NICOLAE MANDRESCU
Institutul National pentru Fizica Pamantului, Bucuresti – Magurele
THE 1986 AND 1990 SUBCRUSTAL VRANCEA EARTHQUAKES
AND THEIR GEOLOGIC AND SEISMOLOGIC SIGNIFICANCE
(ABSTRACT)
The aim of this paper is to present some of the most important peculiarities
of the subcrustal Romanian earthquakes, as regards their occurrence and their
effects. The large Romanian earthquakes (M > 7.0) severely affect more than
one third of the Romanian territory. In this century, the events in 1940 and
1977 produced large damages and casualties. The earthquakes in August 30, 1986
(M = 7.0), May 30, 1990 (M = 6.7) and May 31, 1990 (M = 6.1) have a special
importance due to the great number of obtained accelerograms. The existence
of these records led to this study, which has a double aim: a) to compare the
distribution of the maximum acceleration with the macroseismic maps of older
earthquakes from the same hypocentral region; b) to analyse the attenuation
of ground motion acceleration with distance. The maps elaborated using the
instrumental recordings confirmed the results of macroseismic evaluations,
proving the accuracy of cuantification of Vrancea subcrustal earthquake effects.
The good correlation of these data type (instrumental and macroseismic) leads
to the conclusion of a higher importance of the profound geological structure
and of the sedimentary cover in the Focsani – Odobesti Depression in
the distribution of the effects of large subcrustal events. Thus we can even
state that, during the large Romanian earthquakes (M > 7.0) the regional and
local geological conditions have a more important role than the magnitude or
distance in the amplification/attenuation of the maximum acceleration.
Key words: subcrustal earthquake, peak ground acceleration, attenuation, directivity.