The Nevada Earthquake Safety Council has developed a scenario, or a description of what could happen, if the nearby Genoa fault were to rupture. Over thousands of year the tectonic plates will move several miles. And the motion is for western California to move north along the coastline, not into the ocean. That is an individual decision, which depends on the risk that homeowners are financially willing to take. It also depends on their confidence in the quality of their homes, since there is quite a large deductible on most policies.
Some seismologists do have it.
All of these are earthquakes. Aftershocks are smaller earthquakes occurring after a main shock, and they keep the hazard relatively high for a certain period after any large earthquake. Foreshocks are smaller earthquakes occurring before a main shock. Only with hindsight can we distinguish what are foreshocks and aftershocks. Ideally you should get the same magnitude for an earthquake no matter where you measure it.