A system for downhole wellbore vector strain sensing including a strain sensor positionable between an outer surface of a wellbore casing and a subterranean formation for sensing a plurality of strain tensor elements, the plurality of strain tensor elements comprising multiple components of a strain tensor; a computing device positionable at a surface of a wellbore and communicatively coupled to the strain sensor; and a communication link between the strain sensor and the computing device for communicatively coupling the strain sensor to the computing device to relay strain data, the strain data comprising the plurality of strain tensor elements.