AHMAD FAHIMIFAR - Professor, Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

It has been observed that motion on fault surfaces can take place suddenly to produce an earthquake. Laboratory studies of the fracture and friction of rock have developed as oile of the major approaches to the problem of understanding the earthquake mechanism. An experimental investigation was performed using a ۵ MN servo-controlled stiff testing machine to examine sliding and stick-slip characteristics of different rocks containing a single discontinuity subjected to triaxial testing condition up to ۷۰ MPa confining pressure. Typical stress-strain plots containing regular stick-slip obtained in this investigation are evaluated. On the basis of the experiment carried out, different controlling mechanisms and the theories explaining stick-slip phenomenon and their significance in earthquakes are evaluated. Depending upon the type of stick-slip the mechanism of brittle failure of the interlocked aspirities or the mechanism of plastic instability predominates.