It's likely that they are the result of the impact of an  asteroid-sized body on the Moon, the actual point of impact being at the  centre of the inner mare basin, while the concentric ridges around it were  thrown up by the shock waves propagated by the impact. 
Alternatively, the concentric ridges may represent collapse features, where  the Moon's crust, weakened by fracture during the impact event, subsided  along concentric rings a short time later, as a result of the extrusion of  large volumes of basalt at the surface to form the central lava plain. 
The lava itself must have been originated deep down in the Moon, probably  in the lunar mantle, and it seems as though the scale of the impact was so  great that in effect a hole was blasted through the crust, enabling magma  <tag "515674">derived</> from the mantle to well out on the surface.   

