Issue
EPL
Volume 88, Number 1, October 2009
Article Number 19002
Number of page(s) 5
Section Geophysics, Astronomy and Astrophysics
DOI http://dx.doi.org/10.1209/0295-5075/88/19002
Published online 26 October 2009
EPL, 88 (2009) 19002
DOI: 10.1209/0295-5075/88/19002

About the world-wide magnetic-background noise in the millihertz frequency range

J. Marfaing1, J.-J Bois2, R. Blancon3, E. Pozzo di Borgo3, G. Waysand2, S. Gaffet2, 3, 4, M. Yedlin5, P. Barroy6, M. Auguste2, D. Boyer2 and A. Cavaillou2

1   Universités d'Aix-Marseille, IM2NP, case 142, Faculté des Sciences de Saint Jérôme F-13397 Marseille Cedex 20, France, EU
2   Université de Nice Sophia-Antipolis, Observatoire de la Côte d'Azur, Laboratoire Souterrain Bas Bruit de Rustrel-Pays d'Apt (LSBB) - La Grande Combe, F-84400 Rustrel, France, EU
3   Université d'Avignon et des Pays de Vaucluse, Département de Physique - rue Louis Pasteur, F-84000 Avignon, France, EU
4    Université de Nice-Sophia-Antipolis, UMR Géosciences-Azur - 250 rue Albert Einstein, F-06560 Valbonne, France, EU
5   University of British Columbia, Department of Electrical Engineering - 2356 Main Mall, Vancouver, BC, V6T 1Z4, Canada
6   Université de Picardie-Jules Verne, Département de Physique, Laboratoire de Physique de la Matière Condensée - EA 2081 - 33 rue St Leu, F-80039 Amiens Cedex 1, France, EU

jannie.marfaing@im2np.fr

received 16 July 2009; accepted in final form 28 September 2009; published October 2009
published online 26 October 2009

Abstract
In the millihertz range, a single magnetometer can detect magnetic waves in the near-field regime. For such long wavelengths, it can measure the world-wide magnetic-background noise due to any charge displacement on Earth and within its environment. In this frequency band, the normal modes of the Earth's free oscillations exist and when excited, they shake the air column above them, up to the ionosphere where the moving charges emit a magnetic fluctuation, via Ampère's law. We show the magnetic-background noise spectrum obtained by an FFT analysis of 72 consecutive hours of magnetic-seismic calm. It is mostly due to vertical charge oscillations. Even in the absence of a quake larger than Mw = 5.2, spherical and toroidal modes are deected. Instrumental and analytical perspectives are discussed.

PACS
91.25.fd - Environmental magnetism.
85.25.Dq - Superconducting quantum interference devices (SQUIDs).
91.30.P- - Earthquakes.

© EPLA 2009