passive seismic reflection interferometry a case study from the aquistore co2 storage site saskatchewan canada abstractseismic reflection interferometry has recently been tested in a few resource exploration applications we have evaluated passive seismic interferometry results for data from the aquistore co2 storage site saskatchewan canada with the objective of testing the method s ability to image the subsurface geology and its potential for time lapse imaging we analyzed passive seismic data recorded along two perpendicular geophone lines for two time periods that include 23 days in june 2014 and 13 days in february 2015 beam forming analysis showed that a nearby power plant is the dominant source of ambient noise we retrieved virtual shot gathers not only by correlating long noise panels 1 h for both recording periods but also by correlating shorter noise panels 10 s from two days of each recording period we applied illumination diagnosis to the noise panels from the two chosen days for each period to help suppress the surface waves comparisons of the common midpoints stacked sections resulting

seismic refraction interferometry with a semblance analysis on the crosscorrelation gather crosscorrelating wavefields recorded at two receivers to produce data as if one receiver was a source is commonly referred to as seismic interferometry or the virtual source method an artifact in seismic interferometry related to critically refracted waves allowed us to estimate the velocity in the refracting layer in addition we devised a new semblance analysis on the crosscorrelation of reflection and refraction energy to robustly estimate the depth and velocity of the slow layer tested with a numerical example and field data from the boise hydrogeophysical research site

application of super virtual seismic refraction interferometry to enhance first arrivals a case study from saudi arabia complex near surface anomalies are one of the main onshore challenges facing seismic data processors refraction tomography is becoming a common technology to estimate an accurate near surface velocity model this process involves picking the first arrivals of refracted waves one of the main challenges with refraction tomography is the low signal to noise ratio characterizing the first break waveform arrivals especially for the far offset receivers this is especially evident in data recorded using reflection acquisition geometry this low signal to noise ratio is caused by signal attenuation due to geometrical spreading of the seismic wavefield near surface generated noise and amplitude absorption super virtual refraction interferometry improves the quality of the first break picks by enhancing the amplitude of the refracted waves and attenuating the amplitude of the random noise

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

late quaternary floods and droughts in the nile valley sudan new evidence from optically stimulated luminescence and ams radiocarbon dating our results show that the late pleistocene nile in northern sudan was shifting position and actively aggrading at 145 20 kyr 83 24 kyr 32 8 kyr and 20 7 0 2 kyr and indicate for the first time a phase of high energy flow in the white nile at 27 8 3 2 kyr with still high but somewhat reduced flow in that river at 13 3 kyr 10 kyr and 4 8e4 0 kyr beach ridges associated with a 386 m strandline of the white nile have osl ages of 27 5 2 7 kyr and 14 5 1 6 kyr the holocene terraces and former channels of the main nile have ages of 11 kyr 6 5e5 0 kyr and 4 8e4 0 kyr after which there was a general decline in flood discharge the now arid main nile valley in northern sudan was significantly wetter during the early to middle holocene with a lake up to 450 km 2 in area fed by an overflow channel from the early holocene nile between 9 5 kyr and 7 5 kyr previously stable late pleistocene dunes were reactivated at intervals during the holocene with five samples from the white nile valley indicating brief phases of holocene dune activity at 9 9 2 0 kyr 9 0 2 8 kyr 6 6 0 9 kyr 4 8 0 9 kyr and 2 9 0 5 kyr the earliest of which occurred within periods of generally wetter climate and higher nile flow the youngest freshwater shells on the khor abu habl alluvial fan west of the white nile correspond to a time of regionally wetter climate between 1 7 and 1 0 kyr our results suggest that millennial scale climatic instability may have been characteristic of holocene climates in this region 2010 elsevier ltd all rights reserved

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

vsp traveltime inversion near surface issues p wave velocity information obtained from vertical seismic profiles vsps can be useful in imaging subsurface structure either by directly detecting changes in the subsurface or as an aid to the interpretation of seismic reflection data in the shallow subsurface p wave velocity can change by nearly an order of magnitude over a short distance so curved rays are needed to accurately model vsp traveltimes we used a curved ray inversion to estimate the velocity profile and the discrepancy principle to estimate the data noise level and to choose the optimum regularization parameter the curved ray routine performed better than a straight ray inversion for synthetic models containing high velocity contrasts the application of the inversion to field data produced a velocity model that agreed well with prior information these results show that curved ray inversion should be used to obtain velocity information from vsps in the shallow subsurface

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

thirteen thousand years of southeastern mediterranean climate variability inferred from an integrative planktic foraminiferal based approach over the past 13 ka the hydrology for the southeastern mediterranean was mainly regulated by nile river runoff which in turn was controlled by climate forcing being affected by orbital forcing and the position of the intertropical convergence zone itcz planktic foraminiferal data assemblages stable isotopes and size properties indicate three major periods 1 from 13 0 to 11 5 ka the upper water column was well mixed cold and productive 2 from 11 5 to 6 4 ka hydrology and foraminifers were affected by intensified monsoonal circulation the enhanced size of globigerinoides ruber is interpreted as a response to environmental stress caused by low saline waters 3 after 6 4 ka the southward retreat of the itcz caused a decrease in freshwater discharge and hence a return to ecological equilibrium a drop in foraminifer diversity from 2 9 to 1 1 ka was related to more arid conditions and limited supply of nutrients from the nile river we suggest a link to a negative north atlantic oscillation nao marking the roman humid period in the western mediterranean and in anti phase with the southeastern mediterranean aridity because nile river runoff exerted major control on surface hydrology a connection to indian and pacific climate systems partially controlling precipitation over the nile catchment area is hypothesized from 1 1 to 0 54 ka high foraminifer diversity indicates humid conditions synchronous to the medieval climate anomaly under a positive nao state over the past 0 54 ka encompassing the little ice age another arid period is indicated by a drop in foraminifer diversity

reconstruction of subsurface structure from ambient seismic noise an example from ketzin germany summary passive seismic interferometry is a new promising methodology for seismic exploration interferometry allows information about the subsurface structure to be extracted from ambient seismic noise in this study we apply the cross correlation technique to approximately 25 hr of recordings of ambient seismic noise at the ketzin experimental co2 storage site germany common source gathers were generated from the ambient noise for all available receivers along two seismic lines by cross correlation of noise records this methodology isolates the interstation green s functions that can be directly compared to active source gathers we show that the retrieved response includes surface waves refracted waves and reflected waves we use the dispersive behaviour of the retrieved surface waves to infer geological properties in the shallow subsurface and perform passive seismic imaging of the subsurface structure by processing the retrieved reflected waves

integral view of holocene precipitation and vegetation changes in the nile catchment area as inferred from its delta sediments we compare geochemical and pollen data of several well dated high resolution cores to provide an integral holocene overview of nile outflow sedimentation and vegetation in and around the nile delta we show that the focus point of the nile plume varied considerably as indicated by planktonic foraminifer globigerinoides ruber oxygen isotopes tracing nile discharge differences in an east west delta transect at 13 11 5 cal kyr bp nile discharge was low and runoff was predominantly directed to the western part of the delta sediment arriving in the delta during that period was dominated by ethiopian highland similar to blue nile material shown by high ti al values of the bulk sediment indicating dry conditions in the source area of the blue nile nile discharge increased from similar to 11 5 cal kyr bp and was high across the whole delta from similar to 10 6 5 cal kyr bp during this time the ti al values decreased within most nile delta sediments suggesting that the relative contribution of blue nile sediment decreased this was likely due to an increased vegetation cover causing diminished erosion in the ethiopian highlands nile discharge gradually decreased from similar to 6 5 cal kyr bp to present this decrease was more abrupt in the western province of the delta and became more gradual towards the east as the shrinking nile runoff was directed there the gradual decrease in precipitation in the nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower nile catchment our findings suggest a nonlinear response of northeast african vegetation to precipitation from the middle to late holocene c 2015 elsevier ltd all rights reserved

marine productivity leads organic matter preservation in sapropel s1 palynological evidence from a core east of the nile river outflow the formation of eastern mediterranean organic matter rich deposits known as sapropels is the results of two mechanisms enhanced marine productivity and preservation of organic material at depth however their relative contribution and their leads and lags with respect to each other remain elusive here we address these questions by studying sediments deposited prior to during and after the most recent sapropel s1 10e6 calibrated ka before present bp with an integrated marine and terrestrial palynological approach combined with existing and newly generated geochemical data the studied core was retrieved from an area under strong influence of the nile outflow and has high average sediment accumulation rates allowing a high temporal resolution of several decades to centuries marine productivity as reconstructed with total dinocyst accumulation rates ars and biogenic caco3 content starts to increase 1 ka prior to sapropel formation a shift in the dinocyst taxa contributing tothe productivity signal at sapropel onset indicates the rapid development of seasonal water column stratification pollen and spore ars also increase prior to sapropel onset but a fewcenturies after the increase in marine productivity hence the first shift to a high marine productivity system before sapropel deposition may have been mostly favoured by the injection of nutrients via shoaling of the nutricline with a minor contributionofnutrientsfromlandviariverinputand floodingoftheshelves pollenassemblagesindicatea gradualchangeacrossthesapropelonsetfromasavanna like throughcoastal marshexpansion towardan open woodland assemblage which is consistent with enhanced nile influence and delta development at sapropel onset a marked shift in pollen ars could suggest increased preservation under anoxia however major shifts in pollen assemblages and signs of selective or partial decomposition of terrestrial palynomorphs are absent we therefore suggest that the high pollen ars largely result froman increased influx of pollen by enhanced nile discharge and extension of the freshwater plume three centuries after the sapropel onset dinocyst ars and caco 3 content indicate that marine productivity starts to decrease while sapropeldepositioncontinued organiccarboncontentdecreasedonlylaterandlessdramatically thismay

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

theory of supervirtual refraction interferometry summary inverting for the subsurface velocity distribution by refraction traveltime tomography is a well accepted imaging method by both the exploration and earthquake seismology communities a significant drawback however is that the recorded traces become noisier with increasing offset from the source position and so accurate picking of traveltimes in far offset traces is often prevented to enhance the signal to noise ratio snr of the far offset traces we present the theory of supervirtual refraction interferometry where the snr of far offset head wave arrivals can be theoretically increased by a factor proportional to here n is the number of receiver or source positions associated with the recording and generation of the head wave arrival there are two steps to this methodology correlation and summation of the data to generate traces with virtual head wave arrivals followed by the convolution of the data with the virtual traces to create traces with supervirtual head wave arrivals this method is valid for any medium that generates head wave arrivals recorded by the geophones results with both synthetic traces and field data demonstrate the feasibility of this method there are at least four significant benefits of supervirtual interferometry 1 an enhanced snr of far offset traces so the first arrival traveltimes of the noisy far offset traces can be more reliably picked to extend the useful aperture of the data 2 the snr of head waves in a trace that arrive later than the first arrival can be enhanced for accurate traveltime picking and subsequent inversion by later arrival traveltime tomography 3 common receiver pair gathers can be analysed to detect the presence of diving waves in the first arrivals which can be used to assess the nature of the refracting boundary and 4 the source statics term is eliminated in the correlation operations so that the timing of the virtual traces is independent of the source excitation time this suggests the possibility of applying this method to earthquake data recorded by receivers that are inline with the refraction paths and source locations

nile delta vegetation response to holocene climate variability a 7000 yr palynologic record from burullus lagoon nile delta egypt is assessed to investigate changes in terrestrial vegetation in response to nile flow previous studies in this region have shown that sea level rise in the early to mid holocene and markedly increased human land use during the past several centuries altered vegetation in and around the lagoon the pollen record from this study documents changes in delta vegetation that likely reflect variations in nile flow we suggest that cyperaceae pollen is a sensitive marker of precipitation over the nile headwaters and the resultant nile flow decreases in cyperaceae pollen interpreted as a marker for diminished nile flow as well as the increase in relative abundance of microscopic charcoal occurred at ca 6000 5500 ca 5000 ca 4200 and ca 3000 cal yr b p calibrated years before present these correspond to extreme regional and global aridity events associated with a more southerly mean position of the intertropical convergence zone these changes also recorded by other proxy studies indicate that several marked regional drought events affected the nile delta region and impacted ancient egyptian and middle eastern civilizations

the pace of east african monsoon evolution during the holocene african monsoon precipitation experienced a dramatic change in the course of the holocene the pace with which the african monsoon shifted from a strong early to middle to a weak late holocene is critical for our understanding of climate dynamics hydroclimate vegetation interaction and shifts of prehistoric human settlements yet it is controversially debated on the basis of planktonic foraminiferal ba ca time series from the eastern mediterranean sea here we present a proxy record of nile river runoff that provides a spatially integrated measure of changes in east african monsoon eam precipitation the runoff record indicates a markedly gradual middle to late holocene eam transition that lasted over 3500 years the timing and pace of runoff change parallels those of insolation and vegetation changes over the nile basin indicating orbitally forced variation of insolation as the main eam forcing and the absence of a nonlinear precipitation vegetation feedback a tight correspondence between a threshold level of nile river runoff and the timing of occupation abandonment of settlements suggests that along with climate changes in the eastern sahara the level of nile river and intensity of summer floods were likely critical for the habitability of the nile valley egypt

rupture kinematics and structural rheological control of the 2016 m w 6 1 amatrice central italy earthquake from joint inversion of seismic and geodetic data

estimation of the 3d correlation structure of an alluvial aquifer from surface based multi frequency ground penetrating radar reflection data knowledge about the stochastic nature of heterogeneity in subsurface hydraulic properties is critical for aquifer characterization and the corresponding prediction of groundwater flow and contaminant transport whereas the vertical correlation structure of the heterogeneity is often well constrained by borehole information the lateral correlation structure is generally unknown because the spacing between boreholes is too large to allow for its meaningful inference there is however evidence to suggest that information on the lateral correlation structure may be extracted from the correlation statistics of the subsurface reflectivity structure imaged by surface based ground penetrating radar measurements to date case studies involving this approach have been limited to 2d profiles acquired at a single antenna centre frequency in areas with limited complementary information as a result the practical reliability of this methodology has been difficult to assess here we extend previous work to 3d and consider reflection ground penetrating radar data acquired using two antenna centre frequencies at the extensively explored and well constrained boise hydrogeophysical research site we find that the results obtained using the two ground penetrating radar frequencies are consistent with each other as well as with information from a number of other studies at the boise hydrogeophysical research site in addition contrary to previous 2d work our results indicate that the surface based reflection ground penetrating radar data are not only sensitive to the aspect ratio of the underlying heterogeneity but also albeit to a lesser extent to the so called hurst number which is a key parameter characterizing the local variability of the fine scale structure

application of the virtual refraction to near surface characterization at the boise hydrogeophysical research site seismic interferometry is a relatively new technique to estimate the green s function between receivers spurious energy not part of the true green s function is produced because assumptions are commonly violated when applying seismic interferometry to field data instead of attempting to suppress all spurious energy we show how spurious energy associated with refractions contains information about the subsurface in field data collected at the boise hydrogeophysical research site by forming a virtual shot record we suppress uncorrelated noise and produce a virtual refraction that intercepts zero offset at zero time these two features make the virtual refraction easy to pick providing an estimate of refractor velocity to obtain the physical parameters of the layer above the refractor we analyse the cross correlation of wavefields recorded at two receivers for all sources a stationary phase point associated with the correlation between the reflected wave and refracted wave from the interface identifies the critical offset by combining information from the virtual shot record the correlation gather and the real shot record we determine the seismic velocities of the unsaturated and saturated sands as well as the variable relative depth to the water table finally we discuss how this method can be extended to more complex geologic models

do planktic foraminifera accurately record shifts in the carbon isotopic composition of seawater σco2 abstract both the carbon isotopic composition of seawater and physiological vital effects such as respiration and symbiont photosynthesis influence the 13 c value of foraminiferal calcite the symbiont bearing planktic foraminifera orbulina universa was grown in a series of laboratory experiments to determine whether vital effects differentially obscure the 13 c signal such that changes in the 13 c of seawater co 2 cannot be quantitatively evaluated foraminifera were cultured under three different irradiance levels to elicit a full range of symbiont photosynthetic effects and in seawater with 13 c values ranging between 1 77 ambient and 5 76 power regression analysis of isotope data from individual shells plotted against culture irradiance yields three curves which are nearly parallel but are offset by the difference between the carbon isotopic composition of the culture waters when irradiance groups are combined and o universa 13 c values are plotted against seawater 13 c three parallel linear regressions are obtained with slopes ranging between 0 93 and 0 96 because the slopes are near unity it is concluded that the 13 c of o universa accurately tracks changes in the carbon isotopic composition of seawater regardless of the magnitude of its physiological vital effect o universa oxygen isotope data show that individuals maintained in the low and medium irradiance groups secrete their shells in isotopic equilibrium according to established paleotemperature equations in contrast individuals grown under high irradiance levels maximum symbiont photosynthetic rates are on average 0 35 depleted in 18 o relative to equilibrium symbiont enhanced calcification rates in the high light group may be responsible for the observed 18 o difference

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

significance of porosity for stratigraphy and textural composition in subsurface coarse fluvial deposits boise hydrogeophysical research site recognition and quantitative characterization of subsurface stratigraphic units in coarse unconsolidated fluvial deposits are difficult because large grain size and the large scale of sedimentary structures make direct interpretation from core difficult or impossible in this paper we use porosity data from well logs and grain size distribution gsd data from core to investigate four pebble and cobble dominated units that have been identified in porosity logs in deposits at a research well field boise hydrogeophysical research site lacking direct observation at an appropriate scale questions about distribution of parameters and textural composition in these units are analyzed with statistical tests the four pebble and cobble dominated porosity stratigraphic units may be grouped into two types 1 units 1 and 3 have low porosity mean 0 17 0 18 and low porosity variance and 2 units 2 and 4 have higher porosity mean 0 23 0 24 and higher porosity variance based on gsd data core samples are subdivided into five lithotypes the five lithotypes occur in different proportions and have different vertical transition probability characteristics in the two types of units 1 units 1 and 3 have only framework gravel dominated lithotypes and have random vertical transition probability between these two lithotypes and 2 units 2 and 4 consist of both framework gravel dominated and sand or matrix dominated lithotypes and have structured vertical transition probability the two framework gravel dominated lithotypes occur in all four stratigraphic units but have distinctly lower porosity in units 1 and 3 i e tighter packing than in units 2 and 4 looser packing considering the repeated stratigraphic occurrence of and the statistical significance of differences between the two types of units both the individual unit distinctions and the two unit groupings appear to be valid it is reasonable to interpret that the observed packing differences associated with units 1 and 3 compared with units 2 and 4 are related to different sedimentary processes that produce different bedforms or grain fabrics perhaps under different bedload transport rates

monitoring changes in velocity and q using non physical arrivals in seismic interferometry application of seismic interferometry to records from receivers at the earth s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface when the wavefields experience intrinsic losses during propagation non physical arrivals ghosts would appear in the retrieved result these ghosts appear due to waves that reflect inside a subsurface layer thus a ghost contains information about the seismic properties of the specific layer we show how such ghosts can be used to monitor layer specific changes in the velocity and intrinsic losses in the subsurface we show how to identify the ghosts using numerical modelling results from a vertical well and how to estimate the layer specific velocity and quality factor changes using numerical modelling results from a horizontal well as well as ultrasonic s wave laboratory data

millennial scale sea surface temperature changes in the eastern mediterranean nile river delta region over the last 27 000 years 1 in this study we utilize two organic geochemical proxies the u37k index and tex86 to examine past sea surface temperatures sst from a site located near the nile river delta in the eastern mediterranean em sea the u37k and tex86 records generally are in agreement and indicate sst ranges of 14 c 26 c and 14 c 28 c respectively during the last 27 cal ka during the holocene tex86 based sst estimates are usually higher than u37k based sst estimates which is likely due to seasonal differences between the timing of the haptophyte and crenarchaeota blooms in the em and is related to the onset of the modern flow regime of the nile river both records show that sst varied on centennial to millennial timescales in response to global climate events i e cooling during the last glacial maximum lgm heinrich event 1 h1 and the younger dryas yd and warming during the bolling allerod and in the early holocene during deposition of sapropel s1 the h1 cooling was particularly severe and is marked by a drop in sst of 4 5 c in comparison to pre h1 sst with temperatures 1 c cooler than during the lgm in contrast to high latitude and western mediterranean records which indicate both an abrupt onset and termination of the yd event the transition from the yd to the holocene was much more gradual in the em

the virtual refraction useful spurious energy in seismic interferometry seismic interferometry is rapidly becoming an established technique to recover the green s function between receivers but practical limitations in the source energy distribution inevitably lead to spurious energy in the results instead of attempting to suppress all such energy we use a spurious wave associated with the crosscorrelation of refracted energy at both receivers to infer estimates of subsurface parameters we named this spurious event the virtual refraction illustrated by a numerical two layer example we found that the slope of the virtual refraction defines the velocity of the faster medium and that the stationary phase point in the correlation gather provides the critical offset with the associated critical time derived from the real shot record this approach includes all of the necessary information to estimate wave speeds and interface depth without the need of inferences from other wave types

retrieval of reflections from ambient noise recorded in the mizil area romania we applied seismic interferometry si by crosscorrelation to ambient noise panels recorded in the mizil area romania aiming to retrieve body wave reflections to achieve this goal surface waves in the noise panels input to si should be suppressed we did this by selecting for input to si only noise panels that are not dominated by surface waves the selection was either after visual inspection in the time domain or after automatic slowness evaluation on crosscorrelated panels the latter used the slowness of arrivals passing through the virtual source position at time 0 s we discovered that the automatic slowness evaluation method allows better retrieval of reflections from the retrieved reflection gathers we obtained stacked images of the subsurface comparing the si images to a stacked image from active source data we concluded that some retrieved events correspond to reflectors in the active seismic section including known geologic markers in a previous application of si to ambient noise the retrieved reflections exhibited frequency content lower than that of active data in our results the frequency content of the si retrieved data was comparable to the one of the active data