THE EXPLAINER

Felt reports: what people actually felt

After an earthquake, USGS invites anyone who felt it to file a short report — what moved, what fell, where they were. The program is called “Did You Feel It?” (DYFI). The reports are combined into a community intensity score (called CDI), a 1–10 scale of experienced shaking averaged over the people who reported from each place.

How this site uses them

When a listing says "reported felt by 2,342 people," that is the DYFI report count from the USGS feed — a count of people, quoted as a count. The "most felt" boards rank by that count. It is the most human number in the catalog: it answers "did anyone else feel that?" which is the question most people actually have after a shake.

What felt counts do not mean

Felt counts follow people and internet access, not just shaking. A suburban M4 can draw two thousand reports while a remote Aleutian M6 draws two — the Aleutian quake was vastly larger. Report counts are never used here as a measure of an earthquake's size or damage, and a quiet felt board in a rural area says more about population than about the ground.

Community intensity vs instrument intensity

USGS also computes an instrumental intensity (MMI) from seismometers and a physical model when a ShakeMap is produced. The two measure different things — people's reports versus instruments — and can differ for the same earthquake. This site leads with the people's number, because that is the question being asked, and links every event to its USGS page for the full instrumental picture.

File your own

Felt a quake? Report it on the USGS event page (every listing here links to it) or at earthquake.usgs.gov/dyfi. Reports from low-population areas are scientifically the most valuable, precisely because so few come in.