On some properties in the emergence and evolution of the oscillations of the Earth after earthquakes

The records from wideband seismic stations are analyzed for studying the oscillations of the Earth that emerged after the earthquakes in Sumatra on December 26, 2004 (M = 9.2), Chile on February 27, 2010 (M = 8.8), and after the Tohoku megaearthquake on March 11, 2011 (M = 9.0). Attention is focused on the band with a period of 20.46 min, which includes the free radial mode ₀S₀. It is established that the emergence of oscillations in the frequency interval corresponding to the free oscillations of the Earth is delayed by a lag, which increases with increasing period. Pulsations of the 20.46-min band, which appear in the interval from 5 to 7 days after the earthquake and have a period of 127–129 min, are revealed. The patterns of the amplitude attenuation of the 20.46-min band are different at stations located in zones with different tectonic activity. These features manifest themselves in the search through different stations and through different earthquakes.