Abstract
The main sources of the ambient seismic wavefield in the microseismic
frequency band (peaking in the ∼0.04-0.5 Hz range) are the earth’s
oceans, namely wind-driven surface gravity waves (SGW) coupling
oscillations into the seafloor and the upper crust underneath. Cyclones
(e.g. hurricanes, typhoons) and other atmospheric storms are efficient
generators of high ocean waves with complex but distinct microseismic
signatures. In this study, we perform a polarization (i.e. 3-component)
beamforming analysis of microseismic (0.05-0.16 Hz) retrograde Rayleigh
and Love waves during major Atlantic hurricanes using a virtual array of
seismometers in North America. Oceanic hindcasts and meteorological data
are used for comparison. No continuous generation of microseism along
the hurricane track is observed but rather an intermittent signal
generation at specific oceanic locations along the track. Both seismic
surface wave types show clear cyclone-related microseismic signatures
and are consistent with a colocated generation at near-coastal or
shallow regions, however the Love wavefield is comparatively less
coherent. We identify two different kind of signals: a) intermittent
signals that originate with a constant spatial lag at the trail of the
hurricanes and b) signals remaining highly stationary in direction of
arrival even days after the hurricane passed the presumable source
region. This high complexity highlights the need for further studies to
unravel the interplay between site-dependent geophysical parameters and
SGW forcing at depth, as well as the potential use of cyclone
microseisms as passive natural sources.