Caused by sudden displacement of land.
Earthquakes are vibrations caused by sudden displacement of land. However this was only known recently. But 1400 years ago this was portrayed in the Quran.
[Quran 67.16] Are you confident that the One in heaven will not cause the earth to collapse beneath you as it vibrates?
"Yakhasif in Arabic يَخْسِفَ" means downward collapse . "Tamur تَمُورُ" means vibrate. Here the land collapse causes vibrations.
How could an illiterate man who lived 1400 years ago have known that earthquakes are vibrations caused by displacement of land?
In earthquakes most of the energy is released by the mainshock (first quake). The rest of the energy is released by the following weaker aftershocks. The Quran describes both of them:
[Quran 79.6-7] On the day when the earthquake shakes, followed by the successor
How could an illiterate man who lived 1400 years ago have known that mainshocks are followed by aftershocks?