Seismic Waves: How Are They Produced?

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Discussion Overview

The discussion centers on the production of seismic waves, exploring various sources and mechanisms that generate these waves, including natural events like earthquakes and meteorite impacts, as well as human activities. The conversation also touches on the properties of rocks in relation to seismic energy propagation and the limitations of earthquake magnitudes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Seismic waves are produced by various activities, including earthquakes, meteorite impacts, explosions, and even smaller actions like hitting the ground or animals jumping.
  • Some participants propose that seismic waves are elastic waves that propagate when rocks are squished, squeezed, or twisted, as long as the elastic limit is not exceeded.
  • There is a question about the consequences of surpassing the elastic limit of rocks, with some suggesting that rocks may break while others note that some materials can be permanently deformed without breaking.
  • One participant mentions that the strength of rocks limits the maximum magnitude of earthquakes, suggesting that earthquakes cannot exceed a magnitude of about 10 on the scale due to energy dissipation in breaking rocks.
  • Another participant challenges the claim about the maximum earthquake magnitude, referencing a source that lists larger magnitudes, and highlights the distinction between earthquakes and meteorite impacts.
  • There is a discussion about the obsolescence of the Richter scale in favor of the moment magnitude scale for measuring seismic events.

Areas of Agreement / Disagreement

Participants express differing views on the maximum possible magnitude of earthquakes and the relevance of the Richter scale versus the moment magnitude scale. The discussion remains unresolved regarding the exact limits of earthquake magnitudes and the implications of rock properties.

Contextual Notes

Some claims depend on specific definitions and assumptions about rock behavior and seismic wave propagation. The discussion includes references to historical events and measurement scales that may not be universally accepted or understood in the same way by all participants.

Awsom Guy
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HI,
I want to know how seismic waves are produced?. I cannot find any information on it on google. Any help will be helpful.
Thanks.
 
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Earthquakes, meteorite impact, explosions, drilling activity, hitting the ground with a hammer, kangaroos jumping on the ground, wind blowing trees and shaking the trees. Seismic waves are elastic waves (to a very good approximation), so anything that squishes, squeezes, or twists the rocks will propagate as seismic waves provided that the elastic limit of the rocks is not surpassed.
 
So what would happen if the elastic limit was surpassed?
It would simply break, right?
 
Yes makes very sense, thank you so much.
 
BL4CKCR4Y0NS said:
So what would happen if the elastic limit was surpassed?
It would simply break, right?

That depends somewhat on the properties of the rock. There are some materials, like for example a spring, that when you exceed the elastic limit the spring is permanently deformed -- it doesn't break or snap, it is just stretched beyond its elastic limit.

In rocks, most of the time the rock will break when it has been squeezed or stretched too much (bearing in mind we are sticking to short time scales here -- over very long time scales the rock can behave very differently and change shape a bit like the spring). In that case the rock is squished until it can stand it no longer and it is broken, seismic energy is still propagated but the elastic limit of the rock puts a cap on the maximum amount of seismic energy that can be propagated. Interestingly, the strength of rocks puts a limit to the maximum magnitude of an earthquake (measured in ground shaking), you cannot get earthquakes larger than about a 10 on the magnitude scale, if you try to put in more energy the energy is spent in tearing up the rocks locally and is not propagated as seismic waves.
 
Awsom Guy said:
Are you sure about "you cannot get earthquakes larger than about a 10 on the magnitude scale" cause check the table out in wikipedia. http://en.wikipedia.org/wiki/Richter_magnitude_scale

It has a 12.55. :0

Well as I said it depends on the rocks.

There are though at least two things here that need mentioning:

1) The Chicxulub event was not an earthquake, it was a huge meteorite impact that probably wiped out the dinosaurs 65 million years ago. Actually, a lot of the energy from the Chicxulub impact would've been transmitted as shock waves (which travel faster than seismic waves) which are definitely NOT elastic waves. So meteorites can make things happen which go off the chart, meteorites can also vapourize rocks and excavate huge craters -- you just can't get that with earthquakes.

2) The Richter scale is obsolete. Seismologists now use the moment magnitude scale http://en.wikipedia.org/wiki/Moment_magnitude_scale.
 
Arrrr... moment magnitude scale. Thanks for that information. Quite impressive. Obsolete indeed. Thank you.
 

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