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1 Acta Geophysica Polonica

1 1999

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Models of the Earth's crust structure in the East Carpathian Region determined from inversion of farfied P-waveforms

Starodub G., Gnyp A.

Acta Geophysica Polonica

1999

Vol. 47, nr 4

375-400

P-waveform inversion study of local crustal structure beneath the three broadband seismic stations of the East Carpathian Regional Seismic Network has been carried out. Our inversion technique involves inverting a set of radial components of observed seismograms in the frequency domain to estimate layer thicknesses, Vp, Vs, Qp, Qs. Initial four- and five-layer models of the Earth's crust under the station Uzhgorod (SU, east-northern fringe of the Pannonian deep) and Mizhgirya (SM, Folded Carpathians) were derived from deep seismic sounding data (International Geotraverse II). Final models show comparably moderate changes in the positions of the main seismic boundaries except for the disappeared boundary between two upper layers of the SM model where Vp contrast dropped from 0.9 km/s (in the initial model) to 0.15 km/s (in the final one). The total crustal thickness at SU site changed from 27.0 to 28.7 km and at SM site - from 55.0 to 57.1 km. Low Vs layer at midcrustal depths (7.2-21.0 km) is obtained for the SU model. A significant increase of Vp is observed in the crust-mantle transition layer (38.2-57.1 km) of the SM model. The most unusual result is obtained for the station Kosiv (SK, Frontcarpathian foredeep). SK site is characterized by a complex geological structure. The tectonic boundaries are running very closely there. The initial four layer model was built using common depth point data. Its thickness was 43.0 km and increased to 51.3 km in the final model due to the thickening of three upper layers. The fairly abrupt crust-mantle boundary is found with Vs contrast of 1.2 km/s (against 0.6 km/s initially).