But a study in Earth and Planetary Science Letters suggests that wedges of sediment scraped from the plates can pop up, boosting the resulting tsunami.
It suggests that spotting these wedges could improve large tsunami prediction.
Megathrust earthquakes are the sudden release of “elastic” energy stored as tectonic plates grind against each other, deforming but not slipping.
Typically, as in the Japan earthquake of March 2011 that caused a massive tsunami and the Fukushima nuclear disaster, this occurs at a subduction zone, where one plate is sliding beneath the next.
The quake arises when the deformation becomes too great and the stored energy suddenly releases.
The sudden plate movement is transmitted into the ocean, inducing a tsunami.
Now, two eminent seismology researchers from Cambridge University, Dan McKenzie and James Jackson, have come up with a different idea.Prof McKenzie, a founder of the idea of plate tectonics, explained that the idea arose from studies of the sea floor surrounding the site of the 2011 Tohoku earthquake off Japan.
“A Japanese submersible went down after the Tohoku earthquake and found not at all what everybody expected - which is that actually the tsunami was generated by the Japanese plate overriding the Pacific plate and moving upwards,” he told BBC News.
“But what this submersible found was… there was a fault which had moved the other way: instead of Japan moving upwards over the Pacific (plate), actually Japan had moved downward.” More