Figure 8. Numerical results of Scenario 5. (a) shows the stress
change distribution; (b) shows the total slip distribution. (c) shows
the rupture time contour with an interval of 5 seconds; the red curves
indicate that the rupture front reaches the trench at 47.5 s. (d) shows
the rupture velocity distribution. (e) shows the along-dip profiles of
rupture velocity along the central line (red line in (d)) and along 50
km away along-strike from the central line (black line in (d)). The
crosses in (d) and indicate the locations of the two on-fault stations.
Slip rate time histories (Figure 9a) at the two stations from this
scenario show that the shallow station has similar peak slip rate with
more high-frequency signals compared with the deep station (Figure 9b).
The amplitude spectra at the two stations from this scenario does not
show clear high-frequency depletion at the shallow station compared with
the deep station, also in contrast to all other scenarios. Comparing
with Scenario 1 at the shallow station (Figure 9c), the upper plate
low-velocity layers enhance high-frequency seismic radiation at shallow
depth, in contrast to causing high-frequency depletion there in other
scenarios. Comparing with Scenario 2 at the shallow station (Figure 9e),
in conjunction with Figure 5e, we find that it is the high-frequency
enhancement from the low-velocity layers that cause a complex feature at
~2Hz in high-frequency depletion in Scenario 2, as
described in an earlier section. Scenario 2 has both depth-varying fault
friction and depth-varying velocity structure. The former causes
significant high-frequency depletion at the shallow station, while the
latter cause high-frequency enhancement. At most frequencies above
~0.2 Hz, high-frequency depletion from depth-varying
fault friction dominates over high-frequency enhancement from
depth-varying velocity structure, except at ~ 2 Hz. At
the deep station, Scenario 5 is also rich in high frequency content
comparing to Scenario 1 (Figure 9d), while it is more depleted in high
frequency content comparing to Scenario 2 at frequency > 2
Hz (Figure 9f).