GNGTS 2013 - Atti del 32° Convegno Nazionale

a reflected event but are nevertheless used by the NMO procedure, cause wavelet repetitions, as indicated by the arrows in the corrected panel. Finally, the other reflections are affected by waveform stretching in particular at far offset. The superimposed red line indicates the mute function with a 50% of stretching mute. This mute function rejects completely the first and the second corrected events and the long-offset part of the gather as well. Conversely, the synthetic gather corrected using the NMOPC does not present the distortions of the traditionally corrected CMP (Fig. 2b). The long-offset waveforms are not stretched, the intersecting events are completely separated, there are not any spurious wavelets and also the corrected events have retained much of their amplitude and phase characteristics. Furthermore, since the NMOPC is based on a SVD estimation process and on a series of shaping deconvolutions that use semblance weighted wavelets, the random noise is highly damped. Note that the fourth reflection, which is completely obscured in Fig. 2a, can be detected in this corrected CMP. The minor artifacts that do appear would be effectively attenuated by the stacking process. Real data application. We carry out a real data application on a marine seismic line which pertains to a subset of the 3D data set described in Rocchi et al. (2007) and acquired on the Senegal passive margin. The acquisition parameters for this line are: source interval 100 m, receivers interval 12.5 m, minimum offset 380 m, maximum offset 8100 m and fold coverage of 125. The result of the stacking procedure employing the whole offset range is shown on Fig. 3a. To test the NMOPC, we simulate an undershooting configuration dropping the data acquired with offset shorter than 2300 m. To this data set we apply the conventional NMO technique and the NMOPC to proceed with the stacking process. The stacked section obtained with the traditional NMO correction and mute (30% of stretching threshold) is displayed on Fig. 3b. Many reflected events are muted in this sections, especially in the right hand part, where a low velocity anticline is present. Therefore, the shallow structure is completely lost. On the contrary, the NMOPC stacked section (Fig. 3c) presents all the reflected events, including the shallow ones and shows a signal-to-noise ratio comparable with the full offset section of Fig. 3a. Fig. 2 – a) Synthetic gather corrected using the traditional NMO correction with superimposed a mute function of 50% stretching threshold. b) Result of the application of the NMOPC on the synthetic gather with noise. Note that the fourth reflection, which was buried in the noise before correction, has been highlighted by the SVD and the shaping deconvolutions. 20 GNGTS 2013 S essione 3.1