IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Oral Presentation 2107
Thermal evolution and geometry of the descending lithosphere beneath
the SE-Carpathians
Dr. Alik Ismail-Zadeh
Geophysical Institute Karlsruhe University IASPEI
Gerald Schubert, Igor Tsepelev
We develop a thermal model of the crust and mantle beneath the SE-Carpathians based on the
inversion of P-wave velocity anomalies of recent seismic tomography images into temperature and on
heat flow measurements. The model of the present crustal and mantle temperature is assimilated into
the geological past, and the prominent Miocene thermal state of the lithospheric slab, descending in the
region, is restored quantitatively from its diffuse present state. In Miocene time the slab geometry
clearly shows two portions of the sinking body: one of them has NW-SE orientation and can be
associated with the interface between the East European and Scythian platforms, and another portion
has a NE-SW orientation and is related to the present descending slab. Above a depth of 60 km the slab
had a concave thermal shape, confirming the curvature of the Carpathian arc, and a convex surface
below that depth. The slab maintained its convex shape until it split into two parts at a depth of about
220 km. We suppose that this change in the slab geometry, which is likely to be preserved until the
present, can cause stress localization due to the slab bending and subsequent stress release resulting in
large mantle earthquakes in Vrancea. Our results also support the hypothesis of dehydration and partial
melting of the descending lithosphere as the cause of the reduction in seismic velocities beneath the
Transylvanian Basin.
Keywords: vrancea earthquakes, slab dynamics, data assimilation