GEOSCAN, résultats de la recherche


Titre3-component high resolution seismic profiling, a more holistic approach
AuteurPugin, A; Pullan, S E; Hunter, J A; Cartwright, T; Brewer, K
SourceAGU Fall 2011 Meeting, abstracts; 2011 p. 1
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120188
RéunionAGU Fall 2011 Meeting; San Francisco; US; décembre 5-9, 2011
Mediaen ligne; numérique
Sujetslevés géophysiques; interpretations sismiques; levés sismiques; méthodes sismiques; profils sismiques; géophysique
ProgrammeAquifer Assessment & support to mapping, Géoscience des eaux souterraines
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
High resolution seismic reflection methods have been extensively used throughout Canada by the Geological Survey of Canada to map buried valleys and thick unconsolidated sediment for groundwater and engineering studies. Our acquisition system consists of a landstreamer array of 48, 3-component (3-C), 30 Hz geophones mounted on sleds spaced at 0.75 m, 1.5 m or 3 m. The system is towed by a Minivib I that generates a swept signal from 20 Hz to 350 Hz at source spacings varying between 3 and 6 m. The source spacing chosen depends on the survey objectives, including the target depth and the horizontal coverage required. With these recording parameters, we typically acquire 4 to 6 line-km of data per day, making this technique a viable and cost-effective tool for regional surveying. In a single acquisition pass, the 3-C recording system has the advantage of acquiring P-wave, converted PS-wave and S-wave data. As expected, P-wave data are always best recorded on the vertical component; however, the PS and the S-wave data show various directions of polarisation from vertical to horizontal. We have observed that the velocity characteristics of the ground are a more important factor in the reflection phase polarisation than the orientation of the vibrating mass of the Minivib source. In low shear-wave velocity sediments, the polarisation of the S-wave can evolve from sub-vertical in the near surface to almost horizontal for reflections from higher-velocity sediments or bedrock, irrespective of the source orientation. In more consolidated sediments characterized by higher near surface velocities, the polarisation phase of the S-wave remains predominantly horizontal from surface to bedrock even when the source is vibrated in the vertical mode. The acquisition of 3-C shallow seismic reflection data is providing new insights into the complex behaviour and polarisation of seismic energy in the subsurface, and opening new opportunities for improving the resolution and information on sediment properties obtained by seismic reflection surveys.