No description available.

Thesis (doctoral)--Freie Universität Berlin, 2004. / Title from cover. "Dezember 2004"--P. [2] of cover. Vita. Includes bibliographical references (p. 103-113). Also available via the World Wide Web.

Thesis (doctoral)--Université de Rennes, 2003. / Includes bibliographical references (p. 186-202). Also available on the World Wide Web.

No description available.

Thesis (doctoral)--Freie Universität Berlin, 2004. / Title from cover. Vita. "April 2005"--P. [2] of cover. Includes bibliographical references (p. 115-126). Also available via the World Wide Web.

A study was undertaken to improve the signal quality and the resolution of the velocity profile for deep downhole seismic testing. Deep downhole testing is defined in this research as measurements below 225 m (750 ft). The study demonstrated that current testing procedures can be improved to result in higher signal quality by customizing the excitation frequency of the vibrator to local site conditions of the vibrator-earth system. The earth condition beneath the base plate can be an important factor in the signal quality subject to variations with time when tests are repetitive. This work proposes a convenient method to measure the site localized natural frequency and damping ratio, and recommends using different excitation frequencies for P- and S-wave generation. Properly increasing the excitation duration of the source signal also contributes to the quality of the receiver signal. The source signature of sinusoidal vibratory source is identified. Conventional travel time analysis using vibratory source generally focuses on chirp sweeps. After testing with impulsive sources and chirp sweeps and comparing the results with the durational sinusoidal source, the sinusoidal source was then chosen. This work develops an approach to identifying the source signature of the sinusoidal source and concludes that the normalized source signature is relevant only to four parameters: the fixed-sine excitation frequency, the duration of excitation, the damping ratio of the vibrator-earth system, and the damped natural frequency of the vibrator-earth system. Two of the parameters are designated input to the vibrator and the other two parameters are measured in the field test using the proposed method in this work. A new wavelet-response technique based on deconvolution and consideration of velocity dispersion is explored in travel-time analyses. The wavelet-response technique is also used for development of a new approach to correcting disorientation of receiver tool. The improved downhole procedures and analyses are then used in the analysis of deep downhole test data obtained at Hanford, WA. Downhole testing was performed to a depth of about 420 m (1400 ft) at Hanford site. Improvements in resolving the wave velocity profiles to depths below 300 m (1000) ft are clearly shown. / text

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

No description available.

Landslides have occurred throughout the Holocene geologic epoch and they continue to occur in the Peace River Lowlands of Alberta and British Columbia. This study was conducted to provide an understanding of the processes and extents of one such landslide situated on a major slope at the Town of Peace River, Alberta by means of geophysical techniques with the aim of reducing the geohazard risk to lives and infrastructures. The geophysical characterization involved the acquisition, processing, and joint interpretation of seismic reflection, seismic refraction tomography, vertical seismic profile, and electrical resistivity tomography datasets, thereby providing important information about the subsurface geometry of the landslide, insights into the material properties of the unstable mass in contrast to that of the stable rock, and possible causes of the landslide. This contribution shows that putting considerable efforts into the acquisition and processing of geophysical datasets can yield valuable functional details. / Geophysics

Les capteurs distribués à fibre optique (aussi nommés DAS) sont une nouvelle technologie d'acquisition sismique qui utilise des câbles traditionnels à fibre optique pour fournir une mesure de la déformation le long du câble. Ce système d'acquisition est largement utilisé dans les profils sismiques verticaux (PSV). Le couplage est un facteur clé qui a une grande influence sur la qualité des données. Alors que, pour les acquisitions PSV, les géophones sont attachés à la paroi du puits, le câble de fibre optique est soit cimenté derrière le tubage, soit attaché avec des pinces rigides au tubage ou simplement descendu dans le puits. Cette dernière stratégie de déploiement donne généralement le plus petit rapport signal sur bruit, mais est considérée comme la plus rentable en particulier pour les installations dans des puits existants. Cette thèse porte sur la problématique du couplage du DAS quand le câble est simplement descendu dans le puits. Nous développons des modèles numériques pour analyser les données réelles. L'interprétation de ces résultats nous permet de conclure qu'un contact immédiat du câble avec la paroi du puits avec une force de contact calculée est nécessaire pour fournir des bonnes conditions de couplage. Sur la base de ces résultats, nous proposons des solutions pour optimiser davantage les acquisitions avec le système DAS. Nous modifions numériquement la force de contact et les propriétés élastiques du câble DAS et démontrons comment ces modifications peuvent améliorer mais aussi détériorer la qualité des données. Enfin, nous proposons un algorithme de détection du couplage qui permet d'assurer l'acquisition de données réelles avec un rapport signal / bruit élevé. / Distributed Acoustic Sensing (DAS) is a new technology of seismic acquisition that relies on traditional fibre-optic cables to provide inline strain measurement. This acquisition system is largely used in vertical seismic profiling (VSP) surveys. Coupling is a key factor influencing data quality. While geophones and accelerometers are clamped to the borehole wall during VSP surveys, the fibre cable is either clamped and then cemented behind the casing, or attached with rigid clamps to the tubing, or loosely lowered into the borehole. The latter deployment strategy, also called wireline deployment, usually acquires the lowest level of signal but is regarded as the most cost-effective in particular for existing well installations. This PhD thesis addresses the problematic of coupling of DAS using wireline deployment. We develop numerical models that are used to analyse real data. The interpretation of these results allows us concluding that an immediate contact of the cable with the borehole wall with a computed contact force is required to provide good coupling conditions. Based on those findings, we propose solutions to further optimise DAS acquisitions. We numerically modify the contact force and the elastic properties of the DAS cable and show how these modifications can improve but also deteriorate data quality. Finally, we propose a coupling detection algorithm that is applied to real datasets and allows ensuring the acquisition of data with a high signal-to-noise ratio.