Fault Zone Fabric and Fault Weakness

The apparent weakness of major tectonic fault zones is one of the greatest unsolved problems in geophysics. Working with Cristiano Collettini from the University of Perugia, we collected a suite of rock samples from a low-angle normal fault on the isle of Elba off the coast of central Italy.

Experiments conducted at the Penn State Rock and Sediment Mechanics lab in the fall of 2008 have provided the first laboratory evidence for a weakening mechanism based on common fault zone fabrics. We compared the frictional strength of intact samples of fault rock, sheared in their in-situ geometry, with that of powders of the same fault rock sheared in layers. The fault rocks, which contain well-developed, pre-existing foliation, are extremely weak compared to their powdered equivalents. Micro- and nano-structural studies show that slipping processes occur along very fine-grained foliations composed of tremolite and phyllosilicates (talc and smectite). 

Contact: Chris Marone