Examining the effects of faults growth and their fine-scale structures on rupture development of large earthquake

Faults grow by accumulating displacement and lengthening (i.e., propagating laterally). The lengthening of faults over their long-term growth induces systematic changes of their along-strike structural maturity that can have a strong impact on the rupture process during an earthquake. In this talk, I will show fault maps and fault propagation evidences available in the literature to examine geometrical relations between parent faults and off-fault splays. Faults splays form adjacent to propagating fault tips and participate in the long-term damage of the crustal medium around the fault. They are absent at non-propagating fault ends. I will present scaling relations between parent fault length and length/width of tip splay network, showing that damage zones enlarge as the parent fault length increases. Then, using numerical modeling and observations of about 30 continental large earthquakes (M>6), I will discuss how earthquake slip asymmetry and rupture acceleration are mainly governed by along-strike changes in fault zone strength, due to the evolution of fault segmentation and off-fault damage with increasing maturity. Finally, I will present an analysis of the fine-scale geometry and structure of the San Andreas Fault near Parkfield, CA, and their role in the development of the 1966 and 2004 M6.0 earthquakes using jointly surface fault and rupture traces, associated with high-resolution earthquake locations at depth.