impact of poroelastic response of sandstones on geothermal power production during geothermal power production using a borehole doublet consisting of a production and injection well the reservoir conditions such as permeability k porosity and skempton coefficient b at the geothermal research site gross schoenebeck germany will change besides a temperature decrease at the injection well and a change of the chemical equilibrium also the pore pressure pp will vary in a range of approximately 44 mpa 10 mpa in our reservoir at 3850 to 4258 m depth this leads to a poroelastic response of the reservoir rocks depending on effective pressure p eff difference between mean stress and pore pressure resulting in a change in permeability k porosity and the poroelastic parameter skempton coefficient b hence we investigated the effective pressure dependency of flechtinger sandstone an outcropping equivalent of the reservoir rock via laboratory experiments the permeability decreased by 21 at an effective pressure range from 3 to 30 mpa the porosity decreased by 11 p eff 6 to 65 mpa and the skempton coefficient decreased by 24 p eff 4 to 25 mpa we will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir the most significant changes occur at low effective pressures until 15 to 20 mpa for our in situ reservoir conditions p eff 43 mpa a change of 10 mpa effective pressure will result in a change in matrix permeability of less than 4 and in matrix porosity of less than 2 besides natural fracture systems fault zones and induced hydraulic fractures the rock matrix its only one part of geothermal systems all components can be influenced by pressure temperature and chemical reactions therefore the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir

experimental study of the stress dependence of the absolute and relative permeabilities of some tight gas sandstones connected porosity and dry gas permeability at 5 mpa hydrostatic stress have been measured for thirteen tight gas sandstone samples originating from a rotliegend sandstone reservoir in germany the samples have then been preserved into hermetic chambers at fixed relative humidity rh values until mass and water saturation level stabilisation this allows a first characterisation of pore size distribution showing that most of the pore network is constituted with pores with entrance radii greater than 50 nm the relative gas permeability was then measured for different water saturation and hydrostatic stress up to 60 mpa the analysis of the results has allowed us to identify the limiting conditions water saturation and hydrostatic stress for the apparition of a hydraulic cut off also called the permeability jail dry gas permeability at low confining pressure 5 mpa has appeared to be a good indicator of the sensitivity of a sample to both hydraulic stress and liquid saturation this gives an efficient tool to predict the global behaviour of the gas reservoir despite its heterogeneity with a single gas permeability measure

nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

regional earthquake likelihood models i first order results abstract the regional earthquake likelihood models relm working group designed a 5 year experiment to forecast the number spatial distribution and magnitude distribution of subsequent target earthquakes defined to be those with magnitude 4 95 m 4 95 in a well defined california testing region included in the experiment specification were the description of the data source the methods for data processing and the proposed evaluation metrics the relm experiment began on 1 january 2006 and involved 17 time invariant forecasts constructed by seismicity modelers by the end of the experiment on 1 january 2011 31 target earthquakes had occurred we analyze the experiment outcome by applying the proposed consistency tests based on likelihood measures and additional comparison tests based on a measure of information gain we find that the smoothed seismicity forecast by helmstetter et al 2007 based on m 2 earthquakes since 1981 is the best forecast regardless of whether aftershocks are included in the analysis the relm experiment has helped to clarify ideas about testing that can be applied to more wide ranging earthquake forecasting experiments conducted by the collaboratory for the study of earthquake predictability csep online material figures and tables showing the relm testing region and collection region definitions numerical results associated with the relm experiment and the uncorrected forecast by ebel et al 2007

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

multi fractal distribution analysis for pore structure characterization of tight sandstone a case study of the upper paleozoic tight formations in the longdong district ordos basin abstract with proven gas potential the gas charging and accumulation mechanisms for the upper paleozoic tight gas reservoir in the longdong district of the ordos basin remain controversial pore structure is the most direct and critical factor that affects gas charging and accumulation in the reservoir however the pore structure characterization of tight sandstone is far more difficult than that for conventional reservoir rocks due to significant heterogeneity the present work aims to introduce a new quantitative method for pore structure characterization that integrates multi fractal distribution analysis an effective and profitable method for quantitative heterogeneity analysis and high pressure mercury intrusion porosimetry hpmip twenty one samples from targeted tight formations with different gas bearing status were obtained for analysis the results show that the best formations for gas charging and accumulation in the upper paleozoic tight sandstone formations in the longdong district are the formations with more large pores more homogeneous small pores and well developed micro fractures the existence of micro fractures is the key factor that affects gas charging and accumulation tight sandstone samples were categorized into three types in accordance with the hpmip curve configuration due to the high heterogeneity of pore structures analyses based solely on hpmip curve configuration has its shortcomings which can be compensated by multi fractal distribution analysis the multi fractal distribution of target tight formations could be interpreted as two linear segments representing large pores and small pores the separating points of the two segments vary from 0 1 m to 0 5 m in different samples due to different pore structures large pores are not ideal fractals in gas bearing formations due to the existence of micro fractures whereas they are fractals in dry formations where micro fractures are not developed small pores are all ideal fractals with the highest heterogeneity in type samples and the lowest heterogeneity in type samples a conclusion was made in this work if the slope of segment one in the multi fractal distribution of mercury saturation shg versus capillary pressure pc is larger than 1 this measure could be accepted as an empirical indicator for the existence of micro fractures

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

asian continental nature of87sr 86sr ratios in north central pacific sediments strontium isotopic compositions were determined for silicate detritus in 152 deep sea and continental shelf surface sediment samples from the pacific ocean to trace their provenance the major characteristics of the spatial variation of the sr isotopes and the interpretation of this variation may be summarized as follows 1 sediments in the pacific have a lower average87sr 86sr ratio 0 7112 with a narrower range 0 703 0 724 than in the atlantic 0 7166 0 704 0 743 many western pacific volcanoes together with young continental crust supply material with low87sr 86sr ratios to the pacific in contrast to the large old cratonic crust that supplies material with high sr ratio to the atlantic 2 the87sr 86sr ratio is high in the north central pacific 0 711 0 719 the izu ogasawara and mariana arcs supply low87sr 86sr material to the western pacific but farther to east the abundant supply of loess carried by middle latitude westerlies from the asian continent 87sr 86sr ca 0 720 dominates the north central pacific

a fault based model for crustal deformation fault slip rates and off fault strain rate in california we invert global positioning system gps velocity data to estimate fault slip rates in california using a fault based crustal deformation model with geologic constraints the model assumes buried elastic dislocations across the region using uniform california earthquake rupture forecast version 3 ucerf3 fault geometries new gps velocity and geologic slip rate data were compiled by the ucerf3 deformation working group the result of least squares inversion shows that the san andreas fault slips at 19 22 mm yr along santa cruz to the north coast 25 28 mm yr along the central california creeping segment to the carrizo plain 20 22 mm yr along the mojave and 20 24 mm yr along the coachella to the imperial valley modeled slip rates are 7 16 mm yr lower than the preferred geologic rates from the central california creeping section to the san bernardino north section for the bartlett springs section fault slip rates of 7 9 mm yr fall within the geologic bounds but are twice the preferred geologic rates for the central and eastern garlock inverted slip rates of 7 5 and 4 9 mm yr respectively match closely with the geologic rates for the western garlock however our result suggests a low slip rate of 1 7 mm yr along the eastern california shear zone and southern walker lane our model shows a cumulative slip rate of 6 2 6 9 mm yr across its east west transects which is 1 mm yr increase of the geologic estimates for the off coast faults of central california from hosgri to san gregorio fault slips are modeled at 1 5 mm yr similar to the lower geologic bounds for the off fault deformation the total moment rate amounts to 0 88 1019 n m yr with fast straining regions found around the mendocino triple junction transverse ranges and garlock fault zones landers and brawley seismic zones and farther south the overall california moment rate is 2 76 1019 n m yr which is a 16 increase compared with the ucerf2 model online material table of geological slip rates

determining the porosity exponent m and lithology factor a for sandstones and their control by overburden pressure a case study from the gulf of suez egypt the porosity exponent m represents an important parameter in archie s equation it is routinely used in well logging interpretation and formation evaluation it reflects some petrophysical rock properties such as the petrofabrics pore fabrics and overburden pressure obp data measured at ambient conditions for a total of 55 sandstone core samples were obtained from 8 wells varying in depositional facies geologic age degree of consolidation and cementation material and then measured again at obp similar to the actual reservoir conditions to check the effect of obp on archie s parameters and to introduce a model of high reliability other published data sets were also used to confirm the study results based on the best fit regression analysis several empirical relationships were introduced to relate the porosity exponent to pore volume lithology factor and permeability the effect of obp on the porosity exponent was also investigated in relation to the petrophysical parameters given the above a new statistical model is proposed to relate the porosity exponent to the permeability of the studied sandstone samples in the gulf of suez egypt the effect of confining pressure on the studied porosity exponent m and the lithology factor a is significant when porosity is less than or equal to 10 from the present study categorization of the studied samples into flow units and rock types using the hydraulic flow unit and the discrete rock types increased the reliability of the obtained relationships and increased the applicability of the obtained equations in addition the value of the lithology factor a fluctuates around 1 0 92 1 04 regardless of the applied processing method whereas the value of the porosity exponent m fluctuates around 1 83 the obtained relationships between the formation resistivity factor and porosity have a very high reliability 0 949 correlation coefficient 0 969

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog upper triassic sonsela member of the chinle formation petrified forest national park arizona the upper triassic sonsela member of the chinle formation in the petrified forest national park was evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria along a continuous 0 5 km 0 3 mi outcrop the study interval consists of interbedded sandstones and mudstones and is composed of a two tiered hierarchy of cyclic alluvial deposits with bounding paleosols the succession is composed of 15 fluvial aggradational cycles facs that comprise two fac sets fac sets the fac sets are composed of architectural elements suggestive of a mixed load fluvial system that is alternately dominated by bed load deposits and suspended load deposits a thinning and fining stacking pattern within fac sets is accompanied by an upward increase in pedogenic modification suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain sandstones are classified as litharenites feldspathic litharenites and lithic subarkoses and occur within recycled orogen dissected arc and transitional arc provenance fields sandstone compositional maturity increases upward through the fac sets point counts of intergranular volume as a proxy for primary porosity within channel facies and subsequent transform to syndepositional permeability provide a two dimensional depiction of the lateral variability in reservoir quality paleosols are weakly to moderately developed and have little stratigraphic variation these characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits log compaction at the time of silicification averaged 9 1 suggesting that log silicification and porosity loss occurred soon after deposition

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

optimal interpolation of spatially discretized geodetic data abstract we present an algorithm to calculate horizontal strains or strain rates through interpolation of geodetically derived displacements or velocities this is an underdetermined inverse problem to derive smoothly distributed strains or strain rates using spatially discretized geodetic observations a priori information in the form of weighted smoothing is critical to facilitate the solution at a given site the horizontal displacement or velocity field in its vicinity is approximated by a bilinear function and represented by rigid block translation rotation and strains or their rates the weighted displacement or velocity data in the neighborhood are used to estimate the field parameters through a least squares inversion procedure optimal weightings are prescribed for the neighboring data based on their distances to the interpolation site and their spatial coverage nonelastic strains resulted from surface fault rupture and creep may also be excluded from the solution we apply this method to the southern california earthquake center crustal motion map version 4 0 velocity field and derive the strain rate field in southern california our result shows that 1 distance dependent weighting can be optimally achieved by employing either a gaussian or quadratic decay function with the former offering a slightly sharper result than the latter 2 spatially dependent weighting is important to improve the interpolation and can be done by invoking either an azimuthal weighting or a voronoi cell areal weighting function 3 the strain rate pattern in southern california is dominated by dextral shear of the san andreas fault saf system and the secondary faults surrounding the big bend of the saf strike at oblique angles with respect to the maximum shear direction suggesting that tectonic deformation field on and off the saf is dominated by mechanic processes of the saf

provenance of the north pacific sediments and process of source material transport as derived from rb sr isotopic systematics abstract rb sr isotopic systematics of 111 samples of sediments in nine cores from the north pacific of quaternary and pliocene ages have been investigated they provide information on the provenance the process of particle transport and temporal variation in the flux of source material the rb sr isotopic systematics of the core sediments show well correlated pseudo isochrons the pseudo isochrons reflect the mixing of two types of material i e the asian continental material with high 87 rb 86 sr ratios 4 5 6 5 and high 87 sr 86 sr ratios 0 723 0 727 and the volcanic material with low 87 rb 86 sr ratios and low 87 sr 86 sr ratios from island arc volcanics such as the izu ogasawara mariana and the japanese islands and oceanic islands such as the hawaiian islands 0 0 2 0 0 703 0 708 the clearness of the pseudo isochrons implies that the rb sr isotopic composition of the weathering products derived from the asian continental crust is extremely homogenized the fine fraction a few m with a high 87 rb 86 sr ratio 5 0 6 5 is widely transported into the north pacific by the middle latitude westerlies and contributes largely to pelagic sediments the coarser fraction with a lower 87 rb 86 sr ratio

a geodetic strain rate and tectonic velocity model for china national science foundation of china 41704014 science and technology innovation fund of sichuan earthquake agency 201804

anhydrite cementation and compaction in geothermal reservoirs interaction of pore space structure with flow transport p t conditions and chemical reactions in order to analyze local clogging phenomena due to the precipitation of anhydrite in the pore space we performed a petrophysical study on cores and data from three boreholes probing the rhaetian hydrothermal aquifer in northern germany allermohe neuruppin 1 88 neuruppin 2 87 the pore size geometry of sandstones was studied using among other methods pulsed field gradient nuclear magnetic resonance pfg nmr we found two facies types with clearly different diagenetic history 1 a fine grained sand with small pores mechanically compacted during diagenesis into an average sandstone of fractal pore geometry 2 a coarser sand with larger pores almost completely cemented by anhydrite after compaction had reduced the pore space to a porosity of 30 thus no further mechanical compaction occurred and the pores remained smooth in contrast the fine grained facies was not cemented possibly because anhydrite crystal nuclei are unstable in pores of insufficient size with regard of these two facies types we developed 1 an approach for calculating vertical logs of anhydrite and permeability content from gamma density measurements in boreholes or on core 2 a chemical reaction model to calculate the amount of precipitation and dissolution of each mineral species at high temperature and salinity these petrophysical and geochemical models are integrated into the numerical simulation tool shemat for simulating coupled flow heat and species transport and chemically induced permeability changes a comparison of the diagenesis of the cemented and un cemented facies types yields an improved understanding of the geological conditions required for anhydrite cementation specifically with regard to the studied rhaetian sandstones numerical reactive flow simulations demonstrate that intense local anhydrite cementation may occur when saline formation waters mix with hot brines ascending on faults

estimating irreducible water saturation and permeability of sandstones from nuclear magnetic resonance measurements by fractal analysis abstract understanding the relationships between the pore structure and bulk properties such as irreducible water saturation swir and permeability k of rocks is a crucial problem in geoscience in this study two types of fractal dimension were determined from nuclear magnetic resonance nmr t2 relaxation time distribution and models for estimating swir and k using fractal theory were proposed in view of the data of sandstone samples from upper paleozoic formation in china we found a good agreement between the predicted swir values based on fractal analysis and the experimental measurements and the estimated k values based on the proposed model are within one order of magnitude of measured k additionally another four frequently used k estimation models were compared with our proposed model and the result support that the proposed approach has great potential in investigating k while certain limitation still exists this procedure was applied on another set of sandstone samples collected from a different location and the predicted permeability values are reliable our study suggests that the proposed swir estimation model using nmr t2 data and fractal dimensions provides useful insights into characterizing the pore space properties of sedimentary rocks our work demonstrates that we can use nmr data to infer swir directly and the estimated swir value can be well integrated in permeability prediction model which improves the applications of nmr in characterizing the properties related to rock pores

possible formation mechanisms for the modal coarse silt quartz particles in loess deposits abstract the first major event in the formation of a loess deposit is the production of silt sized quartz particles many particle production methods have been proposed the bulk of loess particles appear to be produced by a glacial grinding to give ice sheet loess or b cold weathering in high regions to give mountain loess there are close relationships between mountain loess and desert loess loess material can be seen as a product of the cold phase of the glacial cycle

late cenozoic history of the polar north atlantic results from ocean drilling abstract dsdp odp drilling in the northern north atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice rafted debris ird in deep sea sediments can be traced back to the middle miocene the greenland ice sheet has probably the longest history on the northern hemisphere leg 151 site 909 fram strait recovered a unique continuous sediment record dating from early middle miocene the composition of the coarse fraction indicates that the oldest ird pulses are documented around 14 ma in the fram strait site 909 and around 12 6 ma on the voring plateau leg 104 site 642 in the norwegian greenland sea fram strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral ird pulses during late miocene between 10 8 and 8 6 ma around 7 2 6 8 and 6 3 ma which ultimately led to a drastic intensification of northern hemisphere glaciation during plio pleistocene the deep sea sediment records show that plio pleistocene strengthening of ird pulses have been observed since approximately 4 0 ma in the westernmost norwegian greenland sea and labrador sea by contrast strengthening of ird pulses are observed at approximately 3 2 2 7 ma on the eastern side of the norwegian greenland sea including the barents sea margin sediment composition and physical properties of the drilled mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre glacial miocene pliocene and early quaternary and to 100 ka periods of eccentricity dominant during the past 600 000 700 000 years the stratigraphy of ice rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the norwegian greenland sea it is particularly evident from the composition of the ice rafted material that the eurasian ice sheets delivered ird to the eastern part of the norwegian greenland sea whereas greenland source areas are represented in the drill sites of the east greenland continental margin and in the labrador sea the stratigraphic sequences on the yermak plateau suggest that the svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then invasions of temperate atlantic waters during interglacials can be observed as short lived and rather irregular events it never reached the area off eastern greenland except during the pliocene interval when tundra floras were able to develop on north eastern greenland and planktonic foraminifers suggesting the presence of temperate water masses in the fram strait as been documented in the drill sites from the yermak plateau

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

permeability prediction for low porosity rocks by mobile nmr estimating permeability from nmr well logs or mobile nmr core scanner data is an attractive method as the measurements can be performed directly in the formation or on fresh cores right after drilling furthermore the method is fast and non destructive compared to t 1 relaxation times commonly measured t 2 distributions are influenced by external and internal magnetic field gradients we performed two dimensional t 1 and t 2 relaxation experiments on samples of rhaetian sandstone a rock with low porosity and small pore radii using a mobile nmr core scanner which operates within a nearly homogeneous static magnetic field because small pore sizes are associated with high internal magnetic field gradients standard methods from nmr logging in the oil industry cannot be applied for accurate permeability prediction therefore a new model theory was developed which describes the pore radius dependence of the surface relaxivity p 2 by both an analytical and a more practical empirical equation using corrected p 2 values permeability can be predicted accurately from the logarithmic mean of the t 2 distribution and the physically based kozeny carman equation additional core plug measurements of structural parameters such as porosity permeability specific inner surface area and pore radius distributions supported the nmr results

evolving geometrical and material properties of fault zones in a damage rheology model we discuss numerical simulations of evolving fault zone structures in a 3 d lithospheric model with a seismogenic crust governed by a damage rheology that accounts for large strain associated with permanent brittle deformation results for the initial propagation of an existing narrow damage zone subjected to oblique loading exhibit strong asymmetry of the evolving damage with respect to the initial fault orientation and predict out of plane directions of the propagating damage zones the orientations of the simulated damage zones agree with analytical expectations based on fracture mechanics for the directions of wing cracks generated at the tips of a crack under mixed mode loading lithosphere scale numerical simulations for the long term evolution of a large strike slip fault zone produce initially a system of stepping en echelon segments associated with the asymmetric generation of new damage zones the simulated fault zone segments evolve with continuing deformation to a throughgoing localized structure large scale perturbation in the geometry of the moho interface together with the regional heat regime can reduce considerably the degree of localization of the fault zone structure and the associated deformation fields

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

spiral arm seismic arrays abstract seismic arrays have many uses for signal enhancement from surface wave characterization of the near surface to teleseismic detection in the context of monitoring nuclear tests many variants of the geometrical configuration of stations have been used with the objective of maximizing potential resolution of the incoming wavefronts direction of arrival a versatile class of array configurations with good resolution properties can be constructed with multiple spiral arms the array response is comparable with the same number of full circles but with far fewer stations and is robust to minor position changes in emplacement the desirable properties of the spiral arm arrays are illustrated for a permanent array in the precambrian pilbara craton in northwestern australia and for a temporary array on ancient sediments in southern queensland australia in each case the practical array response is very good and matches the theoretical expectations the spiral arm configuration allows the deployment of relatively large aperture arrays with a limited number of stations which is advantageous in a broad range of seismic applications including near surface characterization online material figures illustrating the relation between spiral arm and multiring circular arrays

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

accelerated seismic release and related aspects of seismicity patterns on earthquake faults observational studies indicate that large earthquakes are sometimes preceded by phases of accelerated seismic release asr characterized by cumulative benioff strain following a power law timeto failure relation with a term tf t m where tr is the failure time of the large event and observed values of m are close to 0 3 we discuss properties of asr and related aspects of seismicity patterns associated with several theoretical frameworks the subcritical crack growth approach developed to describe deformation on a crack prior to the occurrence of dynamic rupture predicts great variability and low asymptotic values of the exponent m that are not compatible with observed asr phases statistical physics studies assuming that system size failures in a deforming region correspond to critical phase transitions predict establishment of long range correlations of dynamic variables and power law statistics before large events using stress and earthquake histories simulated by the model of ben zion 1996 for a discrete fault with quenched heterogeneities in a 3 d elastic half space we show that large model earthquakes are associated with nonrepeating cyclical establishment and destruction of long range stress correlations accompanied by nonstationary cumulative benioff strain release we then analyze results associated with a regional lithospheric model consisting of a seismogenic upper crust governed by the damage rheology of lyakhovsky et al 39 over a viscoelastic substrate we demonstrate analytically for a simplified 1 d case that the employed damage rheology leads to a singular power law equation for strain proportional to t f t 1 3 and a nonsingular power law relation for cumulative benioff strain proportional to t f t 1 3 a simple approximate generalization of the latter for regional cumulative benioff strain is obtained by adding to the result a linear function of time representing a stationary background release to go beyond the analytical expectations we examine results generated by various realizations of the regional lithospheric model producing seismicity following the characteristic frequency size statistics gutenberg richter power law distribution and mode switching activity we find that phases of asr exist only when the seismicity preceding a given large event has broad frequency size statistics in such cases the simulated asr phases can be fitted well by the singular analytical relation with m 1 3 the nonsingular equation with m 0 2 and the generalized version of the latter including a linear term with m 1 3 the obtained good fits with all three relations highlight the difficulty of deriving reliable information on functional forms and parameter values from such data sets the activation process in the simulated asr phases is found to be accommodated both by increasing rates of moderate events and increasing average event size with the former starting a few years earlier than the latter the lack of asr in portions of the seismicity not having broad frequency size statistics may explain why some large earthquakes are preceded by asr and other are not the results suggest that observations of moderate and large events contain two complementary end member predictive signals on the time of future large earthquakes in portions of seismicity following the characteristic earthquake distribution such information exists directly in the associated quasi periodic temporal distribution of large events in portions of seismicity having broad frequency size statistics withrandom or clustered temporal distribution of large events the asr phases have predictive information the extent to which natural seismicity may be understood in terms of these end member cases remains to be clarified continuing studies of evolving stress and other dynamic variables in model calculations combined with advanced analyses of simulated and observed seismicity patterns may lead to improvements in existing forecasting strategies

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

the erosion of the alps nd isotopic and geochemical constraints on the sources of the peri alpine molasse sediments abstract sm nd data from molasse sedimentary deposits from eastern france and switzerland are used to quantify the erosion of the alps during the oligocene and miocene the average present day nd value of the continental sedimentary deposits increases from 11 for cretaceous and eocene substratum to 9 for the first oligocene molasse sediments this increase requires the erosion of mesozoic marine sediments to explain the average nd value 9 1 of the rupelian and lower chattian sediments then the average nd value 9 7 and the chemical compositions of the upper chattian and aquitanian sediments are consistent with the erosion of granitic rocks of the variscan crust this change in source allows us to define a second cycle in the peri alpine molasse which began at 24 5 ma with the deposition of the calcaires et dolomies this basin wide unit represents the sedimentary record of a halt in the input of alpine detritus in the western part of the molasse basin and we suggest that the limit between lower and upper chattian sediments at 24 5 ma corresponds to a major tectonic event in the alps a further increase of 1 nd unit recorded by the burdigalian marine sandstones average of 8 defines a third molasse cycle which resulted from the erosion of late variscan alkaline granites having high nd values between 1 8 and 5 2 this study concludes that the erosion of the alps increased the nd values of the sedimentary mass in two stages 1 during the rupelian and lower chattian by recycling of marine chemical sediments having nd values similar to that of tethys seawater nd 8 and which represent 90 of the eroded materials and 2 during the burdigalian by the erosion of a variscan crust representing at least 20 of the eroded material half of this variscan material was composed of alkaline granites with high nd values suggesting the addition of mantle derived material to the crust during late variscan events

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

magnetostratigraphy and sedimentology of the jingchuan red clay section and correlation of the tertiary eolian red clay sediments of the chinese loess plateau a 325 m thick loess and red clay sequence was recently discovered at jingchuan which is situated about 45 km north of the previously studied lingtai section in the middle part of the chinese loess plateau the jingchuan section is composed of 199 m of pleistocene loess and 126 m of tertiary red clay deposits paleomagnetic studies show that the jingchuan red clay has a basal age of at least 7 7 ma which represents the oldest red clay deposits presently known in the loess plateau field observations and grain size analyses both suggest an eolian origin of the red clay thus extending available records of the eolian deposits in the loess plateau from about 7 0 ma to 7 7 ma correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late cenozoic red clay records in the loess plateau have a general continuous nature thereby providing potential for deriving long term climatic evolution signals from this eolian loess and red clay sequence

history of terrigenous sedimentation during the past 10 m y in the north atlantic odp legs 104 and 105 and dsdp leg 81 bulk sediment measurements and analyses of the input of 63 m terrigenous particles have enabled us to reconstruct the variability of sediment flux in the norwegian and the labrador seas as a function of paleoceanographic and paleoclimatic changes in both areas minor amounts of coarse terrigenous particles occur in sediments that were deposited between 9 5 and 7 0 ma the higher amounts are only documented in the norwegian sea around 5 7 5 4 ma variations in bulk sediment accumulation are related to a strengthening of denmark strait overflow which is closely connected with the production of norwegian sea deep water between 8 3 and 7 8 ma 6 9 and 6 1 ma and 5 3 and 4 2 ma in the labrador sea reduced bottom water activity coincided with the highest levels of organic carbon accumulation and an increase in bulk sediment accumulation and may correlate with the latest miocene messinian event in both the labrador sea and the norwegian sea a drastic increase in the amount of coarse terrigenous particles rock fragments and quartz started at around 4 0 ma recording a nearly simultaneous onset of large scale ice rafting this was ultimately caused by a deterioration in the northern hemisphere climate possibly related to the final closure of the isthmus of panama

recovery of secular deformation field of mojave shear zone in southern california from historical terrestrial and gps measurements the 1992 mw 7 3 landers and 1999 mw 7 1 hector mine earthquakes struck the eastern california shear zone ecsz in the mojave desert southern california coseismic and postseismic deformation from these events affect efforts to use global positioning system gps observations collected since these events to establish a secular surface velocity field especially in the near field of the coseismic ruptures we devise block motion models constrained by both historical pre landers triangulation and trilateration observations and post landers gps measurements to recover the secular deformation field and differentiate the postseismic transients in the mojave region postseismic transients are found to remain in the southern california earthquake center crustal motion map version 4 plate boundary observatory and scripps orbit and permanent array center gps velocity solutions in the form of 2 3 mm yr excess right lateral shear across the landers and hector mine coseismic ruptures the cumulative deformation rate across the mojave ecsz is 13 2 14 4 mm yr at least twice the geologic rate since the late pleistocene 6 2 1 9 mm yr postseismic gps time series based on our secular velocity field reveal enduring late stage transient motions in the near field of the coseismic ruptures that provide new constraints on the rheological structure of the lower crust and upper mantle

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation

temporal changes in the lead isotopic composition of red clays comparison with ferromanganese crust records abstract a record of changes in pb and sr isotopic composition of two cores dsdp 86 576a and ll44 gpc3 from the red clay region of the central north pacific has been determined for the past 60 65 million years the isotope records of the eolian silicate fraction of the red clays reflect the change in source area as the core sites migrated under different wind systems the sr isotope compositions of eolian silicate material are consistent with asian loess and north american arc volcanism that has been recognized from mineralogical studies the silicate bound eolian pb isotopic compositions similarly reflect asian loess and arc volcanism the isotope records of three ferromanganese crusts from similar locations in the central pacific are similar to the eolian component of red clays but offset to less radiogenic values this may be due to two mechanisms 1 pb that can be removed from eolian material by seawater is much less radiogenic or less likely 2 hydrothermal pb can be transported further away from venting sites through particle exchange with seawater despite hydrothermal venting acting as a net sink of oceanic pb the temporal changes in pb isotopes in the ferromanganese crusts bulk red clays and eolian silicates are similar although offset from each other suggesting that eolian deposition is an important source of pb to seawater and to ferromanganese crusts this contrasts with the atlantic and southern ocean where more intense deep water flow leads to isotopic gradients in femn crusts that do not reflect surface water conditions immediately above the crust a mechanism is proposed which accounts for pacific deepwater pb being isotopically influenced by eolian deposition

stratigraphic evidence for the uplift of the tibetan plateau between 1 1 and 0 9 myr ago uplift of the tibetan plateau is manifest not only in widespread denudation but also by an increased deposition rate of sediment near or far from the exhumed regions our results indicate that the mass accumulation rate mar of eolian dust increased between 1 1 and 0 9 myr ago we associate this increase in mar and median grain size with uplift of the tibetan plateau and its adjacent regions during this period this middle pleistocene uplift can also be evidenced by the age of volcanism in the marginal region the existence of thick conglomerate deposits surrounding the uplifted plateau and the increased sedimentation rate of lacustrine deposits in the qaidam basin northeastern tibetan plateau between 1 1 and 0 9 myr ago the correlation between the loess and marine records indicates that after 0 9 myr ago these two records correlate well this good correlation probably suggest that the middle pleistocene upheaval event not only brought the plateau into the cryosphere but also enhanced the coupling of regional scale chinese loess transportation and deposition to the global ice volume variations through its effects on glacial grinding rock denudation and east asian monsoonal circulation

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

variation of permeability with porosity in sandstone diagenesis interpreted with a fractal pore space model permeability is one of the key rock properties for the management of hydrocarbon and geothermal reservoirs as well as for aquifers the fundamental equation for estimating permeability is the kozeny carman equation it is based on a capillary bundle model and relates permeability to porosity tortuosity and an effective hydraulic pore radius which is defined by this equation whereas in clean sands the effective pore radius can be replaced by the specific surface or by the grain radius in a simple way the resulting equations for permeability cannot be applied to consolidated rocks based on a fractal model for porous media equations were therefore developed which adjust the measure of the specific surface and of the grain radius to the resolution length appropriate for the hydraulic process these equations are calibrated by a large data set for permeability formation factor and porosity determined on sedimentary rocks this fractal model yields tortuosity and effective pore radius as functions of porosity as well as a general permeability porosity relationship the coefficients of which are characteristic for different rock types it can be applied to interpret the diagenetic evolution of the pore space of sedimentary rocks due to mechanical and chemical compaction with respect to porosity and permeability

a geochemical study of loess and desert sand in northern china implications for continental crust weathering and composition abstract chemical compositional variations of desert sands and loess loess like deposits river deposits and saline lacustrine deposits collected mostly from the southern margin of the taklimakan desert china provide strong constraints on the chemical weathering processes of continental crust and also on the provenance compositions of these quaternary deposits constant but lower concentrations of al relative to the average upper continental crust ucc in these quaternary deposits could be attributed to chemical weathering of al rich minerals such as feldspar and mica and removal of clay minerals by wind and water large variations of mobile na ca mg and sr compared to relatively immobile al k and ba resulted from the chemical weathering of plagioclase and carbonate minerals salinization and carbonation of the arid lands most trace elements are not significantly fractionated their variations in absolute concentration are caused by the dilution of quartz evaporates and carbonate minerals variations in sn concentrations probably depend on relative contents of some heavy minerals high sr ba low th u k cs ratios of the saline lake deposits suggest differences in aqueous chemistry of these elements the occurrence of the m type tetrad effect a ree pattern with four convex curves of ree compositions found mainly in the river deposits is considered the result of water particle interaction during chemical weathering of crustal materials y ho ratios of these samples are significantly higher than those of chondrite and the ucc this suggests different chemical behavior of these two elements and possibly the enrichment of carbonate materials the low lree hree feature of the saline lake deposits can be interpreted as due to the different aqueous chemical behavior of the ree s however it can also be reasonably considered as the result of inheritance from their provenance since lree and lree hree variations may be related to the geological setting of the source according to some elements that are not significantly fractionated the average provenance composition of these quaternary deposits are probably characterized by enrichments of ni cr and v over fe higher la th lower la sc and th sc and lower ta w and nb w ratios compared with the ucc composition

modeling flow and reactive transport to explain mineral zoning in the atacama salt flat aquifer chile geochemical processes are typically neglected when modeling groundwater flow in highly saline systems in the atacama salt flat northern chile field data indicate that the main aquifer presents a mineralogical zoning consisting of carbonates sulfates and halite which is a result of precipitation and or dissolution reactions when precipitation and or dissolution of minerals are active processes in the aquifer physical properties that control groundwater flow such as porosity and permeability would also change until now groundwater flow in the atacama salt flat has been simulated with conventional constant or variable density flow models this study for the first time investigated the importance of incorporating geochemical processes in modeling the atacama salt flat aquifer in particular the impact of mineral precipitation dissolution on aquifer s physical properties and flow patterns was studied to this end the shemat code was utilized to develop a two dimensional numerical groundwater flow model in the eastern border of the atacama salt flat the shemat code solves the classic groundwater flow equation coupled to the reactive transport of ions and mineral precipitation with variable density viscosity porosity and permeability when geochemical processes were included in the simulations the model reproduced reasonably well the mineral zoning evidenced by field observations mineral precipitation was responsible of a strong permeability reduction in areas of the aquifer associated with halite and calcite formation permeability alterations were responsible of changes in the equivalent freshwater head that resulted in significant flow pattern variations compared to variable density flow models these results highlight the importance of considering geochemical processes that modify the aquifer s physical properties when modeling groundwater flow in highly saline aquifers such as the atacama salt flat aquifer

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

radiogenic hf isotopic compositions of continental eolian dust from asia its variability and its implications for seawater hf the inorganic silicate fraction extracted from bulk pelagic sediments from the north pacific ocean is eolian dust it monitors the composition of continental crust exposed to erosion in asia 176lu 177hf ratios of modern dust are sub chondritic between 0 011 and 0 016 but slightly elevated with respect to immature sediments modern dust samples display a large range in hf isotopic composition ic 4 70 hf 16 45 which encompasses that observed for the time series of dsdp cores 885 886 and piston core ll44 gpc3 extending back to the late cretaceous hafnium and neodymium isotopic results are consistent with a dominantly binary mixture of dust contributed from island arc volcanic material and dust from central asia the hf nd isotopic correlation for all modern dust samples hf 0 78 nd 5 66 n 22 r2 0 79 is flatter than those reported so far for terrestrial reservoirs moreover the variability in hf of asian dust exceeds that predicted on the basis of corresponding nd values 4 7 hf 2 5 10 9 nd 10 1 this is attributed to 1 the fixing of an important unradiogenic fraction of hf in zircons balanced by radiogenic hf that is mobile in the erosional cycle 2 the elevated lu hf ratio in chemical sediments which given time results in a hf signature that is radiogenic compared with hf expected from its corresponding nd isotopic components and 3 the possibility that diagenetic resetting of marine sediments may incorporate a significant radiogenic hf component into diagenetically grown minerals such as illite together these processes may explain the variability and more radiogenic character of hf isotopes when compared to the nd isotopic signatures of asian dust the hf nd isotope time series of eolian dust are consistent with the results of modern dust except two samples that have extremely radiogenic hf for their nd hf 8 6 and 10 3 nd 9 5 and 9 8 these data may point to a source contribution of dust unresolved by nd and pb isotopes the hf ic of eolian dust input to the oceans may be more variable and more radiogenic than previously anticipated the hf signature of pacific seawater however has varied little over the past 20 myr especially across the drastic increase of eolian dust flux from asia around 3 5 ma therefore continental contributions to seawater hf appear to be riverine rather than eolian current predictions regarding the relative proportions of source components to seawater hf must account for the presence of a variable and radiogenic continental component data on the ic and flux of river dissolved hf to the oceans are urgently required to better estimate contributions to seawater hf this then would permit the use of hf isotopes as a monitor of past changes in erosion

fractal model for permeability calculation from porosity and pore radius information and application to excavation damaged zones surrounding waste emplacement boreholes in opalinus clay abstract an excavation damaged zone edz around emplacement boreholes for radioactive waste represents a potential pathway for radionuclides due to its increased porosity and crack permeability as clay is one of the potential host rocks for radioactive waste disposal a methodical approach was developed for permeability calculation of damaged opalinus clay the approach was based on a permeability porosity relationship and on the theory of fractals which allows the description of rock mass properties by fractal dimensions it was calibrated against laboratory test data and provides the possibility to calculate the permeability from the pore size parameters effective porosity and pore radius as well as from the fractal dimension an application of this relationship was given in terms of calculating the edz permeability around a vertical 50 m deep emplacement borehole in opalinus clay at a german generic repository site the particle flow code pfc was applied to simulate the fissure development in the edz the results of the simulation provide the necessary pore size parameters considering the thermo mechanical impact of adjacent already filled boreholes in an emplacement field for heat generating radioactive waste the crack occurrence and evolution over time in the edz of a newly drilled borehole was calculated on a 2d horizontal plane a 3d calculation as well as a verification against in situ data is still pending

core flooding laboratory experiment validates numerical simulation of induced permeability change in reservoir sandstone 1 numerical simulation of reactive transport was validated in a core flooding experiment simulating conditions in a managed geothermal reservoir permeability was measured along a sandstone core prepared with anhydrite and subjected to a temperature gradient anhydrite was dissolved and precipitated in the cold upstream and hot downstream regions of the core respectively the numerical code shemat was used to simulate coupled transport and chemical reactions at the temperature front http www rwth aachen de geop shemat it comprises an extended version of the geochemical speciation code phrqpitz for calculating chemical reactions in brines of low high ionic strength and temperatures of 0 150 c permeability is updated to porosity via a novel calibrated power law based on a fractal pore space model resulting in a large exponent of 11 3 simulation results agree well with measured permeability this both validates the model and demonstrates that the fractal relationship is crucial for a successful simulation of this type of reactive transport