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Ambient Seismic Source Inversion in a Heterogeneous Earth: Theory and Application to the Earth's Hum
Author(s) -
Ermert Laura,
Sager Korbinian,
Afanasiev Michael,
Boehm Christian,
Fichtner Andreas
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2017jb014738
Subject(s) - geology , ambient noise level , inversion (geology) , northern hemisphere , geophysics , southern hemisphere , noise (video) , schumann resonances , earth's magnetic field , seismology , meteorology , remote sensing , oceanography , climatology , geography , computer science , physics , ionosphere , sound (geography) , artificial intelligence , image (mathematics) , quantum mechanics , magnetic field , tectonics
The sources of ambient seismic noise are extensively studied both to better understand their influence on ambient noise tomography and related techniques, and to infer constraints on their excitation mechanisms. Here we develop a gradient‐based inversion method to infer the space‐dependent and time‐varying source power spectral density of the Earth's hum from cross correlations of continuous seismic data. The precomputation of wavefields using spectral elements allows us to account for both finite‐frequency sensitivity and for three‐dimensional Earth structure. Although similar methods have been proposed previously, they have not yet been applied to data to the best of our knowledge. We apply this method to image the seasonally varying sources of Earth's hum during North and South Hemisphere winter. The resulting models suggest that hum sources are localized, persistent features that occur at Pacific coasts or shelves and in the North Atlantic during North Hemisphere winter, as well as South Pacific coasts and several distinct locations in the Southern Ocean in South Hemisphere winter. The contribution of pelagic sources from the central North Pacific cannot be constrained. Besides improving the accuracy of noise source locations through the incorporation of finite‐frequency effects and 3‐D Earth structure, this method may be used in future cross‐correlation waveform inversion studies to provide initial source models and source model updates.