Aquaplaning in the geological underground—Water pressure as a critical factor for mega-earthquakes

April 2, 2018, Helmholtz Association of German Research Centres
The Nazca Plate pushes from the West against the South American Plate with 66 mm/year, thus building up enormous pressure which is released through huge earthquakes. Credit: M. Moreno et al./GFZ

Scientists have proposed a mechanism that explains the biggest-ever earthquake and how more than 50 years later, another large earthquake in the same region released some of the stress that had built up. Water pressure underground plays a crucial role in both cases.

The 2016 Mw 7.6 earthquake of Southern Chile was the first large earthquake to occur within the rupture bounds of the great 1960 Mw 9.5 Valdivia earthquake, the largest ever observed in historical times. Using GPS, InSAR, gravity, seismic reflection, and geological data, Marcos Moreno and colleagues from GFZ as well as Chile show that the 2016 earthquake occurred at the deep boundary of a persistent asperity on the interface between the subducting Nazca and overriding South American plates, where both plates are coupled and not sliding past each other in spite of the high convergence velocity of 68 mm/year. This asperity broke during the 1960 Chile earthquake b has since healed and recovered.

Their study, published in Nature Geoscience, presents a mechanical model in which the highest stresses gradually accumulate at the deeper edge of such an asperity. The 2016 event released these high stresses. Depending on the frictional parameters of the asperity and the deeper segment of the plate interface, the model predicts the failure times of the deeper and shallower portions of the interface.

According to this model, the shallower failure is representative of a great event (1960-class) and the deeper event represents a large earthquake (2016-class). Given the lag time of 56 years since the 1960 event, the suggests that the of fluid (i.e. largely water) at the plate interface zone is close to lithostatic at the deeper interface and is slightly lower at the shallower interface. If the at the plate interface zone becomes as high as the pressure of the overlying rock column, the strength of the rocks at the plate becomes practically zero—an effect akin to aquaplaning will initiate eventually triggering an . It is proposed that the development of this modelling strategy could enable the estimation of critical failure thresholds for other mapped subduction asperities where subducting and overriding plates are currently locked.

The Nazca Plate is creeping under the South American Plate. Both crustal plates are locked. Depending on the water pressure in various depths, slipping occurs with potentially devastating effects. Credit: M. Moreno et al./GFZ

Explore further: Residual strain despite mega earthquake

More information: Chilean megathrust earthquake recurrence linked to frictional contrast at depth, Nature Geoscience (2018). nature.com/articles/doi:10.1038/s41561-018-0089-5

Related Stories

Residual strain despite mega earthquake

December 13, 2017

On Christmas Day 2016, the earth trembled in southern Chile. In the same region, the strongest earthquake ever measured occurred in 1960. A comparison of data from seismic and geodetic measurements during and after both earthquakes ...

Great earthquakes, water under pressure, high risk

March 28, 2014

The largest earthquakes occur where oceanic plates move beneath continents. Obviously, water trapped in the boundary between both plates has a dominant influence on the earthquake rupture process. Analyzing the great Chile ...

Dissection of the 2015 Bonin deep earthquake

March 15, 2017

Researchers at Tohoku University's Department of Geophysics, have been studying the deep earthquake which occurred on May 30, 2015, to the west of Japan's Bonin Islands.

Recommended for you

Cities as study proxies for climate change

July 18, 2018

Cities can serve as useful proxies to study and predict the effects of climate change, according to a North Carolina State University research review that tracks urbanization's effects on plant and insect species.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Nik_2213
5 / 5 (1) Apr 02, 2018
With an excellent diagram-- Thank you !!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.