Low-frequency microseismic field behavior in seismoactive regions of the Earth and its relation to geodynamic processes
Category: 14-4
УДК 550.34+ 550.348.432(436)+550.344.37+550.34.094
M.Yu. Stepanova, A.V. Gorbatikov
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
Abstract
During five years period before 11 March 2011 mega-earthquake in Japan, spectrogram records at broadband stations located above its source had demonstrated seasonal high-amplitude anomalies in the range of ~30–120 s. Similar anomalies were detected in source areas of four other strong earthquakes which occurred at deep fault zones. Synchronous anomalies with regional peculiarities were also found in seismoactive regions of the Pacific and Alpine-Himalaya belts.
On the basis of spectrogram analysis the following hypothesis was formulated. The microseism’s amplitudes of ~30–120 s period can increase due to simultaneous action of an external and internal factors. The former is global increase in tidal forces in winter months; and the latter, activating some fragments of large seismotectonic structures, is connected with deep dynamic processes in the Earth.
There is one feature in Japanese spectrogram, which is absent in other cases, namely, a strip anomaly which appears on the periods of ~40–45 s two years before the strong earthquake. Its nature differs from that of anomalies with 50–120 s periods and it is presumably connected with creep processes in Benioff zone.
The conclusion was made that in order to increase sensitivity of seismic stations when studying seismic hazard zones, stations should be installed immediately at seismic fault zones.
Keywords: low frequency microseism, geodynamical processes, earthquake preparing
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