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Suppose that a super-powerful earthquake occurred anywhere on Earth, say one with the value 10 on Richter's scale. The quake can have any value but as can be read in a comment below the highest value ever measured was 32 on a superdense star. In that case, it's much more difficult to tear the star apart. The Earth, in contrast, could be torn apart by a quake with value 10 because she is highly less massive.

Suppose the quake was mainly transversal (in a vertical direction). Could it be that correspondingly waves emerged from the center of the quake, traveling the Earth around to come together and reinforced again on the opposite side of the center, with the effect that the quake was felt more strongly on the opposite side of the center than at places halfway from the center (or halfway to the opposite side of the center), to say it in one long breath? Or would too much energy be absorbed from the waves by the Earth to reach the opposite side?

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    $\begingroup$ @Fred Thanks for editing. It really improved, for a part at least, my ability to translate from my native language (Dutch) into English! $\endgroup$
    – Deschele Schilder
    Dec 16, 2019 at 7:35
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    $\begingroup$ Could you clarify that "couldn't even be measured on Richter's scale" part? The biggest event mentioned on Wikipedia was 32 on Richter-scale and measured on a neutron star SGR 1806−20. en.wikipedia.org/wiki/Quake_(natural_phenomenon)#Starquake $\endgroup$
    – Nyos
    Dec 16, 2019 at 14:32
  • $\begingroup$ Note we don't use the Richter scale, but the moment magnitude scale. The Richter suffers underestimation for large and/or deep earthquakes. $\endgroup$
    – OrangeDog
    Dec 17, 2019 at 12:13
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    $\begingroup$ "The Earth, in contrast, could be torn apart by a quake with value 10 because she is highly less massive." The gravitational binding energy of the earth is 2*10^32 J. A magnitude 10 quake is 2*10^19 J. $\endgroup$
    – Acccumulation
    Dec 17, 2019 at 17:38
  • $\begingroup$ Citation needed for "tearing the earth apart". The article originally linked in a comment (now removed) did not support this claim; and @Acccumulation has pointed out that the energy needed to do this is some orders of magnitude beyond M10. $\endgroup$
    – Semidiurnal Simon
    Dec 29, 2019 at 9:19

1 Answer 1

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It is called "antipodal focusing". See for example Antipodal focusing of seismic waves observed with the USArray.

We present an analysis of the M-w = 5.3 earthquake that occurred in the Southeast Indian Ridge on 2010 February 11 using USArray data. The epicentre of this event is antipodal to the USArray, providing us with an opportunity to observe in details the antipodal focusing of seismic waves in space and time. We compare the observed signals with synthetic seismograms computed for a spherically symmetric earth model

The above paper deals with "body waves" that travel through the interior of the Earth.

There are also Rayleigh waves that travel on the surface and can travel around the Earth several times before dissipating (Wikipedia). Antipodal focusing of seismic waves due to large meteorite impacts on Earth does numerical simulations of surface waves at the antipode of the Chicxulub impact. The waves do not arrive at the antipode at the same time because of Earth’s ellipsoidal shape and different rock properties along their paths.

enter image description here
Isosurfaces of the norm of the peak displacement vector after a vertical impact for the impact hemisphere (left-hand side) and antipodal hemisphere (right-hand side).

(They say: "Note that contours of the continents are today’s, not their end Cretaceous positions, and therefore do not show the original Chicxulub antipode 65 Ma.")

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    $\begingroup$ related: arstechnica.com/science/2013/06/… $\endgroup$
    – trond hansen
    Dec 16, 2019 at 5:38
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    $\begingroup$ video from the event,poor quality: youtube.com/watch?v=uYJjMqYdmmo $\endgroup$
    – trond hansen
    Dec 16, 2019 at 5:52
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    $\begingroup$ Your excerpt (from the abstract?) describes what they did, but what was the conclusion? Did they find anything? $\endgroup$
    – gerrit ♦
    Dec 16, 2019 at 10:20
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    $\begingroup$ @trondhansen That video says it shows something that happened after the 2011 earthquake in Japan, not a 2010 earthquake in the Indian Ocean. Also, Norway is not antipodal to Japan, so the sieches may be remnants of the tsunami, but they're not the result of antipodal focusing. $\endgroup$
    – Spencer
    Dec 16, 2019 at 13:24
  • $\begingroup$ @Spencer i do not have the data for the antipodal point(it was probably in the south atlantic off the coast of south america)it could be nice to know what happened there. $\endgroup$
    – trond hansen
    Dec 16, 2019 at 16:28

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