Editors’ Note

Abstract

Friction is one of the central problems for the understanding of earthquake source mechanism and earthquake preparatory processes. Active faults are clearly zones of weaknesses in the crust. On the other hand, some laboratory tests at high pressure indicate that the frictional strength of faults approaches the fracture strength of intact rocks. Therefore some of the major questions are: How is friction along fault planes overcome? Are the local shear stresses high, or could water and clay minerals act as weakening agents? The answers to these questions are fundamental to the proper design of laboratory experiments on precursory changes of rock properties.