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25th Symposium on the Application of Geophpysics to Engineering & Environmental Problems
- Conference date: 25 Mar 2012 - 29 Mar 2012
- Location: Tucson, USA
- Published: 25 March 2012
1 - 50 of 195 results
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Application of Ground Penetrating Radar and Electrical Resistivity Techniques for Subsurface Stratigraphic Mapping in Southwestern Nigeria
Authors O. Fayemi and A.A. AdepelumiThe frequent building collapses in Nigeria have been attributed to lack of pre-construction investigations that will assist engineers obtain in-situ geotechnical information and the structural subsurface settings are often ignored; and when done, it is haphazardly. To address this issue and demonstrate the importance of such survey, a combined Ground Penetrating Radar (GPR) and Vertical Electrical Sounding (VES) data was acquired in a part of Southwestern Nigeria. A 200 MHz antenna was used for the data acquisition along four traverses. The data were subjected to standard GPR processing techniques, and attributes analyses such as instantaneous-frequency, amplitude and phase. Also, for comparative and engineering characterization purposes, longitudinal conductance and coefficient of anisotropy were computed from the VES results and used for determining the competency of the bedrock. From the GPR results, it was observed that the subsurface mapped is characterized by an erosional truncated, low angle, southerly dipping, tangential reflections. Further, stratified rocks dipping at an angle of 32º occurs between 1.0 to 4.5 m depth in all the GPR sections; these strata were truncated by topsoil at shallow depths. Also, some of the sections depict ancient channel structures that have a dimension of 70 m by 40m. The resistivity data suggest that the study area is characterized by four distinct geoelectric sequences. These sequences are comprised of topsoil, which is composed of clayey-sand to lateritic clay whose thickness ranges between 0.25 m – 8.12 m; weathered bedrock with a thickness of 3.84mto 12.61m; stratified bedrock with a thickness ranging between 0.33m – 7.51m and the fresh bedrock. These results reveal that the study area is characterized by a complex subsurface geology. The area has low to moderate longitudinal conductance and anisotropy coefficient values which suggest that incompetent to semi-competent bedrock exists beneath the subsurface. A good correlation between the GPR and resistivity derived thicknesses was established.
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Geophysical and Geotechnical Features of the Levee Systems Damaged by the East Japan Earthquake
By T. InazakiLevee systems in Kanto Region, central Japan, were severely damaged at many places caused by the long-lasting strong ground motion of the magnitude (Mw) 9.0 East Japan Earthquake, which occurred at 05:46 UTC on Friday, 2011 March 11, even located more than 400 km far from the epicenter. Since 2005, we have conducted integrated geophysical surveying for the safety assessment of levee systems at 39 actual levee sites in Japan. Among them, severe damage took place in two sites by the East Japan Earthquake just at the anomaly part delineated by the survey. The anomaly part in one site was characterized as low S-wave velocity and low resistivity both for levee body and substrata. After the earthquake, we conducted comparative surveying on the same levee but the damaged part of which had been soon repaired. As a result, the characteristic low S-wave velocity and low resistivity zone was again identified just at the damaged or repaired part where substantial top subsidence had occurred. This suggests a physical model that nonlinear loosening of underlying clay layers had caused the ground failure and resulted in the damage of levee systems. The other site, where large sliding had taken place on a levee slope during the earthquake attack, was featured by the existence of high resistivity anomaly in the levee body. The anomaly was also identified by the comparative surveying at the same part in the line where the slope sliding had occurred. A different type of levee failure mechanism was interpreted as resulting from high contrast of physical properties in levee body, based on our integrated geophysical surveys. Thus the corresponding survey results lead us to the usefulness of the integrated geophysical surveying for understanding levee failure mechanism and for the assessment of present conditions of levee systems attacked by the earthquake.
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MAPPING FRACTURES IN VERTICAL ROCK CUTS USING A 400 MHZ GROUND PENETRATING RADAR ANTENNA
Authors Adnan Aqeel, Norbert Maerz and Neil AndersonParallel to sub-parallel hidden discontinuities to the slope face of a sandstone bedrock were effectively mapped at four different stations in central Missouri using a continuous-distance-mode ground penetrating radar system equipped with a 400 MHz monostatic antenna. At each station, a suite of 2-D ground penetrating radar profiles were acquired along multiple closely spaced traverses. A small wheel was appropriately and significantly attached to the used antenna to fit with the distance mode that was used in our GPR common offset survey. The exposed rock surfaces were relatively smooth which help to place directly the used attached-wheel 400 MHz antenna on the slope face of the bedrock and record the data effectively.
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NUMERICAL MODELING TO ASSESS THE IMPACT OF POSITIONAL ERRORS DURING THE ACQUISITION OF WATERBORNE CONTINUOUS RESISTIVITY MEASUREMENTS
Authors Brad Hansen and Adam PidliseckyWaterborne continuous resistivity profiling (WCRP) permits rapid collection of direct current (DC) resistivity data over water by means of towing a multi-electrode cable streamer behind a moving vessel. During WCRP electrical current is injected using a pair of electrodes, while multiple potential measurements are made using other pairs of electrodes. This acquisition results in a near continuous profile of measured resistances along the survey path. These data are then processed/inverted to produce a 2.5D resistivity model, which can be used to interpret physical subsurface properties (i.e. lithology, and pore fluid conductivity).
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MONITORING SALT REMEDIATION BY INTEGRATING 3D ELECTRICAL RESISTIVITY TOMOGRAPHY AND POINT CHEMISTRY SAMPLING USING KRIGING WITH LOCAL VARYING MEAN
Authors Franklin Head, Laurence Bentley and Michael CallaghanSalt-affected soils are a common problem for the hydrocarbon industry. A remedial tile drain system was installed at a former oil and gas production facility to collect saline leachate and route it for disposal. Our objective is to evaluate the effectiveness of irrigation during a salt flushing experiment within a 20 by 20 m test plot.
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THREE-DIMENSIONAL RESISTIVITY IMAGING FOR DETERMINATION OF AIR-FILLED PORE SPACE IN THE DESIGN OF GROUNDWATER AIR SPARGING SYSTEMS
Authors Boyce Clark, Mark Klemmer and Bill ZahniserTypical methodologies for determining well spacing in groundwater air sparge systems, such as water table response, dissolved oxygen measurements, and conservative gaseous tracers have been known to give semi-quantitative estimates of the radius of influence. Placement of observation wells that intersect established air channels can lead to data that are very different than wells that do not intersect, while two such wells could be located only a short distance apart. Non-invasive geophysical methods such as electrical resistivity (ER) can provide more detailed data over a larger area, alleviating the data density issues associated with typical test methods. Data are presented from two sites with existing air sparge systems that were not performing to expectations, ER surveys were conducted to evaluate the air-filled pore space induced by the operating air sparge wells. The air sparge systems were turned off in advance for a baseline survey with no air-filled pore space. Multiple repeat surveys were then collected at progressively increasing air flow rates to evaluate differences in radius of influence or volume of air-filled pore space. An increasing area of resistivity values during air sparging at an increased flow rate is attributed to pore-water displacement by injected air, resulting in decreased relative electrical conductivity. This conclusion is supported by direct measurments at various observation wells of dissolved oxygen concentration and changes in depth to water.
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3-D GPR IMAGING ON DIFFICULT TERRAIN: EXAMPLES FROM THE PYRAMID COMPLEX OF PHARAOH SENWOSRET III AND THE THEBAN TEMPLE OF FEMALE PHARAOH TAUSRET (EGYPT)
Authors Douglas Sassen, Lawrence Berkeley and Pearce Paul CreasmanMany of the undisturbed areas of ancient Egyptian temples and pyramid complexes are situated in locations of adverse terrain, inhibiting archaeological excavation. Ground-penetrating radar (GPR) imaging of these difficult terrains can provide archaeologists with insights otherwise only available from excessively expensive or dangerous excavations. GPR imaging algorithms used on data from these terrains must allow for uneven sampling grids and missing traces, while compensating for surface topography and antenna patterns. We introduce an adaption to the Kirchoff topographic migration method that includes compensation for antenna patterns through a heuristic solution to the total field pattern of an antenna over a half space. The compensation of the antenna pattern is based on a stable inverse weighting of the total field pattern from numerical and analytical solutions. We also discuss surveying and interpolating surface topography, calculation of surface normals, pre- and post-processing of the data, attribute extraction, and other concerns for conducting successful remote sensing in Egypt. Examples of the application of this method include surveys from the Middle Kingdom pyramid complex of pharaoh Senwosret the III at Dahshur (ca. 1850 BC), and the New Kingdom Theban temple complex of the female pharaoh Queen Tausret (ca. 1180 BC), West Bank, Luxor, Egypt.
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MAPPING SUBSURFACE CAVITIES AND FRACTURES USING INTEGRATED SURFACE AND BOREHOLE GEOPHYSICS NEAR A SUPERFUND SITE SOUTH OF ROCKFORD, ILLINOIS
Authors Ryan Adams and Phillip CarpenterThe ACME Superfund site is one of many Superfund sites in Northern Illinois. This 20 acre (8.1 ha) site was contaminated by various volatile organic compounds (VOC’s) and heavy metals during the 1960-1980s. These contaminants have seeped into the Wise Lake dolomite (Galena Group) and contaminated local ground water supplies. The field site is located immediately south and hydrologically downgradient of the ACME site, where up to 10 m of unconsolidated sediments overlie the fractured and karstic Wise Lake Formation in a small valley adjacent to residential wells.
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FACILITATING LONG-TERM OUTBACK WATER SOLUTIONS (FLOWS) IN SOUTH AUSTRALIA: THE ROLE OF AIRBORNE GEOPHYSICS
By Tim MundayMining and energy development in South Australia’s far north is set to have significant consequences for the water resources of the region. These sectors generate significant economic value to the State and their support remains a priority for the government. The scale of the planned developments and the potential from current exploration programs facilitated by the South Australian Government through the Plan for Accelerated Exploration (PACE) Program will result in a substantial increase in infrastructure requirements, including access to water resources and Aboriginal lands for exploration and potential mine developments. Increased demand for water and in particular groundwater is compromised by the limited knowledge we have about these resources. This includes information about their character, variability, sustainability and their relationship to environmental and cultural assets, which is most notable in the priority areas for development. There is a recognised need to develop this knowledge so that water is not a limiting factor to development.
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ASSESSING CULTURAL (ELECTRICAL) INTERFERENCE OF DEEP WENNER RESISTIVITY SOUNDINGS AT FLOOD CONTROL STRUCTURES (DAMS) FOR SUBSIDENCE HAZARD STUDIES IN THE DESERT SOUTHWEST
Authors Michael Rucker and Sean HulburtFlood control structures (FRS) or dams in the desert southwest are commonly located at the margins of deep alluvial basins that are subject to groundwater pumping-induced subsidence. Safety assessment of these facilities includes characterizing the existing or potential future hazard to these structures due to subsidence. Differential subsidence can lead to changes in surface hydrology and flood storage capacity, and possible earth fissuring that could cause cracking in an FRS or its’ foundation, resulting in possible piping erosion failure of the FRS during a flood event. Resistivity is an excellent reconnaissance tool to assess compressible basin alluvium that is prone to subsidence. However, with typical water table depths of 30 to over 100 meters, and potential bedrock depths underlying alluvium ranging from 0 to over 300 meters, resistivity soundings require large arrays. The authors use array electrode a spacing up to 300 meters for this work.
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THE DARDADINE PALAEOCHANNEL PROJECT: USING AIRBORNE GEOPHYSICS TO SUPPORT REGIONAL COMMUNITIES IN WESTERN AUSTRALIA
Authors Tim Munday and Jasmine RutherfordHydrogeological investigations in the early 1990s confirmed that the West Arthur Shire in Western Australia’s south west contained the remnants of an ancient palaeodrainage system. Drilling revealed the presence of palaeochannel sediments, containing groundwater that has since been used to develop and support regional town water supplies and local farm water systems. Airborne electromagnetic (AEM) data have been employed to better define the location of these palaeovalleys and the quality of the contained groundwater. In this paper we describe the results from one such survey, which used the SkyTEM TDEM system to accurately locate and characterise aquifers within the Dardadine palaeochannel located near the town of Darkan. The aim of the survey was to identify the location of the palaeochannel, the thickness and width of palaeochannel sand aquifer and to generate a water resource (groundwater quality) map. A secondary, but equally important objective (from a management perspective) was to better understand the connection between aquifers developed in the regolith adjacent to the palaeochannel.
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EARTH’S FIELD NMR FOR REMOTE DETECTION OF OIL UNDER ARCTIC SEA-ICE
Authors Eiichi Fukushima, Andrew McDowell and Stephen AltobelliRemote detection techniques of accidental oil spills under ice are needed to support oil spill response in the Arctic. The various techniques tried so far have not been fully satisfactory. We present preliminary considerations of Earth’s field NMR (EFNMR) from the ice surface for this purpose.
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Uncertainty in Near-Surface Refraction Seismology
By D. PalmerUncertainty in the tomographic inversion of near-surface seismic refraction data can be separated into aleatory variability, which describes the misfit errors and epistemic uncertainty, which describes the suite of acceptable models. Common default implementations of refraction tomography usually focus on reducing aleatory variability and frequently disregard epistemic uncertainty. In this study, the tomograms generated with three models of the seismic velocities in both the weathering and in the sub-weathering, using the generalized reciprocal method (GRM), are consistent with the traveltime data. However, only one tomogram is consistent with the optimum XY value and the attributes derived from the head wave amplitudes and seismic velocities. This study demonstrates that epistemic uncertainty can be explicitly addressed with the GRM, because the most probable tomogram can be selected objectively from a number of acceptable alternatives. The GRM-based tomogram successfully detects, defines and differentiates narrow regions with low seismic velocities which represent shear zones and a massive sulfide ore body. None of these zones is detected with the tomogram generated with the default starting model consisting of smooth vertical velocity gradients. It is concluded that minimizing epistemic uncertainty through the use of the most appropriate starting model is more important than minimizing aleatory variability.
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COMBINING FREQUENCY-DEPENDENT TRAVELTIME TOMOGRAPHY AND FREQUENCY-DOMAIN WAVEFORM TOMOGRAPHY FOR NEAR-SURFACE SEISMIC REFRACTION DATA
Authors Colin Zelt, Jianxiong Chen and Priyank JaiswalSeismic refraction surveys and tomographic methods are commonly used to characterize the near-surface. The advantage of traveltime tomography is its robustness because it uses only traveltimes. Its disadvantage is that it provides relatively low spatial resolution velocity models. The advantage of waveform tomography is its ability to provide high-resolution models. The disadvantage of waveform tomography is its strong dependence on an accurate starting model since it is a very nonlinear inverse problem. The spatial resolution of traveltimes data is related to the Fresnel zone, which can be very wide, whereas for waveform data it is related to the seismic wavelength, typically a smaller length scale by comparison. A new integrated strategy for deriving velocity models from nearsurface seismic refraction data using two complementary tomographic methods is presented.
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FINDING A DEEP BURIED BEDROCK HIGH USING GEOPHYSICS AND REMOTE SENSING AT A FLOOD CONTROL STRUCTURE (DAM) DURING A SUBSIDENCE HAZARD STUDY IN THE DESERT SOUTHWEST
Authors Michael Rucker and Sean HulburtSafety assessment of flood control structures (FRS) or dams located in alluvial basins in the desert southwest commonly includes characterizing the existing or potential future hazard to these structures due to ground pumping-induced subsidence. Differential subsidence can lead to changes in surface hydrology and flood storage capacity, and possible earth fissuring that might cause a piping erosion FRS failure during a flood event. For these studies, the authors typically use deep Wenner array resistivity as a reconnaissance tool to assess compressible basin alluvium and possible relatively shallow (<300 meters depth) bedrock.
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CHARACTERISATION OF BURIED SUBAQUEOUS OUTWASH STRUCTURE BY INTEGRATION OF BOREHOLE AND GEOPHYSICAL DATA
More LessSince 2009, the environment ministry of Quebec (Canada) funded a huge characterization program aiming to improve the knowledge of the groundwater resources throughout the southern part of Quebec. Our research group was mandated to characterize the region of Montérégie Est that covers an area of approximately 9000 km2 at South-East of Montreal. The surveyed area has approximately 577 000 inhabitants, of which 28% use groundwater as a source of supply.
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THE USE OF AIRBORNE EM AS AN AID TO UNDERSTANDING AQUIFERS SYSTEMS IN SOUTH AUSTRALIA’S ARID REGIONS: A CASE STUDY ON THE CAPABILITY OF DIFFERENT SYSTEMS
Authors Yusen Ley-Cooper and Tim MundayThe Musgrave province, located in South Australia’s far north-west, is experiencing accelerated minerals exploration partly in response to new State Government initiatives. Access to water may become a fundamental infrastructure requirement to support developments emerging from these activities. Our current knowledge of the local and regional groundwater systems, the architecture of aquifers, groundwater quality, availability and sustainability is very limited. Current understanding for the area suggests that fractured rock aquifer systems predominate with local palaeovalleys also present. Groundwater is the primary source of water for the indigenous communities and for pastoral purposes. Given its importance for these purposes and given the potential for increased demand, it has been recognised that a more thorough assessment is needed to inform the development of appropriate management policies.
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MOBILE ACOUSTIC SUBSURFACE SENSING (MASS) FOR THE SUBSURFACE PROPERTIES OF PAVEMENTS
Authors Yinghong Cao, Yifeng Lu, Yi Zhang, Gregory McDaniel, Ming Wang and Ralf BirkenSurface waves have been extensively utilized to detect the properties of subsurface materials for geological inspections in many non-destructive testing methods, such as the Spectral Analysis of Surface Waves (SASW) and Multi-channel Analysis of Surface Waves (MASW). In recent years, these stationary measurement methods were also applied to concrete and pavement structures. Most of these implementations are still using contact sensors, such as accelerometers and geophones. The test efficiency is also significantly limited by the conventional inversion algorithms, which were established on the iterative forward analysis with trial solutions. These drawbacks don’t meet the challenges of fast inspection for highway pavements.
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COMPARING SHEAR WAVE VELOCITY MEASUREMENTS FROM MASW AND DOWNHOLE SEISMIC METHODS
Authors Ahmed Ismail, Andrew Stumpf, Neil Anderson and William DeySeismic shear wave velocity profiles were acquired from 10 boreholes in central Illinois and compared to shear wave velocity profiles generated from the multichannel analysis of surface wave (MASW) data acquired at the borehole locations. The main objective was to determine if the shear wave velocity measurements from the MASW are reliable and can be used to characterize the glacial geology in central Illinois. The boreholes penetrated through glacial sediment consisting of multiple units of till, sandy silt, sand and gravel, and silty clay. The downhole data were acquired in PVC-cased holes drilled to depths ranging from 30 to 60 m using a three-component downhole geophone and a surface source. Travel times of the first-arrival seismic waves were analyzed using the direct and interval methods to generate 1-D seismic velocity profiles. The MASW profiles were acquired using 24-channel engineering seismograph with 1.5 m geophone spacing. The data were analyzed to generate 1-D velocity profile at each borehole location. Correlating the velocity profiles from both methods shows that the velocity values compare fairly well and demonstrate that the MASW is a reliable method to measure shear wave velocity of the subsurface materials.
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USE OF ELECTRICAL METHODS TO CHARACTERIZE PREFERENTIAL GROUND WATER FLOW IN ENBANKMENT DAMS
Authors Andre Revil and Abdel JardaniA method is proposed to localize preferential fluid flow pathways in earth dams and embankments based on time-lapse self-potential measurements associated with salt tracer injection upstream. This salt tracer is carried along the ground water flow paths by advection and hydrodynamic dispersion. A network of non-polarizing electrodes located at the ground surface is connected to a highly sensitive voltmeter and used to record the resulting electrical field fluctuations occurring over time at the ground surface. The transport of the salt through the conductive porous materials changes the localized streaming potential coupling coefficient associated with the advective drag of the excess of charge of the pore water and is also responsible for a diffusion current associated with the salinity gradient. Therefore, monitoring of the electrical field at the ground surface can be used to localize a pulse of saline water over time, and to determine its velocity. Possibly in real time This method can be used to track highly localized flow pathways characterized by high permeability that could not be monitored with DC resistivity tomography, which is limited in this regard because of temporal resolution.
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INTERPRETING NUCLEAR MAGNETIC RESONANCE RELAXATION MEASUREMENTS IN UNSATURATED POROUS MEDIA
Authors Sam Falzone and Kristina KeatingNear-surface geophysical applications of nuclear magnetic resonance (NMR) have primarily focused on interpreting NMR measurements under the assumption that the measured volume is fully saturated; however, as NMR is used for a wider set of near surface applications, an improved understanding of NMR measurements of unsaturated porous media will be needed. Our research focuses on using laboratory measurements to understand the relationship between the NMR relaxation time (T- 2) and the water content of unsaturated porous geologic material. A limited number of recent studies have determined how the shape and magnitude of the T2-water content relationship varies with the surface-area-to-volume ratio (S/V) of a porous media. Although it is well known that in fully-saturated porous material T2 is affected by the surface relaxivity (a parameter that quantifies the ability of a pore surface to enhance relaxation) as well as S/V, there have been no studies that explore the effect of surface relaxivity on the T2-water content relationship. We will present results from a laboratory study designed to understand the effect of both surface relaxivity and S/V on the T2-water content relationship.
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UNDERSTANDING THE SPATIOTEMPORAL DISTRIBUTION OF SOIL MOISTURE AT INTERMEDIATE SPATIAL SCALES USING GEOPHYSICAL METHODS
Authors Trenton Franz, Ty Ferre and Marek ZredaThe spatiotemporal distribution of soil moisture is critical for partitioning the water, energy, and carbon cycles at a variety of scales. In drylands, soil moisture is intimately linked to rainfall recycling shown through autocorrelation with future events. In this research, we investigate different soil moisture datasets collected at various scales from the Santa Rita Experimental Range in southern Arizona and Tonzi Ranch in northern California. We will present a series of electromagnetic induction surveys (EMI) that were collected within the footprint of a continuously recording cosmic ray probe (COSMOS). By performing the surveys within a COSMOS footprint we are able to better understand and interpret the information from the less rigorous but data rich EMI surveys. With this spatial information we are able to better understand the controls of topography, texture, and soil depth on the organization of vegetation at the landscape scale. Finally, we are able to quantify the uncertainty and support volume of each instrument through modeling experiments with the goal of obtaining more accurate information about the inferred fluxes.
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Use of Electrical Resistivity Surveying to Evaluate Collapse Potential Related to Road Construction over a Cave
Authors D.W. Lambert, G.L. Adams and B. FodorGeophysical surveying using the electrical resistivity method was used to help determine the potential for collapse that could occur resulting from the construction of a road over a known cave in the City of Kirkwood (City), Missouri. The City is installing a new water main which will require construction of an access road through Koestering Park. Underlying the park is historic Watson Cave, which was mapped in 1961. The width and height of the cave varies and appears to be influenced by the presence of vertical fractures that have been widened by solutioning. The depth to the top of the cave is unknown. Exploration by non-intrusive electrical resistivity surveying was performed rather than drilling or test pit exploration because the City desired to limit damage to the cave and densely wooded areas within the park. Electrical resistivity data were collected using a dipole-dipole array along the proposed road alignment. The data exhibited a valuable signature of a high-resistivity anomaly due to the presence of this cave of known dimensions. Based on the survey results, the depth to the top of the cave was estimated to be approximately 30 feet. Also identified, however, were nine other high-resistivity anomalies (possible voids) along the proposed road alignment. The interpretation of these anomalies, in some cases, suggested possible depths to voids of less than seven feet. It was concluded that the limited traffic loads caused by low speed construction-type vehicles would not significantly increase the potential for cave collapse at Watson Cave due to the approximately 30-foot depth of the feature. However, the interpreted shallower features have a comparatively higher potential for collapse. Recommendations included using a Bailey bridge to span large features and using a geogrid-reinforced crushed rock mat to distribute/dissipate heavy wheel loads over narrower features.
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A COMPARISON OF AEM INVERSION METHODS FOR DISCONTINUOUS PERMAFROST NEAR FORT YUKON, ALASKA
Authors Burke Minsley, Leif Cox, Ross Brodie, Glenn Wilson, Jared Abraham and Micheal ZhdanovPermafrost is a predominant physical feature of Arctic and sub-Arctic regions, and is sensitive to climate change. How warming of the permafrost affects near-surface hydrologic processes, ecosystems, and infrastructure is not clearly understood. A better understanding of the dynamic distribution and physical properties of permafrost, from continuous to discontinuous, provides knowledge of how the permafrost may change in the future and help inform engineering and sustainable management strategies. In June 2010, the US Geological Survey acquired 875 line km of RESOLVE frequency-domain airborne electromagnetic (AEM) data over a ~300 sq. km block near Fort Yukon in Alaska for imaging permafrost characteristics at various scales.
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OPTIMIZING ERT SURVEYS FOR TUNNEL DETECTION
Authors Tomas Goode and Ty FerreWe consider the problem of designing an electrical resistivity tomography (ERT) survey that is best able to discriminate a subsurface target among a population of similar targets. The targets being considered are horizontal buried tunnels with circular cross sections. Potential target tunnels vary in their radius and depth but, they have a constant electrical conductivity. They are evaluated singly, embedded in a homogeneous background with a differing electrical conductivity.
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MONITORING A NOVEL APPROACH TO MONITOR ENHANCED RECHARGE WITH TIME LAPSE GRAVITY
Authors Ty Ferre, Deborah Tosline and Damian GoschWe present work conducted in cooperation with the Bureau of Reclamation as part of their Enhanced Recharge Demonstration Project. The purpose of this project was to monitor the performance of a novel recharge enhancement approach based on diverting water from a main channel through a secondary channel within the floodplain. We located gravity stations along a 75 m transect that was perpendicular to the channels and extended from the midpoint between the main and excavated channels. We monitored over a period of 75 days. During this period, seepage loss measurements and streambed hydraulic conductivity measurements showed decreasing infiltration capacity with time. This response may be due to deposition of fine sediments and/or biological activity. Gravity responses mirrored these changes, showing rapid increases in water mass at early time, followed by a slow, steady decrease in stored mass. In addition, the gravity measurements gave a unique perspective on the extent of lateral movement of infiltrated water. Based on these results, we suggest that gravity monitoring could be a key component of monitoring of water movement adjacent to natural and engineered channels.
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GRAVITY-MEASURED WATER STORAGE CHANGE AND SUBSURFACE HYDRAULIC PROPERTIES AT A MANAGED RECHARGE FACILITY IN TUCSON, USA.
Authors Jeffrey Kennedy, Ty Ferre, Benjamin Creutzfeldt and Andreas GüntnerThe storage of subsurface water is central to Arizona’s future sustainable water supplies. Presently large amounts of water delivered from the Colorado River by Central Arizona Project canals (over 400,000 acre-feet/year permitted capacity) are stored underground at artificial recharge facilities to augment future water supplies. As the demand for Colorado River water increases and the energy required to transport, store, and recover this water becomes more costly, the importance of proper management and siting of recharge facilities increases. In this study, we combine different gravimeters (superconducting, absolute, and spring gravimeters) and advanced analysis methods to improve monitoring of subsurface storage and the characterization of subsurface hydraulic properties at Tucson Water’s Southern Avra Valley Storage and Recovery Project (SAVSARP) infiltration basins.
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SIMULTANEOUS PROXIMAL SENSING OF SOIL PHYSICAL, CHEMICAL, AND BIOLOGICAL PROPERTIES
Authors Erik Lund and Chase MaxtonSoil electrical conductivity (EC) sensing can rapidly delineate areas of contrasting soil properties within agricultural fields. Unless the signal is responding to a dominant soil property such as salinity or claypan, calibrating the signal in farm fields to specific properties has proven difficult. As a result, while the practice of soil EC mapping is receiving widespread acceptance in commercial agriculture, it is being adopted primarily as a soil pattern delineator. Recent advancements in proximal soil sensing allow for the mapping of soil properties such as organic matter using an optical sensor, and pH using an electrochemical sensor, along with soil EC. Also, elevation data from GPS receivers can provide co-located information about the topography of the field. When fields are mapped with all these sensors mounted on one platform, and calibration soil sample data are available, multivariate analysis techniques can be applied to calibrate the sensor readings to specific soil properties. Results from a multi-field, multi-state study show effective calibrations can be accomplished to a variety of soil properties using this sensorfusion approach.
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A SIMPLE AND EFFECTIVE DATA ACQUISITION PLANNING, PROCESSING AND GUIDANCE SYSTEM FOR CONDUCTING PARALLEL SWATH ELECTROMAGNETIC SURVEYS USING GEM 2 IN SUBSURFACE DRIP IRRIGATION MONITORING, POWDER RIVER BASIN, WYOMING
More LessThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2 (Figure 1).
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FIFTH YEAR OF SUBSURFACE DRIP IRRIGATION MONITORING USING GEM2 ELECTROMAGNETIC SURVEYS, POWDER RIVER BASIN, WYOMING
By James SamsThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2.
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UNKNOWN BRIDGE CHARACTERISTICS PROGRAM
More LessThe unknown bridge foundations issue remains one of the most persistent problems facing the bridge engineering community. Bridges are classified as having unknown foundations when the type (spread footing, piles, columns), material (steel, concrete, or timber), dimensions (length, width, or thickness), reinforcing, and/or elevation are unknown (HEC 18). The national cooperative highway research program (NCHRP) Project 21-5 devoted considerable effort in developing new test methods to address this issue and some good progress was reported. However, there are still concerns on the reliability of the available technologies and associated costs.
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A HYBRID METHOD FOR FIRST BREAK AUTO PICKING
By Don ZhaoFirst break picking is a basic procedure in first arrival tomography. There are a few of first break auto picking approaches available, such as energy ratio, AIC, and tracking. These methods work well with noise free data, but applied to field data, none of them are robust and large bias from the desired picks may present. A hybrid auto picking method is proposed. It first uses the energy ratio to generate a sketch of T-X curve, from which a velocity versus offset function is built, then employs AIC approach with the search range limited by the velocity versus offset function, finally adjusts the picks by correlation of the wavelet of adjacent traces. This method is proven by lots of experiments with a variety of data in refraction and cross-well tomography.
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3D GPR Real-Time Automated Detection of Buried Utilities
Authors P. Mazzucchelli, D. Molteni, N. di Buono and E. Cottinomini-trench" technique (addressed in ITU L.83 recommendation) requires that non-destructive mapping of buried services enhances its productivity to match the improvements of new digging equipment. Therefore, the development of a fully automated and real-time 3D GPR processing system plays a key-role in overall optical network deployment profitability. We propose a novel processing scheme whose goal is the automated processing and detection of buried targets, that can be applied in real-time to 3D GPR array system (16 antennas, 900 MHz central frequency). After the standard pre-processing steps, the antenna records are continuously focused during acquisition, by the mean of Kirchhoff depth-migration algorithm, to build pre-stack reflection angle gathers G(x, θ; v) at nv different velocities. The analysis of pre-stack reflection angle gathers plays a key-role in automated detection: by the mean of correlation estimate computed for all the nv reflection angle gathers, targets are identified and the best local propagation velocities are recovered. The data redundancy of 3D GPR acquisitions highly improves the proposed automatic detection reliability. The proposed approach allows to process 3D GPR data and automatically detect buried utilities in real-time on a laptop computer, without the need of skilled interpreters and without specific high performance hardware. More than 100 Km of acquired data prove the feasibility of the proposed approach.
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NEURAL NETWORK AND SUPPORT VECTOR MACHINE CLASSIFICATION OF UXO USING MAGNETICS FINITE ELEMENT MODELING DATA
Authors Matthew Bray, Curtis Link and Clifton YoumansA recently completed Montana Tech study used finite element modeling to calculate magnetic dipole moments for realistic unexploded ordnance (UXO) shapes found at Montana Army National Guard training sites. The modeling approach compared predictions from a simple prolate spheroid model, typical for conventional modeling, with a complex shape constructed using computer aided design (CAD). The complex shapes embody all of the features of the actual UXO bodies. Results showed that the larger, more accurate dipole moments calculated from the complex shape can be used to adjust the dipole moment discrimination level, ultimately reducing the number of targets to be dug.
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CALIBRATING SEISMIC REFRACTION MEASUREMENTS FOR ACCURATE AQUIFER VOLUME ESTIMATION IN A TROPICAL AREA: CAIRNS, AUSTRALIA
Authors Douglas Desper, Curtis Link and Paul NelsonThe Cairns (Australia) Regional Council on Water and Waste is committed to maintaining long term viability of the water supply to the rapidly increasing population of the Cairns region while ensuring a sufficient and safe water supply to maintain the natural environmental values of the rainforests, rivers, and reefs. Currently, the Copperlode Falls Dam supplies the majority of the water to the Cairns region, but this water source will not be sufficient to sustain the projected future growth of the area. The Council is investigating the feasibility of the nearby Mulgrave River Aquifer to supply the future water needs for the Cairns region while at the same time maintaining an equitable distribution of water among domestic, industrial, commercial, and agricultural users.
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MULTIPLE SEISMIC METHODS AND GRAVITY FOR DEFINING THE ANCESTRAL MISSOURI RIVER CHANNEL NEAR GREAT FALLS, MT, USA
Authors Curtis Link and Larry SmithStarting fall 2011 and continuing into spring 2012, the seismic prospecting class at Montana Tech designed and carried out a project focused on defining the preglacial paleochannel of the Missouri river near Great Falls, MT, USA. Although local water well driller’s logs can be interpreted unambiguously to determine presence of the channel, the well control, although dense in developed areas, is sparse throughout the area of interest. Approximate depth to the paleochannel is estimated at approximately 30-100m. As the paleochannel represents a prolific aquifer, there is significant interest in accurately locating it for future development and irrigation use.
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DETECTING BLIND FAULTS USING RAYLEIGH WAVE REFLECTIVITY
Authors Craig Hyslop and Robert StewartFinding faults near the surface is important for construction and engineering applications. It is difficult to locate them because there is often no surface expression, i.e. they are blind faults. We have developed a novel method for extracting Rayleigh wave reflectivity from sharp boundaries and tested it on modeled and field data. Rayleigh waves are particularly suited to detecting blind faults because of their presence extending into the shallow subsurface. Others have studied the complex wavefield due to heterogeneous impedance contrasts in the near surface scattering Rayleigh waves into P, S, and other Rayleigh waves. However, if contrasts are conformed to a boundary, such as a fault, scattered waves give way to reflected waves and a less complex wavefield. To find reflectivity, we determine phase velocity and amplitude for the outgoing Rayleigh wave and deconvolve the reflected wave with the outgoing wave while in a phase matched domain.
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VARIABILITY OF GRM AND REFRACTION TOMOGRAPHY RESULTS EXAMPLE: WATER RESOURCE INVESTIGATIONS IN WESTERN MASSACHUSETTS
More LessFive linear seismic surveys were conducted at the Clark Art Institute in Williamstown, MA to locate water-bearing bedrock fractures. Supply wells and return wells are needed to support an open-loop geothermal system requiring 550 gpm, with future expansion of the system planned.
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UNDERSTANDING GEOLOGIC CONTROLS ON GROUNDWATER USING BOREHOLE GEOPHYSICS EXAMPLE: LANDFILL IN EAST-CENTRAL NEW YORK
More LessBorehole geophysical logging of five bedrock wells was performed as part of a bedrock characterization study in support of groundwater investigations near a landfill in east-central New York. The investigation area is situated within an upland valley. Although the regional hydraulic gradient was generally understood, factors controlling variations in the groundwater flow patterns and potential vertical and horizontal pathways for landfill leachate around the vicinity were not. Contaminants of primary concern within the areas of investigation include VOCs in groundwater at concentrations above drinking water standards.
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ANALYSIS OF THE IVI MINIVIBI PERFORMANCE FOR HIGH FREQUENCY REFLECTION DATA
Authors Craig Hendrix and Richard D. MillerUnderstanding the vibrator-earth response is a pivotal part in addressing problems that decrease the fidelity of vibroseis data. If the vibrator output (ground force) is known, raw vibroseis data can be optimized for resolution and signal-to-noise ratio of the seismic waveform. The source signature, however, is non-unique and varies from shotpoint to shotpoint and from sweep to sweep. Nonlinear complexities within the vibrator’s hydraulic system, tower structure, baseplate flexure, and the ground response to force exerted by the vibrator baseplate increase irregularities in the vibroseis signal. Measuring and analyzing the response of the vibrator baseplate to a specific drive signal can help determine optimal recording positions on the baseplate to recover the ground force signal. When used to correlate or deconvolve raw data, an accurate approximation of the vibrator output will increase data resolution.
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A NOVEL SURFACE NMR PULSE SEQUENCE FOR IMPROVED ESTIMATION OF LONGITUDINAL T1 RELAXATION TIMES
Authors Elliot Grunewald and David WalshObtaining estimates of permeability from NMR methods requires the ability to measure relaxation time parameters that are most sensitive to pore geometry. While surface-NMR (SNMR) measurements can reliably quantify the effective transverse relaxation time T2*, transverse relaxation times are sometimes dominated by the influence of magnetic geology. The longitudinal relaxation time T1 is known to provide a more robust link to pore geometry, but previous attempts to measure T1 by SNMR, have shown mixed success due to fundamental limitations the commonly applied “pseudo-saturation recovery” (PSR) experiment.
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GEOPHYSICAL RESULTS OF MAIN BARTON SPRINGS (PARTHENIA) AND THEIR IMPLICATIONS ON THE GROUNDWATER FLOW PATTERN INTO BARTON SPRINGS POOL, AUSTIN, TEXAS
More LessBarton Springs is a major discharge site for the Barton Springs Segment of the Edwards Aquifer and is located in Zilker Park in Austin, Texas. Barton Springs actually consists of four springs: 1) The Main Barton Springs discharges into the Barton Springs pool from the Barton Springs Fault and several outlets along a fault and from a cave, several fissures, and gravel-filled solution cavities on the floor of the pool west of the fault. The thin-bedded unit on the southwest side of the fault is the regional dense member, and the lower Georgetown Formation of the Edwards Group is exposed on the northeast side of the fault. The offset of the fault is between 40 and 70 feet (12 to 21 m). 2) Old Mill Springs is located in the sunken gardens southeast of the Barton Springs Pool and is primarily fed by relatively mineralized groundwater from the Saline-Line Flow Route. 3) Eliza Springs is also located along the Barton Springs Fault north of Barton Springs pool. 4) The Upper Barton Springs is located upstream of the Barton Springs pool on the south bank.
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GROUNDWATER QUALITY AND GEOPHYSICAL STUDIES IN THE VICINITY OF TAILING PONDS OF THERMAL POWER PLANTS NEAR NAGPUR IN INDIA
Groundwater quality and Geophysical studies have been carried out in a microwatershed surrounding the tailing ponds near Nagpur in India. The study assumes importance in view of the nearby habitations using the groundwater for their drinking requirements. The study area covers approximately 60 sq km. A network of observation wells (23 nos) has been set up for groundwater quality monitoring for the major cations/anions. The results indicate that SO4 concentration has been found to be very high in few wells in the downstream of the tailing ponds. Elevated fluoride concentration (>1.5 mg/L) has been observed in only one observation well.
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Shallow Electrical and Seismic Imaging of The Pineto Mud Volcano (Central Italy)
Authors P. Torrese, M. Rainone, S. Rusi and P. SignaniniShallow underground electrical and seismic imaging was undertaken at the Pineto (Central Italy) Mud Volcano site using 2D-3D electrical resistivity tomography (ERT) and 2D reflection seismic surveys. This mud volcano or mud lump (known by the local population as “Cenerone Mud Volcano”) appears as a dome of about 15x10 m in size. The height is approximately 2 m with a crater 2.5 m of diameter where emission of fluids and solids (cold brine, mud, gas) occurs. Upper Pliocene-Lower Pleistocene foredeep pelitic deposits (clays with silty-sandy levels) overlain by clayey-silty deposits outcrop in the area. Below the Middle Pliocene deposits, a NNW-SSE anticline which runs approximately 2 kilometers to the WSW of the site represents the main element of the compressional tecnonic setting. Ditchs and streams in the area run along fault systems that are oriented NW-SE and NE-SW. These could be related to the upward migration of deep mud fluids. 2D-ERT results were used to determine the geometry of the high conductivity body related to the uprising of mud fluids and detecting changes in deposits. Detailed geometry reconstruction of the shallow upward migration of mud fluids was obtained by using 3D-ERT. A shear wave reflection seismic survey was undertaken to determine stratigraphic limits and to assess the occurrence of fractured zones along which mud fluids could migrate towards the surface. The survey results revealed that the uprising of deep fluids doesn’t occur exactly below the mud volcano at present. Instead, a high conductivity body occurs at approximately 60 m to the ENE, within a fractured zone in the undercompacted clays. The probable occurrence of a high permeability layer approximately between 20 m and 30 m below ground level, confined by clay layers, gives rise to an overpressured mud reservoir. This is the source of mud fluids which flow to the surface through a mud conduit that appears nearly horizontal at depth and then inclined towards the surface up to the mud volcano crater.
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INVESTIGATION OF A COASTAL KARST AREA TO DELINEATE PREFERENTIAL GROUNDWATER FLOWPATHS USING MARINE AND TERRESTRIAL ELECTRICAL RESISTIVITY TOMOGRAPHY
Authors Yvonne O‘Connell, Eve Daly, Garret Duffy and Tiernan HenryA major karst region is located in the west of Ireland in an area comprising the Burren and Gort Lowlands. The geology of this area is dominated by Carboniferous limestones which have experienced extensive dissolution resulting in an underground network of karstified conduits and fissures that define the groundwater flow across the region. In addition, the groundwater discharge to the sea in this area is exclusively intertidal and submarine. Typical winter rainfall conditions result in the karst system becoming saturated. The gradient of groundwater flow is low resulting in temporary lakes (turloughs) in the area acting as large reservoirs which provide storage to enable the transmission of the large volumes of water in the system to the sea.
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EFFICIENT AND SCALABLE ALGORITHMS FOR THE INVERSION OF VERY LARGE AEM DATASETS
Authors Casper Kirkegaard and Esben AukenRecently the standard size of airborne electromagnetic (AEM) datasets has been growing rapidly, while many surveys at the same time focus on modern applications that require very high resolution. Often, the particular target structures of interest cannot be identified directly from the data and approximate inversions or data transform techniques also prove insufficient. This type of application includes environmental studies of aquifers, salinity and geology and also cases of relevance to the mining industry e.g. uranium exploration. In these cases highly accurate full non-linear inversion provides the only reliable solution, which is a computational challenge. In designing an inversion scheme for these types of problems it is further advantageous to utilize as many assumptions as possible. The target structures of interest can often be regarded locally one dimensional, quasi layered and spatially coherent which can be integrated in the inversion. If inverting multiple soundings at a time for a set of spatially constrained 1D models, information is allowed to propagate spatially and a vastly improved model result can be obtained. Ideally, entire surveys should be inverted at a time in huge constrained problems, but poor scaling properties of the underlying algorithms typically makes this impossible.
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COMPARISON OF TIME-LAPSE RESISTIVITY AND WELL DATA IN THE HYPORHEIC ZONE BENEATH STREAMS
Authors Jonathan Nyquist, Laura Toran, David O‘Donnell and Robert RyanCharacterization of the hyporheic zone beneath streams, where surface water and groundwater mix, is critical for understanding stream ecology and contaminant fate and transport. Tracer tests can identify storage zones, but cannot distinguish between tracer lingering in pools and subsurface storage. Wells monitor the subsurface, but prohibitively many may be required to avoid spatially undersampling the plume, and with mixed porosity sediment wells preferentially sample the more hydraulically conductive sediments. Additional information can be obtained by monitoring saline tracer using time-lapse resistivity – continuous spatial coverage and sensitivity to the tracer distribution irrespective of the hydraulic conductivity – at the expense of a more ambiguous interpretation.
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AIRBORNE ELECTROMAGNETIC SURVEYS FOR GROUNDWATER CHARACTERIZATION
Authors Jared Abraham, Burke Minsley, Paul Bedrosian, Bruce Smith and James CanniaAirborne electromagnetic (AEM) surveys provide densely sampled data over large areas (typically several hundred sq. km) that cannot be covered effectively using ground-based methods. AEM data are inverted to estimate the three-dimensional distribution of electrical resistivity structures from shallow depths to several hundred meters. These models convey unparalleled details that are used to make inferences about hydrogeologic properties and processes at the watershed and local scale. This information is being used in groundwater models that are critical to water management decisions, to better understand geologic frameworks, and to improve climate change models. The U.S. Geological Survey (USGS) has been engaged in the application of AEM to many watershed and local scale groundwater projects within United States. We present the results of several frequency- and time-domain AEM surveys acquired by the USGS that have been used for mapping alluvial valleys, buried glacial aquifers, fault-bounded basins, salinity problems, and understanding permafrost distributions.
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EXAMPLES OF THE CONTRIBUTION OF A-PRIORI INFORMATION TO IMPROVING INVERSION OF AEM DATA
Authors Andrea Viezzoli, Tim Munday, Antonio Menghini, Anne-Sophie Hřyer and Esben AukenWe present a simple yet rigorous way of adding a-priori information to inversion of Airborne EM data, using the Spatially Constrained Inversion. Resistivity models are constrained spatially to reflect the lateral homeogeneity expected from the geology. These constraints, that can be considered “soft a-priori”, are fitted together with the AEM data, during the inversion. Moreover “hard a-priori” can be added: they can be, e.g., downhole resistivity logs, geological contacts and layers, hydrogeological units. The a-priori information is treated as an extra data set, by taking into account location, values, uncertainty, and expected lateral variability. The information it contains is spread to the location of the neighbouring AEM soundings. These fields enter the SCI formulations, with the Obs matrix containing the data (AEM and a priori), the Roughening matrix the constraints, the error matrix the uncertainties for all datasets. Constraints and uncertainties are usually different depending on data types and geology. Different datasets, collected by various AEM systems, have been used.
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GROUND PENETRATING RADAR INVESTIGATIONS ON THE RELATIONSHIP BETWEEN SALINITY IN FLUIDFILLED HORIZONTAL SUB-WAVELENGTH ‘THIN-LAYER’ BEDROCK FRACTURES AND REFLECTION AMPLITUDES
Authors Carolyn Tewksbury-Christle and Gregory S. BakerSubsurface fracture characterization is crucial for hydrogeologic modeling as applied to both fresh water resources and contaminant studies. Current methods of fracture geometry estimation for incorporation into groundwater models use cores, boreholes, and surface expression that are extrapolated over the entire study area. Due to the ‘cubic law’ relationship between fracture aperture and discharge—e.g., doubling fracture aperture will result in an eight-fold increase in discharge—there is a critical need to accurately estimate the aperture. Previous theoretical formulations suggested a correlation between ground penetrating radar (GPR) reflection amplitude and fracture aperture as well as groundwater salinity.
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