Figure 6. Comparison of spatial variation of attenuation. (a) t* variability among both the horizontal and vertical bins with values derived from the linear fitting of the difference between ECSs in all the bins from Strategy 5 and the ECS from Strategy 1. Note the layered distribution along depth, indicating depth is the major factor in affecting attenuation correction. Thick black box indicates the 10km by 1 km spatial bin used in the test shown in Figure 4. (b) Histogram of log10 stress drop difference of individual earthquakes between Strategy 3 and 5. (c) ECSs from different Strategies in different horizontal bins for different depth ranges (Red: Strategy 1 with no spatial binning, which is identical in different depths; Magenta: Strategy 3 with depth-only binning; Green: Strategy 5 with spatial binning). (d) Strategy 5 ECSs subtracted by Strategy 1 ECS, different horizontal bins from the same depth range share the same color. Dashed lines are linear fit to the solid curves between 20Hz and 60Hz, and their slopes are used to evaluate t* variation over space in (a).