[J03-3] Deformation of the lithosphere: Integrating seismology and geodesy through modelling III

[J03-3-03] GPS observation of Biot's slow wave in the Earth's crust triggered by Hurricane Sandy's storm surge

^○Geoffrey Blewitt^{1, 2}, Jinhai Zhang^{3, 4}, William E. Holt⁴, Zhenxing Yao³ (1.Nevada Geodetic Lab., Nevada Bureau of Mines & Geology, University of Nevada, Reno, U.S.A., 2.Department of Physics, University of Nevada, Reno, U.S.A., 3.Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 4.Department of Geosciences, Stony Brook University, Stony Brook, New York, U.S.A.)

A phenomenon predicted by *Biot (1956) is an ultra-slow (subsonic) wave in a poroelastic medium with high permeability, in which the fluid and surrounding matrix oscillate with opposite phase. Although there is evidence for Biot's slow wave in specially constructed laboratory settings, its direct observation in nature has remained elusive owing to rapid attenuation and a lack of natural low frequency (~0.1 mHz) excitation sources. Our routine determination of thousands of GPS positions around the globe with centimeter accuracy every 5 minutes presents the opportunity to search for poroelastic phenomena in the relevant bandwidth between seismic and tidal frequencies. Here we show, using 5-minute GPS data observed in northeast USA around the landfall of Hurricane Sandy of October 29-30, 2012, evidence of a highly-attenuated wave propagating in the Earth's crust over hundreds of km inland at ~65 m/s with ~12 cm amplitude. Such a phenomenon is consistent with Biot's slow wave being triggered by the associated 4-m storm surge, then propagating in a highly permeable crust with abundant fluid-saturated interconnected cracks. The ability to observe such waves opens a new window on Earth's poroelastic structure, with prospects to better understand connections between hydrology, seismology, geodesy and tectonics.

*Biot, M.A. (1956), Theory of propagation of elastic waves in a fluid-saturated porous solid, 1. Low-frequency range. Journal of the Acoustical Society of America, 28, 168-178.