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Comment by YeGoblynQueenne | Hacker News Reader

That was a massive earthquake and it's unbelievable luck that there are no reports of casualties (probably because it hit a rural area).

But, please, can the title be corrected? The magnitude of the quake was 7.9 on the (logarithmic) Richter scale. That's considerably different to 8.0 scale (by a few million gigajoules at that).

Edit: Thanks for the correction. To give an idea of the difference in magnitude:

  8.0 Richter in joules: 63,095,730,000,000,000.00
  7.9 Ricther in joules: 44,668,360,000,000,000.00

(According to: http://www.convertalot.com/earthquake_power__calculator.html)

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From the wikipedia article [0]:

> In the United States, the Richter scale was succeeded in the 1970s by the moment magnitude scale. The moment magnitude scale is now the scale used by the United States Geological Survey to estimate magnitudes for all modern large earthquakes

which is similar but not the same. From that page's wikipedia article:

> Popular press reports of earthquake magnitude usually fail to distinguish between magnitude scales, and are often reported as "Richter magnitudes" when the reported magnitude is a moment magnitude (or a surface-wave or body-wave magnitude). Because the scales are intended to report the same results within their applicable conditions, the confusion is minor.

The difference mostly seems to be to do with distinguishing several quakes in a similar location.

I know it's picky, but this is HN...

[0] https://en.wikipedia.org/wiki/Richter_magnitude_scale

The factor changes for a 1 point increase are different.

Richter 10 (to the power 1)

Moment magnitude about 32 (to the power 1.5)

For an increase of 2:

Richter exactly 100

Moment magnitude exactly 1000

Makes sense for the title to reflect the article content, but isn't it normal for the measurement to be updated several times after such incidents? I thought it was based on estimates from nearby locations, with full data only arriving and being analysed after several days. I often see multiple different numbers, and separated by more than 0.1.

And how much difference is a few million gigajoules in terms of observable effects?

I was watching a show on antimatter and it said 1 gram of matter and antimatter combined releases 60 trillion Joules of energy.

So 1,000g (1kg) of antimatter would be roughly equivalent to a 8.0 earthquake.

Isn't 8.0 already 60 trillion according to the parent comment?

Anyway, the Death Star is equivalent to a 15.0 magnitude earthquake.

Edit: stupid phone, didn't see it could scroll horizontally :-)

Parent comment is 63 quadrillion Joules.

Sounds like it would be easier to understand if they just published the energy numbers in GJ.

To confuse things, Japan has its own scale which has similar numbers to the Richter scale but with different meaning.

I find measures of ground movement good for visualising what happened and how violent it must have been. Not that this is helpful sometimes with silent quakes generating a fair amount to movement (via GPS measure) in New Zealand lately. The recent 7.8 caused up to 10m of fault slip and 5.5m of uplift. The changes are truely colossal.

http://info.geonet.org.nz/display/quake/2016/11/17/Coastal+U...

http://info.geonet.org.nz/display/quake/2016/11/18/Viewing+t...

Honestly, would you have pictured the damage in your mind differently if you read about 7.8 vs 7.9? I can imagine the jump from 7 to 8 makes a difference, but it's just 0.1, which I doubt anyone can picture the difference between.

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