Earthquake Magnitude Calculator to Compare the Energy of Two Quakes

Every whole step on the magnitude scale multiplies an earthquake's energy release by about 32 and the wave amplitude on a seismogram by 10, according to the USGS. A magnitude 7 therefore carries roughly 32 times the energy of a magnitude 6, and about 1,000 times that of a magnitude 5.

Set the two sliders to any pair of magnitudes, or start from a preset such as the 1960 Valdivia earthquake (M9.5), the 2011 Tōhoku earthquake (M9.1) or the 2010 Haiti earthquake (M7.0). The calculator answers with two figures. One says how many times larger the bigger quake's recorded wave amplitude is, and the other says how many times more energy it released. Underneath, a chart plots both ratios against the magnitude gap on a logarithmic axis, where each curve becomes a straight line.

How Much Stronger Is a Magnitude 7 Than a 6?

Ten times in wave amplitude, about 32 times in energy. Those two numbers differ because magnitude was defined from the logarithm of amplitude, while the energy behind that amplitude climbs faster. The USGS states the rule in words, with a tenfold amplitude increase and about 32 times more energy for every whole number. The calculator writes it as 10^ΔM for amplitude and 10^{(1.5 × ΔM)} for energy, where ΔM is the difference between the two magnitudes, and 10 raised to the power 1.5 equals 31.6, which rounds to the USGS figure.

The gaps compound quickly. A difference of two whole magnitudes gives 10³, or 1,000 times the energy, and the Live Atlas magnitude glossary notes that a magnitude 9 releases roughly a million times more energy than a magnitude 5. Decimals count as well. The 0.4 gap between Valdivia and Tōhoku already works out to almost four times the energy.

Why Does the Scale Use Logarithms?

Charles F. Richter introduced the concept of earthquake magnitude in 1935 at the California Institute of Technology, and he built it on the logarithm of the wave amplitude that seismographs recorded, as the USGS recounts. A logarithm squeezes an enormous range of sizes into a short ladder of numbers. Seismologists now mostly use moment magnitude (Mw), derived from the physical properties of the rupture itself. The older Richter scale saturates above about magnitude 7, so it cannot separate the largest events from one another.

Does a Bigger Magnitude Mean More Damage?

Magnitude measures the source, and damage depends on what lies above and around it. The 2010 Haiti earthquake was a magnitude 7.0 at a depth of 13 km, yet Live Atlas lists it as the deadliest of the earthquakes recorded since 1900. Put it against Valdivia in the calculator and the Chilean quake comes out with about 5,600 times more energy.

The USGS offers a closer pair from the United States, where the M6.7 Northridge earthquake in California shook harder, and over a wider area, than the slightly larger M6.8 Nisqually earthquake in Washington because its source was much shallower. Distance from the rupture and the ground under a town shape the shaking too.

Questions About Magnitude and Energy

How Many Magnitude 6 Earthquakes Equal One Magnitude 8?

About 1,000, if energy is the yardstick. Two whole steps give 10^{(1.5 × 2)}, which is 10³. Measured by amplitude instead, the magnitude 8 would trace waves about 100 times larger on a seismogram at the same distance.

Is the Richter Scale Still Used?

Rarely. The USGS says the Richter scale (ML) now serves mainly for small earthquakes recorded locally, and that moment magnitude gives a more accurate size for all the others. Moment magnitude was designed to roughly match Richter values where the two scales overlap.

Can This Calculator Tell Me Whether an Earthquake Is Coming?

Not at all. The tool compares sizes after the fact. Quake Lab is an information tool, and alerts or official reports come from the USGS and from the geological survey or civil protection agency of your country.

Sources

• U.S. Geological Survey, Earthquake Magnitude, Energy Release, and Shaking Intensity
• Live Atlas, magnitude glossary (linked above) and the event pages for the presets, 1960 Valdivia, 1964 Alaska, 2004 Indian Ocean, 2011 Tōhoku, 1906 San Francisco, 2023 Turkey-Syria, 2010 Haiti and 1989 Loma Prieta