Role of seismogenic depth and background stress on physical 1 limits of earthquake rupture across fault step - overs

11 Earthquakes can rupture geometrically complex fault systems by breaching fault step-overs. 12 Quantifying the likelihood of rupture jump across step-overs is important to evaluate earth13 quake hazard and to understand the interactions between dynamic rupture and fault growth 14 processes. Here we investigate the role of seismogenic depth and background stress on phys15 ical limits of earthquake rupture across fault step-overs. Our computational and theoretical 16 study is focused on the canonical case of two parallel strike-slip faults with large aspect ra17 tio, uniform pre-stress and uniform friction properties. We conduct a systematic set of 3D 18 dynamic rupture simulations in which we vary the seismogenic depth, step-over distance and 19 initial stresses. We find that the maximum step-over distance Hc that a rupture can jump de20 pends on seismogenic depth W and strength excess to stress drop ratio S as Hc ∝ W/S, 21 where n = 2 when Hc/W < 0.2 (or S > 1.5) and n = 1 otherwise. The critical nucleation 22 size, largely controlled by frictional properties, has a second-order effect on Hc . Rupture on 23 the secondary fault is mainly triggered by the stopping phase emanated from the rupture end 24 on the primary fault. Asymptotic analysis of the peak amplitude of stopping phases sheds 25 light on the mechanical origin of the relations between Hc , W and S, and leads to the scaling 26 regime with n = 1 in far field and n = 2 in near field. The results suggest that strike-slip 27 earthquakes on faults with large seismogenic depth or operating at high shear stresses can 28 jump wider step-overs than observed so far in continental inter-plate earthquakes. 29