Advertisement

We need your help now

Support from readers like you keeps The Journal open.

You are visiting us because we have something you value. Independent, unbiased news that tells the truth. Advertising revenue goes some way to support our mission, but this year it has not been enough.

If you've seen value in our reporting, please contribute what you can, so we can continue to produce accurate and meaningful journalism. For everyone who needs it.

PA
Seismic Activity

# A quick guide to the Richter Scale

It’s important to understand that an earthquake of magnitude 8 isn’t twice as bad as a mag-4 – it’s a million times worse.

Updated, 12.19

WE ARE ALL aware that the severity of an earthquake is measured by the Richter Scale – but it’s less common to understand exactly what a figure on the Richter Scale suggests.

Given that earthquakes measuring 9 or higher are exceptionally rare – and because, since records began, no quake has ever measured a magnitude of 10 – it’s understandable to think of the scale as essentially being a scale from 0 to 10. This isn’t the case, however – there is no upper limit to the scale.

When comparing seismic measurements, however, it’s important to realise that the Richter Scale isn’t a straightforward measurement of activity. It’s easy to assume, for example, that a quake measuring 5 on the scale is exactly twice as severe as one measuring 2.5, and so on.

The scale isn’t quite so simplistic, however: rather than assigning some sort of unit of measurement to severity, the scale is instead a logarithmic one.

What this means, in a nutshell, is that quakes must get progressively more and more severe in order to move upward on the scale. Put simply, a quake measuring 4 on the scale is precisely a thousand times more destructive than one measuring 2. Likewise, a quake measuring 6 is a thousand times more destructive than one measuring 4, and so on.

Similarly, an increase of 0.1 in a quake’s magnitude means its effects are around 1.42 times more severe.

By such calculations, the earthquake experienced in Japan yesterday – measuring 8.9 on the Richter Scale – was a barely credible 700 million times more severe than the 3-magnitude quake that those in Japan had been warned to expect.

Comparing yesterday’s Japanese quake to that of Christchurch in New Zealand last month – which registered 6.3 – shows that the Japanese quake was 7,943 times more powerful.

Update: Thanks to the readers who have pointed out that the Richter Scale, in recent years, has been superseded by the Moment Magnitude Scale – though we’ve checked it out, and the ratios between comparative magnitudes on that scale is identical; an increase of 2 in magnitude means a quake 1,000 times more severe, and so on.

Readers like you are keeping these stories free for everyone...
A mix of advertising and supporting contributions helps keep paywalls away from valuable information like this article. Over 5,000 readers like you have already stepped up and support us with a monthly payment or a once-off donation.

Author
Gavan Reilly
News in 60 seconds