OF THE MECHANICS OF FAULTING

The development of instabilities in geologic materials has been studied using the techniques of both seismology and rock mechanics. In the field the deformation that occurs prior to an earthquake was studied through the analysis of foreshocks. Foreshocks occur before a large fraction of the world's major (M 2 7.0) earthquakes. Teleseismically located events before major earthquakes from 1914 to 1973 were considered together to examine possible average temporal and spatial patterns of foreshock occurrence. Several days before the main shocks and apparently near the epicenters of them (A A 30 km) the activity begins to increase, culminating in a final rapid acceleration of activity in the last day. The acceleration continues up to the time of the main shocks, except for a possible temporary decrease about 6 hours before them. The seismicity increase