Figure 5. Slip rate and the corresponding frequency content for Scenario 1 (a and b) and Scenario 2 (c and d). Frequency content at 8.3 km (e) and at 22.0 km (f) from the two scenarios are also plotted together for comparison.
3.2 Roles of depth-varying fault friction
Scenario 3 (L of 40 km and d of 0 km) and Scenario 4 (L of 40 km and d of 30 km) aim to examine the effects of depth-varying fault friction. Both scenarios exhibit an area of shear stress increase at shallow depth, corresponding to the employment ofL (Figure 6a and 6b) and diminished slip at shallow depth (Figure 6b and 6g). Scenario 4 shows more subdued slip near the trench and smaller peak slip (~7m) at depth than those in Scenario 3, suggesting additional effects of d of 30km on stress and slip distributions. Overall, slip distribution at shallow depth in both Scenarios 3 and 4 is similar to that in Scenario 2, suggesting the depth-varying fault friction dominates shallow slip distribution if the shallow portion of a subduction plane is velocity strengthening.
In Scenario 3, the rupture time contour (Figure 6c), together with the rupture velocity distribution and the depth profile of rupture velocity (Figure 6d and 6e), show that rupture accelerates toward trench and reaches its maximum near the trench (~4 km/s). Therefore, 40 km along-dip transition thickness (L = 40, Figure 3e) cannot slow down the rupture that initiates at the bottom of the seismogenic zone and accelerates through the zone. In Scenario 4, the rupture does not accelerate much upward from the nucleation patch due to the existence of d=30km (Figure 3g). In addition, the rupture appears more confined along strike direction in Scenario 4 (Figure 6h, 6i, 6j), in particular at shallow depth where the rupture does not break the near-trench area away from the central depth profile. By comparing the rupture velocity along the central depth profile (red curves in Figures 6j and 4e, 4j), we find that the depth-varying friction property in Scenario 4 contributes to rupture slowdown towards the trench to a certain degree, but seems not the dominant factor, in particular for shallow 10 km depth.