noise as a source of the Earth's fluctuations

¹ Department d'Astronomia i Meteorologia, UB Martí Franquès 1, E-08028 Barcelona, Spain
² Laboratori d'Estudis Geofísics “Eduard Fontserè”, IEC Martí Franquès 1, E-08028 Barcelona, Spain
³ Departament de Matemàtica Aplicada II, UPC Pla de Palau 18, E-08003 Barcelona, Spain

Corresponding author: ton.correig@am.ub.es

Received: 10 November 2005
Accepted: 10 March 2006

Abstract

In the absence of earthquakes the Earth undergoes continuous oscillations, mainly caused by oceanic/atmospheric fluctuations. For the frequency range of 0.04 to 0.3, these fluctuations are known as microseismic activity and are characterized by a spectrum that depends on the site and on atmospheric storms. However, at its lowest level the microseismic activity appears to be quite stable worldwide and can be considered as an observational invariant which is not explained by standard theories. We interpret this invariant, that appears when the energy input is at a minimum, as Earth's equilibrium fluctuations in an elastic wavefield, independent of the external sources. A phenomenological model has been derived, in which the source of energy is represented as noise that accounts for a superposition of relaxation transients.