Abstract
AbstractAnomalous infrasound waves were recorded at five infrasonic monitoring stations four days before a small earthquake which happened in Beijing on 12 October 2011. Waveforms of these five signals are consistent, which are N‐shaped impulse waves with same duration of about one hour. Using the Wigner‐Ville distribution method, time‐frequency analysis of the signals suggests that waves' energies concentrate mainly below the frequency of 0.025 Hz. Correlation coefficients between two signals are all up to about 0.8. The infrasonic source is imaged and located by the method of beamforming, and the results show that distance between the source and epicenter is about 5 km. This study proves that low‐frequency atmospheric infrasonic waves may appear before earthquakes, so valuable information could be provided by studying this kind of infrasonic waves.
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