Abstract - It is widely recognised that basement faults exercise a strong control on the geometries of normal faults within overlying cover sequences. Details of the evolution of reactivated fault systems are, however, poorly defined. Using high quality seismic data for a fault system from the Timor Sea, we examine how Mesozoic basement normal faults control the initiation and growth of normal faults in a Tertiary cover sequence during subsequent extension. Detailed analysis of fault displacement rates, fault geometry and fault population systematics indicates that cover sequence faults establish their lengths at the early stages of faulting and, during subsequent extension, total strain becomes progressively localised onto fewer and larger faults. Larger basement faults have higher displacement rates than lower displacement faults. A rhombic fault pattern within the basement gives way upwards to a unidirectional Tertiary fault pattern, by way of twists in fault geometry, i.e. hard-linkage, or by fault segmentation, i.e. soft-linkage. New, soft-linked, faults grow just as rapidly as hard-linked faults and are a direct response basement reactivation. Since all faults in the cover sequence establish their lengths before 2% extension has occurred, reactivation and upward propagation of basement faults is not a pre-requisite to early, and rapid, fault propagation.
Abstract of talk given to:
Irish Geological Research Meeting, Queens University, Belfast, February 2003