Ringing Planets

The ground rising (gold) and falling (blue) after the last quake, from its lowest modes, slowed so that ₀S₂ swings in 1.6 s and hugely exaggerated: the football mode squashes the planet one way, then the other, while the spin turns its pattern. ★ the quake, ▲ the station.

The model the modes were solved for, coloured by the speed of shear waves (bluer: faster); a liquid core carries no shear at all, so the twisting (toroidal) modes stop at it.

Gold: the key's note, ₀S₂, and the breathing mode ₀S₀, 2.6 times higher; the rest are the loudest of the other modes. Each tone is a multiplet: with the spin on, look for it split into close peaks.

The surface waves' crack (the high modes) is gone within a tenth of a second; the football mode ₀S₂ and the breathing mode ₀S₀ ring on.