Increased seismic activity recently observed in the Caspian sea and its surroundings place on the background of abrupt changes in its level’s regime (fig. la). As it was shown before, a modern rise in the Caspian sea level corresponds not only to fluctuations in water balance within its bounds but in the whole basin of rivers feeding it and climate characteristics (sediments, temperature etc.) as well (Ashirov et al., 1992). A possible cause for this phenomenon can be asiribed seismotectonic reason which seems to be real when taking into account modern movement along the Caspian sea perimeter (Ashirov et al., 1992; Odekov, Durdyev, 1990; Shikhalibeli, Grigoryante, 1983). It is supposed that the Caspian sea bottom is involved into vertical raising, and, thus, the intensive rise of the basin’s level is due to a change in its geometry. Evidence to the fact are to be found both in geological peculiar formations of the Caspian sea basin and in data characterising its present state - that is in a level regime, seismicity, recent tectonic movement data, etc.

During recent years special investigations of high-frequency seismic noise (HFSN) have been conducted in order to study the nature of temporal regularities of this process. Some correlation between HFSN level and slow changes of stress field have been observed under different geological conditions. These phenomena were interpreted as being due to the presence of a seismic emission component in HFSN which is characterized by a very strong “tensosensitivity”, i.e. sensitivity to the stress changes. Later observations of HFSN carried out at different places using highly sensitive resonant seismometers show that a “modulation” phenomenon, i.e. correlation between HFSN changes and Earth's tides, has been seen with a different degree of confidence both in time and space. This result is explained by the spatial variations in emission activity. It is thought that HFSN is influenced by different kinds of geodynamic processes which change the tensosensitivity and the emission activity with time and with the presence of external seismic noises.