"Simulating the Geomechanical Evolution of a Fold-and-Thrust Belt"
Baiyuan Gao, PhD
Postdoc Candidate for AGL and GeoFluids
I use a geomechanical model to study stress, porosity, and pore pressure in a fold-and-thrust belt. Lateral tectonic loading increases mean effective stress and deviatoric stress and drives the sediments to shear-failure (critical state). My model simulates a porosity-offset across the décollement that is commonly observed in fold-and-thrust belts. The simulated porosity-offset is due to the fact that the hanging-wall sediment has a much higher mean effective stress and higher deviatoric stress than the footwall sediment. The shear-induced porosity-loss accounts for about one third of the total porosity loss. I identify a mechanical ‘transition zone’ that is closely related to the ‘protothrust zone’ where the porosity and stress ratio change rapidly. In the model, the high overpressure is generated rapidly within the protothrust zone. The tectonic-driven high overpressure reduces the basal frictional resistance and cause the décollement to be more prone to slip. My study has broaden impacts on the fault stability analysis, stress and pressure predictions, and earthquake studies.