What magnitude 7.4 means — one step up is 32 times the energy
Magnitude measures the total energy released at the source, so an earthquake has exactly one magnitude and each whole step represents about 32 times more energy, while intensity measures how strongly a specific place actually shook and therefore differs from location to location
The three lines
- One magnitude per earthquake, one intensity per location — they measure different things
- A one-step magnitude difference is roughly 32 times the energy; two steps is about 1,000 times
- Damage is not set by magnitude alone — focal depth, ground conditions and building standards intervene
Key questions
- How strong is a magnitude 7.4 earthquake?
- About 32 times the energy of a magnitude 6.4 and roughly 1,000 times that of a magnitude 5.4. Magnitude is a logarithmic scale: each whole step multiplies recorded amplitude by ten and energy release by about 32. The earthquake that struck western Colombia on August 10, 2026 was magnitude 7.4, the country's strongest in decades. A larger magnitude does not automatically mean greater damage.
- What is the difference between magnitude and intensity?
- Magnitude is the total energy released at the source, computed from seismograph records, and there is exactly one value per earthquake. Intensity describes how strongly the ground actually shook at a particular point, so it is high near the epicentre and low far away, and one earthquake produces many intensity values. Magnitude is written in Arabic numerals, intensity conventionally in Roman numerals.
- Can a big magnitude earthquake cause little damage?
- Frequently. Three factors decide it. Focal depth — energy from a deep event disperses before reaching the surface. Ground conditions — soft sediment amplifies shaking while hard bedrock does not. Buildings — seismic design separates cracking from collapse under identical shaking. A deep magnitude 7 far offshore makes a brief news item; a shallow magnitude 6 under a city does not.
- What is the difference between Richter and moment magnitude?
- The Richter scale, from the 1930s, was computed from seismograph amplitude and saturated on very large earthquakes, understating their true size. Moment magnitude accounts for the fault area that moved, how far it moved and the rigidity of the rock, so it represents large-earthquake energy far more accurately. The USGS now reports magnitudes on the moment magnitude scale, and most figures reported in the press as Richter are in fact moment magnitude.
Earthquake coverage contains two kinds of numbers. Something like magnitude 7.4, and something like intensity VI.
They look similar and measure entirely different things. One describes how large the event was; the other describes how hard the ground moved where you happened to be standing. Miss that distinction and two ordinary questions become unanswerable: why a magnitude 7 left one town untouched, and why a magnitude 5 brought a building down.
1. One-sentence definitions
| Item | Magnitude | Intensity |
|---|---|---|
| Measures | Total energy released at the source | Shaking at a specific point |
| Nature | Absolute | Relative |
| How many | One per earthquake | One per location |
| Derived from | Seismograph records | Felt effects, structural damage, instruments |
| Written as | Arabic numerals (7.4) | Roman numerals (VI) |
| Standard in use | Moment magnitude | Modified Mercalli (MMI) |
The decisive row is how many. An earthquake has exactly one magnitude. It has a separate intensity value for Seoul, for Busan, and for the village at the epicentre.
The analogy that holds: the wattage of a bulb is magnitude, and the brightness you perceive from where you sit in the room is intensity. One bulb, many readings.
2. What one step of magnitude buys
Magnitude is logarithmic. Each whole step multiplies rather than adds.
| Magnitude difference | Recorded amplitude | Energy released |
|---|---|---|
| 1.0 | 10× | about 32× |
| 2.0 | 100× | about 1,000× |
| 3.0 | 1,000× | about 32,000× |
Applied to the Colombia earthquake:
| Comparison | Energy ratio to magnitude 7.4 |
|---|---|
| Magnitude 6.4 | about 32× |
| Magnitude 5.4 | about 1,000× |
| Magnitude 4.4 | about 32,000× |
7.4 and 6.4 differ by one on the page and by a factor of 32 in energy. This is why the decimal place matters in earthquake reporting: even 7.4 against 7.0 is close to a fourfold difference in released energy.
3. Why a large magnitude can do little damage
Magnitude describes energy at the source. It says nothing about how that energy arrives at people. Three things intervene on the way.
Focal depth. An event at 10km and one at 300km deliver very different shaking to the surface. Depth lets energy spread and attenuate. At equal magnitude, shallower is more dangerous.
Ground conditions. Soft sedimentary basins amplify seismic waves. A building on bedrock and a building on reclaimed land receive the same earthquake very differently — which is why damage varies block by block inside a single city.
Buildings. Seismic design is the difference between cracks and collapse under identical shaking.
Because of those three, both of the following are ordinary:
- A magnitude 7 deep and far offshore → a short news item
- A magnitude 5.5 shallow and directly beneath a city → fatalities
Colombia's toll reflects this structure. The epicentre was in mountainous terrain, but shaking carried up to 400km and reached the dense cities of Cali, Pereira, Quibdó and Manizales. Three floors of a major hospital in Cali collapsed. The event is covered in "Colombia earthquake death toll passes 250."
4. Richter versus moment magnitude
The press still says "Richter," but published figures are almost always moment magnitude.
| Item | Richter | Moment magnitude |
|---|---|---|
| Introduced | 1930s | 1970s onward |
| Computed from | Seismograph amplitude | Fault area × slip × rock rigidity |
| Limitation | Saturates on large events, understating them | — |
| Current use | Some small earthquakes | USGS and other agencies' standard |
The failure mode of the Richter scale was saturation. On very large earthquakes amplitude stopped scaling proportionally, so a magnitude 8 and a magnitude 9 could compute to similar values. Moment magnitude solved this by measuring what the fault physically did — how wide an area moved, and how far.
So when you see "magnitude 7.4" today, read it as moment magnitude unless it says otherwise.
5. How intensity is assigned
Intensity began as an observational scale. Descriptions like "felt by people at rest," "dishes rattle," "walls crack" were mapped onto grades. The Modified Mercalli scale runs I to XII.
| Approximate grade | Experience |
|---|---|
| I–III | Not felt by most, or felt only by some indoors |
| IV–V | Felt indoors by most; dishes and windows rattle |
| VI–VII | Felt by all; furniture moves; damage to poorly built structures |
| VIII and above | Substantial structural damage to ordinary buildings |
Modern practice adds instrumental intensity — a grade converted from the ground acceleration and velocity a seismometer recorded. It can produce a location-by-location map within seconds rather than waiting for human reports, which is what makes automated earthquake alerting possible. Intensity values in official announcements are typically reported as whole numbers on this instrumental basis.
6. Three things to check in earthquake news
| Check | Why it matters |
|---|---|
| Magnitude | The size of the event — the basis for comparison |
| Focal depth | At equal magnitude, shallower means worse |
| Epicentre location | Near a population centre, or offshore |
Reacting to magnitude alone is the most common misreading. Magnitude, depth and location have to appear together before damage can be estimated at all.
7. What is unresolved
The 32× figure is an approximation. The precise ratio is about 31.6 per magnitude step, and agencies cite 30 or 32 interchangeably. This article uses the common 32.
Focal depth and location-level intensities for the Colombia earthquake could not be confirmed. Those two values are what would explain precisely why shaking carried 400km, and reporting has not supplied them.
Intensity scales differ by country. Japan uses the JMA seismic intensity scale (0–7); Europe uses EMS-98. The twelve-grade description above is the Modified Mercalli scale, and an identical grade number means something different under a different scale. That is the trap to watch for when reading intensity figures in foreign earthquake coverage.
Sources
- USGS — Earthquake magnitude, energy release, and shaking intensity
- USGS FAQ — How is the magnitude of an earthquake determined?
- IRIS — Earthquake magnitude and intensity
- KALIS (Korea) — Earthquake terminology: magnitude and intensity
- Korea earthquake response system — earthquake size and location
- CNBC — Colombia quake death toll tops 250 (the magnitude 7.4 case)