Key Takeaways
- Magnitude is logarithmic: each whole-number step means about 10× the measured wave amplitude and roughly 32× the energy released.
- A magnitude 7.0 releases about 32× the energy of a 6.0 and about 1,000× the energy of a 5.0 (32 × 32 = 1,024).
- For large earthquakes the USGS uses moment magnitude (Mw), and the damage a quake causes also depends on depth, distance, local geology and building design — not magnitude alone.
A 7.0 Isn't Just a Little Bigger Than a 6.0
Look at two earthquake alerts: magnitude 6.0 and magnitude 7.0. The difference is just one number. It sounds minor.
It isn't. Not even close.
Earthquake magnitude works on a logarithmic scale, meaning each whole-number jump represents a massive increase in the earthquake's size and energy.
That small-looking difference can mean roughly 32 times more energy.
The Two Numbers Behind Every Earthquake
The U.S. Geological Survey (USGS) measures the difference between magnitudes in two important ways:
- About 10 times the measured amplitude: How tall the earthquake's waves appear on a seismogram.
- About 32 times the energy released: How much more energy the earthquake unleashes.
So a magnitude 6.0 earthquake doesn't simply have one more unit of power than a 5.0. Its measured waves are 10 times larger, and it releases roughly 32 times more energy.
Where does 32 come from?
The mathematical relationship is 10^1.5, which equals approximately 31.6. The USGS rounds this to "approximately 32."
Even a 0.1 increase matters: it represents about 1.4 times the energy.
5.0 vs 6.0 vs 7.0: Watch the Numbers Explode
Here's where the scale gets startling.
- 6.0 vs 5.0: 10× the amplitude and ~32× the energy.
- 7.0 vs 6.0: Another 10× the amplitude and another ~32× the energy.
- 7.0 vs 5.0: 100× the amplitude and 1,024 times the energy.
That's right. Two whole-number steps mean roughly a thousand times more energy.
It would take about a thousand magnitude 5.0 earthquakes happening at once to match the energy of one magnitude 7.0 earthquake.
A one-point difference isn't a small upgrade. It's an enormous jump.
Why the Earthquake Scale Has No Ceiling
Most measuring scales eventually run out of numbers. Earthquake magnitude doesn't have a fixed upper limit.
That's deliberate.
Earthquakes range from tiny tremors that nobody feels to the largest events ever recorded. A logarithmic scale makes it possible to describe that enormous range using one system of numbers.
You might still hear the term "Richter scale" in the news. But for large earthquakes, the USGS now relies on moment magnitude (Mw).
Instead of depending only on wave height, moment magnitude is calculated using the physical characteristics of the fault itself: the area that ruptured multiplied by how far it slipped.
It is directly proportional to the energy released.
The USGS considers it the most reliable estimate of size for very large earthquakes, where older scales can saturate and underestimate the quake.
A Bigger Earthquake Doesn't Always Mean More Damage
Here's something the magnitude number doesn't tell you: how badly a particular place will be shaken.
Magnitude measures the earthquake at its source. It's a single number, regardless of where you stand.
Intensity is different. It describes the shaking and its effects at a particular location.
Several factors determine how much damage an earthquake causes:
- Distance from the hypocentre.
- The direction in which the fault ruptured.
- Local geology beneath the ground. Soft sediment can shake harder than solid rock.
- Building design.
That's why a deep, distant 7.0 can cause little harm, while a shallow 6.0 near a city can be devastating.
The magnitude tells you how big the earthquake is. It doesn't tell you how big the disaster will be.
The Twikup Take
The next time an earthquake headline changes from 6.8 to 7.0, don't dismiss it as a tiny adjustment.
That 0.2 difference represents about twice the energy.
On the earthquake scale, small numbers can hide enormous consequences.
Image: AI-generated illustration.