GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 3.1 31 Finally, the CWT can be interpreted as a bank of band pass filters process, but it is more flexible than other time-frequency transform such as the Short Time Fourier Transform (STFT). Unlike the STFT, that uses a window with fixed width, the mother wavelet is dilated and translated in such a way to be designed to balance the resolution between time domain and frequency domain. Furthermore, the CWT is particularly useful to locate and identify signals with exotic spectral characteristics (Sadowsky, 1996). As well as for the seismic attributes, a line by line CWT analysis is carried out. The CWT is tested using three different mother wavelets: the Haar wavelet, the order 2 Daubechies wavelet (db2) and the Morlet wavelet (morl). Although the best result was expected by the application of the Morlet wavelet, that is the commonly used wavelet, if the transform is aimed at improving the quality of the seismic section (Sadowsky, 1996), the db2 is adopted. As an example, the reconstruction of the inline 1560 through the sum of the coefficients of the chosen db2 scales is shown in Fig. 3. The analysis shows that the anomalies related to the igneous bodies can be approximated in a frequency range from 20 up to 30 Hz. This is in agreement with the Instantaneous Frequency response. Furthermore, the application of the CWT is useful to discriminate the igneous bodies within the seismofacies B that are masked due to the presence of a chaotic facies. Conclusions. The Senegal Basin is characterized by the presence of discordant low frequency high amplitude reflection anomalies that are interpreted as Miocene intrusive bodies (Rocchi et al. , 2007). This interpretation is supported by the data obtained from the on-shore survey of the Senegal area. The main result of this survey is the identification of magmatic activity ranges from Oligocene to Quaternary. From the line by line analysis of the eighteen seismic lines results that the detected nineteen sills can be classified on the basis of their age, levels of emplacement and geometries. In particular, most of the sills develop within the seismofacies C at the first level of emplacement Fig. 3 – Reconstruction of the inline1560 through the sum of the coefficients of the chosen db2 scales. The limits between the seismofacies A, B, C and the localized amplitude anomalies L, M and N, related to the igneous bodies, are highlighted.