'Fossil earthquakes' offer new insight into seismic activity deep below Earth's surface

The grey line in the rock, running from the foreground away under the boulder towards the mountains, is one of the shear zones from the study area. Credit: Lucy Campbell

A major international study has shed new light on the mechanisms through which earthquakes are triggered up to 40km beneath the earth’s surface.

While such earthquakes are unusual, because rocks at those depth are expected to creep slowly and aseismically, they account for around 30 percent of intracontinental seismic activity. Recent examples include a significant proportion of seismicity in the Himalaya as well as aftershocks associated with the 2001 Bhuj earthquake in India.
However, very little is presently known about what causes them, in large part due to the fact that any effects are normally hidden deep underground.
The current study, published in Nature Communications and funded by the Natural…

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