A new technique in demodulation of normal modes

Ramin Nawab (1) , Philippe Lognonné (2)

1 IPG Paris - Institut de Physique du Globe de Paris
2 IPGP - Institut de Physique du Globe de Paris

Lateral heterogeneities of the Earth produce amplitude modulations of the so-called unresolved multiplets. A spectral fitting technique based on the polynomial interpolation of Hermite allows the retrieval of these slowly varying modulation functions. No restrictive hypothesis on coupling among multiplets is necessary. Modulation functions are constrained in time within aQ-cycle for data with typical signal-to-noise ratios. Sensitivity to noise is reduced by the introduction of cosine tapers and by a priori information on the modulation functions. The method then damps rapid oscillations caused by noise and becomes stable. These amplitude modulations can be used in a first stage for inversions where both phase and amplitude are necessary, and generalize basic mode observables such as the local frequency.

Domaines: Géophysique [physics.geo-ph]

Ramin Nawab, Philippe Lognonné. A new technique in demodulation of normal modes. Physics of the Earth and Planetary Interiors, 1994, 84 (1-4), pp.139-160. ⟨10.1016/0031-9201(94)90038-8⟩. ⟨hal-03940029⟩