Sorry to disappoint those on the East Coast who would love to have us disappear, but there is no chance that California will fall off and sink into the ocean. Since the the major faults in California are mostly strike-slip, and have little or no vertical motion, there is no way for large blocks of California to fall off. Note that I am not saying that some parts of the state don't fall into the ocean every day in landslides. What I am talking about is the ridiculous belief that huge chunks of California are going to tear away and go sinking into the brine.
Of course, this is not to say that California won't undergo some changes as a result of plate tectonics. If nothing else, the sliver of California which is southwest of the San Andreas Fault is on a different plate from the rest of California. This sliver contains Los Angeles and San Diego, and is moving northwest relative to the rest of the state at a rate of a few centimeters each year - so that in about 20 million years, Los Angeles will be a suburb of San Francisco.
There has never been any recorded case of an earthquake causing cracks to open up and swallow cities. Certainly, earthquakes can cause cracks to form in the Earth, such as happened during the Loma Prieta earthquake in 1989. However, these cracks are generally quite small and only rarely do they exceed a meter or two in width. And certainly these cracks don't again close up and swallow somebody whole.
Below is a nice picture of a large crack which opened in the ground after the Loma Prieta earthquake. It is not actual ground rupture, but is instead ground failure. This is a typical crack for an earthquake --- and as you can see, it hasn't swallowed the house in the background.
Image by J.K. Nakata, U.S. Geological Survey
In fact, there is only one case that I am aware of in which anyone actually died as a direct result of becoming trapped in an earthquake-caused crack. In the 1906 earthquake, near the town of Olema on Pt. Reyes, there was such a casualty -- to a cow, which fell into a crack and was killed.
On hot days with no wind, some people will tell you that an earthquake is coming -- that it is ``earthquake weather'', and you'd better be ready. That is simply not true.
The myth of ``earthquake weather'' dates back to the 4th century B.C., with the Greek philosopher Aristotle. Aristotle believed that earthquakes were caused by winds rumbling around in huge underground caverns, restlessly searching for a way out to the surface. These winds were trapped below ground, so there would be no wind above ground, and it would be stiflingly hot. Clearly, Aristotle was wrong.
However, his folly took hold and even today, there are people who believe in ``earthquake weather.'' To date, however, there have been numerous studies done to try to find a link between weather and earthquakes. No such link has been found.
One of my friends, Dr. Robert Uhrhammer at the UC Berkeley Seismographic Station, has this to say about ``earthquake weather'': `` `Earthquake weather' is whatever the weather was during the last big earthquake.'' In other words, people sometimes see patterns when there are no patterns to be seen. ``Earthquake weather'' simply does not exist.