<p>These are visco-elastic oscillations that cause virtually no permanent deformation.</p>

<p>Following the Tohoku 2011 earthquake, this gravimeter in Metsähovi, Finland, measured a <a href="http://shakingearth.blogspot.com/2011/04/tohoku-quake-and-free-oscillations.html">radial oscillation mode amplitude of 0.06 mm</a>. The Earth's radius is 6371 km. So the resulting strains would be extremely small.</p>

<p>All but the lowest radial mode decays after a few days because the energy of the oscillations gets converted to heat by dissipative processes.</p>

CC BY-SA 3.0
2014-05-09T23:30:56.450Z
2014-05-09T23:30:56.450Z
Mark Rovetta
<p>It is known that when a large earthquake occurs, say $M \ge 9.0$, The surface waves travel around Earth over and over, "ringing the surface like a bell". The GIF below is an example (<a href="http://www.seismology.harvard.edu/research/research_normal_modes_source.html" rel="nofollow noreferrer">Image Source</a>):</p>

<p><img src="https://i.sstatic.net/2z2t0.gif" alt="enter image description here"> </p>

<p>Do these normal modes cause permanent deformation <strong>AWAY</strong> from the earthquake source or does Earth affected simply slide back in place after the wave passes through it? If there is no permeant deformation, why does the surface near (but off source) crack and fault? </p>

CC BY-SA 3.0
2014-04-28T04:40:15.373Z
Normal modes do not cause permanent deformation but rather oscillatory deformations at anti-nodes.  Therefore the simple answer is no the Earth will not be permanently deformed, but will the Earth's anti-nodes continually oscillate?  Also no, because the waves will attenuate with time.
Kenshin
CC BY-SA 3.0
2014-04-28T17:02:45.970Z
I thought that there is at least evidence for antipodal earthquake damage on Mars (or was it after impacts?).
tobias47n9e
CC BY-SA 3.0
2014-04-29T01:16:00.343Z
*"If there is no permeant deformation, why does the surface near (but off source) crack and fault?"* - That's kind of implying that these surface waves are the only type of deformation caused by the earthquake. They clearly aren't (as you mention, cracks and faults happen, and presumably other non-waved based deformations result in surrounding areas to cope with those stresses), so I'm not sure if that last sentence makes much sense.
naught101
<geophysics><seismology><geodesy>
Do normal modes of oscillation cause permanent deformation?
Neo
# Do normal modes of oscillation cause permanent deformation?

(Asked by: username_0 on 2014-04-27)

It is known that when a large earthquake occurs, say $M \ge 9.0$, The surface waves travel around Earth over and over, "ringing the surface like a bell". The GIF below is an example ([Image Source](http://www.seismology.harvard.edu/research/research_normal_modes_source.html)):

![enter image description here](https://i.sstatic.net/2z2t0.gif)

Do these normal modes cause permanent deformation **AWAY** from the earthquake source or does Earth affected simply slide back in place after the wave passes through it? If there is no permeant deformation, why does the surface near (but off source) crack and fault?

**Tags:** geophysics, seismology, geodesy

> **Comments:**
> **username_1**: Normal modes do not cause permanent deformation but rather oscillatory deformations at anti-nodes.  Therefore the simple answer is no the Earth will not be permanently deformed, but will the Earth's anti-nodes continually oscillate?  Also no, because the waves will attenuate with time.  
> **username_2**: I thought that there is at least evidence for antipodal earthquake damage on Mars (or was it after impacts?).  
> **username_3**: *"If there is no permeant deformation, why does the surface near (but off source) crack and fault?"* - That's kind of implying that these surface waves are the only type of deformation caused by the earthquake. They clearly aren't (as you mention, cracks and faults happen, and presumably other non-waved based deformations result in surrounding areas to cope with those stresses), so I'm not sure if that last sentence makes much sense.  

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## 1 answers

### Answer by username_4 on 2014-05-09. Score: 6 | Accepted answer

These are visco-elastic oscillations that cause virtually no permanent deformation.

Following the Tohoku 2011 earthquake, this gravimeter in Metsähovi, Finland, measured a [radial oscillation mode amplitude of 0.06 mm](http://shakingearth.blogspot.com/2011/04/tohoku-quake-and-free-oscillations.html). The Earth's radius is 6371 km. So the resulting strains would be extremely small.

All but the lowest radial mode decays after a few days because the energy of the oscillations gets converted to heat by dissipative processes.


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