Seismic Detection

Did you know that we get earthquakes in Australia? They are usually low magnitude, so not many people (if any) feel them. However, there is sensitive equipment based all over Australia which can detect them when they occur and be used to locate the exact location where they originated from.
Photograph of a seismometer (Wikimedia, accessed 15/6/2020)
Seismometers are used to detect earthquakes. In more basic models, they are a roll of paper which is continuously pulled. Above the paper is a pen which marks the paper as it moves. If there is no ground movement the mark the pen leaves is just a straight line. When there is an earthquake the pen shakes with the movement and this is shown as a seismic trace on the paper. The more the ground shakes the larger the seismic trace. 
Seismogram – this is the graph output by a seismograph. (Wikimedia, accessed 15/6/2020)
  • For more information on how seismometers work watch this video from Geoscience Australia: Earthquake monitoring
  • To have a go at making your own seismometer watch our tutorial video.

The amount the earth shakes at a particular location will depend on a few factors: the proximity to the earthquake, the magnitude of the earthquake and the ground substrate. Generally, the closer you are to the epicentre of an earthquake, the stronger it will feel. A high magnitude earthquake is also usually felt more strongly than a low magnitude earthquake. Also a soft substrate, such as sand, will absorb more of the energy than a hard substrate, like rock, which the waves can pass through more easily. However, building on soft material has its perils – learn more about liquefaction here.
Seismologists can determine how far away their equipment is from the epicentre of an earthquake by measuring the difference between arrival times of different wave types (primary and secondary waves). When they know the epicentre distance from three or more seismic stations, they can then plot these as circles on a map and see where they intersect. The point of intersection gives the location of the epicentre.
When the distance of an earthquake is known from three or more seismic stations the epicentre can be found through triangulation. (Wikimedia, accessed 15/6/2020)
Useful websites and videos