An optical accelerometer includes a beam and at least one optical fiber affixed to one side of the beam such that deflection of the beam changes a length of the optical fiber. A device for sensing the change in length of the optical fiber is functionally coupled to the at least one fiber. A seismic sensor system includes at least two accelerometers, oriented such that their sensitive axes are at least partially aligned along mutually orthogonal directions. Each accelerometer includes a beam, and at least one optical fiber affixed to one side of the beam such that deflection of the beam changes a length of the at least one optical fiber. A device for sensing the change in length of the optical fiber is functionally coupled to the at least one fiber of each accelerometer.