- Home
- Conferences
- Conference Proceedings
- Conferences
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
61 - 80 of 131 results
-
-
Roadside Passive Masw Survey - Dynamic Detection Of Source Location
More LessIn a roadside passive surface-wave survey under a typical urban setting with relatively heavy traffic and a complicated network of roads, a field record usually contains surface wave events generated from multiple source points scattered around the survey location. It is, however, those dominating energy events coming from one common surface point on the road that are used as signal in most advanced dispersion analysis methods based on the 2-D wavefield transformation. Events from other locations interfere adversely with signal events during the analysis if they take comparable energy or are largely ignored in the case of insignificant energy. A long record (e.g., 120 sec) is divided into many subsets of much shorter time of a proper length (e.g., 1 sec) and are treated as independent records of only one (or none) of a dominating event. By utilizing an advanced technique to detect fairly accurately the source location of the event, subsets are processed for their own dispersion images by using the scheme commonly used in the active MASW survey. Multiple data sets of the dispersion image are then stacked to result in an image of the highest signal-to-noise ratio (S/N) ever possible. This is demonstrated by using a field record acquired with a linear receiver array deployed along a busy street that contains events from complex source points and therefore could not be processed for any interpretable dispersion image using other methods currently available.
-
-
-
Comparison Of FK And Spac Methods In Determining Dispersion Curves From Passive Surface Wave
More LessFK and SPAC are the two common approaches in determining dispersion curves from passive surface waves. To conduct a systematic comparison, we stimulate passive surface waves with randomly distributed sources and different types of arrays. A field data is also used in the comparison. The study shows that the SPAC method provides higher resolution on the dispersion image and is able to generate a dispersion curve with a larger frequency range. The FK method performs well within a limited frequency range. To reduce the uncertainty in determining dispersion curves, the combination of both methods is recommended.
-
-
-
Applicability Of A Spatial Autocorrelation Method (Spac) Using A Linear Array In Comparison With Triangular And L-Shaped Arrays
Authors Koichi Hayashi and Takaho KitaWe have examined the applicability of a spatial auto-correlation (SPAC) method using a linear array in comparison with triangular and L-shaped arrays. The SPAC requires two dimensional arrays, such as a circle, a triangle and a crossing for calculating the phase-velocity of the microtremor. Theoretically, isotropic arrays, such as a circle or an equilateral triangle, are preferable in the SPAC analysis. However, the isotropic arrays required wide space and it is difficult to obtain such wide space in urban area. Recently, several theoretical and experimental studies have shown the validity of irregular arrays. Results of these studies have also implied the validity of linear arrays in which receivers are placed only on a line. The use of linear arrays will enable us to apply passive methods in urban area much easily. In this paper, we are going to examine the applicability of the linear array in terms of numerical simulation and field experiments. The result of field experiment showed that the linear array provides almost identical dispersion curves as that of two dimensional arrays although numerical simulation showed clear disadvantage of the linear array. It implies that that the sources of the microtremor are distributed randomly in space and the microtremor does not have any specific propagation direction at most of sites.
-
-
-
Subsurface Tunnel Detection Using Electrical Resistivity Tomography And Seismic Refraction Tomography: A Case Study
Authors Grey I. Riddle, Craig J. Hickey and Douglas R. SchmittSeismic and electrical methods are two geophysical techniques commonly used to detect rock property changes in the subsurface. Surveys are usually carried out with sources and sensors placed at or near the earth’s surface. Various levels of data processing are applied to construct a map of the subsurface distribution of a physical property. Seismic methods are sensitive to velocity and density changes of the rock, while the electrical response is dependent upon the electrical resistivity of the rock. In this paper, we present an evaluation of using both seismic refraction and electrical imaging to locate a tunnel. Although the contrast in seismic velocity and electrical resistivity between the tunnel and its surrounding material can be large, tunnels remain difficult to detect. The difficulty primarily arises because the spatial resolution of these methods is less than or on the order of the size of the tunnels. Detection is further complicated by heterogeneity of the near surface materials within which many tunnels are constructed. In this paper, we present a case study using ERT dipole-dipole data and seismic refraction data at a tunnel site. Both seismic and electrical surveys were acquired at the same time with a lateral offset of about 3m. The results from both techniques show anomalies at the location of the tunnel. The confidence in predicting the location of the tunnel is increased by using data from both techniques.
-
-
-
Geostatistical Analysis Of Borehole And Surface Wave Data A Case Study
Authors Marco de Kleine and Rik NoorlandtA Surface wave study has been executed in the center of Surinam in order to determine the depth to bedrock. The site of investigated is located in the tropical rain forest of Surina so the overburden consists of tropical oils and lateritic soil. The topography at the site is very pronounced. The survey data was combined with other types of data, i.e. boreholes, spt’s, cpt’s. The additional information was used both during the inversion and during the interpretation of the data using an iteratively approach. By combining this data with geological and geostatistcal knowledge not only insight in the thickness of the overburden was obtained but also information about the limitations of the data and the reliability of the results was determined. This additional information is relevant for the construction company who can make better cost estimates based upon this type of information.
-
-
-
Revisiting SH-Wave Data Using Love-Wave Analysis
Authors Jianghai Xia, Richard D. Miller, Recep Cakir, Yinhe Luo, Yixian Xu and Chong ZengAlthough Love waves are widely analyzed in earthquake seismology, there is much less attention on utilizing Love waves than Rayleigh waves by the near-surface community. Unlike incident P and Sv waves, a plane SH wave for a series of horizontal layers refracts and reflects only SH waves, which makes the shallow SH-wave refraction method more popular to define shear (S)-wave velocity in near-surface geologic applications. For this reason, abundant SH-wave refraction data have been acquired and S-wave velocities have been determined using their first arrivals. If signals are recorded long enough, Love-wave energy can be clearly observed on SH-wave refraction data. Wave conversion may occur in an SH-wave refraction and Love-wave analysis only results in SH-wave velocities, which suggest that we may benefit from revisiting the existing SH-refraction data using multichannel analysis of Love waves (MALW). We used numerical modeling results and real-world examples to demonstrate three advantages of revisiting SH-wave data using the MALW method. Owing to a long geophone spread commonly used in SH-wave refraction survey, a sharp image of Love-wave energy can be generated, allowing better pickings for the phase velocities of Love waves. Because Love waves are independent of P-wave velocity, “mode crossing” in an image of Love-wave energy is less common than in Rayleigh-wave images. Fewer unknowns in the method MALW make dispersion curves of Love waves are simpler, which leads to more stable inversion of Love waves and reduces the degree of nonuniqueness.
-
-
-
Seismic Refraction Surveys—How Many Shots Do I Need?
More LessClassical seismic refraction theory as discussed in most textbooks focuses on flat-lying or dipping layers and shows one or two shots. Most modern refraction surveys are shot with far more than two shots and use more sophisticated methods of interpretation and inversion. The use of only two shots, one on each end of a refraction spread, results in a critical lack of coverage, even for fairly simple velocity sections. This is in spite of the fact that the original section can sometimes be effectively recovered if some assumptions are made. Inversions using geophysical inverse theory in two dimensions as well as the Generalized Reciprocal Method (GRM) are applied to synthetic data generated from 2-D models and to field data examples to illustrate the importance of additional shots taken away from the spread ends (far shots) and additional shots taken in the interior of the spread (interior shots). These additional shots allow the interpreter to determine the number of layers in the section, assist in the assignment of arrivals and further constrain the velocities and (time-) depths and the elevation section. This produces a better and more reliable interpretation.
-
-
-
Using Synthetic Data To Guide Processing Of Shallow Seismic Reflection Data Collected Across A High Scarp In Sw Montana
Authors Jose Pujol, Mervin J. Bartholomew, Andrew Michelson and Michael BoneWe collected shallow reflection data in SW Montana across a 5.4 m high tectonic scarp. The goal of this survey was to try to image the fault associated with the scarp, which is visible in a trench close to the seismic line. However, processing the seismic data is challenging because the height of the scarp (about 5.4 m) is comparable to the depths of the reflectors of interest. The problem is most acute for the data from the scarp area, and to find out how to proceed we generated synthetic waveforms using the actual recording geometry and topography. To generate the synthetic data we assumed that the scarp was due to a normal fault and used velocity models based in part on parameters derived from the actual shot gathers. The analysis of the synthetic data shows that the velocity model could be recovered quite well by first determining interval velocities without consideration of the station elevations and then stacking the data after application of station corrections referred to a datum elevation equal to the height of the scarp. This procedure placed horizontal reflectors correctly in time in a relative sense, although those on the low side of the scarp were shifted to a later time. However, this shift is consistent with the velocity used to generate the corrections and the difference in elevation with respect to the datum. Moreover, away from the scarp the highest and lowest elevations can be chosen as datums, which places the horizontal reflectors correctly in time. Applying this procedure to the actual data shows a clear continuous horizontal reflector on the lower side of the scarp and more disrupted reflectors on the higher side with discontinuous reflectors under the scarp. The latter correlate with the main and secondary faults mapped in the trench, but because the early portion of the seismic data was muted, it is not possible to follow this correlation close to the surface.
-
-
-
Application Of Wavefield Transformation To Spectral Analysis Of Surace Wave (Sasw) Data
Authors Chun-Hung Lin and Chih-Ping LinThis paper introduces a source-to-receiver distance gather process to reconstruct the SASW data as MASW-imitating data, to which a wavefield transformation can be applied for dispersion curve analysis. Numerical simulations were performed to demonstrate its feasibility and advantages for analyzing SASW data. Furthermore, a new field testing procedure is suggested for better results when conducting surface wave testing with two or small number of recording channels. The results of this study advocate that multi-channel wavefield transformation can and should be used even though the field testing procedures may differ as restricted by the equipment capacity.
-
-
-
Update On Recent Observations In Multi-Component Seismic Reflection Profiling
Authors André J-M. Pugin, Susan E. Pullan and James A. HunterExamples of multi-component shallow seismic reflection profiling from different environments in eastern Canada are presented to examine the benefits of shear wave reflection data and the latest developments in acquisition methodology, as well as our evolving understanding of the complex nature of seismic wave propagation. Examination of the wave motion through multi-component recording shows that, regardless of the source orientation, shear wave reflections may be polarized in varying directions. In “soft” soils characterized by low shear wave velocities, extremely high-resolution shear wave reflection sections can be obtained, with the highest-resolution data related to in-line or vertical components of motion. Data recorded in the transverse (SH) direction are generally somewhat lower in frequency but may be better able to penetrate into more compact (higher velocity) sediments. Multicomponent recording provides the capacity to record all data, without having to know the main shear wave polarization direction prior to data acquisition.
-
-
-
Ultrasonic Velocities In Laboratory-Formed Gas Hydrate-Bearing Sediments
Authors Marisa B. Rydzy and Michael L. BatzleGas Hydrates are widely distributed in the near surface at high latitudes and many ocean bottoms. Our laboratory measurements help calibrate the seismic and well log data that are used to ascertain the in situ distribution of hydrates. Ultrasonic velocities are measured in unconsolidated sand specimen under thermobaric conditions comparable to those found in shallow oceanic or permafrost regions, i.e. in the gas hydrate stability zone. Compressional-wave (p-wave) velocity data in dry Ottawa Sand samples subjected to a confining pressure that from 2 to 20 MPa range from about 700 to 1500 m/s. Gas hydrates were then formed a partially saturated Ottawa sand sample. As expected, this hydrate formation resulted in a dramatic increase in p-wave velocities from 700 m/s in the partially water saturated sample to 2100 m/s in the hydrate-bearing specimen. The hydrate effectively cements the sand such that nine hours after entering the hydrate stability region, the recorded waveforms remained constant even as the confining pressure was increased by more than 10 MPa.
-
-
-
Phase-Scanning Approach To Correct Static Error In The Surface Wave Walk-Away Method
Authors Edwin A. Obando, Choon B. Park, Nils Ryden and Peter UlriksenSynthesized surface wave records obtained from walk-away surveys normally suffer from time shift inaccuracies due to the abrupt variation in the soil stiffness characteristics which is regarded as static error effect. In this paper we present a method that uses a phase scanning procedure in frequency domain which applies the correction in a phase range from 0 to 2
-
-
-
Seismic Investigation Of Underground Coal Fires; A Feasibility Study At The Southern Ute Nation Coal Fire Site, Durango, Colorado
Authors Sjoerd de Ridder, Nigel Crook, Seth S. Haines and S. Taku IdeWe conducted a near surface seismic test at a coal fire in the Southern Ute Nation near Durango, Colorado. The goal was to characterize and image the unburned coal and adjacent burned zone in order to determine the feasibility of any future seismic surveys. The field survey was preceded by a numerical study to optimize the survey design for the field test. The numerical study suggested that field experiments would rely on creating energy with sufficiently high frequencies, ideally greater than 125 Hz. Reflections or refractions from the top of the coal layer might indicate its presence or absence. Separately imaging of both the top and bottom of the coal layer or burned zone likely would be beyond the resolution of a reflection survey. Data from line 1, which overlies unburned coal at approximately 16 m depth, show useful frequency content above 100 Hz and a reflection that we interpret to originate at approximately 11 m depth. Data from line 2, which crosses the burn front and many fissures, are of lower quality with predominantly jumbled arrivals and some evidence of reflected energy at one or two shot points. It seems that neither the refraction nor reflection method is capable of imaging down to the coal layer; due in part to the presence of unexpected high-velocity layers overlying the coal. We conclude that information about the coal is obscured by a reflection from shallower layers and by chaotic arrivals generated by fissures. Based on our data, we suggest that further seismic work at the site is unlikely to successfully characterize the coal fire zone of interest.
-
-
-
Multi Geometry Approach For Masw Survey
Authors Ali Nasseri-Moghaddam and Choon B. ParkThe effect of source offset distance and the geophone array length on the dispersion curves are discussed in this paper. The source offset distance was changed systematically at sites with various subsurface conditions to investigate its effect on quality of data and the corresponding dispersion curves. Further, tests were carried out at same locations with various geophone intervals to evaluate the effect of the array length on the quality of the data and dispersion curves. Active and passive data were collected and the dispersion images were combined for possible improvement in dispersion image with enhanced multimodal delineation over a broadened bandwidth. It is observed that source offsets in the range of 25% to 45% of the array length provide dispersion curves with reasonable quality. Further, collecting data with different geophone intervals (same array mid station) improves the resolution of the obtained dispersion image. Multi geometry technique is suggested to obtain better quality field data. In this approach two (or more) different geophone intervals are used with same mid station. Passive and active data at two or more offset distances are collected for each of the array geometries. Stacking the obtained dispersion images can also result in a better quality dispersion curve.
-
-
-
Using Ultrasonic Coda Wave Interferometry For Monitoring Stress-Induced Changes In Concrete
More LessThe velocity of ultrasonic coda waves, the diffusive tail of ultrasonic signals, was monitored in a concrete specimen under uniaxial compression. The ultrasonic measurements were taken in two directions: parallel and perpendicular to the loading. A geophysical correlation-based approach called coda wave interferometery (CWI) was used to calculate the incremental stress-induced changes in velocities. Ultrasonic pulse velocities were also calculated using the conventional time-of-flight (TOF) approach. A comparison of TOF and CWI velocities revealed that the CWI velocities are more sensitive to the level of stress and damage within concrete, especially in low stress levels. Also, the CWI velocities measured parallel to the loading showed greater sensitivity.
-
-
-
Combined Parallel Seismic And Cone Penetrometer Testing Of Existing Bridge Foundations And Levee Sheet Piles For Length And Capacity Evaluations
Authors Dennis A. Sack and Larry D. OlsonThe use of the Parallel Seismic (PS) test method has been well documented and has been shown to be effective for foundation length evaluation when used with a cased borehole adjacent to the foundation being evaluated. In addition, the use of the Cone Penetrometer Test (CPT) to evaluate soil properties without a borehole has also been well documented. Recent research, hardware development, and field testing have been conducted on a system which combines the two methods to allow fast and economical evaluation of both soil properties and foundation depth without requiring a drill rig. The combined system collects both PS and CPT data in one or two probe penetrations into the soil. The combined system can be used with a smaller, relatively low clearance CPT rig which is self-propelled and designed for use on rough site conditions. Thus, access is possible to bridge foundations that could not be tested with conventional means. The paper presents details of the principles and operations of the combined system, as well as field test data from driven pile bridge foundations as well as steel sheet
piles under levee walls in New Orleans.
-
-
-
Multiple Impact Surface Waves For Determination Of Pavement System Moduli For Assessment And Design
More LessThe Multiple Impact Surface Wave (MISW) method involves the measurement and modeling of the propagation of surface waves in pavements. MISW can accurately determine not only the surface pavement thickness and low-strain elastic modulus of concrete and asphalt, but also the thicknesses and moduli of underlying base and subgrade layers. The MISW test method was used in a forensic concrete pavement investigation project and the thickness/moduli results for the concrete, base and subgrade layers are compared with Spectral Analysis of Surface Waves (SASW) results. The MISW method is able to accurately estimate the properties of base materials immediately below the much stiffer pavement layers by accounting for higher order wave modes during the inversion process in comparison to SASW results. Example results are presented of the use of MISW combined with Impact Echo (IE) data analyses to predict thickness/moduli of an asphalt pavement. Finally, a discussion is presented of the calculation of asphalt elastic moduli from MISW results for mechanistic-empirical design of asphalt pavements.
-
-
-
Measurement Of Sheet Pile Length By Pile Integrity Testing And The Parallel Seismic Method
Authors Ernst Niederleithinger and Matthias FritscheThe non-destructive measurement of sheet pile lengths at existing constructions is a complex task. Low strain pile integrity testing is an easy and efficient method, but sometimes fails to give meaningful results. Statistical evaluation enhances the reliability and gives hints on length changes. Using the parallel seismic method, which has been developed for the assessment of drilled shafts and similar constructions, is an alternative possibility worth considering. Recently developed interpretation tools allow greater distances between piles and sensor boreholes compared to other methods. Two field examples show the use of both methods and some pitfalls, including ways to overcome them.
-
-
-
Crosshole Sonic Logging Of Secant Pile Walls A Feasibilty Study
Authors Ernst Niederleithinger, Joram M. Amir and Markus HübnerSecant pile walls are used as permanent or temporary elements in foundations, excavations, slope stabilization, retaining walls or hydraulic barriers. In contrast to single piles, reliable non-destructive testing methods are not available so far. The reinforced secondary piles can be checked by standard crosshole sonic logging, but there is no access to the unreinforced primary piles. Experiments at construction sites using ray paths across several piles have shown encouraging results, but there have been several open questions. To evaluate the potential of cross-pile sonic logging, a real scale test model with built in flaws on two primary piles was constructed at the BAM test site. Measurements with two different instruments have been performed. In one primary pile relevant flaws could be detected. At the other one the signals showed anomalous damping, probably due to unintended delamination. The results can be used to interpret real site data.
-
-
-
Quantitative Integration Of Multiple Near-Surface Geophysical Techniques For Improved Subsurface Imaging And Reduced Uncertainty In Discrete Anomaly Detection
Authors Megan E. Carr and Gregory S. BakerThe remote sensing community—in the traditionally-used connotation of satellite and airborne imagery—has been integrating multi-technique geophysical data extensively and successfully for nearly two decades to better discriminate targets, e.g., mineral deposits, specific types of vegetative land cover, etc. Currently, however, there is no quantitative methodology in place for the integration of two or more geophysical data sets collected using near-surface geophysical techniques such as Ground Penetrating Radar (GPR), Magnetic Gradiometry, and other Magnetic/EM methods. The primary objectives of this research are to investigate quantitative methodologies for integrating multi-tool surface geophysical data to improve subsurface imaging and reduce uncertainty in discrete anomaly detection. These objectives will be fulfilled by: (1) correlating multi-tool geophysical data with existing well characterized ―targets‖; (2) developing methods for quantitatively merging different geophysical data sets; and (3) testing these new methods at several different sites with varied targets (i.e., case studies). Three geophysical techniques primarily utilized in this research are: GPR, EM (ground conductivity) methods, and magnetic gradiometry. The two study sites (Cherokee Farm and the University of Tennessee Agricultural Extension Plot 4B) located within alluvial sediments along the Tennessee River will serve as case studies to verify methodologies in a terrestrial environment. A computer model will be developed that will simulate data that would be expected given various parameters such as heterogeneity of the subsurface, type of target, geophysical technique utilized, spatial sampling, etc. The simulated data sets will then be integrated together using the same methodologies as employed with data from Cherokee Farm and Plot B4 to further develop the necessary quantitative assessment scheme to determine if these merged data sets do in fact satisfy the objectives of the research.
-