stress induced anisotropy of partially molten rock analogue deformed under quasi static loading test 1 two quasi static loading tests one with and one without repeated changes in the principal stress directions were performed on a partially molten rock analogue in both runs development of stress induced anisotropy was observed through a continuous nondestructive monitoring of the sample microstructure using ultrasonic shear waves the direction of the shear wave anisotropy showed that the area of the grain to grain contact faces whose normals are nearly parallel to the 3 direction decreased while the area of the other contact faces remained almost unchanged large viscous anisotropy caused by this microstructural anisotropy could be detected through the strong coupling between shear and isotropic stress components the large amplitude of viscous anisotropy relative to the small amplitude of shear wave elastic anisotropy is consistent with the prediction from theoretical models amplitude and direction of this anisotropy almost synchronized with those of shear stress indicating the existence of steady state microstructure under a given shear stress a small hysteresis however was also observed which led to a significant grain boundary wetting due to the repeated changes in the shear direction the present results show the validity of the theoretical models for elasticity and viscosity the coupling between shear and isotropic components produced by viscous anisotropy significantly affects the dynamics of partially molten mantle because it enhances shear induced melt segregation

factors underlying piping in the basilicata region southern italy abstract piping tunnelling erosion is a widely spread process in the plio pleistocene marine clays of the basilicata region in southern italy the pipes are often closely concentrated along the surface drainage networks at different depths with a tunnel length and a diameter varying from just a few centimetres to some metres the formation and evolution of pipes in the badlands can be explained through 1 geo structural characteristics of the clay 2 material properties such as a high exchangeable sodium percentage 3 favourable climatic conditions and 4 hydraulic gradient along the path controlled by the gully or ravine bottom that is acting as a local drain the exposure and the extension of joints at the surface and in the bedrock along the slope are the main factors required for development of the pipes the absence of the piping erosion on the slopes where a reasonably thick layer of the soil material covers the open joints shows that although certain material properties and climatic conditions play an important role they are not sufficient to develop extensive piping erosion in the area

understanding soil pipe flow and its role in ephemeral gully erosion the role of soil pipeflow in ephemeral gully erosion is not well understood experiments were conducted on continuous soil pipes to better understand the role of internal erosion of soil pipes and its relation to ephemeral gully development soil beds of 140 cm length 100 cm width and 20 cm depth had a single soil pipe of different initial sizes 2 4 6 8 and 10 mm diameter extend from a water reservoir to the outlet experiments were run on providence silt loam and smithdale loam soils under a constant head of 15 cm established for 30 min either the tunnel collapsed or the head could not be maintained soil pipes that were initially 2 and 4 mm clogged instantaneously at their mouth and did not exhibit flow whereas pipes initially 6 mm enlarged by 268 397 and 699 on average for the 6 8 and 10 mm diameters respectively critical shear stress values were found to be essentially zero and erodibility values gave erosion indexes that were extremely high the rapid internal erosion resulted in erratic flow and sediment concentrations with periods of no flow as pipes were temporarily clogged followed by surges of high flow and high sediment concentrations tensiometers within 6 cm of the soil pipes did not exhibit pressure increases typically associated with pipe clogging flow through 10 mm diameter soil pipes exhibited tunnel collapse for both soils tested tunnel collapse typically occurred within minutes of flow establishment suggesting that ephemeral gullies could be misinterpreted as being caused by convergent surface flow if observations were made after the runoff event instead of when flow is first established through soil pipes copyright 2011 john wiley sons ltd

evidence of electrical anisotropy in limestone formations using the rmt technique azimuthal resistivity surveys are often applied to complement hydrological information or to improve the location of observation boreholes in pump tests symmetric electrode configurations cannot distinguish anisotropy from lateral changes or dipping layers but asymmetric arrays e g the offset wenner array can tensor radiomagnetotellurics rmt is presented as an alternative method in studies of electrical anisotropy in the shallow subsurface the electromagnetic and geomagnetic transfer functions provide information about the dimensionality of the data these transfer functions can also be used to find the directions of anisotropy data with an anisotropic signature can be inverted for a one dimensional 1d azimuthal anisotropy model the method is faster than the azimuthal resistivity method a 380 m long profile of tensor rmt data 12 7 243 khz from limestones that overlie shale on the island of gotland sweden is used to show the merits of the method the data have a clear anisotropic signatur

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

the effects of burial diagenesis on multiscale porosity in the st peter sandstone an imaging small angle and ultra small angle neutron scattering analysis abstract to examine the effects of burial diagenesis on heirarchical pore structures in sandstone and compare those with the effects of overgrowth formation we obtained samples of st peter sandstone from drill cores recovered from the illinois and michigan basins the multiscale pore structure of rocks in sedimentary reservoirs and the mineralogy associated with those pores are critical factors for estimating reservoir properties including fluid mass in place permeability and capillary pressures as well as geochemical interactions between the rock and the fluid the combination of small and ultra small angle neutron scattering with backscattered electron imaging provided a means by which pore structures were quantified at scales ranging from approximately 1 nm to 1 cm seven orders of magnitude larger scale 10 m porosity showed the expected logarithmic decrease in porosity with depth although there was significant variation in each sample group however small and ultra small angle neutron scattering data showed that the proportion of small scale porosity increased with depth porosity distributions were not continuous but consisted of a series of log normal like distributions at several distinct scales within these rocks fractal dimensions at larger scales decreased surfaces smoothed with increasing depth and those at smaller scales increased surfaces roughened and pores become more isolated higher lacunarity data suggest that changes in pore size distributions are controlled by both physical compaction and chemical effects precipitation cementation dissolution

pipe poiseuille flow of viscously anisotropic partially molten rock summary laboratory experiments in which synthetic partially molten rock is subjected to forced deformationprovideacontextfortestinghypothesesaboutthedynamicsandrheologyofthemantle here our hypothesis is that the aggregate viscosity of partially molten mantle is anisotropic and that this anisotropy arises from deviatoric stresses in the rock matrix we formulate a model of pipe poiseuille flow based on theory by takei holtzman and takei katz pipe poiseuille is a configuration that is accessible to laboratory experimentation but for which there are no published results we analyse the model system through linearized analysis and numerical simulations this analysis predicts two modes of melt segregation migration of melt from the centre of the pipe towards the wall and localization of melt into high porosity bands that emerge near the wall at a low angle to the shear plane we compare our results to those of takei katz for plane poiseuille flow we also describe a new approximation of radially varying anisotropy that improves the self consistency of models over those of takei katz this study provides a set of baseline quantitative predictions to compare with future laboratory experiments on forced pipe poiseuille flow of partially molten mantle

constraints on melt distribution from seismology a case study in ethiopia low seismic velocities and or strong seismic anisotropy are often interpreted as being caused by partial melt to better understand this we used numerical modelling varying the shape and amount of melt to show how seismic phases are affected by melt we observed that seismic waves are more sensitive to the shape than to the amount of melt rayleigh wave velocities were almost always reduced in the presence of melt while pn wide angle p wave refraction and love wave velocities showed low velocity anomalies for vertically aligned melt but little anomaly for horizontally aligned melt these data can therefore be used to determine the alignment of melt shear wave splitting receiver functions showed strong anisotropy and can be used to constrain the strike of vertically aligned partial melt we showed that melt in the mantle beneath ethiopia is probably stored in low aspect ratio disc like inclusions suggesting that the melt is not in textural equilibrium we estimated that 2 7 of the vertically aligned melt is stored beneath the main ethiopian rift 6 of the horizontally and vertically aligned melt is stored beneath the red sea rift and 1 6 of the horizontally aligned melt is stored beneath the danakil microplate this supports the idea of strong shear derived segregation of melt in the narrow main ethiopian rift compared with that observed beneath afar

tunnel erosion and sediment production in the hilly loess region north china in this study detailed monitoring of water and sediment delivery from major tunnel systems was conducted in a small semi arid sub basin locally known as yangdaogou in the hilly loess region north china these deep seated tunnels are located as much as 30 m below the slope surface in deep quaternary loess formations in the yangdaogou these systems have large amphitheatre like inlets with mean diameter and depth of 4 8 and 4 99 m respectively these dimensions represent some of the largest tunnel inlets in the world during 1989 and 1990 fifteen rainstorms were monitored at six tunnel outlets due to practical difficulties only 35 sets of tunnel storm data were obtained observed sediment concentration of tunnel flows ranges from 8 2 to 893 2 g l the peak sediment concentrations in tunnel flows are not distinctively higher than those in channel flows but considerably higher than those measured from untunneled sideslopes no significant correlations between runoff and sediment yield can be found in most tunnels at both within and between storm levels such an erratic relationship is ascribed to the rapid shift of runoff and sediment source area the occurrence of collapses within tunnels and the initiation of new tunnel inlets based on the field monitored data 57 of basin sediment production is delivered by the tunnel systems suggesting that tunnel erosion is a major erosion process in the hilly loess region

soil pipe collapses in a loess pasture of goodwin creek watershed mississippi role of soil properties and past land use little is known about the association of soil pipe collapse features with soil properties or land use history three loess covered catchments in northern mississippi usa were characterized to investigate these relationships soil pipe collapses were characterized for their size type feature and spatial location along with soil properties across the three catchments although mapped as the same soil one of the catchments did not contain pipe collapse features while the other two had 29 4 and 15 4 pipe collapses per hectare these loess soils contained fragipan layers that are suspected of perching water thereby initiating the piping processes pipe collapses associated with subsurface flow paths were not always consistent with surface topography the surface layer tended to be non erodible while layers below even the upper fragipan layers were susceptible to erosion by pipeflow soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible these anthropic soils were previously gullies that were filled in in the 1950s when forested areas assumed to have been established when land was previously converted from crop to forest land were converted to pasture three decades after this land use change from forest to pasture pipe collapses became evident in contrast the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production the surface horizons above the lower fragipan layer were completely removed during this period thus the top soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed this study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role copyright 2015 john wiley sons ltd

hydrologic connectivity and threshold behavior of hillslopes with fragipans and soil pipe networks many concepts have been proposed to explain hydrologic connectivity of hillslopes with streams hydrologic connectivity is most often defined by qualitative assessment of spatial patterns in perched water tables or soil moisture on hillslopes without a direct linkage to water flow from hillslopes to streams this form of hydrologic connectivity may not explain the hydrologic response of catchments that have network s of preferential flow paths e g soil pipes which can provide intrinsic connectivity between hillslopes and streams duplex soils are known for developing perched water tables on hillslopes and fostering lateral flows but the connectivity of localized perched water tables on hillslopes with soil pipes has not been fully established the objectives of this study were to characterize pipeflow dynamics during storm events the relationships between perched water tables on hillslopes and pipeflows and their threshold behavior two well characterized catchments in loess soil with a fragipan were selected for study because they contain multiple laterally extensive over 100 m soil pipe networks hillslopes were instrumented with shallow wells adjacent to the soil pipes and the wells and pipe collapse features were equipped with pressure transducers perched water tables developed on hillslopes during a wetting up period october december and became well connected spatially across hillslope positions throughout the high flow period january march the water table was not spatially connected on hillslopes during the drying out april june and low flow july september periods even when perched water tables were not well connected water flowing through soil pipes provided hydrologic connectivity between upper hillslopes and catchment outlets correlations between soil pipeflow and perched water tables depended on the size and location of soil pipes the threshold relationship between available soil moisture index plus storm precipitation asi p and pipeflow was dependent on the season and strongest during dry periods and not high flow seasons this study demonstrated that soil pipes serve as a catchment backbone of preferential flow paths that provide intrinsic connectivity between upper hillslopes and streams

ephemeral gully erosion by preferential flow through a discontinuous soil pipe abstract subsurface flow through soil pipes can contribute to ephemeral gully erosion but these soil pipes are cut off when tillage fills in the gully the objective was to determine the effect of flow through discontinuous soil pipes on ephemeral gully erosion experiments were conducted on 150 cm long by 100 cm wide soil beds with an artificial soil pipe at the upper end that extended 50 cm into the soil immediately above a water restricting horizon the combination of rainfall with pipe flow produced extensive 63 kg soil losses by mass wasting the mode of mass wasting appeared to be sudden cataclysmic pop out failures total soil loss by sheet erosion with rainfall and pipe flow combined 13 6 kg was four times higher than by rainfall alone 3 4 kg under rainfall with pipe flow soil loss by mass wasting was nearly 20 times higher than sheet erosion from rainfall alone soil conservation practices that treat surface runoff process alone may be ineffective if subsurface flow is contributing

tectonics of the beja acebuches ophiolite a major suture in the iberian variscan foldbelt the beja acebuches ophiolitic complex baoc south portugal spain corresponds to a high grade metamorphic belt along the boundary between ossa morena and the south portuguese zones and comprises a lithostratigraphic sequence including from top to bottom metabasalts metamorphosed multiple dyke intrusions in gabbro flasergabbros and metaserpentinites it is affected by three deformation phases d1 affects the ophiolite lower stratigraphic units and is represented by a mylonitic cleavage with a stretching lineation where shear criteria indicates the sense of shear to be towards the north north east this deformation event can be related to the ophiolite emplacement above the crystalline footwall of the serpa antiform affecting precambrian basement and cambrian cover rocks the obduction polarity ist north eastwards similar to the subduction polarity that generates the beja gabbroic complex bgc implying a flake geometry the second deformation phase d2 is represented by an intense wnw ese sinistral shear event which is responsible for the shattered appearance of the suture d2 is reactivated later by a more brittle d3 event involving thrusting to the south west again with a sinistral component 40ar 39ar isotopic ages were obtained for metamorphosed multiple dyke intrusions in the baoc s gabbro 342 6 1 4 ma for metagabbroic cumulates 340 7 1 9 ma and for the undeformed unmetamorphosed bgc 341 1 1 3 ma occurring to the north of the ophiolitic suture these ages reflect a last regional cooling event in the area which post dates the ophiolite emplacement and the intrusion of the bgc through this oceanic sequence

archaean cratonic roots mantle shear zones and deep electrical anisotropy the extent to which the mantle participated in the growth and stabilization of ancient cratons is central to our understanding of the evolution of the continents1 the detection of seismic anisotropy beneath precambrian north america for example has been interpreted as showing that strain induced orientation of mantle minerals in subcontinental lithospheric mantle can preserve a record of ancient episodes of deformation2 here we present mag netotelluric measurements from the superior province of the canadian shield which reveal pronounced electrical anisotropy in the upper 100 km of the underlying mantle we argue that this anisotropy is best explained by conducting graphite films oriented within fractures or on grain boundaries and associated with metasomatism of the mantle roots of major archaean shear zones which transect the entire superior province the uppermost mantle beneath the canadian shield has therefore remained fixed to the crust and isolated from significant tectonic reworking since the late archaean

magnetotelluric survey of the electrical conductivity of the crust across the ossa morena zone and south portuguese zone suture abstract the transition between the south portuguese zone spz and the ossa morena zone omz is made up of a major geosuture which is indicated by the beja acebuches ophiolite several geological data suggest that this suture is the result of an oblique collision with a northward propagation between the spz and omz from the structural point of view the omz is much more complex than the adjacent central iberian zone and the spz the frequently complicated internal structure is the result of superposition of various structural elements developed during different tectonic events with the aim of providing new constraints to this complex deep structure a magnetotelluric mt survey was designed by the universities of lisbon and barcelona in the scope of the bilateral cooperation and the europrobe programs a first nne ssw profile across the spz and omz was carried out in september 1997 the profile is 40 km long and consists of nine deep mt soundings with periods ranging from 0 0039 to 4000 s the time series were processed using a robust algorithm after visual inspection the study of the dimensionality and directionality of the regional electrical structures is based on the analysis of the induction arrows and the groom bailey decomposition a strike of n125e was determined in accordance with regional geological features 2 d inversion was undertaken on both te and tm modes using the rri method the main feature of the model is a large conductive body

main types of soil mass failure and characteristics of their impact factors in the yuanmou valley china abstract gully erosion is a dominant process causing soil loss in the yuanmou valley of yunnan province china soil mass failure is a common process involved in gully development the development of the gully and the occurrence of mass failure are interdependent and mutually promotive but mass failure types have not been very well understood in this study we identify the main types of soil mass failure and the characteristics of their impact factors in the yuanmou valley a detailed field survey was conducted in may 2010 in a representative area of the studied region and selected soil parameters were measured in the field and laboratory results showed that there are four different soil mass failure types falling sliding exfoliating and toppling each having unique characteristics of geology topography soil and climate examination of these characteristics indicates that the occurrence of mass failure is controlled by four factors 1 the typical geological structure of the yuanmou group represented by alternating layers of sand and clay 2 the different terrain and landforms 3 the different gully development stages and 4 the particular soil properties under special weather conditions including a dry hot climate with distinct wet and dry seasons

mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil pipe ephemeral gully erosion is considered to be driven by convergent surface flow while the role of subsurface flow is often overlooked this study sought to characterize and quantify the soil erosion mechanisms associated with ephemeral gully erosion by pipe flow a soil pipe 1 cm o d was formed in a 10 cm soil bed immediately above a 5 cm water restricting layer flow into the soil pipe was established at steady state rates of 190 and 284 l h 1 experiments were performed for pipe flow alone and with rainfall despite a constant flow rate into soil pipes pipe flow was highly unstable due to internal mass wasting clogging soil pipes until pressure increases forced the debris plug out of the pipe short 10 20 seconds periods of negligible flow were followed by surges in flow with high sediment concentrations that included a high proportion of aggregates increases in soil water pressures associated with these debris flows were observed but were likely not representative of the pressures inside the soil pipes due to hydraulic non equilibrium between the soil pipe and soil matrix hydraulic non equilibrium resulted in hydraulic gradients in the opposite direction of flow through the soil pipe during early stages of pipe flow pipe flow rates and sediment concentrations during debris flow periods were likely more extreme than observed due to integration over the three minute sample collection interval the slot erosion test set was extended to conditions of constant flow rate through an internal soil pipe that was observed at the front face of a soil bed the modified set provided estimates of shear stress between 2 2 to 5 3 kg m 1 s 2 however the technique did not prove effective for estimation of the soil erodibility coefficient published in 2009 by john wiley sons ltd

sensitivity and inversion of marine electromagnetic data in a vertically anisotropic stratified earth the controlled source electromagnetic csem and magnetotelluric method mt are two techniques that can be jointly used to explore the resistivity structure of the earth such methods have in recent years been applied in marine environments to the exploration and appraisal of hydrocarbons in many situations the electric properties of the earth are anisotropic with differences between resistivity in the vertical direction typically much higher than those in the horizontal direction in cases such as this the two modes of the time harmonic electromagnetic field are altered in different ways implying that the sensitivity to the earth resistivity may vary significantly from one particular resistivity component scalar horizontal or vertical to another depending on the measurement configuration range azimuth frequency or water depth in this paper we examine the sensitivity of the electromagnetic field to a vertically anisotropic earth for a typical set of configurations compare inversion results of synthetic data characterizing a vertically anisotropic earth obtained using the isotropic and anisotropic assumptions and show that correctly accounting for anisotropy can prevent artefacts in inversion results

electromagnetic imaging of variscan crustal structures in sw iberia the role of interconnected graphite abstract the western part of the iberian peninsula iberian massif is the best exposed fragment of the variscan orogen in europe its southern half was generated by an oblique collision between three continental terranes belonging to the margins of laurassia avalonia the south portuguese zone spz and gondwana the ossa morena zone omz and the central iberian zone ciz the boundaries between them are considered to be suture zones a 200 km long magnetotelluric profile across the three variscan terranes was done in a nne direction approximately perpendicular to the main tectonic features the results of two dimensional inversion of the mt dataset reveal high conductivity zones coinciding with the transitions spz omz and omz ciz these conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime a high conductivity layer extending along the whole omz was found at a depth of 15 25 km the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile the high conductivity was interpreted as caused by the precambrian serie negra graphite rich rocks carbon and oxygen x ray mapping with electron microprobe on polished sections of serie negra samples from omz revealed the presence of interconnected graphite which supports the hypothesis that graphite is determinant for the high conductivity two graphite types which help to record the geological evolution were identified graphite accumulations in the schistosity surfaces produced by folding and metamorphism and metallic films of graphite developed along late faults the conductive layer shows blobs of higher conductivity suggesting macro anisotropy additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity given that the detachment level is located within the serie negra several high resistivity features were found in the upper crust related to devonian and carboniferous successions and probably to some unexposed plutons in the spz and the palaeozoic series of omz plus some granitic intrusions in the ciz a high resistivity zone extending to the whole crust is correlated with extensive late variscan granite intrusions

macro anisotropy of the electrical conductivity of the crust a magnetotelluric study of the german continental deep drilling site ktb summary the interpretation of magnetotelluric mt data collected in the vicinity of the german continental drilling project ktb has revealed two major structures in the earth s crust first a large scale mid crustal layer of enhanced conductivity is required to fit the regional observations of the anomalous vertical magnetic field second the mt impedances of the area close to the ktb namely the crustal unit of the zone erbendorf vohenstraus zev support a model with a highly anisotropic upper to middle crust the extremely high values of anisotropy derived from the mt measurements exceed the values of anisotropy observed on rock samples in the laboratory by an order of magnitude and therefore exclude intrinsic features as a source for the observed anisotropy the regional mid crustal conductor is in agreement with central europe wide observations of high conductivity layers in the crust while the proposed model of well conducting subvertical dykes within a resistive host rock explains the mt observations and agrees with the steeply dipping seismic reflectors the downhole and core observations from the drilling and the model of the tectonic development of this area however the superposition of both structures leaves some unanswered questions

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

tectonic fabric of the subcontinental lithosphere evidence from seismic magnetotelluric and mechanical anisotropy abstract knowledge of anisotropy is key to our understanding of tectonic fabrics in the lithosphere and sublithospheric mantle anisotropy provides a unique constraint on the character of past and present deformation and thus is critical to our understanding of dynamics of the plate tectonic system in particular how continents with their thick lithospheric mantle roots form stabilize and interact with underlying mantle regions improved observational methods and rapid developments of geophysical inversion techniques are contributing to more realistic earth models that include various types of anisotropy and heterogeneity a more robust characterization of anisotropic parameters can be achieved by integrating complementary datasets incorporating constraints from seismology magnetotellurics geodynamics and mineral physics valid comparisons between different measures of anisotropy however require a solid understanding of the principles and limitations of the various techniques to this end we briefly summarize a new compilation of original articles with a common focus on anisotropy of continental lithosphere including theory laboratory experiments and observations that span a range of different geophysical techniques

magnetotelluric inversion for anisotropic conductivities in layered media abstract electrical anisotropy in the earth s crust and upper mantle has recently gained attention as a significant linking factor between electrical models and underlying structural and tectonic patterns this interest has also motivated new methodological studies into the modelling and inversion for electrically anisotropic structures we present an algorithm for the inversion of magnetotelluric data over layered anisotropic conductors which is a straightforward extension of the standard occam 1 d inversion to anisotropic models owing to the essential limitation of magnetotellurics to resolve the complete conductivity tensor we formulate the inversion for azimuthal anisotropy only we treat the non linear inverse problem as a multi criterion minimization of the structure complexity data misfit and anisotropy to constrain the structure complexity we employ the standard roughness penalty as well as non quadratic penalties of the total variation and gradient support type that produce more focused model sections and thus conform better to the idea about sharp non diffuse boundaries of anisotropic structures in the earth application of the anisotropy penalty is crucial for suppressing spurious anisotropy in the inverse models we use a 2 d extension of the heuristic l curve method to estimate the quasi optimal penalty weights with two non linear iteration solvers specifically the reweighted conjugate gradient method and the lagged diffusivity iteration we can arrive at the minimum of the target functional for one selected pair of regularization weights typically after a few tens of iteration steps to demonstrate the inverse solution we present two simple yet not completely trivial synthetic examples the first one based on data generated by a model with two anisotropic layers with discordant strikes and the other showing possible misinterpretations in case a 1 d inversion with anisotropy is formally applied to data produced by simple 2 d block structures field data from the variscan structures in southern portugal bear indications both geological and geophysical on possible crustal anisotropy due to shearing and graphitization we present results of a 1 d anisotropic imaging and a preliminary 2 d modelling for a short section of five sites over an old suture between the south portuguese zone and ossa morena zone aimed at explaining some essentially non 2 d effects in the data as e g systematic frequency variations of the regional strike or phases rolling out of their natural quadrants

inversion of controlled source tensor magnetotelluric data for a layered earth with azimuthal anisotropy inversion of controlled source tensor magnetotelluric data for a layered earth with azimuthal anisotropy

electromagnetic imaging of a transpressional tectonics in sw iberia forty one magnetotelluric soundings were carried out along a 200 km long profile approximately nne ssw across the three major geotectonic units in sw iberia a model obtained from two dimensional inversion of the magnetotelluric data set reveals high conductivity zones in the middle lower crust 10 30 km two of these zones correspond to the transition between the main geotectonic units one between the south portuguese zone and the ossa morena zone interpreted as having been caused by metasediments and the other between the ossa morena zone and the central iberia zone associated with a shear zone and metasediments another high conductivity anomaly related to black shales with major graphite impregnation was detected within the ossa morena zone the resistive features located preferentially in the upper crust 1 10 km coincide with gabbroic and granitic complexes

dimensionality imprint of electrical anisotropy in magnetotelluric responses abstract dimensionality analysis of magnetotelluric data is a common procedure for inferring the main properties of the geoelectric structures of the subsurface such as the strike direction or the presence of superficial distorting bodies and enables the most appropriate modeling approach 1d 2d or 3d to be determined most of the methods currently used assume that the electrical conductivity of individual parts of a structure is isotropic although some traces of anisotropy in data responses can be recognized in this paper we investigate the imprints of anisotropic media responses in dimensionality analysis using rotational invariants of the magnetotelluric tensor we show results for responses generated from 2d synthetic anisotropic models and for field data that have been interpreted as showing the effects of electrical anisotropy in parts of the subsurface structure as a result of this study we extend the wal dimensionality criteria to include extra conditions that allow anisotropic media to be distinguished from 2d isotropic ones the new conditions require the analysis of the strike directions obtained and take into account the overall behavior of different sites in a survey