  The effect of Ru substitution on the local structure of layered
SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ superconductor has been studied by As
$K$- and Sm $L_3$ - edges x-ray-absorption spectroscopy. The extended
x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As
bondlengths in the Ru substituted samples with the latter being $\sim$0.03 \AA\
longer. Local disorder induced by the Ru substitution is mainly confined to the
FeAs layer while the SmO spacer layer sustains a relative order, consistent
with the x-ray-absorption near-edge structure spectra. The results suggest
that, in addition to the order/disorder in the active active iron-arsenide
layer, its coupling to the rare-earth\textminus oxygen spacer layer needs to be
considered for describing the electronic properties of these layered
superconductors.
