Materials of the International Conference
50th Anniversary of the International Geophysical Year
and Electronic Geophysical Year

16-19 September 2007 • Suzdal, Russia

Seismic hazard assessment on the a base of geological and seismological data (exampled on the Northern Caucasus Region)

E. Rogozhin

Institute of Physics of the Earth, Russian Academy of Sciences, Moscoe, Russia

Abstract

Studies and mapping of potential seismogenic areas for the territory of the Northern 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 detailed explored. On the southern limb of the North-Western Caucasus the primary and secondary seismic ruptures of unknown ancient and known historical strong earthquakes (seismic faults, landslides, fissures) were discovered. This study in trenches allowed define a radiocarbon age of the seismic offsets, that took place in Holocene on few fault zones. The periods of seismic activation of the structures are correspondent 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 being of 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 have become the base 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 activations occurred there repeatedly, both in Late Pleistocene, and in the 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 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 a 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, does not vary through the whole period of Late Pleistocene and in the Holocene. Probably, revealed regularities of the seismic manifestations can be wide-spread on the whole territory of the Great Caucasus.

Citation: E. Rogozhin (2007), Seismic hazard assessment on the a base of geological and seismological data (exampled on the Northern Caucasus Region), in: Materials of the International Conference '50th Anniversary of the International Geophysical Year and Electronic Geophysical Year', GC RAS, Moscow, doi:10.2205/2007-IGY50conf.

© 2007 Geophysical Center RAS and authors


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