The crustal structure beneath SE Romania from teleseismic receiver functions

Due to vigorous Neogene geodynamic processes, including oceanic subduction, slab break-off and mountain building in the Carpathian Arc, the architecture of the lithosphere in Romania is quite complicated. To improve the knowledge about the lithosphere-asthenosphere system in this region the passive seismological CALIXTO99 experiment was conducted in 1999 in the SE part of Romania. Here we present crustal models derived from the analysis of teleseismic recordings with the receiver function (RF) method of the 120 temporarily installed stations and of the permanent GEOFON stations MLR and TIRR. The RF results extend the known crustal models which are based mainly on seismic refraction work and analysis of regional earthquakes. We apply a grid-search inversion at 30 stations and use two different error estimation methods to determine the Moho depth and the average crustal v(p)/v(s) ratio. The complex 3-D intracrustal structure, especially the deep sedimentary basins, distorts significantly the RF waveforms within the whole station network. This leads to ambiguous results at some stations. Our model of the Moho depth has a maximum crustal thickness in the SE Carpathian Mountains at station MLR with a depth of about 45 km and an average crustal v(p)/v(s) ratio of 1.79. The surrounding crust in SE Romania has a thickness of mainly 35-40 km. The RFs at MLR are characterized by clear azimuthal effects that can be correlated with the variation of the sediment thickness in the foredeep of the Carpathian Mountains. A RF waveform inversion verifies these results and gains improved 1-D S-wave velocity models at several stations in SE Romania.