vertical magnetic structure of ocean crust determined from near bottom magnetic field measurements consensus on the source of marine magnetic anomaly stripes has remained one of the most elusive aspects of the vine and matthews seafloor spreading model which has been of such fundamental importance to global plate tectonics the first attempt to measure the vertical magnetic structure of oceanic crust exposed at a scarp face using near bottom magnetic measurements is reported along with the theoretical basis for the reduction and analysis of these measurements magnetometers mounted to deep tow and submersible platforms were used to determine the horizontal and vertical variation of crustal magnetization of the upper 2 km of young oceanic crust exposed by a steep submarine escarpment at the blanco fracture zone in the northeast pacific ocean results show a large amplitude magnetic anomaly is consistently found at the extrusive to intrusive transition indicating that the extrusives are strongly magnetized compared to the weakly magnetized intrusive crust profiles also show the systematic presence of more than one polarity with depth indicating the possibility of dipping polarity boundaries within the extrusives forward models find that a dipping polarity boundary model correctly predicts the amplitude and shape of the overlying sea surface anomaly while a block model with vertical polarity boundaries overestimates the amplitude these in situ results are used to directly assess the contribution made by the extrusive section to the overlying magnetic anomaly signal in essence to define the magnetic source layer it is concluded that the extrusive lavas constitute the main magnetic source for magnetic anomalies in oceanic crust less than 2 m y in age

centrifuge model study on settlement of strip footing subject to rising water table in loess owing to man made activities and natural conditions the groundwater table experiences considerable changes in lanzhou centrifugal model tests were performed to investigate the settlement of strip

on the origin of el chichon volcano and subduction of tehuantepec ridge a geodynamical perspective the origin of el chichon volcano is poorly understood and we attempt in this study to demonstrate that the tehuantepec ridge tr a major tectonic discontinuity on the cocos plate plays a key role in determining the location of the volcano by enhancing the slab dehydration budget beneath it using marine magnetic anomalies we show that the upper mantle beneath tr undergoes strong serpentinization carrying significant amounts of water into subduction another key aspect of the magnetic anomaly over southern mexico is a long wavelength 150 km high amplitude 500 nt magnetic anomaly located between the trench and the coast using a 2d joint magnetic gravity forward model constrained by the subduction p t structure slab geometry and seismicity we find a highly magnetic and low density source located at 40 80 km depth that we interpret as a partially serpentinized mantle wedge formed by fluids expelled from the subducting cocos plate using phase diagrams for sediments basalt and peridotite and the thermal structure of the subduction zone beneath el chichon we find that 40 of sediments and basalt dehydrate at depths corresponding with the location of the serpentinized mantle wedge whereas the serpentinized root beneath tr strongly dehydrates 90 at depths of 180 200 km comparable with the slab depths beneath el chichon 200 220 km we conclude that this strong deserpentinization pulse of mantle lithosphere beneath tr at great depths is responsible for the unusual location singularity and probably the geochemically distinct signature adakitic like of el chichon volcano

the cleft revealed geologic magnetic and morphologic evidence for construction of upper oceanic crust along the southern juan de fuca ridge 1 the geology and structure of the cleft segment of the southern juan de fuca ridge jdfr have been examined using high resolution mapping systems observations by remotely operated vehicle rov rov mounted magnetometer and the geochemical analysis of recovered lavas bathymetric mapping using multibeam em300 coupled with in situ observations that focused on near axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the jdfr a total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen rov dives our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley the geochemically evolved and heterogeneous nature of these near axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone in contrast the most recent axial eruptions are more primitive higher mgo chemically homogeneous lobate sheet and massive flows that generate a distinct magnetic high over the axial valley we suggest that the syntectonic capping volcanics observed off axis were erupted from near axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data this model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the cleft segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle

temporal and spatial variability in the composition of lavas exposed along the western blanco transform fault the northern scarp of the western blanco transform bt fault zone provides a tectonic window into crust generated at an intermediate rate spreading center exposing a 2000 m vertical section of lavas and dikes the lava unit was sampled by submersible during the blancovin dive program in 1995 recovering a total of 61 samples over vertical distances of 1000 m and a lateral extent of 13 km major element analyses of 40 whole rock samples exhibit typical tholeiitic fractionation trends of increasing feo na2o and tio2 and decreasing al2o3 and cao with decreasing mgo the lava suite shows a considerable range in extent of crystallization including primitive samples mg 64 and evolved feti basalts feo 12 tio2 2 on the basis of rare earth element and trace element data all of the lavas are incompatible element depleted normal mid ocean ridge basalts n morb la smn 1 the geochemical systematics suggest that the lavas were derived from a slightly heterogeneous mantle source and crystallization occurred in a magmatic regime of relatively low magma flux and or high cooling rate consistent with magmatic processes occurring along the present day southern cleft segment the bt scarp reveals the oceanic crust in two dimensional space allowing us to explore temporal and spatial relationships in the horizontal and vertical directions as a whole the data do not appear to form regular spatial trends rather primitive lavas tend to cluster shallower and toward the center of the study area while more evolved lavas are present deeper and toward the west and east considered within a model for construction of the upper crust these findings suggest that the upper lavas along the bt scarp may have been emplaced off axis either by extensive off axis flow or off axis eruption while the lower lavas represent axial flows that have subsided with time a calculation based on an isochron model for construction of the upper crust suggests that the cleft segment requires at least 50 kyr to build the lower extrusive section consistent to first order with independent estimates for the construction of intermediate spreading rate crust

investigation of a marine magnetic polarity reversal boundary in cross section at the northern boundary of the kane megamullion mid atlantic ridge 23 40 n near bottom magnetic field measurements made by the submersible nautile during the 1992 kanaut expedition define the cross sectional geometry of magnetic polarity reversal boundaries and the vertical variation of crustal magnetization in lower oceanic crust exposed along the kane transform fault tf at the northern boundary of the kane megamullion kmm the kmm exposes lower crust and upper mantle rocks on a low angle normal fault that was active between 3 3 ma and 2 1 ma the geometry of the polarity boundaries is estimated from an inversion of the submarine magnetic data for crustal magnetization in general the polarity boundaries dip away from the ridge axis along the kane tf scarp with a west dipping angle of similar to 45 degrees in the shallow 1 km crust and 20 degrees in the deeper crust the existence of the magnetic polarity boundaries e g c2r 2r c2an 1n similar to w2 581 ma indicates that the lower crustal gabbros and upper mantle serpentinized peridotites are able to record a coherent magnetic signal our results support the conclusion of williams 2007 that the lower crust cools through the curie temperature of magnetite to become magnetic with the polarity boundaries representing both frozen isotherms and isochrons we also test the effects of the rotation of this isotherm structure and or footwall rotation and find that the magnetic polarity boundary geometry is not sensitive to these directional changes

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

constraining crustal emplacement processes from the variation in seismic layer 2a thickness at the east pacific rise abstract a stochastic model for the emplacement of dikes and lava flows at a fast spreading ridge can generate an upper oceanic crustal structure similar to that observed in seismic data from the east pacific rise epr in ocean drill holes and in ophiolites in this model the location of successive dike intrusion events relative to the ridge axis is determined by a gaussian probability function and the cumulative flow lengths of the erupted lavas are chosen to build a gaussian shaped lava pile we interpret wide angle seismic reflections from the steep velocity gradient at the base of seismic layer 2a to be the extrusive sheeted dike contact seismic data from the northern and southern epr place constraints on the on axis extrusive layer thickness 230 50 m the distance over which the thickening of the extrusive layer occurs width of the accretion zone 1 3 km and its off axis thickness 300 800 m ophiolites and ocean drill holes dsdp hole 504b provide additional estimates of the thickness of the extrusive layer and constrain the thickness of the transition region from extrusives to sheeted dikes 100 200 m a simple stochastic emplacement model where the lavas are described by one mean flow length fits the thickening of the extrusive layer off axis inferred from the deepening of seismic layer 2a but the predicted transition from sheeted dikes to extrusives is too thick in order to match the dimensions and flat topped shape of the seismic layer 2a boundary as well as the thickness of the extrusive sheeted dike transition a bimodal distribution of lava flows is used short flows confined within the axial summit caldera asc build up approximately half the extrusive volume occasional voluminous flows spill out of the asc or erupt outside of the asc and pond at a considerable distance off axis to build up the remainder of the extrusive section the upper part of the final extrusive section will be dominated by the off axis flows while the lower portions will be primarily composed of short flows erupted within the asc magnetic transition widths predicted from the overlap of lavas 2 km in this model are similar to those measured in deep tow studies assuming a smoothing function which acts over one seismic wavelength the upper crustal velocity structure predicted by the bimodal lava emplacement model is consistent with the shallow seismic velocity structure measured on the epr the ages of seafloor lavas in this model are younger than the tectonic spreading model ages by 30 70 kyr in agreement with anomalously young lava ages obtained from radioisotope dating of seafloor basalts near the epr

downhole magnetic measurements of odp hole 801c implications for pacific oceanic crust and magnetic field behavior in the middle jurassic 1 downhole horizontal and vertical magnetic field measurements within the 474 m thick jurassic crustal section drilled at odp hole 801c in the western pacific show anomalies that are in phase indicating that this site formed in the southern hemisphere and moved across the paleoequator to its present location at 18 6 n the inclination computed from the horizontal and vertical anomaly logging data varies significantly downhole and can be explained by progressive rotation of the lava sequence as it is buried during accretion this is compatible with the observed dips in the formation micro scanner fms data which show up to 42 of rotation toward the fossil spreading axis we restore the magnetic inclination to prerotated values and obtain an estimated pretilt inclination of 39 9 6 6 corresponding to a paleolatitude of 22 7 5 s the magnetic logging data document six polarity units within the drilled volcanic extrusive crust the upper 132 m thick logged section of lavas contains four polarity units which apparently formed 7 myr after the formation of the underlying basement the lower 212 m logged section of the hole is reversely magnetized with an intervening normal polarity zone more than one reversal downhole would indicate a rapid reversal rate given the time it takes to form the extrusive section of oceanic crust 45 000 years at a fast spreading rate of 66 km myr previous results from a contemporaneous section in spain suggest rapid reversals throughout the late bajocian early bathonian stage 170 165 ma nevertheless the complicated formation history prevents quantification of the geomagnetic reversal rate for the 801c crustal section

a laboratory study of the expansion of an irish pyritic mudstone siltstone fill material abstract extensive damage to dwellings in the east of ireland arising from the expansive pyritic fill material used beneath the floor slabs prompted the laboratory study presented in this paper to quantify the expansion and study its influencing factors a novel experimental arrangement in which sample height and water supply were varied was used to test a large quantity of active pyritic infill taken from an affected house in the greater dublin area the expansion of ten separate fill specimens was measured over a 175 day period from december 2010 to may 2011 remarkably consistent results were obtained when the expansions were normalised by the sample height with expansion rates of approximately 2 3 mm year m height of fill for specimens standing in water where the rates were largely insensitive to the amount of water supplied more rapid expansion was noted for one specimen to which no additional water was supplied during the test a steady reduction in ph of the water although relatively small was consistent with pyrite oxidation reactions occurring in the samples during the test and also implies the occurrence of leaching of ions from the pores in the mudstone and also that oxidation reactions may have been occurring in the saturated mudstone changes in expansion were found also to correlate strongly with changes in the ambient temperature in all specimens

bulk rock geochemistry and plagioclase zoning in lavas exposed along the northern flank of the western blanco depression northeast pacific insight into open system magma chamber processes abstract the present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the blanco transform fault northeast pacific the studied area consists of a small basin the western blanco depression wbd extending from the southern end of the juan de fuca ridge to a pseudofault trace 60 km eastward the northern scarp of the wbd comprises a volcanic unit overlying a sheeted dike complex major and trace element data coupled with sr nd isotope ratios reveal a two component mantle source composed by an isotopically depleted matrix variably veined by more enriched material one chemical group ns2 indistinguishable from the other northern scarp samples on the basis of trace element data has an unusually depleted isotopic composition typical of a nearly pure mantle end member some cogenetic samples of the northern scarp have been used to constrain the differentiation modalities anorthite and mgo content profiles in plagioclase xenocrysts and phenocrysts reveal i the existence of h2o bearing evolved melts in the mushy zones and ii the occurrence of mixing process between these melts and anhydrous mafic liquids the hydration is supported by other petrographic features such as high magmatic fo2 values calculated from fe ti oxide pairs and the presence of pyroxene inclusions in plagioclase phenocrysts mixing consistent with the existence of ni rich ferrobasalts is interpreted to be the consequence of the reservoir refilling by mafic liquids mg 70 these petrological and geochemical evidences are combined with the evolution of mg with depth to suggest a periodic open system magma chamber evolution beneath the southern end of the juan de fuca ridge

investigation of a vine matthews magnetic lineation from a submersible the source and character of marine magnetic anomalies we report here the first attempt to map directly the boundary of a vine matthews magnetic stripe on the seafloor our objectives are to study the processes of oceanic crustal accretion as recorded in the reversal transition zone and to investigate the formation of the magnetic source of vine matthews magnetic anomalies our deep tow and alvin based magnetic studies focus on the matuyama brunhes reversal transition on the flanks of the east pacific rise near 21 n while the sea level magnetic anomalies are less than average in clarity for the east pacific rise a three dimensional inversion of deep tow data reveals a sharp strike linear polarity transition less than 1 8 km wide macdonald et al 1980a these measurements have been augmented by mounting a vertical magnetic gradiometer on alvin and making 280 reliable polarity determinations along and across the polarity transition zone even on long traverses across both sides of the boundary we find that nearly every magnetic target has the correct polarity i e the same polarity as the regional magnetic lineation this homogeneity in polarity of the magnetic lineations is surprising the magnetic polarity transition in the outcropping volcanic section is sharp and linear along strike delineated in some cases by a clear geologic contact of opposing flow fronts of different ages several weakly magnetized outcrops mapped within the transition zone may have erupted during the time in which the geomagnetic field was reversing the reversal boundary mapped on the seafloor from alvin is displaced 250 m to 500 m nw away from the spreading axis relative to the position of the average boundary as derived from inversion of the deep tow and sea level magnetic data this offset provides a means for estimating the spillover of lava flows away from the spreading axis during the time the crust was formed the combination of deep tow and alvin measurements suggests that circa 0 7 m y ago the crustal accretion zone magnetized volcanic intrusive and plutonic rocks was 2000 2800 m wide while the zone of recent volcanism alone was only 1000 2000 m wide the determination for the most recent reversal agrees well with submersible observations at the present spreading center where the zone of recent volcanism neovolcanic zone varies between 600 and 2000 m in width this very orderly picture for the formation of magnetic lineations and crustal accretion processes appears to conflict with complex deep sea drilling project dsdp magnetic results from the atlantic we suggest that the crustal generating processes and resulting magnetic structure vary significantly with spreading rate on the slow spreading mid atlantic ridge major episodes of volcanism are likely to be infrequent 104 years the magma chamber may be non steady state and the neovolcanic zone shifts or varies in width considerably this sporadic start and stop spreading process will contribute to a highly heterogeneous and complex crustal and magnetic structure as seen in dsdp holes in addition significant faulting and tilting may disrupt slow spreading crust for intermediate to fast spreading centers more frequent volcanism 50 600 years a nearly steady state magma chamber and a narrow stable neovolcanic zone will create a less complex magnetic and crustal structure both as seen from alvin and as inferred from clear sea level magnetic anomalies in the pacific

ocean wave slope observations using radar backscatter and laser altimeters abstract combination of laser and radar aboard an aircraft is used to directly measure long gravity wave surface tilting simultaneously with nadir viewing microwave backscatter from the sea surface the presented dataset is extensive encompassing varied wind conditions over coastal and open ocean wave regimes laser derived slope statistics and ka band 36 ghz radar backscatter are detailed separately to document their respective variations versus near surface wind speed the slope statistics measured for 1 2 m show good agreement with cox and munk s oil slickened sea measurements a notable exception is elevated distribution peakedness and an observed wind dependence in this likely proxy for nonlinear wave wave interactions aircraft ka band radar data nearly mimic ku band satellite altimeter observations in their mean wind dependence the present calibrated radar data along with relevant observational and theoretical studies suggest a large 5 db bias in previous ka band results next wave

hydroconsolidation and subsidence of loess studies from china russia north america and europe abstract various approaches to the widespread problem of the hydroconsolidation and subsidence of loess have been suggested these include considerations of rheology thermodynamics phase movements particle packing interparticle bonding pore structure and distribution catastrophe theory topology and simple structural frameworks chinese north american and most european investigators tend to concentrate on mechanisms of loess collapse the russian literature however retains an extra dimension two approaches the syngenetic and the epigenetic approach to the formation of subsiding loess have been defined in the literature most investigators follow a syngenetic approach which appears to be a consequence of the aeolian idea of loess deposition some russian writers in contrast promote an epigenetic approach in which collapsibility can develop in an originally noncollapsible material which can then suffer from hydroconsolidation and subsidence the basis of the phenomenon is a change in the packing structure of the major loess particles and this can be modelled using simple monte carlo methods to develop appropriate structures this paper aims to review the work done on this important subject serious investigation of hydroconsolidation and subsidence of loess began in the early nineteen forties fifty years ago and this has been reported in a piecemeal manner a detailed critical review of this diverse work is now overdue and this is presented herein in the light of recent work in the united kingdom an attempt is made to describe the process in a phenomenological and a structural sense inherent in this the role of n ya denisov as subsidence pioneer is considered

marine magnetic anomalies the origin of the stripes the results of recent observational and theoretical investigations of lineated magnetic anomalies on the ocean floor are summarized in tables graphs and diagrams and analyzed topics addressed include early lineation models inversions of magnetic anomalies to obtain source functions deep tow studies of magnetic anomalies evidence from the long wavelength component of the magnetic field including magsat observations and direct measurements of the magnetic properties of oceanic rocks it is concluded that the source of the lineated anomalies must reside in most of the oceanic crust not just in the pillow lavas of layer 2a

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

momentum transfer over the coastal zone spatial variations of surface stress over the coastal shoaling zone are studied offshore of duck north carolina by the longez research aircraft equipped to measure both atmospheric turbulence and oceanic waves we find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow than with onshore flow in general the mean square slope of the short waves wavelength shorter than 2 m decreases with offshore distance while the mean square slope of the long waves wavelength longer than 2 m increases with offshore distance with onshore flow the friction velocity is strongly correlated with surface waves in addition the variation of the neutral drag coefficient is well correlated with the atmospheric bulk richardson number with offshore flow the observed momentum flux significantly decreases with offshore distance within the first few kilometer offshore the relationship between the friction velocity and the mean square slope of the short waves and the relationship between the neutral drag coefficient and the atmospheric bulk richardson number are obscured by the direct influence of the upstream land surface on the measured turbulence these relationships for offshore flow agree well with those for onshore flow if the fetch is beyond the immediate influence of the land surface the results in this study suggests that the effects of the strong turbulence advected from over the nearby land surface in offshore flow may lead to ambiguous physical interpretation of the correlation between the momentum flux and the wave state

internal structure of uppermost oceanic crust along the western blanco transform scarp implications for subaxial accretion and deformation at the juan de fuca ridge 1 the uppermost 2 km of oceanic crust created near the southern end of the juan de fuca ridge 60 mm yr full spreading rate is exposed in a tectonic window created along the north wall of the blanco transform fault a total of 27 submersible dives transect this escarpment over a distance of 30 km corresponding to 1 m y of spreading history in this exposure weakly deformed basaltic lavas grade downward into much more intensely fractured lavas cut by basaltic dikes lava flow surfaces dip persistently to the northwest toward the spreading center and the dikes dip southeast away from the spreading center the underlying sheeted dike complex is composed of subparallel dikes that dip moderately to the southeast discrete faults and more distributed cataclastic deformation zones separate the panels of sheeted dikes from one another disruption of the lava and dike units are interpreted as a result of dramatic subaxial vertical mass transport that created the accommodation space for the accumulation of a thickness of 1000 1500 m of basaltic lava the observed patterns of tilting of lavas and dikes imply subsidence beneath the region of active volcanism 3 km wide that is most rapid near the axis and diminishes quickly off axis deformation that accommodates this subsidence has generated extensive fracture porosity in the subaxial region that could strongly influence upper crustal hydrothermal pathways alteration history seismic properties and the distribution of subsurface biological communities

shallow oceanic crust full waveform tomographic images of the seismic layer 2a 2b boundary 1 we present results of full waveform tomographic inversions of four profiles acquired over young intermediate and fast spreading rate oceanic crust the mean velocity depth functions from our study include a 0 25 0 30 km thick low velocity low gradient region beneath the seafloor overlying a 0 24 0 28 km thick high gradient region together these regions compose seismic layer 2a mean layer 2a interval velocities are 3 0 3 2 km s the mean depth to the layer 2a 2b boundary is 0 49 0 54 km and mean velocities within the upper 0 25 km of layer 2b are 4 7 4 9 km s previous velocity analyses of the study areas using 1 d ray tracing underestimate the thickness of the high gradient region at the base of layer 2a we observe differences in the waveform inversion velocity models that correspond to imaging of the layer 2a event regions with a layer 2a event have higher velocity gradients at the base of layer 2a intermittent high velocities which we interpret as massive flows are observed in the waveform inversion velocity models at 0 05 0 10 km below the seafloor bsf over 10 25 of the intermediate spreading profiles and 20 45 of the fast spreading profiles the high gradient region located 0 25 0 54 km bsf at the base of layer 2a may be associated with an increased prevalence of massive flows the first appearance of dikes lava dike transition zone or with increased crack sealing by hydrothermal products the upper portion of layer 2b which begins at 0 49 0 54 km bsf may correspond to sheeted dikes or the top of the transition zone of lavas and dikes

fluctuations of the paleomagnetic field during chron c5 as recorded in near bottom marine magnetic anomaly data near bottom magnetic data contain information on paleomagnetic field fluctuations during chron c5 as observed in both the north and south pacific the north pacific data include 12 survey lines collected with a spatial separation of up to 120 km and the south pacific data consist of a single long line collected on the west flank of the east pacific rise epr at 19 s the north pacific magnetic profiles reveal a pattern of linear short wavelength 2 to 5 km anomalies tiny wiggles that are highly correlated over the shortest 3 8 km to longest 120 km separations in the survey magnetic inversions incorporating basement topography show that these anomalies are not caused by the small topographic relief the character of the near bottom magnetic profile from anomaly 5 on the west flank of the epr formed at a spreading rate more than twice that of the north pacific displays a remarkable similarity to the individual and stacked lines from the north pacific survey area over distances corresponding to 1 m y 19 lows in the magnetic anomaly profile can be correlated between the north and south pacific lines modeling the lows as due to short polarity events suggests that they may be caused by rapid swings of the magnetic field between normal and reversed polarities with little or no time in the reversed state owing to the implausibly high number of reversals required to account for these anomalies and the lack of any time in the reversed state we conclude that the near bottom signal is primarily a record of paleointensity fluctuations during chron c5 spectral analysis of the north pacific near bottom lines shows that the signal is equivalent to a paleointensity curve with a temporal resolution of 40 to 60 kyr while measurements of the smallest separations of correctable dips in the field suggest a temporal resolution of 36 kyr

volume change behavior of collapsible compacted gneiss soil the mechanical behavior of a compacted metastable structured residual gneiss soil was experimentally investigated volume changes were investigated using both a conventional oedometer cell and a triaxial permeameter system where the stress state variables were independently controlled wetting stress paths were utilized to reflect field conditions associated with collapsing earth structures the compacted specimens were consolidated under both isotropic and k0 oedometer conditions measurements of total volume change and water content change were made at specified matric suction values following a wetting stress path under a given loading the experimental data were analyzed to define volume change constitutive relationships for the metastable structured soil best fit modeling was used for predicting the volume change behavior of the compacted metastable structured residual soil during wetting induced collapse the measured data are discussed from both phenomenological and microscopic viewpoints predict

a comparison between the behaviour of swelling and of collapsing soils abstract in recent years there has arisen an increasing awareness of the existence of structurally metastable soils that change in bulk volume when water is applied to them swelling or expansive clays increase in volume while loessial collapsing soils decrease in volume when theirmoisture content increases under constant applied stress documented evidence of the existence of and difficult engineering problems associated with expansive clays and loessial soils is world wide the present paper is aimed at summarizing and comparing the physico mechanical properties of these structurally metastable soils with a special reference to romanian expansive and loessial soils emphasis is placed on the following problems 1 mechanisms of swelling and collapsing processes and influencing factors 2 identification and classification of structurally metastable soils 3 quantification of the amount of heave or subsidence that may occur 4 rheological aspects of swelling and collapsing

loess is not just the accumulation of dust most regrettably there is much misuse of terminology in connection with the concept of loess and the interpretation of its origin people often speak and write incorrectly about loess accumulation even loess specialists who are aware of the fact that loess as a concept has to satisfy at least 10 criteria loess is not simply dust carried and deposited by wind dust only becomes loess after the passage of a certain amount of time in a given geographical zone i e only through diagenesis in certain ecological environments to state that loess is of aeolian origin is an oversimplification and an incorrect definition because an aeolian origin applies only to the dust from which the loess has been formed we are aware of the fact that airborne dust cannot be transformed into loess in every geographical environment but only under those conditions typical of semi arid grassland or steppe or forested steppe the process primarily occurs where the rate of dust accumulation exceeds sheet wash or weathering soil formation rates if the rate of dust accumulation is less than that of surface erosion or of soil biogenetic processes the dust then develops into soil or through intensive weathering and increased precipitation into loam or clay only part of the aeolian dust transported and deposited in a zone suitable for loess formation remains there permanently and is transformed in situ into loess dust not affected by diagenesis is usually further transported by snowmelt or rainwash and is only transformed into loess after it has been redeposited the loess itself however is easily erodible and its minerals are readily reworked and reaccumulated and given the appropriate conditions it readily undergoes diagenesis again we do not always have sufficient evidence to determine whether a given loess body is of primary or secondary origin traditionally the minerals making up primary loess have been regarded as originating in dust accumulated by aeolian processes secondary loess by contrast is different from typical loess in many ways and it is not unusual to find various loess series in which superimposed dust fractions have been transformed into loess by different processes recently we have observed that the origin of various types of loess is governed by differences in litho ecological conditions rather than by the way in which the mineral material from which the loess is derived dust has been primarily accumulated loessification is therefore determined by environmental conditions

seismic constraints on shallow crustal emplacement processes at the fast spreading east pacific rise we present the results of nine on bottom seismic refraction experiments carried out over young east pacific rise crust the experiments are unusual in that both the source and receiver are located within a few meters of the seafloor allowing high resolution determinations of shallow crustal structure three experiments were located within the axial summit caldera asc over zero age crust the seismic structure at these three locations is fundamentally the same with a thin 60 m surficial low velocity 2 5 km s layer a 100 to 150 m thick transition zone with velocities increasing by 2 5 km s and a layer with velocities of 5 km s at a depth beneath the seafloor of 130 190 m the surficial low velocity layer and transition zone are defined as seismic layer 2a and the 5 km s layer is defined as the top of layer 2b both the surficial low velocity layer and the transition zone double in thickness within 1 km of the rise axis we model layer 2a as the extrusive sequence and transition zone and the 2a 2b boundary as the top of the sheeted dikes the primary implication of this interpretation is that the depth to the top of the sheeted dikes deepens from 150 m to 300 m within 1 km of the asc the thickening of the extrusive layer is interpreted to be due to lava that either overflows the asc walls is emplaced through eruptions outside of the asc or travels laterally from the asc through conduits the most probable cause for the thickening of the transition zone is sill emplacement outside of the asc either from magma that does not reach the surface in an off axis eruption or magma that is transported laterally during the drainage process creating the asc we suggest that the mechanism controlling the magnitude and rate of the dike subsidence is the mechanism that determines the thickness of the extrusive section and the total thickness of layer 2a

satellite scatterometer studies of ocean surface stress and drag coefficients using a direct model this study evaluates the accuracy of estimates of sea surface friction velocity derived using a new model function that operates directly on the nasa scatterometer normalized radar cross section nrcs measurements these nrcs data are first collocated with numerous national data busy center buoys within 0 5 latitude and longitude and are then processed using the new weissman et al 1994 frontal air sea interaction experiment model to produce 25 km by 25 km spatial averages of the friction velocity for several contiguous areas within this region one method of validation of these estimates involves comparisons with friction velocity estimates derived from data collected by the buoys using bulk methods this was conducted at numerous locations the atlantic and pacific coastlines and within the gulf of mexico it is found that there is excellent agreement between these two different measurements in addition this approach enabled the derivation of estimates of the surface drag coefficient with the use of the buoy winds neutral stability winds at 10 m elevation u10n and the scatterometer surface friction velocity u this permitted the study of the dependence of this drag coefficient cd on wind speed in these different regions on spatial scales which had not previously been possible comparisons are made to previously published models of cd that only depend on wind speed with generally good agreement at winds over 6 m 1 s but with significant regional differences at winds less than 6 m 1 s

overview of some geological hazards in the saudi arabia the saudi arabia has harsh environmental conditions which enhance some geomorphologic geological processes more than in other areas these processes create different geological hazards the general physiography of the saudi arabia is characterized by the red sea coastal plains and the escarpment foothills called tihama followed by the arabian shield mountains the arabian shelf plateau and finally the arabian gulf coastal plains these types of geological hazards can be categorized into sand accumulations earth subsidence and fissures flash floods problematic soils slope stability problems and karst problems the current study gives an overview of all these hazards with examples as well as develops a geo hazard map for the saudi arabia our findings indicate that the desert environment needs much concern and care national and international agencies have to join together with other people to keep the system balanced and to reduce the resulting geological hazards also remedial measures should be proposed to avoid and reduce these natural hazards

structure and formation of the highly stable marine boundary layer over the gulf of maine 1 a shallow stable boundary layer is ubiquitous over the cool waters of the gulf of maine in summer this layer affects pollutant transport throughout the region by isolating overlying flow from the surface in this paper we explore how the stable boundary layer is formed and describe its characteristics the temperature profile of the lowest 1 2 km of the atmosphere over the gulf of maine is remarkably similar regardless of transport time over water or the time of day when the flow left the land provided only that the flow is offshore this similarity is forced by the roughly constant water temperature and the roughly constant temperature of the free troposphere over the continent however the processes leading to the similar profiles are quite different depending on the time of day when the flow crosses the coast air leaving the coast at night already has a stable profile whereas air leaving the coast at midday or afternoon has a deep mixed layer in the latter case the stable layer formation over the water is of interest using observations of surface fluxes profiles and winds on the noaa research vessel ronald h brown from the 2004 international consortium for atmospheric research in transport and transformation icartt new england air quality study we show that the formation of the stable layer which involves cooling a roughly 50 to 100 m deep layer by 5 15 k occurs within 10 km and a half hour after leaving the coast the internal boundary layer near shore is deeper than predicted by standard relationships historical data are explored and also show deeper internal boundary layers than predicted we also describe one exceptional case where a 200 m deep neutral layer was observed and discuss the degree of isolation of the stable boundary layer and its duration

collapsibility composition and microstructure of loess in china the collapse potential mineralogy microstructure and particle morphology of a loess from the loess plateau china were characterized by double oedometer testing x ray diffraction scanning ele

implications for crustal accretion at fast spreading ridges from observations in jurassic oceanic crust in the western pacific 1 downhole logging data and basement stratigraphy interpretations are used to determine the spreading environment and crustal accretion history of the ocean basement cored at odp hole 801c located in the jurassic magnetic quiet zone of the western pacific high resolution microresistivity data obtained with the formation microscanner are used to measure the dip of the extrusive layers and indicate a 10 30 increase in dip down the drill hole with lava flow contacts dipping back toward the original ridge axis this structural pattern and the high proportion of massive flows relative to pillow units are consistent with prevailing crustal accretion models proposed for faster spreading ridges e g 60 km m y full rate a detailed analysis of the age data basement lithology related geochemistry and structural attitudes suggest the shallowest 100 m of the drilled section e g sequences i iii were emplaced just off the ridge sequence iii or significantly farther off axis up to 5 15 m y later sequences i and ii the remainder of the drilled section e g sequences iv viii has geochemical lithological and physical trends that are assumed to be representative of crust created at faster spreading ridges the pattern of dipping lava flow contacts from this deeper section of the drill hole suggests lava flows emanating from the ridge axis are limited to 1 2 km off axis our results suggest ocean crust drilled at hole 801c was created at faster spreading rates however caution should be used when incorporating sequences i iii into geochemical reference sections for faster spreading ridges

structure of offshore flow abstract the horizontal and vertical structure of the mean flow and turbulent fluxes are examined using aircraft observations taken near a barrier island on the east coast of the united states during offshore flow periods the spatial structure is strongly influenced by the surface roughness and surface temperature discontinuities at the coast with offshore flow of warm air over cool water the sea surface momentum flux is large near the coast and decreases rapidly with increasing offshore distance or travel time the decrease is attributed to advection and decay of turbulence from land the rate of decrease is dependent on the characteristic timescale of the eddies in the upstream land based boundary layer that are advected over the ocean as a consequence the air sea momentum exchange near the coast is influenced by upstream conditions and similarity theory is not adequate to predict the flux the vertical structure reveals an elevated layer of downward momentum flux and turbulence energy maxima over

some specific problems of wetted loessial soils in civil engineering abstract bally r j 1988 some specific problems of wetted loessial soils in civil engineering eng geol 25 303 324 loessial soils wetted above the limit of collapsibility remain in the category of difficult foundation grounds some case histories are presented herein surpassing soil bearing capacity and non stabilized settlements of buildings after initially dry loess wetting slow but nondamped settlements or damped but great and eventually non uniform settlements of structures erected on wet loess supplementary settlements by water level lowering in loessial ground great settlements of deep foundations passing through the collapsible loess to the underlaying wet but noncollapsible loess research on wetted loess performed in the laboratory oedometer triaxial or in situ full scale experiments or real constructions have emphasized the dependence of the soil structural resistance deformability compressibility and deformation under constant volume and final resistance on both the moisture content or stress state and on their history the depth propagation of the active zone of surface loadings on wetted loess is different from that of the linear elastic theory some suggestions to estimate the depth of the active zone are presented the usual foundation systems on wetted loessial grounds or in their vicinity adopted in romania include loessial or gravel cushions surface compaction very efficient results of intensive dynamic compaction foundation stamping or loessial ground reinforcing it is recommendable to take into consideration surveyed wetting under construction until maximum moisture content of the loessial ground in situ columns of stabilized loess the efficiency of geotextiles for filter drainage and antierosional functions in loessial soils

water retention and volumetric characteristics of intact and re compacted loess a laboratory testing program was conducted to investigate the effects of microstructure on the water retention curve wrc and wetting drying induced volume change in loess the axis translation an

evolution of stable internal boundary layers over a cold sea the situation studied in this paper relates to air flow from a heated land surface out over a water surface with much lower temperature observations from the baltic sea where this kind of situati

pile end bearing capacity in crushable sands the occurrence and formation of crushable soils is a widespread phenomenon warm tropical seas give rise to deep deposits of biogenic skeletal sediments in coastal shelf areas or exposed granitic

paleomagnetic constraints on deformation of superfast spread oceanic crust exposed at pito deep rift 1 the uppermost oceanic crust produced at the superfast spreading 142 km ma 1 full spreading rate southern east pacific rise epr during the gauss chron is exposed in a tectonic window along the northeastern wall of the pito deep rift paleomagnetic analysis of fully oriented dike 62 and gabbro 5 samples from two adjacent study areas yield bootstrapped mean remanence directions of 38 9 8 1 16 7 15 6 n 23 area a and 30 4 8 0 25 1 12 9 n 44 area b both are significantly distinct from the geocentric axial dipole expected direction at 23 s regional tectonics and outcrop scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to 1 inward tilting of crustal blocks during spreading area a 11 area b 22 2 clockwise vertical axis rotation of the easter microplate a 46 b 44 and 3 block tilting at pito deep rift a 21 b 10 these data support a structural model for accretion at the southern epr in which outcrop scale faulting and block rotation accommodates spreading related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at hess deep rift these data also support previous estimates for the clockwise rotation of crust adjacent to the easter microplate dike sample natural remanent magnetization nrm has an arithmetic mean of 5 96 a m 3 76 which suggests that they significantly contribute to observed magnetic anomalies from fast to superfast spread crust

occurrence and geotechnical properties of loess in canada abstract sweeney s j and smalley i j 1988 occurrence and geotechnical properties of loess in canada eng geol 25 123 134 there are modest amounts of loess in canada as in most of north america it is probably produced by a combination of glacial grinding and cold weathering atterberg limits of canadian loess are comparable with reference samples from the u s a a deposit at kamloops in british columbia suffers a 15 linear collapse when loaded and wetted earlier estimates that the deposit was more than 100 m thick are probably in error only the top part of the sedimentary deposit is loess

field observations of radar backscatter from the ocean surface under low wind speed conditions unique simultaneous field observations of wind speed and images of vertically polarized radar backscatter from the ocean surface at low grazing angles during low wind and weakly stable stratification show interesting similarities and an important difference depending on whether the average wind is falling or rising when the wind speed begins to fall there is a delay before the area averaged radar backscatter begins to fall when the wind speed begins to rise the backscatter rises immediately this observation points to hysteresis in the relationship between radar backscatter and wind speed such that more wind is necessary to generate radar backscatter of a given intensity than is necessary to maintain it this likely arises from differences between the generation of wind driven gravity capillary waves and the maintenance of gravity capillary waves and or microbores also saturation was observed in the radar backscatter at wind speeds between 2 1 and 2 8 m s 1 for both rising and falling winds this saturation may be related to the energetics of the centimeter scale gravity capillary waves and or microbores that cause the backscatter during rising winds the backscatter may saturate because fine scale features of the ocean surface reach a maximum amplitude well before wind derived energy is transferred upscale to larger waves whose tilting effect would ultimately produce the familiar increase in radar backscatter with increasing wind during falling winds the backscatter may saturate because of residual momentum in the surface wave field finally for both rising and falling winds radar backscatter and wind speed are in general correlated above a wind speed of 1 7 m s 1 while below this value they are not this observation of the critical wind speed necessary to generate or maintain wind related backscatter is consistent with results from a recent field observation and with existing laboratory based observations

structure of uppermost fast spread oceanic crust exposed at the hess deep rift implications for subaxial processes at the east pacific rise the uppermost 2 km of the oceanic crust created at the fast spreading 135 mm yr 1 full rate equatorial east pacific rise epr is exposed for tens of kilometers along escarpments bounding the hess deep rift mosaics of large scale digital images from the remotely operated vehicle rov argo ii and direct observations from the submersible alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units these rock units are characterized by extensive faulting fine scale fracturing and rotations of coherent crustal blocks meters to tens of meters across the uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces through most of the basaltic lava unit however lava flow contacts dip 20 70 w toward the epr and generally increase in dip downward in the section dikes cutting the lavas and in the underlying sheeted dike unit generally dip 90 40 e away from the epr deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units we interpret this upper crustal structure as the result of subaxial subsidence within 1 2 km of the epr that accommodated the thickening of the basaltic lava unit to 500 m variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply these results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the hess deep rift if this type of structure is typical of uppermost oceanic crust generated at the epr these processes may be common along fast spreading mid ocean ridges

some geotechnical characteristics of fragmented queenston shale this paper presents the results of an experimental study to determine the stress strain behaviour of fragmented queenston shale from russell ontario and to investigate how its strength properties altered when the material was subjected to repeated slaking cycles slaking tests showed that large cobble size blocks of the material degrade rapidly to a particle size of 20 mm upon exposure to water and air consolidated drained tests in a large triaxial apparatus under monotonic loading conditions on specimens of fresh and slaked material were performed they indicate that the shear strength of fragmented queenston shale of particle size smaller than 20 mm is not affected by slaking key words queenston shale compaction shale granular material rockfill slaking shear strength consolidated drained tests

distinct element method simulations of rock concrete interfaces under different boundary conditions abstract the shear behaviour of concrete rock interfaces has been the aim of extensive research in geotechnical engineering applications such as rock socketed piles rock bolts and concrete dam arch bridge foundations several experimental studies through direct shear tests have been conducted to evaluate the shear behaviour of rock concrete interfaces under cnl constant normal load and cns constant normal stiffness conditions in this paper pfc2d numerical simulations of unbonded rock concrete planar and saw tooth triangular joints under cnl and cns boundary conditions are conducted using the shear box genesis sbg approach proposed by bahaaddini et al 2013b the numerical simulation results are compared with experimental data published by gutierrez 2013 and gu et al 2003 results indicate that the sbg approach reproduces suitably the shear behaviour failure mode and asperity damage of unbonded planar and triangular rock concrete interfaces specially under cnl conditions

fine scale magnetic anomaly field over the southern juan de fuca ridge axial magnetization low and implications for crustal structure sea surface deep tow and submersible magnetic surveys show that the spreading axis of the cleft segment of the southern juan de fuca ridge sjdf is overlain by a distinctive magnetic anomaly low in contrast to the more typical magnetic anomaly high found over the adjacent vance segment and most mid ocean ridge spreading centers forward iterative thickness modeling based on the near bottom magnetic data shows that this axial magnetic low can be produced by a thin magnetic source layer beneath the cleft axial valley thick crust is required to produce the magnetic anomaly high over the vance axial valley this magnetic modeling demonstrates that variations in the base of the magnetic source layer which is assumed to be equivalent to the base of the extrusive lavas can produce a significant proportion of the observed short wavelength magnetic anomaly signal these magnetic layer thickness models also correlate quite well with nearby seismic results which show that seismic layer 2a thins beneath the axial valley of the cleft and is thicker beneath the vance axial valley recent seismic results over other fast and medium spreading rifts also show rapid changes in the thickness of the uppermost crust near the axis of spreading which could produce significant magnetic contrasts the results of this study and the correlation with independent seismic measurements suggest that while magnetization may vary due to geomagnetic behavior or because of petrology or alteration first order change in upper crustal thickness is one of the most important variables to consider in the production of fine scale magnetic anomalies in young ocean crust

seismic structure of the upper crust from 0 75 ma in the equatorial atlantic ocean on the african plate using ultralong offset seismic data

density and porosity of the upper oceanic crust from seafloor gravity measurements the exposure of 1300 meters of upper oceanic crust at the blanco fracture zone allows near bottom gravity measurements to determine the in situ density of the seafloor as a function of depth gravity measurements along the north wall of the blanco depression indicate an outcrop density of 2530 kg m for the upper 800 meters of crust and a calculated porosity of 23 the lower 500 meters of crust 800 to 1300 meters below the sea floor has a measured density of 2710 130 kg m and a porosity of 14 these data indicate that most of the extrusive volcanic oceanic crust is highly porous and can act as an aquifer and large scale reservoir for hydrothermal fluids these direct crustal density measurements also support previous interpretations that low seismic velocities observed in layer 2 are due to the high porosity of the upper extrusive section

geologic structure of the uppermost oceanic crust created at fast to intermediate rate spreading centers abstract geological investigations of major fault scarps tectonic windows and dsdp odp drill holes provide direct views of the uppermost oceanic crust generated at fast to intermediate rate spreading centers these areas reveal a consistent upper crustal structural geometry with basaltic lava flows defining a pattern of downward increasing inward dip toward the spreading center at which they formed and dikes in the lavas and underlying sheeted dike complex showing a similar degree of outward dip widespread fracturing faulting and hydrothermal metamorphism accompanied magmatic construction these geological relationships can be interpreted in terms of dramatic asymmetrical subaxial subsidence of upper crustal rock units that diminishes across the very narrow few kilometers wide zone of lava accumulation and dike intrusion at the ridge axis this type of crustal structure is in accord with some existing models of spreading but augments these idealized views with more realistic geological

upper crustal structure and axial topography at intermediate spreading ridges seismic constraints from the southern juan de fuca ridge 1 we use multichannel seismic reflection data to image the upper crustal structure of 0 620 ka crust along the southern juan de fuca ridge the study area comprises two segments spreading at intermediate rate with an axial high morphology with narrow cleft and wide vance axial summit grabens asg along most of the axis of both segments we image the top of an axial magma chamber amc the amc along cleft deepens from south to north from 2 0 km beneath the ridge cleft observatory and hydrothermal vents near the southern end of the segment to 2 3 km at the northern end near the site of the 1980s eruptive event along the vance segment the amc also deepens from south to north from 2 4 to 2 7 km seismic layer 2a interpreted as the basaltic extrusive layer is 250 300 m thick at the ridge axis along the cleft segment and 300 350 m thick along the axis of the vance segment however off axis layer 2a is similar in both segments 500 600 m indicating 90 and 60 off axis thickening at the cleft and vance segments respectively half of the thickening occurs sharply at the walls of the asg with the remaining thickening occurring within 3 4 km of the asg along the full length of both segments layer 2a is thinner within the asg compared to the ridge flanks previous studies argued that the asg is a cyclic feature formed by alternating periods of magmatism and tectonic extension our observations agree with the evolving nature of the asg however we suggest that its evolution is related to large changes in axial morphology produced by small fluctuations in magma supply thus the asg rather than being formed by excess volcanism is a rifted flexural axial high the changes in axial morphology affect the distribution of lava flows along the ridge flanks as indicated by the pattern of layer 2a thickness the fluctuations in magma supply may occur at all spreading rates but its effects on crustal structure and axial morphology are most pronounced along intermediate spreading rate ridges

new constraints on the age and style of continental breakup in the south atlantic from magnetic anomaly data abstract we present new constraints on the opening of the south atlantic ocean from a joint interpretation of marine magnetic anomaly grids and forward modelling of conjugate profiles we use 45 000 km of recently collected commercial ship track data combined with 561 000 km of publically available data the new data cover the critical ocean continental transition zones and allow us to identify and downgrade some poorly navigated older ship tracks relied upon in earlier compilations within the final grids the mean cross over error is 14 nt computed from 8 227 ship track intersections the forward modelling used uniformly magnetised bodies whose shapes were constrained from coincident deep seismic reflection data we find the oldest magnetic anomalies to date from m10r 134 2 ma late valanginian north of the falkland agulhas fracture zone and m3 129 3 ma barremian south of the rio grande fracture zone hence assuming the gpts used is correct continental breakup was contemporaneous with the parana and etendeka continental flood basalts many of the landward linear anomalies overlap seismically mapped seaward dipping reflectors sdrs we interpret this to mean that a significant portion of the sdrs overlay crust formed by subaerial seafloor spreading here crustal accretion is envisaged to be similar to that at mid ocean ridges but sheet lava flows that later form the sdrs rather than pillow basalts form the extrusive component segmentation of the linear anomalies generated implies that this stage of continental breakup is organised and parallels the seafloor spreading centre that follows our results call into question the common assumption that at volcanic continental margins the first linear magnetic anomalies represent the start of conventional submarine oceanic crustal generation

fundamental properties of loess from northwestern china abstract in view of the industrialisation of northwestern china widespread research was undertaken on the properties of loess in this area this paper deals with a part of these investigations a brief report is given on the distribution of loess in china and their aeolian origin a microstructure model of chinese loess is suggested which can explain its collapsible behaviour and the sensitivity of the mechanical properties of macroporous loess to slight changes of the water content it is emphasised that the physico chemical and mechanical properties of loess are mainly governed by the granular fraction which contains illites montmorillonites and soluble salts results of physico chemical and mineralogical investigations are presented and analysed the fundamental mechanical properties of loess were determined by oedometer triaxial rheological and permeability testing conclusions and suggestions are presented for practical engineering

changes in loess fabric caused by collapse an experimental study abstract this paper models the collapsibility of loess soils under laboratory conditions and examines fabric changes by scanning electron microscopy collapsibility depends on microstructure and collapsed soils consist of aleurite and psammite grains with clay films grain contacts include clay bridges and clay buttresses which collapse when saturated and loaded collapsibility is also affected by porosity in which pores average about 10 m carbonate content metal oxides and hydroxides and soluble salts

experimental investigation of foundation on collapsible soils abstractgeotechnical engineers face serious problems when building on collapsible soils these types of soil show considerable strength when dry and experience excessive and sudden settlement when

a numerical modeling study of warm offshore flow over cool water abstract numerical simulations of boundary layer evolution in offshore flow of warm air over cool water are conducted and compared with aircraft observations of mean and turbulent fields made at duck north carolina two models are used a two dimensional high resolution mesoscale model with a turbulent kinetic energy closure scheme and a three dimensional large eddy simulation les model that explicitly resolves the largest turbulent scales both models simulate general aspects of the decoupling of the weakly convective boundary layer from the surface as it is advected offshore and the formation of an internal boundary layer over the cool water two sets of experiments are performed which indicate that complexities in upstream surface conditions play an important role in controlling the observed structure the first land sea experiments examine the transition from a rough surface having the same temperature as the ambient lower atmosphere to a smooth ocean surface that is 5 c cooler in the seco

direct measurement of magnetic reversal polarity boundaries in a cross section of oceanic crust magnetic field measurements made by submersible define the cross sectional geometry of a magnetic polarity rever sal boundary and the vertical variation of crustal magnetization in upper oceanic crust measured polarity boundaries show a systematic pattern of shallow dip towards the spreading axis within the upper extrusive lavas and steeper dip in the lower extrusive lavas this geometry is a consequence of the em placement of extrusive lava at a midocean ridge reversal boundary geometry and magnetization estimates are used to calculate the magnetic contribution of the extrusive lava se quence to the overlying marine magnetic anomaly signal from the forward modeling the highly magnetized extrusive lavas contribute the majority 50 75 of the observed sea surface magnetic anomaly consistent with the extrusive crust forming the primary source layer for young marine magnetic anomalies

remanence characteristics of different magnetic grain size categories at xifeng central chinese loess plateau abstract utilizing the thermal unblocking of low temperature remanent magnetization in superparamagnetic sp ferrimagnets and the low temperature demagnetization of multidomain md magnetite remanences the relative proportions of sp md and singledomain sd and sd like ferrimagnets are estimated in the topmost part of a loess section at xifeng china which covers about the past 130 000 yr sp ferrimagnets are commonly regarded as pedogenic authigenic products while the md component is believed to have a detrital origin these measurements therefore provide new data which improve our understanding of the characteristics and distribution of the different magnetic grain size fractions present in loess and soils in particular our measurements indicate a larger md fraction in soil than in loess a result which indicates that although enhancement of the sp ferrimagnet fraction dominates the increased low field magnetic susceptibility of paleosols an enhancement of the md fraction probably through leaching also plays an important role during pedogenesis

mapping of seismic layer 2a 2b boundary above the sheeted dike unit at intermediate spreading crust exposed near the blanco transform 1 we present results from a study mapping the seismic layer 2a 2b boundary in young ocean crust located adjacent to the north wall of the blanco transform fault btf we review seafloor features geochemical and petrologic data seismic imaging and seismic structure and conclude that the btf seismic study region is representative of crust formed at the intermediate spreading juan de fuca ridge the mean layer 2a two way travel time beneath the seafloor is 0 37 0 10 s for the 42 12 km seismic survey area several regions are observed where layer 2a is consistently thin or thick over lateral distances of 5 10 km both in a ridge parallel and ridge perpendicular direction layer 2a thicknesses appear more variable in the ridge parallel isochron direction than the ridge perpendicular flow line direction there is no systematic pattern of layer 2a thickness variability with distance from the btf nor is there a correlation between seafloor topography and layer 2a thickness calculated mean layer 2a thickness for the seismic study region is 485 135 m assuming an interval velocity of 2 65 km s the imaged layer 2a 2b boundary projects on average 600 650 m above the top of the sheeted dike complex mapped on the adjacent btf north wall we argue that the geologic context of the layer 2a 2b boundary will vary as competing processes of magmatic construction and fracturing increasing porosity and crustal thickening compaction dike intrusion and hydrothermal sealing decreasing porosity vary as the crust spreads laterally from the ridge axis to ridge flanks

inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust the oceanic crust makes up two thirds of the earth s surface and has been studied for many years yet the processes by which it is formed are still not fully understood one problem is inaccessibility only a tiny fraction of it has been subjected to drilling and sampling the tools of geology so much relies on remote sensing techniques such as seismic exploration the tools of geophysics these two approaches have led to some confusion over crustal structure christeson et al set out to reconcile the two by a direct comparison between seismic interpretations and geologic mapping the new data question the idea that seismic layer 2a correlates with lava layer thickness instead the layer 2a reflection seems to correspond to an alteration boundary within the lava layer at mid ocean ridges with fast to intermediate spreading rates the upper section of oceanic crust is composed of lavas overlying a sheeted dyke complex these units are formed by dykes intruding into rocks overlying a magma chamber with lavas erupting at the ocean floor seismic reflection data acquired over young oceanic crust commonly image a reflector known as layer 2a which is typically interpreted as defining the geologic boundary between lavas and dykes1 2 3 an alternative hypothesis is that the reflector is associated with an alteration boundary within the lava unit4 5 6 many studies have used mapped variability in layer 2a thickness to make inferences regarding the geology of the oceanic crust including volcanic construction dyke intrusion and faulting7 8 9 10 however there has been no link between the geologic and seismological structure of oceanic crust except at a few deep drill holes here we show that although the layer 2a reflector is imaged near the top of the sheeted dyke complex at fast spreading crust located adjacent to the hess deep rift it is imaged significantly above the sheeted dykes section at intermediate spreading crust located near the blanco transform fault although the lavas and underlying transition zone thicknesses differ by about a factor of two the shallow seismic structure is remarkably similar at the two locations this implies that seismic layer 2a cannot be used reliably to map the boundary between lavas and dykes in young oceanic crust instead we argue that the seismic layer 2a reflector corresponds to an alteration boundary that can be located either within the lava section or near the top of the sheeted dyke complex of oceanic crust

magnetic properties of dikes from the oceanic upper crustal section recovery of dredge samples of upper crustal dikes from the steep north wall of the blanco fracture zone west blanco deep allows an evaluation of this rock type as a possible contributor to the magnetic anomaly source layer magnetic data from these dike sill samples indicate that the majority of the rocks meet the essential criteria as a contributor to the source layer including a high magnetic intensity 2 7 a m a ratio of remanent to induced magnetization that is greater than 1 and a relative stability against large scale viscous remanent magnetization acquisition over long geological time periods however because the natural remanent magnetization intensities of the dike samples are an order of magnitude lower than the extrusive rocks within the axial zone the presence of abundant near surface dikes would lower the net magnetization of a crustal section and may be responsible for the axial magnetic low that has been observed on medium to fast spreading centers if the magnetization of the dikes does not change with time due to low temperature oxidation then the decreasing ratio of extrusive intrusive contribution as the pillow basalts undergo systematic oxidation will cause the magnetic layer to appear to thicken and the polarity transition zones to widen as the crust ages and moves off axis

remanent magnetization of the oceanic upper mantle skewnesses of the marine and magsat magnetic anomalies of the atlantic ocean are explained in terms of the remanent magnetization gradually acquired by the oceanic lithosphere during its cooling magnetizations of the lower crust and the upper mantle are about 20 50 and 10 30 percent of the magnetization of the oceanic basaltic layer 2a respectively the oceanic upper mantle controls the skewness of the magsat anomalies whereas the skewness of the marine anomalies arise primarily from the oceanic lower crust

global equivalent magnetization of the oceanic lithosphere abstract as a by product of the construction of a new world digital magnetic anomaly map over oceanic areas we use an original approach based on the global forward modeling of seafloor spreading magnetic anomalies and their comparison to the available marine magnetic data to derive the first map of the equivalent magnetization over the world s ocean this map reveals consistent patterns related to the age of the oceanic lithosphere the spreading rate at which it was formed and the presence of mantle thermal anomalies which affects seafloor spreading and the resulting lithosphere as for the age the equivalent magnetization decreases significantly during the first 10 15 myr after its formation probably due to the alteration of crustal magnetic minerals under pervasive hydrothermal alteration then increases regularly between 20 and 70 ma reflecting variations in the field strength or source effects such as the acquisition of a secondary magnetization as for the spreading rate the equivalent magnetization is twice as strong in areas formed at fast rate than in those formed at slow rate with a threshold at 40 km myr in agreement with an independent global analysis of the amplitude of anomaly 25 this result combined with those from the study of the anomalous skewness of marine magnetic anomalies allows building a unified model for the magnetic structure of normal oceanic lithosphere as a function of spreading rate finally specific areas affected by thermal mantle anomalies at the time of their formation exhibit peculiar equivalent magnetization signatures such as the cold australian antarctic discordance marked by a lower magnetization and several hotspots marked by a high magnetization

observations of non dimensional wind shear in the coastal zone summary vertical profiles of the time averaged wind stress wind speed and buoyancy flux from the off shore tower site in the rise air sea experiment are used to evaluate similarity theory in the coastal zone the observed dependence of the non dimensional wind shear on stability is compared to the traditional parametrization relationships between the non dimensional shear development of internal boundary layers and wave state are explored we find that the largest scale turbulent eddies are suppressed in shallow convective internal boundary layers leading to larger non dimensional shear than that of the traditional prediction based only on stability in shallow stable boundary layers elevated generation of turbulence leads to smaller non dimensional shear compared to the traditional prediction over young growing waves in stable stratification the observed non dimensional shear is less than that over older more mature waves in otherwise similar conditions the non dimensional shear is a function of wave state for stable conditions even though the observations are well above the wave boundary layer we conclude that development of shallow internal boundary layers and young growing wave fields both of which are common in the coastal zone can lead to substantial departures of the non dimensional shear from the prediction based only on stability

the galapagos axial magnetic anomaly evidence for the emperor event within the brunhes and for a two layer magnetic source the axial brunhes magnetic anomaly over the galapagos spreading center shows consistent short wavelength anomalies that are not consistent with a uniformly magnetized layer we interpret this anomaly to confirm the presence of the emperor reversed event at 0 49 0 05 mybp with a duration about 0 01 m y further this anomaly is consistent with a two layer magnetic source with the lower layer having very broad transition zones offset away from the axis from those of the upper layer by about 10 km

the distribution and geotechnical properties of loess soils lateritic soils and clayey soils in china in china various soils covering vast regions occur loess soils of the yellow river in northern china lateritic soils in southern china and clayey soils in central china the special geotechnical properties of these soils are briefly described the relationship of their material components and microstructural features with their geotechnical properties is studied it is shown that the special geotechnical properties of these soils depend mainly on their material component and microstructural features the distribution of these soils is studied in relation to geographical environment and climatic conditions it is suggested that the formation of the geotechnical properties of these soils have undergone three different development stages

thermal effects on yielding and wetting induced collapse of recompacted and intact loess yielding and wetting induced collapse are two important interrelated aspects of unsaturated loess behaviour previous studies on loess are generally under a single temperature condition the principal objective of this study is to investigate thermal effects on yielding and wetting induced collapse of recompacted and intact loess isotropic compression tests were carried out to determine yield stress at different suctions 0 and 100 kpa and temperatures 5 23 and 50 c moreover wetting tests were conducted at various temperatures and stresses the results of wetting tests were interpreted using the measured yield stress at various suctions and temperatures it is found that yield stress decreases with decreasing suction wetting induced softening the wetting induced softening of recompacted loess is more significant at a higher temperature the observed thermal effects on wetting induced softening are likely because with decreasing suction the stabilizing inter particle normal force decreases more

toward a minimum change model for recent plate motions calibrating seafloor spreading rates for outward displacement summary we use seafloor spreading distances derived from reconstructions of more than 7000 crossings of young magnetic anomalies along seven plate boundaries to study outward displacement a source of systematic bias in estimates of seafloor spreading rates which is caused by a combination of processes that shift magnetic polarity transition zones away from their idealized locations linear regressions of 81 independent sequences of seafloor opening distances as a function of their magnetic reversal ages for anomalies younger than c3n 1 4 19 ma yield 75 positively valued intercepts for zero seafloor age confirming the ubiquitous outward shift of magnetic reversals reported by previous authors grouping these data into 29 locally consistent clusters yields better constrained zero age intercepts that are uniformly positive and average 2 2 0 3 km globally these values which are 1 3 km at most locations and are significantly larger 3 5 km along the well surveyed reykjanes and carlsberg ridges agree well with published magnetic polarity zone transition widths which are estimated directly from nearbottom seafloor magnetic measurements significant variations in outward displacement along the southeast indian ridge are strongly correlated with changes in axial morphology and axial depth however a similar correlation is not observed along other ridges forward magnetic anomaly modelling suggests that variations in outward displacement can be explained by differences in the magnetic source layers that are assumed to characterize different spreading centres if not corrected for outward displacement the implied systematic upward biases in seafloor spreading rates which are averaged over the width of anomaly 1 the youngest reversal that is used for plate reconstructions range from 6 mm yr 1 along the reykjanes ridge where outward displacement is 4 5 km to 3 mm yr 1 along ridges where outward displacement approximates the global average of 2 km

optimization of compaction zoning in loess embankments extensive centrifuge model tests were carried out to investigate optimum compaction density zones within loess embankments 30 and 63 8 m high in these tests water infiltration into the slopes and upstream storm water ponds were modelled to simulate the most unfavourable working conditions displacement contours in the cross sections were measured and crest settlements were monitored during the tests finally the optimum compaction zoning was analysed based on the comprehensive evaluation of the total crest settlement the postconstruction settlement and the slope stability of the embankments it was indicated that a properly designed high loess embankment could perform satisfactorily with the lower part compacted looser than the conventional code requirements in terms of total crest settlement and embankment cracking the degree of compaction k of loess fills should not be less than 0 85 for 30 m high embankments and not less than 0 90 for 63 8 m high embankments in terms of the postconstruction settlement 0 2 0 3 m and construction feasibility it is expedient to compact the lower one third to k 0 85 and the top two thirds to k 0 90 for 63 8 m high embankments for 30 m high embankments the bottom zone with k 0 85 can make up two thirds of the height

a geotechnical survey of some british coal measures mudstones with particular emphasis on durability abstract samples of fresh mudstones were obtained from near tow law and kirkheaton and of weathered mudstones from near wrexham the mineral composition of these mudstones was similar kaolinite being the principal clay mineral the clay mineral fraction dominating quartz was the chief non clay mineral present some basic geotechnical and index properties were determined the fresh mudstones from near tow law had a low plasticity as did the moderately and highly weathered mudstones from near wrexham however the completely weathered mudstones from the latter area possessed intermediate plasticity the strength of the fresh mudstones from near kirkheaton was notably higher than that of the mudstones from near tow law both groups of fresh mudstones displayed significant anisotropy ratios when they underwent axial and diametral point load testing this no doubt was due to the influence of lamination as durability is one of the most important engineering properties of mudstone it was assessed by a number of tests one cycle slake durability testing did not appear to offer an acceptable indication of the durability of mudstones when compared with cyclic wetting and drying cyclic freezing and thawing and geodurability classification cyclic slake durability testing and comparison with unconfined compressive strength would seem to be a more reliable way of determining durability both fresh and weathered mudstones underwent little expansion when subjected to swelling tests however in the case of the weathered mudstones the amount of swelling stress and strain could be related to basic geotechnical properties

crustal magnetization and accretion at the southwest indian ridge near the atlantis ii fracture zone 0 25 ma 1 we analyze geophysical data that extend from 0 to 25 myr old seafloor on both flanks of the southwest indian ridge swir lineated marine magnetic anomalies are consistent and identifiable within the study area even over seafloor lacking a basaltic upper crust the full spreading rate of 14 km myr has remained nearly constant since at least 20 ma but crustal accretion has been highly asymmetric with half rates of 8 5 and 5 5 km myr on the antarctic and african flanks respectively this asymmetry may be unique to a 400 km wide corridor between large offset fracture zones of the swir in contrast to the mid atlantic ridge crustal magnetization amplitudes correlate directly with seafloor topography along the present day rift valleys this pattern appears to be primarily a function of along axis variations in crustal thickness rather than magnetic mineralogy off axis magnetization amplitudes at paleo segment ends are more positive than at paleo segment midpoints suggesting the presence of an induced component of magnetization within the lower crust or serpentinized upper mantle alteration of the magnetic source layer at paleo segment midpoints reduces magnetization amplitudes by 70 80 within 20 myr of accretion magnetic and ocean drilling program odp hole 735b data suggest that the lower crust cooled quickly enough to lock in a primary thermoremanent magnetization that is in phase with that of the overlying upper crust thus magnetic polarity boundaries within the intrusive lower crust may be steeper than envisioned in prior models of ocean crustal magnetization as the crust ages the lower crust becomes increasingly important in preserving marine magnetic stripes

effect of inundation on shear strength characteristics of mudstone backfill a group of lithologies which includes claystone siltstone mudstone and shale also known as mudrocks are indurated sediments widely encountered throughout the world shear strength and deformation characteristics of mudstone were investigated using a fully automated hydraulic stress path testing system under three rock states dry short term inundated and long term it is observed that the maximum deviator stress q appeared to decrease meaning the strength deteriorated as the rock states changed from dry to wetted and to degraded conditions furthermore critical state interpretations of the mudstone under all three rock states have shown unique high curved mohr coulomb failure envelopes which are normally exhibited only by crushable soil nevertheless m which is the slope of stress path and angle shearing resistance values obtained from dry specimens were always higher than the partially saturated specimens however as dry mudstone sheared under higher mean effective stress 700 kpa the m value exhibited is similar to m value of wetted mudstone which is 1 20 and remained the same as mudstone degraded it is believed that the strength of mudstone decreasing as it begins to crush and gradually became constant

surface stress in offshore flow and quasi frictional decoupling aircraft data collected at approximately 15 m above the sea surface in the coastal zone are analyzed to examine the spatial distribution of surface stress advection of stronger turbulence from land dominates the near surface turbulence for the first few kilometers offshore with offshore flow of warm air over cold water strong stratification leads to very small surface stress because the stability restricts the momentum transfer to the waves the aerodynamic surface roughness decreases to very small values which in turn decreases atmospheric mixing the redevelopment of the boundary layer farther downstream is examined computation of fluxes from observations for stable cases is difficult due to a variety of errors including large random flux errors possible instrumental loss of small scale flux difference between the surface flux and that at the observational level and inadvertent capture of mesoscale motions in the computed turbulent fluctuations although the errors appear to be substantial the aircraft momentum fluxes compare favorably with those from sonic anemometers on two buoys and a tower at the end of a 570 m pier even with near collapse of the turbulence

magnetic polarity structure of the lower oceanic crust a newly developed rock drill was used to take the first fully oriented samples from in situ gabbros exposed on atlantis bank which formed 11 m y ago on the southwest indian ridge swir these paleomagnetic data locate the seabed outcrop of a normal polarity magnetic lineation within an outcrop of lower crust that correlates with overlying deep towed and sea surface magnetic field measurements a systematic lateral offset between the seabed boundary and measured anomalies implies that the reversal boundary dips 25 to the south away from the ridge axis paleomagnetic results suggest that following magnetization acquisition the platform tilted south by 20 range 33 south to 7 north implying an original reversal boundary dip of only 5