In Göttingen, Germany, there’s a four-tonne steel ball that can be raised up a 14-metre tower — and then dropped in less than two seconds, crashing back to earth. It makes tiny, artificial earthquakes: here’s why.
image/text credit: Tom Scott
The information that these artificial earthquakes provide information of what’s happening beneath the ground in all directions.Earth tremors moved through the ground in two ways the P waves or primary waves compress the ground back and forth in the direction that the wave is traveling, squeezing it together.
Traveling slightly slower are the S waves the secondary waves which shear the ground side-to-side and those waves behave differently in duration and wavelength and intensity depending on the ground they’re traveling through.
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The observatory team refill that pit every year to make the ground flat, and the ball just digs a hole again. The rock’s just being compressed underneath. They joke that, somewhere in Australia, there’s a slowly growing hill…And finally, the ground steams for a little while after the ball hits: it gets rather warm…
