Abstract
Understanding the dynamics of microearthquakes is a timely challenge
with the potential to address current paradoxes in earthquake mechanics,
and to better understand earthquake ruptures induced by fluid injection.
We perform fully 3D dynamic rupture simulations caused by fluid
injection on a target fault for FEAR experiments generating Mw ≤ 1
earthquakes. We investigate the dynamics of rupture propagation with
spatially variable stress drop caused by pore pressure changes and
assuming different constitutive parameters. We show that the spontaneous
arrest of propagating ruptures is possible by assuming a high fault
strength parameter S, that is, a high ratio between strength excess and
dynamic stress drop. In faults with high S values (low rupturing
potential), even minor variations in Dc (from 0.45 to 0.6 mm) have a
substantial effect on the rupture propagation and the ultimate
earthquake size. Our results show that modest spatial variations of
dynamic stress drop determine the rupture mode, distinguishing
self-arresting from run-away ruptures. Our results suggest that several
characteristics inferred for accelerating dynamic ruptures differ from
those observed during rupture deceleration of a self-arresting
earthquake. During deceleration, a decrease of peak slip velocity is
associated with a nearly constant cohesive zone size. Moreover, the
residual slip velocity value (asymptotic value for a crack-like rupture)
decreases to nearly zero. This means that an initially crack-like
rupture becomes a pulse-like rupture during spontaneous arrest. In
summary, our findings highlight the complex dynamics of small
earthquakes, which are partially contrasting with established crack-like
models of earthquake rupture.