How Deep Do Earthquakes Occur?
Earthquake depth changes what kind of tectonic process caused it, and it strongly affects how the shaking is felt at the surface. Here's how shallow, intermediate and deep earthquakes differ.
Shallow, intermediate and deep earthquakes
- Shallow earthquakes — 0 to 70 km
- Most earthquakes happen here, in the crust near the surface — including nearly all continental faults like California's San Andreas.
- Intermediate earthquakes — 70 to 300 km
- Common where one tectonic plate slides beneath another (subduction zones), as the descending slab bends and deforms.
- Deep earthquakes — 300 to 700 km
- Occurs inside cold, still-brittle slabs hundreds of kilometers down — as deep as earthquakes get. Beneath Japan, Kamchatka, and Tonga are known examples.
Why do deep earthquakes happen?
Deep earthquakes occur inside subducting tectonic slabs — cold oceanic crust that has sunk far enough into the mantle to stay brittle at depths where surrounding rock would normally deform too slowly to fracture. Once a slab warms through, earthquakes stop; that's why roughly 700 km is close to the practical limit.