Evidence of strong lateral inhomogeneous structure beneath SE Carpathians and specific mantle flow patterns

Borleanu, F. and Popa, M. and Radulian, M. and Panaiotu, C. (2008) Evidence of strong lateral inhomogeneous structure beneath SE Carpathians and specific mantle flow patterns. Acta Geodaetica et Geophysica Hungarica, 43 (2-3). pp. 119-130. ISSN 1217-8977

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Abstract

The Vrancea region, in the South-Eastern Carpathians (Romania), represents a unique case among the seismic areas in the world taking into account the extreme concentration and persistence of seismicity and tectonic stress field. Our goal is to show that the particular shape of attenuation and shear wave splitting properties can be interpreted in the light of the decoupling and slab retreat processes, which hypothetically induce a specific configuration of the upper mantle flow. Delamination and break-off processes combined with retrograde motion of the slab imply lateral asymmetry in flow geometry and geotectonic properties. Particularly relevant is the strike-parallel flow localized in front of the downgoing slab, in contrast with the steeply dip flow along the slab in the back side. The local upper mantle flows around the descending seismic active body explains the contrast of the seismic wave attenuation in the back-arc region against fore-arc region and the strong anisotropy anomaly observed in the South-East Carpathians (time delays of 1.5–2 s). Outside the epicentral area, the coherent pattern of the shear wave splitting follows the trends of the deformation field as outlined by the GPS measurements, in favour of a strong coupling between the surface and mantle processes.

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