Deep-focus earthquakes are most commonly found at convergent plate boundaries, specifically where oceanic plates subduct beneath continental plates or other oceanic plates.

Here's why:

* Subduction Zones: At convergent boundaries, denser oceanic plates are forced beneath less dense continental or oceanic plates. This process is called subduction.

* Deep Descent: As the subducting plate sinks deeper into the Earth's mantle, it encounters increasing pressure and temperature. The rocks become brittle and eventually fracture, causing earthquakes.

* Depth of Earthquakes: The depth of these earthquakes can range from about 70 to 700 kilometers (43 to 435 miles). This is much deeper than earthquakes that occur at other types of plate boundaries.

Examples:

* The Pacific Ring of Fire, which encircles the Pacific Ocean, is a prime example of a region with many deep-focus earthquakes due to numerous subduction zones.

* The Andes Mountains in South America are another example, formed by the subduction of the Nazca Plate beneath the South American Plate.

Let me know if you have any other questions!