What a Magnitude 9 Actually Releases
March 16, 2026
The single most misunderstood thing about earthquake magnitude is how quickly it grows. One extra unit is not “a bit bigger.” It is about 32 times more energy. Two units is about 1,000 times. That is why a scatter of magnitude 5s tells you almost nothing about whether a magnitude 8 is coming.
The numbers
The energy radiated by an earthquake can be estimated from its magnitude. Each whole unit multiplies that energy by roughly 32 (precisely, 101.5 ≈ 31.6). Working from the standard Gutenberg–Richter energy relation:
| Magnitude | Energy (joules) | Rough comparison |
|---|---|---|
| 4.5 | ~3 × 10¹¹ | a small tactical explosion |
| 5.5 | ~1 × 10¹³ | a few kilotonnes of TNT |
| 6.0 | ~6 × 10¹³ | the ~15-kilotonne Hiroshima bomb |
| 7.0 | ~2 × 10¹⁵ | about 30 Hiroshima bombs |
| 8.0 | ~6 × 10¹⁶ | about 1,000 Hiroshima bombs |
| 9.0 | ~2 × 10¹⁸ | about 30,000 Hiroshima bombs |
| 9.5 | ~1 × 10¹⁹ | more than the rest of that decade’s earthquakes combined |
Where the energy goes
Only a small fraction — often around 1% or less — of an earthquake’s total energy budget is radiated as the seismic waves that shake buildings. Most of it goes into heat from friction on the fault and into permanently crushing and fracturing rock along the rupture. The waves we feel, and that the map is built from, are the leftover.
This is also why magnitude and shaking are not the same. A deep or distant magnitude 7 can pass almost unnoticed; a shallow magnitude 6 directly underfoot can be violent.
Why small earthquakes don’t “release the pressure”
A common hope is that frequent small earthquakes bleed off stress and prevent a big one. The arithmetic says otherwise. To match the energy of one magnitude 7, you would need about 32 magnitude 6s, or about 1,000 magnitude 5s, or about a million magnitude 3s — all on the same fault. The background rattle of small earthquakes barely touches the energy stored for a great one.
On the map, this is what the circle sizes are trying to convey. A magnitude 8 dot dwarfs a magnitude 5 dot — and even that visual gap is far smaller than the thousand-fold difference in energy.
Is there an upper limit?
Yes, set by geometry. Magnitude depends on the area of fault that can rupture at once. The longest, widest locked subduction zones on Earth can produce a magnitude 9.5 — which is what happened in Chile in 1960. A magnitude 10 would need a continuous rupture longer than any subduction zone that exists, so seismologists consider it physically implausible.
Sources
- U.S. Geological Survey — “How much energy is released in an earthquake?”, “Measuring earthquakes”, “Cool Earthquake Facts.”
- Gutenberg, B. & Richter, C. F. (1956). “Magnitude and energy of earthquakes.” Annali di Geofisica 9, 1–15.
- Kanamori, H. (1977). “The energy release in great earthquakes.” JGR 82(20), 2981–2987.