  Previous literature suggests that the densest structures in the interstellar
medium form through colliding flows, but patent evidence of this process is
still missing. Recent literature proposes using SiO line emission to trace
low-velocity shocks associated with cloud formation through collision. In this
paper we investigate the bright and extended SiO(2-1) emission observed along
the ~5 pc-long W43-MM1 ridge to determine its origin. We used high angular
resolution images of the SiO(2-1) and HCN(1-0) emission lines obtained with the
IRAM plateau de Bure (PdBI) interferometer and combined with data from the IRAM
30 m radiotelescope. These data were complemented by a Herschel column density
map of the region. We performed spectral analysis of SiO and HCN emission line
profiles to identify protostellar outflows and spatially disentangle two
velocity components associated with low- and high-velocity shocks. Then, we
compared the low-velocity shock component to a dedicated grid of
one-dimensional (1D) radiative shock models. We find that the SiO emission
originates from a mixture of high-velocity shocks caused by bipolar outflows
and low-velocity shocks. Using SiO and HCN emission lines, we extract seven
bipolar outflows associated with massive dense cores previously identified
within the W43-MM1 mini-starburst cluster. Comparing observations with
dedicated Paris-Durham shock models constrains the velocity of the low-velocity
shock component from 7 to 12km/s. The SiO arising from low-velocity shocks
spreads along the complete length of the ridge. Its contribution represents at
least 45% and up to 100% of the total SiO emission depending on the area
considered. The low-velocity component of SiO is most likely associated with
the ridge formation through colliding flows or cloud-cloud collision.
