Earthquake Calculator: Energy, Magnitude & Intensity
A Richter or moment magnitude instantly reveals the energy released in joules, metric tons of TNT, Hiroshima bomb equivalents, and Tsar Bomba multiples. Switch to two-earthquake comparison mode to find the amplitude ratio and energy ratio between any two events. Use the seismograph mode to convert a raw wave amplitude and distance correction into a local magnitude.
Formula
Worked example
A M 6.5 earthquake: log E = 4.8 + 1.5 x 6.5 = 4.8 + 9.75 = 14.55, so E = 10^14.55 = 3.55x10^14 J = about 355 TJ. In TNT equivalents: 355e12 / 4.184e9 = about 84,800 metric tons of TNT, or roughly 5,600 Hiroshima bombs.
How earthquake energy is calculated
Seismologists use the Gutenberg-Richter energy relation to convert magnitude to energy: log₁₀(E) = 4.8 + 1.5M, where E is in joules and M is the moment or local magnitude. Because of the factor 1.5 in the exponent, every one-unit increase in magnitude corresponds to 10^1.5, or about 31.6, times more energy. A M 7.0 earthquake releases roughly 32 times the energy of a M 6.0 earthquake and about 1,000 times the energy of a M 5.0 earthquake. This logarithmic growth is why even small differences in magnitude represent enormous differences in destructive potential.
Richter scale vs. moment magnitude
Charles Richter devised the local magnitude scale (ML) in 1935 for Wood-Anderson seismographs in southern California. The formula is ML = log₁₀(A) + (-log₁₀(A₀)), where A is the maximum wave amplitude in millimetres on the seismograph trace and A₀ is a distance correction factor. The Richter scale works well for events up to about M 6.5, but it saturates at higher magnitudes because the seismograph cannot distinguish between progressively larger ruptures. Moment magnitude (Mw) was introduced by Kanamori (1977) to fix this: Mw = (2/3)(log₁₀(M₀) - 16.1) in CGS units, where M₀ = μAD (shear modulus times fault area times average slip). The two scales are numerically similar in the range M 3 to M 7, which is why the terms are often used interchangeably in everyday reporting, but moment magnitude is the modern scientific standard for all sizes.
Modified Mercalli Intensity: what people actually feel
Magnitude measures the energy at the source; intensity describes the shaking people feel and the damage that results at a given location. The Modified Mercalli Intensity (MMI) scale runs from I (detected only by instruments) to XII (total catastrophic destruction). Because intensity falls off with distance and is affected by depth, soil type, and building quality, the same magnitude earthquake can produce very different MMI values at different locations. A shallow M 6.5 directly under a city may cause MMI VIII-IX shaking, while a deep M 7.0 far offshore may produce only MMI IV-V at the nearest coast.
Energy comparison: putting earthquake power in context
The energy numbers for large earthquakes are almost incomprehensible in everyday units. The 1960 Valdivia, Chile earthquake (M 9.5, the strongest ever recorded) released roughly 2x10^18 joules of seismic energy - about 480 million Hiroshima bombs, or 9,500 Tsar Bombas (the largest nuclear weapon ever detonated). A typical M 5.0 earthquake releases about as much energy as a small nuclear power plant generates in a day. At the micro end, a M 2.0 event releases about the same energy as a large truck collision. The comparison mode in this calculator lets you find the exact amplitude and energy ratio for any two events.
Modified Mercalli Intensity Scale
| MMI Level | Description | Approx. Magnitude | Typical Effects |
|---|---|---|---|
| I | Instrumental | < 2.0 | Detected only by seismographs |
| II | Feeble | 2.0-2.9 | Felt by a few people at rest, especially on upper floors |
| III | Slight | 3.0-3.9 | Noticed indoors, like a passing truck; may not be recognized as earthquake |
| IV | Moderate | 4.0-4.4 | Felt by many indoors, dishes and windows rattle |
| V | Rather Strong | 4.5-4.9 | Felt by nearly all; pendulum clocks may stop, small objects displaced |
| VI | Strong | 5.0-5.4 | Felt by all; heavy furniture moved, plaster falls, slight damage |
| VII | Very Strong | 5.5-5.9 | Moderate damage in ordinary buildings, considerable in poorly built ones |
| VIII | Destructive | 6.0-6.4 | Considerable damage to ordinary buildings; some walls collapse |
| IX | Violent | 6.5-6.9 | Great damage; buildings shifted off foundations, ground cracks |
| X | Intense | 7.0-7.4 | Most masonry destroyed; landslides; rails bent slightly |
| XI | Extreme | 7.5-7.9 | Few structures remain standing; bridges destroyed; rails bent greatly |
| XII | Catastrophic | >= 8.0 | Total damage; waves seen on ground; objects thrown into the air |
Approximate shaking intensity and effects near the epicenter. Actual intensity depends on depth, distance, and local geology.
Frequently asked questions
What is the difference between magnitude and intensity?
Magnitude is a single number that measures the total energy released at the earthquake source - it does not change with distance from the epicenter. Intensity (the MMI scale) describes the local shaking effects at a specific location; it typically decreases with distance, so the same earthquake has a high intensity near the epicenter and a low intensity far away. News reports often mix up the two terms, but seismologists keep them distinct.
Why does each magnitude unit mean 32 times more energy?
The Gutenberg-Richter formula is log E = 4.8 + 1.5M. A one-unit increase in M adds 1.5 to the exponent, so the energy multiplies by 10^1.5 = 31.6, which is rounded to 32. Amplitude on a seismograph, by contrast, increases by 10x per unit because the exponent for amplitude is 1 (not 1.5). The factor of 1.5 comes from the physics of how seismic wave energy scales with moment.
What is the strongest earthquake ever recorded?
The 1960 Valdivia earthquake in Chile, with a moment magnitude of 9.4 to 9.6 (commonly cited as M 9.5), is the strongest instrumentally recorded earthquake. It released approximately 10 times more energy than the 2011 Tohoku earthquake in Japan (M 9.1), which caused the Fukushima nuclear disaster.
Why does the Richter scale "saturate" at high magnitudes?
The Richter scale was calibrated for short-period seismic waves (about 1 second period) recorded on Wood-Anderson seismographs within a few hundred kilometres. Very large faults rupture slowly over minutes, generating energy at long periods that short-period seismographs cannot fully capture. Above about M 6.5, the short-period amplitude barely increases even as the true earthquake grows, so the Richter estimate stays nearly constant - it is saturated. Moment magnitude avoids this by using the total seismic moment, which integrates the entire rupture.
How do I use the seismograph mode?
Enter the maximum trace amplitude A in millimetres as read from a Wood-Anderson seismograph record, then enter the distance correction factor for your station. The correction factor (-log A₀) depends on the epicentral distance; many regional seismic networks publish tables of these values by distance. At 100 km, a typical value is around 3.0. The calculator applies Richter's 1935 formula: ML = log₁₀(A) + (-log₁₀(A₀)).
Can a magnitude 10 earthquake happen?
No fault on Earth is known to be long enough to generate a M 10 earthquake. The energy required is about 32 times that of the 1960 Chile event. The longest fault system known, the Cascadia subduction zone off the Pacific Northwest coast of North America, is estimated to be capable of roughly M 9.0 to 9.3 earthquakes. Most seismologists consider M 10 physically impossible with current plate tectonic configurations.