Norwegian Blood in the family

[:)] I have a relative that was born in Portugal in 1857 but I have been told recently that one of his parents may have come from Norway. His mothers name was Mary Murdy or Mundy and I believe that it is possibly her that came from Norway and her husband came from Portugal. His name is listed as Frank Kerdy. Does anyone have any information on this family. Is Murdy or Mundy a Norweign surname or is Kerdy possibly a Norwegian surname.