Fabric induced weakness of tectonic faults

[1] Mature fault zones appear to be weaker than predicted by both theory and experiment. One explanation involves the presence of weak minerals, such as talc. However, talc is only a minor constituent of most fault zones and thus the question arises: what proportion of a weak mineral is needed to satisfy weak fault models? Existing studies of fault gouges indicate that >30% of the weak phase is necessary to weaken faults ‐ a proportion not supported by observations. Here we demonstrate that weakening of fault gouges can be accomplished by as little as 4 wt% talc, provided the talc forms a critically‐aligned, through‐going layer. Observations of foliated fault rocks in mature, large‐ offset faults suggest they are produced as a consequence of ongoing fault displacement and thus our observations may provide a common explanation for weakness of mature faults. Citation: Niemeijer, A., C. Marone, and D. Elsworth (2010), Fabric induced weakness of tectonic faults, Geophys. Res. Lett., 37, L03304, doi:10.1029/2009GL041689.