INFLUENCE OF UNIFORM BASEMENT EXTENSION ON FAULTING IN COVER SEDIMENTS

Abstract

Numerical predictions are compared with the results obtained from sandbox experiments intended to reproduce the effects of uniform basement extension. For mechanically homogeneous or uniformly layered sediments that are not strain-softened, faults are not expected to develop during uniform basement extension. Even in heterogeneous or strain-softening sediments subject to uniform basement extension, the only faults to develop reveal an irregular and uncharacteristic distribution of displacements along the fault plane. It is inferred that minor and inevitable gradients in strain rate are the most important reason why faulting was observed in the sandbox models.Irregularities such as topographic variation can also lead to faulting. Numerical experiments show that with increasing thickness of a basal elastic layer (rubber membranes in sandbox models) faulting of the cover sediments can cause the strain in the underlying elastic ''basement'' layer to become non-uniform.Faulting during uniform basement extension is controlled by irregularities particular to each example, and thus does not give rise to a characteristic structural style in the overlying sediments. Thus, sandbox experiments of this type cannot be used as templates for structural interpretation except for the rare case when the initial distribution of sediment and basement material properties are known and their influence is explored from extensive numerical experimentation.