Megajäristys

Megajäristys is a term used to describe an earthquake of exceptionally large magnitude, typically considered to be greater than magnitude 9.0 on the moment magnitude scale. These catastrophic events are the most powerful earthquakes known to occur on Earth. They happen along convergent plate boundaries, specifically at subduction zones where one tectonic plate slides beneath another. The immense build-up of stress over centuries, or even millennia, at these boundaries is released suddenly in a megajäristys.

The rupture zone of a megajäristys can extend for hundreds or even thousands of kilometers along the fault line. The duration of shaking can be significantly longer than for smaller earthquakes, lasting for several minutes. These extreme events are also strongly associated with the generation of tsunamis, as the large-scale vertical displacement of the seafloor displaces vast amounts of ocean water.

Due to their rarity and the extreme conditions required for their formation, megajäristykset are infrequent. However, when they do occur, the consequences are devastating, causing widespread destruction, loss of life, and significant environmental changes. Understanding the geological processes that lead to megajäristykset is crucial for seismic hazard assessment and preparedness in regions prone to these immense geological forces.