Fig. 5.

(a) Distribution of the EW component of the strain change residual (observation-calculation) calculated at each site. Blue and red areas denote the extension deficit (ED; observation is smaller than calculation) and the extension excess (EE; observation is larger than calculation), respectively. Gray dashed lines encircle the same strain concentration zones as shown in Fig. 1. Open triangles are Quaternary active volcanoes. The thick and thin contour lines indicate 0 and every 0.5 × 10⁻⁶ strain, respectively. Dots are GPS site locations. (b) Same as (a) but with the distribution of the ratios of strain change in the EW component (observation/calculation). The thick and thin contour lines indicate 1 and every 0.02, respectively. (c) The number of included sites for the weighting in the strain calculation at each grid (every 0.01°). The color is filled when the number of included sites is larger then three. (d), (e) and (f) Same as (a), (b), and (c) but the distance decay constant (DDC) is 15 km instead of 20 km.