GNGTS 2015 - Atti del 34° Convegno Nazionale

28 GNGTS 2015 S essione 3.1 Igneous bodies characterization by means of seismic reflection attributes and wavelet transform E. Gianturco, A. Tognarelli, S. Rocchi, L. Pandolfi Earth Sciences Department, University of Pisa, Italy Introduction. The aim of this work is the detection and characterization of several igneous bodies observed in a series of 2D reflection seismic sections. The seismic survey has been acquired offshore Senegal and western African margin, SW of Dakar. The identification, description and characterization of the igneous bodies is carried out by means of the complex seismic attributes. The considered attributes are the Reflection Strength and its first and second derivative, the Instantaneous Frequency, the Instantaneous Phase, the Cosine of the Instantaneous Phase and the Sweetness. Moreover, in order to improve the visualization of the entire seismic dataset, the Continuous Wavelet Transform (CWT) is applied to the data. The CWT helps to better discriminate the geometrical features and the morphologies of the igneous bodies. The seismic attributes analysis and the CWT allow the identification of the amplitude anomalies related to the igneous bodies, the description of the different seismic facies and the understanding of mutual relationship and behavior. Furthermore, this process consents the evaluation of the geometrical properties of the intrusive bodies such as thickness, lateral extent, emplacement depth. It also allows the delineation of the structural deformations that affected the overburden due to the igneous intrusion. Finally, the variation in the attribute response let us to recognize in each seismic profile three seismofacies and to classify the intrusive bodies based on their age, shape and level of emplacement. Seismic reflection data. This study is carried out interpreting eighteen seismic lines extracted from a 3D data volume. In particular, the entire dataset is composed by eleven in- lines and seven cross-lines. In Fig.1 the map of the survey with the position of the seismic lines here analyzed; in Tab.1 the most important acquisition and recording parameters are reported. All the sections are time migrated with zero phase conversion applied. A line by line description of each amplitude anomaly is carried out. The seismic lines are characterized on the basis of their amplitude, phase and frequency by means of the complex seismic attributes (Taner et al. , 1979; White, 1991; Satyavani et al. , 2008; Barnes, 2001; Yushun, 2011; Subrahmanyam and Rao, 2008) Reflection Strength and derivatives, Instantaneous Phase, Instantaneous Frequency and Sweetness. Tab. 1 - Acquisition and recording parameters. Type of energy source Air Guns Number of source 2 groups Source depth 5.5 m (+/- 1m) Shot point interval 25 m Number of streamers 10 Streamer length 6000 m Number of traces 480 / streamer Trace interval 12.5 m Nearest seismic offset 360 m Streamer depth 7 m +/- 1 m Number of channels 10x480 + 37 auxiliary channels used Record length 8100 ms Sample interval 2 ms