When we moved to Tahoe, we never thought about earthquakes. We knew of course about the major quakes that leveled buildings and freeway overpasses and killed lots of people. But Tahoe was never on the list of places with major risk. So when we experienced our first shaker, we were actually excited. This was what everyone talked about! The lamps teetered, the pictures on the wall went crooked, and dishes "walked" across the counters and shelves.
Since then we've experienced many earthquakes that were significant enough to feel. (For those who don't know, there are hundreds and sometimes even thousands of earthquakes a day across the west, most of which are too minor to feel. We only know about them because sensitive instruments pick up the movement.)
We've also learned about plate tectonics. The earth's crust is made up of giant plates that are constantly moving. The reason for their movement is not totally understood, but suffice to say that the interior of our planet is a dynamic place, full of movement. And what goes on down below affects what happens on the surface crust.
The main thing is that those crustal plates move in different directions and at different speeds. The intersection of the plates is where the action is. The stresses build up, and, periodically, those stresses are released when the plates suddenly move. Sometimes one plate pushes up against another, and that process builds mountain ranges. Other times, a plate gets pushed down, or sideways. No matter what direction the tectonic plates suddenly move, we feel it as an earthquake.
In the last two weeks, Tahoe has had two dramatic quakes. They haven't caused much damage. But they sure get your attention!