Seismic monitoring of western Pacific typhoons |
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| Authors: | Wu-Cheng Chi Wan-Jou Chen Ban-Yuan Kuo David Dolenc |
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| Institution: | (1) Institute of Earth Sciences, Academia Sinica, 128 Sec 2, Academia Road, Nankang, Taipei, 115, Taiwan;(2) Department of Earth and Atmospheric Sciences, Saint Louis University , 3642 Lindell Blvd, St. Louis, MO, 63108, USA;(3) Large Lakes Observatory, University of Minnesota Duluth, 2205 E 5th Street, Duluth, MN 55812, USA |
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| Abstract: | Typhoons inflict large damage to societies, but are usually difficult to monitor in close proximity in real-time without expensive
instruments. Here we study the possibility of using seismic waveforms on the seafloor and on land to monitor the turning of
a far away or approaching typhoon. Up to 67% of the typhoons making landfall in Taiwan come from the eastern shore, so that
we deployed broadband ocean-bottom seismometers (OBSs) offshore eastern Taiwan in 2006 to study ground motion in close proximity
to a typhoon. Typhoons generate ocean waves, which generate pressure signals in the water column before being transmitted
to the seafloor as seismic waves and recorded by the OBSs. The ground motions on the seafloor correlate with locally increased
(ocean) wave heights and wave periods, suggesting that the ground motions are mostly induced by in situ or nearby pressure
fields, as shown by coherence function analyses. When a typhoon turns and changes wave-wave interaction near the source region,
a new set of en echelon patterns develops which can be observed by OBSs and land stations. Similar features occur when a typhoon crosses a landmass
and re-enters the ocean. The energy level ratio between the single-frequency and double-frequency microseisms also changes
abruptly when the typhoon turns. These features can potentially help near real-time early warning with little cost to complement
other conventional typhoon early warning methods. |
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