Different shocks in L1157-B1, as traced by HDCO and SiO high- and low-velocity emission. The maps are centred as in Fig. 2. The beams of all the images are reported in Figs. 1 and 2. Left panel: HDCO (2_1,1–1_0,1) integrated emission (grey contours; smoothed to the same beam of the NH₂CHO map; Fontani et al. 2014) tracing the dust mantle release due to the youngest (within B1) impact (the B1a position; northern black triangle) of the jet against the cavity wall (Gueth et al. 1998; Busquet et al. 2014). The magenta contours represent the high-velocity (HV; from –10 km s^-1 up to –18 km s^-1 with respect to v_sys) SiO (2–1) emission, tracing a smaller region associated with the release of SiO from the dust refractory core. For the HDCO image, the first contour and step are 3σ (1σ = 1 mJy beam^-1 km s^-1) and 1σ, respectively. For SiO at HV, the first contour and step are 5σ (1σ = 27 mJy beam^-1 km s^-1) and 10σ, respectively. Middle panel: Same as in the left panel for HDCO. The magenta contours represent the low-velocity (LV; up to –10 km s^-1 with respect to v_sys) SiO (2–1) emission, tracing a large structure extending towards the south (up to 16″, 4000 AU, from B1a), which creates the so-called “finger” feature (southern black triangle; Gueth et al. 1998) that coincides with the location of the oldest shock within B1. For SiO at LV, the first contour and step are 5σ (1σ = 50 mJy beam^-1 km s^-1) and 10σ, respectively. Right panel: p-H₂CO (2_0,2–1_0,1) integrated emission (grey; also smoothed to the same beam of the NH₂CHO image; Benedettini et al. 2013). The first contour and step are 3σ (1σ = 3.3 mJy beam^-1 km s^-1) and 6σ, respectively. In colour is reported the CH₃CHO (7_0,7–6_0,6 E+A)/NH₂CHO (4_1,4–3_1,3) line intensity ratio (derived where both emission is at least 3σ) smoothly decreasing from north to south (see the wedge).