  We present a study of the star formation and central black hole accretion
activity of the galaxies hosted in the two nearby (z$\sim$0.2) rich galaxy
clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured
and unobscured star formation rates, as well as the presence of active galactic
nuclei (AGN) as a function of the environment in which the galaxy is located.
Methods: We targeted the clusters with unprecedented deep infrared Spitzer
observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN
spectroscopy. The extent of our observations ($\sim$ 3 virial radii) covers the
vast range of possible environments, from the very dense cluster centre to the
very rarefied cluster outskirts and accretion regions. Results: The star
forming members of the two clusters present star formation rates comparable
with those measured in coeval field galaxies. The analysis of the spatial
arrangement of the spectroscopically confirmed members reveals an elongated
distribution for A1731 with respect to the more uniform distribution of A983.
The emerging picture is compatible with A983 being a fully evolved cluster, in
contrast with the still actively accreting A1731. Conclusions: The analysis of
the specific star formation rate reveals evidence of on-going galaxy
pre-processing along A1731's filament-like structure. Furthermore, the decrease
in the number of star forming galaxies and AGN towards the cluster cores
suggests that the cluster environment is accelerating the ageing process of
galaxies and blocking further accretion of the cold gas that fuels both star
formation and black hole accretion activity.
