A novel demodulation technique for performing dynamic deformation measurements using a path-unbalanced Michelson interferometer is reported, The method is based on the rf amplitude modulation of a low-coherence source, and demodulation Is achieved by tracking in the frequency domain the position of the minimum of the detected intensity. This technique is particularly suitable for deformation measurements in civil engineering structures where deformations of the order of few millimeters over the sensor length are expected. The method features a measurement range of at least 10 mm, sensitivity better than 10 μm, and dynamic deformation measurements with a bandwidth up to 100 Hz.