What Earthquake Magnitude Really Measures (and What It Doesn't)

Every time a notable earthquake strikes, the first thing reported is a single number: "a magnitude 6.2." It sounds precise and simple — bigger number, bigger quake. But that number hides some genuinely surprising math, and on its own it can badly mislead you about how dangerous a quake actually was.

You can see recent earthquakes worldwide on the LEV map by switching on the Earthquakes layer. Each dot is sized by magnitude and tagged with its depth, so you're seeing all three pieces of the story at once.

The scale is logarithmic — and that changes everything

Here's the fact that trips most people up: the magnitude scale is logarithmic, not linear. Each whole step up isn't "a bit more" — it's about 32 times more energy released.

So a magnitude 6 isn't twice a magnitude 3. Run the steps: a 6 is ~32× a 5, which is ~32× a 4, which is ~32× a 3. Multiply it out and a magnitude 6 releases roughly 32,000 times more energy than a magnitude 3. This is why the gap between a "moderate" 5 and a "major" 7 — just two numbers — is the difference between cracked plaster and collapsed buildings.

(You'll often hear "the Richter scale." Modern earthquakes are actually reported on the moment magnitude scale, which behaves the same way at the low-to-mid range but measures the very largest quakes far more accurately. The logarithmic, ~32×-per-step rule holds either way.)

Magnitude is only one of three things that matter

A common, jarring news story: a "small" earthquake flattens a town while a "huge" one barely registers. Both can be true, because magnitude alone doesn't tell you what the shaking was like. Three factors do:

1. Magnitude — the total energy released at the source.
2. Depth — how far underground it happened. A shallow quake has less rock to soak up its energy before it reaches the surface, so it shakes the ground far harder. A shallow magnitude 5 under a city can out-damage a deep magnitude 7.
3. Distance — how close you are to it. Shaking fades fast with distance.

This is exactly why the live map shows depth next to magnitude on every quake. A magnitude 6 at 8 km depth and a magnitude 6 at 500 km depth are completely different events for the people above them.

Magnitude vs. intensity: size vs. experience

There's one more distinction worth locking in, because the two words get muddled constantly.

• Magnitude is the earthquake's size at its source — one number, the same whether you measure it from next door or across the planet.
• Intensity is how strong the shaking felt at a specific place — so a single earthquake has many intensity values: violent at the epicenter, gentle a few hundred kilometers away.

Put simply: magnitude is the earthquake; intensity is your experience of it.

The connections on the map

Earthquakes don't live alone. Swarms of small quakes beneath a volcano are one of the clearest signs magma is on the move — which ties directly to volcano alert levels. And a large, shallow quake under the seafloor is what can displace enough water to raise a tsunami, where the significant wave height of the open ocean suddenly matters to coastlines thousands of kilometers away. Turning on Earthquakes alongside the Volcanoes layer lets you see those geological stories unfold together.

The bottom line

The magnitude number is real, but it's compressed by logarithms and silent about depth and distance. The honest reading of any earthquake is three numbers, not one: how much energy, how deep, and how close. Get all three and the map stops being a scatter of dots and starts telling you which quakes actually mattered.