* Divergent boundaries: These are where plates move apart, creating new crust. The earthquakes here are relatively shallow because the crust is thin and the pressure is low.

* Convergent boundaries: These are where plates collide, and one plate is forced under the other. The earthquakes can be both shallow and deep, depending on the angle of subduction. Shallow earthquakes occur at the point of collision, where the plates first meet.

* Transform boundaries: These are where plates slide past each other horizontally. The earthquakes here are typically shallow, because the plates are slipping along a relatively flat plane.

However, the majority of shallow focus earthquakes occur at convergent boundaries, specifically at the point of initial contact between the two plates. This is because the collisions generate a lot of stress, which is released in the form of earthquakes.

Here's a summary:

| Plate Boundary | Shallow Focus Earthquakes |

|---|---|

| Divergent | Yes |

| Convergent | Yes (mostly) |

| Transform | Yes |