Abstract

Compressional tectonics in the Eastern Cordillera foothills are investigated using a large strain, two-dimensional finite clement method. The main purpose is to calculate the stress regimes within the Cusiana field and to compare the results with field data.

In the foothills, the NW-SE tectonic push is clearly confirmed by borehole breakouts. The present-day state of stress in the Cusiana field, is investigated through a footwall-hanging wall model with a detachment/ramp thrust fault. The tectonic push was simulated by applying horizontal displacement to the vertical boundary of the model. Simulations with both elastic and elastoplastic rheologies were performed.

To obtain a realistic horizontal stress gradient (in the range of 1.25 to 1.5 psi/fi) at depth, the stiffness of the hanging wall block has to be sufficiently low to accomodate the thrust geometry. With a perfectly sliding fault (zero friction), the tectonic push localizes the plastic deformation into a shear band which can be interpreted as the backthrust observed on the seismic section. Moreover, in the vicinity of the Cusiana thrust, the major principal stress rotates. This rotation is in good agreement with orientation found by core DSCA measurements.

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