Work Balance within Active Fault Systems

Assessment of the efficiency of a fault system requires a complete accounting of the energy budget of the system. Work done in the deformation of a faulted area consists of four components: (1) work done resisting friction during slip on the faults (Wf ); (2) work done against gravity in uplift of topography (Wg ) (this term can be negative where deformation decreases elevation); (3) internal energy of the strained host rock (Wi); and (4) work done in initializing new faults and propagating existing faults (Wp). The energy budget of the system can thus be expressed as Wtot = Wf + Wg + Wi + Wp For a balanced energy budget the total internal work, Wtot, equals the external tectonic work on the system. We examine the work balance within successively more complex fault systems using boundary element method models. The work balance approach has two primary benefits; it permits analysis of an entire system of interacting faults and it aids our understanding of fault system evolution. For example, new fault surfaces develop at the 'cost' of internal strain and/or tectonic work. Because this approach examines the entire system, the locally destructive or constructive interaction of individual faults is tempered by the role of these faults within the larger system.