Catalyzes the conversion of (2E,6E)-farnesyl diphosphate (FPP) to yield the sesquiterpene (+)-(1(10)E,4E,6S,7R)-germacradien-6-ol via a putative 1,10-cyclization, which could require the abstraction of the pyrophosphate from FPP to yield the (E,E)-germacradienyl cation. The only accepted substrate is farnesyl diphosphate (FPP). (2E,6E)-farnesyl diphosphate + H2O = (+)-(1(10)E,4E,6S,7R)-germacradien-6-ol + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Asp-Xaa-Xaa-Xaa-Asp (DDXXXD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.