Three-dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the earthquake-prone southeastern Carpathians based on integrated analysis of seismic, heat flow, and gravity data

The principal purpose of the study is to understand the interplay between intermediate-depth large earthquakes in the southeastern Carpathians (Vrancea) and tectonic stress induced by a high-velocity body (lithospheric slab) descending into the mantle beneath the region. To analyze processes of stress generation and localization in and around the descending slab, we develop a three-dimensional (3D) numerical model of contemporary mantle flow and stress beneath the Vrancea region. The input data of the model consist of: (i) temperatures derived from seismic P-wave velocity anomalies and surface heat flow, (ii) crustal and uppermost mantle densities converted from P-wave velocities obtained from seismic refraction studies, (iii) geometry of the Vrancea crust and slab from tomography and refraction seismic data, and (iv) the estimated strain rate in the slab (as a result of earthquakes) to constrain the model viscosity. We find that major crustal uplifts predicted by the model coincide with the East Carpathian orogen and surround the Transylvanian basin and that predicted areas of subsidence are associated with the Moesian and East European platforms. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress. Modeled tectonic stresses predict large horizontal compression at depths of about 70-220 km beneath the Vrancea region, which coincides with the stress regime defined from fault-plane solutions for the intermediate-depth earthquakes. This implies that buoyancy-driven descent of the lithospheric slab beneath the Vrancea region is directly linked to intermediate-depth seismicity.