High-frequency seismic noise: Results of investigation in Kamchatka

The investigation of seismic noise in Kamchatka is carried out for the control of the medium stress condition and search of the strong earthquakes precursors. The main directions of this research are modulation of high-frequency seismic noise (HFSN, frequency range of the first tens of Hz, amplitudes about 10−9–10−12 m) by the Earth tides and temporal variations of HFSN parameters connected with the strong earthquake preparation. For reception of the statistically significant characteristics of HFSN and tides connection it was necessary to carry out long-term HFSN observations in points free from anthropogenous influence as far as possible. The station of HFSN observation was organized in the settlement Nachiky. The sensor is a narrow-band (Q = 100) piezoelectric seismometer, tuned to frequency 30 Hz. Signal envelope is recorded and analyzed. The continuous HFSN registration was begun in 1990 and proceeds till now. In 2000 the second station was established in the complex geophysical observatory “Karymshina”. The HFSN sensor is set up in the borehole at the depth of 30 m. The research of HFSN structure gave the opportunity to allocate HFSN components connected with the Earth tides. Besides it was revealed that the tidal response is not stable in time: the intervals of the tidal component existence are replaced by intervals of its absence, correlation between tide and HFSN varies in time, while tides have constant parameters. We propose a hypothesis about the connection of variations of the tidal components in HFSN data with the tectonic conditions in region, and consequently, about an opportunity to use this phenomenon for the prediction of strong earthquakes. The phase of the HFSN component connected with a tidal wave O1 (T = 25.8 h) was chosen as a parameter. The choice of wave O1 is connected with its greatest hindrance-immunity. It was shown that the stabilization of this phase is observed before earthquakes with M > 6.0, occurred at distances up to 250 km from the HFSN registration point, within time from several weeks to several months. Since 1996 such an analysis of the HFSN response to tides is conducted in an operative mode, and only in 1 case out of 19 the large earthquake precursor was not shown in any way.