© Harsha Bhat
This illustration, based on computer models, shows how the hanging wall (right) of a thrust fault can twist away from the foot wall (left) during an earthquake.
This illustration, based on computer models, shows how the hanging wall (right) of a thrust fault can twist away from the foot wall (left) during an earthquake.
The study focused on a particular paradox associated with thrust faults, a crack in Earth's crust, where geologic forces are slowly pushing a huge slab of continental crust up and over an oceanic layer.
"For a long time, it was assumed that thrust faults, subduction zone faults being a class of such faults, could not have a large amount of slip close to the Earth's surface," said Harsha Bhat, a research scientist at the École Normale Supérieure (ENS) in Paris and co-author of the new study with California Institute of Technology graduate student Vahe Gabuchian.
A dormant hypothesis
The assumption was made because as the continental slab grinds over the oceanic one below, it scrapes off the soft surface clay and leaves it piled up in the subduction zone. Geologists thought that any energy generated from a seismic event within the thrust fault would peter out once it hit the soft clay and that a large slip wouldn't happen near the surface.
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