What Does Earthquake Magnitude Mean?
Magnitude is the number everyone quotes after an earthquake, but it's widely misunderstood. Here's what it actually measures, why the scale grows exponentially rather than evenly, and how to read the difference between a M5 and a M7.
What does earthquake magnitude measure?
Magnitude estimates the size of an earthquake at its source, based on the amplitude of seismic waves recorded on seismometers — not how strongly the shaking is felt at any particular location, which depends on distance, depth and local geology (see below).
Why is earthquake magnitude logarithmic?
Each whole-number increase in magnitude represents roughly a 10× increase in measured wave amplitude — not a 10% or 20% increase. That's what makes the scale logarithmic: a magnitude 7 earthquake isn't "a bit bigger" than a magnitude 6, it's an order of magnitude bigger in wave amplitude.
How much stronger is M6 than M5?
A magnitude 6 earthquake has roughly 10× the wave amplitude of a magnitude 5, and releases roughly 32× more energy — energy grows faster than amplitude because it scales with the 1.5 power of the amplitude ratio. Use the interactive tool below to compare any two magnitudes directly.
Magnitude vs earthquake damage
Magnitude alone doesn't determine damage — depth, distance, local geology, and building construction all matter. Two similar-magnitude earthquakes can shake very differently.
Richter scale vs moment magnitude
Modern large-earthquake reporting uses moment magnitude (Mw); the "Richter scale" people commonly refer to is rarely the actual measurement anymore. EarthPulse, like USGS, reports moment magnitude (Mw) for the earthquakes it tracks. Source: USGS