As I know, the Earth core is solid. This is known, because it conducts also transverse waves, while liquids conduct only longitudinal waves.

But, how was it found? The inner core is in the outer core, which is liquid. Thus, it is inpermeable for the transverse waves.

So, any transverse wave originating in the crust, shouldn't be able to reach the core and vice versa.

How could it been measured?


1 Answer 1


This is a good observation. The reason we can measure S-wave (transverse) propagation in the inner core is because P-waves can set up S-waves and vice versa. When an S-wave hits the mantle-outer core boundary at an angle it has a vibration component which is normal to the boundary and this sets up a P-wave in the liquid inner core. The opposite happens at the outer core-inner core boundary, where the P-wave at the boundary sets up an S-wave in the solid inner core. In this way, we can measure S-wave transmission through the inner core.

  • $\begingroup$ Is this also applicable to the Moon? It is said that the Moon rings like a bell: nasa.gov/exploration/home/15mar_moonquakes.html Apparently, the earthquake that triggered the tsunami in Thailand in 2004 had the Earth ringing like a bell too. Therefore I would say that we have little knowledge what is down there. $\endgroup$ Dec 3, 2016 at 21:50
  • $\begingroup$ @SnakeSanders I don't quite understand what your point is. The 'ringing like a bell' refers to very large earthquakes (or moonquakes) exciting the normal modes of oscillation of the Earth. $\endgroup$
    – bon
    Dec 4, 2016 at 11:48
  • $\begingroup$ @bon For the moon the "ringing like a bell" was for the impact of a lunar module from the Apollo mission $\endgroup$
    – jean
    Mar 29, 2019 at 19:18

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