Mechanical modeling of compressional basins: Origin and interaction of faults, erosion, and subsidence in the Venture basin, California

Using geophysical observations and some basic geological ideas on the prese nt structure of the Ventura basin, we model its possible mechanical evoluti on during the last 4 million years. We use a two-dimensional finite element model with frictional and elastoviscoplastic rheologies that allow strain localization. This allows us to study the mechanical origin of the San Caye tano thrust fault (SCF) and its interaction with the Oak Ridge fault (ORF). The results of our modeling indicate that the geometry and activity of a s hear zone which mimics the San Cayetano fault are conditioned both by the p reexistence of the Oak Ridge fault and by the shape of the brittle-ductile transition. Furthermore, the presence of a decollement level is shown to fa vor the development of the San Cayetano fault shear zone as a low-angle str ucture. The value of the effective friction on the Oak Ridge fault is evalu ated from this model. Possible values of the viscosity of the sediments are also estimated; it is shown that low sediment viscosity may completely hin der the activity of such a fault at the surface, while slip at depth contin ues. The stratigraphic profile of the basin is also shown to depend on the relative strengths of the ORF and SCF, which also provide an explanation fo r the shortening and rapid subsidence of the basin.