Rahu in 4th house cause second marriage astrology

For marriage 7th house has to be checked thoroughly -Its lord,the aspects and the placement of other planets .

Second marriage is seen from 9th house. Rahu in Fourth house gives extra marital physical relationship sometimes though, depending on other planets. In fourth house it may cause problem for/with mother. It will decrease the quantum of Sukh(joy and pleasures) in life even if life is successful in all aspects.Rahu will never let the native to be satisfied and content with what he has and will drive him to look for more always .

When rahu is in 4rht house ketu is in 10th.Ketu here may cause unusability in career and profession but 10th house Lord's position too has to be checked.
There are other so many aspects to study for chances of more than one marriage yoga.

If 7th house disturbed,
If native is Manglik & Mangal MD yet to come,
If lord of 7th house is disturbed or in vision of Mangal, Shani or Rahu.
Sometimes, Bruhaspati in the 7th house also create such situation as per principle 'Sthan haani karoti guru'.
Rahu in 4th house decrease happiness of life even after native is rich. It decrease love from mother or there are difference of opinion with mother & father-in-law.
For detailed study, chandra kundli is also important.