Teleseismic S wave microseisms

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Science  26 Aug 2016:
Vol. 353, Issue 6302, pp. 919-921
DOI: 10.1126/science.aaf7573

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A seismic “weather bomb” detector

Seismic tomography is like an x-ray of Earth's interior, except that it uses earthquakes for the illumination. Earthquakes are imperfect illuminators because they are clustered on plate boundaries, leaving much of the interior in the shadows. Using a seismic array in Japan, Nishida and Takagi detected seismic waves that they attribute to a severe and distant North Atlantic storm called a “weather bomb” (see the Perspective by Gerstoft and Bromirski). The seismic energy traveling from weather bombs through the Earth appears to be capable of illuminating the many dark patches of Earth's interior.

Science, this issue p. 919; see also p. 869


Although observations of microseisms excited by ocean swells were firmly established in the 1940s, the source locations remain difficult to track. Delineation of the source locations and energy partition of the seismic wave components are key to understanding the excitation mechanisms. Using a seismic array in Japan, we observed both P and S wave microseisms excited by a severe distant storm in the Atlantic Ocean. Although nonlinear forcing of an ocean swell with a one-dimensional Earth model can explain P waves and vertically polarized S waves (SV waves), it cannot explain horizontally polarized S waves (SH waves). The precise source locations may provide a new catalog for exploring Earth’s interior.

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