Julien Gance

Slope Mechanical Modelling: Contribution of Multi-Geophysical Imagery

This work aims at assessing the impact of local heterogeneities consideration in slope mechanical modelling. We choose to use different geophysical techniques to characterize these heterogeneities, and a fuzzy logic data fusion concept to create a geometrical model from these data. The first mechanical simulation, realized with basic elastic constitutive law, gives a surface displacement pattern in agreement with the one measured. This highlights the importance of the model’s layer geometry on the results and also the suitability of geophysical imagery tools to constructs high resolution geometrical models.

Gradient-based Seismic Inversion using a Finite Frequency Assumption for Imaging Velocity and Attenuation

Various studies operate seismic methods for imaging landslide structures. All those methods are more or less based on strong approximations and require complex data preprocessing. The issue of recovering the structural image of a landslide from the seismic velocity field estimated with an accurate, but not too unstable, method is thus posed. To solve it, we choose to revisit first arrival tomography approach which is a good compromise between the strong assumptions featuring simple refraction methods and the complexity of Full-Wave Inversion approach when used in very heterogeneous soils. The proposed method is based on a Quasi-Newton formulation to ensure an optimum convergence of the velocity model. We only use here the first arrivals of the seismic signal due to direct or refracted waves. Nevertheless, we show that some regularization strategies (Fresnel volumes approach, increasing finite frequencies) allow detecting sharp velocity variations tending to reach FWI performances.