GPS detection of ultra-low-frequency crustal resonance caused by Hurricane Sandy

Using 5-minute solutions of vertical component GPS, processed from the CORS network, we observe spatially correlated displacements that appear to propagate for several hundreds of kilometers within the Northeastern U.S., just after the landfall of Hurricane Sandy. This displacement field lasts for about 4.5 hours and shows great attenuation when propagating from the coast into the mainland. Its amplitude is about 10 times bigger than that predicted by a static loading using traditional theory and models. We interpret the propagation of the time-dependent vertical displacement field as a Biot slow wave associated with a medium containing abundant water-filled fractures in the crust. This ultra-long period wave appears to have been excited by the large storm surge that impacted the coastal region during, and just prior to, the Sandy landfall. Our interpretation predicts three key features simultaneously: strong attenuation, low wave speed (no more than 100 m/s) and high displacement amplification (about 10 times). The observations may suggest that poroelastic behavior plays an important role in elastodynamics for the crust, especially for ultra low frequency loading.