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.