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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.

Frictional heat during earthquake rupture raises the pressure of fault zone fluids and affects the rupture process and its seismic radiation. Here, we investigate the role of two key parameters governing thermal-pressurization of pore fluids -- hydraulic diffusivity and shear-zone half-width -- on earthquake rupture dynamics, kinematic source properties and ground-motions. We conduct 3D strike-slip dynamic rupture simulations assuming a rate-and-state dependent friction law with strong velocity-weakening coupled to thermal-pressurization of pore fluids. Dynamic rupture evolution and ground-shaking are densely evaluated across the fault and Earth surface to analyze variations of rupture parameters (slip, peak slip-rate PSR, rupture speed Vr, rise time Tr), correlations among rupture parameters, and variability of peak ground velocity (PGV). Our simulations reveal how variations in thermal-pressurization affect source properties. We find that mean slip and Tr decrease with increasing hydraulic diffusivity, whereas mean Vr and PSR remain almost constant. Mean slip, PSR and Vr decrease with increasing shear-zone half-width, whereas mean Tr increases. Shear-zone half-width distinctly affects the correlation between rupture parameters, especially for parameter pairs slip-Vr, PSR-Vr and Vr-Tr. Hydraulic diffusivity has negligible effects on these correlations. Variations in shear-zone half-width primarily impact Vr, which then may affect other rupture parameters. We find negative correlation between slip and PSR, in contrast to simpler dynamic rupture models, whereas trends for other parameter pairs are in agreement. Mean PGVs decrease faster with increasing shear-zone half-width than with hydraulic diffusivity, whereas ground-motion variability is similarly affected by both parameters., Comment: This paper has been submitted to the Bulletin of the Seismological Society of America for publication