detection of lower mantle scatterers northeast of the marianna subduction zone using short period array data short period university of washington northern california and southern california seismic array records of a sequence of deep mariana subduction zone earthquakes show unexpected clear arrivals nearly 90 and 105 s following p we measure slowness arrival time and arrival azimuth of these phases relative to p using array techniques to find where they emanate in the mantle by combining slowness and back azimuth deviations and the move out with depth of the arrivals from different earthquakes we find their most probable origin is through s to p conversion at point scatterers in the mid to lower mantle at 25 7 n 148 2 e 1590 km and 25 5 n 151 0 e 1850 km respectively separated by 300 km these features indicate elastically distinct material in the middle of the lower mantle which if fragments of subducted slabs are not related to contemporary subduction they may represent upwelling convective material from the deep mantle or d but they are not purely thermal in nature as chemically distinct bodies they may represent potential reservoirs of the isotopic and trace element components recognized geochemically

diagenesis in north sea hpht clastic reservoirs consequences for porosity and overpressure prediction upper jurassic clastic reservoirs of the fulmar formation in the central north sea possess anomalously high porosities for their present day depth of burial reservoirs with the highest overpressures have the highest porosities possess less macroquartz cement and have significant secondary porosity quartz cementation in hpht high pressure high temperature reservoirs has been inhibited by a combination of factors high overpressure limited fluid movement presence of early grain coating cements high pore fluid salinity and possibly petroleum migration secondary porosity has contributed to reservoir quality with an average of 4vol extra porosity created quantitative prediction of porosity would require an improved depositional model for the fulmar accurate thermal and pressure modelling and detailed knowledge of field filling and leakage histories theoretical calculations indicate that diagenetic reactions occurring in the fulmar formation smectite illitisation and quartz cementation did not generate significant overpressure because seal permeabilities were too high and the rate of volume increase associated with the reactions too small therefore diagenetic reactions can effectively be ignored when modelling overpressure generation in the central north sea although cementation will affect rock permeability and rates of fluid dissipation

double beam imaging mapping lower mantle heterogeneities using combinations of source and receiver arrays we present a new technique for imaging spatially distributed heterogeneities using information from combinations of source and receiver arrays the method is based on the single scattering assumption and is closely related to the double beam method of kruger et al 1993 1995 1996 in that it exploits amplitude delay time slowness and azimuth information in two arrays simultaneously a crucial step in the method is the application of static time corrections for a chosen reference phase here pcp one type of image is obtained as a spatial likelihood distribution for prescribed source and receiver array slowness and azimuth values and delay times with respect to a reference phase this allows the determination of the spatial origin of coherent phases in the p coda in a complementary approach we perform a double beam stack migration according to the theoretical slowness and azimuth values for candidate scatterers distributed over a three dimensional 3 d grid the scattering strength is expressed as the resulting beam power beam amplitude or semblance in a time window determined from the theoretical delay time with respect to the reference phase while likelihood mapping provides an image reflecting the probability of a region to explain observed kinematic phase properties by single scattering double beam migration provides information about the scattering strength the method is applied to nuclear explosion sources in eastern kazakhstan recorded at the yellowknife array in northern canada we identify several scattering volumes within the lower mantle below the arctic producing individual anomalous lower mantle phases in the p coda these anomalies range in depth from the core mantle boundary cmb up to 500 km into the lowermost mantle and are mainly located under the eurasian side of the arctic the joint interpretation of these results with the results of previous studies suggests a connection of these anomalies to the cenozoic and mesozoic subduction of the pacific plate and the kula plate the determination of the nature of such 3 d anomalies necessitates further array studies with better azimuthal coverage

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

changes in occurrence of cold surges over east asia in association with arctic oscillation 1 it has been newly found that the occurrence of cold surges in east asia is significantly influenced by the arctic oscillation ao in the present study the events of cold surge are objectively determined based on several synoptic criteria and the phase dependency of its occurrences in association with the ao has been revealed during the negative ao phase the frequency of cold surge occurrence is relatively increased than that of neutral and positive ao phases the variation of upper level trough and jet stream over east asia and the siberian high in association of ao are suggested to explain the change of cold surge occurrences

tropical extratropical interactions associated with east asian cold air outbreaks part ii intraseasonal variation abstractintraseasonal variations of east asian cold air outbreaks caos in relation to the tropical atmosphere during 34 winters djf are investigated this study is a continuation of part i which discussed the interannual variability of east asian caos two types of quantitative east asian caos western and eastern caos are examined their variations are identified by the zonal integration of equatorward flux of cold air mass cam below 280 k at 45 n over 90 135 e and 135 e 180 a day lagged regression analysis reveals that peaks of intraseasonal western and eastern cao events are preconditioned by large scale tropical convection anomalies resembling particular phases of the madden julian oscillation mjo western cao events tend to occur when the convective phase of the mjo crosses over the maritime continent in contrast eastern cao events are triggered by the mjo over the western pacific observations of mjo related atmospheric anomalies indicate the important roles of poleward rossby wave tr

multiparameter two dimensional inversion of scattered teleseismic body waves 3 application to the cascadia 1993 data set this is the third paper in a three part series that examines formal inversion of the teleseismic p wave coda for discontinuous two dimensional 2 d variations in elastic properties beneath dense arrays of three component broadband seismometers in this paper the method is applied to data from the incorporated research institutions for seismology program for array seismic studies of the continental lithosphere iris passcal cascadia 1993 experiment undertaken across central oregon two major features are imaged in the resulting model the continental moho becomes evident 150 km from the coast beneath the western cascades and extends through the eastern end of the profile at 35 40 km depth in the western portion of the model oceanic crust of the subducting juan de fuca plate dips shallowly 12 at the coast and more steeply 27 below the willamette valley and is evident to depths of 100 km beneath the high cascades the abrupt increase in plate dip at 40 km depth coincides with an apparent thickening of the oceanic crust followed by a diminution in its signature building on previous work we argue that these results are consistent with the consequences of prograde metamorphic reactions occurring within the oceanic crust progressive dehydration at lower grade facies conditions culminates in the transformation to eclogite producing a pronounced increase in the seismic velocity density and dip of the subducting plate and structural complexity in the overlying wedge

origin and significance of redistributional secondary porosity abstract redistributional secondary rds porosity is created by the dissolution of framework grains and cements and the simultaneous precipitation of reaction products in the nearby pore space aluminosilicate minerals and in particular feldspars are the usual precursors of rds porosity in sandstones common product minerals are authigenic quartz and clay minerals usually kaolinite this type of secondary porosity is almost ubiquitous in sandstones rds porosity has little effect on the total porosity of reservoir rocks and contrary to popular opinion cannot give rise to higher than expected porosities at depth petrographic criteria alone are an insufficient measure that the rock has undergone leaching resulting in porosity enhancement to demonstrate porosity enhancement due to leaching it is necessary to show that the porosity of the rock is statistically higher than would otherwise be the case for a rock of similar characteristics that has not been leached the dissolution precipitation reactions that give rise to rds arise from the inherent thermodynamic instability of minerals such as the feldspars and other aluminosilicates which formed under magmatic or metamorphic conditions when these minerals dissolve they add aluminium and silica to the pore fluid however the concentration of aluminium and silica in the pore fluid is buffered by clay minerals and quartz respectively during burial diagenesis thus any increase in the concentration of these components leads to the precipitation of an authigenic clay mineral and authigenic quartz carboxylic acids are claimed to have the capacity to complex aluminium and so increase the solubility of aluminium and eliminate the precipitation of a clay phase however they are unlikely to have any major effect on aluminium solubility in natural i e complex pore fluids in fact dissolution will occur in acid neutral or alkaline conditions at a rate that is kinetically controlled reaction rates speed up exponentially with increasing temperature and therefore depth resulting in the destruction of more and more unstable components this increase in the rate of destruction of unstable components at depth can give rise to what appears to be a late leaching event what is seen in fact is the natural culmination of the destruction of thermodynamically unstable phases at an ever increasing rate during burial thus for a rock of a given composition the fraction of the total porosity that is secondary will increase with burial depth until all labile components are consumed the behaviour of mineral mixtures in the presence of a moving pore fluid is an additional contributing factor to the ubiquity of rds porosity where two or more minerals add the same ion to the pore fluid then the steady state concentration of that ion which is reached at some distance down the flow path theoretically an infinite distance is a weighted average of the equilibrium solubilities of that ion with respect to the minerals that contribute the ion thus as the pore fluid approaches a steady state concentration of the ion it will be undersaturated with respect to the least stable minerals and oversaturated with respect to the most stable mineral hence rds porosity must form as a result of the dissolution of the least stable mineral and the precipitation of the most stable mineral although kaolinite is the most common dissolution product of feldspars with increasing temperature its stability field shrinks with respect to other clay minerals such as illite thus it is possible for feldspars and other aluminosilicates to decompose at depth to give illite and authigenic quartz the growth of fibrous illite together with the change from a dominantly primary to a dominantly secondary pore structure can give rise to a rapid loss of permeability with depth where changes in the clay mineral type do not occur the impact of rds porosity on the porosity permeability behaviour of sandstones is minimal up to secondary porosities of about 10 beyond this figure there is at present too little data to make a clear statement

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

observed connection between stratospheric sudden warmings and the madden julian oscillation 1 the effect of the madden julian oscillation mjo on the northern hemisphere wintertime stratospheric polar vortex and major mid winter stratospheric sudden warmings ssws is evaluated using a meteorological reanalysis dataset the mjo influences the region in the tropospheric north pacific sector that is most strongly associated with a ssw consistent with this ssws in the reanalysis record have tended to follow certain mjo phases the magnitude of the influence of the mjo on the vortex is comparable to that associated with the quasi biennial oscillation and el nino the mjo could be used to improve intra seasonal projections of the northern hemisphere high latitude circulation and in particular of the tropospheric northern annular mode at lags exceeding one month

composition diagenesis and weathering of the sediments and basement of the callabonna sub basin central australia implications for landscape evolution abstract the evolution of the callabonna sub basin central australia is described in terms of sediment provenance stratigraphy sedimentology and postdepositional mineral and chemical alteration six mineral exploration drillholes in the mundi mundi plain were studied using a combination of qualitative and quantitative xrd pimatm portable infrared mineral analyzer xrf normative analysis and sem the sedimentary cover consists of 160 210 m of diagenetically modified fluvio lacustrine tertiary clay silt and sand comprising sandy mottled and gray clay units overlain by quaternary soil the basement consists of weathered proterozoic schist gneiss siltstone and shale quartz kaolinite smectite and muscovite are the dominant minerals within the sediments whereas the weathered bedrock contains quartz feldspar kaolinite illite and muscovite characteristic wavelength absorption features from pimatm show that the youngest sandy clay unit exhibits the lowest reflectance intensities because of its lower diagenetic maturity weathering of primary minerals within the basement produced an illite kaolinite rich saprolite whose clays exhibit strong reflectance intensities and well developed crystallinity the micromorphology of all secondary products reflects their environment of crystallization low porosity and anoxic conditions within the sediments resulted in poorly developed clays of variable textures colors and compositions conversely the weathered bedrock developed over protracted periods of in situ weathering resulting in better developed secondary products this study distinguishes between preburial weathering of the basement detrital mineralogy postdepositional alteration of the sedimentary cover and subsequent weathering of previously formed mineral assemblages this has widespread implications for paleotopographic weathering reconstitution and landscape evolution thus 1 the extent of weathering of basement relative to diagenesis and maturity of sediments and gradational nature of their unconformity suggests that most of the alteration of basement occurred prior to and was sustained after deposition of sediments and 2 morphotectonic evolution of the region controlled the composition of transported materials by changing the style and patterns of fluvial systems further influencing the distribution and preservation of sediments and weathered bedrock and hence regional landscape morphology

crustal scattering at the ktb from a combined microearthquake and receiver analysis summary in december of 1994 a fluid injection experiment which triggered several hundreds of microearthquakes was conducted at the ktb main borehole oberpfalz germany these events were recorded with a temporal seismic network at the surface out of the complete data set a cluster of five events recorded at four mini arrays consisting of eight or nine stations was used to investigate the crustal scattering properties in the vicinity of the ktb for this purpose the double beam method dbm kruger et al 1993 1995 1996 and the double beam imaging method scherbaum kruger weber 1997 were extended to curved wave fronts to drop the restriction of plane wave propagation this technique is used for imaging the crustal scattering strength using earthquake clusters recorded at close by mini arrays the results of the array analysis show that the composition of the p coda is mainly avected by the site location of the arrays near surface and deeper crustal scattering contribute in a very complicated pattern furthermore with the present data set it was possible to identify reflections from the top of the erbendorf body this is a very pronounced arrival in most of the recorded traces in one of the arrays its amplitudes are even greater than the direct p phases five to eight coherent phases could be identified by the mini arrays using only these phases synthetic p coda traces were constructed which only contain the coherent part of the observed wavefield by subtracting the synthetic coherent wavefield from the original traces we achieve a variance reduction in the p coda of up to 37 per cent this leads to the conclusion that a large amount of the p coda at the ktb can be modelled by a simple deterministic single scattering model using a small number of individual scatterers

the relation of crustal scattering to seismicity in southern california dense regional array recordings of 377 teleseismic events are used to map geographic variability in upper crustal p to s scattering in southern california scattered wave energy is sensitive to short wavelength heterogeneity and maps of scattering potential offer a powerful complement to travel time tomography in characterizing seismic crustal heterogeneity the scale length of resolved scattering variability is commensurate with the scale lengths of surface fault trace length and microseismicity variations and both mapped faults and seismicity are concentrated in regions of strong scattering fault proximal scattering averaged across strike of predominately strike slip fault zones is highly correlated with microseismicity levels and is predictive of the pattern of microseismicity variation but not of absolute scale north south profiles through the transverse ranges reveal coincident strong gradients in microseismicity and scattering whereas mapped segment bounds along the san andreas fault zone from san francisco to the salton sea coincide with strong along strike gradients in the level of scattering the overall correlation of microseismicity and scattering potential is consistent with structural control of aftershock and background microseismicity production strain energy control of scattering or both prior evidence for fault offset in the pattern of scattering intensity revenaugh and reasoner 1997 favors the former

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

aluminium loss during sandstone diagenesis petrographical observations from a sandstone buried to between 3 2 and 5 7 km in the north sea central graben suggest a significant change in bulk chemistry during burial the sand contained 35 or more feldspar upon deposition but due to extensive dissolution only 5 remains in the deep sandstones this has released much more al than is currently contained as authigenic minerals up to 1460 mol cm 3 of al have been exported this deep secondary porosity is economically important but its recognition by petrographic textures is unreliable as are bulk chemical provenance studies of deeply buried sedimentary and metamorphic strata

theoretical seismic wave radiation from a fluid filled borehole this paper concerns far field radiation of compressional p and shear s waves into the surrounding medium from a fluid filled borehole in an infinite medium and tube waves propagating along a borehole using a low frequency approximation two kinds of sources are considered 1 a volume displacement point source acting on the axis of a borehole and 2 a uniform radial stress source acting on the wall of a borehole when the tube wave velocity is close to the shear wave velocity the effect of the borehole fluid on the p wave radiation pattern and on the s wave radiation pattern is substantial

processes for occurrence of strong cold events over eastern china abstracta strong cold event hit eastern china around 24 january 2016 with surface air temperature reaching more than 10 c below the climatological mean in most regions of eastern china south of 40 n a total of 37 strong cold events similar to the january 2016 event with temperature anomalies over eastern china exceeding 5 c have been identified during the winters from 1979 80 to 2015 16 a comparative analysis of events with surface temperature anomalies of the same intensity but limited to north of 40 n indicates that the southward invasion of cold air to eastern china south of 40 n is related to two factors one is the latitudinal location of the upper level wave train the surface siberian high and the midtropospheric east asian trough over the mid to high latitude eurasian continent the other is a subtropical upper level wave train emanating from the midlatitude north atlantic the emergence of the subtropical wave train is related to the positive phase of the north atlantic oscillation nao wh

characteristics and origin of the major authigenic minerals and their impacts on reservoir quality in the permian wutonggou formation of fukang sag junggar basin western china abstract this research is focused on the characteristics and origin of major authigenic minerals and the influences on the reservoir quality of the permian wutonggou formation sandstones in the eastern slope of fukang sag junggar basin western china authigenic cements were observed and described from thin sections scanning electron microscopy fluorescence and cathodoluminescence the elemental concentrations of the authigenic minerals were measured by electron probe microanalysis additional characterizations were obtained from o and c stable isotope ratios and from the homogenization temperature of aqueous fluid inclusions the results show that the sandstones in the wutonggou formation are dominated by volcanic lithic fragments carbonates and laumontites are the major authigenic minerals in the study area authigenic quartz and kaolinite can also be observed two types of carbonate cements are identified the first type is calcite with yellow fluorescent hydrocarbon inclusions the carbon and oxygen isotopes in the calcites are highly c depleted and o depleted the homogenization temperatures of the aqueous fluid inclusions in the calcite cements are higher than the highest paleogeotemperatures during the burial history combined with the presence of authigenic fibrous illites and the illitization of kaolinites it is determined that the precipitation of the calcites is related to the upwelling of deep fluids and was impacted by the co 2 from the thermal decarboxylation of organic matters during the middle late jurassic the second type is ferroan calcite with blue fluorescent hydrocarbon inclusions and higher contents of fe mn cr and mg than in the calcites the ferroan calcites in the beisantai uplift are rich in 13 c 13 c v pdb values are 22 10 and 22 16 the precipitation of these ferroan calcites was impacted by the co 2 from crude oil biodegradation after the late jurassic two types of laumontites are identified the first type is partially dissolved and is characterized by a high ca na ratio and low fe contents the second type is hardly dissolved has hydrocarbon inclusions with yellow and blue fluorescence and is characterized by a low ca na ratio and high fe contents the first type of laumontite was precipitated prior to hydrocarbon charging and the second type was formed after hydrocarbon charging and meteoric water leaching the hydration of the volcanic debris provided the source materials for both types of laumontite the authigenic quartz and kaolinite were formed by the alteration of feldspars laumontites and volcanic materials the evolution of the reservoir properties was impacted by various degrees of cementation and dissolution as a result the reservoir quality in the beisantai uplift was better than in the shaqiu area

variation of system openness and geochemical features in overpressured sandstones of the yinggehai basin offshore south china sea abstract hydrocarbon discoveries in recent years in the upper miocene of the yinggehai basin show differences in overpressure magnitude gas and mineral components overpressure close to or reaching the leakage threshold has induced high system openness for one field but the overpressure of another field remains to be safely closed a new vision to investigate the interplay between the system openness and the gas chemical and mineralogical features were conducted the gas components in the high openness system are rich in high maturity hydrocarbons and inorganic co2 which both have heavier carbon isotopes low maturity gases with lighter carbon isotopes are dominant in the low openness system the abnormal carbon isotope ratio between iso butane and n butane in the high openness system confirms that early low maturity leakage has generated abnormal compositional and isotopic fractionation although the sedimentation process was uniform in the two systems the high openness system has rare k feldspar grains and chlorite but it is rich in illite smectite mixed layers i s precipitation is characterized by ankerite and kaolinite in the high openness system whereas the low openness system primarily consists of calcite the strong dissolution of k feldspar grains and chlorite should have released abundant potassium and silicon the high abundances of i s and kaolinite which are both sensitive to potassium and the rarity of quartz overgrowths in the high openness system imply that the leakage of potassium silicon from the sandstones has induced a mass imbalance between dissolution and precipitation even the sandstone porosity was slightly increased by the mass imbalance in the high openness system the risk of hydrocarbon expulsion during brine leakage cannot be ignored

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

multimode migration of scattered and converted waves for the structure of the hikurangi slab interface new zealand reflectivity imaging of local earthquake seismograms has revealed the structure of the hikurangi subduction interface at the location of two strong earthquakes that occurred in 1990 the earthquakes originated within the continental plate of the north island of new zealand and below in the subducting pacific slab we used seismograms from 500 well located events in two earthquake sequences recorded by a small temporary seismograph deployment to directly image the structure and multiphase reflectivity of the plate interface synthetic tests of the imaging method show the effects of the poor 3 d geometric coverage afforded by the seismometer array kirchhoff summation image sections computed from synthetics show accurate depth imaging of backscattering interfaces phase converting interfaces imaged with forward scattered waves are smeared by poor ray coverage to 5 km depth inaccuracy and are only imaged over a small range of their horizontal extent from the data we computed image sections for p p p s s p and s s scattering we mitigated imaging artifacts due to poor ray coverage with an obliquity factor an antialiasing criterion and enhancement by resampling statistics imaging used a sharply layered velocity model we tested for the effects of imaging with first arriving headwaves by imaging through smoothly varying velocity models for our ray geometry early arrival headwaves contribute little to the images the plate interface appears as a 3 5 km thick p p and possibly s s backscatterer with 5j nw dip offset 5 km down to the nw above a normal fault in the slab when illuminated from below a wedge of the interface on the downdip side of the slab fault forms a very prominent p p forward scatterer the edges of the wedge forward scatter some s p and s s energy but an order of magnitude less than the p p forward scattering the imbalances between forward scattering of p and s energy suggest a wedge of subducted sediment retaining significant porosity but with rigidity close to that of surrounding rocks d 2002 elsevier science b v all rights reserved

migration of seismic scatterers associated with the 1993 parkfield aseismic transient event the time varying deformation field within a fault zone particularly at depths where earthquakes occur is important for understanding fault behaviour and its relation to earthquake occurrence1 2 3 but detection of this temporal variation has been extremely difficult although laboratory studies have long suggested that certain structural changes such as the properties of crustal fractures should be seismically detectable4 here we present evidence that such structural changes are indeed observable in particular we find a systematic temporal variation in the seismograms of repeat microearthquakes that occurred on the parkfield segment of the san andreas fault over the decade 1987 97 our analysis reveals a change of the order of 10 m in the location of scatterers which plausibly lie within the fault zone at a depth of 3 km the motion of the scatterers is coincident in space and time with the onset of a well documented aseismic transient deformation event we speculate that this structural change is the result of a stress induced redistribution of fluids in fluid filled fractures caused by the transient event

scattering and attenuation abstract an extensive existence of strong small scale heterogeneity in the earth is suggested by the great variability of direct waves and remarkable stability of scattered waves both in the case of teleseismic p coda and in the case of local earthquake s coda quantitative studies of small scoale heterogeneities have been made by the following three methods a lower bound of heterogeneity in the lithosphere has been estimated by the deterministic or stochastic modeling of travel time and amplitude fluctuation of teleseismic p waves across a large aperture seismic array an upper bound of heterogeneity has been estimated by modeling the attenuation of s waves as a scattering loss due to heterogeneity these two approaches suggest the existence of heterogeneity with rms velocity fluctuations from 3 to 10 per cent the third method is based on the estimation of heterogeneity from the amplitude of coda waves we found a significant discrepancy between the result obtained by the third method and those from the first two and attribute the discrepancy to the assumption of a single scattering model adopted in the coda generation theory the need for including multiple scattering as well as for considering vector elastic waves rather than scalar waves is emphasized

material flux and porosity changes during sediment diagenesis understanding the changes in porosity that occur during burial of sediments is of importance both in modelling fluid flow in sedimentary basins and for prediction of petroleum reservoir quality when deposited up to 50 of the volume of sands is intergranular pore space porosity generally decreases with depth because of compaction and precipitation of diagenetic minerals but some sandstones retain an anomalously high porosity whether this is due to dissolution and removal of material or to its local redistribution is not clear we originally intended to quantify losses of major chemical components during burial of a complete sedimentary unit we have investigated ten reservoir sandstones of permian to tertiary age from oilfields worldwide these show consistent results and here we present detailed data from four of them we found that the silica content of these sandstones actually increased by 220 to 350 kg m 3 following compaction no statistically significant changes were observed for aluminium potassium or sodium the flux of silica cannot be modelled satisfactorily using currently accepted values of permeability silica solubility and flow rates posing a challenge for existing models of fluid flow and ore emplacement

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

intraseasonal variation of the strength of the east asian trough and its climatic impacts in boreal winter abstractthe east asian trough eat is a distinct component of the boreal winter circulation whose strength corresponds to the amplitude of the northern hemispheric stationary waves in this study the mechanism and climatic impacts of the intraseasonal variations of the eat s strength are investigated through composite analysis and dynamical diagnostics the significant roles played by the low frequency rossby wave rw and synoptic transient eddy te are revealed before the peaks of strong eat events an upper tropospheric rw train propagates across northern eurasia and interacts with preexisting surface cold anomalies over central siberia this pattern intensifies the siberian high and causes rw convergence toward the eat leading to 30 of the eat s amplification directly via the rw induced feedback forcing meanwhile rw weakens the background baroclinicity and reduces te activities near the entrance region of the north pacific storm track the te induced feedback forcing leads to another 30 of th

northern hemisphere mid winter vortex displacement and vortex split stratospheric sudden warmings influence of the madden julian oscillation and quasi biennial oscillation we investigate the connection between the equatorial madden julian oscillation mjo and different types of the northern hemisphere mid winter major stratospheric sudden warmings ssws i e vortex displacement and vortex split ssws the mjo ssw relationship for vortex split ssws is stronger than that for vortex displacement ssws as a result of the stronger and more coherent eastward propagating mjos before vortex split ssws than those before vortex displacement ssws composite analysis indicates that both the intensity and propagation features of mjo may influence the mjo related circulation pattern at high latitudes and the type of ssws a pronounced quasi biennial oscillation qbo dependence is found for vortex displacement and vortex split ssws with vortex displacement split ssws occurring preferentially in easterly westerly qbo phases the lagged composites suggest that the mjo related anomalies in the arctic are very likely initiated when the mjo related convection is active over the equatorial indian ocean around the mjo phase 3 further analysis suggests that the qbo may modulate the mjo related wave disturbances via its influence on the upper tropospheric subtropical jet as a result the mjo related circulation pattern in the arctic tends to be wave number one wave number two 25 30 days following phase 3 i e approximately phases 7 8 when the mjo related convection is active over the western pacific during easterly westerly qbo phases which resembles the circulation pattern associated with vortex displacement vortex split ssws

relationship between the arctic oscillation and cold surges over east asia abstract the present study reveals the changes in the characteristics of cold surges over east asia associated with the arctic oscillation ao based on circulation features cold surges are grouped into two general types wave train and blocking types the blocking type of cold surge tends to occur during negative ao periods that is the ao related polarity of the blocking type however the wave train type is observed during both positive and negative ao periods although the wave train features associated with negative ao are relatively weaker the cold surges during negative ao are stronger than those during positive ao in terms of both amplitude and duration the cold surges during positive ao in which the extent of effect is confined to inland china passes through east asia quickly because of weaker siberian high and aleutian low leading to short duration of these cold surges in contrast the cold surge during negative ao characterized by a well organized anticyclone cyclone couplet with high p

interannual variations of east asian trough axis at 500 hpa and its association with the east asian winter monsoon pathway interannual variations of the east asian trough eat axis at 500 hpa are studied with the european centre for medium range weather forecasts 40 yr reanalysis data the associated circulation pattern and pathway of the east asian winter monsoon eawm with the eat axis tilt are specially investigated with a trough axis index which is closely related to the midlatitude baroclinic process and mainly represents the intensity of the eddy driven jet over the east asia north pacific sector when the tilt of eat is smaller than normal the eawm prefers to take the southern pathway and less cold air moves to the central north pacific however the eawm prefers the eastern pathway and brings more cold air to the north pacific when the tilt of eat is larger than normal these differences induce pronounced changes in both the precipitation and the surface air temperature over east and southeast asia furthermore the tilt status of the eat has a significant modulation effect on the regional climate anomalies related to the intensity of the eawm the findings suggest an increase in the temperature anomaly associated with the eawm intensity and a clear northward southward shift in its pattern in anomalous tilt phase of the eat in addition the modulation tends to be confined mainly to east asia and expanded to a larger area during the weak and the strong eawm winters respectively the possible reasons for interannual variations of the eat tilt are discussed and it is speculated that the midlatitude air sea interaction in the north pacific plays a dominant role this study on the eat tilt may enrich knowledge of the east asian winter monsoon beyond the conventional intensity index and may be helpful to improve regional climate prediction in east asia

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

systematic destruction of k feldspar in deeply buried rift and passive margin sandstones systematic patterns of detrital k feldspar decline with increasing burial depth are revealed during deep burial 1 5 4 5 km of sandstones in diverse sedimentary basins from three rift and two passive margin settings in the north sea and usa gulf coast k feldspar destruction is predominantly by dissolution though in situ alteration to albite also occurs dissolution can remove up to 15 solid volume of the rock by 4 5 km so that primary arkosic sandstones become diagenetic quartzarenites at depth with increased secondary primary porosity ratios the quantity of k feldspar destroyed during temperature increase is very variable 0 05 1 0 solid volume c compaction continues during deep burial and petrographic textures diagnostic of secondary porosity are destroyed so that many sandstones preserve exceptions to this scenario of detrital k feldspar dissolution are noted proximity of k rich evaporites high sio 2 and k activity due to the breakdown of volcanic clasts or very low p co 2 can stabilize both k feldspar and a suite of k rich cements

spatial distribution of relative scattering coefficients determined from microearthquake coda a coda envelope inversion technique is developed to image the three dimensional spatial distribution of relative scattering coefficients the technique is applied to the norris lake community georgia earthquake swarm of 1993 the relative scattering coefficient is the ratio of the scattering coefficient to a regionally determined average used to normalize the coda amplitudes the inversion problem was solved using the algebraic reconstruction technique art with the relative scattering coefficient constrained to positive values although coda envelope inver sion is based on the theory for single scattering we show that it may with a correction factor be used to characterize the distribution of relative scattering coefficients when multiple scattering contributes significantly to the coda the coda envelope inversion for the norris lake community earthquake swarm revealed a highly nonuniform distribution of relative scattering coefficients the zones of strong scattering are correlated with the hypocenters and areas of rough topography moreover at shallow depths the relative scattering coefficients are frequency dependent with scattered energy increasing with frequency we interpret this frequency dependence to imply that open fractures less than 250 m in length are responsible for strong scattering in the coda of these shallow earthquakes at greater depths scattering is independent of frequency and probably relates to velocity layering a strong reflecting layer was identified at or below 7 km which is consistent with the thrust plain identified in the georgia cocorp reflection lines the inhomogeneous distribution of scattering strength obtained in this study argues strongly against the observation based as sumption that the scattering structures are uniformly distributed in the crust

a scattered wave image of subduction beneath the transverse ranges over 5600 short period recordings of teleseismic events were used to create deterministic maps of p wave scatterers in the upper mantle beneath southern california between depths of 50 and 200 kilometers the southern flank of the slab subducting beneath the transverse ranges is marked by strong scattering the marked scattering indicates that the edge of the slab is a sharp thermal boundary such a boundary could be produced by slab shearing or small scale convection in the surrounding mantle the northern limb of the slab is not a strong scatterer consistent with thicker lithosphere north of the transverse ranges

dissolution of granitic sand by ph buffered carboxylic acids a flow through experimental study at 100 degrees c and 345 bars 1 experiments were performed to investigate the effects of monofunctional and difunctional carboxylic acids on feldspar dissolution and aluminum mobility under conditions which approximate diagenesis including low temperature high mineral surface area fluid volume and open system conditions granitic sand 63 feldspar was reacted at 100 degrees c and 345 bars with distilled water ph buffered oxalic acid and ph buffered acetic acid in a flow through system at various flow rates at essentially constant ph the concentrations of al sio 2 and other components are enhanced in acetate bearing and oxalate bearing pore fluids for example steady state concentrations of al reached 80 ppm in buffered oxalic acid approximately 1000 ppm oxalate and 14 ppm buffered acetic acid approximately 4000 ppm acetate these concentrations are higher by factors of 800 and 130 respectively than previously calculated values for kaolinite solubility at the same ph in the absence of organics in general al and sio 2 in the pore fluid vary directly with oxalate and inversely with flow rate elevated metal concentrations are apparently due to formation of organic anion complexes and or increased reaction kinetics al si al k and al na molar values in solution exceed stoichiometric ratios for feldspar al favored ratios seem to be due to incongruent dissolution of feldspars by preferential formation of al oxalate complexes geologically reasonable concentrations of both monofunctional and difunctional carboxylic acids can enhance substantially the solubility of al under moderately acidic conditions although oxalate has a much greater effect than acetate the acetate system may buffer the ph in formation waters and allow rapid dissolution of aluminosilicates and creation of secondary porosity through reaction with carboxylic acid anions the effectiveness of the buffering and dissolution processes depends on many factors including type and availability of organic acids ph temperature flow rate mineralogic composition and associated reaction kinetics

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

computation of porosity redistribution resulting from thermal convection in slanted porous layers unlike fluid displacement due to regional hydraulic head thermoconvective motions are generally slow the thermal impacts of such movements are very weak whereas their chemical impacts may be significant because of their cumulated effects over geologic time for nonhorizontal thick sedimentary reservoirs the fluid velocity due to thermal convection can be accurately approximated by an explicit function of the dip of the reservoir the permeability and the difference in thermal conductivity between the aquifer and the confining beds the latter parameter controls the rotation direction of the flow and for clastic reservoirs bounded by impervious clayey media fluid moves up the slope along the caprock layer as the fluid velocity is small the major rock forming minerals control the fluid composition by thermodynamic equilibrium thus whereas the volume of redistributed minerals depends on the volume of water circulated the localization of porosity enhancement is strongly controlled by the reservoir mineralogy with realistic values of permeability and layer thickness several per cent of secondary porosity per million years can be created or lost at shallow depth 2 km depending on the chlorinity the set of representative minerals and the temperature in sandstone reservoirs and high chlorinity calcarenite reservoirs the porosity decreases under the caprock where hydrocarbons can accumulate in chloride depleted carbonate aquifers the simultaneous control by carbonates silica and aluminosilicates can produce a decrease of porosity above the bedrock and an enhancement of porosity under the caprock however computations show that the quality of the upper part of the reservoir is mainly reduced by the precipitation of silica and clays

diagenetic traps in sandstones diagenesis may be an important agent in trapping hydrocarbons in sandstones by formation of reservoirs or seals reservoirs are formed by the creation of secondary porosity during burial seals are formed by heavy cementation which may allow sandstones to retain large hydrocarbon columns formation of a diagenetic trap requires that parts of the sandstone unit react differently from each other during burial this can be caused by differences in 1 detrital mineralogy resulting from grain size or depositional environment controls 2 early diagenetic mineralogy largely depositional environment controlled 3 burial history structural movement induced and 4 fluid content hydrocarbon or water saturation each of these factors can lead to differences in porosity and permeability of the sandstone sufficient to form reservoirs and seals in the correct configuration diagenetic traps may be formed basin center gas accumulations result from diagenetic trapping in some instances

model for the evolution of oxygen isotope ratios in the pore fluids of mudrocks during burial abstract the determination of oxygen isotopic ratios in authigenic silicates and pore fluids provides vital information on the nature of water rock interactions in the subsurface and the origin of porosity occluding phases in reservoir rocks the 18 o values of pore fluids generally increase during burial through water rock interaction the transformation of detrital smectite to illite is thought to have a major influence on the isotopic evolution of pore fluids but previous attempts to model this effect have failed to accurately reproduce the observed water rock isotopic trends with depth a revised model has been developed which incorporates an empirical rate equation for the illitization reaction the input variables include the initial mineral and pore water isotopic compositions time porosity depth functions and geothermal histories and the assumption is made that the isotopic equilibration of the solid phases with pore waters only takes place during reaction the model is tested against the most complete data set available from the texas gulf coast usa and produces a good fit with the available pore fluid and mineral data the sensitivity of the model is tested for variations in the following parameters the illite water fractionation factor the fractionation of oxygen isotopes between the smectitic and illitic components of the detrital illite smectite the oxygen isotope fractionation between pore waters and the interlayer water within the smectite and the porosity depth function the results of the model are shown to be strongly dependent on the porosity depth function the best fit between the model and real data is provided by the dickinson equation for undercompacted shale modified to have a constant porosity below 2600 m to simulate the effects of overpressuring the model is also sensitive to the degree of oxygen isotopic fractionation between the illite and smectite within the sediment at the time of burial but not to the extent of fractionation between interlayer water within smectite and the adjacent pore waters the uncertainty within the illite water fractionation factor has only a minor effect on the results of the model although only incorporating a single mechanism for water rock interaction the model provides a tool for testing the interpretations of subsurface pore fluid evolution trends during sediment diagenesis

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

diagenetic evolution and chemical changes of deep water mudstones of shahejie formation in the dongying sag jiyang depression eastern china abstract the diagenetic evolution and chemical changes of mudstones have a significant influence on the reservoir quality of the mudstones and their interbedded sandstones to investigate a variety of methods were applied to the mudstones in the middle of the third member of the shahejie formation es3z which were formed in a lacustrine basin during 43 7 38 2 ma optical microscopy and xrd analysis show that the mudstones are dominated by clay minerals 56 8 followed by carbonate 18 2 quartz 14 9 feldspar 8 4 pyrite 0 9 anhydrite 0 8 and total organic carbon toc 2 4 cementation and replacement are the main diagenetic events in the mudstone of es3z carbonates and clay minerals are the most common cements but occasionally authigenic pyrite albite and quartz are also present at the eogenetic stage the diagenetic events comprised precipitation of pyrite siderite dolomite and calcite besides transformation of k feldspar into kaolinite during the mesogenetic stage the main diagenetic events included precipitation of fracture filling calcite ferroan calcite ankerite microcrystalline quartz quartz overgrowth and transformation of k feldspar into illite and albite the limited variation of the nb ta and zr hf ratios and the almost identical distribution pattern of the ree and trace elements indicate that the detrital material in the mudstones was sourced by a common provenance of felsic igneous rocks the cia values of es3z mudstones vary from 50 59 to 65 05 and the pia values vary from 50 86 to 75 58 which confirm a low intensity weathering of the source area thus the variation in the bulk rock geochemical composition of the mudstones may not be primary but instead a result of mass transfer with the interbedded sandstones during diagenesis changes ratios between aim elements al si ca and k and immobile elements with burial depth in combination with mass balance calculation indicate that aluminum and silicon were retained by the precipitation of authigenic minerals in the mudstone the mudstones have received progressively more potassium with increasing depths whereas calcium has been expelled the reservoir quality of the es3z sandstones has mainly been affected by the diagenetically induced decrease in the carbonate content in the mudstones causing carbonate cementation in the sandstones

a synoptic and dynamical characterization of wave train and blocking cold surge over east asia through an agglomerative hierarchical clustering method cold surges over east asia are classified into two distinct types based on the spatial pattern of the geopotential height anomalies at 300 hpa one is the wave train type that is associated with developing large scale waves across the eurasian continent the other is the blocking type whose occurrence accompanies subarctic blocking during the wave train cold surge growing baroclinic waves induce a southeastward expansion of the siberian high and strong northerly winds over east asia blocking cold surge on the other hand is associated with a southward expansion of the siberian high and northeasterly winds inherent to a height dipole consisting of the subarctic blocking and the east asian coastal trough the blocking cold surge tends to be more intense and last longer compared to the wave train type the wave train cold surge is associated with the formation of a negative upper tropospheric height anomaly southeast of greenland approximately 12 days before the surge occurrence further analysis of isentropic potential vorticity reveals that this height anomaly could originate from the lower stratosphere over the north atlantic cold surge of the blocking type occurs with an amplifying positive geopotential and a negative potential vorticity anomaly over the arctic and the northern eurasia in stratosphere these anomalies resemble the stratospheric signature of a negative phase of the arctic oscillation this stratospheric feature is further demonstrated by the observation that the blocking type cold surge occurs more often when the arctic oscillation is in its negative phase

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

mass transport in sandstones around dissolving plagioclase grains the dissolution of plagioclase and precipitation of kaolinite is a common late diagenetic process in sandstones the common occurrence on a thin section scale of patchy kaolinite adjacent to a dissolving plagioclase grain is consistent with diffusional transport of dissolved constituents combined with precipitation on a favorable nucleation site the absence in thin section view of a diffusionally related halo of kaolinite around a dissolving grain can be explained by a lack of a halo of favorable nucleation sites numerical modeling results are presented for the transport of aqueous al by diffusion coupled with fluid flow in sandstones at 100 c within a few months the al in the anorthite component of plagioclase grains can be removed by diffusion during diagenesis fluid velocities needed to overcome diffusion to prevent precipitation on the upstream side of a dissolving grain depend on the unknown minimum supersaturation needed for precipitation these velocities are less than those predicted by the peclet number but are of the order of metres per year at a distance of a few tenths of a millimetre from the dissolving grain the nonlinear inverse relation of these velocities to the distance from the dissolving grain implies that mass transport to precipitation sites is dominated by fluid flow at distances greater than 1 cm

source processes of 15 september 1998 m 5 0 sendai northeastern japan earthquake and its m 3 8 foreshock by waveform inversion a moderate earthquake m 5 0 occurred on 15 september 1998 in sendai city northeastern japan causing slight damage in a portion of the city it was located at about 12 km depth on the nagamachi rifu fault an active reverse fault passing through the center of the city we investigate rupture processes of the earthquake and its largest foreshock m 3 8 by an empirical green9s function method we use waveform data recorded by nearby dense strong motion arrays and by short period and broadband stations waveform inversion results for the mainshock show that the spatial extent of its rupture area is about 3 3 km 2 which is roughly consistent with that of the aftershock area most of the moment release was contained in two asperities aftershocks precisely relocated by a homogeneous station method show that their activity is high in areas with a relatively small amount of moment release of the mainshock rupture of the largest foreshock m 3 8 that occurred 6 min before the mainshock started approximately at the mainshock hypocenter its rupture area with a radius of about 300 m does not strongly overlap with the asperities of the mainshock

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

lithospheric imaging via teleseismic scattering tomography summary the coda of the teleseismic p phase consists largely of energy scattered by small inhomogeneities in the receiver side lithosphere given large collections of teleseismic data from dense permanent networks previous workers have successfully back propagated coda energy back to scattering source points using various kinematic migration schemes as well as by inverting using an inverse scattering radon transform approach under the born approximation seismic scattering is a linear process therefore it is possible to approach coda scattering as a linear waveform inversion problem mathematically similar to transmission based tomography assuming ray theoretical propagation and rayleigh scattering we pose the inverse scattering problem in tomographic form and recover perturbations in density and p and s velocities from pp and ps scattered data the method is applied to data from the southern california seismic network scsn covering the san jacinto anza region the results show a considerable correlation between seismicity and velocity perturbation structure particularly in the region between the mission creek and banning fault branches features connecting the coyote creek and elsinore faults at right angles are correlated with seismicity lineations and may represent conjugate faulting with no surface expression

foreshock and aftershock sequence of the 1998 m 5 0 sendai northeastern japan earthquake and its implications for earthquake nucleation we investigated foreshock and aftershock sequences of a m 5 0 earthquake that occurred on 15 september 1998 near the nagamachi rifu fault an active fault crossing the urban area of sendai city northeastern japan the focal mechanism of this event was a reverse fault type with a nearly horizontal p axis parallel to the plate conversion direction aftershock distribution located by the homogeneousstation method delineates the fault plane of this event dipping to the northwest at an angle of 30 in the depth range of 10 12 km the location of the fault plane and the slip direction thus estimated suggest that this event was a slip at a deep portion of the nagamachi rifu fault three days prior to the mainshock many foreshocks with similar waveforms started to occur very close to the mainshock hypocenter we estimated relative locations of these similar foreshocks based on crossspectrum analyses of waveforms recorded at nearby stations they are located at the deepest portion of the mainshock fault plane and just above the mainshock hypocenter migration of the foreshocks is observed from deeper to shallower depths cumulative coulomb stress changes caused by preceding events show negative values at hypocenters of similar waveform foreshocks our results do not support the cascade model for the process of foreshock generation nucleation phase prior to the high speed rupture of the mainshock is observed in seismograms at nearby stations the initial point of the nucleation phase is located on a deeper extension of the foreshock area the high speed breakout point is located in the area where a large amount of seismic moment release was estimated from waveform inversions these observations probably reflect an underlying aseismic nucleation process preceding the main dynamic rupture of the m 5 0 event

characteristics and formation mechanisms of the unconformity related paleokarst reservoirs in the upper sinian northwestern tarim basin china abstract in the late sinian the tarim basin experienced regional tectonic uplift and subaerial exposure a regional unconformity was extensively distributed during the succession from the sinian to cambrian as a result a large number of secondary pores were developed in the upper sinian qegebulake formation an integrated study based on petrographical and petrophysical analysis geochemistry karstology and fluid inclusions was performed to provide insight into the characteristics and formation mechanism of the upper sinian carbonate reservoirs the reservoir rocks mainly include microbial dolomite crystalline dolomite and breccias reservoir matrix porosity and permeability range from 0 30 to 11 06 and from 0 00156 md to 1 49 md respectively geological and geochemical characteristics suggest that three phases of dissolution were determined to be responsible for the development of the reservoirs within about 70 m beneath the unconformity they are meteoric dissolution during subaerial exposure and deep seated hydrothermal dissolution and organic acid dissolution during the burial stage the upper sinian dolomite underwent strong meteoric dissolution which is supported by the appearance of the unconformity and the associated caves the geochemical characteristics of the cave filling calcite further indicate the diagenetic overprint from meteoric water including the relatively negative values of 18o 18 46 to 8 5 vpdb and wide range of 13c 8 11 to 0 24 vpdb low ree 1 77 4 23 ppm and yb la and yb ca variation the occurrence of saddle dolomite as well as analytical results such as 13c 0 67 2 52 vpdb and 18o 13 21 to 9 81 vpdb isotope signature and high homogenization temperature of fluid inclusions in quartz 87 2 to 220 c and saddle dolomite 82 3 135 4 c suggest that the reservoirs rocks experienced interaction with hydrothermal fluids only bitumen occurred in the edge of secondary pores formed by dissolution of quartz and saddle dolomite which suggests that organic acid dissolution likely occurred during the evolution of reservoirs a geological model for the evolution of the paleokarst reservoirs is proposed through the analysis of major reservoir controlling factors the primary pore types and reservoir petrophysical property of the qigebulake formation mainly depend on the sedimentation supergene karstification is the most important process for reservoir formation deep seated hydrothermal activity has both positive and negative attribution on the formation of reservoirs organic acid dissolution plays an active role in the formation and preservation of reservoirs this study provides a useful reference for hydrocarbon exploration in the deep buried sinian carbonate reservoirs

a closer comparison of early and late winter atmospheric trends in the northern hemisphere abstract decadal trends are compared in various fields between northern hemisphere early winter november december nd and late winter february march fm months using reanalysis data it is found that in the extratropics and polar region the decadal trends display nearly opposite tendencies between nd and fm during the period from 1979 to 2003 dynamical trends in late winter fm reveal that the polar vortex has become stronger and much colder and wave fluxes from the troposphere to the stratosphere are weaker consistent with the positive trend of the arctic oscillation ao as found in earlier studies while trends in nd appear to resemble a trend toward the low index polarity of the ao in the tropics the hadley circulation shows significant intensification in both nd and fm with stronger intensification in fm unlike the hadley cell the ferrel cell shows opposite trends between nd and fm with weakening in nd and strengthening in fm comparison of the observational results with general circul

small scale heterogeneities below the grafenberg array germany from seismic wavefield fluctuations of hindu kush events summary small scale elastic heterogeneities 5 km are found in the upper lithosphere under neath the grafenberg array southeast germany the results are based on the analysis of broadband recordings of 17 intermediate depth 201 272 km events from the hindu kush region the wavefront of the first p arrival and the following 40 s coda are separated into coherent and incoherent scattered parts in the frequency range from 0 05 to 5 hz the frequency dependent intensities of the mean and fluctuation wavefields are used to describe the scattering characteristics of the lithosphere underneath the receivers it is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below approximately 1 5 2 5 hz and a strong fluctuation regime starting at 2 0 2 5 hz and continuing to higher frequencies in order to explain the observed wavefield fluctuations an approach with seismic scattering at random media type structures is proposed the preferred model contains heterogeneities with 3 7 per cent perturbations in seismic velocity and correlation lengths of 0 6 4 8 km in the crust this is compatible with models from active seismic experiments scattering in the lithospheric mantle is not required but cannot be excluded at weak velocity contrasts 3 per cent

imaging of crustal heterogeneous structures using a slowness weighted back projection with effects of scattering modes 2 application to the nagamachi rifu fault japan area 1 this is the second paper in a two part series on a newly developed imaging approach for small scale heterogeneities 1 km in the crust with effects of scattering modes in the present paper we estimated a detail three dimensional spatial distribution of small scale heterogeneities around the nagamachi rifu fault northeastern japan in a frequency range of 2 16 hz using the imaging approach presented in the first paper we used seismograms recorded by dense three component seismic arrays that were deployed in this region for 15 explosion sources as one of our important results there are concentrations for only p s but not p p scatterers near the surface trace of the fault p s scatterers in a frequency range of 8 16 hz are localized near the surface trace of the fault implying the possibility of strong heterogeneities with a size of 0 08 km there in the shirasawa caldera region the characteristics of seismic scatterers seem to convert from large p s to large p p relative scattering coefficients with its transition depth range of 5 8 km this feature implies that the materials composed of seismic scatterers may show a systematic variation with depth finally the strength of scattering coefficients is rather weak in the coseismic area of the 15 september 1998 earthquake with a magnitude of 5 2 the largest recent event in this area this result suggests that this coseismic area is rather homogeneous and can hold local stress larger than in the surrounding portions of the fault system

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

diagenetic carbonate in miocene sandstone reservoir san joaquin basin california stevens arkosic sandstones deposited about 7 ma in a deep marine environment form the north coles levee reservoir dolomite and calcite cements occur as zones averaging 1 ft thick and having less than 300 ft of lateral continuity based on dgr18o measurements and estimated pore fluids between 0 and 2 8 the dolomite formed at 30 40 c an early calcite cement formed at 50 60 c and a late pore filling and plagioclase replacing calcite formed at 70 80 c corresponding to these temperature estimates dolomite formed in the zone of methanogenesis dgr13c 4 to 8 and calcites in the zone of decarboxylation dgr13c 3 to 12 dolomite has between 4 and 12 mole fe and calcites contain up to 8 mole o fe mg mn with a characteristic fe mn mg ratio of about 3 1 the latest calcite is the most ca rich due in part to ca sourced from plagioclase dissolution calcite cements in nonmarine sections have markedly high mn contents to 5 mole compared with the marine section at north coles levee the volume of cement systematically decreases from about 40 20 over the cementation temperature interval suggesting progressive compaction of the sandstones present day mean porosity of the reservoir 15 appears to be largely a result of mechanical compaction a very late dolomite cement with high fe content 13 mole and light carbon dgr13c 14 is found in the cleavage flakes of crushed biotite the dolomite is calculated to have formed from a fluid with a dgr18o of 0 9 at present reservoir temperatures of 105 c suggesting precipitation in the past 20 years during release of the gas cap and injection of isotopically light water calcite also forms thick scales in production tubing primarily as a result of pressure drops from 4 900 to 400 psi in the tubing string the calcites have high mg contents 7 mole due to the composition of the injection water calculated distribution coefficients for fe and mn are similar to published values but mg is two times higher than published values at 90 c similar results are obtained for late calcite cements a time temperature plot for north coles levee constrains the timing of dolomite cementation between 5 and 6 ma and the calcite cementation between 4 and 2 5 ma plagioclase dissolution and hydrocarbon emplacement occurred within the past few million years suggesting that the presence of the hydrocarbons and associated byproducts of kerogen maturation enhance porosity despite the narrow window for diagenesis minimum fluid fluxes of only 0 02 cm3 yr per 100 cm3 rock are required to account for the volume of dissolved plagioclase

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

quartz cement and its origin in tight sandstone reservoirs of the cretaceous quantou formation in the southern songliao basin china abstract the tight sandstones of the cretaceous quantou formation are the main exploration target for hydrocarbons in the southern songliao basin authigenic quartz is a significant cementing material in these sandstones significantly reducing porosity and permeability for efficient predicting and extrapolating the petrophysical properties within these tight sandstones the quartz cement and its origin need to be better understood the tight sandstones have been examined by a variety of methods the sandstones are mostly lithic arkoses and feldspathic litharenites compositionally immature with an average framework composition of q43f26l31 which are characterized by abundant volcanic rock fragments mixed layer illite smectite i s ordered interstratified with r 1 and r 3 is the dominating clay mineral in the studied sandstone reservoirs two different types of quartz cementation modes namely quartz grain overgrowth and pore filling authigenic quartz have been identified through petrographic observations cl and sem analysis homogenization temperatures of the aqueous fluid inclusions indicate that both quartz overgrowths and pore filling authigenic quartz formed with a continuous process from about 70 c to 130 c sources for quartz cement produced are the conversion of volcanic fragments smectite to illite reaction and pressure solution at micro stylolites potassium for the illitization of smectite has been sourced from k feldspar dissolution and albitization silica sourced from k feldspars dissolution and kaolinite to illite conversion is probably only minor amount and volumetrically insignificant the internal supplied silica precipitate within a closed system where the transport mechanism is diffusion the quartz cementation can destroy both porosity and permeability but strengthen the rock framework and increase the rock brittleness effectively at the same time

modulation of the qbo on the mjo related surface air temperature anomalies over eurasia during boreal winter previous studies have indicated the modulation of the madden julian oscillation mjo by the quasi biennial oscillation qbo and the influence of the mjo on surface temperature over eurasia during boreal winter the present study reveals that the mjo related circulation anomalies are different in easterly and westerly qbo years leading to distinct surface temperature anomaly patterns over eurasia during the easterly qbo years the surface air temperature anomalies over eurasia display a meridional dipole pattern in mjo phase 2 associated with the mid latitude surface anticyclonic anomalies the development of surface anomalous anticyclone is attributed to a combined effect of negative north atlantic oscillation nao related mid latitude wave train and stronger mjo convection triggered poleward propagation of rossby wave train the negative nao is related to the easterly qbo through the holton tan relationship the anomalous overturning circulation excited by the stronger mjo convection in easterly qbo years also contributes to the development and eastward extension of anomalous anticyclone the anticyclonic anomalies induce the meridional temperature anomaly pattern by horizontal advection during the westerly qbo years the surface air temperature anomalies over eurasia show a zonal alternating pattern in mjo phase 3 which corresponds to the development of mid latitude rossby wave train associated with positive nao with a stronger mjo nao connection in westerly qbo years the mjo convection induces upper level divergent wind anomalies contributing partially to the development of the rossby wave source and helping the building of the mid latitude wave train the zonal temperature anomalies over eurasia are also contributed by the horizontal advection associated with surface cyclonic anomalies

another look at influences of the madden julian oscillation on the wintertime east asian weather 1 as one of the major predictability sources on an intraseasonal time scale the madden julian oscillation mjo exerts a profound influence on the subseasonal forecast of the east asian ea surface air temperature sat and precipitation in this study we examine the direct link of the mjo with the ea sat and precipitation and its dynamical mechanism to represent the mjo we perform an empirical orthogonal function eof analysis on pentad outgoing longwave radiation olr over 20 s 20 n 60 e 150 w the eof1 mode is mostly characterized by a single convection center near the maritime continent 90 150 e whereas the eof2 mode has an east west dipole structure with enhanced convection over the eastern indian ocean and suppressed convective activities over the tropical western pacific at the same pentad of a positive eof1 phase large areas of cold anomalies with reduced precipitation emerge in the ea region north of 20 n and persist through two pentads later at the same pentad of a positive eof2 phase sat and precipitation exhibit a zonal dipole pattern with cold and dry anomalies covering the ea region west of 120 e and warm and wet anomalies to the east these dipole anomalies in sat and precipitation systematically move eastward in the next two pentads a linearized global primitive equation model is utilized to assess the cause of the intraseasonal variability in sat and precipitation over east asia associated with the tropical heating of the mjo the model responses to heating sources that mimic the eof1 and eof2 olr patterns match well the general features of the observed circulation anomalies under forcing of a positive phase of the eof1 pattern strengthened local hadley cell or monsoon circulations within 90 e 150 e are reproduced with anomalous northerly winds and dry anomalies prevailing in the lower troposphere over east asia the processes that influence east asia are mainly associated with intraseasonal changes in local hadley circulation and the northern hemisphere branch of the equatorially trapped rossby wave gyres forced by the mjo heating

diagenesis and reservoir quality evolution of the eocene sandstones in the northern dongying sag bohai bay basin east china abstract the eocene sandstones in the northern dongying sag bohai bay basin china are reservoirs for large accumulations of hydrocarbons the sandstones are mainly lithic arkoses and feldspathic litharenites texturally and compositionally immature these sandstones have a wide range of porosity 0 4 37 and permeability 0 004 6969 md and show an overall decrease in reservoir quality from 1500 m to 5000 m below sea level the reduction in reservoir quality is a product of several digenetic processes these include compaction precipitation of dolomite and calcite in eodiagenetic stage compaction feldspar dissolution precipitation of quartz cements and clays kaolin and illite and precipitation of ferrocalcite and ankerite in mesodiagenetic stage mineral distribution pattern and isotopic composition suggest carbonate cements in sandstones originate from sources outside the sandstones carbonate cementation together with compaction reduced the sandstones porosity and permeability significantly in a sandstone bed marginal sandstones with distance to sandstone mudstone interface less than one meter always have lower porosity than central sandstones as burial depth exceeds 4000 m marginal sandstones have very low porosities 2 m can be potential effective reservoirs feldspar dissolution and precipitation of clays and quartz cements have little impact on absolute porosity mineral distribution pattern and quantitative data show that leached feldspars are the internal source of authigenic quartz and clays in sandstones and the volume difference between feldspar secondary porosity and related authigenic cements is generally less than 0 25 however although there is little or no net import of matter to the sandstones the pore architecture changes dramatically primary macropores are lost as clays and quartz precipitate while the proportion of microporosity increases occurring mainly between clay crystals the overall result is that permeability is significantly degraded

migration of hydrocarbons and secondary porosity in sandstones a unified hypothesis concerning generation and migration of hydrocarbons and development of secondary porosity in sandstones is presented carbonic acid is considered to be the primary reagent responsible for dissolution in the development of secondary porosity in sandstones the degree to which reservoir quality is enhanced by development of secondary porosity may be proportional to the amount of hyrocarbons generated as well as to the amount of unstable constituents during diagenesis in some cases formation of secondary porosity may be responsible not only for development of reservoir but also for a significant element of entrapment by the partial but areally and stratigraphically selective dissolution of sandstone in the migration path of hydrocarbons jmt

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

impact of diagenesis on reservoir quality and heterogeneity of the upper triassic chang 8 tight oil sandstones in the zhenjing area ordos basin china abstract reservoir quality and heterogeneity are critical risk factors in tight oil exploration the integrated analysis of the petrographic characteristics and the types and distribution of diagenetic alterations in the chang 8 sandstones from the zhenjing area using core log thin section sem petrophysical and stable isotopic data provides insight into the factors responsible for variations in porosity and permeability in tight sandstones the results indicate that the chang 8 sandstones mainly from subaqueous distributary channel facies are mostly moderately well to well sorted fine grained feldspathic litharenites and lithic arkose the sandstones have ultra low permeabilities that are commonly less than 1 md a wide range of porosities from 0 3 to 18 1 and two distinct porosity permeability trends with a boundary of approximately 10 porosity these petrophysical features are closely related to the types and distribution of the diagenetic alterations compaction is a regional porosity reducing process that was responsible for a loss of more than half of the original porosity in nearly all of the samples the wide range of porosity is attributed to variations in calcite cementation and chlorite coatings the relatively high porosity reservoirs formed due to preservation of the primary intergranular pores by chlorite coatings rather than burial dissolution however the chlorites also obstruct pore throats which lead to the development of reservoirs with high porosity but low permeability in contrast calcite cementation is the dominant factor in the formation of low porosity ultra low permeability reservoirs by filling both the primary pores and the pore throats in the sandstones the eogenetic calcites are commonly concentrated in tightly cemented concretions or layers adjacent to sandstone mudstone contacts while the mesogenetic calcites were deposited in all of the intervals and led to further heterogeneity this study can be used as an analogue to understand the variations in the pathways of diagenetic evolution and their impacts on the reservoir quality and heterogeneity of sandstones and is useful for predicting the distribution of potential high quality reservoirs in similar geological settings

imaging of three dimensional small scale heterogeneities in the hidaka japan region coda spectral analysis summary while large scale heterogeneities have been studied intensively by seismic tomography with traveltime data small scale heterogeneities are not fully investigated yet we obtained the 3d spatial distribution of small scale heterogeneities as relative scattering coefficients in the hidaka japan region using the spatial variation of high frequency coda power spectra we analysed 530 seismograms recorded at 62 stations for nine local earthquakes in the frequency range of 1 32 hz after correcting source station and propagation effects we assigned the spatial and temporal variations of observed power spectra of coda waves into the 3 d distribution of scattering coefficient based on single and isotropic scattering models small scale heterogeneities are distributed not only in a non uniform manner but also differently among scale lengths estimated from their frequency dependence an area of large relative scattering coefficient in 2 and 16 hz is located at a depth shallower than 45 km in the southwest of the hidaka mountains correlating well with a highly active area of microearthquakes at a depth of 60 120 km two dipping zones of large scattering coefficient are imaged beneath the summit of the hidaka mountains these zones may imply two layers of strong seismic wave reflection consistent with the upper and lower planes of the double seismic zone in the subducting pacific plate as determined by the hypocentral distribution in this region

parameters influencing porosity in sandstones a model for sandstone porosity prediction thirteen parameters were reviewed for their influence on porosity in sandstone core material during compaction in basins of average geothermal gradients the first order parameters are age time of burial detrital quartz content maximum depth of burial and sorting overpressure may slow the compaction process depending on onset of overpressure during burial approximately 2 primary porosity may be preserved for every 1 000 psi 6 9 mpa above hydrostatic pressure depth related temperature and median grain size were found to be only second order parameters on the basis of 428 cases function coefficients were calculated for the relationship between porosity and the first order parameters this function permits porosity prediction with a high degree of accuracy th equation is valid for sandstones older than 3 ma with little or no cement no leaching depth of burial in excess of 500 m and little or no shear stresses secondary porosity is excluded and estimations will therefore be conservative where leaching occurred due to interrelationship of compaction and cementation the porosity reduction by cement is usually only a small fraction of the total reduction the function can therefore also be applied to little cemented sandstones

deep crustal heterogeneity along and around the san andreas fault system in central california and its relation to the segmentation the three dimensional distribution of scatterers in the crust along and around the san andreas fault system in central california is estimated using an inversion analysis of coda envelopes from local earthquakes i analyzed 3801 wave traces from 157 events recorded at 140 stations of the northern california seismic network the resulting scatterer distribution shows a correlation with the san gregorio san andreas hayward and calaveras faults these faults seem to be almost vertical from the surface to 15 km depth some of the other scatterers are estimated to be at shallow depths 0 5 km below the diablo range and these may be interpreted as being generated by topographic roughness the depth distribution of scatterers shows relatively stronger scattering in the lower crust at 15 25 km depth especially between the san andreas fault and the hayward calaveras faults this suggests a subhorizontal detachment structure connecting these two faults in the lower crust several clusters of scatterers are located along the san andreas fault at intervals of 20 30 km from south of san francisco to the intersection with the calaveras fault this part of the san andreas fault appears to consist of partially locked segments also 20 30 km long which rupture during m6 7 events and segment boundaries characterized by stronger scattering and stationary microseismicity the segment boundaries delineated by the present analysis correspond with those estimated from the slip distribution of the great 1906 san francisco earthquake and from the fault geometry as reported by the working group on california earthquake probabilities 1990 although the segment boundaries along the san andreas fault in and around the san francisco bay area are still uncertain

sedimentological aspects of the humber group upper jurassic of the south central graben uk north sea complex structure poorly understood sedimentology and poor biostratigraphic control make the upper jurassic humber group of the south central graben one of the least understood and most complex hydrocarbon reservoirs of the north sea detailed logging of available core from 19 exploration wells has been combined with an improved understanding of the relevance of trace fossils and a recognition of important base level variations to provide a greatly enhanced understanding of the depositional system active within the area at that time a new sedimentological model based upon the distribution of facies and facies associations illustrates that upper jurassic structure and consequent basin geometry were the principal controls upon the distribution of depositional environments rifting and second order transgression controlled the back stepping onlap patterns observed and higher frequency base level fluctuations controlled the internal architecture of individual sandbodies the model presented accounts for features of these deposits that were previously considered anomalous such as the thickness of bioturbated sandstones paucity of foreshore deposits and complex age relationships of sands

burial evolution of evaporites with implications for sublacustrine fan reservoir quality a case study from the eocene es4x interval dongying depression bohai bay basin china abstract eocene sublacustrine fan sandstones that developed in a rift basin are important tight gas reservoirs in the dongying depression bohai bay basin northeastern china two units of evaporites developed at the top and bottom of the lower unit of the es4 interval es4x consist predominantly of anhydrite with subordinate gypsum evaporite and related diagenetic processes greatly influenced reservoir quality 13 c values for micritic dolomite cements in es4x are depleted 7 45 to 2 57 due to microbial sulfate reduction msr under shallow burial conditions and this interpretation is supported by large 34 s fractionation between anhydrite and framboidal pyrite precipitation temperatures for micritic dolomite are calculated as 57 5 72 8 c anhydritization of gypsum probably occurred at 100 5 145 2 c during progressive burial as evidenced by homogenization temperatures of aqueous inclusions within anhydrite cements this process resulted in dehydration fractures within anhydrite cements that increased reservoir permeability by connecting isolated pores thermochemical sulfate reduction tsr probably resulted in dissolution of gypsum and anhydrite cements under relatively deep burial conditions ankerite cements are replaced by anhydrite cements and are enclosed by solid bitumen in es4x ankerite cements likely were derived from tsr as reflected in negative 13 c values 7 12 to 3 70 and high calculated temperatures 121 3 185 1 c dissolution by products e g saddle dolomite ankerite nodular pyrite related to tsr precipitated in adjacent pores a lack of significant 34 s fractionation between parent sulfate and nodular pyrite indicates that tsr occurred in a relatively closed system therefore dissolution of gypsum and anhydrite related to tsr contributed little to reservoir quality middle fan lithofacies with better sorting porosity and permeability than inner and outer fan lithofacies constitute high quality reservoirs in es4x