procedure to evaluate earthquake induced settlements in dry sandy soils a simple method is proposed for the evaluation of earthquake induced settlements in dry sands the method consists of a set of equations that can be used to predict directly the settlements of a sand layer subjected to seismic loading this new analytical method is based on tokimatsu and seed s 1987 procedure but does not require numerous iterations or the use of charts tables or diagrams one of the main advantages of the proposed method is that it can be easily implemented numerically and allows the expeditious analysis of complicated profiles it is particularly useful for sensitivity analyses and for analyzing profiles with numerous layers its application to case histories shows that this new method is in agreement with the settlements observed at two sites it also agrees with predictions obtained using other methods

petrology and geochemistry of lavas from antuco volcano a basaltic volcano of the southern andes 37 25 s sierra velluda plio pleistocene cerro condor pleistocene and antuco holocene volcanoes form a volcanic group located in the southern andes at latitude 37 25 s lavas from these volcanoes become less silicic with decreasing age antuco volcano consists of two units pre and post caldera collapse antuco i and antuco ii and a parasitic cone antuco lavas are basalts and those from antuco i and ii are relatively uniform in mineral and chemical composition common phenocrysts are plagioclase an65 an81 18 33 vol olivine fo 78 3 18 vol and clinopyroxene 0 5 3 vol the same phenocrysts occur in the parasitic cone lavas but plagioclase is much more abundant key compositional features of antuco lavas are 52 sio2 17 al2o3 3 3 4 2 na2o 1 2 tio2 0 9 k2o and mg mg fe ratios 0 60 these major element features characterize many circumpacific basalts in island arc and continental margin environments the antuco i and ii lavas have light ree abundances equal to 26 33 chondrites and heavy ree abundances equal to 8 9 chondrites some samples have positive 10 eu anomalies but no negative eu anomalies occur in these lavas trace element abundances in the antuco lavas are similar to those in theoretical liquids derived by 5 10 partial melting of garnet free peridotite followed by 10 fractionation of a clinopyroxene 40 and olivine 60 cumulate thus a plausible model is that the lavas were derived from the mantle by partial melting followed by mafic mineral fractionation

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

simplified empirical method for predicting earthquake induced settlements and its application to a large area in spain abstract most of the commonly used existing empirical methods to predict earthquake induced settlement s in sandy soils require numerous iterations or the use of charts tables and diagrams in general these methods estimate the one dimensional settlement of dry sandy soil on level ground by using a well known step by step procedure based on standard penetration test spt values which is particularly effective for practical applications a review of the state of the art methods shows that seismic settlement in all cases increases as the layer thickness h of sandy soils increases and corrected spt blow count n 1 60 decreases with that in mind we propose a novel simple way to estimate s based on the h n 1 60 ratio for a reference earthquake magnitude this approach provides a tool that can rapidly obtain s in numerous sites and can be applied to large areas in the last fifty years the population of the metropolitan area of granada mag has doubled the amount of developed land has increased by approximately 4650 ha and the areas with the greatest population and construction growth are located on sedimentary deposits the land beneath the urbanized areas of the mag is located on alluvial colluvial silt and clay deposits with different thicknesses of granular soils and varying water table depths the mag is acknowledged to be the most seismically active zone in spain and seismically induced phenomena such as liquefaction and ground settlement were reported in specific zones during moderate 1806 and strong 1431 historical local earthquakes the present study focuses on differential vertical displacement assessment in this large area of southern spain for two earthquakes of magnitude mw 6 6 and 7 0 the maximum expected settlement due to earthquake shaking of alluvial soils sandy soils and fine soils clay and or silt was obtained by correlating the mentioned h n 1 60 ratio with the s predicted by two well known methods v s values have been estimated from n 1 60 data using methods proposed in the literature and tested with v s local data from spac and refraction profiles the results from the new formula proposed here show predictable settlement ranging from 0 1 to 21 4 cm and up to 24 7 cm for the 6 5 and 7 0 earthquakes respectively these were greater than 2 0 cm and 3 3 cm in the north central and north western sectors of the study area especially in the town of atarfe and along the road between pinos puente and atarfe the same zones where settlements were observed in the 1806 earthquake zones where earthquake building damage may appear have been detected by comparing the maximum s and the maximum permitted settlements derived from different angular distortion values considering 5 and 6 m as typical distances between supporting structures

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

role of cryptic amphibole crystallization in magma differentiation at hudson volcano southern volcanic zone chile hudson volcano chile is the southern most stratovolcano of the andean southern volcanic zone and has produced some of the largest holocene eruptions in south america there have been at least 12 recorded holocene explosive events at hudson with the 6700 years bp 3600 years bp and 1991 eruptions the largest of these hudson volcano has consistently discharged magmas of similar trachyandesitic and trachydacitic composition with comparable anhydrous phenocryst assemblages and pre eruptive temperatures and oxygen fugacities pre eruptive storage conditions for the three largest holocene events have been estimated using mineral geothermometry melt inclusion volatile contents and comparisons to analogous high pressure experiments throughout the holocene storage of the trachyandesitic magmas occurred at depths between 0 2 and 2 7 km at approximately 972 c 25 and log fo2 10 33 10 24 0 2 one log unit above the nno buffer with between 1 and 3 wt h2o in the melt pre eruptive storage of the trachydacitic magma occurred between 1 1 and 2 0 km at 942 c 26 and log fo2 10 68 0 2 with 2 5 wt h2o in the melt the evolved trachyandesitic and trachydacitic magmas can be derived from a basaltic parent primarily via fractional crystallization entrapment pressures estimated from plagioclase hosted melt inclusions suggest relatively shallow levels of crystallization however trace element data e g dy yb ratio trends suggests amphibole played an important role in the differentiation of the hudson magmas and this fractionation is likely to have occurred at depths 6 km the absence of a garnet signal in the hudson trace element data the potential staging point for differentiation of parental mafic magmas i e 20 km e g annen et al in j petrol 47 3 505 539 2006 and the inferred amphibolite facies 24 km e g rudnick and fountain in rev geophys 33 267 309 1995 combine to place some constraint on the lower limit of depth of differentiation i e 20 24 km these constraints suggest that differentiation of mantle derived magmas occurred at upper mid to lower crustal levels and involved a hydrous mineral assemblage that included amphibole and generated a basaltic to basaltic andesitic composition similar to the magma discharged during the first phase of the 1991 eruption continued fractionation at this depth resulted in the formation of the trachyandesitic and trachydacitic compositions these more evolved magmas ascended and stalled in the shallow crust as suggested by the pressures of entrapment obtained from the melt inclusions the decrease in pressure that accompanied ascent combined with the potential heating of the magma body through decompression induced crystallization would cause the magma to cross out of the amphibole stability field further shallow crystallization involved an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the hudson suite

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

origin of 226ra 230th disequilibria in arc lavas from southern chile and implications for magma transfer time abstract improved understanding of mantle melting processes and melt transport requires knowledge of how fast magma is generated and transferred from source region to surface the rate of magma transfer can in favorable cases be estimated from radioactive disequilibria between nuclides of the 238u series young lavas from southern chile in which 238u 230th disequilibria have been measured sigmarsson et al nature 346 1990 163 165 sigmarsson et al nature 394 1998 566 569 were analyzed for 226ra abundances the disequilibrium between 226ra and 230th in these lavas is found to correlate with 238u 230th disequilibria and 10be be morris et al nature 344 1990 31 36 these correlations strongly suggest that the excess of 226ra over 230th is due to the addition of a slab derived fluid to the magma source since ra and u are fluid mobile elements and the cosmogenic 10be is most likely derived from the subducting nazca plate beneath the andes the largest slab signature is observed in the lavas of villarrica volcano which is the most active volcano in south america a model for subduction fluxing is discussed in which the u series disequilibria in arc lavas will reflect the integrated dehydration process during metamorphism of the subducting plate and the metasomatized mantle but be principally controlled by the latest hydrous mineral breakdown in the mantle wedge repeated precipitation and dehydration mineral reactions of the hydrated mantle could be the homogenization process of the slab input needed to explain the 10be be b be correlation for different arcs morris et al nature 344 1990 31 36 the fact that excesses of 226ra and 238u over 230th are correlated indicates that linear arrays on the 230th 232th 238u 232th diagram are not isochrons reflecting time elapsed since a fluid addition but rather mixing lines between a fluid phase and melts the 226ra 230th disequilibrium in arc lavas suggests significantly shorter timescales for magma transfer or less than 8000 years this disequilibrium is consistent with minimum magma transfer rate through the mantle wedge on the order of 10 m year finally the correlations of 226ra 230th with 238u 232th and 10be be in andean magmas imply that magma chamber residence time is of the same order of magnitude beneath the stratovolcanoes studied

combined sr o isotope relationships and petrogenesis of andean volcanics of south america active andesitic type volcanism in the southern andes lat 42 36 s is characterized by low sr and o isotopic compositions which fall in the range 87sr 86sr 0 7036 0 7043 18o 5 2 6 8 in contrast volcanic centres in the central andes lat 24 21 s are significantly enriched in both 87sr and 18o we present the first combined sr and o isotope study of the southern volcanic zone svz in chile crustal thickness 40 km 1 and of the southern part of the central volcanic zone cvz in the borderlands of bolivia chile and argentina crustal thickness 60 70 km 1 only one of 13 volcanic centres studied lascar exhibits a correlated increase in both 87sr and 18o parallel with the basalt andesite rhyolite compositional change indicative of contamination by upper crust through a fractional crystallization assimilation mechanism the other centres of the cvz for which there is an overall sr o correlation document the variable contamination of mantle derived magmas at depth in the lower crust which had been thickened by mesozoic and earlier plutonism

partial assimilative recycling of the mafic plutonic roots of arc volcanoes an example from the chilean andes at long lived arc volcanic centers open system interactions between new magma and the plutonic roots of the arc will increase with time relative to interactions with older crust assimilative recycling of mafic plutonic arc roots will have different isotopic consequences than incorporation of aged continental crust in the tatara san pedro complex 30 comagmatic basaltic lavas are characterized by xenocrysts and microxenoliths of olivine augite and plagioclase derived from solidified cumulates wide but poorly correlated ranges of incompatible and compatible major and trace elements and limited isotopic variability this mineralogical chemical signature reflects assimilation wherein grain boundary melting and disaggregation of xenoliths led to blending of incompatible element enriched melts derived mainly from hornblende phlogopite and plagioclase in combination with variable retention of xenocrysts hence variable but high compatible element concentrations

empirical methodology to estimate seismically induced settlement of partially saturated sand abstractsettlement of soil layers during and after earthquake shaking is a major cause of damage to buildings and geotechnical structures the available empirical design methods to consider seismically induced settlement focus on sands in dry or water saturated conditions and there is currently a gap in the basic understanding of the mechanisms of seismically induced settlements of partially saturated sands an effective stress based empirical methodology is proposed to estimate the seismically induced settlement of a free field layer of sand in partially saturated conditions this approach estimates the settlement by separately considering the volumetric strains caused by compression of void space during strong shaking seismic compression and dissipation of excess pore water pressures generated during earthquake shaking postcyclic reconsolidation a parametric evaluation of the methodology indicates that the small strain shear modulus the parameters of the modulus reduction curve the approach to e

seismic compression susceptibility in dry loose sandy and silty soil in a seismic microzonation perspective abstract seismic microzonation studies hereafter sms or sm studies have a strategic application in land use planning in the perspective of territory protection at urban scale sms are finalized to forecast the spatial distribution of stratigraphic and topographic local amplification effects of ground motion and the co seismic instabilities such as landslides or liquefaction phenomena in this regard the co seismic instability due to the seismic compression or densification in dry loose sands silty sands and sandy silts has been addressed in this paper through a numerical approach in order to provide simplified charts to evaluate the effect of the instability in terms of earthquake induced settlements to be incorporated in sms in specific subsoil conditions seismic cyclic loads can result in contractive volumetric strains inducing damages to structures infrastructures and lifelines accordingly with well documented post earthquake damages of past events in the present work a procedure has been adopted to define the abovementioned simplified charts to predict the possible effect of the phenomenon in terms of soil permanent displacements the proposed charts provide the estimation of settlements in function of three different pga classes the thickness of the soil layer susceptible to seismic compression densification its relative density and shear wave velocity the proposed charts have been tested for the case study of santa clarita valley california during the 1994 northridge earthquake probably the best documented seismic compression case history available in the technical literature

geology of the devonian black shales of the appalachian basin abstract black shales of devonian age in the appalachian basin are a unique rock sequence the high content of organic matter which imparts the characteristic lithology has for years attracted considerable interest in the shales as a possible source of energy the recent energy shortage prompted the u s department of energy through the eastern gas shales project of the morgantown energy technology center to underwrite a research program to determine the geologic geochemical and structural characteristics of the devonian black shales in order to enhance the recovery of gas from the shales geologic studies by federal and state agencies and academic institutions produced a regional stratigraphic network that correlates the 15 ft black shale sequence in tennessee with 3000 ft of interbedded black and gray shales in central new york these studies correlate the classic devonian black shale sequence in new york with the ohio shale of ohio and kentucky and the chattanooga shale of tennessee and southwestern virginia biostratigraphic and lithostratigraphic markers in conjunction with gamma ray logs facilitated long range correlations within the appalachian basin basinwide correlations including the subsurface rocks provided a basis for determining the areal distribution and thickness of the important black shale units the organic carbon content of the dark shales generally increases from east to west across the basin and is sufficient to qualify as a hydrocarbon source rock significant structural features that involve the black shale and their hydrocarbon potential are the rome trough kentucky river and irvine paint creek fault zone and regional decollements and ramp zones

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

experimental constraints on the effects of pressure and h 2 o on the fractional crystallization of high mg island arc basalt h2o undersaturated melting experiments of synthesized basalt sio2 50 7 wt mgo 8 3 wt mg 60 were conducted at fo2 corresponding to nno 1 and nno 1 to clarify the effects of pressure 2 7 kbar and h2o on fractional crystallization in island arcs h2o content was ranged from nominally anhydrous to 4 4 wt differentiation trends namely the liquid lines of descent change sensitively according to pressure h2o relations tholeiitic differentiation trends are reproduced with h2o 2 wt in primary magma with such quantities of h2o fractional crystallization is controlled by olivine plagioclase at 2 kbar increasing the pressure from 2 to 4 kbar induces early crystallization of orthopyroxene instead of olivine and therefore sio2 enrichment in the residual melts is suppressed increasing h2o 2 wt in primary magma stabilizes clinopyroxene relative to orthopyroxene and or magnetite although the phase relations and proportions strongly depend on fo2 and h2o content differentiation trends are always calc alkaline

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

arc magma compositions controlled by linked thermal and chemical gradients above the subducting slab 1 global arc magmatism is sustained by a continuous fluid flux that is returned to the mantle in subduction zones despite considerable advances in simulations of melting processes models of arc magmatism remain incompletely tested against erupted products here we show that a suite of primitive volcanic rocks from across the southern chilean arc preserves the signature of a systematic down slab gradient in fluid chemistry the chemical gradient is consistent with predictions from modeling geothermometry and experiments we infer that increasing slab surface temperatures cause the sub arc slab flux to become less water rich and increasingly dominated by hydrous melts over a distance of a few kilometers behind the arc front this change exerts a first order control on magma chemistry and implies discrete melt transport pathways through subduction zones our results replicate patterns in other arcs implying common sub arc slab surface temperature ranges in thermally diverse subduction zones

probabilistic and spatial assessment of liquefaction induced settlements through multiscale random field models abstract evaluation of liquefaction induced settlements over an extended area requires the integration of different solution models that can account for the liquefaction resistance of a given soil profile and its spatial dependence across scales in this paper a cpt based liquefaction model is adopted to estimate the liquefaction induced settlement at individual sounding locations the model is then integrated with multiscale random field models to account for spatial variability of soil properties one important advantage of the proposed framework is its ability to consistently refine and provide settlement estimations across different scales from regional and geologic unit scales down to a local site specific scale the proposed methodology is then applied to the alameda county california an earthquake prone region to illustrate the procedure for probabilistic and spatial assessment of liquefaction induced settlements at different scales

geochemical paleoredox indicators in devonian mississippian black shales central appalachian basin usa the degree of anoxia that existed during accumulation of devonian mississippian black shales in central kentucky has been debated widely in this study geochemical data were used to elucidate paleodepositional environments for these units using analyses from ten cores collected from the outcrop belt in central kentucky sulfur carbon and selected trace element relationships were compared the sunbury shale tournasian lower mississippian and the cleveland and huron members of the ohio new albany shale fammenian upper devonian show different relationships between carbon sulfur and trace elements c s fe relationships for the sunbury suggest anoxic possibly even euxinic conditions prevailed during sediment accumulation analysis of c s fe data suggests that the cleveland may have accumulated under anoxic conditions with intermittent dysoxia whereas the huron member may have accumulated under a relatively wide range of conditions from anoxic to dysoxic to possibly oxic these three units exhibit different degrees of trace element enrichment with the approximate order of enrichment relative to an average shale being mo pb zn v ni cu cr co the sunbury shows the highest levels of enrichment followed by the cleveland with the huron showing only slight enrichment for most of these trace elements differing degrees of enrichment may reflect differences in depositional environment during accumulation high mo concentrations in the sunbury generally 200 550 ppm may infer euxinic conditions prevailed during sediment accumulation the cleveland and the huron both show considerably lower mo contents averaging around 100 ppm geochemical ratios including ni co v cr and v v ni also indicate variable paleoredox conditions for these shales based on previously established thresholds v cr and ni co ratios infer at least anoxic conditions during accumulation of the sunbury anoxic to dysoxic conditions during cleveland accumulation and dysoxic to oxic conditions for the huron v v ni ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators and this discrepancy is greatest for the huron member it is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly but that relative differences in these indicators collectively can infer variations in the degree of anoxia in addition relationships between corg and redox elements may help elucidate the role of anoxia in om accumulation it may be concluded from this study that the devonian mississippian black shales of central kentucky accumulated under variable bottom water conditions at least anoxic conditions prevailed during accumulation of much of the sunbury shale and the upper part of the cleveland member and possibly euxinic conditions for the sunbury bottom water conditions may have been intermittently anoxic and dysoxic during deposition of the lower cleveland during accumulation of the huron member it is likely that conditions ranged from anoxic to dysoxic to marginally oxic possibly being close to normal marine conditions at times during accumulation of the lowermost huron sediments

accumulation of organic matter in the rome trough of the appalachian basin and its subsequent thermal history we used geochemical data to examine the origin and preservation of organic matter contained in the lower part of the huron member of the ohio shale formation and the rhinestreet shale member of the west falls formation devonian in kentucky ohio west virginia and virginia the thermal history of the organic matter was determined by relating relative temperatures experienced by the organic matter to the geologic setting the organic matter in these formations is predominantly marine in origin and was most probably derived largely from algal organisms although the rate of production of marine organic matter may have been uniform within the basin its preservation apparently was controlled by the existence of a set of fault bounded anoxic subbasins associated with the rome trough a cambrian structural complex these subbasins apparently were anoxic because they limited oxygen recharge by circulating waters preservation of organic matter was also enhanced by periodic blooms of the alga tasmanites and similar organisms in the waters above the subbasins during both early huron and rhinestreet deposition a significant negative correlation was identified between the vitrinite reflectance peak temperature an integrated measure of the thermal history of a rock and the hydrogen index a measure of the remaining hydrocarbon generation potential of kerogen although peak temperatures were controlled by burial depth excess heating occurred locally perhaps by hot brines rising from depth through fractures associated with major structures in the study area

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

sedimentary and geochemical indicators of productivity and oxygen contents in modern and ancient basins the holocene black sea as the type anoxic basin data on the accumulation rates of organic carbon total phosphorus and reduced sulfur over the past 7000 yr from modern abyssal black sea sediments are examined as geochemical monitors of variations in biologic productivity and the development of deep water masses variations in organic carbon accumulation rates at both intermediate and deep water sites are believed to be controlled by the combined effects of enhanced preservation of organic matter under anoxic bottom conditions and the regulation of primary productivity in surface waters by nutrient availability estimates of variations in water column and pore water organic carbon consumption by sulfate reducing bacteria can be made using average carbon and sulfur accumulation rates for various depositional episodes and are examined in the light of changes in the thickness of the h2s zone in the water column the amount of available sulfate within this zone and the reactiveness of particulate organic matter sulfur and phosphorus accumulation rates are used to estimate the maximum amount of phosphorus regenerated from organic matter during bacterial sulfate reduction processes total phosphorus accumulation rates are found to markedly increase over the part 1000 yr and are not proportionally paralled by organic carbon accumulation rates these accelerated phosphorus accumulation rates appear to stem from organic matter degradation adsorption on surfaces of caco3 and perhaps diffusion into sediments from bottom waters and authigenic precipitation of phosphate minerals accumulation rates of organic carbon and phosphorus in black sea sediments are low in comparison to those typical of modern highly productive upwelling zones peru south west africa namibia accumulation rates of reduced sulfur and the ratios of reduced sulfur to organic carbon burial may be higher in anoxic basins than in oxic ones knowledge of accumulation rates therefore rather than concentrations alone may help to differentiate black shales which resulted from enhanced organic matter preservation under anoxic conditions from those resulting from high biologic productivity with or without accompanying oxygen deficiencies

composition gaps critical crystallinity and fractional crystallization in orogenic calc alkaline magmatic systems the recognition of a three way correlation between magmatic sio2 content critical crystallinity and the size magnitude of crystal fractionation generated composition gaps in calc alkaline magmatic systems suggests an important control of magmatic critical crystallinity on the formation of such composition gaps to explain this correlation it is proposed that fractionation generated composition gaps are caused by 1 simultaneous interior i e non substrate crystallization and vigorous chamberwide convection which leads to progessive crystal suspension 2 cessation of convection when the percentage of suspended crystals reaches the critical crystallinity of the magma and 3 eventual buoyancy driven crystal liquid segregation producing a discrete body of fractionated magma which is separated from the initial magma by a composition gap this mechanism implies that many if not most magma bodies are characterized by interior crystallization and vigorous convection conditions which are not universally agreed upon at present given that such conditions characterize natural magma bodies fractional crystallization through crystal settling in low velocity boundary layers should be an important mechanism of fractional crystallization in a crystallizing and convecting body of magma composition gap formation should represent one endmember of a complete spectrum of possible evolutionary paths governed by the relative rates of crystal settling and crystal retention as a given volcanic plumbing system matures with time average settling retention ratios within individual magma bodies should increase due to higher average wall rock temperatures it follows that within a given volcanic center early stage volcanism should be more likely to display fractionation generated composition gaps than later stage volcanism such a temporal evolution has been documented at at least two aleutian calc alkaline volcanic centers

understanding crystal populations and their significance through the magma plumbing system crystals are rarely composed of a single crystal population that have grown solely from the batch of magma in which they are resident on emplacement either by eruption or shallow intrusion close investigation of the majority of crystal populations reveal that they comprise up to four main components phenocrysts crystals co genetic with their magmatic host xenocrysts crystals wholly or in part foreign to the magmatic host and magma system antecrysts crystals which are recycled one or several times before inclusion in the host magma but have an origin within the magmatic system and microlites which represent small co genetic crystals which nucleate and grow rapidly on decompression and eruption textural analysis techniques are employed to quantify key aspects of the crystal population including crystal shape crystal size distributions spatial distribution patterns and textural modification using dihedral angles santorini provides a case study of an active volcanic system where a combined textural analysis study has been developed highlighting how the crystal population is being continuously modified by a series of replenishment and mixing events developing textural and microgeochemical techniques provides the next stage in the interrogation of crystal populations linking textures to isotopic heterogeneities and providing fingerprints of where crystals are sourced and re cycled

accumulation of organic matter in the rome trough of the appalachian basin and its subsequent thermal history discussion 666 this discussion is intended to correct a major error of fact concerning the organic carbon concentration of the lower huron member of the ohio shale in eastern kentucky figure 2 of curtis and faure 1997 showed a map of total organic carbon concentrations in the lower huron shale based on data collected for the gas research institute this map is essentially identical to those previously published by curtis 1988 his plate ii and curtis 1990 his figure