Earthquake Magnitude & Energy Calculator

The Richter Scale — Origin and Limitations

In 1935, seismologist Charles Richter at the California Institute of Technology developed the first practical magnitude scale for earthquakes, originally intended only for Southern California earthquakes measured on a specific type of seismograph (the Wood-Anderson torsion seismograph). The Richter scale (technically called “local magnitude” or ML) worked well for nearby, moderate earthquakes, but had significant limitations: it could not be applied globally, it saturated for very large earthquakes (magnitudes above about 7.0 were underestimated), and it required specific equipment calibrated for a specific region.

Moment Magnitude — The Modern Standard

In 1979, seismologists Hiroo Kanamori and Thomas Hanks developed the Moment Magnitude scale (Mw), now the standard used by the United States Geological Survey (USGS) and seismologists worldwide. Moment Magnitude is based on the seismic moment — a physical quantity derived from the area of the fault that ruptured, the amount of slip along the fault, and the rigidity of the rock. It does not saturate at high magnitudes and can be calculated consistently for earthquakes anywhere on Earth.

For magnitudes between 3.0 and 7.0, Richter and Moment Magnitude give nearly identical numbers, which is why the “Richter scale” label remains in media reporting even though scientists no longer use it.

The Logarithmic Scale — Why Each Step Is 31.6× More Energy

Earthquake magnitude is logarithmic, meaning each whole number increase represents a fixed multiplicative change. Specifically:

• Each +1.0 in magnitude = 10× more ground shaking (amplitude of seismic waves)
• Each +1.0 in magnitude = 31.6× more energy released (approximately 10^1.5 ≈ 31.6)
• Each +2.0 in magnitude = 1,000× more energy released (31.6² ≈ 1,000)

This means a M7.0 earthquake releases about 1,000 times more energy than a M5.0 earthquake, and a M9.0 releases about 1 million times more energy than a M5.0.

Energy Formula

The energy released in joules is: E = 10^(1.5 × M + 4.8)

For comparison: the atomic bomb dropped on Hiroshima in 1945 released approximately 6.3 × 10¹³ joules — equivalent to about a M6.0 earthquake.

Famous Earthquakes

• 1960 Valdivia, Chile — M9.5: The largest earthquake ever instrumentally recorded. Triggered a Pacific-wide tsunami. The energy released was equivalent to approximately 178 billion tons of TNT.
• 2004 Indian Ocean — M9.1: Triggered the catastrophic Boxing Day tsunami, killing over 230,000 people. One of the deadliest natural disasters in recorded history.
• 1906 San Francisco — M7.9: Caused widespread fires that destroyed much of the city. Resulted in fundamental changes to building codes and emergency response planning.
• 1964 Alaska — M9.2: The largest earthquake in U.S. history. Raised some areas of land by 11 meters and dropped others by 2 meters.

Magnitude vs. Intensity

Magnitude (Mw/Richter) measures the energy at the earthquake’s source — a single number per earthquake. Intensity measures the shaking experienced at a particular location — it varies across the affected region. The Modified Mercalli Intensity (MMI) scale (I to XII) is used to describe felt effects, from barely perceptible (I) to total destruction (XII). Two people in different cities can experience the same earthquake at very different intensities.