Premium
The horizontal hum of the Earth: A global background of spheroidal and toroidal modes
Author(s) -
Kurrle Dieter,
WidmerSchnidrig Rudolf
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl033125
Subject(s) - toroid , physics , geophysics , amplitude , excited state , normal mode , schumann resonances , excitation , inner core , earth (classical element) , quiet , geology , computational physics , mechanics , atomic physics , optics , acoustics , vibration , quantum mechanics , ionosphere , plasma , mathematical physics
It is well known that the fundamental spheroidal modes of the Earth are continuously excited. The vertical motions of this ‘hum of the Earth’ can be observed at many stations all over the world. However, there exists no hum observation based on horizontal seismic data yet. In this article, we present observations of continuous horizontal background oscillations of the Earth at four exceptionally quiet seismic stations and show the existence of a so far unknown global background of long‐period Love waves and, equivalently, fundamental toroidal modes. Spheroidal and toroidal modes exhibit similar horizontal amplitudes which, for the spheroidal modes, agree with those expected from the vertical component data. Neither earthquakes nor spheroidal‐toroidal mode coupling can explain a permanent excitation of toroidal modes at this level.