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Understand earthquakes, tsunamis and volcanoes

Plain explanations of how the ground moves, what the warnings mean, and what actually helps - each one citing the agencies the data comes from.

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Earthquakes

Aftershocks: what follows a big earthquake

Most large earthquakes are followed by a sequence of smaller ones. A small number are followed by something bigger. Here is what is actually known about how aftershock sequences behave, and how the USGS turns that into a forecast.

Seismic science

Magnitude and intensity are not the same number

One earthquake, one magnitude - but the shaking you felt is a different measurement entirely, and the two get confused constantly.