 Megathrust earthquake

A megathrust earthquake releases accumulated elastic strain by slip on a large part of a subduction zone plate interface. Between events, a locked region can resist relative plate motion while the surrounding plates deform. Failure lets the interface move rapidly and radiate seismic waves.

The rupture's geometry, slip distribution and speed determine the ground motion and deformation. Vertical displacement of the seabed can generate a tsunami when it moves a sufficiently large water volume rapidly. Earthquake magnitude alone does not specify that displacement, and a deep or predominantly horizontal rupture can have a different tsunami effect from a shallow one.