Earthquakes at continental plate boundaries are generally characterized by being longer in duration and beginning deeper in the Earth's crust, while earthquakes at mid-ocean ridges tend to be shorter in duration and begin closer to Earth’s surface. Therefore, if you need to choose one statement that accurately describes the difference, the following would be correct:
They begin deeper in Earth’s crust.
This highlights that earthquakes at continental plate boundaries typically originate at greater depths compared to those at mid-ocean ridges, which are usually shallower and associated with tectonic plate divergence.