Florian Bleibinhaus

Effects of surface scattering in full-waveform inversion

In full-waveform inversion of seismic body waves, often the free surface is ignored on grounds of computational efficiency.Asyntheticstudywasperformedtoinvestigatetheeffectsofthissimplification.Intermsofsizeandfrequency,the testmodelanddataconformtoareallong-offsetsurveyofthe upper crust across the San Andreas fault. Random fractal variations are superimposed on a background model with strong lateral and vertical velocity variations ranging from 1200to6800m/s.Syntheticdatawerecomputedandinverted forthismodelanddifferenttopographies.Afullyviscoelastic time-domain code was used to synthesize the seismograms, and a viscoacoustic frequency-domain code was utilized to invert them. The inversion was focused on early arrivals, which are dominated by P-waves but also contain strong P-Rayleigh wave conversions from the near-field of the receiver. Resulting waveform models show artifacts and a loss of resolution from neglecting the free surface in the inversion, but the inversions are stable, and they still improve the resolution of kinematic models. The extent of deterioration dependsmoreonthesubsurfacethanonthesurfacestructure. Inversion results were improved at no additional expense by introducing a weak contrast along a staircase function above shotsandreceivers.

New results from amplitude preserving prestack depth migration of the Münchberg/Vogtland segment of the MVE deep seismic survey

Abstract A part of the deep seismic near normal-incidence Munchberg–Vogtland–Erzgebirge (MVE) observations located in the Saxo-Thuringian Belt at the northern rim of the Bohemian Massif has been reprocessed using the method of amplitude preserving 3D prestack depth migration. The advantage of this method is its ability to deliver a quantitative and geometrically correct image of the crustal reflectivity without preference of certain dips. The application of a prestack migration method is preferable in complex areas where diffractions and reflections with alternating dips are expected. Along the reprocessed part of the profile, location and dip of many reflective elements have considerably changed compared to the poststack migration [Z. Geol. Wiss. 22 (1994) Appendix 3.4]. The Franconian Line (FL), a major post-Variscan fault, is imaged down to 11 km depth and its fault throw can be assessed at 6 km. Observations of reflecting elements in the prolongation of the FL and a significant change of reflectivity give rise to the idea of an extent of the FL into the lower crust. High reflection amplitudes in the Vogtland area are interpreted within the scope of fluids ascending from a magmatic body at the crust-mantle boundary.