Talk:Richter scale/Archive 3

Archive 1

Archive 2

Archive 3

Negative magnitude

berkeley.edu usgs.gov It seems it arises from the fact that when the Richter scale was invented, sensors weren't as precise and quakes below 1 could not be detected. It is important to cover in the article (especially because it seems it's in contradiction with tha nature of logarithm). Setenzatsu.2 (talk) 14:07, 31 January 2020 (UTC)

Why is it "important to cover" negative magnitude in the article?

And how do you figure that is "in contradiction with th[e] nature of logarithm"? ♦ J. Johnson (JJ) (talk) 23:00, 31 January 2020 (UTC)

Logarithms go negative for sufficiently small values. I believe that sufficiently strong acids get a negative pH. As for earthquakes, at sufficiently small values, you run into non-quake natural or human vibration, but otherwise, for scaling reasons, they become so common as to be meaningless. That might still allow from some negative values, though. Gah4 (talk) 00:30, 1 February 2020 (UTC)

Sorry, what I said about logarithm is nonsense. I was in a hurry and thinking about sth else. Contradiction is with defitiniton of magnitude in mathematics and physics. Magnitude is a positive value. In physics it usually refers to distance and quantity and in mathematics usually to the size of a mathematical object. That is why it is importan to cover negative magnitute. Because it's counter intuitive and nonstandard. Setenzatsu.2 (talk) 17:16, 22 March 2020 (UTC)

From this page we find that a magnitude 1 is about 1.8kg of explosive, maybe two sticks of TNT, and magnitude -1 about 1.8g, maybe about the size of a firecracker. Also from the graph, you find that magnitude -1 occurs about 1,000,000,000 times a year, or about 30 every second. So in theory the scale goes down that far, but in practice it is, as they say, in the noise. The natural noise of continuous motions within the earth. I suspect that this was considered at the time, and helped set the origin of the scale. Gah4 (talk) 06:00, 23 March 2020 (UTC)

Possible error about the original definition?

Apologies if this is not how wikipedia editing is done. I don't know the norms here. The article originally said:

The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1μm, or 0.001 millimeters) on a seismogram recorded by a Wood–Anderson torsion seismograph.

I changed the 3 to a 0, but I don't know anything about geology, so I'm terrified this isn't correct and I've broken the internet. However:

The second citation (page 5) says the following:

As originally defined by Richter 1935), the local magnitudes M L were calculated from amplitudes recorded on Wood-Anderson torsion instruments and were calculated only for southern California earthquakes. To assign absolute values of magnitudes, Richter arbitrarily defined the zero-magnitude earthquake to be one for which the maximum trace amplitude at a distance of 100 km is 1 μm.

I couldn't find anything as explicit as that from the first citation (the original), but it does say the following:

A representative example is the shock of February 15, 1932, recorded at stations distant 39, 100, 107, 255, 260, and 345 kilometers with amplitudes of 6, 3, 1.2, 0.3, 0.3, and 0.2 millimeters. The magnitudes derived from Table I are then 3.20, 3.48, 3.13, 3.29, 3.31, and 3.54.

Thus, there was an event in which a 3 millimeter amplitude was recorded from 100 km away, and that produced a Richter magnitude of 3.48. Note that: log_10(3/.001) = 3.47712

That would imply that the .001 millimeter case should be the one with a Richter magnitude of 0. 2pt71828 (talk) 03:00, 16 October 2020 (UTC)

frequency

A recent edit removed: The larger the magnitude, the less frequently the earthquake happens. This is well known, and I am sure that there are references, for the range that Richter allows for. Above about 8, the statistics aren't very good. I had figured this out to answer the question above about negative magnitudes. They are possible, but occur so frequently to be meaningless. Gah4 (talk) 19:09, 25 January 2021 (UTC)

Why?

There is a why on the 3/2 exponent. Exponents like this come from scaling laws, sometimes empirical, sometimes not. Sometimes one can find a partial explanation for empirical relations, such as Zipf's law. Conveniently, we can speculate in talk pages, but not articles. It looks like Richter made his scale based on how the amplitude changed with distance. The change with distance depends on depth, in not so obvious ways. You can make some arguments based on volume:area ratios, but I suspect that it is at least semi-empirical. But it really doesn't matter: that is the way that Richter defined it, for whatever reason. Gah4 (talk) 12:52, 19 August 2021 (UTC)

9+ frequency contradiction

The table says 9+ earthquake occurs once every ten to fifty years, but the description below the table says it's once every year on average... Which is it ? It cannot be both. 2A02:2788:405:FA5C:DD7C:3940:D25:43F6 (talk) 09:35, 13 February 2023 (UTC)

Thanks for reporting this. I have changed the text in the article to refer to magnitudes of ≥8.0 instead of 9+. A USGS weblink showing that 78 earthquakes of magnitude ≥8.0 have occurred in the last 100 years is at https://earthquake.usgs.gov/earthquakes/map/?extent=-87.25291,-187.73438&extent=87.21901,547.73438&range=search&timeZone=utc&search=%7B%22name%22:%22Search%20Results%22,%22params%22:%7B%22starttime%22:%221923-02-06%2000:00:00%22,%22endtime%22:%222023-02-13%2023:59:59%22,%22minmagnitude%22:8,%22eventtype%22:%22earthquake%22,%22orderby%22:%22time%22%7D%7D — GeoWriter (talk) 18:11, 13 February 2023 (UTC)