# Seismic Identification and Characterization of Deep Strike-Slip Faults in the Tarim Craton Basin
## 4 Seismic Attribute Generation
### Correlation Attributes  
Correlation attributes reflect the similarity of seismic datasets at different locations. The essence is to reflect the continuity of strata in a certain property by analyzing the proximity and dissimilarity between data. Correlation functions can be used to detect seismic channel discontinuities and predict stratigraphic discontinuities due to different changes in the lithology, overcomplexities, and unconformities. (1) Coherent  
The coherence attribute is used to calculate the similarity between adjacent seismic tracks and analyze the transverse changes in strata and lithology in the same phase axis to achieve fault identification. Many methods can be used to calculate the coherent volume, including the cross-correlation method, multi-channel similarity method, feature-based structure method, and gradient structure tensor (GST) method [52]. The energy of the mean amplitude of all seismic channels in the time window divided by the sum of the energies of all seismic channels represents the discontinuity of seismic waveforms, as shown in Equation (19):  
\[c_{s}=\frac{\sum_{k=K}^{+K}\left(\frac{1}{1}\sum_{j=1}^{J}\left[u\left(k\Delta t -px_{j}-qy_{j}\right)\right]\right)^{2}}{\sum_{k=K}^{+K}\left(\frac{1}{1}\sum_{ j=1}^{J}\left[u\left(k\Delta t-px_{j}-qy_{j}\right)\right]^{2}\right)} \tag{19}\]  
Faults are often mixed with other geological sequence features and structural features that can cause seismic amplitude changes (Figure 6a). Especially when the signal-to-noise ratio of the seismic dataset is low or the geological structure is complex, the fault or other discontinuity features shown by the coherence attribute are generally effective in horizontal sections or stratigraphic sections but difficult to identify and interpret in vertical sections. Figure 6: _Cont._(2) Likelihood  
The likelihood attribute enhances the difference between fault and non-fault responses. The likelihood attributes of the inclination and dip of each data sample point are scanned, and the maximum value is obtained when accurate inclination and dip are scanned [52]. The semblance value range is 0-1, and the formula is as follows:  
\[\left\{ \begin{aligned} & Semblance=\frac{\left[(g)^{2}\right]_{f}}{ \left[(g^{2})\right]_{s}}\\ & Likelihood=1-Semblance\end{aligned} \right. \tag{20}\]  
In the equation, _Semblance_ is the similarity attribute; \(g\) is the 3D data volume; the subscript \(s\) represents the constructed information, which guides smoothing; and the subscript \(f\) is the dip angle enhancement. According to the identification results of the strike-slip faults in the cratonic basin with the maximum likelihood attribute, the strike-slip faults are not clear, and there is much pseudo-fault information. Thus, it is not suitable for fine identification (Figure 6b). Figure 6: Attributes of seismic correlation. Several major branch faults can be seen, but the whole branch is a network that is significantly affected by false faults, and it is difficult to distinguish true and false faults. (**a**) Map of coherent attribute. The coherence attribute is used to calculate the similarity between adjacent seismic tracks and analyze the transverse changes in strata and lithology in the same phase axis to achieve fault identification. (**b**) Map of the likelihood attribute. The likelihood attribute enhances the difference between fault and non-fault responses. The likelihood attributes of inclination and dip of each data sample point are scanned, and the maximum value is obtained when accurate inclination and dip are scanned. (**c**) Map of the ant tracking attribute. (**d**) Map of the AFE attribute. AFE is directional weighted coherence, which is obtained by further directional filtering based on sharpening. (3) Ant tracking  
The principle of ant tracking technology is to distribute a certain number of \"artificial ants\" in the seismic dataset according to the initial boundary setting value and let each \"ant\" move forward along the possible fault plane under the constraints of the tracking parameters [53].