  Anticipating the maximum magnitude of injection-triggered earthquakes is
highly valuable for the safe and efficient exploitation of geoenergies. The
recent work by Li et al.(2021) reached the conclusion that unexpectedly large
injection-triggered earthquakes are primarily caused by large pre-existing
critical shear stresses on seismogenic faults. Also of great interest is the
proposal of the ratio of fault slip to dilation as an index to anticipate the
fault rupture energetics. However, their fluid injection experiments were
conducted under fully drained conditions, where the fluid pressure distribution
on the fault plane is always uniform. As already pointed out by the authors,
local fluid pressure perturbations inside faults under locally undrained
conditions also have the potential to cause unexpectedly large seismic events.
Here we add more datasets and possible explanations for this viewpoint, which
has not been explored in such detail by Li et al.(2021).
