Low frequency seismic noise before and after the Sumatra megaearthquake December 26, 2004

The paper aims at detailed study of the structure of seismic noise before and after the Sumatra mega-earthquake with M = 9.1 of December 26, 2004. The records by IRIS seismic stations in the different regions of the world, equipped with STS-1 seismometers providing ground motion velocity recording in a broad range of periods from 0.2 to 360 s with the use of standard equipment, form the empirical base of the research. In the records by each station, the intervals free of the earthquakes, interference of manmade impacts, and noise enhancement due to cyclone propagation were selected. The noise bursts in the ranges 40-80, 80-160, and 160-320 s differ by the shape and time of occurrence suggesting different sources of their generation. The absence of the correlation between the noise recordings at the neighboring seismic stations spaced 102 - 103 km apart indicates the influence of local processes. The noise reflects turbulent processes in the Earth’s atmosphere whereas the exponential growth of the noise with the increase of the oscillation period is consistent with A.N. Kolmogorov’s theory of locally isotropic turbulence in the atmosphere. The noise amplitude after the Sumatra mega-earthquake with M = 9.1 of December 26, 2004 has increased by a factor of 1.5-2 in January 2005 compared to January 2004 irrespective of the location of a seismic station.