My guess is that earthquakes are really so scary because you don't have any warning. It's the only thing besides a nuclear war that can really… one second you're living in a big beautiful city and ten seconds later it's flat.
Every day the earth is shaken by hundreds of small earthquakes. Most go unnoticed. They usually occur along the boundaries of the templates that cover the earth like an eggshell. Driven by the heat deep within the earth's core, the plates grind against each other on long lines called faults.
When the plates find their motion blocked, stress builds up. Finally, the fault gives way. The released energy raises through the earth in the form of seismic waves. For much of the world, the movement of plates like these is also an indispensable creative force.
If we didn't have earthquakes, if we didn't have this great flow of heat through the interior of the earth, the earth would be a cold dead place. If it wasn't for this great flow of heat, they'd be no continents, no oceans, no atmospheres, the earth would be as dead and dry and cold as the moon. It's really the earthquakes that create the topography, the valleys, the mountains.