First International Conference on MOLDAVIAN RISKS – FROM ...

<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE
16-19 May 2012, Bacau, Romania
SEISMIC HAZARD WITHIN SE CARPATHIANS AND
RELATED FORELAND IN THE GEODYNAMIC CONTEXT OF
THE BLACK SEA OPENING
Lucian Besutiu
Institute of Geodynamics of the Romanian Academy, Solid Earth Dynamics Department
Corresponding author: Lucian Besutiu, besutiu@geodin.ro
Abstract: The paper mainly deals with two major aspects revealed by the seismicity map
of Romania: the unusual craton seismicity of the E Moesian Platform and the strange
intermediate-depth earthquakes within full continental environment in the bending
zone of East Carpathians (EC). Both aspects are considered to be closely related to the
geodynamic evolution of the Black Sea inland following the opening of the west sea basin.
Unlike some previous models claiming for the Black Sea opening as a consequence of an
unique geodynamic event (the extensional environment created behind Pontide by
northward subduction of the Neotethys Ocean floor), geophysical evidence advocate for a
distinct opening of the west and east basins. Residual geomagnetic and gravity anomalies
reveal a NE striking rift in the west basin and a NW-SE one in the E Black Sea. Besides,
off-shore seismics show a slight overthrust of E Pontide over W Pontide advocating for an
earlier opening of W Black Sea. The opening of the west sea basin had important
consequences on the NW inland of the Black Sea. Lithosphere expelled by rifting split the
Moesian Plate (MoP) into several compartments by creating or reactivating major NW
trending faults, well known on the territory of Romania, SE Ukraine and Bulgaria (e.g.
Odessa Fault (OdF), Sfântu Gheorghe (Izmail) Fault (SGF), Peceneaga-Camena Fault,
Ostrov-Sinoe Fault (OSF), Capidava-Ovidiu Fault (COF), Intra-Moesian Fault (IMF),
Varna-Giurgiu Fault (VGF). This also explains the occurence of the Dobrogean sector of
the Moesian Platform. Fingerprints of phenomenon are revealed in the seismic tomography
images showing the large (lithospheric) in-depth extent of some faults (e.g. PCF, COF,
IMF, VGF). After the Black Sea rifting ended its evolution, the above mentioned
lithospheric compartments are still pushed towards the Carpathians by northward
displacement of Arabian Plate (due to the Red Sea and Aden Bay rifts). Part of the Arabian
Plate movement is transmitted (through the numerous micro-plates located at the contact
between the major African Plate and Eurasian Plate) towards the Black Sea and further on,
towards the EC bending zone. Therefore, the above mentioned MoP compartments are
pushed towards EC staying together by friction. However, from time to time, when
tectonic forces overpass the friction, they may relatively slip each other and crust
earthquakes may occur in their upper, brittle part. Geophysical evidence show three major
lithospheric compartments joining the Vrancea intermediate-depth seismic zone: 130 km
thick MoP, 90 km thick Intra-Alpine micro-plate (IaP) and more than 150 km thick East
European Plate (EEP).The Black Sea opening provided the necessary speed excess to
MoP, thus creating the unstable environment for the Vrancea FFT triple junction (VTJ).
Consequently, the VTJ central compartment has been pushed down into the hotter upper
mantle into a thermo-baric disequilibrium to which intermediate-depth seismicity may be
associated. Among major phenomena that might generate seismic energy in the upper
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