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The Three-Dimensional Dynamics of a Nonplanar Thrust Fault

Department of Earth Sciences
University of California, Riverside
Riverside, California 92521
david.oglesby{at}ucr.edu
(D.D.O.)

Department of Geological Sciences and Institute for Crustal Studies
University of California, Santa Barbara
Santa Barbara, California 93106
ralph{at}crustal.ucsb.edu
(R.J.A.)

Advances in computational methodology have made it possible to explore the dynamics of earthquake rupture on nonplanar faults. Using a method that allows geometrical flexibility, we simulate in three dimensions the dynamics of a fault that has an abrupt change in dip with depth. Using a homogeneous prestress on both fault segments, we find that while the resultant final stress field is strongly influenced by the fault bend, the fault slip and low-frequency ground motion are relatively insensitive to the pure dynamic effects of the nonplanar fault. The ground velocity from the nonplanar fault is qualitatively quite similar to that of a planar fault with the same dip angle as the nonplanar fault's shallow segment. As the effects of multiple earthquakes accumulate on this fault, stress concentrations at the fault bend are compounded, but the effect of the free surface on the stress appears to approach a steady state. The results of this study imply that for the prediction of peak ground motion from faults that intersect the surface of the Earth, a bend in the fault at depth may not be a significant factor. The very long term effects of the fault bend are not fully determined, but could lead to complexity in the rupture and slip process in future events.

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