Three boundary types and their hazards
Convergent boundaries, where plates collide and compress, produce the deepest earthquakes and highest mountains. Divergent boundaries, where plates pull apart and new oceanic crust forms, are relatively quiet except for rift-zone volcanism. Transform boundaries, where plates slide past each other, generate shallow, frequent earthquakes along their length. The San Andreas is a transform; the Mid-Atlantic Ridge is divergent; the Pacific Ring of Fire is mostly convergent.
Plate speeds vary by orders of magnitude
The Atlantic Ocean spreads at 2 centimeters per year. The Pacific plates move at up to 10 centimeters per year. This speed difference affects earthquake frequency and mountain-building rates. Faster-moving plates can accumulate stress more quickly and release it in more violent ruptures.