Richter scale: what each magnitude means
What the press calls the Richter scale has in practice been replaced by moment magnitude (Mw), which the USGS uses for medium and large earthquakes.
Automatic information from scientific catalogues. In an emergency, follow your local emergency service and geological survey.
Range
| Range | What it means |
|---|---|
| Micro (below 2) | Only seismographs record it. Nobody feels it. |
| Minor (2 to 3.9) | Sometimes felt near the epicentre, no damage. |
| Light (4 to 4.9) | Widely felt, objects rattle, damage is rare. |
| Moderate (5 to 5.9) | Damage to weak buildings near the epicentre. |
| Strong (6 to 6.9) | Can destroy buildings up to a hundred kilometres away. |
| Major (7 to 7.9) | Serious damage over a wide area. |
| Great (8 and above) | Destruction across hundreds of kilometres; tsunami risk. |
Magnitude · Value
| Magnitude | Energia (x M4) | What it means |
|---|---|---|
| 4.0 | 1× | Widely felt, objects rattle, damage is rare. |
| 5.0 | 32× | Damage to weak buildings near the epicentre. |
| 6.0 | 1,000× | Can destroy buildings up to a hundred kilometres away. |
| 7.0 | 31,623× | Serious damage over a wide area. |
| 8.0 | 1,000,000× | Destruction across hundreds of kilometres; tsunami risk. |
| 9.0 | 31,622,777× | Destruction across hundreds of kilometres; tsunami risk. |
| Depth | What it means |
|---|---|
| Shallow (up to 70 km) | usually felt more strongly at the surface. |
| Intermediate (70 to 300 km) | the shaking reaches the surface weaker. |
| Deep (over 300 km) | felt far away, with little destruction. |
- U.S. Geological Survey — Earthquake Hazards ProgramLicence: Domínio público (U.S. Public Domain) · Credit: U.S. Geological Survey (USGS)
How to read these numbers
Charles Richter built his scale in 1935 for Californian quakes measured on one specific seismograph. It saturates: above magnitude 7 it stops separating events. Moment magnitude, from the 1970s, measures the energy actually released by the fault rupture and does not saturate.
Both scales are logarithmic. One magnitude step means ten times the amplitude on the seismograph and roughly 31.6 times the energy. From 6 to 8 is therefore about a thousand times more energy.
Magnitude is not intensity. The modified Mercalli scale (I to XII) describes what was felt and damaged in each place, so one earthquake has a single magnitude and many different intensities.
Frequently asked questions
- What is the difference between Richter and Mercalli?
- Richter (or moment magnitude) measures the energy of the event and applies to the whole quake. Mercalli measures the shaking experienced at a given point, in Roman numerals, and changes from one neighbourhood to the next.
- Could there be a magnitude 10?
- No known fault is long enough. The largest instrumentally recorded earthquake was Chile in 1960, at magnitude 9.5.