Thibaut Astic

PhD

Ph.D. Candidate in Geophysics

ESB-4037
(604) 767-5522
graduate

Geophysics is an essential tool for imaging the subsurface. It relies on physical properties contrasts between subsurface bodies, such as density, magnetic susceptibility or electrical conductivity. These contrasts produce a physical response that can be measured remotely by geophysical instruments. Data from geophysical surveys are processed to provide information about those physical properties. These can help solve a variety of problems in resource exploration, environmental or geotechnical areas.

However, attempting to extract complex geological information from geophysical inversion can be challenging, even with the required expert knowledge. Moreover, while there is room for practitioners in the choice of the prior parameters (reference model or the importance of smoothness), it can be difficult to relate the resulting models to some of the complex geological questions that are being asked (how many different units are there? Can we still explain the data by assuming this structural configuration?).

A large improvement in the recovery of the subsurface structures, and a significant reduction in the uncertainty of the recovered features, can be achieved by incorporating petrophysical and geological information into the inversion of geophysical data. That prior information allows me to restrain the space of acceptable solutions to the inverse problem.

My research focuses on developing a new framework for incorporating petrophysical and geological information into voxel-based geophysical inversion. By developing the geophysical inverse problem from a probabilistic perspective, I redesign the objective function and the iteration steps as a suite of cyclic optimization problems. Three separate MAP optimization problems are solved using geophysical, petrophysical and geological data respectively. By quantitatively linking these data into a single framework, I recover a final inverted model that reproduces the observed, or desired, petrophysical and geological features while fitting the geophysical data.

Astic, T., Fournier, D., & Oldenburg D.W., 2020a. Joint inversion of potential fields data over the DO-27 kimberlite pipe using a Gaussian mixture model prior, Interpretationhttps://doi.org/10.1190/int-2019-0283.1

Astic, T., Heagy, L. J., & Oldenburg, D. W., 2020b. Petrophysically and geologically guided multi-physics inversion using a dynamic Gaussian mixture model, Geophysical Journal International. https://dx.doi.org/10.1093/gji/ggaa378

Astic T., Oldenburg D.W., 2019. A framework for petrophysically and geologically guided geophysical inversion using a dynamic Gaussian mixture model prior, Geophysical Journal International, ggz389,  https://doi.org/10.1093/gji/ggz389

Astic, T. & Chouteau, M., 2019. Geological interpretation of the northern flank of the Matagami camp, Québec, using gravity and magnetic inversions, Canadian Journal of Earth Sciences, 56(5), 471–482. https://doi.org/10.1139/cjes-2018-0049

Mir, R., Perrouty S., Astic T., Bérubé C.L., Smith R.S., 2019. Structural complexity inferred from anisotropic resistivity: Example from airborne EM and compilation of historical resistivity/induced polarization data from the gold-rich Canadian Malartic district, Québec, Canada, Geophysics, 84(2), B153-B167. https://doi.org/10.1190/geo2018-0444.1

Astic, T. & Oldenburg, D. W., 2018. Petrophysically guided geophysical inversion using a dynamic Gaussian mixture model prior, in SEG Technical Program Expanded Abstracts 2018, pp. 2312–2316. https://doi.org/10.1190/segam2018-2995155.1