a double layered seismic zone in arica northern chile a double layered seismic zone is determined in arica northern chile using locally recorded events at depths 100 km two planes of seismicity can be observed one dipping at 30 e with 10 km of thickness and a second parallel plane 20 25 km deeper with the same average thickness fault plane solutions for both layers show a wide variability even between nearby events the genesis of the arica double seismic zone seems to be independent of the age the relative convergence rate and direction of the nazca plate because all of these parameters are almost the same along the whole northern chile and a clear separation of the seismicity into two layers is only observed around the arica elbow moreover it cannot be responsible of the double layered seismic zone because no similar significant changes are observed in the other well studied double seismic zones

sedimentary architecture and 3d ground penetrating radar analysis of gravelly meandering river deposits neckar valley sw germany sedimentological outcrop analysis and sub surface ground penetrating radar gpr surveys are combined to characterize the three dimensional sedimentary architecture of quaternary coarse grained fluvial deposits in the neckar valley sw germany two units characterized by different architectural styles are distinguished within the upper part of the gravel body separated by an erosional unconformity i a lower unit dominated by trough shaped depositional elements with erosional concave up bounding surfaces that are filled by cross bedded sets of mainly openwork and filled framework gravel and ii an upper unit characterized by gently inclined sheets of massive and openwork gravels with thin sandy interlayers that show lateral accretion on a lower erosional unconformity the former is interpreted as confluence scour pool elements formed in a multi channel possibly braided river system the latter as extensive point bar deposits formed by the lateral migration of a meandering river channel the lateral accretion elements are locally cut by chute channels mainly filled by gravels rich in fines and by fine grained abandoned channel fills the lateral accretion elements are associated with gravel dune deposits characterized by steeply inclined cross beds of alternating open and filled framework gravel floodplain fines with a cutbank and point bar morphology cover the gravel deposits the gpr images revealing the three dimensional geometries of the depositional elements and their stacking patterns confirm a change in sedimentary style between the two stratigraphic units the change occurred at the onset of the holocene as indicated by 14 c dating of wood fragments and is related to a re organization of the fluvial system that probably was driven by climatic changes the integration of sedimentological and gpr results highlights the heterogeneity of the fluvial deposits a factor that is important for modelling groundwater flow in valley fill aquifers

three dimensional high resolution fluvio glacial aquifer analog part 1 field study summary describing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation however hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved aquifer analogs serve as surrogates to construct models of equivalent heterogeneity and thus imitate those features relevant for flow or transport processes gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil this paper describes an approach to also inspect the third dimension by mapping during the ongoing excavation it is possible to obtain a three dimensional representation of the subsurface within a short period of time a detailed description of a case study is presented and the findings from sedimentological hydrogeological and geophysical analyses are compared the gravel pit is located near the town of herten in southwest germany where relatively young unconsolidated fluvio glacial and fluvial sediments in the rhine basin are mined the excavated gravel body is built up by architectural elements typical for braided river deposits the study generated a high resolution data set of lithofacies hydrofacies and ground penetrating radar gpr profiles it represents the basis for a full three dimensional geostatistical reconstruction presented in the second part comunian et al 2011

resolving scales of aquifer heterogeneity using ground penetrating radar and borehole geophysical logging accurate and reliable characterization of aquifer heterogeneity remains one of the foremost problems in hydrogeology in this study ground penetrating radar gpr and borehole geophysical logging are used to investigate scales of heterogeneity present locally 500 m laterally within an outwash deposit comprised of inter bedded and cross bedded sands and gravels of glaciofluvial origin at a small scale 15 m laterally gamma log data in adjacent boreholes show evidence of fining upward sequences occasional coarsening upward sequences and abrupt changes in grain sizes which appear to be laterally continuous at scales of 10 m at the site scale 500 m laterally gpr profiles show a strong reflection interpreted as the water table reflectors in the unsaturated zone are more clearly defined than those beneath the water table due to signal attenuation within the saturated sediments undulating to discontinuous reflectors at scales of 10 15 m are interpreted to result from interbedded and cross bedded sands and gravels a few laterally continuous horizontal to sub horizontal reflectors which extend at least up to 360 m are interpreted as unconformities based on evidence of gravel bars truncation of underlying units as well as scour and fill features in a nearby gravel pit exposure overall the integration of these two geophysical methods provided evidence of unit correlation at the two scales of investigation

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

a model of isotope fractionation in reacting geochemical systems the authors present a numerical technique that predicts how the stable isotopes sup 2 h sup 13 c sup 18 o and sup 34 s fractionate among solvent aqueous species minerals and gases over the course of a geochemical reaction process this model is based on mass balance techniques similar to those already presented in the literature but differs from previous techniques in that it allows minerals to be segregated form isotopic exchange instead of remaining in isotopic equilibrium such an approach allows us to simulate the fractionation of isotopes between rock and fluid resulting solely from mineral dissolution and precipitation the technique was tested by modeling isotopic fractionation during several reaction processes including 1 dolomitization of limestone by a migrating pore fluid 2 diagenetic alteration of the permian lyons sandstone in the denver basin and 3 hydrothermal alteration of the okanagan batholith in southern british columbia the results of calculations in which minerals are segregated from isotopic exchange compare well to isotopic trends observed in nature but differ markedly from calculations that assume isotopic equilibrium 54 refs 4 figs 3 tabs

joint application of satellite remote sensing ground penetrating radar gpr and resistivity techniques for targeting ground water in fractured ophiolites of south andaman island india the ophiolitic complex of the study area oriented in n s direction having moderate to steep slopes of the topography and characterized by strong heterogeneity repetitive deformations and multiple intrusions ophiolites of the study area encompass the major groundwater bearing zones generally these formations have shallower fractured aquifers of a thickness 30 45 m and sometimes due to deep tensile fractures the thickness of aquifer exceeds more than 60 m with a considerable groundwater yield a joint venture of satellite remote sensing geoelectrical resistivity and ground penetrating radar gpr techniques has been used to assess the groundwater potential of the fractured ophiolites the interpreted resistivity inversion model and gpr results were incorporated with borehole lithologs for their subsurface properties and structural variations the integration of using multiple techniques has increased the accuracy of interpretation and thus conflated results significantly rendered the existence of weathered and fractured zone having hydrogeological importance based on the parameters viz geoelectrical properties of layers reflection configuration thickness of weathered and fractured aquifer zone a typical aquifer model for the study area that contains various layers and subtle structural variation has been developed further the derived integrated geophysical data also detail on various lithological characteristics and advances the understanding about aquifer systems of fractured ophiolites and the distribution of groundwater in fractures

towards realistic aquifer models three dimensional georadar surveys of quaternary gravel deltas singen basin sw germany abstract understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management the methods used so far for aquifer characterization e g pump test coring analysis cannot provide the needed resolution for a sufficient prediction of the subsurface properties e g sudicky 1986 this calls for the application of the outcrop analogue approach to aquifers e g macfarlan et al 1994 aigner 1995 in this project we used georadar ground penetrating radar or gpr to acquire the subsurface information for high resolution three dimensional images and radar facies mapping of glaciolacustrine delta sediments in the singen basin sw germany a three dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining gpr profiling and outcrop information a case study is presented showing a complex three dimensional architecture of a quaternary gravel body consisting of the following three types of architectural elements 1 glaciolacustrine delta foresets 2 erosional surfaces with scour pool fills and 3 horizontal glaciofluvial gravel sheets although this seems a relatively simple architectural inventory the three dimensional georadar profiling shows considerable internal heterogeneities the radar data are interpreted following the seismic stratigraphic approach i e the delineation of radar facies types and of radar sequences the three dimensional heterogeneities are visualized by means of time slices 3 d block or chair diagrams or series of radar facies maps

earthquakes in the subducting slab beneath northern chile a double seismic zone abstract available mechanism solutions of most intermediate depth earthquakes in northern chile have t axes aligned subparallel to the direction of plate subduction down dip tension however the mechanism of the 1977 january 17 earthquake 24 9 s 68 7 w is quite different from this general pattern and shows an almost horizontal compression in east west direction the focal depth was reexamined by two independent methods master event method and travel time difference between direct and surface reflected waves and it was concluded that this earthquake occurred at about 120 km depth within the subducting slab the systematic discrepancies observed in the focal depths of intermediate earthquakes in northern chile between those obtained by the least squares method and those by travel time differences can be ascribed to the effect of a higher p velocity within the subducting plate there is a suggestion of a two layer like structure in the e w cross section at about 24 s if we only plot the earthquake foci determined by pp p time difference the 1977 earthquake either 1 1 is an event in the compressional part of the double seismic zone or 2 2 shows an anomalous stress orientation because it occurred near the break in the dip angle of the subducting slab

accurate source depths and focal mechanisms of shallow earthquakes in western south america and in the new hebrides island arc synthetic seismograms are matched to long period p waveforms in order to obtain accurate depths of shallow earthquakes with known focal mechanisms accurate depths are obtained for a large sample of moderate sized 6 ms 7 events which produced relatively simple p waveforms and do not require intensive analysis the estimated error in the determination of depth is about 5 km or less for most of the events considered the procedure is applied to two suites of events one in south america 83 events and one in the new hebrides 61 events in these two areas of contrasting styles of subduction the accurate depths provide new information on the bending of descending plates near trenches the seismicity and tectonics of the upper plate and the geometry and structure of the zone of contact between the upper and descending plates depths of suboceanic earthquakes which occurred near the trench and which have either tensional and compressional horizontal stress axes agree well with chapple and forsyth s 1979 preferred model of a bending elastic perfectly plastic plate however an unusually deep event occurred beneath the fiji plateau in an area of young ocean floor supposed to have been formed by sea floor spreading processes only since late miocene time the calculated depth of the event 48 km places it below the lithosphere asthenosphere boundary derived from thermal models vertical cross sections through the shallow parts of the subduction zones show that most of the earthquakes with thrust faulting focal mechanisms can be interpreted to be interplate events located in a thin 10 km thick curved zone of contact dipping arcward or landward from the trench axis however a few events with focal mechanisms similar to the interplate events do not fit on the inferred thin zone of contact these events would be accommodated by an interplate zone 15 km thick in both subduction zones interplate events occur at depths between about 15 and 50 km however the downdip width of the south american interplate zone is 2 to 3 times larger than that in the new hebrides most of the intraplate events near the interplate boundary are located in the descending plate in the upper plate seismicity is more pronounced in the back arc regions of the two subduction zones thus our results support the generality of a relatively aseismic zone in the upper plate located trenchward of the magmatic arc depths of shallow earthquakes in the eastern andes and sub andean regions of south america range between about 9 and 36 km indicating that both the upper and middle crust are seismically active about 75 of the events occurred in the upper 25 km furthermore the focal mechanisms indicate that from ecuador to argentina the crust of the eastern side of the andean cordilleran is in a state of east west compression oriented nearly parallel to the direction of convergence between the nazca and south american plates the depths the orientations of the earthquake nodal planes and the close relationships to quaternary tectonics imply basement involved crustal shortening in much of the eastern andes and sub andean zones of peru and argentina

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

using two and three dimensional georadar methods to characterize glaciofluvial architecture abstract the threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport to characterize these heterogeneities we have conducted extensive two dimensional 2 d and three dimensional 3 d ground penetrating radar gpr or georadar surveys in two quarries within the rhine valley of northeastern switzerland the quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum wurm stage glaciation after the surveys the terrace walls beneath the two study sites were photographed as they were being excavated by combining information extracted from the 2 and 3 d georadar images with the outcrop photographs it was possible to correlate georadar facies with the various glaciofluvial architectural elements the dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions architectural elements were generally elongated parallel to the mean flow directions of the ancient river system variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction time slices showed structural trends not evident on 2 d georadar images and photographs data interpretation was quicker more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone

an apparent double planed benioff zone beneath northern chile resulting from misidentification of reflected phases epicenters of intermediate depth events located by the isc taken together with focal depths determined from the reflected phase pp define a double planed seismic zone beneath northern chile and northwestern argentina the lower zone of seismicity however is the result of a systematic misidentification of sp as pp at many north american seismograph stations the lower seismic plane consists of 14 earthquakes located between 22 and 24 5 s that occurred between 1964 and 1984 depths calculated from pp arrival times reported to the isc are heavily biased by the abundance of reports from high gain stations in western north america reports from these stations place the lower zone events at 125 150 km depth 35 45 km below the main wadati benioff zone short period seismograms produced by the lower zone earthquakes at north american stations show only one clear reflected phase following p which is often incorrectly identified as pp our identification of this phase as sp results in a shallower depth determination that is in agreement with pp and sp arrival time reports from stations in africa and southern europe the absence of a strong pp phase from north american records for the 14 events can be explained by the proximity of its take off angle to a nodal plane on the focal sphere the majority of intermediate depth events in the region lie in the upper plane these earthquakes do produce recognizable pp phases hence no clear evidence exists for a double planed seismic zone in this region

the use and application of gpr in sandy fluvial environments methodological considerations ground penetrating radar gpr is a popular technique for imaging and interpreting sedimentary architecture however current literature shows a wide range in the quality of information provided on the gpr methodology and processing technique it is therefore difficult to judge the validity of the gpr interpretations and this produces inherent difficulties for comparison between surveys this paper describes the key steps required to collect process and interpret gpr surveys in sandy fluvial sediments gpr data from the south saskatchewan river canada are used to illustrate each stage of data collection and processing particular attention is given to the appropriate set up conditions for the gpr software and hardware the selection of data processing techniques and velocity analysis methods for the interpretation of gpr reflectors are also investigated using ground truth control provided by a cut face exposure this paper presents recommendations for a systematic and rigorous methodology for the collection processing and interpretation of gpr data in sandy fluvial environments the paper suggests that all data collection parameters and processing steps should be recorded or tabulated in any gpr publication to facilitate comparisons between surveys

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

imaging rainfall drainage within the miami oolitic limestone using high resolution time lapse ground penetrating radar 1 the vadose zone of the miami limestone is capable of draining several centimeters of rainfall within a fraction of an hour once the water enters the ground little is known about the flow paths in the oolitic rock a new rotary laser positioned ground penetrating radar gpr system enables centimeter precise and rapid acquisition of time lapse surveys in the field two dimensional 2 d gpr time lapse surveying at a 3 min interval before during and after rainfall shows how buried sand filled dissolution sinks efficiently drain the bulk of the rainwater hourly repeated 3 d imaging of a dissolution sink in response to surface infiltration shows how the wetting front propagates at a rate of 0 6 1 2 m h traversing the 5 m thick vadose zone within hours at the same time some of the water migrates laterally into the host rock guided by stratigraphic unit boundaries average lateral propagation measured over a 28 hour period was of the order of 0 1 m h on a seasonal time frame redistribution involves the entire rock volume comparing 3 d surveys acquired after wet summer and dry winter conditions shows good gpr event correspondence but also time shifts up to 20 ns caused by the change of overall water content within the vadose zone high precision time lapse gpr imaging can therefore be used to noninvasively characterize natural drainage inside the vadose zone ranging from transient loading to seasonal variation

hierarchical dynamic stratigraphy in various quaternary gravel deposits rhine glacier area sw germany implications for hydrostratigraphy the approach of dynamic stratigraphy aims to understand genetic processes that form stratigraphic units in a hierarchy of spatial and temporal scales this approach was used to investigate quaternary gravel deposits in terms of their sedimentology and in order to characterize the various sedimentary units in terms of their hydrogeological properties facies analysis within 62 gravel pits laboratory permeability measurements of field samples and geophysical surveys 3 d georadar 2 d seismic reflection led to the detection and classification of sedimentary heterogeneity according to the following six scales whereby each scale can be translated into defined hydrostratigraphic units 1 particles and pores micro scale that reflect depositional and diagenetic fluid dynamics as well as source material behaviour e g grain size roundness lithological composition this was found to be important for the hydrogeochemistry of groundwater in gravel aquifers e g higher sorption capacity of carbon rich limestone particles for organic pollutants 2 strata meso scale contain the recognition of sorting fabric texture and stratinomic features which can give an indication of transport and depositional dynamics five major lithofacies groups for example were distinguished within fluvial gravel bed deposits their variable hydraulic properties led to their subdivision into 12 hydrofacies types they form the smallest mappable hydrostratigraphic units which may result in either preferred pathways for fluid flow or flow barriers 3 depositional elements macro scale enable reconstruction of sedimentary geomorphic elements and their dynamics within a depositional system e g gravel bed braided river systems are dominated by gravel sheet gravel dunes and scour pool depositional elements hydrostratigraphically the architecture of depositional elements influences the hydraulic connectivity and local permeability structure distribution within an aquifer body five types of depositional elements in fluvial gravel bed deposits were distinguished and their geometries dimensions quantified 4 facies bodies mega scale composed of a stack of depositional elements and strata recording distinct environmental systems and their dynamics e g a coarse grained prograding delta system hydrostratigraphically facies bodies represent major compartments of an aquifer six major types of meltwater controlled facies bodies were identified in the study area 5 genetic sequences mega scale reflect the shifts of depositional environments caused by allocyclic changes e g glacial advance recorded by a coarsening upward sequence or autocyclic changes of landscape shaping events these sequences may form separate hydrostratigraphic units or aquifer storeys 6 basin fill giga scale comprising the lateral and vertical stacking of facies bodies and genetic sequences controlled by either long term glacier dynamics or short term flood events the regional distribution of permeable gravel units and for example less permeable diamicts builds the larger scale hydrostratigraphy

anatomy of a bioclastic grainstone megashoal middle silurian southern ontario revealed by ground penetrating radar porous grainstones deposited as offshore carbonate sand shoals are important hydrocarbon reservoirs but little is known about their internal architecture and its effect on reservoir heterogeneity the middle silurian amabel formation exposed along the niagara escarpment of southern ontario provides an unparalleled opportunity to examine such a deposit in three dimensions with photomosaics and ground penetrating radar the amabel is a dolomitized bioclastic grainstone unit up to 25 m thick composed mainly of crinoid ossicles it thins and grades westward to thin bedded argillaceous dolostones although previously assumed to be reefal the undulating and oblique bedding that dominates the internal geometry was caused by vertical and lateral accretion on hummocky topography and scour surfaces some scours are huge as much as 15 m deep and attest to the dramatic nature of sediment movement by storms and hurricanes ground penetrating radar successfully detects the large scale bedding pattern and in conjunction with outcrop observations has potential for mapping the three dimensional architecture of ancient lithified deposits

mapping the architecture of glaciofluvial sediments with three dimensional georadar three dimensional 3 d ground penetrating radar georadar mapping offers new opportunities for determining the geometries and facies of surficial sedimentary units to investigate the potential of this high resolution technique and at the same time study the architecture of quaternary glaciofluvial deposits georadar data have been collected on a dense grid established across a sequence of braided river gravels and sands in northeastern switzerland results of this survey are striking 3 d images that provide many more details and much more reliable information on the heterogeneities of the shallow underground than are afforded by conventional georadar profile data continuous subhorizontal and oblique reflections can be traced throughout vertical sections and horizontal slices of the georadar data block to a depth of approx 15 m clearly defined are the dominant flow direction of the ancient braided river system the boundaries between different sedimentary facies and the level of the ground water table trough fill sediments and subhorizontal channel deposits observed on 7 m high quarry walls can be followed confidently in the subsurface the orientation shape and size of the troughs and the strike and dip of the cross bedding are all well resolved

application of resistivity and gpr techniques for the characterization of the coastal litho stratigraphy and aquifer vulnerability due to seawater intrusion abstract the objective of this study is to identify geological properties and structural settings allowing salt water intrusion to the aquifers in oceanic originated rock formations of the south andaman island to evaluate the impact of seawater in groundwater aquifer several geophysical surveys using ground penetrating radar gpr and resistivity sounding were performed through the most significant sites located near coastal areas tidal channels and agriculture land high resolution gpr images were obtained and combined with resistivity sounding which allows to identify the mixing transition zone of fresh and saline groundwater and also successfully delineated the structural geometry and litho stratigraphic details of aquifers we show that the sedimentary formations are highly susceptible to seawater intrusion than the mantle originated ophiolites further potential impacts from seawater intrusion are higher along the west coast than the east coast because of macro pore tendency of soils allows seawater filtration

fine structure of the dipping seismic zone and subduction mechanics in the shumagin islands alaska microearthquake data from a permanent telemetered array have been used to elucidate the structure and tectonics of the subduction zone in the shumagin islands alaska the shallow microseismicity is characterized by active interplate thrusting in the 25 45 km depth range arcward of this interplate activity microearthquakes in the overlying plate have a strike slip mechanism the near horizontal p axis of this mechanism is oriented in the direction of plate convergence suggesting that the plate interface at shallow depths is currently efficiently coupled below 45 km depth the dipping seismic zone appears to be double planed the upper plane dips at 32 from 45 to 100 km depth where it exhibits a kneelike bend below the volcanic front the lower plane begins at about 65 km depth where it is separated from the upper plane by some 25 km and appears to converge with the upper plane at about 120 km depth the inferred geometry of the plate interface suggests that the double planed portion of the dipping seismic zone is a product of elastic unbending of the subducted plate a composite fault plane solution for events in the upper plane indicates however that downdip tension is currently present rather than the downdip compression that would be expected from unbending it is proposed that because of locking of the plate interface at shallower depths slab pull is currently overprinting the unbending stresses which predominate at times when the plates are unlocked this model is consistent with previous interpretations that there is a high probability of a great earthquake in the shumagin islands seismic gap within the next decade or two

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

three dimensional models of p wave velocity and p to s velocity ratio in the southern central andes by simultaneous inversion of local earthquake data the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 seismological network of 31 digital broad band and short period three component seismometers was deployed in northern chile between the coastal cordillera and the western cordillera more than 5300 local seismic events were observed in a 100 day period a subset of high quality p and s arrival time data was used to invert simultaneously for hypocenters and velocity structure additional data from two other networks in the region could be included the velocity models show a number of prominent anomalies outlining an extremely thickened crust about 70 km beneath the forearc region an anomalous crustal structure beneath the recent magmatic arc western cordillera characterized by very low velocities and a high velocity slab a region of an increased vp vs ratio has been found directly above the wadati benioff zone which might be caused by hydration processes a zone of lower than average velocities and a high vp vs ratio might correspond to the asthenospheric wedge the upper edge of the wadati benioff zone is sharply defined by intermediate depth hypocenters while evidence for a double seismic zone can hardly be seen crustal events between the precordillera and the western cordillera have been observed for the first time and are mainly located in the vicinity of the salar de atacama down to depths of about 40 km

introduction to the special issue on aquifer sedimentology problems perspectives and modern approaches abstract progress towards a better understanding of groundwater circulation and transport processes in aquifers demands a multidisciplinary approach to a host of unresolved problems although much progress has been made within recent years in interpreting the dynamic character of groundwater systems many key issues remain to be addressed in particular several areas demand attention the role of sedimentological information heterogeneity in groundwater and transport models the scaling up of observations from outcrop scale to larger scales and the integration of geological and geophysical information of different quality into the description of an aquifer structure still nowadays many of the heterogeneities cannot be recognized directly because of the limitation of measurement techniques this is probably one of the reasons for the limited application of aquifer sedimentology and geophysics in practical cases in order to consolidate expand and make a larger number of people aware of the contribution of modern aquifer sedimentology including modelling and ultra high resolution geophysical methods several lines of intervention were identified 1 a better collaboration of the different disciplines on site specific applied problems 2 development of new modelling techniques combining data of different quality 3 development of optimizing tools position and number of wells additional geophysical methods baysian techniques 4 development of a common language among sedimentologists and hydrogeologists to overcome communication problems

architectural element analysis within the kayenta formation lower jurassic using ground probing radar and sedimentological profiling southwestern colorado abstract a well exposed outcrop in the kayenta formation lower jurassic in southwestern colorado was examined in order to delineate the stratigraphy in the subsurface and test the usefulness of ground probing radar gpr in three dimensional architectural studies two fluvial styles are present within the kayenta formation sandbodies within the lower third of the outcrop are characterized by parallel laminations that can be followed in the cliff face for well over 300 m these sandbodies are sheet like in appearance and represent high energy flood deposits that most likely resulted from episodic floods the remainder of the outcrop is characterized by concave up channel deposits with bank attached and mid channel macroforms their presence suggests a multiple channel river system the gpr data collected on the cliff top together with sedimentological data provided a partial three dimensional picture of the paleo river system within the kayenta formation the 3 d picture consists of stacked channel bar lenses approximately 50 m in diameter the gpr technique offers a very effective means of delineating the subsurface stratigraphy its high resolution capabilities easy mobility and rapid rate of data collection make it a useful tool its shallow penetration depth and limitation to low conductivity environments are its only drawbacks

aquifer aquitard units of the dakota aquifer system in kansas methods of delineation and sedimentary architecture effects on ground water flow and flow properties abstract in the near future the demand for water in many parts of central and western kansas will exceed the supply available from near surface aquifers forcing exploitation of the underlying dakota aquifer the dakota aquifer framework consists of discontinuous sandstone aquifers confined by mudstone aquitards belonging to the cretaceous cheyenne sandstone and the kiowa and dakota formations these strata were deposited in a variety of nonmarine through marine settings associated with several cycles of sea level rise and fall the aquifer comprises two entire and one partial unconformity bounded sequences recognized in the western interior cheyenne kiowa lower dakota j sequence and upper dakota d sequence scale dependent heterogeneity characterizes the dakota aquifer because of the inf uence of sedimentary processes on the arrangement and geometry of sandstone bodies and on the fabric of the sandstones a multidisciplinary approach is being employed in the dakota aquifer program of the kansas geological survey to delineate aquifer aquitard units and characterize scale dependent heterogeneity using a variety of techniques colorized images of the subsurface from gamma ray logs in cross sections reveal the complex arrangement of sandstone bodies within the dakota due to deposition in fluvial and deltaic estuarine to marine settings at the more local scale borehole geophysical logs are being used both to delineate local aquifer zones and to estimate overall ground water quality pumping test results indicate that the contrast of hydraulic properties between a sandstone aquifer and its surrounding mudstone aquitard significantly channels the flow of ground water through the aquifer he geometric mean hydraulic conductivity of fluvial sandstones is generally higher than in deltaic estuarine sandstones in either the dakota or kiowa formations overlapping ranges of hydraulic conductivity values in fluvial and deltaic estuarine sandstones may be due to the uniformity of the sediment supplied from source areas combined with variations in the energy of transport and winnowing within each of these depositional systems permeameter tests of coreplugs and gamma ray response on logs indicate that the better sorted coarser and less radioactive sandstones make the most permeable aquifer units in two cores of fluvial and deltaic estuarine sandstones experimental variograms using coreplug data indicate that bedding is a significant control on the partitioning of hydraulic con uctivity within sandstone bodies succeeding efforts will focus on using the results presented in this paper combined with techniques such as indicator kriging and geologic process modeling to map the distribution of sandstone aquifers and their properties in the subsurface within small geographic areas of manageable size where detailed information is needed

the ms 8 tensional earthquake of 9 december 1950 of northern chile and its relation to the seismic potential of the region abstract the only known great m s 8 intermediate depth earthquake localized downdip of the main thrust zone of the chilean subduction zone occurred landward of antofagasta on 9 december 1950 in this paper we determine the source parameters and rupture process of this shock by modeling long period body waves the source mechanism corresponds to a downdip tensional intraplate event rupturing along a nearly vertical plane with a seismic moment of m 0 1 10 28 dyn cm of strike 350 dip 88 slip 270 m w 7 9 and a stress drop of about 100 bar the source time function consists of two subevents the second being responsible for 70 of the total moment release the unusually large magnitude m s 8 of this intermediate depth event suggests a rupture through the entire lithosphere the spatial and temporal stress regime in this region is discussed the simplest interpretation suggests that a large thrust earthquake should follow the 1950 tensional shock considering that the historical record of the region does not show large earthquakes a slow earthquake can be postulated as an alternative mechanism to unload the thrust zone a weakly coupled subduction zone within an otherwise strongly coupled region as evidenced by great earthquakes to the north and south or the existence of creep are not consistent with the occurrence of a large tensional earthquake in the subducting lithosphere downdip of the thrust zone the study of focal mechanisms of the outer rise earthquakes would add more information which would help us to infer the present state of stress in the thrust region

transition from double to single wadati benioff seismic zone in the shumagin islands alaska a discontinuity exists in the moderate depth seismicity located by the shumagin seismic network in the eastern aleutian subduction zone the boundary is nearly perpendicular to the arc and has a double planed wadati benioff zone to the west and a single planed zone to the east the transition does not appear to be an artifact of mislocations as shown by three dimensional ray trace modeling and examination of phases of representative earthquakes current theory on the presence or absence of double seismic zones suggests a change in stress across the boundary if so the east and west regions may either have different aseismic to seismic slip ratios or be in different stages of the earthquake cycle

earthquakes plate subduction and stress reversals in the eastern aleutian arc plate subduction beneath the 1500 km long segment of the eastern aleutian arc between kodiak and atka islands 154 w and 176 w longitude is studied with observations from teleseismic data the primary data base consists of hypocenters of earthquakes for the period 1965 1975 carefully selected from the bulletins of the international seismological centre and of 44 new focal mechanism solutions the principal results of this study are that hypocenters of intermediate depth earthquakes in the eastern aleutians appear to define a weakly developed double seismic zone at depths between 70 and 170 km additional evidence for a double seismic zone comes from focal mechanisms which generally show downdip directed p axes for earthquakes in the upper zone and downdip directed t axes in the lower zone major features of the double zone can be explained by thermoelastic stresses in the downgoing plate the observed predominant downdip stress polarity at intermediate depths in the descending plate reverses along strike of the arc this stress reversal coincides in map view with a change from a continental to an oceanic arc the coincidence may result from spatial differences either in the coupling between the plates at shallow depths or in the rheology of the surrounding oceanic versus continental mantle alternatively the stress reversal may be related to the time since the last great earthquake if the observed stress polarity relates to the elapsed time since the last great earthquake it may be a significant observation for long to intermediate term prediction of great thrust earthquakes in subduction zones portions of the eastern aleutian arc where downdip tension predominates contain one or more seismic gaps that appear to have a high probability for great earthquakes in the next few decades a moderate sized bathymetric feature in the pacific plate the amlia fracture zone modifies subduction and produces a bend or offset in the downgoing plate as well as an offset in the line of active volcanoes in the upper plate subduction of the fracture zone appears also to cause formation of summit basins on the arc platform and some aseismic behavior of a 100 km long segment of the main thrust zone

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

aquifer architecture analysis using ground penetrating radar triassic and quaternary examples s germany applying the concept of analogue studies long used in reservoir characterization outcrop analogues in two aquifer units of southern germany have been investigated upper triassic keuper alluvial sandstones stubensandstein and quaternary glaciofluvial gravels architectural element analysis of the outcrops is combined with ground penetrating radar profiles derived a few meters behind the outcrop walls such calibration is used to better understand the three dimensional sedimentary architecture many sedimentary units at the same time represent hydraulic flow units and are characterized by specific radar signatures this approach leads to promising results not only in unconsolidated aquifers but also in fully consolidated sedimentary rocks our studies will lead to a database with which more realistic predictions of the hydraulic behaviour of sedimentary aquifers systems needed for numerical hydrogeological simulations will be possible

characterizing heterogeneity in a glaciofluvial deposit using architectural elements limehouse ontario canada major hydrocarbon and groundwater reservoirs are commonly hosted within coarse grained alluvial deposits that contain a high degree of sedimentary heterogeneity this paper presents a detailed characterization of the sedimentary heter ogeneity of fluvial deltaic deposits using architectural element analysis aea sedimentological data collected from outcrop faces exposing late quaternary glaciofluvial deposits in southern ontario canada is recorded in 31 sedimentary logs these logs are used to identify nine different facies types including gravel facies gm gp gt sand facies sr sp st ss and fine grained facies fl and fd variations in facies associations and geometries are defined by five architectural elements aes sand complex sc gravel sheet gs fine grained sheet fs gravel foreset body gfb and concave fill cf elements the spatial arrangement of bounding surfaces first to fifth order and aes allows the classification of six eas which in this study are defined as the largest scale architectural subunits that allow for architectural based mapping over a large area eas delineated in this study are sandy braided river ea1 delta front ea2 gravelly braided river to delta top ea3 delta front to lacustrine ea4 braided river to deltaic ea5 and sand dominated fluvial ea6 aea is utilized here to capture three levels of heterogeneity which allow detailed reservoir characterization based on geometric objects and can be readily used for computer based modelling outcrop analogue studies such as this one provide insight to the geometries of more deeply buried coarse grained deposits that form potential reservoirs and enhance paleoenvironmental reconstruction of subsurface alluvial deposits in canada and elsewhere resume les grands reservoirs d hydrocarbures et d eau souterraine sont frequemment situes dans des depots alluviaux agrains grossiers afort degre d heterogeneite sedimentaire cet article presente une caracterisation detaillee de l heterogeneite sedi mentaire des depots fluvio deltaiques effectuee par analyse des elements architecturaux aea des donnees sedimentologiques recueillies d affleurements exposant des depots fluvio glaciaires du quaternaire tardif dans le sud de l ontario canada sont contenues dans 31 diagraphies sedimentaires ces diagraphies servent aidentifier neuf differents types de facies incluant un facies de gravier gm gp gt un facies de sable sr sp st ss et un facies agrain fin fi et fd les variations dans les associations de facies et les geometries sont definies selon cinq types d elements architecturaux ae un complexe de sable sc une couche de gravier gs une couche agrain fin fs un amas frontal de gravier gfb et un remplissage concave cf l arrangement spatial des surfaces limitrophes 1er au 5e ordre et les elements architecturaux permettent une classification de six associations d elements ea lesquels dans cette etude sont definis comme etant les sous unites ala plus grande echelle architecturale permettant de cartographier selon l architecture sur une grande superficie les associations d elements ea definis dans la presente etude sont riviere sablonneuse anastomosee ea1 front deltaique ea2 riviere graveleuse anastomosee asommet d un delta ea3 front deltaique alacustre ea4 riviere anastomosee adeltaique ea5 et environnement fluvial domine par le sable ea6 l analyse des elements architecturaux est utilisee ici pour saisir trois niveaux d heterogeneite qui permettent une caracterisa tion detaillee des reservoirs basee sur des objets geometriques et qui peuvent facilement servir pour une modelisation informa tique des etudes analogues d affleurements telles que celle ci fournissent des apercus de la geometrie des depots agrains grossiers enfouis aplus grande profondeur formant des reservoirs potentiels elles aident ala reconstruction paleoenvironne mentale des depots alluviaux sous la surface au canada et ailleurs traduit par la redaction

significance of porosity for stratigraphy and textural composition in subsurface coarse fluvial deposits boise hydrogeophysical research site recognition and quantitative characterization of subsurface stratigraphic units in coarse unconsolidated fluvial deposits are difficult because large grain size and the large scale of sedimentary structures make direct interpretation from core difficult or impossible in this paper we use porosity data from well logs and grain size distribution gsd data from core to investigate four pebble and cobble dominated units that have been identified in porosity logs in deposits at a research well field boise hydrogeophysical research site lacking direct observation at an appropriate scale questions about distribution of parameters and textural composition in these units are analyzed with statistical tests the four pebble and cobble dominated porosity stratigraphic units may be grouped into two types 1 units 1 and 3 have low porosity mean 0 17 0 18 and low porosity variance and 2 units 2 and 4 have higher porosity mean 0 23 0 24 and higher porosity variance based on gsd data core samples are subdivided into five lithotypes the five lithotypes occur in different proportions and have different vertical transition probability characteristics in the two types of units 1 units 1 and 3 have only framework gravel dominated lithotypes and have random vertical transition probability between these two lithotypes and 2 units 2 and 4 consist of both framework gravel dominated and sand or matrix dominated lithotypes and have structured vertical transition probability the two framework gravel dominated lithotypes occur in all four stratigraphic units but have distinctly lower porosity in units 1 and 3 i e tighter packing than in units 2 and 4 looser packing considering the repeated stratigraphic occurrence of and the statistical significance of differences between the two types of units both the individual unit distinctions and the two unit groupings appear to be valid it is reasonable to interpret that the observed packing differences associated with units 1 and 3 compared with units 2 and 4 are related to different sedimentary processes that produce different bedforms or grain fabrics perhaps under different bedload transport rates

frequency domain electromagnetic and ground penetrating radar investigation of ephemeral streams case study near the southern high plains texas a frequency domain electromagnetic fdem and ground penetrating radar gpr study was conducted on an ephemeral stream in north central texas to determine if fdem and gpr measurements can be combined to determine the electrical characteristics of current and ancient stream channels gpr data were collected at several frequencies to image sedimentary structures of different scale lengths and to determine the formation porosity and water content of stream sediments fdem measurements were collected using geonics em31 and em34 loop loop instruments on a profile along the current stream channel and five profiles perpendicular to the channel the results indicate that the greater spatial resolution of the em31 mapped the current and possible ancient channels better than the em34 however the em34 provided depth information on the formations underlying the channel sediments that the em31 could not image gpr measurements taken along a point bar deposit with 200 100 and 25 mhz antennae indicated that the higher frequency antenna better resolved channel structures including laminar bedding trough scours and cross bedding however lower frequency antenna 25 mhz imaged sedimentary structures within the underlying channel sediments common midpoint gpr measurements collected along the point bar deposit were used to estimate the sediment formation porosity 26 and the water content during a dry period of the unsaturated 12 and saturated 26 or 100 of the pore space sediments the combined results indicated that the fdem data should be collected first because of the speed and ease of measurements the fdem data especially the em31 pointed to the locations of possible sedimentary structures which can then be resolved by using different frequency gpr measurements

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

moho geometry beneath the eastern margin of the andes northwest argentina and its implications to the effective elastic thickness of the andean foreland the seismically constrained shape of the moho beneath the eastern margin of the northwest argentine andes 24 s is interpreted in the context of regional isostasy to constrain the flexural rigidity of the lithosphere in this actively deforming orogen seismic travel time residuals from regional intermediate depth earthquakes are inverted for three dimensional variations in the moho depth beneath a portable seismic network spanning the eastern margin of the puna plateau and the santa barbara foreland system beneath the easternmost santa barbara ranges the moho is relatively flat and lies at 40 45 km depth farther west beneath the eastern margin of the puna the moho dips 10 15 to the west before flattening out at a depth of 60 65 km beneath the plateau the moho inversion model and coincident gravity data constrain the flexural rigidity of the foreland lithosphere to be between 1021 and 1022 m the corresponding effective elastic thickness of 6 12 km is a factor of 2 to 4 less than that estimated in previous published studies for the bolivian altiplano and subandean ranges farther to the north these results indicate that in contrast to the bolivian andes the foreland lithosphere in northwest argentina does not provide significant flexural support to the plateau margin and the eastern margin of the andes is nearly in a state of local isostatic compensation the north to south decrease in the effective elastic thickness of the andean lithosphere supports published seismic wave attenuation studies which indicate that south of 23 s the lithospheric thickness decreases beneath the plateau and foreland

geophysical conceptualization of a fractured sedimentary bedrock riverbed using ground penetrating radar and induced electrical conductivity summary bedrock rivers exhibit very different hydraulic and ecological regimes compared to alluvial rivers groundwater surface water interaction in rivers that flow directly on sedimentary bedrock surfaces with exposed fracture and conduit networks is generally based on alluvial river conceptual models however the dual and triple porosity systems of sedimentary rock e g matrix fractures and vugs leads to highly variable hydraulic pathways and groundwater velocities that in turn result in processes that are very different than those derived from alluvial concepts relative to alluvial rivers there has been very little direct examination of dynamic interactions such as fluxes groundwater velocities and mechanisms affecting water quality across the channel interface this is largely because bedrock rivers are difficult to instrument and monitor given their heterogeneous and anisotropic flow systems in this study we evaluate the capacity of non invasive low impact ground penetrating radar and frequency domain electromagnetic induction methods capable of detecting discrete fracture and conduit features mapping complex distributions of lithostratigraphic interfaces and providing information about formation properties along a partially exposed section of the eramosa river located in ontario canada geophysical data are supported by direct hydrogeologic and geologic information obtained from a nearby borehole piezometer cluster and a continuous 15 m rock core valuable insights were gained into the lateral extent and geometry of structurally controlled whydrostratigraphic units e g dissolution enhanced fractures epikarst and karst features which are expected to strongly influence groundwater and surface water interaction along the channel an integrated application of gpr and emi methods was necessary to fully understand the complex geometry of geologic boundaries and karst features within the shallow bedrock aquifer the identification of epikarst below fluvial sediment and its relationship to the formation of dissolution features exposed fracture conduit networks and sinkholes represents the basis for understanding the dynamic hydraulic responses between the surface water and the shallow bedrock aquifer

relating lithofacies to hydrofacies outcrop based hydrogeological characterisation of quaternary gravel deposits abstract a considerable part of today s drinking water supplies in europe and north america rely on clean groundwater from gravelly valley aquifers of quaternary age the sedimentary architecture the distribution of lithofacies and of architectural elements in such heterogeneous deposits are of fundamental importance for the analysis of groundwater flow and contaminant transport as the aquifers are not directly accessible for observation representative outcrop analogues were used to study the sedimentology on a local scale conventional sedimentological classification schemes were adapted for the purpose of hydrogeological evaluations measurements of hydraulic properties were then used to define a set of 5 hydrofacies from 23 possible sediment lithofacies a digital photographic mapping procedure was developed to allow fast data acquisition in the field the sedimentologically interpreted outcrops were stored in a gis style database and thus allow the output for further sedimentological or hydrogeological analysis

architecture and directional scales of heterogeneity in alluvial fan aquifers abstract a wide range of structural volcanic and depositional processes produce heterogeneity in alluvial fan aquifers this heterogeneity is commonly abrupt and more importantly it is directional prevalent concepts of scales of heterogeneity and stochastic hydrology emphasize nested or hierarchical aquifer structures that can be represented by stationary models the argument for stationarity is that heterogeneity becomes homogeneous or spatially periodic at some scale stationarity may exist in some braided and meandering aquifers but stationarity is generally not valid for alluvial fan aquifers because hierarchical structure is generally present only at the microscopic and partially at the mesoscopic scale alluvial fans are directional landforms that extend downdip from a point sou ce grain size and bed thickness generally decrease down fan abrupt to gradational facies relationships change down fan and may be substantially different in adjacent fans hydrogeologic properties which can vary over 14 orders of magnitude may parallel the down fan fining trend or may show a humped pattern in a down fan direction as fans subside prograde and retrograde a directional aquifer is created whose complex heterogeneities require a directional model the directional alluvial fan aquifer is best characterized by three directional scales of heterogeneity from smallest to largest 1 within fan microscopic scale to facies relationships 2 between fan parallel to depositional and structural strike and 3 cross fan perpendicular to depositional and structural st ike a directional view of heterogeneities in alluvial fan aquifers is essential for correct site characterization and for design of well networks aquifer tests and flow models