regional source scaling of the 9 october 2006 underground nuclear explosion in north korea abstract the 9 october 2006 underground nuclear explosion une test in north korea was well monitored by dense regional seismic stations in south korea japan and china this observation allows extensive investigation of the regional source properties of the une the moment for isotropically radiated energy from the une is estimated to be 2 92 10 14 n m source spectra of major regional phases from the une are studied by inverting for apparent moments corner frequencies overshoot parameters attenuation factors and frequency power dependence parameters the overshoot parameters of p phases from the une are estimated to be high while those of s phases are estimated to be significantly low the inverted source spectra agree well with conventional models the low overshoot parameters of s phases suggest that their excitation sources may be different from those for pn and pg it is shown that pn lg and pg lg amplitude ratios are useful for discriminating between unes and natural earthquakes in the frequencies of 1 8 hz

biological markers in lower jurassic synrift lacustrine black shales hartford basin connecticut u s a abstract the east berlin formation lower jurassic hartford basin connecticut u s a is distinctive for its six cyclic units of lacustrine black shale and gray mudstone separated by playa and fluvial redbeds the black shales are each about a meter thick and were deposited in subtropical thermally strastified oligomictic lakes the youngest of which lakes 3 through 6 were large enough to flood most of the basin and attained depths of several tens of meters the saturate fractions of solvent extracts of organic rich black shales from each of the six lakes collected at fresh roadcuts near east berlin are dominated by extended homologous series of n alkanes alkylcyclohexanes and branched chain alkanes a striking feature of the black shales is the presence of a series of extended tricyclic terpanes from c20 to at least c41 hopanes are either not detectable or present only in subordinate quantities relative to the tricyclic terpanes the samples are depleted in hopanes in part because of the elevated maturity level mid to late oil window tricyclic terpane concentrations may also have been enhanced by fractionation effects related to oil expulsion out of the black shales in addition the original organic matter may have been exceptionally rich in tricyclic terpane precursors i e fossil lipids of prokaryotes present in anoxic moderately saline alkaline lakes

sn propagation in the western united states from common midpoint stacks of usarray data 1 the regional seismic phase sn propagates horizontally in the uppermost mantle and is sensitive to lateral variations in mantle lid thickness temperature and melt sn is therefore often used as an indicator for physical properties of the lithosphere it has previously been noticed that sn is not observed at many stations in the western united states and sn seems especially highly attenuated for paths across the basin and range here we apply stacking methods to usarray data to identify highly attenuating regions in the uppermost mantle and increase the spatial resolution of the sn propagation image we find evidence for sn propagation at short ranges in the central great basin and the northeastern part of the colorado plateau both regions where lithospheric stability and thickness is debated and observe strong sn attenuation around the perimeter of the central great basin

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

stratigraphy and source potential of the smackover formation in the northern manila embayment southwest alabama abstract petrographic studies of conventional cores and correlation of electric logs indicate that upper smackover hydrocarbon reservoir facies are more widely distributed in the northern manila embayment than previously recognized the embayment does not appear to have been a separate basin during early smackover deposition but rather was an extension of the mississippi salt basin a carbonate shelf and starved basin topography developed in the manila embayment during deposition of the smackover formation and is reflected in the distribution of smackover lithofacies fine grained clastics are abundant in shelf and backshelf environments source rock geochemistry of the manila embayment appears to be atypical of the eastern smackover trend because of a strong terrestrial influence although the upper smackover is organic rich potential for generation of crude oil is limited by abundant terrestrially derived kerogen and thermal immaturity the updip lower smackover nearest the paleoshoreline also appears to be characterized by terrestrial kerogen thermal maturity and source potential for crude oil in the lower smackover increase southward this contributes to explaining the clustered distribution of crude oil discoveries downdip in proximity to the thermally mature lower smackover source facies

source and thermal history of oils from lockhart crossing livingston parish louisiana abstract in 1982 lower tuscaloosa production at the lockhart crossing field was supplemented with a major discovery of significant petroleum reserves in the wilcox whole oil and biomarker source parameters definitively prove that the oils found in wilcox reservoir rocks constitute one single oil family oils produced from the tuscaloosa formation comprise a separate oil family unrelated to the oils in the wiilcox formation within each formation the oils become progressively more mature with depth this is believed to be due to thermal cracking which as taken place after the oil charged with the reservoirs the chemistry of the oils produced from wilcox reservoirs shows that these oils were generated from clay rich shales with a significant input of bacterial organic matter eukaryotic algae and higher plants also contributed organic matter to the source rocks comparisons with cuttings from nearby wells prove that wilcox shales are the source facies for these oils biomarker and other maturity parameters indicate that the wilcox oils were generated from source rocks that were within the thermal regime associated with early oil generation tuscaloosa reservoir fluids are significantly more thermally mature than the petroleum in the wilcox the tuscaloosa oils are presently in the thermal conditions associated with late stage oil gas condensate generation because of this advanced degree of thermal stress correlation of the tuscaloosa oils to their source sediments is difficult cuttings from wells updip from lockhart crossing indicate that the lower marine tuscaloosa shales are viable source rocks equivalent downdip shales are the likely source for the lockhart crossing tuscaloosa gas condensates the study proves that future wilcox discoveries in the area need not be associated with deeper tuscaloosa production

geochemical relationships of petroleum in mesozoic reservoirs to carbonate source rocks of jurassic smackover formation southwestern alabama algal carbonate mudstones of the jurassic smackover formation are the main source rocks for oil and condensate in mesozoic reservoir rocks in southwestern alabama this interpretation is based on geochemical analyses of oils condensates and organic matter in selected samples of shale norphlet formation haynesville formation trinity group tuscaloosa group and carbonate smackover formation rocks potential and probable oil source rocks are present in the tuscaloosa group and smackover formation respectively extractable organic matter from smackover carbonates has molecular and isotopic similarities to jurassic oil although the jurassic oils and condensates in southwestern alabama have genetic similarities they show significant compositional variations due to differences in thermal maturity and organic facies lithofacies organic facies reflect different depositional conditions for source rocks in the various basins the mississippi interior salt basin was characterized by more continuous marine to hypersaline conditions whereas the manila and conecuh embayments periodically had lower salinity and greater input of clastic debris and terrestrial organic matter petroleum and organic matter in jurassic rocks of southwestern alabama show a range of thermal transformations the gas content of hydrocarbons in reservoirs increases with increasing depth and temperature in some reservoirs where the temperature is above 266 f 130 c gas condensate is enriched in isotopically heavy sulfur apparently derived from thermochemical reduction of jurassic evaporite sulfate this process also results in increased h2s and co2 in the gas and depletion of saturated hydrocarbons in the condensate liquids thermochemical sulfate reduction probably depends on the mineralogic composition of the reservoir rock as well as temperature because some deep 18 000 ft or 5 5 km and hot 320 f or 160 c smackover and norphlet reservoirs contain low sulfur petroleum

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

regional seismic characteristics of the 9 october 2006 north korean nuclear test we investigate the regional seismic signature of the 9 october 2006 north korean nuclear test broadband regional data for the nuclear test and a group of earthquakes close to the test site were obtained between december 2000 and no vember 2006 epicentral distances from the stations to the test site are between 371 and 1153 km we first use these regional events to calibrate the lg wave magnitude in the network then the network is used to calculate mblg 3 93 for the north ko rean nuclear explosion using a modified fully coupled magnitude yield relation the yield of the north korean nuclear test is estimated to be 0 48 kt because of large uncertainties in the source depth the estimate is preliminary the p s type spectral ratios pg lg pn lg and pn sn are calculated for the nuclear explosion and a group of earthquakes close to the test site at frequencies above 2 hz the network averaged p s spectral ratios clearly separate the 9 october 2006 explosion from the regional earthquakes our result indicates that a single blast explosion in the north korea re gion shows different seismic characteristics from an earthquake any well coupled single blast explosion detonated in this region with yield similar to that for the north korean nuclear test has a large probability of being identified by a regional seismic network such as the one adopted in this study

pn wave geometrical spreading and attenuation in northeast china and the korean peninsula constrained by observations from north korean nuclear explosions we investigate the geometric spreading and attenuation of seismic pn waves in northeast china and the korean peninsula a high quality broadband pn wave data set generated by north korean nuclear tests is used to constrain the parameters of a frequency dependent log quadratic geometric spreading function and a power law pn q model the geometric spreading function and apparent pn wave q are obtained for northeast china and the korean peninsula between 2 0 and 10 0 hz using the two station amplitude ratios of the pn spectra and correcting them with the known spreading function we remove the contributions of the source and crust from the apparent pn q and retrieve the p wave attenuation information along the pure upper mantle path we then use both pn amplitudes and amplitude ratios in a tomographic approach to obtain the upper mantle p wave attenuation in the studied area the pn wave spectra observed in china are compared with those recorded in japan and the result reveals that the high frequency pn signal across the oceanic path attenuated faster compared with those through the continental path

lg attenuation near the north korean border with china part i model development from regional earthquake sources we have collected broadband data from three seismic networks two portable and one permanent in a remote part of northeast china bordering north korea the combined network coverage allows first hand investigations of seismic wave propagation in a region of import for nuclear test ban monitoring research application of the reversed two station method to the newly acquired data has pro duced stable measurements of the quality factor q q0f for lg waves the re sults a weighted regional average over 23 interstation paths involving 51 events and 21 stations point to 1 hz q or q0 of 345 and of 0 38 in a jarring incongruity with what appears to be a popular perception of the region as being of very low attenuation for lg waves the results also show that lg q varies from one interstation path to another the highest lg wave attenuation 110 q 0 140 is found along intersta tion paths that crossed two recently active volcanoes huangyishan and chang baishan the subregion exhibiting the next highest lg attenuation is bohai an extensional basin known to feature above average heat flow

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

correlations of gulf coast petroleums on the basis of branched acyclic alkanes abstract mass 211 chromatograms of c 15 n alkane free saturated hydrocarbon fractions of oils represent numerous homologous series of methyl branched acyclic alkanes including isoprenoids mass 211 patterns facilitated the subdivision fingerprinting of 88 of 282 gulf coast petroleums into merely seven classes evaluation of reservoir ages suggests that the patterns undergo progressive change with time an end member pattern occurs in jurassic reservoirs a second closely related occurs principally in oils found in lower cretaceous reservoirs minor changes result in an upper cretaceous pattern which is duplicated in numerous oils occuring in all succeeding tertiary and quaternary stages over most of coastal and offshore louisiana laterally extensive source formations and pervasive vertical migration are indicated although branched alkane concentrations can be brought toward thermodynamic equilibrium by mineral catalysis the consistency of the observations indicates that this is minor suggesting a biomarker status for the compounds involved both facies variability and metabolic evolution might be significant in the generation of the observed patterns

geochemical and carbon isotopic studies of crude oil destruction bitumen precipitation and sulfate reduction in the deep smackover formation abstract crude oil generated by the lower smackover source facies migrated to upper smackover reservoirs where slow thermal cracking of crude oil resulted in the formation of gas condensate and late solid bitumen ultimately only pyrobitumen methane and nonhydrocarbon gases including hydrogen sulfide persist in the deepest smackover reservoirs the carbon isotopic compositions of crude oils became heavier during crude oil destruction the carbon isotopic compositions of asphaltenes nso compounds and saturated hydrocarbons in late solid bitumen and the lower smackover source facies became isotopically lighter during crude oil destruction it is suggested that some isotopically light components from crude oils were incorporated in late solid bitumen by reactions involving thermochemical sulfate reduction thermochemical sulfate reduction and crude oil destruction occurred over a long span of geologic time at temperatures in the 120 150 c range

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

attenuation of high frequency p and s waves in the crust of central and western tien shan in order to better understand the attenuation characteristics in the crust of the central and western tien shan orogenic belt we investigate both qp and qs values by applying the extended coda normalization method we estimate the frequency dependent attenuation of both p and s waves in the frequency band of 1 0 20 0 hz using data from local networks the average frequency relations of qp and qs have been derived as qp 61 9 f 1 21 0 08 and qs 77 6 f 1 11 0 04 by fitting a power law frequency dependence model for the study region the low q0 and high values indicate that the central and western tien shan is a tectonically and seismically active region we also find lateral variations of both qp s and qs qp values reflecting complex tectonic structures in the study area in general the relatively high attenuation areas corresponding to tectonically active regions are found beneath mountainous ranges in the central tien shan whereas the relatively low attenuation areas are associated with stable regions such as fergana basin and issyk kul lake besides regions in the central tien shan with qs qp 1 are likely partially saturated with fluids or rich in scattering heterogeneities whereas regions in the western tien shan display qs qp 1 possibly suggesting almost complete fluid saturation

abstract petroleum classification based on the ratio of sulfur to nitrogen application in the east texas basin abstract petroleum families are characterized by limited ranges of organic sulfur to nitrogen s n ratios despite thermal crack ing in the east texas basin three families are recognizable on the basis of both carbon isotopic and s n ratio data jurassic oils possess modal saturated hydrocarbon values of 25 13c and s n ratios close to 20 lower cretaceous oils values of 26 and 10 and upper cretaceous oils values of 28 and 3 numerous published analyses of sulfur and nitrogen in oils facilitated mapping the detailed geographic distributions of the families recognized both source rock and petroleum data demonstrate that upper cretaceous oil including that of the supergiant east texas field was generated only beyond the confines of the east texas basin principally to the south and west in the gulf coast basin migration distances to present pool sites are of the order of 30 to 200 miles end of record last page 602

the 9 september 2016 north korean underground nuclear test we characterize the seismic events that occurred in north korea on 9 september 2016 and south korea on 12 september 2016 the 9 september 2016 event was identified as an explosion and the two 12 september 2016 events were identified as natural earthquakes using the p s p and s wave spectral ratios pg lg pn lg and pn sn as discriminants the explosive event was relocated within the north korean nuclear test site using a relative location method and the 2006 north korea underground nuclear test as the master event and the epicenter was identified at 41 2976 degrees n latitude and 129 0804 degrees e longitude from the regional lg and rayleigh waves the body and surface wave magnitudes for the 9 september 2016 event were calculated as m b lg 4 8 0 2 and m s 4 2 0 1 by adopting an empirical magnitude yield relation for the body wave magnitude and assuming that the explosion was fully coupled and detonated at a normally scaled depth we estimated that the seismic yield was similar to 6 kt and the uncertainty range was between 3 and 11 kt if an overburied depth range between 780 and 1200 m was applied then the yield would be increased to 16 22 kt

the origins of petroleum in the northern gulf of mexico abstract the distribution and chemistry of oils in the northern gulf of mexico and the adjacent onshore can be explained by multiple sources fades variations maturation and post generation alteration genetic families include jurassic smackover flexure trend upper cretaceous and paleogene oils smackover oils have high sulfur contents pristane phytane ratios c 35 c 34 hopane ratios 1 0 and c 30 c 29 hopane ratios usuall 1 0 flexure trend oils are similar and contain abundant extended hopanes high sulfur contents and v ni v 0 5 these oils are inferred to be sourced in upper jurassic lower cretaceous strata upper cretaceous oils contain a distinctive suite of tricyclic and nonhopanoid triterpanes oleanane is low or absent paleogene oils can be recognized by the presence of 18 h oleanane and a lack of extended hopanes these oils occur from south texas to southern and offshore louisiana two subfamilies can be recognized based on the relative abundance of triterpanes and steranes these oils have a presumed paleogene source mixing of oil types is quite prevalent at the geographic boundaries of oil types the initial control on the distribution of oil and gas in the northern gulf of mexico is provided by the areal extent of source rocks secondary control is due to cenozoic deposition which provides the thermal stress to generate as well as destroy oil salt tectonics provide conduits for migrating fluids to escape the zone of thermal destruction mesozoic source strata again become important in the deep gulf of mexico where cenozoic sediments thin

regional seismic observations of the 9 october 2006 underground nuclear explosion in north korea and the influence of crustal structure on regional phases 1 the crustally guided shear wave lg is typically the most prominent phase of a nuclear explosion at regional distance this lg phase is analyzed often to discriminate a nuclear explosion from a natural earthquake in addition the lg phase allows us to determine the size of the detonation a nuclear explosion test in north korea was conducted on 9 october 2006 the epicenter was located close to the eastern shore of the korean peninsula resulting in raypaths that vary significantly according to the azimuths in particular rays radiated in the southern direction experience lateral variation of crustal structures at the continental margin we examine the influence of raypaths on regional seismic phases by comparing the spectra and waveforms from different raypaths three natural earthquakes in north korea are also examined to determine the raypath effect we find that the lg from the nuclear explosion dissipated significantly as result of energy leakage into the mantle resulting from variations in crustal thickness along the portion of the raypath traversing the western tip of the sea of japan east sea some of the leaked energy develops into mantle lid waves sn causing a large energy increase to sn a similar feature is observed in the records of natural earthquakes this feature is confirmed by seismic waveform modeling the raypath effect also causes underestimation of magnitude the lg body wave magnitude mb lg is estimated to be 3 8 4 2 for records from pure continental paths and 2 6 3 4 for records from paths crossing continental margins this result illustrates the need to consider raypath effects for the correct estimation of magnitudes of regional events including a nuclear explosion

geometrical spreading and q of pn waves an investigative study in eastern canada abstract station site effects uncertainties in seismic source spectrum and instrument response errors are among the well known frequency dependent contaminating factors that limit the reliability of short period q measurements of regional phases for the pn wave a regional phase of importance for both magnitude determination and nuclear test ban verification the problem is made worse by the added uncertainty of its geometric spreading function for realistic earth models the pn geometric spreading function is likely to depart drastically from that expected of canonical head waves the extent of this departure is sensitively dependent upon the regional crust mantle structure making geometric spreading assumption a conspicuous source of disagreement among the published pn attenuation q pn estimates we describe a technique referred to here as the extended reversed two station method rtsm for simultaneous determination of q pn and geometrical spreading function the formulation being designed to bring about direct cancellation of the contaminating source station and instrument effects is a reliable tool for mapping the pn propagation characteristics over continental paths long and short the extended rtsm has been tested using pn spectral amplitude data derived from seismic records of the eastern canada telemetered network ectn we find the spreading rate coefficient n in the power law representation of the geometric spreading d n d being epicentral distance to be frequency dependent increasing from 1 11 at 1 hz to 1 77 at 20 hz our q pn model in eastern canada takes the form of q pn 189 f 0 87 the results from eastern canada suggest that a there exists a significant positive velocity gradient in the uppermost mantle 0 0037 sec 1 b the regionally recorded pn waves are dominated by the superposition of a series of interfering diving waves bent by the velocity gradient and internally reflected at the underside of the moho discontinuity and c the very strong frequency dependence of q pn we found in this study region may not be unique among low attenuating shield and platform regions

a geophysical and geochemical approach for seawater intrusion assessment in the acquedolci coastal aquifer northern sicily vertical electrical sounding ves surveys and chemical analyses of groundwater have been executed in the coastal plain of acquedolci northern sicily with the aim to circumscribe seawater intrusion phenomena this urbanized area is representative of a more general problem interesting most of mediterranean littoral areas where intensive overdraft favors a heavy seawater intrusion through the coastline aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region schlumberger ves together with piezometric and chemical physical information of groundwater allowed us to perform hydrogeological and geophysical elaborations to propose the occurrence of a relatively narrow belt marked by fresh salt water mixing in the considered plain pollution risk studies have been already realized by authors with the proposal to identify by parametric and synthetic zoning of significant hydrogeological elements the most vulnerable sectors in detail an intrinsic vulnerability mapping has been already performed applying the well known sintacs system this paper intends to give in this sector of sicily an example of integration of different methodologies showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better

organic geochemistry of dsdp site 467 offshore california middle miocene to lower pliocene strata abstract results of the analyses of twenty three samples from the middle miocene to lower pliocene strata from dsdp site 467 offshore california are presented the analyses were performed with the aim of determining the origin of the organic matter the stratigraphic section s hydrocarbon generation potential and extent of organic diagenesis organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments suggesting an anoxic depositional environment and elevated levels of primary productivity hydrocarbon generation potentials are above average for most samples the results of elemental analyses indicate that the kerogens are primarily composed of type ii organic matter and are thermally immature analysis of the bitumen fractions confirms that the samples are immature in cores from 541 to 614 meters the gas chromatograms of the c 15 non aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17 h 18 h 21 h 28 30 bisnorhopane this interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane phytane ratios this correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments

pathways of migration of oil and gas in the south mississippi salt basin abstract the south mississippi salt basin is one of three interior basins characterized by structures formed by movement of the late jurassic louann salt an analysis of pathways of migration within the basin has revealed that it is possible to explain why hydrocarbons have accumulated in some structures yet are absent from others that would appear to be favorable of the more than 840 fields within the basin 74 including the largest known accumulations have hydrocarbons stacked in reservoirs in more than one formation these stacked reservoirs result from vertical migration brought about by faulting more than 750 fields have hydrocarbons confined to one formation in traps associated with four distinct trends of production that decrease in age systematical iy from the margin of the basin into the interior the hydrocarbons in these trends have accumulated by intrastratal migration without the agency of faulting from a nearby source in the same unit as the reservoir on the northwest side of the basin migration between units brought into contact along unconformities has resulted in ten fields vertical migration brought about by faulting around shallow salt diapirs has allowed hydrocarbons to escape so that only 5 of 56 such structures have ever produced oil or gas these conclusions derived from geological deductions are supported by preliminary geochemical data but more extensive and detailed geochemical analyses of oils from the various sources are under way

maturity mapping of northern gulf of mexico oils using biomarkers abstract the observed maturity trends determined from 481 northern gulf of mexico oils and offshore seeps follow the major geological trends of the basin in a manner consistent with published heatflow measurements onshore the luling mexia gilbertown pickens pollard fault zones appear to act as areas of enhanced heatflow as indicated by the high maturity of nearby oils near base of oil window to the north and south of these fault lines oils of reduced maturity are encountered offshore louisiana oils of lower maturity comparable to the middle to early oil window are found the low maturity of these oils appears to be linked to salt diapirism by contrast the mature condensates offshore texas appear to link in part with shale diapirism and growth faulting analyses of oils and seepage from the flexure trend area indicates that hydrocarbon maturity is reduced towards the south where the tertiary overburden thins

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

classification of offshore gulf of mexico oils and gas condensates five groups of petroleums can be recognized in the offshore gulf of mexico on the basis of carbon isotope and sulfur isotope ratios sulfur content and relative abundances of nickel and vanadium of 355 oils analyzed 341 96 1 are evidently closely related and cannot be subdivided on the basis of carbon or sulfur isotopes we suggest that these oils represent a single broad superfamily however two subgroups within this set are distinguishable on the basis of sulfur content and relative abundances of nickel and vanadium group 1a sigma 13 c 26 5 0 4 parts per mil sigma 34 s 5 6 2 4 parts per mil s 0 25 0 15 v ni v 0 27 0 10 and group 1b sigma 13 c 26 5 0 3 parts per mil sigma 34 s 5 9 1 2 parts per mil s 0 73 0 43 v ni v 0 67 0 07 group 1a oils are broadly distributed across the louisiana and adjacent texas continental shelf whereas group 1b oils are found along the louisiana shelf edge and continental slope group 1b oils have substantial genetic affinities to those from the campeche shelf offshore mexico of mesozoic origin the remaining 14 analyzed petroleums include supermature condensates from offshore texas and oils from offshore southern florida believed to be cogenetic with those from the jurassic smackover formation a three dimensional appraisal of geohistory suggests that petroleum generation began in the eocene in the region of the rio grande delta progressed coastwise to the mississippi delta area by the miocene and then occurred in regions of progres ively deeper water during the pliocene pleistocene

intrinsic vulnerability assessment of saturnia thermal aquifer by means of three parametric methods sintacs gods and cop three different parametric methods for the evaluation of intrinsic vulnerability to pollution have been applied in a hydrothermal carbonate aquifer located in central northern italy and the results obtained were compared with each other the study area large approximately 152 km2 lies in an area of the northern apennines the investigated aquifer feeds the hot thermal springs of saturnia the vulnerability assessment methods used are sintacs gods and cop the vulnerability maps obtained were first individually examined and then they were compared with each other by means of spatial analysis these maps show similar results for the estimation of the vulnerability just in some areas sintacs yields areas potentially vulnerable to pollution along the albegna river and its major tributaries in the northern part of the study area the gods index map reflects the great importance that this method gives to the lithological characteristics of the unsaturated zone in the subdivision of areas with different vulnerability gods and cop methods agree in classifying low vulnerability in the most part of central southern study area where the aquifer is confined by the pliocene clay deposits based on the conceptual model of groundwater flow developed for the aquifer under investigation cop seems the most appropriate method among those applied in this work in particular with regard to the assessment of the vulnerability of the recharge area of thermal groundwater located in the northern part of the study area where karst carbonate formations of the tuscan nappe outcrop this recharge area is classified by the cop method as highly vulnerable to pollution

lateral variations of crustal seismic attenuation along the indepth profiles in tibet from lg q inversion 1 fourier spectra of crustal guided lg waves are collected to study seismic attenuation or q along the indepth profiles the 1 hz lg q q0 values are measured between many pairs of two stations and input to a back projection algorithm to obtain laterally varying q0 models along the indepth iii profile in central tibet the q0 model consists of low and nearly constant values of 90 these low values are consistent with abnormally high temperature as well as partial melts in the crust along the indepth ii profile in southern tibet the q0 values increase southward they are extremely low 60 over the northernmost segment but increase by a factor of 2 over a distance of 100 km between the indus yalong suture and the kangmar dome farther south and into the high himalayas q0 values are higher than 300 regional rayleigh waves observed along the northern indepth ii profile are used to infer a low velocity low q layer at midcrustal depths between 15 and 30 km in southern tibet the aqueous fluid trapped in the upper crust and a midcrust partial melting zone associated with the underthrusting of the indian lithosphere are the likely causes of the high lg attenuation in southern tibet low q rather then a systematic lg conversion along a dipping moho is the main cause of the previously observed lg blockage over paths crossing the southern tibetan boundary

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

yield estimation of the 25 may 2009 north korean nuclear explosion we collect nine vertical component broadband seismograms from the 25 may 2009 north korean nuclear explosion for a regional seismic network in which eight stations also recorded the 9 october 2006 north korean nuclear test comparing the observed waveforms and spectra from the two events we estimate that the amplitudes of the records from the second event are approximately five times those from the first one additionally we use 599 vertical broadband seismograms from 82 regional events recorded on the regional network between december 1995 and may 2009 to calibrate the network lg wave magnitude the calibrated network is used to calculate the lg wave body wave magnitude m b lg 4 53 for the 25 may 2009 north korean nuclear explosion based upon 15 first arrivals from the two north korea nuclear explosions the regional pn velocity in the northeast china north korea region is calculated to be 8 0 km s this result along with the regional geological structures suggests that the north korean test site nkts is located at a relatively stable continental region we thus use a modified fully coupled magnitude yield relation to estimate the explosion yield and the result shows that the yield of the 25 may 2009 north korean nuclear test is approximately 2 35 kt under the minimum burial depth assumption online material epicentral parameters computed m b lg and corrected m b lg for 82 events used in the study

shallow magma chamber under the wudalianchi volcanic field unveiled by seismic imaging with dense array the wudalianchi volcano field wdf is a typical intraplate volcano in northeast china with generation mechanism not yet well understood as its last eruption was around 300 years ago the present risk for volcano eruption is of particular public interest we have carried out a high resolution ambient noise tomography to investigate the location of magma chambers beneath the volcanic cones with a dense seismic array of 43 seismometers and 6 km spatial interval significant low velocity anomalies up to 10 are found at 7 13 km depth under the weishan volcano consistent with the pronounced high electrical conductivity anomalies from previous magnetotelluric survey we propose these extremely low velocity anomalies can be interpreted as partial melting in a shallow magma chamber with volume at least 200 km3 which may be responsible for most of the recent volcanic eruptions in wdf therefore this magma chamber may pose a serious hazard for northeast china

lateral variation of pn and lg attenuation at the cdsn station lsa abstract the propagation efficiencies of the regional phases lg and pn are indicative of how active and recent tectonics influence crust and uppermost mantle properties respectively in this study regional scale lateral heterogeneity of lg and pn attenuation for the region in and around the southern tibetan plateau is investigated the data set is comprised of seismograms recorded at the chinese digital seismogram network cdsn station lsa from regional events with epicentral distances within 11 attenuation of lg and pn is calculated using spectral methods and assuming constant q lg and q pn models for the frequency bands 0 3 to 3 0 hz and 0 5 to 4 0 hz respectively lateral variation in attenuation is estimated by analyzing data on an event by event basis significant lateral variation is observed with q lg decreasing from about 520 for events south of lsa to about 340 for events north of lsa and q pn 670 for southern backazimuths while q pn 240 for northern events for pn this north south variation is consistent with other observations indicating partially melted upper mantle beneath north central tibet for lg the azimuthal variation in attenuation indicates that lg propagation as observed at lsa is efficient for paths crossing the southern boundary of the tibetan plateau relative to paths within the plateau itself

seismic structure and origin of active intraplate volcanoes in northeast asia abstract three dimensional p wave velocity structure beneath the changbai and other intraplate volcanic areas in northeast asia is determined by inverting 1378 high quality p wave arrival times from 186 teleseismic events recorded by 61 broadband seismic stations low velocity low v anomalies are revealed beneath the changbai longgan xianjindao volcanoes high velocity high v anomalies are found in the mantle transition zone where deep focus earthquakes under hunchun occur at depths of 500 600 km the high v anomaly reflects the deep subduction of the pacific slab under ne asia which may have contributed to the formation of the changbai longgang xianjindao and jingpohu intraplate volcanoes a low v anomaly is also revealed in the mantle transition zone which may have a close relationship with the occurrence of deep earthquakes under the hunchun area our results support the big mantle wedge bmw model by zhao et al zhao d lei j tang y 2004 origin of the changbai volcano in northeast china evidence from seismic tomography chin sci bull 49 1401 1408 zhao d maruyama s omori s 2007 mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics gondwana res 11 120 131 who proposed that the intraplate volcanoes in ne asia are caused by the back arc magmatism associated with the deep dehydration process of the subducting slab and convective circulation process in the bmw above the stagnant pacific slab

weathering of hydrocarbons in mangrove sediments testing the effects of using dispersants to treat oil spills abstract this field study was a combined chemical and biological investigation of the relative effects of using dispersants to treat oil spills impacting mangrove habitats the aim of the chemistry was to determine whether dispersant affected the short or long term composition of a medium range crude oil gippsland stranded in a tropical mangrove environment in queensland australia sediment cores from three replicate plots of each treatment oil only and oil plus dispersant were analyzed for total hydrocarbons and for individual molecular markers alkanes aromatics triterpanes and steranes sediments were collected at 2 days then 1 7 13 and 22 months post spill over this time oil in the six treated plots decreased exponentially from 36 6 16 5 to 1 2 0 8 mg g dry wt there was no statistical difference in initial oil concentrations penetration of oil to depth or in the rates of oil dissipation between oiled or dispersed oil plots at 13 months alkanes were 50 degraded aromatics were 30 degraded based upon ratios of labile to resistant markers however there was no change in the triterpane or sterane biomarker signatures of the retained oil this is of general forensic interest for pollution events the predominant removal processes were evaporation 27 and dissolution 56 with a lag phase of 1 month before the start of significant microbial degradation 17 the most resistant fraction of the oil that remained after 7 months the higher molecular weight hydrocarbons correlated with the initial total organic carbon content of the soil removal rate in the queensland mangroves was significantly faster than that observed in the caribbean and was related to tidal flushing

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

pn attenuation for a spherically symmetric earth model this paper presents the results of a theoretical study of the sensitivity of pn attenuation to the elastic and anelastic structure of the uppermost mantle for frequencies between 1 and 15 hz and distances between 200 and 1000 km synthetic seismograms are computed using wavenumber integration for an elastic model consisting of a crastal layer over an upper mantle with a slight linear velocity gradient approximately equal to the earth flattening transformation of a spherically symmetric homogeneous upper mantle these are compared to synthetic seismograms for a crustal layer over a mantle halfspace pure elastic head wave we find that earth sphericity alone causes a significant departure in pn attenuation from that of a canonical head wave almost two orders of magnitude at 1000 km and 15 hz and that high frequencies attenuate less rapidly than low frequencies if the spherical earth velocity gradient is greater than or equal to zero this implies that methods that assume frequency independent pn geometric spreading will produce biased estimates of the anelasticity of the upper mantle this is demonstrated using synthetic seismograms computed for an anelastic spherical earth model these results show that the velocity structure must be carefully considered when relating observed pn spectral amplitudes to the anelastic structure of the upper mantle

upper jurassic depositional systems and hydrocarbon potential of southeast mississippi abstract upper jurassic sedimentation in southeast mississippi was controlled by eustatic sea level fluctuations and locally modified by salt tectonism and basement structure the present study using conventional core data and geophysical logs indicates that a stable carbonate platform developed along the updip margin of the mississippi interior salt basin the basin was partially barred from the main gulf of mexico water mass by the wiggins uplift and became evaporitic during the upper jurassic the smackover and haynesville formations are separate sedimentologic packages deposited during two distinct sea level cycles high energy carbonates extended across the northern basin margin as sedimentation kept pace with subsidence and slowing sea level rise near the close of each transgression an effective shelf margin barrier did not develop lime mud generally accumulated under subtidal conditions within the interior salt basin however the basin was sufficiently shallow for wavebase sedimentation to occur on crests of salt cored bathymetric highs resulting in localized reservoir facies to the south eolian conditions initially prevailed on the wiggins uplift later as the wiggins subsided subaqueous shoals fringed and capped individual basement islands eustatic sea level fluctuations and salt movement controlled diagenesis and porosity formation limestone porosity dominates in upper smackover platform carbonates with a transition from secondary moldic porosity updip to preserved primary porosity downdip moldic intercrystalline and vuggy dolomite porosity is developed on the crests of intermediate and high amplitude salt highs and on the wiggins uplift jurassic source rocks are lower smackover laminated lime mudstones migration into adjacent reservoirs postdated formation of porosity and the growth of salt anticlines the most common trap type a large potential norphlet smackover gas play extends along the southern flank of the wiggins uplift salt anticlines within the interior basin remain viable targets small oil discoveries should continue in stratigraphic traps subtle salt structures and basement blocks on the platform

sterane and triterpane patterns as diagnostic tools in the mapping of oils condensates and source rocks of the gulf of mexico region abstract four hundred and eighty one gulf of mexico oils and condensates can be subdivided into nine major families based on their sterane m z 217 218 and triterpane m z 191 177 biomarker mass chromatogram patterns these families are 1 carbonate sourced oils reservoired in jurassic cretaceous reservoirs onshore and plio pleistocene reservoirs offshore 2 austin chalk reservoired oils 3 tuscaloosa oils 4 wilcox reservoired oils la 5 south texas palaeogene reservoired oils 6 mississippi delta oils 7 post mature oils of uncertain affinities 8 migration contaminated oils showing attributes of a mixing of immature and post mature sources and 9 oils and condensates lacking biomarkers each oil family is concentrated in specific age defined producing trends ranging in age from jurassic to pleistocene for tertiary reservoirs these producing trends shift geographically with time in a manner analogous to the clockwise migrating cenozoic depocenter model for the northern gulf of mexico at least six ages of marine source rock deposition may be implicated in the genesis of these oils 1 the kimmeridgian oxfordian including smackover and norphlet formations 2 the aptian including pine island bexar and sunniland formations 3 the albian paluxy formation 4 the cenomanian turonian including eagle ford and tuscaloosa formations 5 the coniacian santonian eagle ford and austin chalk and 6 the palaeocene wilcox midway sparta formations the jurassic and cretaceous source rocks correspond to described oceanic anoxic events of probable global significance this paper will concentrate on describing the biomarker patterns of the oils and postulated source rocks but due to reasons of space isotopic elemental and other data will only be briefly discussed

distribution of hydrocarbon source potential in the jurassic smackover formation abstract there are regionally consistent differences in source potential between the upper and lower members of the smackover formation measurements of total organic carbon and visual kerogen assessments indicate that the lower smackover has source potential for crude oil from texas to florida source potential is largely restricted to the laminated lime mudstone facies of the lower smackover where deposition occurred in a subtidal environment that was anoxic and probably hypersaline algal derived amorphous kerogen is concentrated in laminations of depositional origin carbonate diagenesis during burial enhanced source potential by further concentrating kerogen along stylolites we suggest that the efficiency of hydrocarbon expulsion has been enhanced by depositional and diagenetic factors that concentrate source rock kerogen along conduits for fluid movement the upper smackover serves mainly as a reservoir rock and other jurassic formations lack source potential

advanced seismic analyses of the source characteristics of the 2006 and 2009 north korean nuclear tests in 2006 and 2009 north korea conducted underground nuclear tests at a remote mountainous site in the northeastern part of the country both events were small leading to uncertainties for location yield estimation and discrimination based on seismic observations the objectives of the studies described in this paper have been to more fully exploit data from the international monitoring system ims network and other unclassified sources e g incorporated research institutions for seismology iris japanese national research institute for earth science and disaster prevention nied to analyze these nuclear tests we have used differential waveform interferometry dwif to refine relative locations for the tests and extended the methodology using observations from regional stations to estimate relative emplacement depths which are consistent with explosion source model predictions for broadband regional p wave spectral ratios topographic data from the test site were analyzed to constrain relative locations and depths needed for containment of the two tests based on normal testing practice network averaged teleseismic p wave spectra were inverted using a model based approach and provide explosion yield estimates in the range 0 6 1 0 kt for the 2006 test and 2 0 4 8 kt for the 2009 test depending on assumed emplacement depth detailed spectral analysis of broadband regional p observations are most consistent with theoretical explosion models with yields of 0 9 and 4 6 kt for the 2006 and 2009 tests respectively with associated source depths of 200 and 550 m consistent with previous studies the surface wave m s magnitudes for the 2006 and 2009 tests provide anomalously large m s yield estimates and problematic m s m b identification characteristics finite difference simulations of long period surface wave signals incorporating tensile prestress consistent with the regional tectonics lead to predicted m s values that agree much better with the observed values

upper mantle velocity structure beneath the tibetan plateau from pn travel time tomography we inverted 1510 p arrival times from regional distances 333 1600 km in and around the tibetan plateau to map the lateral velocity variation within the uppermost mantle previous studies have placed first order constraints on upper mantle velocities but relied on data recorded almost exclusively at stations outside of the plateau we improve resolution by using 40 events recorded at stations within the tibetan plateau we combine these data with observations obtained from the international seismological centre isc to extend our coverage by including pn arrivals from 85 additional plateau events relocated in previous studies and recorded at stations in and around the tibetan plateau we use synthetic travel time data to evaluate the resolution of our data set the observations provide good resolution to about 1 over most of the plateau and surrounding regions our results show average pn velocities that are about 3 lower in the northern plateau relative to the southern plateau these variations correlate well with major tectonic features and previous geophysical observations in the qiangtang terrane of the northern plateau an area known to be inefficient for sn propagation pn is slow relative to both the plateau south of the banggong nujiang suture and the tectonically stable tarim basin north of the plateau this is strong evidence for the existence of partial melt within the uppermost mantle beneath the northern tibetan plateau however when laboratory estimates of relationships between temperature velocity and attenuation are applied a relatively small temperature variation 240 to 370 c is required to explain our pn velocity observations when combined with geochemical constraints from volcanics in the northern plateau our results strongly suggest that the mantle lid is intact beneath the northern plateau this result would preclude tectonic models involving wholesale delamination of the mantle lithosphere in the northern tibetan plateau

effects of laterally varying mantle lid velocity gradient and crustal thickness on pn geometric spreading with application to the north korean test site abstract the pn phase for crustal earthquakes refracts through the uppermost mantle to become the first seismic wave arrival at distances of 200 to 1500 km the amplitude of pn is particularly sensitive to the mantle lid radial velocity gradient and the elastic geometric spreading is frequency dependent lateral variations in the radial velocity gradient and in the crustal thickness encountered by pn phases that traverse boundaries of geological provinces further complicate the frequency dependent geometric spreading behavior we use 2d finite difference fd calculations to explore the effects of smoothly varying lateral structures in the lid and crust on pn phases in the 0 4 10 hz frequency range pn geometric spreading for 1d structures with mantle lid gradients is calculated first to ensure that the fd calculations correctly capture the expected frequency dependence then 2d models with smooth laterally varying radial lid gradients are computed to explore how the phase samples the structures to give the overall geometric spreading the direction of propagation through the laterally varying structure affects the frequency dependence and the transition from source side to receiver side dominance in the spreading laterally varying crustal thickness is explored in the context of the north korean nuclear test site for which many observations of pn are made by stations with paths either through continental structure or along paths with variation from continental to oceanic to arc structure in japan frequency dependent amplitude effects are observed on the paths through oceanic structure 2d fd calculations for structures with a central region of thin oceanic crust reproduce the observed first order frequency dependence of pn along corresponding paths including rapid amplitude decay for frequencies above 6 hz these analyses demonstrate that even though pn propagation is very complex modeling approaches can guide interpretations of the behavior when constraints on the structure are available electronic supplement figures of pn wave snapshots first pn arrival times and frequency dependence of the pn amplitudes

the framework of hydrocarbon generation and migration gulf of mexico continental slope abstract the occurrence of large volumes of crude oil and thermogenic gas in plio pleistocene reservoirs and holocene seeps of the gulf of mexico slope argues that the process of hydrocarbon generation and migration continues at the present time calculated thermal maturity models based on deep seismic stratigraphy indicate that cretaceous and possibly early tertiary sediments are presently within the thermal maturity range for generation and expulsion of crude oil the cretaceous and early tertiary sediments are suggested as possible source rocks because younger sediments are thermally immature for crude oil generation and older sediments are thermally overmature for crude oil preservation the calculated thermal maturity profile for the slope indicates that some generation of crude oil could occur as shallow as 6 km and that liquid hydrocarbons could be preserved as deep as 9 km thermogenic gas is stable at even greater depths migration with a strong vertical component must be invoked to explain thermogenic hydrocarbons in shallow reservoirs and seeps of the slope the great depth at which liquid hydrocarbons and dry gas can be preserved in reservoirs of the gulf of mexico salt basin indicates that huge volumes of prospective section remain essentially unexplored

pn attenuation beneath the tibetan plateau abstract pn spectra are collected from three passcal seismic experiments in the tibetan plateau tp over four path groups to study pn attenuation the first and second path groups run southward from the lop nor test site lts to stations in north and south central tibet the third and fourth path groups form two north northeast oriented profiles in the eastern tp events recorded by the first two path groups are also recorded over central asian paths running westerly from the lts to the khyrghistan network knet a comparison of pn spectra from these events reveals that the mantle lid under the north central tp attenuates pn more severely than the lid under central asia apparent q 0 and pn q at 1 hz and its frequency dependence are estimated with a simplified geometrical spreading gst of 1 3 over path group 1 that heavily samples the northern tp q 0 and are estimated to be 183 33 and 0 3 0 1 respectively over path groups 2 and 3 that sample either a mixture of northern and southern tibet or eastern tibet q 0 and are between about 250 270 and 0 0 0 1 respectively over the fourth path group that samples the easternmost tp the respective estimates are 374 51 and 0 3 0 1 respectively similar to the estimates of 364 and 0 5 for central asian paths from lts to knet a comparison of the total pn attenuations that include the effects of both gst and q in continental regions shows that they are similar in relatively stable regions of central asia scandinavia and the canadian shield within the tp pn attenuation is the highest under north central tibet and decreases toward the south and east in easternmost tibet pn attenuation becomes similar to that in stable regions lateral variation of pn attenuation inversely correlates with that of the pn velocity possible causes of this variation include 1 a thermally driven mantle q p and 2 region specific velocity structures which may be characterized by different lid gradients and density and aspect ratios of 3d scatterers in the vicinity of the moho

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico ii structure the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope

geochemical studies of crude oil generation migration and destruction in the mississippi salt basin abstract the main source for crude oil in the mississippi salt basin is the laminated lime mudstone facies of the lower smackover crude oil generation and migration commenced at a level of thermal maturity equivalent to about 0 55 vitrinite reflectance short range lateral migration of crude oil was focused to upper smackover and norphlet reservoirs but vertical migration also charged some overlying cotton valley rodessa lower tuscaloosa and eutaw reservoirs following migration from the lower smackover thermal maturity history of reservoir rocks controls the preservation of crude oil gas condensate and methane slow thermal cracking of crude oil occurred in deep upper smackover reservoirs resulting in formation of gas condensate and precipitation of solid bitumen the maximum thermal maturity for preservation of condensate is equivalent to about 1 3 vitrinite reflectance only methane pyrobitumen and nonhydrocarbon gases including hydrogen sulfide persist at higher levels of thermal maturity early destruction of methane in deep upper smackover reservoirs near the wiggins arch is driven by thermochemical sulfate reduction lesser availability of sulfate in norphlet reservoirs in lower mobile bay could account for methane preservation at higher levels of thermal maturity one basic geochemical strategy for further exploration of the mississippi salt basin is to focus exploration effort on traps with reservoirs in the thermal maturity window for hydrocarbon preservation another strategy is to avoid drilling traps with overmature reservoir rocks

fluorescent microscopy of particulate organic matter sparta formation and wilcox group south central louisiana abstract particulate organic matter pom isolated from core samples of mudstones in the mid eocene sparta formation and the late paleocene early eocene wilcox group in louisiana was characterized using transmitted and fluorescent light microscopy and rock eval pyrolysis observations of maceral fluorescence combined with programmed pyrolysis results better define source potential than visual examination using transmitted white light alone transmitted light microscopic characterization of pom indicates that amorphous macerals of mixed terrestrial and marine origin dominate samples from both the lagoonal and shelf depositional environments microscopic examination under fluorescent light indicates that some of the amorphous matter including terrestrially derived material fluoresces to some degree hydrogen index values show a positive correlation with the total number of fluorescing particles in the isolate as well as with the relative fluorescence levels comparison of sparta and wilcox samples indicates that significant changes occur in the assemblages at levels of thermal maturation associated with the onset of petroleum generation thermally mature samples contain a higher percentage of moderately fluorescent particles and lesser percentages of highly and weakly fluorescent particles this phenomenon is readily apparent in specific particle types namely amorphous nonstructured protistoclasts miospores and dinoflagellate cysts

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

observations of frequency dependent sn propagation in northern tibet summary we present new observations of the frequency dependent propagation efficiency of the seismic phase sn over the tibetan plateau our measurements are the ratio of the sn amplitude to the pg coda amplitude on tibetan regional seismograms and we map the lateral variation in the maximum and mean values of this ratio across the plateau good path density and azimuthal coverage allow the area of sn blockage identified by previous studies to be better constrained an important result is that at low frequencies 0 2 hz sn propagates efficiently over the entire plateau whereas at higher frequencies 1h z sn is blocked for a region of the northern plateau as we take measurements at higher frequencies we find that the southern boundary of the region of inefficient propagation migrates to the south the observation that low frequency sn propagates efficiently across the whole plateau suggests that at the length scales sampled by these waves the upper mantle has an overall positive shear velocity gradient which could indicate that the high velocity seismic lid or seismic lithosphere beneath tibet is still intact and has not delaminated as some researchers have previously proposed the observation that high frequency sn does not propagate beneath northern tibet suggests that at the shorter length scales sampled by the higher frequency waves the upper mantle has a negative shear velocity gradient this could indicate that at shallow depths the sub moho upper mantle is hot and may contain some melt

prediction of source rock characteristics based on terpane biomarkers in crude oils a multivariate statistical approach abstract the distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous rq mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments five categories of source rocks are evident nearshore marine i e paralic deltaic deeper water marine lacustrine phosphaticrich source beds and ordovician age source rocks the first two factors of the rq mode factor analysis describe 45 percent of the variation in the data set the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples lacustrine oils are characterized by greater relative abundances of c 21 diterpane and gammacerane nearshore marine sources by c 19 and c 20 diterpanes and oleanane deeper water marine facies by c 24 and c 25 tricyclic and c 31 plus c 32 extended hopanes and ordovician age oils by c 27 and c 29 pentacyclic terpanes although thermal maturity trends can be observed in factor space the trends do not necessarily obscure the source rock interpretations also since bacterial degradation of crude oils rarely affects tricyclic terpanes biodegraded oils can be used in predicting source rock features the precision to which source rock depositional environments are determined might be increased with the addition of other biomarker e g steranes and stable isotope data using multivariate statistical techniques

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

comparison of aquifer vulnerability assessment techniques application to the neblon river basin belgium five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared the test area was a slightly karstified district in the condroz region of belgium the basin covers about 65 km2 and the karst aquifer provides a water supply of about 28 000 m3d 1 the methods tested were epik doerfliger et al 1999 drastic aller et al 1987 german method von hoyer and sofner 1998 god foster 1987 and isis civita and de regibus 1995 the results are compared and critically examined from the analysis it seems that reducing the number of parameters is unsatisfactory due to the variety of geological conditions the various methods produce very different results at any given site as only physically based methods can be checked for their reliability it is clear that future vulnerability mapping techniques must incorporate such methods

effects of 2d random velocity heterogeneities in the mantle lid and moho topography on pn geometric spreading pn wave energy refracts through the uppermost mantle with the first seismic wave arrival at distances of 200 to 1500 km from crustal sources the pn phase provides important constraints on source type location and magnitude but its propagation is complicated by frequency dependent sensitivity to the earth s sphericity and lithospheric velocity structure converging on an acceptable pn geometric spreading correction and specifying its uncertainties a requirement for accurately determining frequency dependent attenuation models for pn depends on improved understanding of the behavior of pn geometric spreading for various heterogeneous models we investigate the effects of radial mantle lid velocity gradi ents mantle lid random volumetric velocity heterogeneities and moho topography on pn geometric spreading using reflectivity and two dimensional 2d finite difference 1 hz wave propagation calculations for elastic earth models mantle lid velocity gra dients systematically modify the frequency dependent geometric spreading from that found for models with constant velocity but retain the same overall functional form pn amplitudes are also sensitive to the presence of modest 2d random lateral velocity heterogeneities within the uppermost mantle with geometric spreading approaching a power law behavior as the root mean square strength of heterogeneity increases 2d moho topography introduces scatter into the amplitude of pn but the overall behavior remains compatible with that for a laterally homogeneous model given the lack of knowledge of specific small scale structure for any particular pn path the preferred geometric spreading parameterization is the frequency dependent model for a constant mantle lid velocity structure unless pn travel time branch curvature can constrain the radial gradient in the mantle lid

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

intricate heterogeneous structures of the top 300 km of the earth s inner core inferred from global array data ii frequency dependence of inner core attenuation and its implication abstract we apply a nonlinear waveform inversion method that we developed previously iritani et al 2010 iritani et al 2014 to broadband 0 02 2 hz core phase data recorded by global seismic arrays in order to investigate the frequency dependence of inner core attenuation the results show a prominent difference of the frequency dependence of attenuation between the eastern hemisphere and the western hemisphere while attenuation is frequency dependent in the western hemisphere not so in the eastern hemisphere moreover in the western hemisphere a stronger frequency dependence of the attenuation is observed beneath africa compared to beneath north america this intricate quasi hemispherical property of the frequency dependence of the inner core attenuation together with the quasi hemispherical variability of seismic velocity and attenuation strength at around 1 hz that we reported earlier can be consistently understood in terms of the relative location of the seismic observation frequency band and the absorption band peaks that are different for regions the variability of the absorption band peak may reflect the variability of the iron grain size of the inner core the grain size is larger in the eastern hemisphere than the western hemisphere and in the western hemisphere beneath north america it gradually increases with depth however caution should be taken in this inference as the physical mechanism of attenuation in the inner core is still poorly constrained both theoretically and observationally

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

application of very fast simulated annealing to the determination of the crustal structure beneath tibet summary the simulated annealing method has recently been applied to several multiparameter optimization problems including those of geophysical inversion a new variant of simulated annealing called very fast simulated annealing vfsa overcomes some of the drawbacks of a conventional simulated annealing it has been found to be a practical tool for geophysical inversion sen stoffa 1995 the method is particularly useful for non linear problems with multiple parameters where a grid search method is prohibitively expensive here we have applied vfsa to retrieve the crustal structure beneath seismic stations in tibet using teleseismic body waveform data our approach is to compare the radial component records with generalized ray synthetics directly in the time domain for any given crustal structure we have formulated a direct relationship between the radial and the vertical component signal so that we can generate synthetic radial component data from recorded vertical component seismograms zhao frohlich 1996 we have tested the vfsa inversion algorithm using synthetics and confirmed that it works very well i e it finds solutions very close to the true solution using the algorithm we have determined the crustal structures beneath 11 stations in tibet from south to north the total crustal thickness is quite uniform our tectonic interpretation of these crustal models is that they may represent crust from the eurasian plate injected beneath the crust of the converging indian plate certain features of the models are consistent with the presence of a small convection cell or plume beneath north central tibet as suggested by molnar 1990

origin of crude oil in the wilcox trend of louisiana and mississippi evidence of long range migration abstract geochemical characterization of crude oils from wilcox reservoirs in central louisiana and southwest mississippi suggests that they represent a single crude oil family that is distinct when compared to crude oils in deeper tuscaloosa and smackover reservoirs this observation is consistent with geologic constraints that suggest an origin of crude oil from within the wilcox group itself although shales of the shallow wilcox group in central louisiana and southwest mississippi contain gas prone kerogen and are thermally immature a more oil prone source facies is present in marine shales of the deep wilcox group in southcentral louisiana thermal maturity measurements based on pyrolysis suggest a broad area of effective wilcox source rock in southcentral louisiana migration distances from source to reservoir rocks of the downdip wilcox trend of southcentral louisiana appear to be relatively short however long range updip migration sometimes greater than 100 km from deeply buried wilcox source facies provides the best explanation for emplacement of crude oil in the shallow wilcox trend of central louisiana and southwest mississippi

numerical modelling of groundwater vulnerability the example namibia the unsat h help3 and macro4 3 computer codes which have been developed for simulating the water balance of the unsaturated zone of soils and unconsolidated sediments are also capable simulating water flow in low porosity media such as fractured rock the codes can be used to model the ability of rocks and overlying soils in the vadose zone to protect the groundwater in the uppermost aquifer the net infiltration rates simulated by the different codes are compared against recharge determined by the chloride balance method in namibia the dual permeability code macro4 3 was found to produce more realistic estimates of net infiltration than the unsat h and help3 codes which are based on a single permeability or effective continuum method the net infiltration rate together with the water storage in the unsaturated zone and the groundwater depth are used to calculate the residence time of pore water in the unsaturated zone this parameter determines the intrinsic vulnerability of the aquifer

amplitude corrections for regional seismic discriminants a fundamental problem associated with event identification lies in deriving corrections that remove path and earthquake source effects on regional phase amplitudes used to construct discriminants our goal is to derive a set of physically based corrections that are independent of magnitude and distance and amenable to multivariate discrimination by extending the technique described in taylor and hartse 1998 for a given station and source region a number of well recorded earthquakes is used to estimate source and path corrections the source model assumes a simple brune 1970 earthquake source that has been extended to handle non constant stress drop the discrimination power in using corrected amplitudes lies in the assumption that the earthquake model will provide a poor fit to the signals from an explosion the propagation model consists of a frequency independent geometrical spreading and frequency dependent power law q a grid search is performed simultaneously at each station for all recorded regional phases over stress drop geometrical spreading and frequency dependent q to find a suite of good fitting models that remove the dependence on m b and distance seismic moments can either be set to pre determined values or estimated through inversion and are tied to m b through two additional coefficients we also solve for frequency dependent site phase excitation terms once a set of corrections is derived effects of source scaling and distance as a function of frequency are applied to amplitudes from new events prior to forming discrimination ratios thus all the corrections are tied to just m b or m 0 and distance and can be applied very rapidly in an operational setting moreover phase amplitude residuals as a function of frequency can be spatially interpolated e g using kriging and used to construct a correction surface for each phase and frequency the spatial corrections from the correction surfaces can then be applied to the corrected amplitudes based only on the event location the correction parameters and correction surfaces can be developed offline and entered into an online database for pipeline processing providing multivariate normal corrected amplitudes for event identification examples are shown using events from western china recorded at the station makz

propagation of regional seismic phases lg and sn and pn velocity structure along the africa iberia plate boundary zone tectonic implications we used over 1000 regional waveforms recorded by 60 seismic stations located in northwest africa and iberia to map the efficiency of l g and sn wave propagation beneath the gulf of cadiz alboran sea and bounding betic rif and atlas mountain belts crustal attenuation is inferred from the tomographic inversion of l g pg amplitude ratios upper mantle attenuation is inferred from maps of sn propagation efficiency derived by inversion of well defined qualitative efficiency assignments based on waveform characteristics regions of l g attenuation correlate well with areas of thinned continental or oceanic crust significant sedimentary basins and lateral crustal variations comparison of the sn efficiency results with velocities obtained from an anisotropic pn traveltime inversion shows a fairly good correlation between regions of poor sn efficiency and low pn velocity a low pn velocity 7 6 7 8 km s 1 and significant sn attenuation in the uppermost mantle is imaged beneath the betics in southern spain in sharp contrast to the relatively normal pn velocity 8 0 8 1 km s 1 and efficient sn imaged beneath the alboran sea slow pn velocity anomalies are also imaged beneath the rif and middle atlas in morocco we do not identify any conclusive evidence of lithospheric scale upper mantle attenuation beneath the rif although the crust in the gibraltar region appears highly attenuating making observations at stations in this region ambiguous paths crossing the gulf of cadiz eastern atlantic and the moroccan and iberian mesetas show very efficient sn propagation and are imaged with high pn velocities 8 1 8 2 km s 1 the spatial distribution of attenuation and velocity anomalies lead us to conclude that some recovery of the mantle lid beneath the alboran sea must have occurred since the early miocene episode of extension and volcanism we interpret the low velocity and attenuating regions beneath the betics and possibly the rif as indicating the presence of partial melt in the uppermost mantle which may be underlain by faster less attenuating mantle in the light of observations from other geophysical and geological studies the presence of melt at the base of the betic crust may be an indication that delamination of continental lithosphere has played a role in the neogene evolution of the alboran sea region

frequency dependent attenuation in eastern kazakhstan and implications for seismic detection thresholds in the soviet union abstract the frequency dependent attenuation of regional seismic phases recorded by three stations near the nuclear explosion test site in eastern kazakhstan is estimated by inverting spectra from 21 events with magnitudes between 2 3 and 4 6 at distances between 200 and 1300 km the pn spectra are inverted between 1 and 10 hz and the lg spectra are inverted between 0 5 and 2 5 hz the motivation for this study is that previous estimates of detection capability in the soviet union are based on data recorded in other regions eastern north america and scandinavia and therefore have large uncertainty the data recently recorded in eastern kazakhstan provide an excellent opportunity to compare regional wave propagation and noise characteristics at these sites to conditions assumed in previous detection capability simulations it is found that attenuation in eastern kazakhstan is not much different from attenuation in scandinavia but it is greater than attenuation in eastern north america this implies that estimates of detection thresholds that assume attenuation like that observed in eastern north america will be lower than estimates of detection thresholds that assume attenuation like that observed in eastern kazakhstan or scandinavia however it is not known how well data recorded in eastern kazakhstan represent conditions in other areas of the soviet union

p wave tomography and origin of the changbai intraplate volcano in northeast asia abstract we present the first seismic image of the upper mantle beneath the active intraplate changbai volcano in northeast asia determined by teleseismic travel time tomography the data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations our results show a columnar low velocity anomaly extending to 400 km depth with a p wave velocity reduction of up to 3 high velocity anomalies are visible in the mantle transition zone and deep focus earthquakes occur at depths of 500 600 km under the region suggesting that the subducting pacific slab is stagnant in the transition zone as imaged clearly by global tomography these results suggest that the intraplate changbai volcano is not a hotspot like hawaii but a kind of back arc volcano related to the deep subduction and stagnancy of the pacific slab under northeast asia

crustal flow pattern beneath the tibetan plateau constrained by regional lg wave q tomography abstract as a prominent geophysical anomaly unusually high seismic wave attenuation is observed in the crust and upper mantle of the tibetan plateau particularly along its northern area theoretical and laboratory investigations show that the strong seismic attenuation can indicate high temperatures and partial melting which may decrease the viscosity of the material and cause it to flow thus seismic attenuation distribution may provide useful constraints to the crust flows if they exist using lg wave q tomography we construct a 0 05 10 0 hz broadband high resolution crust attenuation model for the tibetan plateau and its surrounding regions the maximum spatial resolution is approximately 1 0 1 0 in well covered areas and for frequencies between 0 05 and 1 5 hz this attenuation model reveals an apparent low qlg belt stretching along the northern and eastern tibetan plateau combining the lg wave q model with other geophysical data two possible crust flow channels are found in the tibetan plateau the main flow channel is from north to east and then turns to southeastern tibet along the western edge of the rigid sichuan basin while a second channel starts from southern tibet and crosses the eastern himalayan syntaxis

bulk and position specific isotope geochemistry of natural gases from the late cretaceous eagle ford shale south texas abstract a dataset of bulk and position specific isotope compositions of shale gases from the late cretaceous eagle ford shale south texas is reported the chemical and bulk isotopic compositions of the seven samples in this study and those available from the literature show that across the play produced natural gas from the eagle ford shale preserves a wide range of gas compositions wetness 5 to 90 and 13c values of c1 c3 the depth profiles of the isotopic compositions suggest that the western region of the eagle ford shale deposit had experienced as much as 700 800 m of uplift erosion or gas migration the timing of and lost gas fractions by gas expulsion events very likely affected their gas compositions and bulk isotope compositions some deep 3000 3500 m matured ro 1 5 gases with heavy 13c c1 c3 values indicate significant loss 50 of the early stage gases for the position specific isotope deviations of propane the c2 1 values of the five samples show small decrease with well depths while the h2 1 values have a general increasing trend although some samples fall very close to the equilibrium model trajectories with reasonable calculated temperatures 138 148 c the position specific isotope compositions of propane from the eagle ford shale gases are likely results of thermal cracking of various organic molecules within the source rocks which have different activation energy for cracking and non statistical distributions of c h isotope within them

biomarkers and carbon isotopes of oils in the jurassic smackover trend of the gulf coast states u s a abstract the geochemistry of 25 oils from 23 fields in alabama and the mississippi and louisiana arkansas jurassic salt basins was evaluated results show that the oils were generated by a carbonate source rock which was deposited under highly anoxic conditions and which contains mainly marine derived organic matter the mississippi and louisiana arkansas oils are geochemically similar indicating similar depositional environments for the source although the alabama oils were also derived from a carbonate source rock they are dissimilar to the mississippi and louisiana arkansas oils terpane biomarkers suggest that in addition to marine derived organic matter the source for the alabama oils had an organic input from a more near shore paralic environment i e with a component of terrestrially derived kerogen within each area the oils are similar therefore the norphlet and upper smackover oils in alabama share a common source and the upper smackover cotton valley and some of the lower tuscaloosa oils where production is from faulted structures in mississippi also share a common source maturities of the oils in the three areas vary from low in the updip mississippi salt basin high in the louisiana arkansas salt basin to very high in portions of alabama based on the maturity of oils in mississippi oil generation and migration commenced during the cretaceous when the source was at modest levels of thermal maturity oils migrated relatively short distances into nearby reservoir rocks some oils reached high maturities in the reservoirs resulting in abundant late forming bitumen and pyrobitumen deposition in pore spaces