From the Latin for "shake", it's a synonym for earthquake
... Old French trembler < 
Vulgar Latin *tremulre, derivative of Latin tremulus tremulous ... Its new board 
member is part of the reason that tyrants in the Middle East are now trembling in 
their... [DOC] [TLE] Tremble | Define Tremble at Dictionary.com [PAR] Tremble definition, to shake involuntarily with quick, short movements, as from 
fear, excitement, weakness, or cold; quake; quiver.