Don,

Briefly, the Landers earthquake perturbed the stress around the Big Bear earthquake quite a bit (a good part of a bar?) in the direction to encourage the Big Bear earthquake. The close time association of just a few hours meant triggering could be inferrred.

For this latest earthquake, if it has the same mechanism as the one just after Landers, then Landers also encouraged it. However, the 1992 Big Bear earthquake might have discouraged it. I don't know the geometry well enough to say if this is the case.

There is a less clear case for triggering with a long time separation, since regular tectonic loading also pushes California faults toward failure, and over decades tectonic loading is likely to be more important than the perturbation of one prior earthquake at a distance.

John