Tectonic plates move very slowly relative to each other, typically a few centimetres per year, but this still causes a huge amount of deformation at the plate boundaries, which in turn results in earthquakes.
These slabs form the lithosphere, which is comprised of the crust (continental and oceanic) and the upper part of the mantle. The Earth’s outermost layer is fragmented into about 15 major slabs called tectonic plates. We also know that the outer part of the core is liquid, because S-waves do not pass through it. The core is composed of iron and we know that it exists because it refracts seismic waves creating a ‘shadow zone’ at distances between 103º and 143º.
