Question

How fast does this outer layer move usually?

Answer 1

The tectonic plates move about 4cm a year, including subduction.

Answer 2

On average, at about the rate that fingernails grow, approximately 3-4 cm per year. This is variable, however, often even across an individual plate, from between 1-2 cm per year for the slowest moving plates to around 10 cm per year for the fastest.