This research is a continuation of a study to investigate the hypothesis that variations in normal stress across a fault surface are a primary factor controlling stick-slip behavior in laboratory simulations and in earthquakes. The hypothesis has been suggested on the basis of recent work on stick-slip behavior in foam rubber and, if true, will have a major impact on current ideas about rupture nucleation and the characteristics of premonitory slip. The existence of normal vibrations during stick-slip has implications for rupture mechanics, fault behavior, and short-term earthquake prediction. This research is a component of the National Earthquake Hazard Reduction Program.
