What Is #13: An Earthquake

The 'What Is' Series

A couple of months ago I started a new series on this blog titled "What Is". Thus far the focus is on the field of astronomy where we hear all sorts of cool science taking place in space. The goal of this series is to explain the details of different objects we hear about relatively frequently.

Earth Science

For the second post in a row in this series, the topic does not focus on space science. Instead, the focus is on earth science. A well-rounded astronomy enthusiast needs a good education in earth science. Last time I discussed frostquakes, which were quite frequent in the much of the U.S. during January's extreme cold spell. They are very different, however, from earthquakes, so today let's talk about earthquakes.

What is an Earthquake?

Earthquakes are the result of energy released from the ground when rock shifts against itself. That's a very basic definition, but a good one for the purposes of this post. Given this process of rock shifting is very slow, the energy build-up is slow, unlike a frostquake which is a quick build-up and release of energy. Given the slow build-up, earthquakes can be far, far, far more damaging than a frostquake. When the stress in the shifting rock causes the rock to break or fracture, all of this energy is released at once. This is much more common near fault lines in Earth's crust where plates shift against each other. Fault lines exist all over the world, as shown in the image below.

Major fault lines across the world. (www.mapsoftheworld.com)

This map only shows major fault lines, but there are many others. Take the mid-west U.S. for example. Although not known for earthquakes, compared to the west coast, there are fault lines throughout the mid-west and earthquakes have occurred. I've lived my entire life in the mid-west U.S. and experienced two earthquakes, although neither was much more than a small tremor. It felt as if a large semi was driving right by my house. No damage was done and there was no risk of life involved.

Earthquake hazards in U.S. - USGS

Richter Scale

Earthquake strength is measured by the Richter Scale, which ranges from 1 to greater than 9. It is a logarithmic scale, meaning the amplitude of the seismic waves for a magnitude 4 earthquake are ten times that of a magnitude 3 earthquake. It takes a about a magnitude 3 earthquake to feel something, although it is possible to feel a slight tremor below that. Once you get to a magnitude 4, some slight damage can occur and this increases quickly as the strength of the earthquake increases. The strongest earthquake on record took place in 1960 in Chile and measured 9.5 on the Richter Scale.

Preparation

No matter where you live, you need to prepare for an earthquake. Growing up as a kid we never had earthquake drills, but now schools throughout the mid-west, despite the lower likelihood, do annual earthquake drills. It's better to be safe and prepared than unsafe and unprepared. Many areas that rarely had earthquakes are now experiencing many more earthquakes due to fracking for natural gas. Earthquakes have become quite common in Oklahoma and parts of Texas due to fracking. For more information on preparing for earthquakes, go here:

https://www.ready.gov/earthquakes