Low-Frequency Seismic Noise Before and After the Sumatra Megaearthquake of December 26, 2004

Resumo

The records from 59 identical broadband seismic stations located in different regions of the world, made before and after the strong earthquake off Sumatra Island on December 26, 2004, with magnitude M = 9.1, are studied. Oscillations with periods of 40 to 360 s are analyzed. Stations located several hundred kilometers away from each other demonstrate different pulses of seismic noise with periods of 40–80, 80–160, and 160–320 s, which indicates that this effect is connected to local sources in the atmosphere. The exponential growth of the spectral amplitude of noise with elongation of the periods of oscillations corresponds to the theory by A.N. Kolmogorov about local isotropic turbulence in the atmosphere. The level of seismic noise increased twice after the Sumatra earthquake at stations located both in the seismoactive subduction zones and within the platforms.