Plain-English explainers: what magnitude, alerts, AQI, hurricane categories and volcano alert levels mean, and where the official information comes from.
Nov 9, 2026
The USGS event page packs a lot into a few lines. Here is what automatic and reviewed mean, how the location text is built, what PAGER colors stand for and why the tsunami flag is not a warning.
Nov 8, 2026
Magnitude is one number for the whole earthquake. Here is how USGS calculates it, what the letters after the number mean and why the first value you see can change.
Nov 8, 2026
ShakeAlert can warn people seconds before strong shaking arrives. Here is where it works, how alerts reach phones, which thresholds apply and why some people get no warning.
Nov 8, 2026
Some of the strongest shaking in US history happened far from any plate boundary, along the Mississippi River. Here is what the USGS records show about 1811–1812 and the hazard now.
Nov 8, 2026
The Pacific plate is moving into and under Alaska at about 2 inches a year. Here is what that produces, from tens of thousands of small quakes to the largest earthquake in US history.
Nov 8, 2026
The United States has four tsunami alert levels and two warning centers. Each level comes with a different action from the National Weather Service.
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