Q: Scientists weren't just wrong about earthquakes in the centuries leading up to the 1906 San Francisco quake. They were really wrong. What did they believe?--Marshal Zeringue
A: If you go back to the Enlightenment, they thought they were related to chemical explosions. By the 19th century, many scientists said they were caused by large volcanic explosions happening within the Earth.
There was no wide acceptance of the idea that earthquakes were actually caused by the sliding of great crustal blocks against each other until the 1906 earthquake, which ruptured the earth's surface for almost 300 miles. The ground had actually slid tens of feet along that rupture.
Q: Earthquakes can happen when giant chunks of land relieve the pressure that builds as they press against each other. You write that this is akin to what happens to a railroad car when it's pushed.
Could you explain that?
A: Imagine you're in a railroad car with the brakes on. It's getting pushed by another car, but it won't slide because of the brakes.
Eventually, however, the friction is overcome and the wheels start to slide on the iron rails. This makes the whole car shudder.
Another way to look at it is to put your hands palm down on a table and...[read on]