Megaskjelv

Megaskjelv is a term used in some Norwegian-language discussions to refer to extraordinarily large earthquakes, typically associated with very large slip on fault systems. The term emphasizes the extreme scale of energy release and ground shaking. It is not a formal category in most international seismology databases; conventionally, scientists describe such events as great earthquakes or megathrust earthquakes, with the magnitude threshold often set at around Mw 8.5 or higher, though definitions vary.

Megathrust earthquakes occur at subduction zones where one tectonic plate is forced under another. They can rupture along long segments and produce powerful ground shaking and, frequently, tsunamis that affect coastal regions far from the epicenter.

Notable examples include the 1960 Great Chilean earthquake (Mw about 9.5), the 2004 Sumatra-Andaman earthquake (Mw about 9.1–9.3), and the 2011 Tōhoku earthquake (Mw 9.0). These events illustrate typical megaskjelv characteristics: long rupture duration, large moment release, broad geographic impact, and substantial aftershock sequences.

Prediction and assessment rely on seismic networks, GPS, InSAR, and tsunami detection. Understanding megaskjelv improves hazard models and early-warning capabilities, but precise timing and rupture extent remain challenging. See also great earthquakes, megathrust earthquakes, subduction zones.