Frigoris is often the forgotten mare because it lacks the concentric fractures
, sinuous rilles, and magnificent craters common to other major maria.
Fractures caused by excessive exposure to heat can always be distinguished from those caused by impact, since those that are due to heat do not show a regular pattern of radial and concentric fractures, but are characteristically wave-shaped.
Fractures that form a series of broken circles, or arcs, around the point of impact are called concentric fractures. They extend from one radial fracture to another.
These are among the most observationally interesting craters on the Moon because their floors are cut by concentric fractures
and ridges, and they often contain rilles, dark halo craters, and ponds of lava.
Forty years ago many lunar scientists thought that mare ridges resulted from volcanic eruptions along concentric fractures
. This idea was consistent with the fact that ridges occur in the mare and are made of mare materials, which we know are lavas.
This explains the lack of concentric fractures
and rilles around the basin.
Peter Schultz of Brown University and his student Robert Wichman proposed the widely accepted interpretation that the appearance of FFCs is due to ponding of upward-rising magma under the crater, which lifts up the original floor and causes radial and concentric fractures
and sometimes allows lava to leak onto the crater floor.