Geoacoustic emission response to deformation processes activation during earthquake preparation
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The results of geoacoustic emission investigations carried out on the seismoactive Kamchatka Peninsula since 1999 are presented. The experiments are characterized by the application of broadband piezoceramic sound receivers (hydrophones) for recording the emission. The hydrophones were installed at the bottom of natural and artificial water reservoirs. As compared with the standard hydrophones, such receivers allow us to broaden the registration frequency range up to 0.1 Hz–11 kHz. Three-component vector receivers with the same frequency range were used simultaneously to study the spatial structure of the geoacoustic emission and the mode of the medium particle movement in a wave. In the course of the investigations, it was established that anomalies of the geoacoustic emission in the kilohertz frequency range are recorded 1–3 days before strong earthquakes at a distance of a few hundred kilometers from the epicenter. A sharp increase in the amplitude and frequency of the geoacoustic impulses, which resemble microearthquakes in pattern and last from tens of minutes to several hours, is interpreted as an anomaly. Signals at such frequencies cannot propagate from the epicenters of preparing earthquakes and represent the response of the medium at the registration point to the change of its stress-strain state. The stress field created therein determines the primary orientation of the emission sources, which can be assessed by vector-phase methods. The results of the integrated investigations of the geoacoustic emission and the Earth’s surface deformation revealed that anomalies are observed before earthquakes with a considerable increase in the strain rate during both the compression and extension of the near-surface rocks.
Keywordsgeoacoustic emission deformations hydrophone combined receiver laser strainmeter-interferometer Kamchatka
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