Fault terminations and barriers to fault growth

Field observations of strike slip faults in jointed granitic rocks of the central Sierra Nevada, California, combined with a mechanical analysis of fault interaction, provide insight into how fault terminations vary with scale. We document here a strike-slip fault system 2-3 km long. Clustered about the west end of the fault system are several dozen faults that parallel the three main fault zones in the system. We interpret this cluster of small faults as a barrier that inhibited growth of fault zones in the fault system. A two-dimensional mechanical analysis shows that a cluster of small faults flanking the tip of a large fault zone will tend to diffuse the stress concentration near the fault zone tip-an analogous effect in engineering is known as crack-tip shielding. Near-tip stress concentrations promote fault growth, and processes that decrease these stress concentrations inhibit fault growth. As faults lengthen and grow, they interact with features at greater distances and over a broader area, so the potential for tip shielding effects will increase as fault length increases. This effect can account for why the mechanisms and character of fault terminations would tend to vary as a function of scale. (C) 2004 Elsevier Ltd. All rights reserved.