This research is to verify and understand the phenomenon of earthquake fault interface waves involving separation of the fault during rupture. Based on earlier work by Schallamach and Comninou- Dundurs, and on laboratory fault-rupture experiments with foam rubber and polycarbonate-solid models, further modeling will be done along with finite difference calculations. If confirmed, the work bears on questions of low heat flow along faults, weak stress along faults, large overthrusts, and the locking-slip pulse model of rupture. This research is a component of the National Earthquake Hazard Reduction Program.