observations of planetary boundary layer structure in the eastern equatorial pacific abstract atmospheric soundings were collected from a research ship in the eastern equatorial pacific to determine the kinematic and thermodynamic structure of the planetary boundary layer pbl in the vicinity of a strong front in sea surface temperature sst these observations have been used to test the hypothesis proposed by wallace et al and hayes et al that the low level wind shear was enhanced on the cold side of the front because of greater static stability the pbl structure was analyzed from a transect along 110 w from 10 n to 5 s with a focus on the 500 m deep atmospheric mixed layer as defined with respect to virtual potential temperature v significant mixed layer variability was found due to diurnal and other effects but there were systematic differences in mean structure as a function of latitude the mixed layer was neutrally stratified over warm water between 6 5 n and 1 5 n and was slightly stably stratified over the cooler water between 1 n and 2 s the mean total vertical wind

low altitude aeromagnetic reconnaissance for petroleum in the arctic national wildlife refuge alaska variations in the earth s magnetic field arising from local concentrations of shallow subsurface magnetite were mapped in the arctic national wildlife refuge and elsewhere in northern alaska the anomalies were delineated with a magnetic horizontal gradiometer mounted on a low flying 300 ft or 90 m above ground fixed wing airplane limited data from stable carbon isotope and remanent magnetism measurements of rock cores from the cape simpson region strongly suggest that the magnetic anomalies result from the chemical reduction of iron oxides in the presence of seeping hydrocarbons the magnetic contrast between sedimentary rocks of normally low magnetic susceptibility and those locally enriched with this epigenetic magnetite results in distinctive high wavenumber and low amplitude total field anomalies magnetometers extended from each wing tip and in a tail stinger permit calculation of the resultant horizontal gradient vector relative to the flight path this calculation allows more meaningful interp

quasi lagrangian large eddy simulations of cross equatorial flow in the east pacific atmospheric boundary layer using a large eddy simulation les the atmospheric boundary layer abl is numerically modeled along 958w from 88 st o 48n during boreal autumn and compared to observations from the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 since the local abl winds are predominantly southerly in this season a quasi lagrangian forcing is used in which the abl air column is forced as if it were advecting northward with the mean september october 2001 meridional wind across the equatorial cold tongue and the rapidly warming ssts to the north pressure gradients and large scale zonal advective tendencies are prescribed as a function of latitude where possible observations from the epic 2001 experiment are used for forcing and for comparison with model results the abl s modeled vertical structure accords with the conceptual model of wallace et al and agrees well with observations surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north stability of the lower abl over the cold tongue allows a jet to accelerate at about 500 m height relatively uncoupled to the frictional surface layer vertical mixing over the warm water to the north distributes this momentum to the surface additional simulations were performed to explore the modeled abl s sensitivity to pressure gradients zonal advection free tropospheric humidity and initial conditions the model abl was robust changing the forcings resulted in little change in the modeled structure the strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud top radiative cooling once formed at the southern edge of the cold tongue modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops the persistence of thin stratocumulus clouds in this lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

optimal scaling of aftershock zones using ground motion forecasts the spatial distribution of aftershocks following major earthquakes has received significant attention due to the shaking hazard these events pose for structures and populations in the affected region forecasting the spatial distribution of aftershock events is an important part of the estimation of future seismic hazard a simple spatial shape for the zone of activity has often been assumed in the form of an ellipse having semimajor axis to semiminor axis ratio of 2 0 however since an important application of these calculations is the estimation of ground shaking hazard an effective criterion for forecasting future aftershock impacts is to use ground motion prediction equations gmpes in addition to the more usual approach of using epicentral or hypocentral locations based on these ideas we present an aftershock model that uses self similarity and scaling relations to constrain parameters as an option for such hazard assessment we fit the spatial aspect ratio to previous earthquake sequences in the studied regions and demonstrate the effect of the fitting on the likelihood of post disaster ground motion forecasts for eighteen recent large earthquakes we find that the forecasts in most geographic regions studied benefit from this optimization technique while some are better suited to the use of the a priori aspect ratio

the marine atmospheric boundary layer during semaphore i mean vertical structure and non axisymmetry of turbulence this paper describes the vertical structure of the marine atmospheric boundary layer analysed using aircraft measurements in the azores region during semaphore structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale the flights were performed in the middle of the solar day during near anticyclonic conditions with weak to moderate winds and weak surface sensible heat flux over a homogeneous oceanic area the boundary layer was characterized by a mixed layer driven by surface fluxes which was not coupled to the overlying broken stratocumulus layer this decoupling is demonstrated by the shape of the continuous profile of the dissipation rate of turbulent kinetic energy computed from the continuous slant profiles performed by the aircraft this method makes it possible to determine the thickness of the mixed layer which is a relevant scale for the parametrization of the profiles the turbulence field is analysed through the wavelength of the spectrum peak of the vertical velocity computed on 392 runs more or less parallel or perpendicular to the mean wind it demonstrates a stretching of the most energetic eddies along the mean wind the consequences of this non axisymmetric behaviour of the turbulent field on the flux estimates from aircraft data are discussed

sources of aeromagnetic anomalies over cement oil field oklahoma simpson oil field alaska and the wyoming idaho utah thrust belt geochemical and rock magnetic studies undertaken to determine the cause of magnetic anomalies over cement oil field anadarko basin oklahoma simpson oil field north slope basin alaska and the wyoming idaho utah thrust belt have revealed different magnetic sources developed under different sedimentologic geochemical and structural settings at cement ferrimagnetic pyrrhotite fe7s8 typically intergrown with more abundant nonmagnetic pyrite fes2 formed as a result of hydrocarbon seepage sulfur isotopic data indicate that sulfur in the fe s minerals was probably derived from two different sources 1 isotopically heavy thermochemical h2s in petroleum and 2 isotopically light h2s generated by sulfate reducing bacteria that derived metabolic energy from leaking hydrocarbons or organic compounds derived from hydrocarbons although pyrrhotite may make a minor contribution to the reported total magnetic field anomalies at cement the measured anomalies are probably mostly caused by man mad

a study of the relationship between hydrocarbon migration and the precipitation of authigenic magnetic minerals in the triassic chugwater formation southern montana to test the hypothesis that hydrocarbons can cause the precipitation of authigenic magnetite hydrocarbon saturated bleached and unaltered samples of the chugwater red beds were examined using petrographic rock magnetic and paleomagnetic techniques samples were collected from the crest of red dome in carbon county montana where the chugwater is saturated with hydrocarbons and bleached around fractures the fractures formed during laramide deformation and provided conduits for oil migration the red beds contain triassic and rotated triassic magnetizations which reside in hematite the magnetization of the oil saturated sandstones predominantly resides in magnetite and there is some rock magnetic evidence for pyrrhotite the intensity of the natural remanent magnetization nrm in these sands is at least an order of magnitude less than that observed in the red beds a stable magnetic direction could not be isolated from the oil saturated sandstones petrographic studies indicate that both detrital and authigenic magnetite are present in the oil saturated sandstones the bleached specimens possess intermediate magnetic characteristics and contain abundant secondary authigenic specular hematite these specimens contain an early tertiary magnetization that resides in the authigenic hematite the chemical conditions created by the hydrocarbons caused the dissolution of the hematite which uncovered and relatively enhanced the magnetization residing in detrital magnetite it is also likely that hydrocarbons caused the precipitation of some authigenic magnetite and pyrrhotite the early tertiary magnetization in the bleached sandstones is interpreted to be of chemical origin and a byproduct of hydrocarbon migration at red dome the magnetization was probably acquired when the dissolved iron from the red beds precipitated as specular hematite the results of this study have implications for understanding hydrocarbon induced diagenesis and remagnetization mechanisms and for aeromagnetic hydrocarbon exploration

association between magnetic susceptibilities and hydrocarbon deposits in the barinas apure basin venezuela we have measured the magnetic susceptibility of 5425 drill cuttings coming from 20 oil wells distributed in eight fields of the petroliferous barinas apure basin barinas venezuela seeking evidence of magnetic anomalies associated with the presence of hydrocarbon deposits the rock samples are located between the near earth s surface and the basement s top approximately 4000 m in the magnetic susceptibility profiles we observed high magnetic susceptibilities at the top of the sedimentary units corresponding to reservoir and source rocks of oil producing wells whereas in the case of nonproducing wells we observed low magnetic susceptibilities a basic statistical analysis of the magnetic susceptibility measurements shows a significant difference between the mean values across producing and nonproducing wells at the correspondent oilrelated formations with a ratio of 4 1 of producing to nonproducing wells in the producing wells we have found a relation between the magnitudes of the magnetic susceptibility and the age of the formation the larger the magnetic susceptibility the younger the geological stratum the age and depth of the formations where the cuts were obtained exclude the presence of cultural human origin contamination of the samples suggesting the evidence of authigenic origin of the magnetic minerals due to the reductive effect of hydrocarbons in rocks

magnitudes and locations of the 1811 1812 new madrid missouri and the 1886 charleston south carolina earthquakes we estimate locations and moment magnitudes m and their uncertainties for the three largest events in the 1811 1812 sequence near new madrid missouri and for the 1 september 1886 event near charleston south carolina the intensity magnitude m i our preferred estimate of m is 7 6 for the 16 december 1811 event that occurred in the new madrid seismic zone nmsz on the bootheel lineament or on the blytheville seismic zone m i is 7 5 for the 23 january 1812 event for a location on the new madrid north zone of the nmsz and 7 8 for the 7 february 1812 event that occurred on the reelfoot blind thrust of the nmsz our preferred locations for these events are located on those nmsz segments preferred by johnston and schweig 1996 our estimates of m are 0 1 0 4 m units less than those of johnston 1996b and 0 3 0 5 m units greater than those of hough et al 2000 m i is 6 9 for the 1 september 1886 event for a location at the summerville middleton place cluster of recent small earthquakes located about 30 km northwest of charleston

the magnetization of clay rich rocks in sedimentary basins low temperature experimental formation of magnetic carriers in natural samples abstract rocks are often magnetically altered during burial thus providing a useful method to study their thermo chemical history in order to improve the understanding of burial diagenetic magnetization we experimentally synthesized magnetite in natural samples lower jurassic argillites from the paris basin were heated to 150 c under a confined atmosphere of argon when a magnetic field was applied during the heating a chemical remanent magnetization was acquired rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite using anhysteretic remanent magnetization as a measure of the quantity of magnetite an increase of up to 150 after heating was observed ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3 calcite and new magnetite is sometimes completely absent in samples containing less than 0 5 calcite hysteresis measurements suggest that the new magnetite is in the pseudo single domain state scanning electron microscope studies indicate that the new magnetic carriers are associated with pre existing pyrite the magnetic transformations during the experiments involved a fluid which reacted with iron bearing and sulfur bearing minerals in ways depending on local redox conditions this study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins without any external supply from long range fluid flow

including foreshocks and aftershocks in time independent probabilistic seismic hazard analyses time independent probabilistic seismic hazard analysis treats each source as being temporally and spatially independent hence foreshocks and aftershocks which are both spatially and temporally dependent on the mainshock are removed from earthquake catalogs yet intuitively these earthquakes should be considered part of the seismic hazard capable of producing damaging ground motions in this study i consider the mainshock and its dependents as a time independent cluster each cluster being temporally and spatially independent from any other the cluster has a recurrence time of the mainshock and by considering the earthquakes in the cluster as a union of events dependent events have an opportunity to contribute to seismic ground motions and hazard based on the methods of the u s geological survey for a high hazard site the inclusion of dependent events causes ground motions that are exceeded at probability levels of engineering interest to increase by about 10 but could be as high as 20 if variations in aftershock productivity can be accounted for reliably

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

sequence based probabilistic seismic hazard analysis abstract earthquakes are typically clustered both in space and time only mainshocks the largest magnitude events within each cluster are considered by classical seismic hazard which is expressed in terms of rate of exceedance of a ground motion intensity measure at a site of interest cornell 1968 this kind of probabilistic seismic hazard analysis psha is used for structural design or assessment in the long term recently for short term risk management purposes a similar approach has been adopted to perform aftershock probabilistic seismic hazard analysis apsha conditional to mainshock occurrence yeo and cornell 2009 psha often refers to a homogeneous poisson process to describe event occurrence whereas apsha models aftershock occurrence via a conditional nonhomogeneous poisson process the rate of which depends on the magnitude of the mainshock that has triggered the sequence on the other hand the clusters each of which is composed of the mainshock and the following aftershocks may be seen as single events occurring at the same rate of the mainshocks this may allow accounting for aftershocks in hazard analysis in a relatively simple manner as first argued by toro and silva 2001 and further investigated by boyd 2012 in fact this short note focusing on the probabilistic aspects shows the feasibility of analytically combining results of psha and apsha to get a seismic hazard integral accounting for mainshock aftershocks seismic sequences which was still missing from the mentioned studies the results of the application presented help to preliminarily assess the increase in seismic hazard in terms of rate of occurrence of events causing the exceedance of an acceleration threshold e g that considered for structural design also considering aftershocks that is a relevant aspect from the earthquake engineering perspective

on the characteristic height scales of the hurricane boundary layer in this study data from 794 gps dropsondes deployed by research aircraft in 13 hurricanes are analyzed to studythecharacteristicheightscalesofthehurricaneboundarylayer theheightscalesaredefinedinavariety of ways the height of the maximum total wind speed the inflow layer depth and the mixed layer depth the height of the maximumwind speed and the inflow layerdepth are referred to asthe dynamical boundarylayer heights while the mixed layer depth is referred to as the thermodynamical boundary layer height the data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights consistent with previous studies on the boundary layer structure in individual storms the dynamical boundary layer height is found to decrease with decreasing radius to the storm center the thermodynamic boundary layer height which is much shallower than the dynamical boundary layer height is also found to decrease with decreasing radius to the storm center the results also suggest that using the traditional critical richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer these different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

observed relation of soil magnetic susceptibility and soil gas hydrocarbon analyses to subsurface hydrocarbon accumulations magnetic susceptibility ms studies on soils over 19 oil and gas fields showed anomalously large amounts of diagenetic magnetic minerals in shallow depth samples in about 89 of the cases tested soil ms anomalies were compared with soil gas hydrocarbon ghc anomalies over 12 oil and gas fields including several stratigraphic traps and one gas storage reservoir samples were collected along the same profiles six examples are presented with detailed data listings our goal is to test the utility of soil magnetic susceptibility and soil gas hydrocarbons as petroleum prospecting methods we emphasize statistical evaluation of anomalies and their empirical correlation with producing areas and leads identified by other geochemical geological or geophysical data for direct comparison of anomaly strengths data are expressed statistically in terms of the appropriate background mean and standard deviation soil ms and soil ghc data complement each other providing better guidance to productive areas than either data set alone when used in an integrated exploration program their combined positive evidence of hydrocarbon presence under prospects could result in fewer dry holes than when drilling with structural information only

formation of single domain magnetite by a thermophilic bacterium magnetite is a common product of bacterial iron reduction and may serve as a potential physical indicator of biological activity in geological settings here the authors report the formation of single domain magnetite under laboratory conditions by a thermophilic fermentative bacterial strain tor 39 that was isolated from the deep subsurface time course analyses were performed at 65 c to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of tor 39 run products were examined by transmission electron microscopy magnetite particles formed exclusively outside of bacterial cells and exhibited octahedral shapes having relatively equal length and width 15 difference tiny magnetite particles 12 nm nucleated between 10 and 11 h of incubation and increased to average lengths of 55 4 26 8 nm after 24 h of incubation between 24 h and 22 d of incubation magnetite particles maintained average lengths of 56 2 24 8 nm based on size constraints greater than 85 of the particles observed fell within the magnetic single domain little to no magnetite was detected in abiotic controls at 65 or 95 c or in tor 39 cultures whose activity was suppressed unlike mesophilic iron reducing bacteria e g gs 15 tor 39 produced crystals having shapes and sizesmore similar to some particles produced intracellularly by magnetotactic bacteria thus the single domain magnetite produced by thermophiles such as tor 39 may represent a heretofore unrecognized biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments less

evidence for a relationship between hydrocarbons and authigenic magnetite establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to 1 elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite 2 developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods and 3 evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool the direct association of hydrocarbon migration and the precipitation of authigenic magnetite has however not been established in this paper we report palaeomagnetic rock magnetic petrographic and geochemical results of a study of samples from permian spelebthems and gilsonite found in the ordovician arbuckle group in southern oklahoma the results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic magnetite

remagnetization in bituminous limestones of the neoproterozoic araras group amazon craton hydrocarbon maturation burial diagenesis or both 1 neoproterozoic carbonates of the araras group exhibit two distinct magnetic components across the same carbonate succession in a cross section between the amazon craton and the paraguay fold belt pink dolostones of the mirassol d oeste formation carry a dual polarity primary component whereas black bituminous limestones of the guia formation yield a secondary postfolding component magnetic signatures of the guia limestones such as high anhysteretic remanence magnetization saturation isothermal remanence magnetization ratios high frequency dependent magnetic susceptibility and contradictory lowrie fuller and cisowski tests are typical of remagnetized carbonates unblocking temperatures suggest that the stable high temperature remanence is carried by both pyrrhotite and magnetite for which an authigenic origin is suggested by scanning electron microscope observations the different magnetic properties noted between dolostones with or without bitumen and between dolostones and limestones in the same metamorphic conditions lead to the hypothesis that the amount of hydrocarbon as well as the lithology influence nucleation of authigenic magnetic minerals in these rocks presence of magnetite pseudoframboids and euhedral iron sulphide crystals occurring in fracture and voids are in favor of a chemical remanence crm the presence of pyrrhotite as one of the main carriers of crm in these rocks and its association with bitumen in fractures is probably related to an epigenetic enrichment of sulfur due to hydrocarbon seepage however hydrocarbon maturation solely could not explain the differences of the magnetic mineralogy observed in the craton and the fold belt enhanced magnetite formation in the thrust and fold belt is interpreted to be the result of higher temperatures leading to stronger diagenesis of clay minerals

spatial variability of atmospheric boundary layer structure over the eastern equatorial pacific abstract variations in the atmospheric boundary layer structure over the eastern equatorial pacific are analyzed using 916 soundings collected during the first global atmospheric research program global experiment unstable boundary layer structures are observed much more frequently in soundings north of the ocean front located near 2 5 n in the eastern equatorial pacific than in soundings south of the front an objective criterion is applied to identify the presence of the transition layer a weak stable layer near cloud base in the soundings the transition is observed in about 45 of the soundings in both the unstable and the inversion categories a comparison of soundings over the cold tongue with those over the itcz indicates that differences in static stability between these regions are limited to the layer from the surface to about 850 mb which is the mean height of the inversions capping the cloud layer over the cold tongue the cold tongue soundings on average are found to be drier from the sur

correlating biodegradation to magnetization in oil bearing sedimentary rocks abstract a relationship between hydrocarbons and their magnetic signatures has previously been alluded to but this is the first study to combine extensive geochemical and magnetic data of hydrocarbon associated samples we report a detailed study that identifies a connection between magnetic mineralogy and oil biodegradation within oil bearing sedimentary units from colombia canada indonesia and the uk geochemical data reveal that all the oil samples are derived from mature type ii kerogens deposited in oxygen poor environments biodegradation is evident to some extent in all samples and leads to a decrease in oil quality through the bacterially mediated conversion of aliphatic hydrocarbons to polar constituents the percentage of oil components and the biodegradation state of the samples were compared to the magnetic susceptibility and magnetic mineralogy a distinct decrease in magnetic susceptibility is correlated to decreasing oil quality and the amount of extractable organic matter present further magnetic characterization revealed that the high quality oils are dominated by pseudo single domain grains of magnetite and the lower quality oils by larger pseudo single domain to multidomain grains of magnetite and hematite hence with decreasing oil quality there is a progressive dominance of multidomain magnetite as well as the appearance of hematite it is concluded that biodegradation is a dual process firstly aliphatic hydrocarbons are removed thereby reducing oil quality and secondly magnetic signatures are both created and destroyed this complex relationship may explain why controversy has plagued previous attempts to resolve the connection between magnetics and hydrocarbon deposits these findings reinforce the importance of bacteria within petroleum systems as well as providing a platform for the use of magnetization as a possible exploration tool to identify subsurface reservoirs and a novel proxy of hydrocarbon migration

chemical and microbial processes causing anomalous magnetization in environments affected by hydrocarbon seepage aero magnetic anomalies have been reported from several commercial hydrocarbon accumulations however the processes responsible for such anomalies are relatively poorly understood this paper conceptually discusses chemical and microbiological processes involved in generating anomalous magnetization related to hydrocarbon accumulations including hydrocarbon seepage environments based on thermodynamic criteria and microbiologic activity the formation and destruction of magnetic mineral assemblages can be predicted under the influence of hydrocarbons magnetite and pyrrhotite are the most important magnetic minerals formed and the most abundant magnetic mineral destroyed is hematite hence the invasion of hydrocarbons may result in positive absent or negative magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending upon the amounts of authigenic magnetite and pyrrhotite formed relative to the amounts of hematite destroyed magnetism may be generated al

the generation of magnetic anomalies by combustion metamorphism of sedimentary rock and its significance to hydrocarbon exploration low temperature exothermic oxidation of fine pyrite in carbonaceous marine rocks can lead to spontaneous combustion as a result the organic material in the rocks is consumed as fuel but unlike burnt coal seams and lignite beds the host rock remains after combustion thermal metamorphism and in some cases partial to complete melting of the rock will result zones of combustion metamorphism are frequently associated with oil fields these occurrences can be related to either surface outcrops of source rock or leakage from reservoirs a study of the magnetic properties of a suite of combustion metamorphosed specimens of the monterey and sisquoc formations in southern california shows orders of magnitude increases in magnetic intensity and susceptibility for both thermally metamorphosed and fused samples these changes reflect both the production of new magnetic minerals derived mainly from oxidized iron sulfide and their acquisition of thermal remanence ground magnetic surveys across combustion metamorphism zones in three southern california oil fields reveal anomalies of up to 2 000 gammas associated with the metamorphosed and melted rock large scale aero magnetic anomalies are also associated with extensive combustion metamorphism zones in the marcelina formation of venezuela and the ghareb and taquiya formations the mottled zone in israel the recognition of magnetic anomalies caused by combustion metamorphism in areas of oil production suggests that closely spaced low altitude aeromagnetic surveying can be a useful petroleum exploration tool

on the modified mercalli intensities and magnitudes of the 1811 1812 new madrid earthquakes we reexamine original felt reports from the 1811 1812 new madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks in many cases we interpret lower values than those assigned by earlier studies in some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues additionally earlier studies had assigned modified mercalli intensity mmi values of v vii to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high we investigate several approaches to contouring the mmi values using both analytical and subjective methods for the first mainshock on 02 15 lt december 16 1811 our preferred contouring yields m 7 2 7 3 using the area moment regressions of johnston 1996 for the 08 00 lt on january 23 1812 and 03 45 lt on february 7 1812 mainshocks we obtain m 7 0 and m 7 4 7 5 respectively our magnitude for the february mainshock is consistent with the established geometry of the reelfoot fault which all evidence suggests to have been the causative structure for this event we note that the inference of lower magnitudes for the new madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern united states we also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811 1812 sequence

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

the seasonal cycle over the tropical pacific in coupled ocean atmosphere general circulation models abstract the seasonal cycle over the tropical pacific simulated by 11 coupled ocean atmosphere general circulation models gcms is examined each model consists of a high resolution ocean gcm of either the tropical pacific or near global means coupled to a moderate or high resolution atmospheric gcm without the use of flux correction the seasonal behavior of sea surface temperature sst and eastern pacific rainfall is presented for each model the results show that current state of the art coupled gcms share important successes and troublesome systematic errors all 11 models are able to simulate the mean zonal gradient in sst at the equator over the central pacific the simulated equatorial cold tongue generally tends to be too strong too narrow and extend too far west ssts are generally too warm in a broad region west of peru and in a band near 10 s this is accompanied in some models by a double intertropical convergence zone itcz straddling the equator over the eastern pacific and in others

dynamical adjustment of the trade wind inversion layer abstract in schematic north south cross sections the trade inversion layer is often depicted as sloping upward as air flows toward the intertropical convergence zone this conceptual view is consistent with purely thermodynamic boundary layer models which predict a deeper boundary layer with increasing sea surface temperature and decreasing large scale subsidence the slopes implied by such thermodynamic models and incorporated into schematic diagrams are approximately 2000 m 1000 km in contrast observational studies of the inversion structure over the atlantic and pacific oceans reveal a less dramatic slope on the order of 300 m 1000 km to address this inconsistency the authors adopt a somewhat different view of the trade inversion layer in particular rather than regarding it as a purely thermodynamic structure it is regarded as a dynamical structure by formulating a generalization of the rossby adjustment problem the authors investigate the dynamical adjustments of a trade wind inversion laye

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

observations of wind shear over the southern ocean 1 the thermodynamic structure of the lower troposphere over the southern ocean is analyzed by employing over 16 years of high resolution upper air soundings from macquarie island 54 62 s 158 85 e the soundings are analyzed to develop an understanding of the structure of the boundary layer and wind shear occurring through the lower levels over this region and to compare this to european centre for medium range weather forecasts ecmwf model level reanalysis data for the year of tropical convection yotc a multiple layered structure is commonly observed in the high resolution soundings and is also observed in yotc but with a lower frequency the climatological mean and variability of a number of variables are calculated for both data sets which reveals that yotc performs well but has weaknesses in modeling the observed moisture and wind fields particularly evident in wind shear profiles a distinction between a number of boundary layer types is made and the frequency with which they occur is quantified for both data sets this highlights important differences between the observations in the macquarie island soundings and the reanalysis product proxy cloud fields are constructed for the two data sets and these suggest that clouds are commonly observed in a region between the top of the boundary layer and a secondary temperature inversion i e a buffer layer in the words of russell et al 1998 the peak relative frequency of observing these clouds lies roughly around 912 5 hpa for both data sets an examination of the wind shear across the cloud boundaries finds wind shear over cloud base occurs more frequently than cloud top suggesting that the cloud fields are not embedded in a well mixed boundary layer

seismic moment assessment of earthquakes in stable continental regions iii new madrid 1811 1812 charleston 1886 and lisbon 1755 summary the sizes of three major or great historical earthquakes are reassessed using the isoseismal area regression tools developed in parts i and ii of this study of stable continental region scr seismicity the earthquakes are 1811 new madrid central united states and its following sequence 1886 charleston coastal south carolina and 1755 lisbon oceanic intraplate off the continental shelf of portugal the analysis confirms the large size of these events and for the first time places constraints on the uncertainty of their seismic moment release because of the exceptionally low seismic wave attenuation of eastern north america ena a separate north american regression of seismic moment on isoseismal area was developed additionally the unknown western extents of the new madrid isoseismal areas were calibrated with the patterns of the m 6 3 6 6 1843 and 1895 earthquakes application of part ii analysis procedures with these corrections yields new madrid size estimates expressed as moment magnitude of m 8 1 0 31 for the 1811 december 16 m 7 8 0 33 for the 1812 january 23 and m 8 0 0 33 for the 1812 february 7 principal events the charleston earthquake s magnitude decreases from m 7 4 to m 7 3 0 26 after compensation for the effect of coastal plain sediments on its inner isoseismals intensity regressions for lisbon are calibrated against the isoseismal pattern of the nearly co located m 7 8 1969 st vincent earthquake which in this case increases the predicted size of lisbon from m 8 4 to m 8 7 0 39 these size estimates are supported by data from independent phenomena extent and severity of liquefaction the maximum distance of induced landslides and for lisbon tsunami wave amplitudes estimated source parameters are controlled by crustal or lithospheric temperature which governs the depth extent of brittle faulting using estimated continental and oceanic geotherms viable fault lengths are 30 80 km for charleston 120 180 km for 1811 new madrid and 180 280 km for lisbon for average displacements of 2 4 m 8 11 m and 10 14 m respectively and for average static stress and strain drops at the estimated seismic moments of this study the 1811 new madrid and the 1755 lisbon events are respectively the largest known scr and oceanic lithosphere earthquakes

violation of ekman balance in the eastern pacific itcz boundary layer abstractthe intertropical convergence zone itcz is one of the most striking features of earth s climate system often forming a narrow band of convection over many oceanic regions especially in

deposition of magnetic pyrrhotite during alteration of crude oil and reduction of sulfate abstract crude oil seepage is widespread in carbonate cap rock and in overlying sediments of the damon mound salt dome brazoria county texas scanning electron microscopy of calcite lined cavities provides insight to the latest stage of mineral deposition in this salt dome environment solid crude oil residues and microbes occur in association with surface minerals such as gypsum and barite deposition of pyrrhotite pyrite marcasite sphalerite and elemental sulfur is attributed to microbial sulfate reduction and deposition of aragonite and calcite is related to microbial oxidation of crude oil hydrocarbons the c1 c4 hydrocarbons in pyrrhotite bearing cap rock samples are a biodegraded residue derived from crude oil higher molecular weight crude oil components in cap rock are altered by water washing and to a lesser extent by biodegradation hydrocarbon compositions could be explained by limited aerobic biodegradation but a component of anaerobic biodegradation cannot be excluded some damon mound samples are highly magnetic because of abundant ferrimagnetic pyrrhotite this study provides new evidence of a link between crude oil migration microbial activity and diagenetic magnetic anomalies in rocks

occurrence of secondary magnetite within biodegraded oil samples of solid bitumen from the thornton quarry illinois and the cynthia quarry mississippi were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from re magnetized paleozoic carbonate units from other localities organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil the occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in our samples we infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons the discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration

conserved variable analysis of the convective boundary layer thermodynamic structure over the tropical oceans abstract an analysis of fgge dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial pacific deeper boundary layers show a double structure reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

seismicity declustering and hazard analysis of the oklahoma kansas regionseismicity declustering and hazard analysis of the oklahoma kansas region

a statistical and graphical workflow for the analysis of magnetic susceptibility data from drill cuttings in a hydrocarbon exploration setting abstractwe have analyzed the magnetic susceptibility measurements for more than 5000 samples of drill cuttings from oil gas wells in the venezuelan oil fields to facilitate information extraction and improve data presentation including the determination of threshold values used in hydrocarbon exploration the values for each well typically ranged over several orders of magnitude we have developed a new scale called the magnetization contrast magnitude scale m based on a logarithmic transformation of to better represent the data collectively the m data appear to be influenced by more than one process source resulting in skewed bimodal distributions with a significant degree of overlap between the individual modes each mode or subpopulation of the m data could be modeled with a lognormal distribution we have determined that a method based on normal probability plots could be used to decompose the observed bimodal distributions into their individual components and to obtain initial estim

relations among hydrocarbon reservoirs epigenetic sulfidization and rock magnetization examples from the south texas coastal plain this paper focuses on the association between concentrations of iron disulfide fes2 minerals in the shallow subsurface and underlying hydrocarbon accumulations such fes2 concentrations are the result of migration of either h2s or organic constituents from the underlying hydrocarbons the h2s from reservoirs is produced inorganically from sulfate in the reservoir rocks at high temperature 90 c and migrates to shallower beds to react inorganically with iron to form fes2 organic constituents from reservoirs in contrast provide nourishment for sulfate reducing bacteria in shallow relatively cool 90 c beds sandstone in the ray point uranium district in live oak county texas contains abundant fes2 which formed both from deep seated h2s and from h2s produced in the shallow subsurface by bacteria that utilized organic materials from depth deep petroleum reservoirs were physically connected to near surface 100 m beds containing epigenetic fes2 by the oakville fault epigenetic iron sulfide format

a generalized omori s law for earthquake aftershock decay 1 earthquake aftershock sequences have been found to approximately satisfy three empirical scaling relations i the gutenberg richter frequency magnitude scaling ii bath s law for the difference in the magnitude of a mainshock and its largest aftershock and iii the modified omori s law for the temporal decay of aftershock rates the three laws are incorporated to give a generalized omori s law for aftershock decay rates that depend on several parameters specific for each given seismogenic region it is shown that the characteristic time c first introduced in the modified omori s law is no longer a constant but scales with a lower magnitude cutoff and a mainshock magnitude the generalized omori s law is tested against earthquake catalogs for the aftershock sequences of the landers northridge hector mine and san simeon earthquakes

introducing probabilistic aftershock hazard mapping aftershocks to large earthquakes pose a significant hazard a fact that was highlighted by damaging aftershocks to the 1999 turkey and taiwan mainshocks a new approach is introduced to quantify this hazard in terms of physical parameter maps that forecast the probabilistic aftershock hazard based on the observed spatially varying aftershock activity for two case studies the landers and northridge mainshocks probabilistic aftershock hazard maps are shown to improve conventional aftershock hazard assessment

a moist pbl parameterization for large scale models and its application to subtropical cloud topped marine boundary layers abstract a new general purpose boundary layer parameterization that permits realistic treatment of stratocumulus capped boundary layers scbls with coarse vertical resolution is described it combines a 1 5 order turbulent closure model with an entrainment closure at the boundary layer top three different implementations of the entrainment closure in which the boundary layer height is respectively prognosed reconstructed from thermodynamic values at the grid points or restricted to lie on a flux level of the host model grid are tested in a single column modeling framework at both fine and coarse vertical resolution the first two approaches permit a stratocumulus top and base to lie between grid levels and evolve continuously with time but are more complicated to implement in a three dimensional model the model performs very well in cases of dry convection whatever the inversion implementation and the vertical resolution with 15 mb or better vertical resolution all approaches properly simulate

a bimodal hybrid model for time dependent probabilistic seismic hazard analysis the evaluation of evidence provided by geological studies and historical catalogs indicates that in some seismic regions and faults multiple large earthquakes occur in cluster then the occurrences of large earthquakes confront with quiescence and only the small to moderate earthquakes take place clustering of large earthquakes is the most distinguishable departure from the assumption of constant hazard of random occurrence of earthquakes in conventional seismic hazard analysis in the present study a time dependent recurrence model is proposed to consider a series of large earthquakes that occurs in clusters the model is flexible enough to better reflect the quasi periodic behavior of large earthquakes with long term clustering which can be used in time dependent probabilistic seismic hazard analysis with engineering purposes in this model the time dependent hazard results are estimated by a hazard function which comprises three parts a decreasing hazard of last large earthquake cluster and an increasing hazard of the next large earthquake cluster along with a constant hazard of random occurrence of small to moderate earthquakes in the final part of the paper the time dependent seismic hazard of the new madrid seismic zone at different time intervals has been calculated for illustrative purpose

causes and spatial distribution of anomalous magnetization in hydrocarbon seepage environments in diagenetic environments containing hydrocarbons the most important magnetic minerals formed appear to be magnetite and pyrrhotite whereas the most important magnetic mineral dissolved or replaced is hematite hence hydrocarbon seepage and migration may result in positive absent or negative anomalous magnetization magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending on the amounts of magnetite and pyrrhotite formed relative to the amounts of hematite destroyed where anomalous magnetization is formed by hydrocarbon seepage the magnetic contrasts are located in relatively reducing geochemical plumes such plumes are located above leaking subsurface hydrocarbon accumulations if buoyancy is the predominant driving force for hydrocarbons commonly however migration of the escaping hydrocarbons is dominated by advection hydrocarbon seepage therefore may be vertical or may have any direction other than vertical depending on the position of the leaking hydrocarbon accumulation in the prevailing flow system and on the distribution of high permeability pathways such as carrier beds and faults in these cases magnetic contrasts are deflected or displaced and they are not likely to be vertically above the hydrocarbon source anomalous magnetization magnetic contrasts has been documented from some hydrocarbon seepage environments and can be used for hydrocarbon exploration in association with other surface exploration methods similar magnetic contrasts should also be detectable in core and could be used for evaluation of subsurface proximity to hydrocarbon traps the magnitude and spatial distribution of such magnetic contrasts whether at the surface or in the subsurface depend on geochemical microbial geophysical sedimentologic and hydrogeologic processes these factors must be taken into consideration in aeromagnetic and ground based prospecting for hydrocarbons in particular the use of anomalous magnetization as an exploration tool should always be accompanied by a hydrogeologic study the results of this study suggest that magnetic contrasts could also be used in environmental studies for example to detect hydrocarbons leaking from storage tanks or waste disposal sites on the other hand magnetic contrasts may be generated also by natural and anthropogenic processes that have no genetic relationships to hydrocarbons consequently anomalous magnetization may or may not be genetically related to natural or anthropogenic hydrocarbon accumulations

marine atmospheric boundary layer height over the eastern pacific data analysis and model evaluation the atmospheric boundary layer abl height h is a crucial parameter for the treatment of the abl in weather and climate models about 1000 soundings from 11 cruises between 1995 and 2001 over the eastern pacific have been analyzed to document the large meridional zonal seasonal and interannual variations of h in particular its latitudinal distribution in august has three minima near the equator in the intertropical convergence zone itcz and over the subtropical stratus stratocumulus region near the west coast of california and mexico the seasonal peak of h in the itcz zone between 5 68 and 11 28n occurs in the spring february or april while it occurs in august between the equator and 5 68n comparison of these data with the 10 yr monthly output of the community climate system model ccsm2 reveals that overall the model underestimates h particularly north of 208n in august and september directly applying the radiosonde data to the ccsm2 formulation for computing h shows that at the original vertical resolution with the lowest five layers below 2 1 km the ccsm2 formulation would significantly underestimate h in particular the correlation coefficient between the computed and observed h values is only 0 06 for cloudy cases if the model resolution were doubled below 2 1 km however the performance of the model formulation would be significantly improved with a correlation coefficient of 0 78 for cloudy cases

magnetofossil dissolution in a palaeomagnetically unstable deep sea sediment magnetofossils1 the fossil remains of bacterial magneto somes2 are found in various deep sea sediments and have been linked to the preservation of stable natural remanent magnetization in many of them1 3 5 they have also been extracted and identified from lithified carbonates of jurassic5 and precambrian6 age showing that magnetotactic bacteria have been a sedimentary source of fine grained magnetite for much of geological time some clay rich deep sea sediments however do not record a stable remanent magnetization for unknown reasons here we report results from a high resolution transmission electron microscope study on samples of this type collected by the deep sea drilling project dsdp the material contains a complex mixture of single domain magnetic minerals well preserved magnetofossils show the same crystal structures as those found in magnetosomes from recent bacteria7 10 whereas others in these same preparations display a wide range of dissolution corrosion and aggregation effects rock magnetic measurements are consistent with the presence of these alterations in many dsdp sediments including those that preserve reliable palaeomagnetic directions as we were unable to fina authigenic magnetic minerals in our sample and as the magnetic fraction is dominated by well preserved magnetofossils we suggest that the poor preservation of the magnetization is a result of diagenetic interactions between the magnetofossils and the clay minerals in the matrix

the coastal boundary layer at the eastern margin of the southeast pacific 23 4 s 70 4 w cloudiness conditioned climatology abstract a basic climatological description of 29 years of surface and upper air observations at a coastal site 23 4 s 70 4 w in northern chile is presented the site is considered to be generally representative of the eastern coastal margin of the southeast pacific stratocumulus region which plays an important role in the global radiative balance the analysis focuses on two of the main elements affecting coastal weather in this region low level cloudiness and the state of the subsidence temperature inversion the objectives of the paper are 1 to present the basic climatological features of these elements and 2 to document the differences in the structure of this coastal boundary layer bl associated with the presence or absence of low level clouds low level clouds defined here as ceilings less than 1500 m agl occur at the site mostly in the night especially during austral winter and spring elevated subsidence inversions show a very large prevalence in the 1200 utc 0800 local time lt rad

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

relation between mean boundary layer structure and cloudiness at the r v valdivia during astex abstract the relationship between boundary layer thermodynamic structure and cloud fields and their diurnal variation are explored using seven days of data from dw r v valdivia during the atlantic stratocumulus transition experiment cloudiness is at a maximum before dawn when the boundary layer bl has the thermodynamic structure of a partially mixed conditionally unstable stratocumulus layer which is close to mean saturation below the inversion cloudiness falls during the daytime and in the late afternoon the bl has two distinct layers a warmer drier cloud layer characteristic of trade cumulus above a more well mixed subcloud layer the observed mean profiles are consistent with an earlier suggestion that there is a cloud cover transition once the bl mixing line slope exceeds half that of the moist adiabat in contrast the bl structure in the ecmwf model for the same week has a much drier warmer more stable cloud layer than the observations

an observational study of cloud topped mixed layers abstract the turbulence and mean structure of oceanic stratocumulus was studied using aircraft data collected during the summer of 1976 off the coast of california three cloud topped mixed layers were studied in detail they consisted of 1 a thin cloud capped by an inversion at a height of 1000 m 2 a relatively thick but broken cloud layer capped by a weak inversion at 600 m and 3 a solid cloud capped by a strong inversion at 600 m the mean temperature moisture liquid water and radiative characteristics obtained for these three cases were compared heat and moisture fluxes were also calculated and compared although there was considerable variation in the characteristics of the three cloud topped mixed layers studied all indicated the validity of the general approach used in simple mixed layer models of stratocumulus but for these models to be useful they should be generalized to allow clouds other than solid clouds to be modeled the measurements indicate that cloud microphysics may be impo

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

iron sulfide minerals at cement oil field oklahoma implications for magnetic detection of oil fields aeromagnetic anomalies at cement oil field anadarko basin oklahoma have been attributed to authigenic magnetite the following characteristics of the magnetite however indicate that it is contamination introduced by drilling 1 occurrence as sharp angular blades and as spheres commonly with metallographic textures typical of industrial alloys and with associated steel and wustite feo 2 presence only in well cuttings and absence from core and quarry samples and 3 lack of association with detrital framework grains or with authigenic carbonate and sulfide minerals ferrimagnetic pyrrhotite occurs in well cuttings cores and quarry samples at cement and is a possible natural source of the magnetic anomalies pyrrhotite which is intergrown with more abundant fes 2 minerals formed as a result of hydrocarbon seepage pyrrhotite is confined to beds above oil and gas reservoirs these beds which lack detrital organic matter contain higher mineral sulfide and lower mineral sulfate sulfur 1 7 and 0 1 wt respectively than do correlative beds off the field 0 2 and 1 1 wt respectively in the field isotopic values of sulfide s show a systematic decrease upward through the permian section from positive values maximum 12 per mil at 610 760 m depth to negative values 1 to 11 per mil between 32 and 230 m 26 to 30 per mil at the surface geochemical results together with time temperature data derived from burial curves limit the major sources of the sulfide in the fe s minerals to two possibilities isotopically heavy sulfide was generated either inorganically at temperatures 90 c in beds beneath permian beds or by bacterial sulfate reduction at temperatures

source of anomalous magnetization in area of hydrocarbon potential petrologic evidence from jurassic preuss sandstone wyoming idaho thrust belt the jurassic preuss sandstone which crops out in the central part of the wyoming idaho thrust belt on trend with a hydrocarbon producing region to the south has been previously identified as the source of anomalous magnetization in the area elsewhere anomalous magnetization in sedimentary rocks near hydrocarbon accumulations has been attributed to hydrocarbon engendered magnetic minerals but magnetization of the preuss is controlled by detrital magnetite evidence of a detrital origin for magnetite includes 1 concentration of magnetite grains along laminations containing other heavy minerals 2 the presence of exsolved ilmenite hematite and spinel in the magnetite grains and 3 titanium contents typical of igneous derived magnetite that detrital magnetite is responsible for the anomalous magnetization in the preuss is further indicated by the systematic eastward decrease in magnetite abundance corresponding to a similar eastward decrease in magnetic susceptibility and remanent magnetization of the unit petrologic and vitrinite reflectance studies indicate a complex low temperature 150 c or 302 f diagenetic history for the preuss nevertheless preservation of detrital magnetite the presence of diagenetically early ferric oxide minerals and the absence of sulfide minerals all indicate that the preuss has not experienced sulfidic reducing conditions common in areas of hydrocarbon seepage the marine carbon isotopic composition of calcite that cements most preuss sandstones dgr13c values ranging from 2 47 to 1 48 pmil is evidence that carbonate diagenesis also was not influenced by hydrocarbons the results of this multidisciplinary study of the preuss underscore the importance of similar studies when evaluating the sources of aeromagnetic anomalies in areas of hydrocarbon potential

structure of the entrainment zone capping the convective atmospheric boundary layer the authors use large eddy simulation les to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer pbl over a range of bulk richardson numbers ri the les code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer extensive flow visualization is used to examine the structure of the inversion layer and to illustrate the temporal and spatial interaction of a thermal plume and the overlying inversion it is found that coherent structures in the convective pbl that is thermal plumes are primary instigators of entrainment in the ri range 13 6 ri 43 8 at ri 5 13 6 strong horizontal and downward velocities are generated near the inversion layer because of the plume interface interaction this leads to folding of the interface and hence entrainment of warm inversion air at the plume s edge at ri 5 34 5 the inversion s strong stability prevents folding of the interface but strong horizontal and downward motions near the plume s edge pull down pockets of warm air below the nominal inversion height these pockets of warm air are then scoured off by turbulent motions and entrained into the pbl the structure of the inversion interface from les is in good visual agreement with lidar measurements in the pbl obtained during the lidars in flat terrain field experiment a quadrant analysis of the buoyancy flux shows that net entrainment flux or average minimum buoyancy flux wu min is identified with quadrant iv w2u1 0 motions that is warm air moving downward plumes generate both large negative quadrant ii w1u2 0 and positive quadrant iii w2u2 0 buoyancy fluxes that tend to cancel the maximum vertical gradient in potential temperature at every x y grid point is used to define a local pbl height zi x y a statistical analysis of zi shows that skewness of zi depends on the inversion strength spectra of zi exhibit a sensitivity to grid resolution the normalized entrainment rate we w where we and w are entrainment and convective velocities varies as ari21 with a 0 2 in the range 13 6 ri 43 8 and is in good agreement with convection tank measurements for a clear convective pbl the authors found that the finite thickness of the inversion layer needs to be considered in an entrainment rate parameterization derived from a jump condition

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

epic 95 w observations of the eastern pacific atmospheric boundary layer from the cold tongue to the itcz abstract the atmospheric boundary layer abl along 95 w in the eastern equatorial pacific during boreal autumn is described using data from the east pacific investigation of climate epic 2001 with an emphasis on the evolution of the thermodynamic abl properties from the cold tongue to the cold advection region north of the sea surface temperature sst front surface sensible and latent heat fluxes and wind stresses between 1 s and 12 n are calculated from data from eight ncar c 130 research aircraft flights and from tropical atmosphere ocean tao buoys reduced surface wind speed and a 10 m s 1 jet at a height of 500 m are found over the equatorial cold tongue demonstrating the dependence of the surface wind speed on surface stability the abl exhibits a maximum in cloud cover on the north downwind side of the warm sst front at 1 3 n turbulent mixing driven by both surface buoyancy flux and radiative cooling at the cloud tops plays a significant role in maintaining the depth and structure of t

the historical development of the magnetic method in exploration the magnetic method perhaps the oldest of geophysical exploration techniques blossomed after the advent of airborne surveys in world war ii with improvements in instrumentation navigation and platform compensation it is now possible to map the entire crustal section at a variety of scales from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale methods of data filtering display and interpretation have also advanced especially with the availability of low cost high performance personal computers and color raster graphics the magnetic method is the primary exploration tool in the search for minerals in other arenas the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications such as locating intrasedimentary faults defining subtle lithologic contacts mapping salt domes in weakly magnetic sediments and better defining targets through 3d inversion these new applications have increased the method s utility in all realms of exploration in the search for minerals oil and gas geothermal resources and groundwater and for a variety of other purposes such as natural hazards assessment mapping impact structures and engineering and environmental studies

magnetic susceptibilities of rocks of the antarctic peninsula implications for the redox state of the batholith and the extent of metamorphic zones a combination of 1555 magnetic susceptibility measurements from the antarctic peninsula between 65 s to 72 s for which the raw data are made available and petrological structural and metamorphic data has been used to improve understanding of 1 magma sources for the antarctic peninsula batholith 2 genetic relationships between granitoids and metamorphic rocks and 3 to provide a semi quantitative measure of the extent and grade of metamorphic zones the redox state of jurassic plutonic rocks indicates that these had continental magma sources in the tectonostratigraphic terranes of the central and eastern domains triassic and cretaceous plutons on the other hand had subduction related sources in the central domain of the western antarctic peninsula and continental sources in the gondwana margin eastern domain circum pacific comparisons of magnetite ilmenite belt geometries identify the antarctic peninsula belt as a natural continuation of comparable south american belts susceptibility trends are generally retained by orthogneisses suggesting that they formed by deformation of plutonic rocks mostly at or below upper amphibolite facies conditions metasedimentary rocks are weakly magnetic across the peninsula and are spatially associated with continentally derived or crustally contaminated plutons ilmenite series orthogneisses and metabasites from strongly magnetic plutonic environments show areas of very low magnetic susceptibilities that may be linked to fluid enhanced tectonometamorphism induced reduction of magnetic susceptibility the distribution of reduced magnetic susceptibility areas follows the surface traces of major shear and fault zones in palmer land our results are consistent with tectonic interpretations of oblique compression and uplift of an arc block on the pacific margin of gondwana during the palmer land event