Can an earthquake affect the speed of the Earth’s rotation?

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Again, we answer the subscriber’s question:

It may seem strange, but earthquakes do affect the speed of the Earth’s rotation and the length of the day.

Many processes play a role in this, but the main and long-term influence is exerted by the movement of huge masses of matter in the bowels of the Earth, and, as a consequence, a change in the moment of inertia of the planet.

An earthquake can either prolong or shorten the day, depending on whether the moment of inertia has increased or decreased. In a sense, this is similar to how a skater performing a pirouette can change the speed of his rotation by spreading his arms to the sides or vice versa — pressing them to the body.

There is no direct connection between the strength of the earthquake and the time by which the day changed, so as a result of the earthquake on the island. Sumatra in 2004 with a magnitude of 9.1 according to Richter, the length of the day increased by 6.8 μs, as a result of the 2010 Chilean earthquake of magnitude 8.8 according to Richter — by 1.26 μs, and as a result of the earthquake in Japan in 2011 with a magnitude of 9 according to Richter — by 1.6 μs.

These are rather small values, compared to the fact that due to the interaction of the Earth with other bodies of the solar system, the length of the day changes on average by 20 microseconds per day.