Here is why earthquake magnitude is not what you think it is

By Robin Andrews

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So, apart from magnitude, here’s what else determines how damaging an earthquake will be.

Geographical location

This is the most obvious one, because an earthquake that happens far at sea or in a remote part of the world, and which does not produce a tsunami, harms no-one. The earth shifts, energy is released, but if there aren’t any people around, no infrastructural damage can be done. Conversely, if the same powerful quake happens right beneath a populated city, the potential for damage and lethality is far higher.

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Shaking intensity

Depending on the type of fault and type of tremor, how the fault moved during the event, and for how long, the ground will shake differently for each quake. In general, higher magnitudes produce more shaking, and the more shaking an earthquake generates at the surface, the more destructive it will be for any buildings sitting up there.

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Depth

Earthquakes also don’t happen at the same depths. From those happening just a handful of kilometres beneath the surface to ultra-deep quakes buried 680 kilometres (423 miles) under our feet, this value varies plenty.

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Building codes and architectural designs

I cannot emphasize how under-appreciated and influential this factor is. Building codes – the standard to which architecture is constructed with respect to earthquake proofing – have the potential to save millions of lives during major earthquakes, so long as they are properly enforced.

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