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Seismic Imaging in Fold-and-Thrust Belt

LACR Andes Basins Research Symposium 2020
AAPG Distinguished Lecture


Rob Vestrum, Thrust Belt Imaging

In the complex-structure land areas of Andean basins, low data density and high structural complexity cause traditional seismic-imaging technologies to break down. The structural complexity results in wave-propagation complexity that makes it difficult to resolve the imaging of subsurface structures. Armed with an understanding of the local geology and in collaboration diverse geoscientists, we do our best to correct for the effects of near-surface geologic complexity to reduce exploration risk of subsurface targets.

Whether we wear glasses or if we use a hand lens to see details of a rock sample, we see refraction effects in our daily lives. In subsurface imaging, the near-surface geology is the lens through which we see subsurface structures on our seismic images. The bending of rays—either light rays or seismic rays—is caused by velocity variation, so understanding rock velocities is key to seismic imaging. We get velocity information from the redundancy of the seismic experiment and our understanding of the local geology.

We work to enter a postive-feedback loop between geology and geophysics. We can use our geologic understanding to build a velocity model that produces a reasonable seismic image. Our first attempt at using our geologic model to optimize the seismic image usually fails—after all, if we already knew the subsurface velocity structure perfectly, we would not need seismic data. We can use the seismic diagnostics to refine the velocity model. With each iteration, as more geologic features come into focus, the structural geologists can then refine the velocity model, resulting in further imaging improvements. Collaboration between structural geologist and imaging geophysicst can significantly improve the imaging of sub-Andean structures.


Rob Vestrum, Thrust Belt Imaging

Rob earned a BSc from the University of Alberta, a MSc from the University of Calgary, and a PhD also from the University of Calgary.

His 26 years of experience in the industry include working in companies as Shell (1994-1997), Kelman Seismic (1997-2000), Veritas (2000-2004) and TBI (2004-present), where he currently is Chief Geologist at Alberta, Canada, responsible for seismic imaging in complex-structure land areas from the Andes to the Zagros.

Rob is a member of Association of Professional Geoscientists and Engineers of Alberta, SEG and EAGE.

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