London, March 28 (IANS): Water pressure in the pores of the rocks making up the oceanic plates boundary zone takes the dominant role in determining how big an earthquake is, new research has found.

Large earthquakes are results of oceanic plates movement beneath the earth. The stress builds up before an earthquake and the magnitude of subsequent seismic energy release are substantially controlled by the mechanical coupling between both plates.

Stress build-up and its lateral distribution, in turn, are dependent on the distribution and pressure of fluids along the plate interface, the study noted.

For the study, the researchers analysed the great Chile earthquake of February 27, 2010.

"We combined observations of several geoscience disciplines - geodesy, seismology, petrology,” said Onno Oncken from GFZ - the German Research Centre for Geosciences.

“For the first time, our results allow us to map the spatial distribution of the fluid pressure with unprecedented resolution showing how they control mechanical locking and subsequent seismic energy release," Oncken explained.

Zones of changed seismic wave speeds reflect zones of reduced mechanical coupling between plates, showed the findings of the study.

The study appeared in the journal Nature Geoscience.