- Home
- Conferences
- Conference Proceedings
- Conferences
20th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 01 Apr 2007 - 05 Apr 2007
- Location: Denver, Colorado, USA
- Published: 01 April 2007
81 - 100 of 164 results
-
-
Twenty Years Of Progress In Electromagnetic Exploration For Near-Surface Geophysics
More LessProgress in electromagnetic exploration for engineering and environmental investigations is characterized by development and adaptation in practice of three technologies. New metods now extensively employed are, terrain conductivity meters for shallow electrical conductivity profiling, time domain electromagnetic soundings in the dept range from about 30 m to 1,500 m and time domain electromagnetic profiling for detecting small buried metal objects. The relatively rapid acceptance of these technologies in engineering practice appears the result of merging of several factors, such as the existence of a solid theoretical foundation, instrument manufacturers who developed instrumentation specific for needs in engineering and environmental studies, and professionals willing to introduce new technologies in practice.
-
-
-
Two Decades Of Near-Surface Seismology Progress
Authors Don W. Steeples and Rick MillerShallow seismic methods have matured noticeably over the two decades since the first SAGEEP was held in 1988. At that time, the world’s scientific literature contained no more than a dozen refereed papers on shallow (less then 30 meters deep) reflection, but now there are hundreds of such examples. Analysis of surface waves was done with two-channel seismic systems in the 1980’s, whereas seismographs with dozens of recording channels are used today. Even refraction, the shallow-seismic method in use for nearly three quarters of a century, has undergone evolutionary change over the past two decades as tomographic methods have become available for near-surface geophysical applications. Much of the improvement in shallow seismic methods is related to the revolution in microelectronics and the associated several orders of magnitude decrease in computational costs, while developments in sources, seismographs, computers, and methods have all played a role to differing degrees. In many cases, the concepts and methods have been around for decades, but only recently has the computing power been available to put these into play in a cost-effective way. Clearly, advances in microprocessorbased technology have been the primary catalyst for growth in number and diversity of shallow seismic applications as well as the significant improvements in overall data quality.
-
-
-
Compressional And Shear Wave Seismic Refraction Tomography At Success Dam, Porterville, California
Authors Michael H. Powers, Seth Haines and Bethany L. BurtonSuccess Dam is an earthen embankment located near Porterville, Calif., and is of interest due to earthquake-related collapse potential. In order to characterize the geologic setting of the current dam and to help guide planning for a replacement dam, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, has undertaken a multi-method geophysical investigation of the site. The seismic component of this investigation consists of three transects, each with compressional (P) and horizontally polarized shear (S) wave coverage. Along each transect, we calculated tomographic velocity models of P-wave velocity (Vp) and S-wave velocity (Vs). These velocity models agree with available well information and show the transition from unconsolidated sediment at the surface to consolidated sedimentary rock to crystalline basement at depth. Weak zones such as soft sand in the upper sediments and highly weathered/fractured rock are manifested as low-velocity zones. Because Swave velocity is closely tied to engineering properties such as shear strength, low-velocity zones in the S-wave velocity models are of particular interest. We identify several zones of concern using calculated Vp/Vs ratios and Poisson’s ratio; these results will be used to guide future plans at the site.
-
-
-
Engineering And Environmental Applications Of The Potential Field Methods Of Geophysics.
More LessGravity and magnetic methods are potential field methods and used for a wide range of applications and scales in geosciences. Traditionally, they have been used for regional, large scale investigation of geological structure, such as basement relief and fault structure delineation. Despite the initial contribution of gravity methods to oil/petroleum exploration by detection and mapping of salt domes, “gravity data” is viewed primarily as a “reconnaissance tool in oil exploration” and “to provide constraints in seismic interpretation.” (quotes from Telford et al.,
1990) A familiar, smaller-scale (higher resolution) application of the gravity and magnetic methods is for ore body detection and mapping. The key geological factor required for
application of the gravity and magnetic methods is lateral variation in physical properties of subsurface materials. If the only variation in physical properties is in the vertical direction, such
as is the case for horizontally layered, homogeneous strata, the gravity and magnetic methods are applicable only for confirmation of the uniformity and lack of anomalous conditions.
Engineering and environmental (near-surface) applications of the gravity and magnetic methods were limited prior to the 1960's. Equipment developments and the emergence of new
classes of high priority applications have brought about a resurgence of interest in the potential field methods of geophysics and the development of high-resolution, high-accuracy field
procedures. The new classes of applications can be summarized as environmental (hazardous and toxic waste site assessments), archaeological, abandoned mine lands reclamation, cavity and tunnel detection and mapping, site investigations in karst areas, seismotectonic investigations, and other specialized problems. The gravity and magnetic methods are noted for two facts, one positive and the other somewhat negative: (1) the methods, which rely on measurement of variation in a naturally occurring potential fields, are fundamentally non-invasive and nondisturbing; (2) the interpretation of survey results is complicated by the fundamental, inherent nonuniqueness or ambiguity of source determination. The inherent ambiguity of gravity and
magnetic interpretation often requires the exercise of more geological insight and constraining direct information, such as from boreholes, for quantitative interpretation than required by many
of the other geophysical methods (although in fact interpretation of all geophysical survey results involves varying degrees of nonuniqueness and ambiguity). For purely qualitative, anomaly
mapping applications, the gravity and magnetic methods often can be used when other geotechnical methods are not effective. And, with apologies for not including other near-surface
geophysical methods that are legitimately potential field methods, e.g., direct current resistivity and self-potential, this paper only addresses gravity and magnetic methods and their engineering and environmental applications.
-
-
-
Adventures In Seeing The Unseen – From Borehole To The Moon
More LessIn 1967, I met Prof. David W. Strangway, who introduced me to geophysics as a freshman at MIT. From then to now, I’ve had a lot of fun doing geophysics in my head, on the computer, in the lab, and in the field. Two of the geophysical methods that I use the most are nonlinear complex resistivity (NLCR) and ground penetrating radar (GPR). I have advanced the state of the art in both, but hardly claim to be a pioneer, as both techniques were pioneered before I was born. I am honored to be invited to give this paper. This is a personal account and perspective on the applications of NLCR and GPR to environmental and engineering applications that barely scratches the surface of what has been accomplished by the geophysical community in the past more than 20 years.
-
-
-
‘In The Land Of The Blind A One-Eyed Man Is King’
More LessBorehole geophysics has grown from analog/digital hybrid technology to fully digital tools with the implementation of modern PC technology over the last two decades. New logging hardware is ‘smarter’ and easier to use, more sophisticated, and smaller. At the same time, post-acquisition software has become more advanced allowing for more quantitative log analysis to be performed faster. Despite this advancement, modern hardware and software has not matured enough to meet the expectation of industry and to insure quality data and solutions without experienced personnel. The human factor is complicated by a ‘graying’ of the work force and loss of experience at a time of increased demand. Education of a new younger work force is the single biggest issue facing the industry today. Education needs to include an understanding of the specifications, algorithms and limitations of the hardware and software as well as a better understanding of the physical sciences (geology, hydrology, etc.). Only then will the industry and personnel understand ‘Why log?’ or how to apply borehole geophysics and what type of type of information that is needed from the logs. Lastly, the new work force needs to be able to integrate borehole geophysical data with the other available information such as laboratory analysis,
geologic information, hydrologic information, etc. to constrain and optimize underdetermined solutions.
-
-
-
Great Expectations – Geophysics And Geotechnics
More LessHow could 20 years have passed since the first SAGEEP and the groundwork that conference laid for the formation of the Environmental and Engineering Society? Looking back is an interesting and sometimes informative exercise and in this situation, it provides for this “pioneer” a reassuring hope for the future.
-
-
-
From Polaroid Film To Data Acquisition Systems And Field Laptops
By F.P. HaeniThe theme of this paper is captured in a paragraph written by one of the early environmental geophysicsts and one of the founders of EEGS - John Greenhouse - in the Leading Edge (Greenhouse, 1991). In his article, John is documenting the rising interest in the field of environmental studies, including hydrogeology and geophysics, by students at the University of Waterloo during the 1980s and describing the emerging field of environmental geophysics. It is during this time period that the seeds were planted for the formation of a new organization that would represent this new breed of scientist. “Finally, is it appropriate to talk about fun? In this growing field there are few megaprojects, few specialists. One must do almost everything oneself, run magnetometers, seismic reflection, radar, process data, massage clients, advertise, write reports, juggle books… you name it. What a pleasure to see the rise of a grass roots geophysical industry where all hands are dirty, where responsibility comes early, where ingenuity, perseverance and luck must compliment technical skills. It’s reminiscent of the stories we read in THE LEADING EDGE of pioneer days in the oil industry. What a contrast to the specialized jobs that so many in the geophysical profession put up with, jobs conducted from the tenth floor of office buildings in London, Houston or Calgary. Environmental geophysics is fun and it is relevant; Students should be told that.”
-
-
-
Shallow Seismic Reflection Methods For The Delineation And Hydrogeological Characterization Of Buried Eskers In Eastern Ontario
Authors Susan E. Pullan, André J.-M. Pugin and James A. HunterThe surficial deposits of Eastern Ontario include a series of buried and/or confined glacial features, such as esker and fan deposits, which are currently the primary municipal drinking water source for a number of towns and villages. The Geological Survey of Canada is conducting a field program using shallow seismic reflection profiling to delineate the three-dimensional structure of the buried eskers and the surrounding basin stratigraphy
-
-
-
Comparison Of Compressional And Shear Wave Seismic Reflection Methods For Characterizing Aquifer Stratigraphy At The Former Fort Ord, California
More LessAt the former Fort Ord, in Monterey County, California, contamination threatens an aquifer that provides drinking water for local communities. Assessment and remediation of contamination requires accurate hydrological modeling, which in turn requires a thorough understanding of aquifer stratigraphy. In order to help guide remediation efforts, the U.S. Geological Survey has undertaken seismic re ection surveys at the site, testing both compressional (P) and horizontally polarized (SH) waves. Sledgehammer-source SH data show re ections from interfaces up to approximately 60 m deep which correspond with the major boundaries between aquifers and aquitards. In contrast, P wave data show only the re ection from the water table at approximately 30 m depth. The interpreted SH-wave images agree with available well information, constrain the geology for groundwater models, and provide guidance for future geophysical studies. These favorable results demonstrate the effectiveness of SH re ection methods for imaging unconsolidated aquifer layers.
-
-
-
Principle And Application Of 4D Microgravity Survey For Engineering Purpose, Case Example: Groundwater Level Lowering And Subsidence In Residential Area Of Jakarta
Authors Wawan G.A. Kadir, Djoko Santoso and Susanti AlawiyahBouguer gravity anomaly derived from observed gravity in the surface reflects all of possibilities of subsurface density change relating to their volume in its lateral and depth variation. In the time-lapse microgravity anomaly, gravity value is observed more than one measurement at certain time period. The difference between both gravity measurements, called as time-lapse microgravity, represents subsurface density contrast and station elevation change. Hence, in the area undergoing surface subsidence and high ground water exploitation, the elevation change and the ground water lowering could be a target of microgravity survey with resolution which depends on gravimeter used and its applied correction. As a case example, three (3) times of gravity measurements had been conducted in the residential area of 2 x 1 km2 with 4 to 6 months period between two (2) measurements. 168 gravity stations were carried out in the area with 50 – 100 m station spacing. In order to investigate subsidence and ground water lowering of the area, gravity gradient and water-pass elevation measurements were also used to support advance analysis. The survey result shows that all of the area undergoes subsidence with 15 cm average rate per year and more than 20 cm per year in the west part of the area. The rate of subsidence was influenced by season with the highest rate is in the dry season. In addition, it was identified the existence of ground water level lowering, sea water intrusion and compaction zone in the east part of the area.
-
-
-
Evaluating The Feasibility Of Artificial Recharge Sites Using High Resolution Electrical Methods Near Victorville, California
Authors John R. Jansen, Lance Eckhart, Anna Garcia and Ted L. PowellArtificial recharge and water augmentation are important aspects of many groundwater management programs. The subsurface must be understood in reasonable detail to design an efficient
and effective artificial recharge system. Often the cost to collect this data by drilling alone is prohibitively high. When properly applied, geophysical methods can provide subsurface information at a much lower cost. Geophysical data provides more complete coverage and can be used to target drilling efforts toward the most important areas. This presentation illustrates a recent project where geophysical methods were used to help a water agency design a testing program to develop an artificial recharge project. The Mojave Water Agency (MWA) was studying the feasibility of storing water in the unconsolidated material of the Oro Grande Wash due to its thick unsaturated zone and coarse-grained soils that allow for rapid infiltration, as well as its proximity to the California Aqueduct. A test boring installed in 2003 encountered an unexpected thick sequence of clay and silt above the water table. The presence of these fine-grained deposits could potentially impair the ability of the area to store and produce water and forced MWA to collect more data to test the conceptual model of the recharge system. A geophysical survey was used to collect subsurface information over an area of several square miles in an efficient and economic manner. Nine electrical resistivity resistivity profiles and 34 time domain electromagnetic soundings were collected to map the grain size of the soil to depths of over 1,000 feet. The results of the geophysical survey indicated that the subsurface geology was more
complex than originally expected. The deeper sediments are clay rich and poorly suited to recharge the aquifers used by the local municipal well fields. The shallow coarser grained sediments could be used to store water. However, the volume of water that could potentially be stored and recovered with a dedicated well field has yet to be determined. A modeling study of the recharge system is currently being conducted to determine if an economic system can be developed. Other areas are also under consideration.
-
-
-
The Applicability Of Dc Resistivity Imaging To Investigating The Feedback Mechanism Between Water Quality And Transpiration Beneath Circular Islands In The Okavango Delta, Botswana: A Case Study Of Thata Island
Authors Loago N. Molwalefhe and Elisha M. Shemang2-D Resistivity Survey was carried out in the Thata Island, one of the numerous circular islands in the Okavango Delta to investigate the mechanism governing the interactions between surface water, vegetation and groundwater. Seven profiles were laid across the island and the imaging results indicate that the centre of the island has very low resistivities (less than 10 ohm-m), while outside the island margins resistivity values increase laterally. This lateral resistivity zoning responds to shallow groundwater chemistry below the islands; high solutes load inside and the presence of fresh water outside the islands. Results of borehole to surface resistivity imaging in the island indicate a sinking blob of saline water to depths of 60 m. Groundwater salinities below the island range from 11.7g/l from outside the fringe to 122g/l at the centre of the island. Beyond the depth of 60m, the groundwater salinity drops to about 0.33 g/l at the centre of the island. Depth to water table in all the boreholes is less than 3 m below ground level. Results of the lateral and down-hole imaging as well as water salinity values show a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment.
-
-
-
Electrical Characterization Of Success Dam In Porterville, California
Authors Ted Asch, Bethany L. Burton, Michael H. Powers, Brian Rodriguez and Paul BedrosianAn integrated geophysical investigation of Success Dam, near Porterville, California, evaluated the foundation of a proposed new dam and delineated zones of underground water seepage. In fall 2005, the U.S. Geological Survey (USGS) conducted seismic refraction tomography, direct current (DC) resistivity, self-potential (SP), and audio-magnetotelluric (AMT) surveys of the
base of the current Success Dam. The seismic refraction tomography delineated alluvium and bedrock and mapped the bedrock surface. The DC resistivity survey delineated more electrically
conductive zones (ground water) and less conductive (unsaturated) zones within the alluvium. The DC survey also mapped resistive bedrock and indicated subsurface displacement east of the
spillway. Interpretation of self-potential data confirmed the fault by modeling it as a sheet flow source. A repeat SP survey, performed along the dam face in June 2006 during the high water levels, indicated much stronger seepage along the eastern end of the dam. The AMT survey provided corroborating evidence of the conductive zones representing water in unconsolidated materials. Integration of the geophysical information has helped resolve ambiguities and brought out subtleties in data sets that might have been overlooked if another data set with similar, but physically different, information were not present. These geophysical investigations have been successful in characterizing variations in lithology and geologic structure that should be of assistance to the designers of the new Success Dam under development.
-
-
-
Mapping Salt-Loads Of The Murray River, Australia, Using Airborne And In-River Electromagnetic Methods
Authors A. Fitzpatrick, T.J. Munday, V. Berens, M.A. Hatch and A.L. TelferSalinity in the River Murray and in adjacent floodplains of south-central Australia, has important environmental, economic and social consequences. Methods to monitor the temporal state of river and particularly river-groundwater interactions, have been in place for many years now. However, few have the capacity to define variability at a resolution appropriate for developing effective salinity management strategies, such as salt interception schemes. The use of geophysical methods for rapid high resolution mapping of river sediments has been successfully trialed in Australia, particularly using the “in stream” NanoTEM, a time domain ground EM system, deployed in a boat with the transmitter and receiver towed behind on a rigid floating boom. More recently, tests have been conducted using two different helicopter EM systems; a frequency domain EM system (FDHEM) and a time-domain EM system (TDHEM). Comparisons between conductivity-depth sections derived from the “in stream” NanoTEM and the airborne datasets suggest that the different approaches are comparable. This paper examines the potential of using the FDHEM RESOLVE system as basis for mapping reaches of the river that contribute to elevated salt loads in the Murray River to the south east of Mildura in Victoria. The advantages of the airborne systems become more apparent when data coverage and acquisition costs are considered, particularly in a situation where a parallel swath approached is
employed. This entails the acquisition of adjacent lines of EM data along the centre and along the margins of the river. We suggest this approach provides for a better understanding of recharge and discharge processes and links between the floodplain and the main-river channel. Compared with data acquired along the river alone, this study demonstrated our ability to use Helicopter EM data to map losing and gaining (from a salt load perspective) stretches of the river and to provide insight into which parts of the groundwater-floodplain system were significant contributors to river salt loads. The rapid acquisition of airborne EM data makes these systems more suited to providing temporal snapshots of a river-floodplain environment during dramatic climatic events, such as flooding. In the Murray basin this may assist our understanding of how salt stores are mobilised during such occasions.
-
-
-
Improved Mapping Of Conductive Clays And Groundwater Salinity Using Attitude-Corrected Helicopter-Borne Em
Authors G. Hodges, T. Munday, A. Heydorn and A. FitzpatrickThe interpretation of airborne electromagnetic (AEM) data has always assumed that the systems maintain a fixed geometry and attitude relative to the earth during survey. However, recent testing has demonstrated that the systems commonly experience significant vertical and horizontal offsets and rotations during flight. Failure to take account of variations in the observed conductivity induced by these movements have limited the potential for AEM systems to accurately resolve shallow conductive features that are often the target in environmental applications.
We present some initial results on the effects of variations in EM bird attitude on the observed response from the RESOLVE FDHEM system, in a recent study conducted in South Australia. Bird attitude was measured using three-antenna GPS array mounted on a boom at the front of the bird during survey. The intent of the survey was to define the thickness and extent of near surface, conductive clays as part of a saline water disposal management strategy being developed by the South Australian State Government. These clays have a significant influence on the rates of groundwater recharge in the study area, and the accurate definition of clay thickness was required as an input into a groundwater recharge model, which in turn was used to determine salt flux to the Murray River system from planned and extant disposal basins in the area. It has been shown that correction for normal changes in bird attitude in relatively smooth terrain
does create a small but measurable change to the HEM data amplitudes, but virtually no measurable change to the apparent resistivity. However, when precision results are desired for inversion of the data, where the amplitude of the response is the most sensitive parameter to the depth to target layers, the geometric correction may be necessary.
-
-
-
After The Helicopter Is Gone: Investigating Anomalies In Stream-Axis Em Data From The Colorado River, Texas
Authors Jeffrey G. Paine and Edward W. CollinsOngoing investigations of salinization along the upper Colorado River, Texas present an opportunity to integrate results from a stream-axis airborne geophysical survey, well drilling and sampling, and groundand borehole-geophysical surveys. Airborne electromagnetic induction (EM) measurements along 437 km of river and tributary stream axes identifi ed discrete salinized streambed segments, including several near oil fi elds. An initial round of monitor wells verifi ed groundwater salinization in one of the oil fi elds, but did not adequately delineate salinization nor identify specifi c salinity source areas. Subsequent ground and borehole geophysical surveys complemented airborne EM and well data by establishing lateral and vertical salinization bounds, discovering possible salinity source areas, and determining optimal locations for additional monitor wells.
-
-
-
Spatio-Temporal Monitoring Of Floodplain Environments Using Electromagnetic Methods: A Scaled Approach To Understanding Surface Water- Groundwater Interactions On The Chowilla Floodplain, South Australia
Authors T.J. Munday, I. Overton, A. Fitzpatrick, K. Cahill, V. Berens, M. Hatch and R.C. BrodieGeophysical methods are used in Australia to provide detailed spatial information to help predict the impact of current and future irrigation developments, the design of salt interception schemes and protection of floodplain values. RESOLVE frequency domain helicopter electromagnetic data were acquired over the Chowilla Floodplains, in the Lower Murray region of southern Australia, to provide detailed baseline data on the spatial distribution of near-surface salt stores and materials in the floodplain and their relationship with in-river salinity. Degradation across the floodplain and wetlands has resulted primarily from a significant reduction in flood events, and overgrazing. Restoration of the floodplain will involve the reduction of salinity flow from groundwater into the river and increasing H87environmental flows across the floodplain. Conductivity models predicted from HEM data help identify local recharge and discharge areas,
and links with river salinity. The baseline data provided by the airborne data are used with high resolution ground EM surveys including EM31 and time-domain EM, over targeted areas. Ground methods can be repeated, to monitor affects of artificial flooding designed to restore vegetation health. Similarly the combination of airborne and ground data, allows piezometers to be effectively targeted with the resulting information interpreted within the context of the baseline conductivity structure defined form airborne data.
-
-
-
The Effect Of Lateral Inohomogeneities On The Interpretation Of Shallow Refraction Seismic Data (Lateral Effects Problem)
More LessLateral effects problem deals with the effect of the lateral changes along the upper refracting interfaces on the lower refractors. The recorded traveltime curve from the lower refractors usually has pseudo number of inflection points and traveltime elements. An increase or decrease in the number of the traveltime elements along the traveltime curve is a result of these lateral variations. Linear traveltime elements are defined as linear segments with the same slope and consequently the same apparent velocity. Such traveltime curves cannot be explained directly by most of shallow refraction seismic interpretation methods. To identify this problem two traveltime parameters are used. These are layer reciprocal time and the apparent refractor velocity. Reversed profiling technique is essential. The ray tracing technique is used in this study to compute the synthetic traveltime curves of first arrivals. Surprisingly, this problem is rarely discussed in literature, and if ever, it is often without suggestions for interpretation, so the name lateral effects is used to define it.
-
-
-
Design Of Linear Phase Iir Filters With Application To Processing Of Seismic Data
By H.A. MansourIt is possible to design FIR filters with exact linear phase, however high orders are required. Typical group delay specifications can be met with approximately linear-phase IIR filters of lower
order, resulting increased processing speed. In this paper, a lower order linear phase IIR filter is designed from a corresponding FIR one via model reduction techniques. Also, the effects of linear phase FIR and IIR filtration on acquired seismic signals are demonstrated. It is found that the filtration effects are similar, with IIR filter order of only one- half that of FIR, which recommends the changing of FIR filters chain in NRIAG (National Research Institute of Astronomy and Geophysics) digital seismic stations by their alternatives IIR.
-