How Earthquake Magnitude Is Really Measured

On August 10, 2026, a strong earthquake struck western Colombia, centred near San José del Palmar in the Chocó department, and was felt in cities such as Cali, Manizales and Pereira. In the first hours, two different magnitudes circulated for the same quake — and that difference, far from being a mistake, is a perfect way in to understanding how the strength of an earthquake is actually measured.

The Chocó Quake, With the Data Available

According to the Colombian Geological Survey (SGC), the event occurred at 7:34 in the morning (local time), centred near San José del Palmar, Chocó, at a depth of about 82 kilometres. The SGC's preliminary bulletin reported a magnitude of 6.7.

The United States Geological Survey (USGS), by contrast, preliminarily reported a magnitude of 7.4 and a somewhat greater depth. In other words, two serious agencies published different figures for the same earthquake in the first hours.

This isn't a contradiction or an oversight: it's exactly how real-time seismology works. The first magnitudes are rapid estimates based on partial data, and they're revised as more records arrive from more stations. The definitive figure can take hours or days to settle.

A More Recent Case: the Flores, Indonesia Earthquake (M7.7)

Just days later, on August 15, 2026, a stronger quake — magnitude 7.7 — struck the sea off the island of Flores, in eastern Indonesia, and triggered a tsunami alert. According to the USGS, its epicentre was about 68 km north-northwest of the city of Ende, at a shallow depth of just 10 km. Indonesia's BMKG agency issued a tsunami warning across 22 zones; the waves ultimately measured were small (0.19–0.36 m), and at least two fatalities were confirmed. (Figures verified as of August 15, 2026, subject to official revision.)

It's a useful contrast with Chóco. A magnitude 7.7 releases roughly 32 times more energy than a 6.7 — the same one-point, ~32× jump the scale is built on. Even against Chóco's higher reported figure (M7.4), Flores still released about 2.8 times more energy. And both are dwarfed by the 2004 Sumatra earthquake (M9.1), which released more than 100 times the energy of Flores. If you want to see any of these side by side, the earthquake magnitude comparator now includes Flores and Chóco as ready-made presets.

Flores also shows why depth and location matter as much as magnitude: a shallow, undersea quake can lift the seafloor and set off a tsunami, while a deeper one — like Chóco — releases much of its energy before it reaches the surface. We unpack that mechanism in how a tsunami forms.

Why the Scale Is Logarithmic (and What That Means)

Here's the most misunderstood idea. The magnitude scale isn't linear: the numbers don't grow a little at a time, they shoot up.

On a linear scale, an 8 would be twice a 4. On the magnitude scale, each whole point you go up multiplies the energy released by about 32 times. And because it's cumulative, two whole points aren't 64 times more, but 32 × 32 ≈ 1,000 times more energy.

A direct example with the Chocó quake itself: the difference between the two reported magnitudes, 6.7 and 7.4, looks tiny — just 0.7 points — but represents about 11 times more energy. That's why refining the magnitude matters so much: a small adjustment in the number is a huge change in what that number describes. See it in the widget.

The Richter Scale Isn't the One in Use (Even Though Everyone Names It)

It's worth clearing up a point that confuses many people. The famous Richter scale, created in 1935, worked well for moderate, nearby earthquakes, but it "saturated" for the largest quakes: above a certain magnitude it stopped distinguishing well between a huge one and a colossal one.

That's why, for decades now, agencies like the USGS have used the moment magnitude scale (Mw), which measures the released energy directly from the size of the rupture and the fault slip. It's the one that gives those figures of 6.7 or 7.4. People still say "Richter scale" out of habit, but what the authorities actually report today is moment magnitude.

The Largest Earthquakes Ever Recorded

To really grasp the scale, it helps to see where the most powerful quakes in instrumental history sit. And the top spot belongs, by a wide margin, to an earthquake in South America.

The last column is the hard-to-believe part: the 1960 Valdivia earthquake — the largest ever measured, at magnitude 9.5 — released on the order of 16,000 times more energy than a magnitude-6.7 quake. Not "a bit more": tens of thousands of times more. That's the logarithmic nature of the scale made real.

Why Does Depth Change So Much of What You Feel?

A key detail of the Chocó quake is that it was relatively deep: its focus was about 80 to 100 kilometres below the surface, depending on the source. Depth hugely affects how an earthquake is felt, in a way that seems counterintuitive.

Think of seismic energy as waves radiating out from the focus in all directions, like ripples in a pond. If the focus is shallow (a few kilometres), those waves reach the surface with almost all their force, but concentrated in a smaller zone around the epicentre: very destructive right there, less noticeable at great distance.

If the focus is deep, the waves travel farther before reaching the surface, so they spread over a much wider area. The result is that a deep quake tends to be felt across an enormous region — in this case, in cities hundreds of kilometres away like Cali, Manizales, Pereira and even Bogotá — but, at equal magnitude, tends to be less destructive right at the epicentre than a shallow one, because the energy dissipates part of the way up.

That's why "it was felt very far away" and "it was very destructive" aren't the same thing, and don't always go together. Depth is one of the reasons two earthquakes of equal magnitude can have very different effects.

Common Misunderstandings to Avoid

• "The magnitude changed because someone made a mistake." No. The first figures are rapid estimates refined with more data; revising the magnitude is a normal part of the process, not an error.
• "A 7 is barely stronger than a 6." In energy, a 7 releases about 32 times more than a 6. The scale deceives because the numbers are compressed.
• "Magnitude and damage are the same." Magnitude measures released energy; damage also depends on depth, soil type, building quality and proximity to populated areas.
• "The Richter scale is still in use." The name lives on in everyday speech, but authorities have used the moment magnitude scale for decades.

The Takeaway

An earthquake's strength is measured on a logarithmic scale where each point means about 32 times more energy — which is why a small difference in the number, like the one seen between the Chocó quake's preliminary figures, is an enormous difference in reality. Those revisions in the first hours aren't errors: they're science refining its answer as more data arrives.

Understanding the scale helps you read seismic news with more calm and less confusion: to tell a technical adjustment from a contradiction, and a magnitude from a level of damage. If you want to compare two earthquakes and see how many times more energy one released than another, the interactive scale above does the math instantly.

Information on the August 10, 2026 event is based on the preliminary reports of the Colombian Geological Survey and the USGS, verified as of that date and subject to official revision. For up-to-date data, consult the official sources.