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23rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 11 Apr 2010 - 15 Apr 2010
- Location: Keystone, Canada
- Published: 11 April 2010
41 - 60 of 131 results
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Integrated Three Dimensional GPR And EM Study Of Three Large Water Supply Pipes
Authors Steven P. DiBenedetto and Heron R. MochnyA new 16-inch municipal water supply line is to be installed between two siphon chambers in the right-of-way (ROW) of three very large diameter (9+ft) steel water supply conduits in the northeastern United States. While excellent as-built records of the conduits were available, given the age of the infrastructure, exact surveyed locations of the large water supply pipes were unknown within the ROW, and were required during the design phase of the project in order to safely perform geotechnical borings and facilitate the routing of the installation trench for the 16-inch line. Additionally, the mapping of any underground utilities within the ROW and adjacent to an existing pump station was required for design in advance of excavation and construction activities relating to the expansion of the pump station. A geophysical survey was performed by Underground Imaging Technologies, Inc. (UIT), acting as a subcontractor to Malcolm Pirnie along the ROW in order to determine the precise location of the large water supply pipes and also the locations of any underground utilities or other subterranean features that may interfere or otherwise impact the installation of the new waterline. Multi-channel Ground Penetrating Radar (GPR), multi-sensor Time Domain Electromagnetic Induction (TDEMI) and a Ground Conductivity Electromagnetic (GCEM) survey was performed to obtain the requisite data. The geophysical survey was performed between May 19th and 22nd, 2009 and over 182,000 square feet were surveyed. The results of the geophysical survey were able to accurately determine the horizontal positions and depths of the water supply pipes throughout the investigation area, in addition to mapping the positions of utilities in the vicinity of future construction for a pump station upgrade. Several geological anomalies were detected that warrant consideration in any excavation or construction activities. Depth below ground surface of the pipes obtained via GPR was converted to elevation by subtracting from USGS 10m DEM ground surface elevation. This allowed for the construction of a fully georeferenced, elevation-based, three-dimensional digital model of the pipes within the investigation area in AutoCAD.
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Continuous Exploration Ahead Of The Tunnel Face By Tswd - Tunnel Seismic While Drilling
Authors Ewald Brückl, Werner Chwatal, Stefan Mertl and Alexander RadingerSeismic measurements using the VSP principle have been carried out for over 20 years to investigate the rock ahead of a tunnel face and made a contribution to reduce the risks during construction for conventional tunnelling, as well as for tunnelling with a Tunnel Boring Machine (TBM). However, reflecting horizons intersecting the tunnel axis obliquely cannot be imaged at their intersection with the tunnel. This circumstance imposes a major uncertainty on the prediction of the geological situation ahead of the tunnel face. A possibility to image all reflecting horizons, regardless of their orientation, at least near to their intersection with the tunnel axis is offered by continuous monitoring with the drilling head of a TBM as the seismic source (Tunnel Seismic While Drilling - TSWD). In this study we present continuous TSWD data from a gallery drilled in limestone and dolomite of the Northern Calcareous Alps, Austria. This gallery intersects a deeply incised valley, filled with sediments. The two main goals for the processing were the derivation of high signal to noise seismograms from the pilot and receiver signals and the removal of the first arrivals from the data in order to uncover reflected phases, even from reflectors very near to the TBM drilling head. Both goals were achieved satisfactorily and the main geological structure was well resolved. Geophysical issues which need further investigation are addressed. The results of our study suggest that substantial risk reduction could be achieved by continuous TSWD. However, the high production rate of modern TBMs imposes a major challenge on real time monitoring, processing and prediction.
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Geoelectrical Imaging For Detection Of Water Migration In A Bioreactor Landfill
Authors Håkan Rosqvist and Torleif DahlinIn this paper we describe field investigations of leachate recirculation at a bioreactor landfill using geoelectrical imagining technique (i.e., electrical resistivity) combined with a tracer test. The use of geoelectrical imagining techniques is an established practice for environmental investigations and monitoring of various landfill processes and in recent years also the bioreactor landfill concept has been emphasised. In the study, the electrical resistivity technique was evaluated and the possibility to detect water and gas migration in the waste mass was investigated. Results showing moisture migration through the bioreactor landfill, during leachate flushing and during a tracer test, are presented. Also results indicating the resistivity technique being useful for biogas detection are shown.
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An Evaluation Of The Potential Of The Geoelectrical Resistivity Method For Mapping Gas Migration In Landfills
Authors Håkan Rosqvist, Virginie Leroux, Torleif Dahlin, Sara Johansson and Mats SvenssonMethane is a powerful greenhouse gas and growing concern regarding global climate changes over the last years has pointed out the need to quantify and control the leaking of methane into the atmosphere. Landfill gas is regarded as one of the major sources for methane migration to the atmosphere. In this study we present research work with the objective to evaluate the use of geoelectrical resistivity to detect gas migration in landfills. Extensive field experiments were conducted at the Filborna landfill site in Helsingborg, Sweden, in August 2008. In general, the resistivity measurements showed results corresponding to results reported from previous investigations in waste. However, also large variations in resistivity were indicated. Relatively high variability and high mean resistivity in the surface-near layers clearly indicate influence on the resistivity in the upper zone of the landfill. The variability and high resistivity may partly be explained by appearance and migration of landfill gas.
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Case History: Monitoring Resin Injections With The Aid Of 4D Geophysics
Authors Justin B. Rittgers, Phil Sirles, Gianfranco Morelli and Marco OcchiGround improvement is an important practice in areas where the combined presence of expansive soils and fluctuating moisture content often result in differential heaving and settling soils and variable confining forces exerted on foundations. In fall of 2009, three-dimensional (3D) seismic pressure wave (p-wave) refraction and 3D electrical resistivity tomography (ERT) surveys were performed to determine the effectiveness of seismic refraction tomography in imaging the permeation of resin injected during ground improvement efforts within problematic soils. A test site near Piacenza, Italy was selected for this undertaking: Data were collected around the perimeter of an existing house suffering damage due to differential ground settlement. Three independent yet identical surveys were conducted using both methods, producing 3D images of the spatial distribution and variations in subsurface material properties before, during and after resin injection. The site is underlain primarily by a two to three meter thick layer of silt and clay with some sand lenses over an alluvial silty sand base layer. Prior to resin injection, substantial variations in both electrical resistivity and p-wave velocity are evident beneath the particular corner of the structure that exhibits the highest extent of damage (e.g., cracking and settling). During and after resin injections and curing, resistivities and velocities can be seen to change in the surrounding vicinity of injection points, and the magnitude of change in both data sets appears to be related to the amount of resin injected at each point. Geophysical measurements confirm the heterogeneous nature of the near-surface soil at this site, results from both methods correlate well with each other and additional field data (i.e., CPT data), and resultant 3D models are clearly useful in siting injection points as well as time-lapse monitoring the extent of resin permeation.
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Identification Of The Polaris Fault Using Lidar And Shallow Geophysical Methods
Authors Lewis E. Hunter, Michael H. Powers and Bethany L. BurtonAs part of the U.S. Army Corps of Engineers’ (USACE) Dam Safety Assurance Program, Martis Creek Dam near Truckee, CA, is under evaluation for earthquake and seepage hazards. The investigations to date have included LiDAR (Light Detection and Ranging) and a wide range of geophysical surveys. The LiDAR data led to the discovery of an important and previously unknown fault tracing very near and possibly under Martis Creek Dam. The geophysical surveys of the dam foundation area confirm evidence of the fault in the area.
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Internal Structure Of An Ilmenite Mine Waste Rock Pile Modelled From Ip Imaging And Laboratory Measurements
Authors Michel Chouteau, Rachid Intissar and Michel AubertinNickel concentrations occasionally above the allowed norm have been measured in water samples in the vicinity of the Petitpas waste rock pile at the Tio mine, Québec, Canada. In order to understand the chemical and hydrodynamic mechanisms responsible for the nickel dissolution and release in the environment a large hydrogeological/geotechnical/geophysical study was undertaken on the very large rock pile (600 m x 300 m x 150 m). Geotechnical and physical properties were measured in the laboratory on samples of waste with various moisture content and salinity. Induced polarization allowed the determination of electrical resistivities and chargeabilities that were to be used to interpret time-domain IP tomography surveys carried out on the waste rock pile. IP survey data were inverted in 2-D. The resistivity models for all survey lines show common features. From surfae to 25-30 m depth, the subsurface is resistive and show lateral changes which suggests large grain size heterogeneities and low water content; below and up to 50 m, a quasi uniform layer with resistivities in the range 50-250 ohm.m suggests fine-grained material with increased saturation. Finally below a depth of 50 m, the subsurface becomes very resistive again, indicative of coarse low-moisture content material. The chargeability model shows no structural correlation with the resistivity model. In general, chargeabilities are very large (up to 100 mV/V) and show no layering. From the laboratory and the survey results, we interpret the resistivity to be sensitive to water content and salinity while chargeability is sensitive to the metal concentration. The geoelectrical model and the interpreted hydrogeotechnical model will be useful for modeling water flow and reactive transport through the waste rock pile.
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Mapping Bedrock Topography Beneath Glacial Overburden Near Cape Horn, South America
More LessPlacer gold mining operations were carried out on several of the small islands between Tierra del Fuego and Cape Horn in the late 1800’s, just before the Klondike gold rush. As soon as the Klondike rush was announced to the world many of the miners and prospectors working in this isolated region went north. The area was quiet for nearly a hundred years before there was any renewed interest in it. This was due to the dispute between Chile and Argentina over ownership of these islands. Although the Chilean government was eventually granted ownership of these islands it is only recently that any exploration activity has occurred. A placer gold exploration program that included surface sampling, geological mapping and bulk sampling was carried out in the early 1990’s. The project looked promising but there was difficulty in unravelling the glacial history and obtaining estimates of gravel thickness for tonnage calculations. Bemex Consulting International was asked to set up a program to map the bedrock topography and estimate gravel thickness. The project was carried out in two phases. The first phase was carried out during the summer season (December) to determine if time-domain EM soundings would provide the necessary accuracy to meet the above objectives. At the end of this phase the conclusion was the Geonics EM-47 system was capable of mapping the gravel thickness and bedrock topography. The second phase was conducted the following summer (January and February) and consisted of carrying out more than two hundred 40 m x 40 m loop soundings at the site. The results of this survey were verified with a series of manholes dug to depths varying from 15 m to more than 30 m. The depth to bedrock in these holes was consisted with the 1D interpretation provided from the Interpex software.
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Earthquake Hazard Maps Of The City Of Ottawa, Canada, Using Near-Surface Geophysical And Geological Methods
The city of Ottawa, Ontario, Canada, is in an area of elevated earthquake shaking hazard and is considered to be the Canadian city third-most at risk to damage (after Vancouver and Montreal). Maps showing regional variation of Vs30, fundamental site period, and an example map of the spectral accelerations at Sa=0.2s have been completed for the city at a reconnaissance scale. These have been developed from combined geological information from ~21,000 boreholes (water wells and geotechnical borings) within the city limits as well as ~700 surface and borehole shear wave seismic measurement sites. Borehole and surface shear wave measurement techniques developed for the operational area included: surface reversed refraction and reflection sites, MASW, downhole shear wave and horizontalto- vertical spectral analyses of ambient noise. The surficial geology was subdivided into three basic units based on their geotechnical properties: (i) soft, fine-grained, post-glacial sediments, (ii) glacial till and coarse-grained, till-derived sediments, and (iii) firm Paleozoic and PreCambrian bedrock. A series of shear wave velocity-depth functions were assigned to each borehole based on interpolation from proximal geophysical sites. The resulting three-dimensional shear wave velocity database was then used to determine parameters such as Vs30 and fundamental site period. The Vs30 map of the city is subdivided in terms of the U.S. National Earthquake Hazard Reduction Program (NEHRP) zones which have been adopted by the 2005 National Building Code of Canada. Since the City of Ottawa has a large areal extent and is close to the West Quebec Seismic zone, the base accelerations for the 2% in 50 year
earthquake event vary extensively within the city boundaries. Hence an example map of the spectral accelerations at Sa=0.2s has been developed to demonstrate regional variations and the effects of NEHRP zones.
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Finding Faults Using High-Resolution Aeromagnetic Data In Great Sand Dunes National Park And Vicinity, San Luis Valley, Colorado
Authors V.J.S. Grauch, David V. Fitterman and Benjamin J. DrenthHigh-resolution aeromagnetic data reveal faults near the Great Sand Dunes National Park and Preserve (GRSA) and vicinity that offset both bedrock and sediments, even under the dunes themselves. Complicated fault patterns evident in the aeromagnetic data over the exposed range front may represent multiple-age events. The range-front and parallel faults to the west together suggest that basement steps down along high-angle faults. A prominent linear feature parallels the range front from the dunes southward (“the parallel fault”). Preliminary analysis suggests that the top of the parallel fault is about 50-70 m deep, with near-vertical dip, and offsets sediments with differing magnetic properties as well as basement rocks at greater depths. In places, it is paralleled by less prominent aeromagnetic features, which may also be faults. TEM soundings across the parallel fault indicate that sediments juxtaposed there contain abundant clay to the west and mostly sand to the east. The clay-rich sediments are underlain by eastward-shallowing sand at depth. This result suggests that the eastern limit of the confining clay in this area is fault-bounded at shallow depths and may be interfingered with sand at greater depths. These relations have implications for groundwater modeling, geologic studies, and seismic hazards.
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Airborne Full Tensor Gravity
Authors John H. Mims and James MataragioThe gravity tensor measures changes in the three dimensional gravity field along the three axes of motion, giving a nine component array of differentials. Because of symmetry and the Laplacian character of gravity, only five of the components are independent. Gravity has been used for resource exploration since the early 20th century. The first exploration gravity surveys used a ground based gradiometer that was eventually replaced with ground based gravimeters. In the late 20th century, a moving platform full tensor gradiometer was developed for use on submarines. Eventually the technology was declassified and applied to commercial resource exploration using marine and airborne acquisition. Since much of acceleration caused by the vessel motion is removed as the gradient is being measured, the gradiometer can provide a high resolution gravity image in a fraction of the time it takes for an equivalent ground gravity survey to be completed. A case study of alluvial diamond exploration provides one example of using airborne gravity gradiometry for resource exploration.
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The Falcon Airborne Gravity Gradiometer For Engineering Applications
Authors Greg Hodges, Mark H. Dransfield and Tai-chyi SheiWhile airborne gravity has been available for decades, only with the advent of airborne gravity gradiometry (AGG), and specifically the FALCON AGG installed in a helicopter, has airborne gravity measurement reached a sensitivity and spatial resolution that can be effective for a wide range of engineering applications. Survey examples and gravity models comparing fixed-wing and helicopter AGG measurements demonstrate that voids as small as 10 m, or tunnels of 4 m width can be detected.
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Airborne EM Data Complement Magnetics In An Unexpected Way
In the fall of 2008, a low-altitude airborne geophysical survey was carried out at a military installation in Australia, the primary goal of which was detection and mapping of infrastructure, buried wastes, and other buried and surface metallic objects within a 1738 hectare area. The primary survey system was the Battelle VG-16 vertical magnetic gradient system. Because the base is active, the time frame for conducting the survey was limited to a few weeks. The short time frame and the added expense of an additional system were factors against adding on an electromagnetic survey. However, the Australian Department of Defence suggested that there might be non-ferrous targets of significance that the magnetic system would not detect. Moreover, the base was located some tens of kilometers from a field of extinct volcanoes, presenting the possibility of magnetic geology in the form of mafic igneous units. Therefore, it was determined that an airborne transient electromagnetic system should be included in the project. The added electromagnetic system proved valuable, but not in the way that was expected. Concentrations of strong anomalies appeared in the magnetic data, the sources of which could be either buried debris or geological. The TEM-8 system was flown over some of the more dense concentrations of magnetic anomalies. In some of these areas the TEM data showed very few anomalies, indicating that either the VG-16 anomalies are associated with magnetic rock types, or that the metallic sources detected by the VG-16 system are too deeply buried to be detected with the TEM-8 system. A few carefully located excavations indicated that the sources of the magnetic anomaly concentrations without associated electromagnetic anomalies were localized concentrations of very magnetic iron-bearing rock.
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Mapping Epikarst In The Arbuckle-Simpson Aquifer, Southcentral Oklahoma, Using Helicopter Electromagnetic Survey Data
Authors David V. Smith, Maryla Deszcz-Pan and Bruce D. SmithThe U.S. Geological Survey has been actively using helicopter electromagnetic surveys over karstic aquifers as part of on-going research to aid in the creation of highly detailed three-dimensional geologic models. The geologic models are the basis for understanding the geohydrologic framework of the aquifers, and they provide essential information needed for groundwater models used to manage an increasingly important resource. As part of this research, the USGS has developed and applied methods for mapping epikarst, which plays an important role in groundwater recharge. A case study in the Arbuckle-Simpson aquifer in south-central Oklahoma is presented here.
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Hydrogeophysical Surveys Of The Trinity And Edwards Aquifers At Camp Bullis, Northern Bexar County, Texas, 2006
Authors Jason D. Payne, Bruce D. Smith and Allan K. ClarkIn 2002, the U.S. Geological Survey (USGS), in cooperation with the U.S. Army, began hydrogeologic studies of Camp Bullis in northern Bexar County, Texas, with mapping of hydrogeologic features and hydrostratigraphic units (Clark, 2003) at a scale of 1:24,000. In 2003, a USGS-contracted helicopter electromagnetic (HEM) resistivity and magnetic survey was flown over Camp Bullis and the adjacent Camp Stanley (Figure 1). This paper describes the integrated ground electrical and electromagnetic geophysical surveys that were conducted in 2006 in order to follow up on the previous studies and to map hydrogeologic features in more detail. The goal of the project is to better understand the hydrogeologic framework and structure of the Trinity and Edwards aquifers within the study area. The Edwards aquifer is classified as a sole-source water supply for the city of San Antonio.
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Subsurface Imaging Of Karst Geology For Energy Infrastructure Expansion
Authors John A. Mundell and Gabriel J. HebertThe development of building infrastructure on top of karst geology always presents challenges and has the potential for catastrophic failure. Recently, an electrical substation located in southern Indiana known to sit atop potentially karstic limestone was scheduled to be expanded onto an adjacent 10-acre parcel. A standard preliminary geotechnical investigation consisting of 18 soil borings with three rock cores conducted across the parcel indicated that although the bedrock was slightly to moderately fractured, it was sufficiently competent to build upon. However, the presence of several active sinkholes across the parcel led the local electrical power company to request a more thorough, geophysical investigation of the bedrock. For this project, a preliminary terrain conductivity survey was performed to yield information regarding the thin residual soils and shallow bedrock, followed by twodimensional resistivity profiling to detect any karst features deeper within the bedrock. The end result of the geophysical study gave the structural engineer and his client what they wanted - greater assurance that they had exercised diligence in their efforts to define site conditions and avoid hazards.
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Urban Geophysics: A Mapping Of Mount Bonnell Fault And Its Karstic Features In Austin, Tx
More LessAlthough most karstic regions are characterized by caves, collapsed features, and sinkholes, such features often do not have surface expressions, and their presence may go unrecorded. Central Texas and the Greater Austin metropolitan area have been built on the karstic limestone (Lower Cretaceous of Glen Rose Formation and Edwards Aquifer) in the Balcones Fault Zone (BFZ), and their growth is expanding. Near-surface karst features in the Austin area have a profound effect upon geotechnical engineering studies, such as structural foundations (residential buildings, shopping malls), utility excavations, tunnels, pavements and cut slopes. Thus the practice of geotechnical engineering is and has been a challenging proposition in the Austin area. Geophysical methods are sporadically used to estimate the locations and parameters of these karst features prior to any of these above-mentioned geotechnical studies. Opinions concerning the effectiveness of these geophysical surveys are mixed, and geophysical techniques are not generally recognized as primary tools in engineering-scale studies. However, remarkable advances in the manufacturing of geophysical instruments over the last ten years have made geophysics a viable tool for geotechnical studies of these karstic features. Data quality has been increased by the advent of continuous data collection. The data are better processed and interpreted by new and improved software packages, which produce improved sub-surface imaging and mapping. Thus integrated geophysical surveys can provide new insight into the near-surface karstic features in the Glen Rose Formation and Edwards Aquifer. I have conducted geophysical surveys (ground penetrating radar [GPR], resistivity imaging, magnetic [G-858], conductivity [EM-31] and natural potential [NP]) at three locations where the Mount Bonnell fault (MBF) is present, along the northern limiting boundary of the BFZ. Results indicate that all methods successfully imaged significant karst anomalies across the known fault locations. Integration of all these anomalies provides a much better understanding of near-surface geology defined by the caves, voids, collapsed materials, sinkholes and the fault itself.
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3D Masw Characterization Of Sinkhole: A Pilot Study At Usf Geology Park, Tampa, Fl
Authors Choon B. Park and Chris TaylorBy running three parallel and one crossing lines of conventional 2D MASW surveys followed by normal 1-D MASW inversions, a 3D characterization was attempted as a pilot study over an area of a known sinkhole 10-40 ft deep with lateral dimension smaller than 50 ft. Shear-velocity (Vs) data sets from each line were then used as constraints to calculate a cubic grid data in x (east-west), y (southnorth), and z (depth) directions by using a 3D inverse-distance-weighted (IDW) interpolation scheme. When displayed in depth-stripping mode at 5-ft depth intervals, velocity anomalies of substantially lower values than those in the ambient are recognized in the surface and depth locations that correlate fairly well with those identified in a geologic cross section previously compiled from other methods of well drilling, CPT, and GPR surveys. Properly selecting offset range during data acquisition and subsequent dispersion analysis seems critically important for the successful detection of a sinkhole.
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A Multi-Level Approach To Site Characterization C.W. Bill Young Regional Reservoir Hillsborough County, Florida
Authors Thomas L. Dobecki and Sam B. UpchurchThe C.W. Bill Young Reservoir is located in southeastern Hillsborough County (Tampa Bay Area) of Florida and is a 15.5 billion gallon, above-ground reservoir designed for temporary storage of excess surface water flow during rainy periods with the intent of recovery during dry periods. The water is held by a continuous earthen embankment that is 300-ft wide at its base with a circumference of five miles along the top. During the site selection and reservoir planning stages of the project, it was recognized that several factors would have an impact on the reservoir’s ability to retain water. Included among these are the risk of sinkholes and the presence of an abandoned phosphate strip mine underlying about one third of the 1,100 acre reservoir footprint. Each of these caused concern for both the ability of the reservoir to hold water (bottom leakage) and the ground stability beneath the embankment. The subsurface investigation included a multi-level approach to site characterization including:
• Photolinear analysis,
• Ground penetrating radar,
• Shear wave seismic refraction,
• High resolution seismic reflection, and
• Nearly 17,000 ft of soil borings
The intent of this program was to progress (going down this listing) from broad reconnaissance to successively more detailed investigations as important subsurface features became identified. The net result was identification and remediation of potential sinkhole and mining areas risks, which has resulted in a reservoir whose actual leakage volumes are less than the original design estimates.
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Wave-Energy Source For MASW?
Authors Mario Carnevale and Choon B. ParkSince its inception as a subsurface imaging technique, the multichannel analysis of surface waves (MASW) seismic method has been used in a variety of environmental and geotechnical applications. One of the more interesting applications is performing subsurface imaging in a beach environment. Although the loose and dry ground surface appears to present a formidable obstruction to the application of MASW for deep imaging, there could be an anonymous unexploited source of energy to make it happen. We look at the possibility that low frequency energy from ocean wave fronts can be introduced into seismic recordings made during MASW surveys along a beach or shoreline. Seismic data from MASW beach and shoreline surveys in Massachusetts will be examined for possible evidence of constructive or destructive interference from energy produced by ocean waves. The possible relationships of MASW survey geometry and the geography of the project settings are also examined. This study aims at evaluating the possible exploitation of ocean energy for deep MASW surveys in beach and shoreline environments.
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