Middle panel: overlay of the 217 GHz continuum emission (grayscale) on the blue-shifted (blue contours) and red-shifted (red contours) SiO (5–4) averaged emission. The blue-shifted emission has been averaged over the (73, 90) km s⁻¹ velocity interval and the red-shifted emission over the (103, 119) km s⁻¹ one and are indicated in blue and red dotted vertical lines in the top left and lower right spectra. Contour levels are 3, 6, 12, and 24 times 1σ, where 1σ is 1.1 mJy beam⁻¹. Grayscale contours for the continuum emission range from 7.5 to 232.5 mJy beam⁻¹ in steps of 90mJy beam⁻¹. The synthesized beam is shown in the lower left-hand corner. Left and right panels: SiO (5–4) spectra toward selected positions in the G31 core. The vertical dashed line indicates the systemic LSR velocity of 96.5 km s⁻¹.