How big is the largest possible earthquake? - Livescience.com

One man, quoted in a U.S. Geological Survey (USGS) report(opens in new tab) about surviving the quake and its subsequent tsunami, initially thought the Cold War had escalated into nuclear Armageddon.

These dipping faults, so named because they're at an oblique angle rather than vertical, have the largest areas of rocks that can get stuck against one another, building up stress and then finally breaking.

(Some scientists think the end-Cretaceous asteroid impact that killed off the nonavian dinosaurs 66 million years ago triggered earthquakes with double-digit magnitudes, though pinpointing the size is tricky.)

The largest ancient quake that has been estimated based on geological evidence was also in Chile, approximately 3,800 years ago, and likely also measured about 9.5 in magnitude, according to 2022 research.

Smaller quakes have caused many, many deaths, just by virtue of hitting populated regions and areas with buildings prone to collapse.

Even the 1994 Northridge earthquake, a mere magnitude 6.7 that occurred on a fault no one had even noticed before, killed 57 people, injured thousands, and caused billions of dollars' worth of damage because it impacted Los Angeles.