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21st EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 06 Apr 2008 - 10 Apr 2008
- Location: Philadelphia, USA
- Published: 06 April 2008
81 - 100 of 136 results
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Electrical Imaging Of A Triassic Fault System In Northern New Jersey
Authors Peter J. Hutchinson and Jeffrey M. DereumeContinuous vertical electrical sounding (CVES) imaged early Triassic normal faults on the southeastern side of Mount Arlington Ridge, part of the northeast-southwest trending ridges within the New Jersey Highlands physiographic province of north-central New Jersey. The site had been previously characterized with a regional normal (down to the east) fault, the Longwood Valley Fault that places undefined Proterozoic bedrock units against the sandstone/conglomerate Silurian Green Pond Formation. The sandstone/conglomerates of the older Cambrian Hardyston Formation conformably overlie the Green Pond Formation. The Hardyston with the overlying Leithsville Formation and veneer of Pleistocene-aged glacial deposits comprises most of Long Valley within the study area. CVES profiles collected normal to the Longwood Valley Fault show displacement within the Mesozoic sediments that are beneath the Pleistocene-aged glacial sediments in the contiguous valley. This previously unnamed fault system is termed the Kenvil Works Fault. Further, four or more synthetic faults exist between the Kenvil Works Fault and the Longwood Valley Fault. These faults accommodate right-rotational torsion between the two fault systems. The synthetic faults and Kenvil Works Fault System can act as a migration pathway for the movement of groundwater from the upland impermeable bedrock to the more permeable valley-fill sequences.
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Walsh Transforms For Depth Determination Of A Finite Vertical Cylinder From Its Residual Gravity Anomaly
More LessWalsh functions, which are defined as a set of complete and orthogonal functions of nonsinusoidal waveform, have been used for estimating the top and the bottom depths of isolated vertical cylinder gravity data. Calculating the Walsh transforms for a vertical cylinder, Walsh power spectrum and its analysis proved to be affective in the depths determination. A fully interpretation scheme has been devised from Walsh transforms for the depths determination of a vertical cylinder model. Furthermore, the effect of profile length, sampling interval and noise analysis on the interpretive technique has been investigated. Spectral analysis, which is conventionally referred to the Fourier transform, has been widely utilized for geophysical interpretation. However, Walsh functions, which have only discrete amplitude of +1 and -1, can as well be used in geophysics. Thus, Walsh transform can be implemented for geophysical interpretation which is much faster and simpler than the spectral analysis. A scheme of the interpretation has been applied first to a synthetic data and then to the real data of the famous Humble Dome anomaly to evaluate its validity. The interpreted results of the target showed a good agreement with other published techniques of more commonly utilized methods.
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Field Applicability Of Masw Data
More LessOne-dimensional multi-spectral analyses of surface waves (MASW) are used to predict subsurface shear-wave interval velocities. Shear wave velocities can also extract additional
velocity-related information such as mechanical properties of soils and rocks. In general, MASW data compare favorably to other geophysical methods for predicting interval velocities. Furthermore, comparisons to vertical seismic profiles correlate well with MASW predicted shearwave interval velocities. Over 100 one-dimensional MASW records and 30 vertical seismic profiles in 5 states were collected and compared. Surface waves saturate the geophones (5-foot spread with 5-foot hammer offset) on bedrock and dispersion curves are difficult to evaluate. Consequently, MASW-derived shear-wave velocities are elevated above those derived from down-hole vertical seismic profile methods (VSP). MASW-derived shear-wave velocities collected in areas with a veneer to thick sequences of unconsolidated soil have predicted MASW shear-wave interval velocities that compare favorably to those derived from VSP data.
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Assessment Of Geological Conditions Of Barrage Seat Area Through Seismic Tomography: A Case Study
Authors S.L. Kapil and R. ChandraA hydro power project of 750 MW capacity is proposed on the Tawang Chu river. The Project area lying within the Higher Himalayas is located about 35 Km from Tawang, a district headquarter of Arunachal Pradesh, India. Presently, the project is under active iinvestigation. Seismic tomography was undertaken in April 2007 at one of the proposed location of barrage site, for assessment of bedrock profile and in-situ rockmass properties of barrage seat area. Three drill holes on barrage axis were utilized for taking measurements. Sparker source with TTL triggering system and high frequency active hydrophones were used for signal generation and detection respectively. Data was recorded with Terraloc MK-VI, 48-channel seismograph. More than 2000 ray measurements between the drill holes were taken and data was processed in two stages. Initially, the complete data was utilized for assessment of bedrock profile within the scanned area. In second stage, data recorded within bedrock was analysed and strong evidence of anisotropy was inferred in this data set. Accordingly, inversion was carried out with anisotropy and this reduced the RMS residuals significantly. Seismic tomography provided in-situ characteristics of bedrock and helped in avoiding some of the expensive riverbed drill holes.
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Helicopter Magnetic Survey At The Teapot Dome Oilfield (Naval Petroleum Reserve No. 3) - A Case History
Authors G.A. Veloski, R.W. Hammack, V.W. Stamp, R. Hall and K. ColinaA helicopter magnetic survey was conducted in August 2007 over the 40.5 km2 Teapot Dome Oilfield (Naval Petroleum Reserve No. 3) near Casper, Wyoming. The primary purpose of the survey was to accurately locate wells that had been drilled there during more than 90 years of continuous oilfield operation. The survey was conducted at low altitude and with closely spaced flight lines to improve the detection of wells with weak magnetic response and to increase the resolution of closely spaced wells. The survey was conducted partly in preparation for a planned enhanced oil recovery demonstration that requires a complete well inventory with accurate locations for all existing wells. The magnetic survey was intended to identify wells that are missing from the well database and to provide accurate locations for all wells. The ability of the helicopter magnetic survey to accurately locate wells was accomplished by comparing airborne well picks with well locations from an intense ground search of a small test area. This paper describes the results of the survey.
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A Successful Mixed Land-Underwater 3D Resistivity Survey In An Extremely Challenging Environment In Amazônia
Authors Guilherme P. Castilho and Daniel F.S. MaiaPlanning the best acquisition design for a specific objective is one of the most important phases of the whole acquisition/processing/interpretation process, mainly when it is necessary to surpass the environmental difficulties and the HSEQ issues. This work will demonstrate some of the challenges that had to be confronted in order to conclude a 3d resistivity survey through mixed terrain-underwater environment with rough topography and dense vegetation in Amazonia. It also presents the measures that had to be taken to collect a reliable resistivity dataset. Nevertheless, the survey was successful and subsequent ground-truthing confirmed the impacted areas predicted from the geophysical data.
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Geophysical Investigations Of Earthen Dams: An Overview
Authors Lewis E. Hunter and Michael H. PowersThe Sacramento District U.S. Army Corps of Engineers (USACE) controls 16 dams in the state of California. Three of these dams were classified in the 2006 USACE Screening for Portfolio Risk Analysis as being in Class I or Class II, where the hazards associated with potential failure are considered either urgent and compelling, or urgent, respectively. These dams are Isabella and Martis Creek, both Class I, and Success Dam, identified as Class II. All three dams are earthen structures with either an impervious core or blanket on the upstream toe. Starting in 2005, the USACE teamed with the U.S. Geological Survey in acquiring geophysical data on these dams to provide geotechnical information to be used in assessing the dams and their foundations. The goal of this paper is to provide a review on the status of these surveys, one of which is complete (Success Dam), another underway (Isabella Dam), and a third (Martis Creek) where detailed surveys are planned for the spring of 2008. The techniques being applied include direct current (DC) resistivity, compressional (P) and shear (S) wave seismic reflection and refraction tomography, audio-magnetotellurics (AMT), frequency- and time-domain electromagnetics (EM and TDEM), and self potential (SP). Other techniques are continually being evaluated as project demands change.
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Tight Location Requirements For Geophysical Investigations On Urban Sites Using RTS
Authors Sandra Takata, Mark Kick, Lester Tyrala, Martin Miele, Colin Chang and Sally LambFor geophysical surveys, the accurate location and documentation of measurement points, lines and features in densely-built areas with limited survey control and sky-view is challenging. Yet in the present day, urban sites containing numerous obstructions are more often the norm for geophysical applications. Historic site information may span generations of data ranging from as-designed drawings to generated 3-D plans. Frequently, each dataset is probably in different coordinate systems with widely differing accuracies. Using a robotic total station (RTS) theodolite for survey location/navigation control has significant advantages over conventional gridding, tick wheel, and global positioning system (GPS) techniques including:
Survey-grade X,Y,Z precision
In-field verification of positional accuracy
Operation wherever line-of-sight can be established
Data collection directly in agreed-upon or convenient coordinate systems
Locations are continuously streamed by radio-link to geophysical loggers/equipment
Remote-control RTS operation
Follow-up relocation independent of changing ground conditions
Geophysical survey and utility mapping results from five “urban” sites are presented illustrating typical location/navigation problems, collection of high locational accuracy survey data around complex structures, and considerations for survey planning, design, and reporting.
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Geophysical Characterization Of A Levee With Dc Resistivity And Electromagnetic Measurements
A geophysical characterization of a portion of American River levees in Sacramento, California was conducted in May 2007. Targets of interest included sand lenses that
underlay the levees and the depth to a clay unit that underlies the sand. The concern is that the erosion of these sand lenses can lead to levee failure in highly populated areas of
Sacramento. DC resistivity and electromagnetic surveys were conducted over a 6 mile length of the levee on roads and bicycle and horse trails. 2-D inversions were conducted
on all the geophysical data. The OhmMapper and SuperSting surveys produced consistent inversion results that characterized the targets of interest. GEM-2 apparent resistivity data were consistent with the DC inversion results. However, the GEM-2 data could not be inverted due to large system drifts. While this would not be as large a problem in conductive terrains, it is a problem for a small induction number electromagnetic profiling system such as the GEM-2 in a resistive terrain (the sand lenses). Despite issues with the GEM-2 inversion, this geophysical investigation was successful in detection of the sand lenses and the depth to the clay zone of interest.
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Comparison Of Airborne Magnetic And Electromagnetic Systems For Ordnance Detection And Mapping
Magnetic and electromagnetic data collected by helicopter boom-mounted systems at the same survey sites permit direct comparison of the systems as to their suitability for buried ordnance detection. The ORAGS-TEM system is an airborne electromagnetic system developed specifically for unexploded ordnance mapping and detection. Although airborne boom-mounted magnetic systems are at a more advanced stage of development than their electromagnetic counterparts, in basaltic terrain, electromagnetic systems have proven capable of detecting buried ordnance, whereas magnetic systems sometimes fail altogether. Magnetic systems use passive sensors and these can be distributed along the boom structure such that dense data can be collected with sensors spaced 1-2 m apart over a broad swath, up to 12 m wide. Current airborne electromagnetic systems are unable to match this data density. The ORAGS electromagnetic system, having only two receivers, must rely on interleaved flight lines to obtain data of a spatial density approaching that of the airborne magnetic systems. Active electromagnetic fields decay at greater rate than magnetic fields, and this constrains current electromagnetic systems to practical survey altitudes of no more than about two meters for ordnance detection. Tests at the Badlands Bombing Range indicate that in some circumstances, the signal-to-noise for the ORAGS electromagnetic system exceeds that of airborne magnetic systems.
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Using Ground Based Geophysics To Evaluate Hydrogeologic Effects Of Subsurface Drip Irrigation Systems Used To Manage Produced Water In The Powder River Basin, Wyoming
Authors ames I Sams III, Brian A. Lipinski and Garret VeloskiThe U.S Department of Energy’s National Energy Technology Laboratory has been evaluating various geophysical methods for site characterization regarding environmental issues associated with fossil fuels including produced water management. A relatively new method of managing produced water from coal bed natural gas production is through subsurface drip irrigation. This system involves disposing the produced water near the bottom of the root zone in agricultural fields, which would provide a beneficial use of this resource. The focus of this paper is to present results from a pre-injection geophysical survey for site assessment and background data. A pre-construction survey of approximately 1.2 km2 was completed in June 2007 using a Geophex GEM-2 broadband sensor over six fields along the Powder River floodplain. Quality assurance measures included drift checks, duplicate line surveys, and repeat field surveys using the Geometrics OhmMapper instrument. Subsequent surveys will be completed once the system is installed and operational. Geophysical inversion models were completed to provide a detailed cross-section of the subsurface geoelectrical structure along each line. Preliminary interpretations reveal that the subsurface conductivity distribution correlates to geomorphologic features.
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Imaging Dispersion Of Passive Surface Waves With Active Scheme
More LessIn passive surface-wave surveys under urban environments there is usually one surface location from which a major portion of the surface wave energy—used for the dispersion analysis—originates. This is similar to an active survey, in which exact relative coordinates of both source and receivers are known prior to data processing. Using a method that scans through all possible incoming directions of those passive surface waves, the azimuth of the responsible source point can be estimated fairly accurately, especially when a method employing an integral approach for the calculation of surface wave energy at a particular azimuth and phase velocity is incorporated. Then, along with the distance information that only needs to be estimated very roughly, the passive data set can be processed by any active scheme. Key concepts are explained using both synthetic and field data sets, with comparisons made to some of the existing methods.
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Distinguishing Between GPR Subsurface Reflections And Surface/Air Waves At Cluttered Urban Sites
More LessAt sites where relatively deep exploration is desired for GPR, 100 MHz or lower frequencies are required. These large antenna are either unshielded, or their shielding is not 100% effective, allowing radiation to escape parallel to the earth’s surface in all directions. At typical industrial sites with linear or planar grounded structures, such as power lines, chain-link fences, railroads, and metal-sheathed buildings, reflections of the air and surface waves are common. While the experienced user can recognize many of these events on a profile, particularly those reflections returning from directly in front of, and from behind the antennas, the patterns from lateral reflectors whose distance from the survey line is not constant may be mistaken for real undulating subsurface reflectors. The early use of true CMP or expansion surveys is used to recognize which reflectors on the GPR display are actually from the subsurface. The horizontal reflections arrive at nearly constant times at all expansions regardless of their direction from the center of the CMP survey, while the true geologic reflections arrive in the expected half-hyperbola pattern. An example from Michigan is shown, where only two shallow reflectors were found to be valid using the CMP, while the profiles showed numerous other realistic apparent deep reflections.
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Multiple Frequency Electromagnetic Response Of The Dispersive Layer
Authors Zeng Zhaofa, Liu Fengshan, Sun Jiguang and Liu CaiThe electromagnetic (EM) detection method with the frequency between Transient Electromanetic method TEM) and ground penetrating radar (GPR), has a wide potential application in engineering and environmental geophysics. The study on the method mostly based on the real dielectric and conductivity. Unfortunately the surface medium such as soil and water saturated rock is mostly frequency dispersive medium. In this paper, we simulate electromagnetic response of the near-surface layer medium using Cole-Cole model and Debye model. Our algorithm use the high density sampling filtering since it has advantages on efficiency and accuracy over linear filtering and Chave’s Gauss integration algorithm. From the simulation we can clear see different response of the dispersive layer from the non-dispersive layer which may play an important role in data inversion.
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An Integrated Geophysical Approach For Groundwater And Seismic Hazard Management In Joshua Tree National Park, Southern California
Authors Darcy K. McPhee, Victoria E. Langenheim, Bruce A. Chuchel and Louise PellerinTwo-dimensional inversion of audiomagnetotelluric (AMT) sounding data define buried resistivity distributions that reflect subsurface geology and structure within the upper kilometer beneath Pleasant Valley, a 1-2 km-deep pull-apart basin in Joshua Tree National Park, southern California. The Park lies within the Eastern California Shear Zone just east of the San Andreas Fault, and is surrounded by developing desert communities. Understanding the subsurface in and around the Park is important for management of groundwater resources, for mitigation of seismic hazards, and for unraveling the tectonic evolution of the region. Our resistivity models, interpreted in conjunction with gravity inversions, show transitions between coarse-grained and fine-grained alluvium, resistive (> 400 ohm-m) crystalline rocks, and the locations of range-front and intra-basin faults.
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A Quadrature Approach To Detection, Localization And Estimation Of Magnetic Dipoles
We describe a matched filter algorithm for detecting, locating and characterizing magnetic dipoles. The matched filter operates on an array of vector magnetic field measurements
at an arbitrary set of orientations and points in space. For a given dipole location, the algorithm finds a best-fit magnetic dipole moment by projecting the N-dimensional vector representing the magnetic measurements onto the three-dimensional subspace spanned by the calculated data vectors for all possible magnetic moments at that location. It then varies the dipole location to find a best global match between the calculated and measured data. This approach, which is analogous to quadrature decomposition of a signal into sine and cosine components of a given frequency, removes the need to search exhaustively through all possible magnetic moments at each trial location. The algorithm provides optimal detection of a magnetic dipole in a background of white Gaussian noise, and unbiased estimation of the location and vector moment of an isolated dipole within the spatial sampling resolution defined by the user. An application to UXO is demonstrated using a moving magnetic tensor gradiometer to detect and localize inert artillery shells. The extension of the algorithm to active EM systems is explored in theory and computer simulations.
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VSP And Well Logs From A Shallow Test Well
Authors Joe Wong, Soo K. Miong, Laurence R. Bentley and Robert R. StewartShallow VSP and geophysical well logging surveys were undertaken in a 127 m-deep well drilled at the Rothney Astrophysical Observatory site near Priddis, Alberta. The well was drilled through interbedded sands and shales of the Tertiary Paskapoo formation. A suite of geophysical well logs (including natural gamma-ray, single-point resistance, focused-beam resistivity, density, neutronneutron, caliper, temperature, and SP) was acquired in the open hole immediately after drilling. After PVC casing was inserted into the well and grouted to the formation rocks, we obtained natural gammaray and full-waveform sonic logs. The logs were useful for delineating the sandstone and shale beds, and for providing hydrogeological information at the well site. For the VSP surveys, we used a 5.5 kg sledge hammer source with a downhole clamping 3C geophone. From the full-waveform sonic logs and VSP data, we determined P-wave velocities to lie between 1.7 to 3.0 km/s. Standard VSP processing resulted in a corridor stack of up-going reflections that correlate reasonably well with a 1-D synthetic seismogram constructed from the density and P-wave velocity logs.
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Watershed Characterization For A Water Resource Decision Support System In Honduras
Authors Weldon W. Hammond Jr., Louis R. Manz, Ronald T. Green and Omar A. Andino CruzWatershed characterization studies in southeastern Honduras are being conducted by the Center for Water Research at the University of Texas at San Antonio (UTSA), the National Autonomous University of Honduras and several non-governmental entities. The major emphasis of these studies is the application of a Decision Support System for Village Water Resources (DSSVWR) developed as a research project at UTSA to determine sustainable water supplies in remote areas of Honduras. In order to quantify water resources available on a seasonal basis, drainage basins were delineated and will be characterized by precipitation, runoff characteristics, soil type, land use and geology. Drainage basins are being studied for potential groundwater yield from extensive Miocene ignimbrite sequences and alluvial deposits in numerous structural and erosional valleys. Two types of regional aquifers were identified: (i) ignimbrite sequences with low potential yields and (ii) excellent alluvial aquifers in valleys. Groundwater investigations included geophysical resisitivity surveys. Because of the heterogeneous nature of both the ignimbrite sequences and the alluvial deposits variations in the geoelectrical properties of these units in the subsurface can be used to interpret depth to water table. Results from these hydrologic studies will be used in the DSSVWR to estimate yields on a seasonal basis from various sources for individual watersheds in rural Honduras.
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Submarine Slides At Finneidfjord (Norway): Geophysical Investigations
On June 20th, 1996, a submarine land failure in a fjord near the village of Finneidfjord (Northern Norway) developed into a retrogressive quick clay slide encroaching 100-150 m inland, resulting in the loss of life and significant material damage. Reports in the aftermath of the slide concluded that build up of excess pore pressure may have been the main reason for the slide, though other causes are invoked too. The geological settings at this location involve many of the processes typical for large offshore slides. As the fjord is sheltered and accessible, this location is ideal as a field laboratory for studying submarine slide hazards. Such a project for evaluating instrumentation and site investigation techniques for studying submarine slope stability was initiated in 2004 by the International Centre for Geohazards (ICG, Oslo). Initial field campaigns since 1997 have consisted of sediment coring, VHR seismic surveys, and the deployment of long term in situ instrumentation. A larger campaign is planned in 2008, including shear-wave acquisition, and, to support that campaign with land data, several geophysical investigations were carried out onshore in July 2007 in cooperation with the University of Strasbourg. The field studies have included several students to train them in field practice. Seismic, GPR and
resistivity investigations were all carried out, and preliminary results are presented.
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Ground Truth Verification Of An Integrated Geophysical Investigation For The Assessment Of An Earthen Levee
We proposed an integrated geophysical technique to assess the vulnerability of earthen levees to flooding and earthquakes. The geophysical technique mainly consists of multi-channel surface wave dispersion measurements (MASW) using Land Streamer, capacitively-coupled resistivity (CCR) measurements, and additional multi-frequency electromagnetic (EM) survey. The effective performance of field measurements using these methods is assured because sensors are not fixed on the levee surface. The geophysical properties evaluated by these methods, resistivity and S-wave velocity, are essential to evaluate the permeability and stiffness of the levee body. We also demonstrated the usefulness of crossplots of the measured data as criteria for the assessment of levee conditions. However, the collection of ground truth data is imperative for the validation of the criteria. Consequently, we then conducted detailed field measurements at an open-cut of an earthen levee on which the integrated geophysical survey had been applied. The investigated levee, which runs along the right bank of
Chikuma River in central Japan, was damaged by a high water event in 2006. In addition, open-cut work was planned within the surveyed line to replace an old sluice. We therefore could observe the internal structure of the levee and take samples of levee materials for grain size analysis at the open-cut. In conclusion, the mapped resistivity profile was concordant with the surface survey results. Moreover, a clear relationship was recognized between grain size and measured resistivity. We interpreted the high resistivity anomalies in the levee body detected by means of surface geophysical survey as potential high-permeability zones. Actually, seepage was observed along the rear slope of the levee just in anomaly zones delineated by the integrated geophysical investigation.
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