Computing Near-surface S-wave Velocity Models by Inversion of Converted-wave Traveltime Differences
R. Cova and K. Innanen
Event name: 77th EAGE Conference and Exhibition 2015
Session: Multi-component - P and S Wave Field Acquisition and Processing
Publication date: 01 June 2015
Info: Extended abstract, PDF ( 1.09Mb )
Price: € 20
Characterizing the near-surface is an important part of solving seismic static problems. It is also a critical step as input for more general iterative inversion methods applied to land seismic data. In the case of converted waves this becomes even more true due to the large magnitudes of the shear-wave statics. In this study, a solution based on the difference in conversion traveltimes between receivers is proposed. This solution may be useful for inverting delay times retrieved by interferometric techniques. Due to the complexity of the partial derivatives of the forward modelling operator for this case we decided against local descent-based methods, adopting instead a simulated annealing inversion method. This is also justified by the complex topography of the objective function. Performing a representative number of iterations of the proposed algorithm successfully retrieves the true parameters of the model. Since traveltime differences were used, the inverted parameters only allowed us to compute changes in the depth of the base of the near-surface rather than its absolute value. This can be fixed through a calibration process given the depth of the low velocity zone for at least at one receiver location.