Human-induced and natural quakes indistinguishable: study

The stresses released by naturally occurring and human-induced earthquakes are indistinguishable, meaning that existing tools to predict shaking damage can be applied to both types, scientists have found.
"Our study shows that induced earthquakes and natural earthquakes in the central US are inherently similar, and we can predict the damaging effects of induced earthquakes using the same framework as natural earthquakes," said Yihe Huang, an assistant professor at the University of Michigan in the US.
"Our finding simplifies the task of hazard assessment because we don't have to treat the shaking from these two kinds of earthquakes differently," said Gregory Beroza, from Stanford University in the US.

A key question is whether induced earthquakes excite ground motions that are substantially different than those of naturally occurring earthquakes.
If so, then human-induced earthquakes could result in different levels and types of damage to buildings and infrastructure.
However, if the ground motions in induced and natural earthquakes are largely the same, then equations used to predict damage from natural earthquakes can also be applied to human-induced quakes.

Researchers used available instrumental recordings to estimate the stress drop - the difference between the stress across a fault before and after an earthquake - of 39 moderate-magnitude induced and natural earthquakes in the central US and eastern North America.

They found that the stress drops of induced and natural earthquakes in the central US are "indistinguishable" once the faulting mechanism and the depth of the quakes are accounted for.
The finding suggests that ground motion prediction equations (GMPEs) used to predict damage from naturally occurring earthquakes can also be applied to induced quakes.
The results are also consistent with the idea that both naturally occurring and induced earthquakes are driven by stresses along geologic faults and that the injection of fluids in deep disposal wells advances the timing of induced earthquakes, triggering them.