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2 2006

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Lithospheric structure of the western part of the East European Craton investigated by deep seismic profiles

Grad M., Janik T., Guterch A., Środa P., Czuba W.

Geological Quarterly

2006

Vol. 50, No. 1

9-22

The Palaeoproterozoic collision of Archaean Fennoscandia, Volgo-Uralia and Sarmatia, viewed as a large composite of terranes, each with an independent history during Archaean and Early Proterozoic time, formed the East European Craton. This paper summarizes the results of deep seismic sounding investigations of the lithospheric structure of the southwestern part of the East European Craton. On the basis of the modern EUROBRIDGE’94–97, POLONAISE’97 and CELEBRATION 2000 projects, as well as of data from the Coast Profile and from reinterpreted profiles VIII and XXIV, the main tectonic units of Fennoscandia and Sarmatia are characterized. The crustal thickness in the whole area investigated is relatively uniform, being between 40 and 50 km (maximum about 55 km). For Fennoscandia, the crystalline crust of the craton can be generally divided into three parts, while in Sarmatia the transition between the middle and lower crust is smooth. For both areas, relatively high P-wave velocities ( 7.0 km/s) were observed in the lower crust. Relatively high seismic velocities of the sub-Moho mantle (~8.2–8.3 km/s) were observed along most of the profiles. The uppermost mantle reflectors often occur ca. 10 to 15 km below the Moho. Finally, we show the variability in physical properties for the major geological domains of Fennoscandia and Sarmatia, which were crossed by the network of our profiles.

Modeling with seismic ray tracing in inhomogeneous geological formation

Cygan S.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

2006

T. 32, z. 4

451-462

Seismic ray tracing is an useful tool to solve the complicated problem of wave propagation. It makes possible obtaining essential information about wave propagation in geological media without necessity of computing the full wave field. In this paper the theoretical principle of seismic ray tracing has been presented. Moreover few typical models of inhomogeneous geological media have been taking into account. Ray tracing methods have been divided into several categories and shooting method has been particularly described. Using results of modeling realized with the SEISMIC UN*X system, advantages and possibilities of the practical application in seismic tomography have been shown.

Śledzenie promienia sejsmicznego jest narzędziem do rozwiązywania złożonego zagadnienia propagacji fal. Pozwala uzyskać istotne informacje o rozchodzeniu się fal sejsmicznych w ośrodku geologicznym bez konieczności wyznaczania pełnego pola falowego. W artykule przedstawiono podstawy teoretyczne śledzenia promieni sejsmicznych w kilku wzorcowych modelach niejednorodnych ośrodków geologicznych. Szczególną uwagę zwrócono na modele ośrodków o stałym i o zmiennym gradiencie prędkości w warstwach. Szczegółowo opisano metodę "punkt strzałowy - punkt odbioru". Wykorzystując wyniki modelowania wykonanego za pomocą systemu SEISMIC UN*X, pokazano jego zalety oraz możliwości wykorzystania zarówno w sejsmice głębokiej, jak i płytkiej.