Emma Finch¹

(1) University of Manchester, Manchester, United Kingdom

ABSTRACT: Segmentation, Growth and Linkage of Normal Fault Arrays: A Three-Dimensional Numerical Analogue of Rift Evolution

Active and ancient normal fault arrays comprise fault zones that are discontinuous along strike and consist of a number of distinct segments at a variety of scales. It is known that the progressive growth of normal faults ultimately results in linkage of originally isolated fault segments to form large (25-50 km) fault zones. Current understanding of the development of such zones, however, is restricted by an inability to resolve the temporal evolution of relationships between the spacing, length and along-strike segmentation of natural faults in three dimensions over geological time scales.

A three-dimensional numerical analogue of extension is applied to investigate the effect of thickness of the brittle crust (seismogenic layer) on the growth and linkage of faults during tectonic extension. The model represents the crust as spherical particles that interact through physically realistic forces in a two-layer, brittle/ductile system and includes terms for gravitation and isostatic flotation.

The fault population evolves from a large number of isolated structures to a complex array of linked faults. Horizontal and vertical sections through the crust indicate that linkage of the fault population varies with depth and seismogenic thickness. Fault activity is traced through time and demonstrates that extension is accommodated through rotation and locking of fault blocks forcing either new faults to initiate or dormant faults to re-activate. Results from these experiments provide templates for interpretation of structures imaged in 3D subsurface datasets and allow investigation of sub-seismic fault populations.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado