Seismic Moment & Moment Magnitude Calculator
Moment magnitude Mw from fault area, slip and rigidity (or seismic moment), the energy released in joules and TNT tons, and how two earthquakes compare in energy.
How it works
M₀ = μ·A·D (rigidity × rupture area × slip); Mw = ⅔·log₁₀(M₀) − 6.07; log₁₀E(J) = 1.5·Mw + 4.8
Moment magnitude replaced the Richter scale because it measures the physical size of the rupture — how much rock slipped how far — and does not saturate for great earthquakes. Each whole magnitude step is 10 times more moment and about 32 times more energy, so an M7 releases a thousand times the energy of an M5. The energy figure is what is radiated as seismic waves, a small fraction of the total; it still dwarfs nuclear weapons for large events.
Worked example
A 100 × 20 km fault slipping 3 m in 30 GPa rock: M₀ = 1.8 × 10²⁰ N·m → Mw 7.4, radiating 8 × 10¹⁵ J (2 megatons) — 4,000 times an M5.
Frequently asked questions
Is Mw the same as Richter?
They roughly agree between 3 and 7; above that Richter (local magnitude) saturates and understates size, which is why agencies report Mw.
What is a negative magnitude?
Tiny events — the scale is logarithmic with no floor; M −1 is a small rockfall detected by nearby instruments.
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This calculator is for educational purposes. Double-check important results before acting on them.