We study the propagation of frequency disturbances across large-scale interconnected power systems using ambient synchrophasor frequency measurements. Inspired by recent discoveries in geophysics on data-driven estimation of the Green’s function (impulse response), we analyze the applicability of this approach for second-order oscillation networks. Specifically, we have shown for uniformly damped systems, the impulse response can be estimated by cross-correlating ambient output measurements under white noise input excitation. This result opens up the opportunity to develop a model-free approach to study power system dynamics and stability. In this talk, we will demonstrate the effectiveness of the proposed approach using both simulated and real ambient synchrophasor data. The cross-correlation estimates from real data collected at the Eastern Interconnection (EI) grid have been validated by the recorded frequency disturbance propagation during the 2008 Florida blackout.