Data and methods

Where the numbers come from

Sources, coverage, update frequency and how each figure on the site is computed.

Earthquakes: USGS ComCat

All earthquakes come from the USGS Earthquake Catalog (ComCat), public domain, which merges the U.S. and international networks. We keep:

magnitude 4.5 and above worldwide since 1900;
magnitude 2.5 and above since 2000.

Every few minutes we ask USGS for events added, revised or deleted since the last check. Early magnitudes and locations are often revised in the first hours, and a quake is marked "reviewed" once a seismologist has checked it.

Coverage

Small earthquakes (below magnitude 4.5) are recorded completely in and around the United States, but only partly elsewhere, so worldwide comparisons on this site use magnitude 4.5 and above. Before the 1970s far fewer stations existed, so older years undercount the smaller of those quakes; strong ones (magnitude 6+) are reliable since 1900.

Places and countries

Cities come from GeoNames (CC BY 4.0): places with 15,000+ people. Each earthquake is linked to its nearest city; it counts for that city's country when it is within 300 km (so offshore quakes count too), or when the USGS region names the country.

How the figures are computed

Energy: log₁₀E = 1.5 M + 4.8 (joules), converted at 4.184 GJ per ton of TNT; the Hiroshima bomb is taken as 15 kilotons.
Aftershocks: earthquakes of M2.5+ in the 60 days after, within a zone that grows with magnitude (about 1.5 rupture lengths, 30–500 km).
"Strongest since": the last earthquake at least as strong within 300 km before this one, in our catalog.
Depth classes: shallow under 70 km, intermediate 70–300 km, deep beyond 300 km.