the oceanic crust in 3d paleomagnetic reconstruction in the troodos ophiolite gabbro the troodos complex cyprus provides an opportunity to study the structural configuration along a fossil intersection of a spreading axis and a transform fault we complement studies at troodos that have reconstructed the brittle deformation of the upper crust by new paleomagnetic data from the gabbro suite the gabbro suite is exposed at the extinct spreading axis continuing the solea graben toward the intersection with the fossil arakapas oceanic transform this is a unique exposure of deep crustal rocks formed at both an inside corner and an outside corner of a ridge transform intersection remanence directions from gabbros 23 sites were used as indicators for rigid body rotation the spatial distribution of rotation axes allow recognition of three regions to which deformation is partitioned 1 a western region outside corner that experienced primarily tilt about horizontal axis 2 a central region with minor rotation and 3 an eastern area inside corner where vertical axis rotations are dominant the absence of significant rotation in the 6 km wide central domain together with its location between the inside and the outside corner uncover the root of a fossil axial volcanic zone a zone sufficiently hot so the upper crust can decouple from the substrate clockwise rotation in the gabbro increases from the axial zone eastward similar to that in the overlying dikes indicating coupling of the lower crust with the brittle upper oceanic crust the transition from the decoupled layers of sheeted dikes and gabbro in the axial zone to the dikes gabbro coupling in the inside corner is in keeping with deepening of the brittle ductile transition from the dike gabbro boundary into the lower crust away from the axial zone our conclusions are consistent with one of the previous reconstructions in which the solea spreading axis was orthogonal to the arakapas trunsform fault and with recent studies of the present day lower oceanic crust however the newly inferred surface trace of the solea spreading axis is further to the east probably reflecting the tilt of axial upper crust rotated blocks c 2006 elsevier b v all rights reserved

an efficient and comprehensive method for drainage network extraction from dem with billions of pixels using a size balanced binary search tree abstract with the increasing resolution of digital elevation models dems computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion pixel scales the efficiency of the most time consuming depression filling pretreatment has been improved by using the o n log n complexity least cost path search method but the complete extraction steps following this method have not been proposed and tested in this paper an improved o n log n algorithm was proposed by introducing a size balanced binary search tree bst to improve the efficiency of the depression filling pretreatment further the following extraction steps including the flow direction determination and the upslope area accumulation were also redesigned to benefit from this improvement therefore an efficient and comprehensive method was developed the method was tested to extract drainage networks of 31 river basins with areas greater than 500 000 km 2 from the 30 m resolution aster gdem and two sub basins with areas of approximately 1000 km 2 from the 1 m resolution airborne lidar dem complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in o n log n complexity the results indicate that the developed method can be used to extract entire drainage networks from dems with billions of pixels with high efficiency

calibration of magnetic granulometric trends in oceanic basalts abstract the validity of magnetic granulometric estimates relies heavily on the ability to distinguish ultrafine particles from coarser grains for example populations with dominantly superparamagnetic sp or multidomain md grains both are characterized by low remanence and coercivity and distinguishing these endmembers may provide valuable clues to the origin of magnetization in the intervening stable single domain sd size range the natural grain size variations associated with variable cooling rates in submarine lavas provide a rare opportunity for examining progressive changes in average magnetic grain size from sp sd mixtures in submarine basaltic glass to sd md mixtures in flow interiors based on microanalysis and rock magnetic measurements on pillow basalt samples dredged from the flanks of the mid atlantic ridge ages

crystallographic and shape orientations of magnetite micro inclusions in plagioclase plagioclase hosted oriented magnetite micro inclusions are a frequently observed phenomenon in magmatic and metamorphic rocks understanding the orientation relationships between these inclusions and the plagioclase host is highly relevant for interpreting paleomagnetic measurements the systematics of the shape and crystallographic orientation relationships between needle and lath shaped magnetite micro inclusions and their plagioclase host from oceanic gabbro were investigated using optical microscopy including universal stage measurements scanning electron microscopy and crystal orientation analysis by electron backscatter diffraction the magnetite inclusions show preferred shape orientations following six well defined directions and with specific crystallographic orientation relationships to the plagioclase host these relationships are rationalized based on angular and dimensional similarities between the crystal structures of magnetite and plagioclase which favor the parallel alignment of oxygen layers with similar lattice spacing in both phases the parallel alignment of oxygen layers in plagioclase and magnetite can be traced back to the oriented nucleation of magnetite which occurs by the accommodation of feo6 octahedra in six membered rings of sio4 and alo4 tetrahedra of the plagioclase structure the orientation systematics of the magnetite micro inclusions is related to four orientation variants for placing the feo6 octahedra into the plagioclase structure

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

transient fluvial incision as an indicator of active faulting and plio quaternary uplift of the moroccan high atlas one of the challenges facing earth scientists is to determine the extent to which geomorphic features can be used to extract tectonic signals from landscapes here we quantitatively analyse the long profiles of rivers that drain southwards across the south atlas fault saf a thrust fault that forms the southern margin of the high atlas mountains in morocco to derive new data on the late cenozoic activity of this fault system river long profiles were extracted for 32 major rivers flowing southwards into the ouarzazate basin of these eleven exhibit concave up river profiles with a mean concavity of 0 64 and normalized steepness indices in the range 47 5 219 0 m 0 9 by contrast 21 rivers exhibit at least one knickpoint upstream of the thrust front knickpoint height varies from 100 1300 m with calculated incision at the range bounding fault ranging from 80 900 m despite the drainage areas upstream of the knickpoint ranging over several orders of magnitude in map view knickpoint locations generally plot along sub parallel lines and there are no obvious relationships with lithological units for knickpoints exhibiting slope break morphology channel reaches below slope break knickpoints have higher mean concavities 0 76 than above the knickpoint indicative this observation combined with a lithological or river capture origin for the knickpoints having been ruled out suggests that an increase in uplift rate along a planar fault zone during the plio quaternary caused the initiation of the transient response i e knickpoint formation to a change in base level observed in the river profiles this uplift event can be correlated to the convective removal of the lithospheric root to the atlas mountains resulting in the anomalously high topography at the present day

direct evidence for dynamic magma supply fossilized in the lower oceanic crust of the troodos ophiolite 1 temporal and spatial variabilities of mantle upwelling and melt supply in mid ocean ridges mors have long been documented such variabilities span a range of scales and have a profound effect on the structure as well as the composition of the oceanic crust previous seismic and gravity studies have suggested that the lower oceanic crust plays a major role in accommodating these changes in melt supply here we report the first direct evidence for a sharp transition from coherent sub horizontal to near vertical magma flows frozen in the lower oceanic crust of the troodos ophiolite at the segment edge near a fossil ridge transform intersection we constrain the preferred petrofabric lineation directions at 13 gabbroic sites using anisotropy of magnetic susceptibility ams verified by electron backscatter diffraction pre emplacement accretion related rotations were corrected using magnetic remanence directions we identify two provinces of nearly uniform susceptibility directions principal axes and attribute them to two magmatic episodes a more focused mantle upwelling and melting episode near the segment midpoint may have resulted in lower crustal lateral magma flows along the fossil segment edge whereas uniform mantle upwelling and melt supply along the entire axis may have resulted in vertical magma flows at the segment edge overall our data verify the vital role of the lower oceanic crust in accommodating changes in mantle upwelling and melt supply beneath mors

wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation we obtain the wave velocities and quality factors of clay bearing sandstones as a function of pore pressure frequency and partial saturation the model is based on a biot type three phase theory that considers the coexistence of two solids sand grains and clay particles and a fluid mixture additional attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas fluid mixing law that satisfies the wood and voigt averages at low and high frequencies respectively pressure effects are accounted for by using an effective stress law by fitting a permeability model of the kozeny carman type to core data the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies including the effects of partial saturation testing of the model with laboratory data shows good agreement between predictions and measurements

kinematic dispersion in stream networks 2 scale issues and self similar network organization 1 when the flow parameters such as celerity and hydrodynamic dispersion coefficient are allowed to vary spatially within a basin three mechanisms namely geomorphologic kinematic and hydrodynamic dispersion contribute to the variance of the instantaneous response function the relative contributions of the three dispersion mechanisms as a function of scale or strahler order of the basin are studied this analysis is performed for two study basins the vermilion and the mackinaw river basins in central illinois log linear trends for all the dispersion coefficients as a function of scale are observed these trends can be cast in the form of horton law type of relations the asymptotic behavior of the dispersion coefficients of basins with self similar network structure is consistent with the observations

on the propagation of a disturbance in a smoothly varying heterogeneous porous medium saturated with three fluid phases abstractfrom the equations governing the deformation of a porous medium containing three fluid phases i derive expressions for the phase velocity of the various modes of displacement these expressions are valid for a medium with smoothly varying heterogeneity there is a single mode of transverse displacement similar in nature to an elastic shear wave the four phase velocities of the longitudinal modes of displacement are derived from the solutions of a quartic equation the coefficients of the polynomial equation are written as linear sums of the determinants of 4 4 matrices the matrices contain various combinations of the parameters from the governing equations the three phase expressions are compared to two phase estimates for the case in which one of the fluid saturations vanishes also in a numerical illustration velocity variations of around 10 are associated with the cyclic injection of carbon dioxide and water into an oil saturated reservoir

oriented inclusions of magnetite in clinopyroxene source of stable remanent magnetization in gabbros of the messum complex namibia 1 crystallographically oriented and highly elongate magnetite inclusions in clinopyroxene are the dominant source of highly stable remanent magnetization in gabbros of the early cretaceous messum complex namibia rock magnetic properties determined for individual pyroxene crystals indicate a high proportion of single domain magnetite consistent with the observed sizes and shape anisotropy of the magnetite inclusions as in previous studies of similar inclusions these are inferred to have formed by exsolution two arrays of inclusions are regularly present in the messum clinopyroxenes inclined at about 74 consistent with formation at about 800 c deduced from optimization of phase boundary orientations virtual geomagnetic poles from these rocks are consistent with reference data confirming that the magnetization is of thermoremanent origin bipolar magnetizations are recorded at one site as well in individual clinopyroxene crystals suggesting that remanence acquisition upon initial cooling of the gabbro spanned a geomagnetic polarity reversal

tectonic forcing of longitudinal valleys in the himalaya morphological analysis of the ladakh batholith north india abstract longitudinal valleys form first order topographic features in many mountain belts they are commonly located along faults that separate tectonic zones with varying uplift histories the indus valley of ladakh northern india runs northwestwards following the boundary between the relatively undeformed ladakh batholith to the north east and the folded and thrusted zanskar mountains to the south west in this region the shyok valley on the northern side of the batholith approximately parallels the course of the indus this study investigates geomorphic variations in transverse catchments that drain the ladakh batholith into the indus and shyok rivers the batholith has been divided into three zones based on varying structural characteristics of its northeastern and southwestern boundaries morphometric analysis of 62 catchments that drain into the indus and shyok valleys was carried out using three digital datasets and supported by field observations morphometric asymmetry is evident in the central zone where the shyok valley is considered tectonically inactive but the indus valley is bound by the northeastwardly thrusting indus molasse and the batholith in this zone the catchments that drain into the indus valley are more numerous shorter thinner and have lower hypsometric integrals than those that drain into the shyok by linking these observations with the regional geology and thermochronological data it is proposed that high sediment discharge from the deformed indus molasse indus valley has progressively raised base levels in the indus valley and resulted in sediment blanketing of the opposing tectonically quiescent catchments that drain southwestwards off the batholith the indus molasse thrust front has propagated at least 36 km towards the ladakh batholith over the last 20 ma hence it is proposed that this long term asymmetric structural deformation and exhumation has forced the indus longitudinal valley laterally into the ladakh batholith resulting in the morphometric asymmetry of its transverse catchments

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

lidar based quantification of lava flow susceptibility in the city of auckland new zealand abstract lava flows represent one of the most significant volcanic hazards from basaltic monogenetic volcanoes such as spatter cones scoria cones maars and tuff rings they are common features emanating from parasitic vents on the flanks of polygenetic volcanoes and in dominantly flat lying intraplate volcanic fields the auckland volcanic field avf is a volcanic field that has been active for the last ca 250 ka hosting at least 50 monogenetic volcanoes morphometric parameters of lava flows such as volume length thickness and area were used to quantify the potential lava flow inundation susceptibility to new zealand s most densely populated area the city of auckland based on an airborne light detection and ranging lidar digital surface model dsm the morphometric parameters of fifteen studied flows included average length of 2 5 km range 0 7 6 5 km overall average thickness of 14 8 m range 3 4 43 8 m average of maximum thicknesses of 48 2 m range 18 3 180 5 m average area occupied of 5 1 km 2 range 0 4 25 1 km 2 and average volume of 0 12 km 3 range 0 005 1 km 3 based on these parameters and a lidar derived dsm the present topography was classified into sea topographic depressions low lying areas prone to inundation by an average lava flow buffer zones prone to inundation only by extremely thick lava flows and peaks or ridges which are unlikely to be overtopped in monogenetic fields each new vent occurs in a new location creating uncertainty around the spatial location of the volcanic hazard thus this research provides a general vent location independent approach to describe the lava flow susceptibility for a potentially active monogenetic volcanic field what this analysis reveals is that the city of auckland can be divided into two distinct areas with strongly different susceptibility to lava flow inundation the southern part of the city is predominantly flat without hindrance to lava flow whereas the hilly northern and central part has many ridges that can limit or channelise lavas these contrasting properties must be accounted for in scenario based or probabilistic hazard and risk models developed for the avf

identification of peneplains by multi parameter assessment of digital elevation models the concept of peneplains has existed since the end of the nineteenth century typical peneplains are elevated geomorphological features with a low relief surface on top they may be tilted due to tectonic activity or intersected by evolving erosion until now neither a standardized definition for peneplains nor an established procedure to identify and quantify well preserved peneplains as prominent landforms existed at present the global availability of homogeneous digital elevation models dems provides an accurate characterization of the morphology of the earth surface in this study a new numerical dem based fuzzy logic approach is presented for the delineation of peneplains solely from a morphological perspective the approach is based on a morphometric analysis of the 90 arcsec shuttle radar topography mission srtm dem four critical parameters are employed which are implemented within a geographic information system gis the parameters for the correct and unambiguous description of a flat top mountain are i slope ii curvature iii terrain ruggedness index and iv relative height the approach was developed using a test area in the central tibetan plateau which is characterized by representative and well preserved peneplains and for which additional field data were collected in order to verify the method peneplains were delineated in different regions with various geological settings for which potential peneplains were already described in the literature the results from the appalachian mountains andes massif central and new zealand confirm the robustness of the proposed approach copyright 2015 john wiley sons ltd

an algorithm to extract more accurate stream longitudinal profiles from unfilled dems abstract morphometric features observed from a stream longitudinal profile slp reflect channel responses to lithological variation and changes in uplift or climate therefore they constitute essential indicators in the studies for the dynamics between tectonics climate and surface processes the widespread availability of digital elevation models dems and their processing enable semi automatic extraction of slps as well as additional stream profile parameters thus reducing the time spent for extracting them and simultaneously allowing regional scale studies of slps however careful consideration is required to extract slps directly from a dem because the dem must be altered by depression filling process to ensure the continuity of flows across it such alteration inevitably introduces distortions to the slp such as stair steps bias of elevation values and inaccurate stream paths this paper proposes a new algorithm called maximum depth tracing algorithm mdta to extract more accurate slps using depression unfilled dems the mdta supposes that depressions in dems are not necessarily artifacts to be removed and that elevation values within them are useful to represent more accurately the real landscape to ensure the continuity of flows even across the unfilled dem the mdta first determines the outlet of each depression and then reverses flow directions of the cells on the line of maximum depth within each depression beginning from the outlet and toward the sink it also calculates flow accumulation without disruption across the unfilled dem comparative analysis with the profiles extracted by the hydrologic functions implemented in the arcgis was performed to illustrate the benefits from the mdta it shows that the mdta provides more accurate stream paths on depression areas and consequently reduces distortions of the slps derived from the paths such as exaggerated elevation values and negatively biased slopes that are commonly observed in the slps built using the arcgis the algorithm proposed here therefore could aid all the studies requiring more reliable stream paths and slps from dems

determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network abstract distributed hydrological models require a detailed definition of a watershed s internal drainage structure the conventional approach to obtain this drainage structure is to use an eight flow direction matrix d8 which is derived from a raster digital elevation model dem however this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed this is largely due to limitations of the d8 approach and the lack of information over flat areas and pits the d8 approach alone is also unable to differentiate lakes from plain areas to avoid these problems a new approach using a digital river and lake network drln as input in addition to the dem has been developed this new approach allows for an accurate fit between the drln and the modelled drainage structure which is represented by a flow direction matrix and a modelled watercourse network more importantly the identification of lakes within the modelled network is now possible the proposed approach which is largely rooted in the d8 approach uses the drln to correct modelled flow directions and network calculations for dem cells overlapped by the drln flow directions are determined using drln connections only the flow directions of the other dem cells are evaluated with the d8 approach which uses a dem that has been modified as a function of distance to the drln the proposed approach has been tested on the chaudiere river watershed in southern quebec canada the modelled watershed drainage structure showed a high level of coherence with the drln a comparison between the results obtained with the d8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure the proposed approach will benefit hydrological models which require data such as a flow direction matrix a river and lake network and sub watersheds for drainage structure information

petrology and rock magnetism of the gabbro of troodos ophiolite abstract in order to determine the nature of remanence carriers of the layered gabbro of the troodos ophiolite cyprus we report optical and electron microscopic observations together with rock magnetic and paleomagnetic experiments above all the study aims to understand and clarify the time of magnetic acquisition relative to the brittle deformation of the oceanic crust manifested by the ridge transform intersection solea graben and the arakapas transform petrographic examination of pyroxene grains revealed isolated magnetite inclusions ranging in size from single domain sd to multi domain md and in addition md pyrrhotite inclusions residing in veins and cracks thermal demagnetization and thermomagnetic procedures indicate two components low and high temperature we argue that the low temperature component the sd magnetite inclusions exsolved in pyroxene are the dominant carriers of magnetic remanence in troodos gabbro the initial formation of these inclusions occurred via exsolution reaction at temperatures between 520 and 850 c above the curie temperature of pure magnetite during the solidification of the magma therefore acquisition of remanent magnetization of the troodos gabbro took place during the earliest stages of crustal accretion before any brittle deformation associated with the spreading ridge and the transform fault occurred

fossil ridge transform intersection in the troodos ophiolite new perspectives from rock magnetism in the gabbro suite and fracture mechanics analysis 1 the missing link in the comprehensive view of the ridge transform intersection rti frozen in troodos is that portion of the extinct spreading axis between the solea graben and the fossil arakapas transform directional indicators of magma flow verified by paleomagnetic tests along with tectonic indicators permit tracing the extinct spreading axis through the gabbro suite at the continuation of the solea graben axis these indicators of axial deformation include measurements of the anisotropy of magnetic susceptibility ams and petrofabric determinations in the gabbro dikes major normal faults and fabric of mantle rocks the inferred axis is curved as it approaches the fossil transform the sense of curvature is in agreement with dextral slip along the fossil transform assuming curvature has resulted from transform induced shear stresses fracture mechanics analysis predicts the control on the axis shape by the ratio between driving stresses of spreading sh and resistance for sliding along the fossil transform t accordingly the curved shape of the spreading axis frozen in troodos indicates t sh 0 1 0 2 whereas for straight axis and orthogonal rti the analysis predicts t sh 0 01 these results suggest that the fossil curvature reflects a strong transform relative to curvature free rtis a strong arakapas transform is also in agreement with previous evidence of diffused deformation north of the transform such as block rotation and sigmoidal structure of dikes and faults

application of the promethee technique to determine depression outlet location and flow direction in dem with the fast growing progress of computer technologies spatial information on watersheds such as flow direction watershed boundaries and the drainage network can be automatically calculated or extracted from a digital elevation model dem the stubborn problem that depressions exist in dems has been frequently encountered while extracting the spatial information of terrain several filling up methods have been proposed for solving depressions however their suitability for large scale flat areas is inadequate this study proposes a depression watershed method coupled with the preference ranking organization method for enrichment evaluations promethees theory to determine the optimal outlet and calculate the flow direction in depressions three processing procedures are used to derive the depressionless flow direction 1 calculating the incipient flow direction 2 establishing the depression watershed by tracing the upstream drainage area and determining the depression outlet using promethee theory 3 calculating the depressionless flow direction the developed method was used to delineate the shihmen reservoir watershed located in northern taiwan the results show that the depression watershed method can effectively solve the shortcomings such as depression outlet differentiating and looped flow direction between depressions the suitability of the proposed approach was verified

characterization of fluvial activity in parana valles using different age dating techniques martian valley networks provide the best evidence that the climate on mars was different in the past although these features are located primarily in heavily cratered terrain of noachian age 3 7 ga the ages of the features and the time when they were active is not well understood from superposed craters several recent global studies determined that most valley networks formed during the late noachian to early hesperian however there were some disparities between the techniques in this study our principal objective was to test the reliability of the different age dating techniques to better understand their accuracy and limitations we applied these techniques to parana valles using a variety of high resolution images taken from different instruments that allow us to identify smaller craters d 125 m while providing sufficient coverage to support a statistically reliable sampling of crater populations which is necessary to reduce the uncertainties in age determination our results indicate that parana valles formed during the early hesperian period but that the crater density d 353 m is heterogeneous inside the parana valles basin the crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub basins the terrain near the source area is late noachian to early hesperian in age while terrains closer to the outlet are early to late hesperian in age crater densities d 125 m inside the valley are also heterogeneous and record several resurfacing events on the valley floor where the width of the valley network narrows to 2 km we found evidence of an amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences our results validate the reliability of several proposed age dating techniques but we also determined the accuracy and applicability of these techniques our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

emplacement and deformation of mesozoic gabbros of the high atlas morocco paleomagnetism and magnetic fabrics a paleomagnetic and magnetic fabric study is performed in upper jurassic gabbros of the central high atlas morocco these gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults these structures were reactivated as anticlines during the cenozoic compressional inversion gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization carried by magnetite which has been interpreted as a primary component this component shows an important dispersion due to postemplacement tectonic movements the absence of paleoposition markers in these igneous rocks precludes direct restorations a novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks paleomagnetic vectors are distributed along small circles with horizontal axes indicating horizontal axis rotations of the gabbro bodies these rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases due to the uncertainties inherent to this work the igneous bodies recording strong rotations interpretations must be qualitative the magnetic fabric is carried by ferromagnetic s s minerals mimicking the magmatic fabric anisotropy of magnetic susceptibility ams axes using the rotation routine inferred from paleomagnetic results result in more tightly clustered magnetic lineations which also become horizontal and are considered in terms of magma flow trend during its emplacement nw se parallel to the general extensional direction in the western sector and ne sw parallel to the main faults in the easternmost structures

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

exsolved magnetite inclusions in silicates features determining their remanence behavior submicroscopic needle shaped titanomagnetite inclusions exsolved in silicate minerals commonly occur in mafic intrusive rocks and are protected from alteration by their silicate hosts making them excellent candidates for paleomagnetic studies a suite of samples containing clinopyroxene and plagioclase hosted magnetite inclusions from five geologically diverse sites was examined using magnetic force microscopy to image the inclusions magnetic domain state alternating field demagnetization experiments indicate that some inclusions are more stable recorders than others the two factors controlling the remanence behavior of the inclusions are internal microstructures and inclusion dimensions magnetite ulvospinel unmixing within an inclusion subdivides the original titanomagnetite solid solution into a boxwork structure composed of 103 105 magnetite prisms separated by thin ulvospinel lamellae the conversion of multidomain sized needles into assemblages of interacting single domains increases the coercivity and hence relaxation time of the inclusions and results in a thermochemical magnetic remanence in samples without this exsolution microstructure the inclusions diameters determine coercivity and their magnetization is thermoremanent both styles of high coercivity inclusions successfully record paleomagnetic directions in mesozoic rocks and their ubiquity within silicate minerals clinopyroxene and plagioclase of mafic intrusive rocks indicates their value as chemically and magnetically stable tools for elucidating the ancient magnetic field marine magnetic anomalies and crustal kinematics

height above the nearest drainage a hydrologically relevant new terrain model summary this paper introduces a new terrain model named hand and reports on the calibration and validation of landscape classes representing soil environments in amazonia which were derived using it the hand model normalizes topography according to the local relative heights found along the drainage network and in this way presents the topology of the relative soil gravitational potentials or local draining potentials the hand model has been demonstrated to show a high correlation with the depth of the water table providing an accurate spatial representation of soil water environments normalized draining potentials can be classified according to the relative vertical flowpath distances to the nearest drainages defining classes of soil water environments these classes have been shown to be comparable and have verifiable and reproducible hydrological significance across the studied catchment and for surrounding ungauged catchments the robust validation of this model over an area of 18 000 km2 in the lower rio negro catchment has demonstrated its capacity to map expansive environments using only remotely acquired topography data as inputs the classified hand model has also preliminarily demonstrated robustness when applied to ungauged catchments elsewhere with contrasting geologies geomorphologies and soil types the hand model and the derived soil water maps can help to advance physically based hydrological models and be applied to a host of disciplines that focus on soil moisture and ground water dynamics as an original assessment of soil water in the landscape the hand model explores the synergy between digital topography data and terrain modeling presenting an opportunity for solving many difficult problems in hydrology

magnetite rods in plagioclase as the primary carrier of stable nrm in ocean floor gabbros abstract the ubiquitous occurrence of magnetite rods in plagioclase may account for the stable intense magnetization of ocean floor gabbros these single domain grains are formed by the subsolidus exsolution of fe 2 and fe 3 incorporated into the plagioclase at higher temperatures we expect that this process will be particularly important in the upper portions of the oceanic gabbro unit because of the relative paucity of femic minerals at these levels the geometry of accretion prohibits a constructive contribution to marine magnetic anomalies by the lower olivine rich gabbros as a result of the presence of these rods ocean floor gabbros may constitute an important source for marine magnetic anomalies

improving hydrological information acquisition from dem processing in floodplains extraction of hydrological information from digital elevation models dems is a required step when conducting any spatially distributed hydrological modelling in particular automated methods are proposed to extract the drainage structure from the dem however a realistic river network is not always derived from conventional dem processing methods indeed inaccuracy occurs in flat areas corresponding to floodplains in these areas additional sources of information are required to extract the correct drainage direction from the dem in this study it is demonstrated that traditional approaches of dem preprocessing such as the commonly known stream burning fail to provide correct maps of drainage directions and catchment areas when the extension of flat areas is large a new method is proposed to take advantage of available imagery data this method is based on a double dem burning process dem is first burned in the main rivers using the channel network and then in the floodplain using the spatial distribution of floodplains provided by classified satellite images in this sense the method has been referred to as the floodplain burning approach or simply fb approach spatial distribution of floodplains is derived from a multitemporal sar image classification a system of equations is used to vary the elevation offset required to be burnt in each cell representing the floodplain according to the minimal distance from the channel network which is calculated by a distance transformation the fb approach was applied to a sub basin located within the larger amazon river basin the region is characterized by large floodplain extensions basin delineation maps derived from the new method were compared with those obtained from the traditional stream burning method and highlighted more realistic results copyright 2008 john wiley sons ltd

seismic low frequency effects in monitoring fluid saturated reservoirs there is a complex relationship between seismic attributes including the frequency dependence of reflections and fluid saturation in a reservoir observations in both laboratory and field data indicate that reflections from a fluid saturated layer have an increased amplitude and delayed traveltime at low frequencies when compared with reflections from a gas saturated layer comparison of laboratory modeling results with a diffusive viscous theory model show that low 5 values of the quality factor q can explain the observations of frequency dependence at the field scale conventional processing of time lapse vsp data found minimal changes in seismic response of a gas storage reservoir when the reservoir fluid changed from gas to water lowfrequency analysis found significant seismic reflectionattribute variation in the range of 15 50 hz the field observations agree with effects seen in laboratory data and predicted by the diffusive viscous theory one explanation is that very low values of q are the result of internal diffusive losses caused by fluid flow this explanation needs further theoretical investigation the frequencydependent amplitude and phase reflection properties presented in this paper can be used for detecting and monitoring fluid saturated layers

river reach length and slope estimates for large scale hydrological models based on a relatively high resolution digital elevation model application of regular grid based distributed hydrological models requires information related to river drainage networks such as flow directions flow accumulated areas basin delineation and length and slope of river reaches for every grid cell most of those data may be extracted automatically from digital elevation models dem however when dealing with large basins available dems are usually in higher spatial resolution than the model grid upscaling procedures have therefore been developed to extract low resolution flow directions and flow accumulated areas from relatively high resolution dems this paper presents a new methodology which extends the upscaling method to automatically extract length and slope of river reaches for large scale grid based hydrological models the proposed method is new and is believed to be the first attempt to produce such information automatically from dems the methodology was applied to parts of the uruguay river basin in south america using the globally wide available dem produced by the shuttle radar topography mission srtm 90m quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks which were assumed to be correct it was shown that the proposed methodology adequately assigns river lengths to every model cell while ensuring that the whole length of the streams is considered the effect of dem resolution on calculated river length errors was analyzed by resampling the srtm dem to three different cell sizes with best results obtained for the higher resolution dem the modification of the original high resolution dem through the process known as stream burning was also tested largely improving the quality of the results finally optimal distance transforms were used for the calculation of distance increments instead of euclidean local distances giving results that were generally better the quality of results for calculated slope values could not be assessed because no reliable data were available for comparison

on the propagation of a disturbance in a heterogeneous deformable porous medium saturated with two fluid phases the coupled modeling of the flow of two immiscible fluid phases in a heterogeneous elastic porous material is formulated in a manner analogous to that for a single fluid phase an asymptotic technique valid when the heterogeneity is smoothly varying is used to derive equations for the phase velocities of the various modes of propagation a cubic equation is associated with the phase velocities of the longitudinal modes the coefficients of the cubic equation are expressed in terms of sums of the determinants of 3 3 matrices whose elements are the parameters found in the governing equations in addition to the three longitudinal modes there is a transverse mode of propagation a generalization of the elastic shear wave estimates of the phase velocities for a homogeneous medium based upon the formulas in this paper agree with previous studies furthermore predictions of longitudinal and transverse phase velocities made for the massilon sandstone containing varying amounts of air and water are compatible with laboratory observations

a channelization model of landscape evolution the geomorphic evolution of many landscapes is fundamentally deter mined by the evolution of the river channels and their interactions with hillslopes consequently models of landscape evolution ought to track the evolution of the channel geometry so as to quantify the rate of erosion of channel bottoms and to follow the changes in hillslope channel coupling over time unfortunately the spatial resolution required to describe channel morphology adequately is computationally impractical it is also beyond the resolution of most digital elevation data what is required is a parameterization scheme for approximating fine scale channel morphol ogy at a coarse pixel scale such a parameterization is already implicitly employed in most models by assuming channel equilibrium which ties the width and depth of a model channel to the square root of discharge through a pixel channel fluxes are thereby predictable and a closed form of the governing equations is attained in reality mountain river channels do not take a simple equilibrium form and show great spatial variability and evident disequilibrium geometry since the time scales of changes in channel geometry bedrock channel erosion and hillslope response are all closely related it is reasonable to infer that the spatio temporal development of the landscape is determined by their interaction and that channel disequilibrium is a fundamental factor in the dynamics of landscape evolution if this is the case we need an alternative sub grid scale parameterization that aggregates channel properties such as surface morphology roughness cross sectional geometry so that the time depen dent behavior of these properties can be estimated at the coarse pixel scale we introduce such a parameterization measure which we term channelization after extensive investigation of the pixel resolution dependence of topographic relief we focus in particular on the effect of coarse graining on digital elevation data for derived measures such as channel slope and upstream area and demonstrate that we can approximately correct for this effect we show that a very simple geomorphic model can be constructed around the channelization parameter and the resolution invariant topographic measures this model demonstrates that channel disequilibrium may play a significant role in mountain landscape dynamics it also shows how geomorphic models in general could be modified to incorporate such sub pixel scale complexities and to better model these dynamics

pre processing algorithms and landslide modelling on remotely sensed dems abstract terrain analysis applications using remotely sensed digital elevation models dems nowadays easily available permit to quantify several river basin morphologic and hydrologic properties e g slope aspect curvature flow path lengths and indirect hydrogeomorphic indices e g specific upslope area topographic wetness index able to characterize the physical processes governing the landscape evolution e g surface saturation runoff erosion deposition such dems often contain artifacts and the automated hydrogeomorphic characterization of the watershed is influenced by terrain analysis procedures consisting in artificial depression pit and flat area treatment approaches combined with flow direction methods in shallow landslide deterministic models when applied using topographic dataset at medium scale e g 30 m of resolution the choice of the most suitable dem processing procedure is not trivial and can influence model results this also affects the selection of most critical areas for further finer resolution studies or for the implementation of countermeasures aiming to landslide risk mitigation in this paper such issue is investigated using as topographic input the aster dems and comparing two different combinations of dem correction and flow routing schemes the study areas comprise ten catchments in italy for which hydrogeomorphic processes are significant aims of this paper are 1 to introduce a parameter estimation procedure for the physically based dem correction method pem4pit physical erosion model for pit removal 2 to investigate the influence of different terrain analysis procedures on results of the slope stability model shalstab shallow landsliding stability using remotely sensed aster dems 3 trying to assess which of terrain analysis methods is more appropriate for describing terrain instability

pressure and fluid saturation prediction in a multicomponent reservoir using combined seismic and electromagnetic imaging this paper presents a method for combining seismic and electromagnetic em measurements to predict changes in water saturation pressure and co2 gas oil ratio in a reservoir undergoing co2 flood crosswell seismic and em data sets taken before and during co2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity shear velocity and electrical conductivity during a co2 injection pilot study a rock properties model is developed using measured log porosity fluid saturations pressure temperature bulk density sonic velocity and electrical conductivity the parameters of the rock properties model are found by an l1 norm simplex minimization of predicted and observed differences in compressional velocity and density a separate minimization using archie s law provides parameters for modeling the relations between water saturation porosity and electrical conductivity the rock properties model is used to generate relationships between changes in

impact of fluid saturation on the reflection coefficient of a poroelastic layer the impact of changes in saturation on the frequencydependent reflection coefficient of a partially saturated layer was studied seismic attenuation and velocity dispersion in partially saturated i e patchy saturated poroelastic media were accounted for by using the analytical solution of the 1d white s model for wave induced fluid flow white s solution was applied in combination with an analytical solution for the normal incidence reflection coefficient of an attenuating layer embedded in an elastic or attenuating background medium to investigate the effects of attenuation velocity dispersion and tuning on the reflection coefficient approximations for the frequency dependent quality factor its minimum value and the frequency at which the minimum value of the quality factor occurs were derived the approximations are valid for any two alternating sets of petrophysical parameters an approximation for the normal incidence reflection coefficient of an attenuating thin compared to the wavelength layer was also derived this approximation gives insight into the influence of contrasts in acoustic impedance and or attenuation on the reflectivity of a thin layer laboratory data for reflections from a water saturated sand layer and from a dry sand layer were further fit with petrophysical parameters for unconsolidated sand partially saturated with water and air the results showed that wave induced fluid flow can explain low frequency reflection anomalies which are related to fluid saturation and can be observed in seismic field data the results further indicate that reflection coefficients of partially saturated layers e g hydrocarbon reservoirs can vary significantly with frequency especially at low seismic frequencies where partial saturation may often cause high attenuation

downstream trends in discharge slope and stream power in a lower coastal plain river conceptual models of river estuary interaction are typically based on a notion of systematic downstream change in the intensity of fluvial processes low slopes backwater effects and effects of antecedent topography and landforms may complicate downstream tends in water and sediment flux in coastal plain rivers an analysis of the lower trinity river texas shows no consistent downstream pattern of increases or decreases in the discharge stream power or water surface slope flows may decrease downstream due to coastal backwater effects in the lowermost reaches and due to diversion of flow into valley bottom depressions during high flows in both the fluvial and fluvial estuarine transition reaches in general however stream power and slope decrease in the lower reaches consistent with earlier findings of limited fluvial sediment delivery to the coastal zone some tributaries may become distributaries at high but sub bankfull flows as backwater effects reverse flows into depressions associated with paleomeanders the paleomeanders and possibly the locations of these reversible channels are related to antecedent topography associated with aggradation degradation cycles over the past 100 ka low gradient coastal plain rivers may not function as simple conduits from land to sea further the transition from fluvial to coastal dominance may be variable along the river with the variability controlled not just by the relative magnitude of river and tidal or backwater forcing but also by valley topography controlled in part by antecedent landforms

the squirt flow mechanism macroscopic description we introduce a poroelasticity model that incorporates the two most important mechanisms of solid fluid interaction in rocks the biot mechanism and the squirt flow mechanism this combined biot squirt bisq model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase porosity permeability saturation fluid viscosity and compressibility and the characteristic squirt flow length squirt flow length is a fundamental rock property that does not depend on frequency fluid viscosity or compressibility and is determined experimentally we find that the viscoelastic response of many sandstones is dominated by the squirt flow component of the bisq mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega r 2 kappa where omega is angular frequency r is the characteristic squirt flow length and kappa is hydraulic diffusivity the biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation and the viscoelastic behavior of many sandstones

watershed delineation using hydrographic features and a dem in plain river network region watershed delineation is a required step when conducting any spatially distributed hydrological modelling automated approaches are often proposed to delineate a watershed based on a river network extracted from the digital elevation model dem using the deterministic eight neighbour d8 method however a realistic river network cannot be derived from conventional dem processing methods for a large flat area with a complex network of rivers lakes reservoirs and polders referred to as a plain river network region prnr in this study a new approach which uses both hydrographic features and dem has been developed to address the problems of watershed delineation in prnr it extracts the river nodes and determines the flow directions of the river network based on a vector based hydrographic feature data model the river network lakes reservoirs and polders are then used to modify the flow directions of grid cells determined by d8 approach the watershed is eventually delineated into four types of catchments including lakes reservoirs polders and overland catchments based on the flow direction matrix and the location of river nodes multiple flow directions of grid cells are represented using a multi direction encoding method and multiple outflows of catchments are also reflected in the topology of catchments the proposed approach is applied to the western taihu watershed in china comparisons between the results obtained from the d8 approach the stream burning approach and those from the proposed approach clearly demonstrate an improvement of the new approach over the conventional approaches this approach will benefit the development of distributed hydrological models in prnr for the consideration of different types and multiple inlets and outlets of catchments copyright 2015 john wiley sons ltd

colluvial sediment dynamics in mountain drainage basins abstract colluvial sediment dynamics are examined using a 70 year landslide inventory in formerly glaciated mountain drainage basins of coastal british columbia canada landslide sediment transfer is documented by identifying landslide types and by characterizing preferential sites of landslide initiation delivery and storage across spatial scales data analysis reveals that open slope landslides delivering material to seasonal or perennial channels and fluvial terraces are the dominant mechanisms of sediment transfer this finding suggests high instability of the low order channel network and its ongoing re organization degradation after generalized sediment recharge occurred in the last glacial maximum in the study period landslide activity across the landscape has generated net degradation on planar slopes and first order colluvial channels whereas unchannelled valleys higher order colluvial channels and alluvial channels have accumulated material the scaling relation of the landslide sediment yield appears to be controlled by the spatial arrangement of the relict glacial macro forms landslide yield is highest in unchannelled topography decreases at the scale of channel initiation ad 0 002 km2 and remains constant for drainage areas where length scales of cirque valley walls and hanging valley floors overlap 0 002

single domain and superparamagnetic titanomagnetite with variable ti content in young ocean floor basalts no evidence for rapid alteration high resolution electron microscope studies have been carried out on zero age new flow basalts from the juan de fuca ridge and on young 20 ka basalts from the axis of the east pacific rise at 12 n such data lead to characterization of the magnetic minerals especially those of smaller grain size which have been hypothesized by kent and gee to have undergone grain size dependent alteration in addition to larger titanomagnetite grains abundant submicrometer titanomagnetite has been observed in globules within a glassy matrix these grains likely to be single domain sd or superparamagnetic are associated with apatite uncommon pyrrhotite and residual glass the submicrometer titanomagnetite grains have a wide compositional range 0 x 0 8 where x is the fraction of ulvospinel component whereas the larger multi domain md sized titanomagnetite grains have a narrow composition range of approximately x 0 6 this variability in ti content provides a ready explanation for the thermal rock magnetic properties observed by kent and gee and eliminates the need to invoke extremely rapid 20 ka alteration of these young basalts

effects of internal mineral structures on the magnetic remanence of silicate hosted titanomagnetite inclusions an electron holography study 1 titanomagnetite inclusions in pyroxene and plagioclase are carriers of stable magnetic remanence in some slowly cooled rocks such as gabbros anorthosites granulites and diorites needle shaped inclusions with average dimensions of 1 1 25 m form epitaxially by exsolution from their host silicate close examination of clinopyroxene hosted inclusions reveals an internal microstructure which consists of magnetite fe3o4 prisms and ulvospinel fe2tio4 lamellae that formed as a result of phase unmixing during initial cooling this internal structure exerts a profound influence on the magnetic remanence properties of each inclusion primarily by transforming it from a multidomain grain into an assemblage of magnetostatically interacting single domain prisms here we use off axis electron holography to image the magnetization states of individual prisms and the magnetostatic interactions between them we show that the inclusions exhibit both single domain and collective magnetic states that depend primarily on the shape anisotropies of individual magnetite prisms magnetostatic interactions between closely spaced prism stacks and the shape anisotropy of the needle itself prisms that are separated by thick ulvospinel lamellae show uniformly magnetized and or vortex states in contrast closely spaced magnetite prisms behave as multipart vortices or as long composite columns whose strong net magnetization may not be related directly to the orientation and shape of either the needle or the constituent prisms the overall remanence direction recorded by clinopyroxene crystals containing finely exsolved inclusions is a reflection of both the inclusions elongation directions and the prism arrangements within them

long term landscape trajectory can we make predictions about landscape form and function for post mining landforms a significant issue for the application of numerical landscape evolution models lems is their calibration parameterisation and validation lems are now at the stage of development where if calibrated they can provide meaningful and useful results however before use each lem requires a set of data and parameter values for it to run reliably and most importantly produce results with some measure of precision and accuracy this calibration validation process is largely carried out using parameter values determined from present day or recent surface conditions which are themselves product of much longer term geology soil climate vegetation interactions here we examine the reliability of an lem to predict catchment form over geological time 500 000 years for a potential rehabilitated mine landform using defensible parameters derived from field plots the findings demonstrate that there is no equifinality in landscape form with different parameter sets producing geomorphically and hydrologically unique landscapes throughout their entire evolution this shows that parameterisation does matter over geological time scales however for shorter time scales 10 000 years the geomorphic differences in hillslope form are minimal as described by the hypsometric curve area slope and cumulative area distribution yet there are large differences in sediment output therefore obtaining reliable and defensible parameters for input to lems is essential

an algorithm for treating flat areas and depressions in digital elevation models using linear interpolation 1 digital elevation model dem data are essential to hydrological applications and have been widely used to calculate a variety of useful topographic characteristics e g slope flow direction flow accumulation area stream channel network topographic index and others except for slope none of the other topographic characteristics can be calculated until the flow direction at each pixel within a dem is determined however flow direction cannot be accurately calculated until depressions and flat areas within a dem have been rectified this is a routine problem in hydrologic modeling because virtually all dems contain flat and sink pixels both real and artifactual that if left untreated will prevent accurate simulation of hydrologic flow paths although a number of algorithms are available for rectifying flat and sink pixels in dem data treatment of flat areas and depressions and calculation of flow direction remain problematic for reasons of complexity and uncertainty a new algorithm that effectively rectifies flat and sink pixels was developed and tested the approach is to use linear interpolation between low elevation grid cells on the edge of each flat area or depression defined as outlets and higher elevation grid cells on the opposite side defined as inflow pixels the implementation requires an iterative solution to accommodate the irregular geometry of flat areas or depressions and exceptions that arise linear interpolation across flat areas or depressions provides a natural way to scale elevation adjustments based on the vertical scale of the surrounding topography thereby avoiding the addition or subtraction of arbitrary small numbers that we regard as a disadvantage in some prior techniques tests for two virtual terrains and one real terrain show that our algorithm effectively rectifies flat areas and depressions even in low relief terrain and produces realistic patterns of flow accumulation and extracted channel networks

digital terrain modeling abstract this article examines how the methods and data sources used to generate dems and calculate land surface parameters have changed over the past 25 years the primary goal is to describe the state of the art for a typical digital terrain modeling workflow that starts with data capture continues with data preprocessing and dem generation and concludes with the calculation of one or more primary and secondary land surface parameters the article first describes some of ways in which lidar and radar remote sensing technologies have transformed the sources and methods for capturing elevation data it next discusses the need for and various methods that are currently used to preprocess dems along with some of the challenges that confront those who tackle these tasks the bulk of the article describes some of the subtleties involved in calculating the primary land surface parameters that are derived directly from dems without additional inputs and the two sets of secondary land surface parameters that are commonly used to model solar radiation and the accompanying interactions between the land surface and the atmosphere on the one hand and water flow and related surface processes on the other it concludes with a discussion of the various kinds of errors that are embedded in dems how these may be propagated and carried forward in calculating various land surface parameters and the consequences of this state of affairs for the modern terrain analyst

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

detectability of petrophysical properties of subsurface co2 saturated aquifer reservoirs using surface geophysical methods the process of capturing carbon dioxide co2 and injecting it into deep saline aquifers is becoming an important method to reduce future atmospheric emissions of co2 key challenges facing carbon capture and storage ccs are the storage reservoir s size and safety the storage size can be addressed by focusing on large saline aquifer reservoirs the safety concern may be lower if co2 is injected into depleted hydrocarbon reservoirs because their cap rock integrity is already proven but such capping systems are generally potentially compromised by poorly cemented abandoned wells and compared to saline aquifers their storage size is small therefore the long term focus of ccs is on saline aquifers to reduce the corresponding risks comprehensive long term monitoring is inevitable

how does modifying a dem to reflect known hydrology affect subsequent terrain analysis summary many digital elevation models dems have difficulty replicating hydrological patterns in flat landscapes efforts to improve dem performance in replicating known hydrology have included a variety of soft i e algorithm based approaches and hard techniques such as stream burning or surface reconditioning e g agree or anudem using a representation of the known stream network these methods trench or mathematically warp the original dem to improve how accurately stream position stream length and catchment boundaries replicate known hydrological conditions however these techniques permanently alter the dem and may affect further analyses e g slope this paper explores the impact that commonly used hydrological correction methods stream burning agree aml and anudem v4 6 3 and anudem v5 1 have on the overall nature of a dem finding that different methods produce non convergent outcomes for catchment parameters such as catchment boundaries stream position and length and differentially compromise secondary terrain analysis all hydrological correction methods successfully improved calculation of catchment area stream position and length as compared to using the dem without any modification but they all increased catchment slope no single method performing best across all categories different hydrological correction methods changed elevation and slope in different spatial patterns and magnitudes compromising the ability to derive catchment parameters and conduct secondary terrain analysis from a single dem modification of a dem to better reflect known hydrology can be useful however knowledge of the magnitude and spatial pattern of the changes are required before using a dem for subsequent analyses

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

extraction of multithread channel networks with a reduced complexity flow model quantitative measures of channel network geometry inform diverse applications in hydrology sediment transport ecology hazard assessment and stratigraphic prediction these uses require a clear objectively defined channel network automated techniques for extracting channels from topography are well developed for convergent channel networks and identify flow paths based on land surface gradients these techniques even when they allow multiple flow paths do not consistently capture channel networks with frequent bifurcations e g in rivers deltas and alluvial fans this paper uses multithread rivers as a template to develop a new approach for channel extraction suitable for channel networks with divergences multithread channels are commonly mapped using observed inundation extent and i generalize this approach using a depth resolving reduced complexity flow model to map inundation patterns for fixed topography across an arbitrary range of discharge a case study for the platte river nebraska reveals that 1 the number of bars exposed above the water surface bar area and the number of wetted channel threads i e braiding index peak at intermediate discharge 2 the anisotropic scaling of bar dimensions occurs for a range of discharge 3 the maximum braiding index occurs at a corresponding reference discharge that provides an objective basis for comparing the planform geometry of multithread rivers mapping by flow depth overestimates braiding index by a factor of two the new approach extends channel network extraction from topography to the full spectrum of channel patterns with the potential for comparing diverse channel patterns at scales from laboratory experiments to natural landscapes

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

evidence from gabbro of the troodos ophiolite for lateral magma transport along a slow spreading mid ocean ridge the lateral flow of magma and ductile deformation of the lower crust along oceanic spreading axes has been thought to play a significant role in suppressing both mid ocean ridge segmentation and variations in crustal thickness direct investigation of such flow patterns is hampered by the kilometres of water that cover the oceanic crust but such studies can be made on ophiolites fragments of oceanic crust accreted to a continent in the oman ophiolite small scale radial patterns of flow have been mapped along what is thought to be the relict of a fast spreading mid ocean ridge here we present evidence for broad scale along axis flow that has been frozen into the gabbro of the troodos ophiolite in cyprus thought to be representative of a slow spreading ridge axis the gabbro suite of troodos spans nearly 20 km of a segment of a fossil spreading axis near a ridge transform intersection we mapped the pattern of magma flow by analysing the rocks magnetic fabric at 20 sites widely distributed in the gabbro suite and by examining the petrographic fabric at 9 sites we infer an along axis magma flow for much of the gabbro suite which indicates that redistribution of melt occurred towards the segment edge in a large depth range of the oceanic crust our results support the magma plumbing structure that has been inferred indirectly from a seismic tomography experiment on the slow spreading mid atlantic ridge

the hysteresis properties of multidomain magnetite and titanomagnetite titanomaghemite in mid ocean ridge basalts abstract hysteresis measurements have been carried out on a suite of ocean floor basalts with ages ranging from quaternary to cretaceous approximately linear yet separate relationships between coercivity bc and the ratio of saturation remanence saturation magnetization mrs ms are observed for massive doleritic basalts with low ti magnetite and for pillow basalts with multi domain titanomagnetites with x 0 6 even when the morb has undergone low temperature oxidation resulting in titanomaghemite the parameters are still distinguishable although offset from the trend for unoxidized multidomain titanomagnetite the parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types this plot provides a previously underutilized and non destructive method to detect the presence of low titanium magnetite in igneous rocks notably morb

automatic watershed delineation in the tibetan endorheic basin a lake oriented approach based on digital elevation models abstract watershed delineation from digital elevation models dems is an essential prerequisite for land surface hydrology studies although existing automatic methods perform well in exorheic basins finding a suitable watershed delineation approach in endorheic basins is still challenging this study develops a lake oriented approach given that lakes are important hydrological components in the tibetan endorheic basin the designed workflow of the proposed approach contains four steps flow direction calculation hydrological structure features extractions classification of lake types and watershed labeling the experiments are conducted on a sub region of the inner tibetan plateau with an area of 119 055 km2 extraction results prove that the proposed strategies i e elevation profile judgment and overflow point control correction can support the accurate delineation of watershed boundaries in addition the proposed approach can achieve two level watershed boundaries in which the independences of all the endorheic basins can be maintained meanwhile further delineation within extracted exorheic basins satisfies various application requirements at different spatial scales unlike manual processing and existing datasets e g hydrosheds the proposed approach can fully explore the advantages of high quality dems and can be expanded to much larger regions to handle scientific and engineering issues

a view into the cretaceous geomagnetic field from analysis of gabbros and submarine glasses the nature of the geomagnetic field during the cretaceous normal polarity superchron cns has been a matter of debate for several decades numerical geodynamo simulations predict higher intensities but comparable variability during times of few reversals than times with frequent reversals published geomagnetic paleointensity data from the cns are highly scattered suggesting that additional studies are required here we present new paleointensity results from 18 sites collected from the lower oceanic crust of the troodos ophiolite cyprus 92 1 ma old together with recently published data from the troodos upper crust we obtain three independent paleointensity time series these sequences reveal quasi cyclic variations of intensities about a mean value of 54 20 z am 2 providing insight into the fluctuating nature of the cretaceous magnetic field our data suggest the cns field was both weaker and more variable than predicted by geodynamo simulations the large amplitudes of these variations may explain the wide range of dipole moments previously determined from the cns 2007 elsevier b v all rights reserved

avulsion regimes in southeast texas rivers avulsions relatively sudden changes in course or establishment of new anabranches are an important process in alluvial rivers their key role in floodplain construction and alluvial architecture and the general conditions favouring avulsions are well known however avulsion processes and evolution and the factors controlling avulsion regimes are poorly understood in the southeast texas coastal plain where avulsions are common features of the river valleys avulsions were studied on the lower brazos navasota trinity neches and sabine rivers using a combination of aerial imagery digital elevation models and field surveys avulsions have important influences on the surface morphology and contemporary processes in all five rivers features associated with avulsions are active and distinct throughout the study area and all the rivers have experienced geologically if not historically recent avulsions however no two of the study rivers have the same contemporary avulsion regime first order differences in avulsion style are controlled by the stage of valley filling and within the three rivers characterized by an unfilled incised valley antecedent morphology associated with late quaternary and holocene coastal and fluvial deltaic processes accounts for the major differences in the navasota 27 avulsions in 185 km and neches 21 in 340 km rivers subchannels associated with avulsions exist in all stages of development from active to infilled and some have occurred in recent decades the other rivers have fewer avulsions but both the sabine and trinity have experienced historic channel shifts only the brazos river has experienced no avulsions within the past c 300 years results show that even within a region of similar environmental controls and geological history local variations in inherited morphology can result in different avulsion regimes copyright 2008 john wiley sons ltd