“Did the Earth move for you too?”

Well, when it comes to earthquakes, maybe not! That’s because even if you live in an earthquake zone like around the San Andreas Fault many times earthquakes pass by without notice. Most earthquakes are not felt as they are so small and will never be noticed by people standing on the surface. It may amaze you to find out that in southern California there are about 10,000 earthquakes alone!

Thank goodness they aren’t all felt as I don’t think anyone would ever get any sleep at all! But what about those earthquakes that we do feel? How are they measured and classified?

An earthquake is measured in two ways. These two values are magnitude and intensity. Magnitude is a measurement of the actual size of the earthquake. No matter where you were standing and how much the earth shook the magnitude of the earthquake is always the same. Intensity is a variable measurement and is based on the actual shaking. This means that this earthquake statistic will vary dependant on location.

So now that we know how one measures an earthquake, let’s talk a little bit about the earthquake in general. Or put another way, just what makes the earth move?

Simply put an earthquake is when two blocks of earth suddenly slip past one another. The surface of this slippage is what is called a fault. Where the exact place the slippage takes place is called the hypocenter. This is actually the more important of the locations in evaluating an earthquake but the lesser known one. I am sure you have heard of the epicenter of an earthquake but this is actually the location directly above on the surface where the earthquake took place.

The Earth has four layers. These four layers from the inside out are the inner core, the outer core, the mantle, and the crust. The smallest of these layers is the crust and it is actually more like a puzzle consisting of many pieces all moving around sliding around and bumping into each other.

These pieces are called tectonic plates while the edges of the pieces are called the plate boundaries. Getting to the heart of the earthquake, the plate boundaries are made up of many faults and it is on these faults that earthquakes happen. The reason for this is that the faults have edges which are rigid and rough. While the rest of the plate keeps movie the edges get stuck.

Thus when a tectonic plate moves far enough and the edges finally come un-stuck there is an earthquake.

So while scientists are still trying for ways to predict earthquakes and help minimize the damage caused by earthquakes, you can now say when someone asks, “Did the earth just move for you too?” answer them with all your newly learned earthquake knowledge.