4.2.2 Effect of Depth Bins, constant β or Variableβ (Strategies 3 and 4)
To investigate the effects of allowing the ECS to vary with depth, and
account for possible variation in attenuation with depth, we divide the
dataset into four depth bins (1-4, 4-5, 5-8 and 8-15km) guided by the
velocity structure (Figure S3) and earthquake distribution, ensuring
sufficient earthquakes within each bin for a stable inversion. We repeat
the analysis both assuming a constant shear wave (and rupture) velocity
(Strategy 3) and allowing shear wave velocity to vary with depth
(Strategy 4). The results are compared to those in the previous
inversions in Figure 4 and Table 1.
At shallower depth, the depth-dependence of stress drop is significantly
reduced by using variable β (slope reduces by 60% comparing
Strategy 3 and 4), but only slightly reduced with only depth-dependent
attenuation (slope only reduces by 22% comparing Strategy 1 and 3).
However, at deeper depth, the depth-dependent attenuation correction has
significant impact on the depth-dependence of stress drop (slope
reduction of 85% between Strategy 1 and 3). Slopes of magnitude
dependence are also reduced, albeit slightly.