Флуктуации геомагнитного поля, сопровождавшие чуйские землетрясения в сентябре – октябре 2003 г.

Urgency. There is an urgent need to study the interactions in the Earth – atmosphere – ionosphere – magnetosphere system. To identify direct and reverse, positive and negative links among the subsystems, sources producing massive releases of energy are commonly used. In this paper, the Chuysk earthquakes whose Richter magnitudes vary from 4.5 to 7.3 are considered as such a source. The aim of this paper is to present the findings of studying a possible response of the geomagnetic field in the 1 – 1000-s period variations to the preparation and occurrence of the Chuysk earthquakes of September – October 2003. Techniques and Methodology. The measurements were carried out using the fluxgate magnetometer located at the V. N. Karazin Kharkiv National University Geomagnetic Observatory. The sensitivity of the magnetometer is 0.5 – 500 pT in the 1 – 1000-s period range. The data processing was performed in three stages. First, the signals from the magnetometer, recorded in relative magnetometer units, were converted into absolute units, taking into account the magnetometer frequency response. Second, band-pass filtering was performed in the 1 – 10-s, 10 – 100-s, and 100 – 1000-s period ranges. Third, a system spectral analysis of time variations in the H- and D-components of the geomagnetic field was undertaken. Results: Forty three minutes and one-hundred-sixty-three minutes prior to the earthquake of Richter magnitude 7.3, quasi-periodic variations of the geomagnetic field were observed. These variations may be an earthquake magnetic precursor, and the mechanism of such a precursor has been described. After the earthquakes of Richter magnitudes 7.3, 6.7, and 7.0, quasi-periodic variations of the geomagnetic field were detected. Such variations may be caused by the perturbation transfer due to seismic waves with speeds in the 1.9 – 5.3-km/s range and owing to atmospheric gravity waves traveling with speeds in the 320- to 670-m/s range. On October 1, 2003, the changes in the character of the variations occurred with time delays of 0 to 5 min. If these variations were associated with earthquakes, the magnetohydrodynamic waves could act as an agent that transferred the disturbances. Conclusions: The moderate earthquakes are determined to be able to cause geomagnetic field disturbances recordable at distances of about 3,500 km from the epicenter.