Talk:Richter magnitude scale

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This is the talk page for discussing improvements to the Richter magnitude scale article.
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Boffman 21:16, 25 March 2006 (UTC) March25 - reverted to old version due to vandalism.

Contents

[edit] TNT energy table

What's the difference between Approximate TNT for Seismic Energy Yield and TNT equivalent of example? The numbers are significantly different in certain cases, and I'm not sure why we need both columns. -- nae'blis (talk) 16:20, 7 June 2006 (UTC)


Not sure if that table is right, it's reproduced a lot of junk but the orders of magnitude in ergs don't add up. I agree with this table http://www.cwp.mines.edu/~john/empirical/node7.html

The TNT equivalents don't add up either: 6.0=1MT contradicts 7.0=50MT (surely it's 32MT?), also 8.0 = 1GT contradicts 9.0=5.6GT (did they mean 8.5=5.6GT?) and 9.3=32GT (did they mean 9.0=32GT?) HairyDan 21:45, 25 August 2007 (UTC)

[edit] Richter Magnitudes

The table in this section has a column heading "Retro Earth magnitudes". This term does not appear anywhere else in the article, and I can't find a definition of it elsewhere (using Google). Either it needs to be changed to "Richter magnitude" or else "Retro Earth magnitude" needs to be introduced and defined before the table.

[edit] "estimate for a 10 km rocky bolide impacting at 25 km/s"

The TNT equivalent given here disagrees with the value given here by a factor of one-hundred.

If I've done the math correctly (?) than if the Tsar Bomb was 50 megatons it should have a Richter Magnitude of more than 10.

2/3*(log((4.2*10^12)*50,000,000)-4.8) = 10.348

So why is it catagorized as around 7? The Tsar Bomb link even discusses 4.2 megaton underground nuclear tests as resulting in siesmicity of around 7 -- so something's off about this table. 24.16.93.26 21:52, 18 January 2007 (UTC)

[edit] Rocky Bolide Math

Crunching the numbers:

A 10-km diameter bolide, with a density of 5 g/cm^3 (or 5 times the density of water. Iron is 7.86 g/cm^3, the Earth is 5.5), has a mass of about 2.6*10^12 g. Traveling at 25 km/s, the bolide would have an energy of 1/2 * m * v^2 = 8*10^20 J

At the rate of 4418 J / gram of TNT (See TNT equivalent), this generates 1.8 * 10^17 g of TNT = 0.18 teratons (metric) of TNT, give or take 20%. So in order to generate the requisite 1 teraton of TNT-force on impact, a 5-fold increase in the mass, or a 5^(1/3) = 1.7 increase in the radius, is a 17-km bolide. But given the limited precision of these calculations, I left it at one significant figure, or 20-km.

Lifthrasir1 19:40, 19 January 2007 (UTC)

Actually, the mass is 2.6*10^12 tons. Thus, the energy has to be multiplied by 1000,000.--SiriusB 12:06, 22 August 2007 (UTC)
However, there are some other mistakes, so now correctly: 2.6*10^15 kg *0.5*(25000 m/s)^2 = 8*10^23 J or 190 Teratons TNT (1 T TNT equivalent is 4.184*10^9 J). Given the formula in the German WP article we get a magnitude of roughly 11.5 for that impact but 7.1 for Tsar Bomba. But the latter had only about 5 (see Tsar Bomba) which may be due to the atmospheric explosion and the fact that only a small fraction of the air shock (about 1/1000 according to the magnitudes) is transmitted into ground shock.--SiriusB 12:17, 22 August 2007 (UTC)

[edit] problem with table

There are two examples of 5.0 with radically different numbers. Which is correct? —The preceding unsigned comment was added by 134.219.128.121 (talk) 12:58, 23 January 2007 (UTC).

Both are correct. The richter scale is actually a measure of ground motion, and there are a number of factors which prevent there being a direct correlation between the amount of ground motion and the amount of energy released. In these cases, there was an equivalent amount of ground movement, but a different amount of energy released. This is due to the fact that the Nagasaki atomic bomb was detonated fairly close to the ground, as it was being used as a weapon, and the Tsar Bomba was detonated quite far from the ground, as it was simply being tested.Upthorn 10:32, 22 April 2007 (UTC)

[edit] The base of energy release of the Richter scale is empirical and is over 30

The relationship of the base of the Richter scale to energy release is empirical. Estimates put the base at slightly more than 30. In other words, an increase of two on the scale is over 900 times as much energy release. Although the base is stated several paragraphs into the article, since this is a very significant practical fact, it might be good if it appeared earlier. A lot of the confusion about energy release (see other talk posts) is probably traceable to the article leading off by saying that the base of the scale is 10, and people casually assuming that this is the base of the energy output rather than the amplitude. Brian Hill 07:37, 7 March 2007 (UTC)

The relationship is not quite so simple. The richter scale measures the amount the ground moves, and for this measurement, the logarithmic base is precisely 10, (a 2.0 quake means 10 times as much shaking as a 1.0), however, there are many factors which prevent this from reliably converting into a consistent amount of energy. The most common approximation, however, is that for energy, there is a logarithmic base of 32, starting from 1 pound of TNT at magnitude 0. Upthorn 10:29, 22 April 2007 (UTC)
The explanation for this used to be on the page a while ago, it's as follows:
So, for example, an earthquake of magnitude 5 is ten times greater than one of magnitude 4 and an earthquake of magnitude 8 is 10(8-4) or 10000 times greater than one of magnitude 4.
However, the energy of an earthquake is proportional to the square root of the cube of the amplitude. So each step of the Richter scales has an energy 103/2 (~ 31.6) times that of the previous step. So a magnitude 9 has 10,000 times the amplitude of a magnitude 5, but a million times more energy.
The diminution of amplitude due to distance between the earthquake epicenter and the seismometer is corrected for by subtracting the common logarithm of the expected amplitude of a magnitude 0 event at that distance. This correction for distance is intended to make the local magnitude an absolute measure of earthquake size.
The magnitude of the earthquake, M, is given by:
M = log10A + 3log10(8Δt − 2.92)
where A is amplitude in millimeters and t is time in seconds.
It's a shame that this explanation was lost to the article, but I guess someone didn't like it. Sekiyu 04:35, 16 August 2007 (UTC)
I hadn't heard the sqrt(1000) explanation before. Richter's original scale was pretty much entirely empirical, with 0 being the smallest detectable (as described in the article under Development). 10 was expected to be the largest imaginable. I learned about the empirical definition after living through Northridge and spending a lot of time in the UCLA physics library during the aftershocks. It is interesting to see statements about the modern and original empirical scales coexisting. Brian Hill 04:46, 21 August 2007 (UTC)

Anyway, based on our discussion here, the importance of the energy released for purposes of damage and comparison with things like explosions, and the widespread confusion on the subject that you see in typical conversation and newspapers, I added a sentence at the beginning of the article making the base 32 point. Hope it works for people. I don't intend this to detract or conflict from the more sophisticated explanations later in the article. Brian Hill 04:48, 21 August 2007 (UTC)

[edit] Corrections to table

Removed non-USGS approved adjectives like "massive" and "meteoric" from the table and added supporting references. Ztolstoy 21:51, 9 August 2007 (UTC)

[edit] Common misbelief about the Richter Scale

It is commonly believed that a 2 is twice as bad as a 1, that a 4 is twice as bad as a 2, and so on. This is far from correct. I believe it is best to think of the numbers as exponents rather than multiples.

A 2 is a 1 squared.

A 3 is a 1 cubed.

A 4 is a 1 to the fourth or a two squared.

A 5 is a 1 to the fifth.

A 6 is a 1 to the sixth

A 7 is a 1 to the seventh.

An 8 is a 1 to the eighth or a 2 cubed

A 9 is a 1 to the ninth or a 3 squared.

A 10 is a 1 to the tenth.

67.188.172.165 19:51, 24 August 2007 (UTC)

So they all equal 1? 128.232.242.178 16:12, 2 October 2007 (UTC)
Yeah... 1^1=1 1^2 or 1X1=1 and so on 2^3 doesn't equal 1^8 2^3=8 1^8=1 Where did you learn math at?
I think it's fairly obvious that when 67.188.172.165 says "a 1" he/she means "the energy released by a magnitude 1 earthquake". Warrickball (talk) 15:28, 12 May 2008 (UTC)

[edit] Wrong Scale?

The Indian Ocean earthquake is listed as 9.3 ML in the table however this magnitude relates to the Moment magnitude scale. I believe this earthquake was 8.9 - 9.0 on the Richter scale, but don’t quote me on it. —Preceding unsigned comment added by Allmyfaultsarenormal (talk • contribs) 02:35, 5 September 2007 (UTC)

I'm seconding this. Having clicked on many of the links, notably the 1960 Anchorage earthquake, it appears that the table of magnitudes often lists the moment magnitude scale measurement rather than the Richter magnitude. Warrickball (talk) 15:28, 12 May 2008 (UTC)

[edit] Table of Quakes

Exactly. So the table of quakes is wrong and inconsistent. An 9.0 quake is 32 times that of 8.0, not 5.6. And a 8.0 is listed as 20 times that of a 7.0. See TNT equivalent. Also, Indian Ocean Earthquake and Tsar Bomba figures are wrong too on the table and their respective pages. 71.117.93.160 11:08, 2 November 2007 (UTC)

This edit was added after nearly the entire talk page was removed by a vandal. I am replacing it here, as it appears to be useful discussion. Argyriou (talk) 18:33, 14 December 2007 (UTC)

[edit] New Madrid

What about the New Madrid Earthquake... shouldn't that be listed as an example?

[edit] Scale Inconsistencies

Logically, 12 in the Richter Scale should be equivalent to 1,000 teratons or a petaton. (If 4 is 1 kiloton, 6 is 1 megaton, 8 is 1 gigaton and 10 is 1 teraton)

Another inconsistency is that the Earth's daily receipt of solar energy is listed as 672 ZJ, while http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy) lists it as being 15 ZJ (A big difference). —Preceding unsigned comment added by 189.25.157.16 (talk) 19:41, 23 April 2008 (UTC)

[edit] Development POV

The Development section says that this was developed by Richter in partnership with Gutenberg, yet the POV seems to infer that Richter was the only person involved. "His inspiration was..." , "His motiviation...". It speaks nothing of Gutenberg's contributions to the development. Can anyone who is knowledgeable on the development comment?Bgautrea (talk) 16:31, 12 May 2008 (UTC)

[edit] Inconsistant information in article?

In the article section "Development" there appears the statement "Because of the limitations of the Wood-Anderson torsion seismometer used to develop the scale, the original ML cannot be calculated for events larger than about 6.8." Surely if this is the case then no quakes should appear in the tables above this magnitude, unless I am misunderstanding what the text means. Can anyone clarify this for me?

Doc John —Preceding unsigned comment added by 72.214.244.130 (talk) 22:35, 14 May 2008 (UTC)

[edit] accuracy issues

I'm not quite sure that it's practical to calculate the energy yield of earthquakes. The duration of an earthquake is also a major factor. For example, I'm pretty sure that a 10-minute 7.8 earthquake would release more energy than a two-second 8.2 earthquake. --Ixfd64 (talk) 19:38, 16 May 2008 (UTC)