Hello! I'm an Earthquake!

You don’t know me. But in a little while, you may feel me shake your house and maybe even send your books crashing to the floor. I will set off car alarms with a single shudder and send the wildest of animals scrambling for shelter. I’m not boasting, I’m just saying my power can be so great that sometimes, if you live on land where my type is often found, you may have to learn in school what steps to take if I come crawling along. Yeah, yeah, you’ve probably guessed by now. I’m an earthquake!

You may have seen reports of earthquakes like me on the news. It’s true, we can be rough. We can cause damage to buildings, highways, and bridges, and if we’re strong enough, we can destroy entire towns and cities. We create tsunamis, which are very long and high sea waves that can flood and flatten entire coastal areas. We are often responsible for landslides, which is when huge amounts of rock or earth come tumbling down a slope, and avalanches too, which is similar to a landslide, except we’re now talking snow and ice falling from a hill or mountain. You see, the thing is…a lot of people know all about the destruction that we can cause, but not as many know how I am born, you know? Like, how I get started and do the things I do.

So, let me tell you my story.

What exactly am I? Well, people would describe me as a sudden and violent shaking and rolling of the ground. But there’s more to me than that. This shaking is caused by a very specific movement inside the earth. You might think that the surface of the earth is solid. But it’s actually like a big jigsaw puzzle, with 20 pieces that float on the crust and mantle of the earth, which are like different layers between the surface of the earth and its core. These puzzle pieces on the surface are called tectonic plates. The cracks, or boundaries, between the plates are called faults. The tectonic plates are always slowly moving (yes, you heard me correctly, there’s nothing really stable about the land you are living on) and sometimes these plates bump against each other and get stuck. The pressure builds up at these faults because neither plate can move. Finally, something has to give, and the sudden release of all that energy creates an earthquake like me.

If the plates are forced so that one moves above the other, it is called a reverse fault. If one plate is forced to drop below the other, it is a normal fault. If they suddenly slip sideways by each other, it is a strike-slip fault. I get going when two tectonic plates meet each other at a strike-slip fault. The pressure between them builds up until they finally move by each other. This is the focus, or origin, and it’s where I am born! I am so excited that I send seismic waves of energy in all directions, including up to the earth’s surface. Seismic waves are an energy wave or vibration that moves through the earth. The area right above the focus is what’s known as my epicenter or, to you, “the earthquake’s epicenter.”

The epicenter is the place on earth’s surface where my seismic waves begin. My first seismic waves travel through the body of the earth itself and move really fast, 20 times faster than the speed of sound! They are the first of my waves that scientists can measure, using a very delicate instrument called a seismograph. Other types of waves follow, and people begin to feel me. They run out of their houses because they are afraid. Sure, I rattle glass windows, and even crack some of them. I knock dishes off shelves and onto the floor, and those may break too. But, really, I’m not a very big earthquake. There are worse earthquakes than me! How can people tell? Well, scientists measure me with the Moment Magnitude Scale, or MMS (which used to be called the Richter Scale). I am a 6.0: big enough to do some minor damage, but not big enough to destroy buildings and bridges. I’m okay with that!

And even after I get started, very quickly I feel myself running out of steam, and growing tired and weak. Most earthquakes only last 10-30 seconds, you see. That said, even after my waves are finished, there will be many others that come after me; smaller earthquakes that will occur over the next weeks or months. These are called aftershocks and are caused by the readjustment of the earth after I am finished.

But even though I’m done being an earthquake, I should warn you I have many relatives all over the world. There are around 20,000 earthquakes every year, or about 55 every day. That’s a lot of earthquakes! Some will be small like me, and a few will be huge and cause severe damage and injuries. I’m sorry about that. But whether we are huge or so small that it just feels like just a big truck driving by your house, it's worth knowing how and why we get going, and that we all begin in the same way.