A seismic hazard map proposed as part of a new building code for Romania is
presented here on basis of the recommendations in EUROCODE 8.
Seismic source zones within an area of about 200 km around Romania
were constructed considering seismicity, neotectonics and geological
development. The probabilistic seismic hazard assessment in terms of intensities
is performed following Cornell (1968) with the program EQRISK (see Mc Guire, 1976),
modified by us for use of intensities.
To cope with the irregular isoseismals of the Vrancea intermediate
depth earthquakes a factor Ω is introduced to the
attenuation law (Kövesligethy, 1907). Using detailed macroseismic maps of three
earthquakes Ω is calculated by fitting
the attenuation law to
observed intensities, i.e. to local ground conditions. Strong
local variation of Ω is avoided by a gridding of 0.5°
in longitude and 0.25° in latitude. The contribution
of the Vrancea intermediate depth zone to the seismic hazard at each
grid point is computed with the corresponding representative Ω.
A seismogenic depth of 120 km is assumed.
The final seismic hazard is the combination of both contributions,
of zones with crustal earthquakes and of the Vrancea intermediate depth
earthquakes zone. Calculations are done for a recurrence period of
95, 475 and 10000 years. All maps show the dominating effects of
the intermediate depth earthquakes in the
Vrancea zone, also for the capital Bucharest.
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