Students investigate the effect of different 'earthquake' positions on the signals received by two 'seismic stations', using two microphones connected to a PC with sound-editing software.
This is intended to be a relatively short activity to model how the size and arrival times of seismic waves vary with distance from the source. The comparison of traces is meant to be one of overall appearance, and does not need detailed knowledge of what a seismogram shows. There are two aspects to look at: amplitude and arrival time.
Additionally, students might examine the time difference between the two signal peaks and relate this to the different distances travelled (using distance = speed x time, and speed of sound in air is roughly 330 m/s).
The examples in task B introduce a simplified model of how seismologists use the records from several stations to establish exactly where an earthquake occurred. This could be done as a demonstration or as a small-group activity.
It is important to check that the software is already installed on the computer(s) you plan to use and to confirm any further set-up details before you use this activity in class: in this case, you need to be able to see two channels of input on screen (i.e. stereo input). You can find details of how to download and use Audacity (free, open source software) in the pdf 'Downloading and using the Audacity software'.
It is important to make sure that the sound is travelling through the air - not through a table - to both microphones, so clapping is preferable to tapping the bench.
Each group will need: