SE5

Studies and mapping of potential seismogenic areas for the territory of the North Caucasus (in Western deep of the Main Ridge and in the Elbrus area) were carried out. The areas of the largest neotectonic faults were most detailedly explored. On the southern limb of the North-west Caucasus the primary and secondary seismic ruptures of unknown ancient and known historical strong earthquakes (seismic faults, landslides, and fissures) were discovered. This study in trenches allowed to define a radiocarbon age of the seismic offsets that took place in Holocene in few fault zones. The periods of seismic activation of the structures correspond to the time of about 700, 3000, 5000, 6600, 8400 years ago. Magnitude of the paleoearthquakes generating ancient ruptures was estimated from the amplitude of co-seismic offsets in the active faults as 7.0-7.5. The recurrence interval of strong earthquakes in the region is measured as 1-2 thousand years approximately. Seismological (pre-historical, historical and instrumental) data concerning earthquakes with M = 4-7.5 become the basis of magnitude-frequency relation with slope b = -0.94 and coefficient correlation R = 0.986. Local variations of the modern soil thickness in the zone of three active faults, studied in trenches manifest the vertical and horizontal creeping movements along the fault planes during past 100 years with average velocities of 1.5-2.0 mm per year. These studies have shown also that volcanic area of Elbrus is as well as potentially seismoactive region. Volcanic activities occurred there repeatedly, both in Late Pleistocene and in Holocene (39+5, 28+3, 23+2, ~21, ~9.2-9.3, ~7.8-8.0, ~7.2, ~6.0, ~4.9, ~4.6 and 1.8-1.9 thousand years ago). The seismic reactivation periods occurred in 5500, 3800, 2300 and 300-400 yr ago. The greater periods of recurrence (many hundred and even thousand years) of strong earthquakes, characteristic for the Caucasian region as a whole, as well as disastrous eruptions are the reason of the apparent tranquility of the Elbrus volcano on the modern stage. Received results allow to confirm, that seismic, geological and volcanic forms of hazard of dangerous natural processes for the region of the Great Caucasus extremely high, and seismic mode, velocity of geological motion and repeatability of strong eruptions there, probably, do not vary through the whole period of Late Pleistocene and Holocene. Probably, revealed regularities of the seismic manifestations can be widespread on the whole territory of the Great Caucasus.