High Resolution Seismic Reflection Imaging of Complex Stratigraphic Features in Shallow Aquifers

• Main Authors: FRANCESE, Roberto, Zoltan Hajnal, Douglas Schmitt, Annalisa Zaja
• Other Authors: Francese, Roberto, Zoltan, Hajnal, Douglas, Schmitt, Annalisa, Zaja
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2007
• Subjects: High-Resolution Shallow Seismic; Near- Surface Deposit; Aquifer Sedimentology; Groundwater Flow Modeling; Canada; canada basin
• Online Access: http://hdl.handle.net/11381/2741109

A series of near surface multifold high-resolution seismic reflection experiments were recently conducted in the Western Canada basin and in the Po Plain in Italy. The primary objectives of the investigations were to define stratigraphy and physical properties of shallow fresh water aquifers contained in late tertiary and quaternary deposits. The seismic signature of the major geologic units was recorded down to the target depth of exploration. The local hydrogeological framework and the spatial extents of the most prominent aquifers were defined in details. The different experiments faced typical shallow exploration problems. Source deployment was, in some cases, complicated because of difficulties in placing the explosive charge at the proper depth. Shallow P-wave velocity anomalies introduced significant time shifts reducing the effectiveness of stacking common mid point traces. Near surface geology caused also strong coherent noises when elastic energy was propagated in the subsurface and the resulting records exhibited very low signal to noise ratio. The urban environment with its associated complications introduced further difficulties to accomplish the expected results. Some of these problems were resolved relying on the results of forward modeling of wellbore information. The numerical simulation was vital in assisting the design of the data acquisition, in the preliminary choices of the processing parameters, and ultimately in tying borehole stratigraphy to the reflecting horizons. The better quality seismic sections were reprocessed to gain a better insight in the aquifer sedimentology and some attempts to predict petrophysical properties from the stacked data outlined the potentials of this post-processing analysis when the signal to noise ratio is sufficiently high. Functional data acquisition and processing procedures were developed for seismic mapping of shallow alluvial and glacial deposits and these techniques could be utilized in other regions with similar near surface stratigraphy.