Testing robust inversion strategies for three-dimensional Moho topography based on CELEBRATION 2000 data

Abstract

SUMMARY In this paper, we present results of the 3-D tomographic modelling of the crustal structure and Moho topography applied to data recorded in SE Poland during the CELEBRATION 2000 seismic experiment. The target area covers ca. 500 km × 500 km and represents a complex geological setting from old Precambrian platform (East European Craton, EEC), through the crustal blocks (terranes) that form the Trans-European Suture Zone, to the young Alpine orogen—the Carpathians. We test two different inversion strategies using two different algorithms: (i) coupled inversion of Pg and PmP arrivals to constrain both the crustal velocities and the Moho depths; (ii) decoupled inversion of PmP arrivals only using previously obtained smooth 3-D crustal velocity model. The coupled inversion of 11 700 Pg and 3100 PmP arrivals results in a much smoother crustal velocity field than the one previously obtained by inversion of first arrivals only. Also, the obtained Moho structure is much smoother than the Moho map compiled from the existing 2-D models. Decoupled inversion of the PmP reflections provides Moho structure comparable in resolution to the compiled map. Synthetic tests indicate that with our data set we are able to resolve larger than 100-km-size Moho structures. The modelled Moho is shallowest in the area of the Upper Silesian Block (ca. 32 km), then it is deepening by ca. 10 km over 100-km-wide zone along the margin of the EEC and finally it reaches up to 48 km depth in the area of the EEC. Our favoured strategy for modelling large refraction/wide-angle reflection data set consists of derivation of a smooth crustal velocity model by a first-arrival tomography and then complementing this model by a decoupled inversion of PmP reflections in order to constrain minimum-structure Moho topography.