Westward Migration

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Science  29 Sep 2006:
Vol. 313, Issue 5795, pp. 1855-1857
DOI: 10.1126/science.313.5795.1855e

The effects of Hurricane Katrina have been felt further afield seismically as well as politically. Gerstoft et al. detected seismic activity in California corresponding to pressure and surface waves generated by pounding ocean waves in the Gulf of Mexico during the height of the storm, 28 to 29 August 2005. The seismologists used beam-forming techniques to back-project very low frequency seismic energy received at an array of stations in southern California. Body waves at double the ocean wave frequency (0.1 to 0.2 Hz) rattled deep through the earth from their source in shallow water east of New Orleans during the storm and for 9 hours after its landfall. Surface waves were also detected across the Gulf and tracked the ocean wave frequency and higher harmonics. The seismic surface waves mimicked the ocean wave pattern, with higher frequencies emanating from the eastern side and lower frequencies to the west of the eye. Thus, both surface and body seismic waves were generated in shallow water by breaking ocean waves from Katrina, but different physical mechanisms couple the water and ground motions that produce them. — JB

Geophys. Res. Lett. 33, 10.1029/2006GL027270 (2006).

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