FAQ - Measuring Earthquakes

Q: What does it mean that the earthquake occurred at a depth of 0 km?

A: An earthquake cannot occur at depth of 0 km. In order for an earthquake to occur, two blocks of crust must slip past one another, and it is physically impossible for this to happen at the surface of the earth. So why do we report that the earthquake occured at a depth of 0 km sometimes? Sometimes it is simply a very shallow event with poor depth resolution, but more often it is not actually an earthquake, but a quarry blast. These explosions are recorded by the seismic network and located by the software. When they are reviewed by a seismic analyst, they are labeled as a quarry blast in the earthquake catalog.

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