Which geographic region is especially at risk for megathrust earthquakes?

• A. The Pacific Ring of Fire (Chile, Japan, Alaska, Cascadia, New Zealand, Indonesia)
• B. The Central Atlantic region
• C. Continental interior plains
• D. The African Rift Valley

Answer: (A)

Megathrust earthquakes occur where a subduction zone locks and then ruptures, releasing massive energy along a very long thrust fault as one plate is forced beneath another. The Pacific Rim—the Pacific Ring of Fire—is full of these subduction zones, so it experiences the largest earthquakes. Think of the Chilean, Japanese, Alaskan, Cascadia, New Zealand, and Indonesian regions here; they sit at boundaries where oceanic plates dive under another plate, leading to enormous slips and huge quakes.

In other areas, the picture is different. The Central Atlantic region is a passive margin with little active subduction today, so megathrust events aren’t characteristic there. Continental interior plains are far from plate boundaries and mainly experience smaller, intraplate earthquakes. The African Rift Valley is a continental rift where crust is being pulled apart, producing earthquakes from normal faulting rather than subduction megathrusts. So the Pacfic Ring of Fire stands out as the region especially at risk for megathrust earthquakes.