They tick every 4 seconds.

Alt1:
/castsequence reset=7 Tremor Totem,,,

Alt2:
/castsequence reset=7 ,Tremor Totem,,

Alt3:
/castsequence reset=7 ,,Tremor Totem,

Alt4:
/castsequence reset=7 ,,,Tremor Totem

And just push it every .5-1second.

The reset is there incase 1 shaman is CCed while you attempt to use this, so he doesn't get stuck dropping his Tremor at the same time as another shaman.

Lokked