A. Adamczyk

Application of first-arrival tomography to characterize a quick clay landslide site in Southwest Sweden

First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Göta River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles.

Full-waveform Inversion of Conventional Vibroseis Data Using Preconditioning Focused on Low Frequency Enhancement

Despite the popularity that full-waveform inversion (FWI) has gained in recent years, its application to Vibroseis data is still challenging, due to the problematic low-frequency content. We present the results of acoustic frequency-domain FWI of Vibroseis data with sweep starting at 6 Hz, acquired with standard 10 Hz geophones in 2010 in south-east Poland. 4.5 Hz matching filter and curvelet denoising in the frequency domain are used to enhance the low-frequency content of the data. This, together with dense sampling of the frequencies in the first inversion group, resulted in a geologically plausible P-wave velocity model, which correctly reproduces the data, including the far-offset arrivals and wide-angle reflections.

Full-waveform Inversion Applied to Regional Vibroseis Profile from SE Poland

We show a case study of full-waveform inversion (FWI) applied to a regional 240 km long seismic profile POLCRUST located in south-east Poland. The experiment is unique because it portrays different tectonic deformation styles over a relatively short distance. It was designed for deep reflection imaging, but we decided to use FWI to provide a high-resolution P-wave velocity model of the shallow (down to 4 km) subsurface. The acquisition parameters, namely the use of 10 Hz geophones and Vibroseis sweeps starting at 6 Hz, made it necessary to design a non-standard data preconditioning workflow for enhancing low frequencies including match filtering and curvelet denoising. Final model was validated using multiple procedures, such as comparison with borehole data and independently processed Kirchhoff prestack depth migration. Velocity profiles from our model match the check shot-data and the anomalies in our model coincide very well with the events in migration, imaging the Carpathian Thrust or small natural gas reservoirs in the Miocene sediments of the Carpathian Foredeep.

Strategies for Complex Thresholding in Curvelet-based Data Denoising

Discrete Curvelet Transform (DCT) introduce minimal overlapping between coefficients representing signal and noise in the curvelet domain, hence being well-suited for data denoising. However, appropriate and optimal weighting of these coefficients remain challenging and the most important stage of curvelet-based noise attenuation. Setting one threshold level for all coefficients may be insufficient for optimal noise attenuation, hence we focus on more complex, scale- and angle-adaptive approach to thresholding. We find empirically that adjusting threshold levels according to certain frequency bands and dips gives results superior to global thresholding. We demonstrate our noise attenuation approach by applying DCT to 3D post-stack seismic data and conditioning input data for 2D full-waveform inversion.