The problem is that earthquakes start out many miles beneath the surface, too deep for us to observe them directly. So we study them from afar by
- Observing the geological changes at the ground surface,
- Analyzing the symphony of earthquake vibrations recorded on seismographs, and
- Monitoring the tectonic changes in the Earth’s crust by surveying it repeatedly, using land survey techniques for many years and now using satellites.
In addition, we have laboratory experimental results on how rocks behave at the depths and temperatures where earthquakes form, which helps us understand what happens during an earthquake. One of the important things to recognize is that rocks, like rubber bands, are elastic.