User talk:Ampuero

Welcome!

Hello, Ampuero, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are a few links to pages you might find helpful:

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Please remember to sign your messages on talk pages by typing four tildes (~~~~); this will automatically insert your username and the date. If you need help, check out Wikipedia:Questions, ask me on my talk page, or ask for help on your talk page, and a volunteer should respond shortly. Again, welcome! Quinton Feldberg (talk) 23:47, 7 August 2017 (UTC)[reply]

Re "Richter" vs. Mw

Hi Pablo! Thanks for that last edit at Moment magnitude scale. I hadn't done it as I have been trying to find sources to do it better. A key point is to document the USGS policy of unstated but implicit Mw, which used to be found at https://earthquake.usgs.gov/aboutus/docs/020204mag_policy.php, but was lost when they rebuilt the website. When I previously inquired about that I got the brush-off. So lately I've been thinking of getting together a small band of seismological "heavies" to get that statement of policy re-posted. Would you be interested in helping with this? ♦ J. Johnson (JJ) (talk) 22:20, 3 December 2018 (UTC)[reply]

Hi. Maybe this USGS page is what you're looking for: https://earthquake.usgs.gov/learn/topics/mag-intensity/magnitude-types.php Ampuero (talk) 22:03, 4 December 2018 (UTC)[reply]

I've seen that (although I see they have since expanded it a bit). What I am referring to is the statement of policy regarding magnitude. The original is archived at here. ♦ J. Johnson (JJ) (talk) 00:59, 5 December 2018 (UTC)[reply]

I will ask my USGS colleagues for an appropriate reference to that policy. In the meantime, the table I linked above summarizes well their policy for "authoritative" magnitude reporting. Ampuero (talk) 09:56, 5 December 2018 (UTC)[reply]

The table explains which magnitudes are explained, but not about using just "magnitude" or plain "M" without further specification. A key point is to have that specific url restored, as there are quite a few sites (including some government sites) that still link to it, and (besides being in the nature of a historical document) not only does the former text state the policy behind the preferences, the attribution to the working group gives it stronger official legitimacy.

I am thinking of asking Lucille Jones about this, as she was on the working group. If I do, should I cc you? ♦ J. Johnson (JJ) (talk) 20:25, 5 December 2018 (UTC)[reply]

I now see why restoring that webpage is important. You can cc me if you ask Lucy (although she has retired from USGS). I have asked Sue Hough.Ampuero (talk) 20:58, 5 December 2018 (UTC)[reply]

I knew she was about to retire; hopefully she's still answering e-mail. Sue would be good, too, although I think she had a low opinion of Wikipedia a while back. You might tell her I relied greatly on her book for guidance in re-writing the Earthquake prediction article, and I hope she will find the result acceptable. ♦ J. Johnson (JJ) (talk) 00:53, 6 December 2018 (UTC)[reply]

On the development of seismic moment

Hi Pablo. Would you have time to give me a brief overview of development of seismic moment? Kanamori credits Aki (1966), but also Knopoff (1958) for "elastic stress relaxation model of an earthquake". But I don't quite follow just how that runs, nor where the "Burridge-Knopoff model" (1964) fits in. I've been diving deep (for me), and maybe just a little tangled in the weeds.

Google Scholar gave me an intriguing hit: "There are only 21 independent components of the fourth-order tensor...". Which I see is your text (!), but that is below my crush depth. ♦ J. Johnson (JJ) (talk) 23:28, 31 January 2019 (UTC)[reply]

The seismic moment was introduced by Aki (1966). This is acknowledged in Kanamori (1978, section "Seismic moment"). Aki (1966) made use of the double-couple theory by Burridge and Knopof (1964). Kanamori (1977) cites Knopoff (1958) in a different context, that of elastic energy (equation 3).

Ah, I missed the context. Thanks. As to Burridge and Knopoff 1964: I don't see that Kanamori cited them in 1977, 1978, or 1979 (with Hanks). Nor are they mentioned in Hanks & Boore 1984 or NMSOP Ch. 3. They are cited in Kanamori & Anderson 1975, but why not later? Did he presume it was common knowledge? ♦ J. Johnson (JJ) (talk) 22:54, 1 February 2019 (UTC)[reply]

Context, again: B & K 1964 (and others) introduced the representation of earthquakes as a system of body forces (double-couple). K & A 1975 cited them for that. Later, Aki 1966 introduced seismic moment. His derivation requires B & K 1964's results, so he cited them for that. Note that B & K 1964 don't mention anything close to Aki's concept of seismic moment; they only compute the net moment, aka torque (a different concept), to show it is zero. Ampuero (talk) 10:20, 2 February 2019 (UTC)[reply]

The problem I have is: I don't see that Aki cited B & K in either 1966a or 1966b (full citations). (I am also quite curious as to why Kanamori didn't cite B & K later on. Well, I have a lead on an article by Pujol that might explain some of that.) Also, my grasp of the difference between seismic moment and net moment appears to be deficient; I'll try to be alert to that. ♦ J. Johnson (JJ) (talk) 00:26, 3 February 2019 (UTC)[reply]

As I wrote above, B & K have been cited by both Aki and Kanamori when the context warranted it (that is, when the body force representation of earthquakes was being discussed): in Aki (1966 b) at the bottom of page 83, and in Kanamori and Anderson (1975) above equation 5. Seismic vs net moment: earthquake slip is represented by a double-couple (two pairs of forces); seismic moment is basically the torque of one pair of forces only; net (or total) moment is the sum of the torques of both pairs, and it is zero (consistently with conservation of angular momentum).Ampuero (talk) 08:52, 3 February 2019 (UTC)[reply]

Duh! Yeah, right there, bottom of p. 83. To check whether my quick scan might have missed such an item, I used the search function .. on a non-searchable document. I definitely need to get more sleep (what do I think I'm doing-- graduate study??). Thank you for patiently pointing that out.

I am still weak on various aspects of seismic moment, but possibly getting a better handle on it. A question: Although in all cases the net moment cancels to zero, I gather that the magnitude of the moments canceled is significant, and therefore the interest in seismic moment. (Right?) But is seismic moment different from the analogous moment in a non-seismic context? ♦ J. Johnson (JJ) (talk) 22:06, 4 February 2019 (UTC)[reply]

It's somewhat analogous to an electric quadrupole: the sum of its four charges is zero, but the quadrupole produces an electric field which depends on the quadrupole moment tensor. The relation to the "moment" (torque) in classical mechanics is more obvious when earthquake slip is represented as a double-couple, two pairs of forces.Ampuero (talk) 22:57, 4 February 2019 (UTC)[reply]

Quadrupoles and moment tensors are beyond me, but I'm getting a better handle on torques. Thanks. ♦ J. Johnson (JJ) (talk) 00:04, 5 February 2019 (UTC)[reply]