Guide
Earthquake Magnitude Explained: What M4, M6 and M7 Really Mean
By the GlobalRisk team · Published 2026-10-06
When an earthquake is reported, the headline number is its magnitude: a single value describing how much energy the quake released at its source. It is the number you see on GlobalRisk's map markers and in the event tables, and it comes from the U.S. Geological Survey (USGS) feed.
The scale is logarithmic
Each whole step up in magnitude means roughly 32 times more energy released and about 10 times more ground motion measured on a seismogram. A magnitude 7.0 earthquake is therefore not "a bit more" than a 6.0. It releases around 32 times the energy, and about 1,000 times the energy of a magnitude 5.0.
Common size classes
| Magnitude | Class | Typical effects |
|---|---|---|
| 2.5 – 3.9 | Minor | Often felt by people close to the epicenter; rarely causes damage. |
| 4.0 – 4.9 | Light | Noticeable shaking and rattling objects indoors; significant damage is unlikely. |
| 5.0 – 5.9 | Moderate | Can damage poorly built structures near the epicenter; well-designed buildings usually have slight damage at most. |
| 6.0 – 6.9 | Strong | Can be destructive in populated areas within tens of kilometers. |
| 7.0 – 7.9 | Major | Can cause serious damage across larger areas. |
| 8.0 and above | Great | Can cause severe damage across regions hundreds of kilometers wide and may trigger tsunamis. |
How often do they happen?
Worldwide, the USGS estimates there are roughly 1,300 earthquakes of magnitude 5.0–5.9 each year, around 130 of 6.0–6.9, about 15 of 7.0–7.9, and on average one of magnitude 8 or greater. Smaller quakes are far more frequent; magnitude 2.5 and above are recorded many times every day.
Magnitude is not the same as intensity
Magnitude describes the quake itself. Intensity describes how strongly it is felt at a particular place, and it varies with distance, depth, local geology and building quality. A deep magnitude 6.5 beneath a sparsely populated region can cause little harm, while a shallow magnitude 5.5 under a city can be damaging. That is why GlobalRisk shows location and country context beside every magnitude, and why a high number alone does not always mean a disaster.
Why numbers change after the first report
The first magnitude published within minutes of a quake is an estimate. Agencies revise it as more seismic stations report, so a value can move by a few tenths. GlobalRisk reads the feed regularly, but an event page shows the value at the time it was last collected. The original USGS event page, linked from each GlobalRisk event, always has the latest figure.
What GlobalRisk shows
Earthquakes of magnitude 2.5 and above appear on the live map. Each one links to its own page with a location map, nearby activity and country context, and quakes of magnitude 5.5 and above are listed under significant events. See also what to do during an earthquake and our methodology.
More guides
- Earthquake Safety: What to Do Before, During and After
- GDACS Alert Levels Explained: Green, Orange and Red
- Tropical Cyclone Categories Explained: Hurricanes, Typhoons and the Saffir-Simpson Scale
- How Satellites Detect Wildfires: A Plain-Language Guide to Thermal Hotspots
- The Pacific Ring of Fire: Why So Many Earthquakes and Volcanoes Cluster Here
General information only, not professional or emergency advice. Our methodology · Browse by country