Formation of Oscillations with an 11-Hour Period after the Tohoku Earthquake

Abstract

Records of 68 identical broadband seismic stations of different world regions were studied after the catastrophic Tohoku earthquake on March 11, 2011. The oscillations with a period of ~11 hours lasted for a week. Their properties are distinct from similar 12-hour oscillations of the terrestrial tides. Stations at distances up to several hundred kilometers from each other provide similar records. The increase in the distance changes their structure. The oscillation phases have opposite and coincident polarity at distances of ~3800 and ~7600 km between stations, respectively. Vertical channels of seismographs react in this period range both to the rate of the ground displacement and to the variation in the force of gravity. The amplitude of these oscillations after the Tohoku earthquakes exceeds the variations of the terrestrial tides. They are probably related to excitation of internal gravitation waves in the atmosphere and ionosphere.