TREMR

Nearly 90% of all earthquakes happen in one zone — a horseshoe of tectonic fire encircling the Pacific Ocean. Here's what it is, why it exists, and why it shows up as a permanent ring of dots on Tremr's map.

On May 22, 1960, southern Chile shook with a force the world had never measured before. Magnitude 9.5. The resulting tsunami crossed the Pacific and killed people as far away as Japan. This is the story of the earthquake that reset what we thought was possible.

Every earthquake you see on Tremr was detected by a network of instruments buried in the ground around the world. Here's how those sensors work, how they communicate, and how a wiggle on a graph becomes the magnitude number you see on your screen.

Tens of millions of people live directly above one of the most studied fault systems on Earth. What does that actually mean for daily life? How likely is the "Big One"? And what should Californians actually be doing to prepare?