  Fault-damage zones comprise multiscale fracture networks that may slip
dynamically and interact with the main fault during earthquake rupture. Using
3D dynamic rupture simulations and scale-dependent fracture energy, we examine
dynamic interactions of more than 800 intersecting multiscale fractures
surrounding a listric fault, emulating a major fault and its damage zone. We
investigate ten distinct orientations of maximum horizontal stress, probing the
conditions necessary for sustained slip within the fracture network or
activating the main fault. Additionally, we assess the feasibility of
nucleating dynamic rupture earthquake cascades from a distant fracture and
investigate the sensitivity of fracture network cascading rupture to the
effective normal stress level. We model either pure cascades or main fault
rupture with limited off-fault slip. We find that cascading ruptures within the
fracture network are dynamically feasible under certain conditions, including:
(i) the state-evolutional distance scales with fracture and fault size, (ii)
favorable relative pre-stress of fractures within the ambient stress field, and
(iii) close proximity of fractures. We find that cascading rupture within the
fracture network discourages rupture on the main fault. Our simulations suggest
that favorable relative pre-stress fractures within a fault damage zone may
lead to cascading earthquake rupture reaching off-fault moment magnitudes up to
$Mw \approx 5.6$, shadowing the main fault slip. Our findings offer fundamental
insights into physical processes governing cascading earthquake dynamic rupture
within multiscale fracture networks. Our results have implications for the
seismic hazard of naturally activated fracture or fault networks and
earthquakes induced in geo-energy exploitation activities.
