The development of seismotectonic and earthquake preparation processes in the central part of the Baikal Rift Zone according to results of tectonomagnetic studies

The technique, interpretation algorithms, and some results of long (since 1 968) tectonomagnetic monitoring in the central part of the Baikal Rift Zone are considered. Today precisional geomagnetic observations are performed a t 7 stationary and 280 ordinary stations. In the region of the Ust'-Selenga basin 3-4-year periods of the increased amplitudes of tectonomagnetic anom alies have been revealed (1969-72, 1979-82, and 1991-93), which evidences m ore quick and intense stress changes in the Earth's crust in these years. T his is confirmed by the occurrence of strong earthquakes (M greater than or equal to 5) in these periods, It is noted that such periods of seismotecto nic activity repeat roughly every 11 years. The causes of the lower amplitu des of tectonomagnetic anomalies in the BRZ, compared with the Central-Asia n regions, are discussed. The possible mechanisms of magnetic-field changes depending on the seasonal variations in the Baikal water level are conside red. Interpreting tectonomagnetic anomalies permitted a quantitative estima tion of stress changes at the final stage of an earthquake preparation, whi ch are in most cases no more than 0.5-1 determined. This permitted timely r evealing the MPa. Some tectonomagnetic criteria of an intermediate-time for ecast of earthquakes with M greater than or equal to 5 have been preparatio n of earthquake in the delta of the Selenga River (13 July 1993, M = 5) - e ight months before it.