Strike-slip Fault Network Evolution in the Scaling Organization of Fracture Tectonic Model

Wednesday, October 10, 2001 - 2:00pm - 3:00pm
Keller 3-180
Clement Narteau (California Institute of Technology)
From laboratory experiments, we are recognising that fractures are rough and irregular. Field surveys show that faults exhibit similar geometrical features despite the geological complexities. Meanwhile, slip distribution and the speed of rupture front propagation along planar faults have become standard seismological observables of earthquakes.

We are interested in the spatial-temporal properties of the stress dissipation within an active tectonic region. Therefore, in our approach, fractures play a central role and we focus on their interrelated evolution at different scales, from the micro-fractures to continental-scale faults.

We adopt a binary description of the microscopic scale to distinguish between two blocks of rock separated by a fracture and a solid rock. In a multiple scale system, geometric interactions extend this description at larger scales. In return, we define how any point in space is affected by the fracturing process from the distribution of fractures at all scales and from the local shear stress. By calling any perturbation and numerical structure from their geophysical counterparts, we study the evolution of our dynamical systems.

From the statistical results of a model of seismicity along an isolated fault segment, we extend our approach to the fault network scale. We present typical patterns of formation and evolution of a population of faults. Different phases of development are described: nucleation, growth, interaction, concentration, branching and relocation. We show that the geometry of the networks converges to a configuration in which all the stress dissipation is accumulated on a megafault aligned with respect to the orientation of the stress field. We conclude that the fault networks organize themselves in order to dissipate more and more efficiently the excess of stress. Different processes are isolated: localization and homogenization of the state of the stress along faults at different periods of time and structural regularization of the fault trace. We discuss the interrelated evolution of the faults within the network and relationships between the seismicity and the geometry of the fault network.