Fig. 4. (A) Change in the Coulomb failure stress resolved on the San Andreas fault caused by MŽ6 earthquakes in southeastern California since 1979. Model fault is vertical and passes between the two San Andreas branches east of Yucaipa. (B) Corresponding slip distribution along the San Andreas fault needed to relieve shear stress imposed by MŽ6 earthquakes since 1979. Immediate changes are calculated in an elastic halfspace, and so the base of the fault restrains displacement. Long-term changes are calculated in an elastic plate, with upper and lower surfaces stress-free. Induced right-lateral slip (added loads) are solid fields; left-lateral slip (remvoed loads) are stipled.