The idea behind the solution is to implement a new custom measure giving the rank of each Webpage for each quarter. The formula would be the following:
CASE WHEN
[Measures].[Page visits]>0
THEN
Rank(
[Webpages].CurrentMember,
Order(
Filter(
[Webpages].[Webpages].Members,
[Measures].[Page visits]>0
),
[Measures].[Page visits],
BDESC
)
)
END