Microseism oscillations: from deterministic to noise-driven models

Microseism time series, recorded in a broadband seismic station located at the eastern Pyrenees, 50 km far from the Mediterranean Sea, have been analyzed by means of the dynamical system tools in an attempt to elucidate whether the recorded time series are linear or nonlinear, deterministic or stochastic. We have detected strong evidences that microseism time series are stochastic, and no evidence of nonlinearity and/or determinism has been found. In order to get more insight on the underlying mechanism, we tested a toy model that reproduces some observable characteristics of the microseisms. This toy model consists in a forced, damped nonlinear oscillator in which the force term is composed of two harmonic forces and additive white noise. We have concluded that noise contribution is of fundamental importance in modeling the spectral properties of observed time series, and assimilate it to the ubiquitous local, high frequency noise. A global mechanism for microseism generation is suggested in terms of atmospheric turbulence at different wavelengths.