The San Andreas and similar faults separate two tectonic plates slowly moving in opposite directions. The faults can remain locked for many years, then catch up in sudden dramatic rupture events perceived as earthquakes. These occasional fast motions co-exist with much slower fault slips. This talk will describe how laboratory-derived friction laws and sophisticated numerical models can reproduce, in remarkable detail, all stages of past fault behavior - locked, slowly moving and earthquake-producing - bringing us closer to understanding earthquake physics.