Fabric induced weakness of tectonic faults

摘要

Mature fault zones appear to be weaker than predictedby both theory and experiment. One explanation involvesthe presence of weak minerals, such as talc. However, talcis only a minor constituent of most fault zones and thusthe question arises: what proportion of a weak mineral isneeded to satisfy weak fault models? Existing studies offault gouges indicate that >30% of the weak phase isnecessary to weaken faults - a proportion not supported byobservations. Here we demonstrate that weakening of faultgouges can be accomplished by as little as 4 wt% talc,provided the talc forms a critically-aligned, through-goinglayer. Observations of foliated fault rocks in mature, large-offset faults suggest they are produced as a consequence ofongoing fault displacement and thus our observationsmay provide a common explanation for weakness of mature faults.