The processes controlling earthquake nucleation remain enigmatic. Scientists from Utrecht University now found an important piece of the puzzle, claiming that natural earthquakes may be caused by microscale grain rearrangements. The results of their study appeared this week in Nature Communications.
The Earth’s crust is roughly composed of two parts: a ductile deep part and a brittle shallow part. The strongest natural earthquakes often occur at a depth corresponding to the transition zone between ductile and brittle rock. Using unique laboratory equipment, the researchers reproduced fault behaviour at depth conditions simulating this transition zone. The results showed that rearrangements on the scale of a micrometre (= 0.001 millimetre) may lead to an earthquake via some kind of geological snowball-effect.
‘It is not necessarily problematic when two masses of rock in the crust move past each other,’ says Earth scientist and first author Bart Verberne of the High Pressure and Temperature (HPT) laboratory at Utrecht University. ‘As long as grains in the fault rock can deform fast enough there’s no problem. However, when grains deform too slow internally, they have to rearrange. This leads to cavities, which may trigger an instability leading to an earthquake.’