Some dynamical characteristics of microseism time-series

Abstract

Summary Microseism time‐series are non‐stationary, non‐linear and stochastic, and these characteristics can be reproduced by a forced non‐linear damped oscillator. In the present study we show that such an oscillator is also able to explain other widely observed features, such as the variation, for a given seismic station, of the frequency of the secondary peak; the variation of the frequency of the primary peak for different seismic stations relative to the same source; the variations of amplitude of the power spectrum for stormy days with respect to quiet days; and the incoherent propagation of microseisms. Numerical simulations with the proposed phenomenological model suggest i) that the main spectral peak may be due to a competitive process between the resonant response of the medium and an external harmonic force (Longuet–Higgins model), ii) that the secondary peak may be generated by the process associated with the activity of the coastal waves or as a subharmonic of the resonant frequency and iii) that the large amplitude variations between quiet and stormy days refers in fact to variations in the source (storm) distance. From a general point of view we can say microseism activity can be interpreted as the resonant response of the Earth to atmospheric cyclonic storms coupled with the oceans.

Wavefield decomposition and phase space dynamics of the seismic noise at Volcàn de Colima, Mexico: evidence of a two-state source process

“…Correig and Urquizu, 2002;Ryabov et al, 2003;Correig et al, 2007). In this framework, our results suggest to associate the quasi-monochromatic IC with frequency peak at 0.15 Hz to the external forcing, which acts with different intensities in the two phases, as inferred by the time-evolution of R(t).…”

“…In this phase, an imprint of the periodic forcing is however visible in the other nearly monochromatic independent component, making the total dimension ∼ 2 also in this case, whereas the volcanic effects are masked by the increase of the energy of the external source. We remark that a system with elements of chaoticity and with nonlinear interactions between the forcing effects and the medium can explain the evidence that microseismic noise can be not coherent in space (e.g., Correig and Urquizu, 2002). Moreover, this scheme implies that this sub-system can be described (in a first approximation) by a nonlinear second-order differential equation with a harmonic forcing in Phase A (e.g., Godano and Capuano, 1999;Correig and Urquizu, 2002), whereas in Phase B such synchronization phenomena must be associated with the interaction between two nonlinear oscillators (Ott, 1993).…”

Ambient noise levels in north central Italy

“…Since the three intervals correspond to periods of low industrial and anthropic activities (summer and Christmas holidays in Italy), we conclude that the 1.1 Hz peak is correlated with the level of the anthropic activities. Array measurements will be performed both to determine the noise sources for the 1.1 Hz peak and to investigate alternative explanations for its origin [e.g., Correig and Urquizú , 2002], since the presence of a spectral peak at multiple stations with a constant frequency could be exploited to study temporal variation in the properties of the Earth's crust.…”

Insights into the dynamic processes of the 2007 Stromboli eruption and possible meteorological influences on the magmatic system

“…Microseismic noise is mainly composed of Rayleigh waves, with the most significant spectral peak around 0.2 Hz. However, seismic signals can be corrupted over almost any frequency [e.g., Correig and Urquizu , 2002, and references therein].…”