Quick answer: Earthquake magnitude measures the overall size of an earthquake at its source. Earthquake intensity describes the strength of shaking at a specific location. A single earthquake has a preferred magnitude estimate but can produce different shaking intensities in nearby towns, depending on distance, ground conditions, depth and rupture characteristics. The U.S. Geological Survey (USGS) explains why the two measurements answer different questions.
Students often hear that an earthquake was “6.5 on the Richter scale” or that an area experienced “intensity VII.” These statements do not measure the same thing. Understanding the difference helps you read USGS earthquake maps and avoid mixing the earthquake’s total size with the effects at your home or school.
Earthquake magnitude vs. intensity: quick comparison
| Question | Magnitude | Intensity |
|---|---|---|
| What does it measure? | Overall size of the earthquake source | Shaking experienced at a particular location |
| Same across cities? | One preferred magnitude for the event on a given scale | Can vary greatly from city to city |
| Examples of scales | Moment magnitude (Mw), local magnitude (ML) | Modified Mercalli Intensity (MMI) |
| Usually written as | A number such as 6.7 | Roman numerals such as IV, VI or IX |
| What is it useful for? | Comparing event sizes | Understanding local shaking and possible impacts |
What causes an earthquake?
Stress builds as rocks on opposite sides of a fault move relative to one another. When friction can no longer hold them in place, part of the fault slips and releases seismic waves. The hypocenter, also called the focus, is the place underground where the rupture begins. The epicenter is the point on Earth’s surface directly above the hypocenter. The epicenter is not necessarily the place that experiences the most severe shaking or damage.
See USGS: The Science of Earthquakes for the earthquake source and fault terminology.
How is earthquake magnitude measured?
Seismometers record ground motion generated by earthquakes. Scientists use information about seismic waves and earthquake-source properties to estimate magnitude. Different techniques can produce slightly different reported magnitudes, especially early in an earthquake sequence when new information is still arriving.
Richter scale vs. moment magnitude (Mw)
Charles F. Richter developed the local-magnitude scale (ML) for earthquakes recorded on a particular type of seismograph in southern California. The name “Richter scale” remains common in headlines, but it is not a precise general label for every earthquake magnitude reported today. For many large events, the USGS uses moment magnitude (Mw), based on seismic moment, which relates to the amount of fault area that slipped, the amount of slip and the rigidity of the rocks. Read the USGS magnitude-measurement explanation.
Does one magnitude point mean ten times more energy?
No. Roughly speaking, an increase of one magnitude unit corresponds to ten times the seismic-wave amplitude and approximately 32 times the released energy. An increase of two magnitude units corresponds to about 100 times the amplitude and roughly 1,000 times the energy. These are approximate scale relationships, not predictions of the damage to a specific building.
Worked example: A magnitude 7 earthquake releases around 32 times more energy than a magnitude 6 earthquake, even though that does not mean the shaking is 32 times more intense at every location.
What is the Modified Mercalli Intensity (MMI) scale?
Modified Mercalli Intensity describes observable shaking and effects, with intensity written in Roman numerals. The traditional 12-level MMI scale spans I (not felt) through XII (extreme destruction). Some USGS public-facing mapping products group or cap displayed extreme intensities; always read the legend for the specific map instead of assuming every map has 12 distinct display colors.
| Typical MMI examples | General description |
|---|---|
| I | Not felt under ordinary conditions |
| II–III | Weak shaking, felt by relatively few people |
| IV–V | Noticeable shaking; objects can rattle or move |
| VI–VII | Strong to very strong shaking; damage can occur |
| VIII and higher | Severe shaking or damage, depending on building vulnerability and conditions |
These descriptions are simplified study aids, not a substitute for official damage surveys. See the USGS Modified Mercalli intensity scale table for the full definitions.
Real example: 1994 Northridge earthquake in California
USGS reports a magnitude 6.7 for the 1994 Northridge earthquake. Local shaking intensities ranged from approximately IX (violent) near the source to V (moderate) in some areas 60–200 miles away, and I (not felt) at greater distances. Those different intensity values describe different locations after the same event, not separate magnitudes.
Primary source: USGS “Did You Feel It?” scientific background. This historical case is used only as an example and does not describe a present-day earthquake warning.
Why might two neighborhoods experience different shaking?
- Distance: Ground shaking often weakens with increasing distance from the rupture, though not uniformly.
- Local soil: Soft sediments can amplify certain types of motion compared with firm bedrock.
- Depth and fault geometry: A shallow rupture or the direction the rupture propagates can concentrate shaking in particular places.
- Buildings: Structural design, age and maintenance affect damage, so building damage alone is not an exact measure of earthquake size.
How to read a USGS ShakeMap
- Open the official USGS ShakeMap information page or an event’s USGS report.
- Find the reported event magnitude and note its scale when provided.
- Read the ShakeMap legend for the mapped shaking or instrumental-intensity estimates.
- Look up your location on the map; do not assume the epicenter has the highest intensity.
- Check the event timestamp and whether the report is preliminary or updated. A map can evolve as new measurements arrive.
ShakeMap intensity is estimated using available observations and models. A city-wide map color cannot certify that an individual building is safe or damaged.
Practice quiz: earthquake magnitude and intensity
1. What does a magnitude 6.7 value measure?
Answer: An estimate of the size of the earthquake source, not a particular city’s shaking intensity.
2. Can one earthquake have both intensity V and intensity IX?
Answer: Yes. Intensity depends on location and local conditions.
3. About how much more energy is released by magnitude 7 than magnitude 6?
Answer: Roughly 32 times as much energy.
4. What is the difference between the hypocenter and the epicenter?
Answer: The hypocenter is where rupture starts underground. The epicenter lies directly above it on the surface.
5. Is “Richter scale” an accurate name for every modern USGS magnitude estimate?
Answer: No. Moment magnitude and other magnitude scales are also used.
Safety note, related lessons and photo credit
For immediate earthquake safety, follow local emergency alerts and official Ready.gov earthquake guidance; measuring magnitude or intensity is not a substitute for protective action. For more student science lessons, read The Rock Cycle Explained, our latitude and longitude tutorial and Earth Science & Geology.
Image source: Hawai‘i Volcanoes National Park / National Park Service, public domain. The image depicts earthquake-related damage on Crater Rim Drive near Keanakāko‘i in 2018, not the 1994 Northridge earthquake described in the text, and it does not illustrate a current incident.
Sık Sorulan Sorular
What is the difference between earthquake magnitude and intensity?
Magnitude describes overall earthquake source size. Intensity measures how much shaking or damage people experience at a particular location, so intensities vary from place to place for the same event.
Is magnitude the same as the Richter scale?
Not exactly. Richter introduced a specific local-magnitude method; modern USGS earthquake reports often use moment magnitude (Mw), especially for large earthquakes.
How many times stronger is a magnitude 7 earthquake than a magnitude 6 earthquake?
A one-unit magnitude increase corresponds approximately to ten times the measured wave amplitude and 32 times the energy released; the specific amount of shaking at your location can differ.
Does a smaller earthquake always cause less damage?
No. Building vulnerability, soil, distance to rupture, depth and local conditions can make a smaller nearby earthquake cause severe damage locally.
.jpg){kind=link}