity flows are considered the main process for sediment supply to the rise the modern sedimentary environment of the deep margin is affected by turbiditic down slope sediment transfer with a minor contribution from along slope contour currents the wega channel is currently affected by transport and settling of sediment through high salinity shelf water hssw originating on the continental shelf we infer that thermohaline circulation has contributed to sediment transport and deposition since the mid pleistocene

observations in support of rg scattering as a source for explosion s waves regional and local recordings of the 1997 kazakhstan depth of burial experiment abstract in august and september of 1997 three 25 ton chemical explosions were detonated at nominal depths of 550 300 and 50 m in boreholes at the former soviet test site at balapan kazakhstan one objective of this experiment was to evaluate the effect of differing source depth on the regional wave field analysis of regional seismic phases lead to the observation that regional p s wave amplitude ratios in the 1 to 5 hz band increase as a function of source depth however at frequencies greater than about 5 hz the relative amplitudes of p and s waves remain approximately constant for the differing depth shots similarly regional coda spectra are amplified in the 1 to 5 hz band for the shallow shots at local distances rg is the dominant seismic phase with peak amplitudes in the 0 7 to 5 hz range and rg is strongest for the shallower shots within the short distance spanned by the local stations rg is rapidly attenuated and the attenuation is accompanied by a significant shift in peak amplitude toward lower frequency at regional distances rg is below the noise level the coincident frequency band in which local rg rapidly loses energy and regional s phases are amplified points toward rg scattering as the dominant mechanism causing the discrepancies between p s amplitude ratios in this study these observations are particularly relevant to the understanding of physical processes affecting regional p s discriminants and may lead to improvements in discriminant methods

patterns of caco3 deposition in the eastern tropical pacific ocean for the last 150 kyr evidence for a southeast pacific depositional spike during marine isotope stage mis 2 1 we constructed biogenic mass accumulation rate mar time series for eastern pacific core transects across the equator at 105 and 85 w and along the equator from 80 to 140 w we used empirical orthogonal function eof analysis to extract spatially coherent patterns of caco3 deposition for the last 150 kyr eof mode 1 51 variance is a caco3 mar spike centered in marine oxygen isotope stage 2 mis 2 found under the south equatorial current eof mode 2 19 of variance is high north of the equator eof mode 3 9 of variance is an east west mode centered along the north equatorial counter current the mis 2 caco3 spike is the largest event in the eastern pacific for the last 150 kyr caco3 mars are 2 3 times higher at 18 ka than elsewhere in the record including mis 6 it is caused by high caco3 production rather than minimal dissolution eof 2 while it resembles deep water flow patterns nevertheless shows coherence to corg deposition and is probably also driven by caco3 production index terms 4267 oceanography general paleoceanography 1615 global change biogeochemical processes 4805 1030 geochemistry geochemical cycles 0330 3022 marine geology and geophysics marine sediments processes and transport keywords late pleistocene paleoproductivity pacific calcite biogeochemistry carbon cycle

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

regional phase excitation and propagation in the lop nor region of central asia and implications for p lg discriminants ital pn and ital lg spectra for lop nor explosions and nearby earthquakes were analyzed for source and propagation effects using a modified inversion method of ital xie 1993 spectral analyses were performed on waveform data from incorporated research institution for seismology chinese digital seismic network kazakhstan and krgyzstan networks ital pn amplitude variations of a factor of 20 are observed across the small aperture lt 200 km kyrgyzstan network and are probably related to three dimensional moho structure close to the network comparisons of ital pn amplitudes and spectral ratios provide evidence for nonisotropic radiation pattern effects in the case of earthquakes and overshoot in explosion time histories complex source effects are born out in our inversion results 1 logarithm of seismic moment m sub 0 from ital pn and ital lg spectra scale linearly with body wave magnitude m sub b for explosions 5 0 le m sub b le 6 0 and for earthquakes 4 0 le m sub b le 5 5 2 pn m sub 0 estimates are similar to lg m sub 0 for earthquakes but are higher than lg m sub 0 for explosions 3 corner frequency f sub c scale as quarter root of m sub 0 for explosions and cube root for earthquakes 4 at the same m sub 0 level pn f sub c aremore 4 endash 5 times higher than lg f sub c for earthquakes and explosions and 5 ital pn source spectra are characterized by significant overshoot for explosions our results suggest that the cause of maximum separation between earthquake and explosion populations on plots of p lg spectral ratios which typically occurs for frequencies above explosion pn f sub c between 2 and 4 hz for explosions in this study may be related to overshoot in the reduced velocity potential copyright 1999 american geophysical union less

active earth pressure on retaining wall for c phi soil backfill under seismic loading condition this technical note describes the derivation of an analytical expression for the total active force on the retaining wall for c phi soil backfill considering both the horizontal and vertical seismic coefficients the results based on this expression are compared with those obtained from earlier analytical expressions for the active force for c phi soil backfill under seismic conditions and found to have a similar trend of variation the parametric study shows that the inclination of the critical failure plane with the horizontal plane decreases with the increase in values of seismic coefficients the decrease being more for their higher values the total active force increases with the increase in value of horizontal seismic coefficient while it decreases with the increase in value of vertical seismic coefficient except for a very high value of horizontal seismic coefficient design charts are presented for various combinations of horizontal and vertical seismic coefficients kh and kv and values of cohesion and angle of shearing resistance for estimating the total active force on the retaining wall for c phi soil backfill for practical applications

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

impact of cohesion on seismic design of geosynthetic reinforced earth structures abstractthis paper calculates the thrust of lateral earth pressures exerted by unstable slopes comprised of c soil and subjected to seismic pseudostatic loading conditions although the proposed method can be used for seismic stability analysis of geosynthetic reinforced earth structures gress the formulation and results are also applicable to many other relevant earth retention systems to study the impact of cohesion the authors develop formulations to determine the seismic active earth pressure coefficient for c soils resulting in a closed form solution the pseudostatic formulation considers the effect of tensile cracks backslope inclination and batter while assuming a log spiral failure surface two formulas are presented one is for the conventional inclination of thrust the second formulation considers a more feasible inclination of the thrust when it is likely to act against facing units with large setbacks constructed for large batter walls the authors perform parametric studies and

patterns of export production in the eastern equatorial pacific over the past 130 000 years 1 productivity at six core locations in the eastern equatorial pacific eep was reconstructed with a benthic foraminiferal transfer function the core records show strong regionality especially where affected by peru margin upwelling of deeper equatorial undercurrent water euc originally coming from the subantarctic this peru margin record differs from that seen along the equator where divergence leads to shallow upwelling and it is generally inverse to that seen in cores outside the areas of equatorial upwelling principal components analysis shows that the main productivity pattern correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4 in addition to this equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during mis 3 and 2 the reconstructions based on benthic foraminifera were tested against those from nonaccumulation rate based inorganic chemical proxies of export production these were found to correlate well in the region influenced by peru upwelling and also to share common features for sites along the equator all the nonaccumulation rate based paleotracers are consistent with one another and differ from accumulation rate derived proxies the differences between the two classes of paleotracers may result from uncertainties in calculating actual biogenic fluxes since 230th normalized results conform more to those we obtained analysis of planktonic carbon isotope values for the eep and their comparison to the record of the pacific subantarctic indicates that the subantarctic contribution to the euc was reduced during mis 3 and 2

isotopic constraints on glacial interglacial changes in the oceanic nitrogen budget early deglacial maximum in nitrate 15 n 14 n in suboxic zones and no significant glacialto late holocene change in global ocean nitrate 15 n 14 n consistent with the work of brandes and devol 2002 we find that the steady state 15 n 14 n of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column therefore a deglacial peak in the ratio of water column to sediment denitrification caused by either a strong feedback between water column denitrification and the n reservoir or by an increase in sediment denitrification due to sea level rise can explain the observed deglacial 15 n 14 n maximum in sediments underlying water column denitrification zones the total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate 15 n 14 n for this reason modeling a realistic deglacial 15 n 14 n maximum further requires that the combined negative feedbacks from n2 fixation and denitrification are relatively strong and n losses are relatively small our results suggest that the glacial oceanic n inventory was at most 30 greater than today s and probably less than 10 greater index terms 4267 oceanography general paleoceanography 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes keywords feedback nitrogen isotopes paleoceanography

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

analytical solution for rankine s seismic active earth pressure in infinite slope abstractthis paper presents an analytical solution to determine seismic active earth pressure on a rigid frictionless retaining wall of c soil backfill with an infinite slope considering horizontal and vertical seismic coefficients this solution is a generalized explicit expression and was derived based on the rankine earth pressure theory and the mohr coulomb yield criterion to verify the derived solution a special case was analyzed and its result is identical to that obtained by earlier researchers by analyzing the distribution of the seismic active earth pressures along the wall depth a tension crack zone behind the wall was identified and the seismic active earth pressure coefficient considering the tension crack was obtained this study also investigated the effects of wall friction soil friction angle and dimensionless cohesion backfill slope and horizontal and vertical seismic coefficients on the seismic active earth pressure coefficients design charts for seismic active earth pressur

corner frequency scaling of regional seismic phases for underground nuclear explosions at the nevada test site model fits are used to estimate source spectral corner frequencies of regional seismic phases pn pg and lg from underground nuclear explosions unes at the nevada test site nts based on recordings by lawrence livermore national laboratory llnl nts network stations the spectra are corrected for instrument response distance and station effects and then network averaged explicit information regarding geophysical working point properties depth of burial and some announced yields for nts explosions springer et al 2002 is utilized for the spectral modeling scaling of pn pg and lg corner frequencies with source yield is examined for sets of explosions at yucca flat pahute mesa and rainier mesa with similar material properties medium type density velocities and gas porosity the unes are limited to those in media with gas porosity of 10 or less so that a source spectral model with a rolloff of f 2 is applicable model comparisons are also examined for regional p lg discriminants a key result is that lg corner frequencies for ntsunes exhibit similar scaling with source size as for p waves but shifted lower analogous to observations by fisk 2006 for the lop nor semipalatinsk and novaya zemlya test sites this appears to corroborate an important effect that is that major contributions to s wave generation by explosions occur near the source with a similar length scale comparable to the elastic radius as for p waves from explosions although the explicit physical mechanism is not yet understood the implications are important regarding where and perhaps how s waves are predominantly generated by explosions a related key result is that the increasing separation of p lg at higher frequencies between nts explosions and earthquakes has a consistent model based explanation as at other nuclear test sites in terms of the difference between explosion p and s corner frequencies

seismic recordings of the carlsbad new mexico pipeline explosion of 19 august 2000 on 19 august 2000 two seismometer networks in southeastern new mexico recorded signals from a natural gas pipeline explosion analysis of the particle motion arrival times and durations of the seismic signals indicates that three impulsive events occurred with origin times of 11 26 18 8 1 9 11 26 43 6 2 1 and 11 27 01 7 2 0 uct the first event was caused by the explosive blowout of the buried high pressure pipeline and the second event was caused by the ignition of the vented natural gas the nature of the third event is unclear however it was likely created by a secondary ignition there were also two extended seismic events that originated at the same time as the first two impulsive events the first resulted from the preignition venting of the gas and lasted for about 24 sec while the second resulted from the postignition roaring of the flames and lasted for about 1 hr many of the source constraints provided by the seismic data were not available from any other investigative technique and thus were valuable to a diverse range of parties including the new mexico state police law firms involved in litigation related to the accident the national transportation and safety board and the general public manuscript received 13 september 2002

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

the excitation of lg waves by explosions a finite difference investigation several mechanisms have been proposed to explain the excitation of the regional lg phase by explosions we examine some of these mechanisms with finite difference simulations an energy flux technique is used to analyze the synthetic signals the method is adapted from conventional array analysis techniques and gives a clear characterization of wave field intensity wave slow ness and propagation direction the vector energy flux in the model is studied instead of the scalar distribution of energy in the space time domain the cal culations show that for an explosive source in a high p wave velocity crust p wave energy cannot be effectively trapped in the crust and the nongeomet rical phase s may be the primary contributor to thelg phase for an explosive source buried in a low velocity upper crust i e where the p wave velocity is lower than the upper mantle s wave velocity part of the ps wave can be trapped in the crustal wave guide to form the lg phase the relative lg excitation de pends on the ratio between the p wave velocity in the source region and the s wave velocity in the uppermost mantle scattering effects can transfer p wave or surface wave energy into lg but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers any source process that directly excites s waves is more efficient for generating lg than the afore mentioned mechanisms spall directly generates s wave energy and conse quently is an efficient source for lg for actual explosions all of these factors may simultaneously contribute to lg excitation determining their relative im portance and interactions requires additional observations

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

mb ms screening revisited for large events abstract event screening of large magnitude events m w 5 based on m b m s is revisited to account for the effect of the source corner frequency relative to the fixed frequencies of the long period m s and short period m b for large events this source effect increases the slope of m b m s relative to the 1 1 value expected for small events the effect is demonstrated in the large earthquake m b m s population and in the behavior of large theoretical explosions that are consistent with the more limited explosion population the behavior is used to create a more conservative screening criterion that ensures large explosions are not inadvertently screened out by m b m s while not appreciably decreasing the number of screened earthquakes this change also makes the variance of the earthquake and explosion populations more equal which is of utility in statistical analysis a slight trend in the explosion population and a case study of two large u s underground nuclear tests provide support for adopting a more conservative approach

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

climatically linked oscillations in arabian sea denitrification over the past 1 m y implications for the marine n cycle water column and core top 15n data show that arabian sea denitrification produces large nitrogen isotopic enrichments that are regionally recorded with fidelity in the sediments these results facilitate interpretation of a 1 m y 15n record for ocean drilling program site 722b on the owen ridge in terms of climatically linked oscillations in denitrification at the major orbital periods as at present denitrification was greatest during interglacial periods and apparently was not active during most glacial intervals cross spectral analysis of 15n with foraminiferal 18o global climate sea level index and lithogenic grain size monsoon strength index suggests forcings by changes in hydrography and productivity acting through the extent and intensity of the oxygen minimum zone the data suggest that denitrification may be an internal forcing mechanism for climate change during major glacial interglacial transitions through influence on marine n inventory and atmospheric co2 however compensation or amplification may occur from other sinks sediment denitrification or sources nitrogen fixation

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process