Global climate imprint on seismic noise

Abstract

[1] In the absence of earthquakes, oceanic microseisms are the strongest signals recorded by seismic stations. Using the GEOSCOPE global seismic network, we show that the secondary microseism spectra have global characteristics that depend on the station latitude and on the season. In both hemispheres, noise amplitude is larger during local winter, and close to the equator, noise amplitude is stable over the year. There is an excellent correlation between microseism amplitude variations over the year and changes in the highest wave areas. Considering the polarization of the secondary microseisms, we show that stations in the Northern Hemisphere and close to the equator record significant changes of the secondary microseism source azimuth over the year. During Northern Hemisphere summer, part or all of the sources are systematically located farther toward the south than during winter. Stations in French Guyana (MPG) and in Algeria (TAM) record microseisms generated several thousand kilometers away in the South Pacific Ocean and in the Indian Ocean, respectively. Thus, secondary microseism sources generated by ocean waves which originate in the Southern Hemisphere can be recorded by Northern Hemisphere stations when local sources are weak. We also show, considering a station close to Antarctica, that primary and secondary microseism noise amplitudes are strongly affected by changes of the sea ice floe and that sources of these microseisms are in different areas. Microseism recording can therefore be used to monitor climate changes.Components: 5366 words, 7 figures.

Green's Functions for Surface Waves in a Generic Velocity Structure

“…For example, a wide range of ambient noise cross-correlation studies make use of surface-to-surface Green's functions, either explicitly or implicitly (e.g., Shapiro et al, 2005;Lin et al, 2008;Prieto and Beroza, 2008). Other studies of near-surface phenomena such as river sediment transport (Burtin et al, 2008;Tsai et al, 2012), sea ice (Kedar et al, 2008;Stutzmann et al, 2009;Tsai and McNamara, 2011), landslides (Hibert et al, 2011;Ekstrom and Stark, 2013), and volcanic tremor (McNutt and Nishimura, 2008) also make use of surface-to-surface surfacewave amplitudes. For such studies of near-surface seismic sources, the tabulation of the coefficients N L and N R ij will provide a useful estimate of the expected ground-motion amplitudes, which is a first step to utilize the seismic data to constrain physical processes.…”

Sources of secondary microseisms in the Indian Ocean

“…In these oceans, one observes a variability of the SM over the year correlated with the latitude of the stations and the season, with more SM signals during the local winter in both Northern and Southern Hemispheres (e.g. Stutzmann et al 2009;Schimmel et al 2011).…”

Seismic Wave Interactions Between the Atmosphere - Ocean - Cryosphere System and the Geosphere in Polar Regions

“…On a global scale, microseism amplitudes are generally highest during local winter, because nearby oceans are stormier in winter than in summer (Stutzmann et al, 2009). In polar regions, particularly from the evidence of Antarctic stations, the opposite observation is made: microseism amplitude is attenuated during local winter for both primary and secondary microseisms (Hatherton, 1960).…”