Understanding the Earthquake Magnitude Scale
Why a magnitude 7 is not just slightly bigger than a magnitude 6, plus what Richter, moment magnitude, and intensity actually measure.
The single number attached to every earthquake hides a surprising amount of nuance. Getting it right changes how you interpret the news and the live feed.
Magnitude is logarithmic, not linear
Each whole step up the magnitude scale means roughly 32 times more energy released. So a magnitude 6 is not 20% bigger than a magnitude 5, it is about 32 times bigger. A magnitude 7 releases around 1,000 times the energy of a magnitude 5. This is why a single great earthquake can dwarf the combined energy of every small quake recorded that year.
Richter versus moment magnitude
Most people still say "the Richter scale," but seismologists largely retired it decades ago for large quakes. The Richter scale saturates, meaning it stops giving useful numbers above about magnitude 7. Today the standard is moment magnitude (Mw), which is based on the physical size of the fault rupture and the rock's rigidity. When you see "M6.2" on this tracker, that is almost always moment magnitude.
Magnitude is not the same as shaking
Magnitude measures energy at the source. How hard the ground shakes where you stand is intensity, measured on the Modified Mercalli scale from I to XII. Intensity depends on distance, depth, and the soil under your feet. A shallow magnitude 5 directly beneath a city can cause more felt damage than a deep magnitude 6 far offshore.
Why depth belongs in the conversation
This is why the feed shows depth next to every quake. Two events with the same magnitude can feel completely different. Shallow ruptures concentrate their energy near the surface, while deep ones spread it out before it reaches you. When you scan the list, read magnitude and depth together rather than treating the headline number as the whole story.
Putting it to use
Next time a quake appears in the feed, check three things: magnitude for total energy, depth for how concentrated the shaking is, and location for who was nearby. Those three together tell you far more than the magnitude alone ever could.