The pulse of the planet. Unlocking the secret to earthquakes

So, moving on to earthquakes, this maps shows Australia’s past earthquake activity. As you can see in Queensland there is very little seismic activity compared to areas like  and Victoria New South Wales. But in general we have very little compared to other countries, like Japan or New Zealand as these sit on the ring of fire.

How do we know where earthquakes ocur apart from seeing the damage like in this photo? In case you did not notice the rails were originaly straight. The simple answer to that is seismic stations.

In this photo you can see all the seismic stations in Australia. As you can see, they all have two or three letter acronyms.

Now let's take a peek inside of a seismic station to see what it looks like. In the image below you can see it is nothing too fancy, just a sensor, a solar panel for power and the data recording and transmiting equipment. In the next post I will show you how to build a D.I.Y one at home for only 300 billion dollars ... just joking only twenty five.

Now I will tell you a bit about the different types of waves when a earthquake happens in real life. There are two different types of waves: the P wave arrives moving in a compressive motion (forward and back), the S wave arrives next with a shearing motion and has more power than the P wave. These two waves are the fastest as they travel through the mantle that is why they are called body waves. Then the superficial waves arrive. These waves are more powerful; they travel through the crust hence their reduced speed. The first of the superficial waves is the Rayleigh which comes in a motion that is very similar to how the sea moves. And finally the most destructive wave arrives the Love wave.

Now I will tell you how to calculate the epicentre of an earthquake first you need to see the signal from the seismic station and you need to grab the time difference in between the P wave and the S wave as I have done in this chart. This is from a nice exercise book from Geoscience Australia. You can download here as well.

Then you can put the seconds on the chart and convert it to kilometres for that station.

Then you draw a circle around the station. Use the scale at the bottom to determine the opening of the compass. Repeat the process for the rest of the stations until three or more match in one point and that is the epicentre.

In real life seismometer have three axes because there is not just one direction of movement but three: East/West, North/South and up/down. In this video from IRIS.edu you can see an animation explaining how all four types waves behave in the three axes. In the next blog post I will show you how to build your own 3-axis seismometer with a Microbit.

sources: Geoscience Australia, IRIS.edu