Colombia’s earthquake was magnitude 7.4 at a depth of about 103 kilometres. Both numbers matter, and the second one is almost always left out of headlines.

What magnitude measures

Magnitude describes the energy released at the source. It is not a measure of how much damage was done, and it is not a scale you can read intuitively.

The scale is logarithmic. Each whole number represents roughly 32 times more energy released. A magnitude 7 event is not slightly worse than a magnitude 6 — it releases about 32 times the energy, and a magnitude 8 releases about a thousand times more than a 6.

This is why the difference between reported magnitudes of 7.4 and 7.6 is more significant than it looks, and why a “moderate” magnitude 5 sits in an entirely different category of event.

What depth changes

Energy released deep underground has to travel through rock before it reaches the surface, and it weakens along the way.

A shallow earthquake — a few kilometres down — concentrates violent shaking into a relatively small area directly above it. That is the pattern behind many of the deadliest earthquakes in history: a moderate magnitude, very close to the surface, directly beneath a populated place.

A deep earthquake does the opposite. The shaking at any single point is less severe than a shallow quake of the same magnitude would produce, but it is distributed across a far wider region. Colombia’s quake was felt in Ecuador and Panama for exactly this reason.

Neither is straightforwardly better. A deep quake exposes many more people to moderate shaking, and moderate shaking is sufficient to collapse a poorly built structure.

Why deep earthquakes happen at all

At great depth, rock is under such pressure and temperature that it should deform slowly rather than snap. Earthquakes at 100 kilometres and below were a genuine puzzle for decades.

They occur in subduction zones — places where one tectonic plate is being driven beneath another. The descending slab of cold, relatively brittle crust carries its own conditions down with it, and it can fracture at depths where the surrounding rock would not.

Colombia’s Pacific margin is one such zone, part of the Ring of Fire that encircles the Pacific Ocean and produces most of the world’s earthquakes.

The measure that actually predicts damage

Seismologists use a second scale that describes shaking as experienced at a given place rather than energy at the source. It is expressed in Roman numerals and is based on observed effects — whether objects fall from shelves, whether walls crack, whether structures collapse.

One earthquake has a single magnitude and many intensities: severe near the epicentre, mild hundreds of kilometres away. Intensity is what determines whether a building survives, and it depends on magnitude, depth, distance, local soil conditions and construction quality all at once.

Soft ground amplifies shaking considerably — sediment-filled valleys and reclaimed land shake harder than solid rock. It is entirely possible for one neighbourhood to suffer badly while another a few kilometres away is barely affected.

The number that is missing

Magnitude is reported because it is a single figure available within minutes and comparable between events. That is a genuine virtue.

But it tells you about the earth, not about people. Whether an earthquake kills 20 or 20,000 depends far more on what was built above it — which is a matter of decisions, budgets and enforcement rather than geology.

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Background: US Geological Survey and Colombian Geological Service data on the 10 August 2026 earthquake; standard seismological references.