Megathrust earthquakes are typically associated with which characteristics?

• A. Very small magnitude and minimal tsunami potential.
• B. Moderate magnitude with potential localized tsunamis.
• C. Very large magnitude on subduction boundaries with potential tsunamis.
• D. They occur only at transform boundaries.

Answer: (C)

Megathrust earthquakes rupture the huge fault interface where one tectonic plate dives beneath another at subduction zones. Because the rupture covers a vast area and the slip can be enormous, these events reach very large magnitudes. The sudden vertical displacement of the ocean floor during such an earthquake displaces large amounts of seawater, spawning tsunamis that can travel across oceans. That combination—very large magnitude along subduction boundaries with the potential for tsunamis—is what defines megathrust earthquakes. The other options don’t fit: they imply small or moderate sizes or place megathrusts at transform boundaries, which don’t involve the same large-scale ruptures or associated tsunamis.