# Seismic Identification and Characterization of Deep Strike-Slip Faults in the Tarim Craton Basin
## 4 Seismic Attribute Generation
### Energy Attributes  
The amplitude attribute, indicating reflection intensity, directly captures changes in the reflection coefficient (at the wave impedance interface), amplitude variation with offset (AVO), and fluid presence within reservoir pores. It reflects the variation in adjacent lithology underground or the existence of oil-bearing rock strata [44]. The gradual change in the amplitude in the lateral direction usually reflects the change in lithology or the change in lithofacies, and its sudden change may indicate the existence of faults or the edges of oil and gas rocks. Therefore, the amplitude attribute can be directly used to describe the formation changes and predict oil and gas attributes. (1) Root mean square amplitude \begin{table}
\begin{tabular}{c c c c} \hline
**Categories** & **Types of Attributes** & **Results** & **Score** \\ \hline \multirow{4}{*}{Energy} & Root mean square amplitude & Not clear fault & 3 \\ \cline{2-4}  & Low-frequency energy & Clear fault with the large noise disturbance of the whole area & 6.5 \\ \cline{2-4}  & High-frequency attenuation & Not clear fault & 4 \\ \hline \multirow{4}{*}{Curvature} & Maximum positive curvature & Clear fault with the large noise disturbance of the whole area & 6 \\ \cline{2-4}  & Minimum negative curvature & Clear fault with the large noise disturbance of the whole area & 7 \\ \cline{2-4}  & Dip & Clear fault with the large noise disturbance of the partial area & 7.5 \\ \hline \multirow{4}{*}{Correlation} & Coherent & Clear fault with the large noise disturbance of the partial area & 7 \\ \cline{2-4}  & Likelihood & Not clear fault & 3 \\ \cline{2-4}  & Ant tracking & Clear main fault with false branch fault & 8.5 \\ \cline{2-4}  & Auto fault extraction (AFE) & Clear fault with the large noise disturbance of the partial area & 7 \\ \hline \multirow{4}{*}{Gradient} & Amplitude variance & Clear fault with the large noise disturbance of the whole area & 7.5 \\ \cline{2-4}  & Amplitude gradient & Clear main fault and clear branch fault & 9 \\ \hline \end{tabular}
\end{table} 
Table 1: Seismic attributes applied to the identification of strike-slip faults in cratonic basins. The root mean square (RMS) amplitude is the most commonly used attribute in seismic datasets. It has a good correlation with the rock density and is often used in lithologic phase transition analysis [45]. According to the calculation formula, the RMS amplitude is positively correlated with the amplitude. The amplitude information is correlated with the reflection coefficient of the stratum [46]. When the seismic wave is vertically incident, the relation between the amplitude and density is as follows:  
Incident wave reflected wave:  
\[R=\frac{A_{\mathrm{i}}}{A_{\mathrm{r}}}=\frac{\rho_{2}v_{2}-\rho_{1}v_{1}}{ \rho_{2}v_{2}+\rho_{1}v_{1}} \tag{12}\]  
where \(R\) is the reflection coefficient of the interface; \(\rho_{1}\) is the density of the medium above the reflecting surface; \(\rho_{2}\) is the medium's density below the reflecting surface; \(v_{1}\) and \(v_{2}\) are the velocities above and below the reflecting surface, respectively; \(A_{\mathrm{r}}\) is the amplitude of the reflected wave; and \(A_{\mathrm{I}}\) is the amplitude of the incident wave. According to [PERSON]'s law,  
\[\rho=av^{0.25} \tag{13}\]  
where \(\rho\) is the density, g/cm\({}^{3}\); \(v\) is the velocity; and \(a\) is the constant, 0.31. By substituting Equation (13) into Equation (12), we obtain  
\[R=\frac{\rho_{2}^{5}-\rho_{1}^{5}}{\rho_{2}^{5}+\rho_{1}^{5}} \tag{14}\]  
According to the above formula, the root mean square amplitude is positively correlated with the rock density. The RMS amplitude extracted from the fault development model is significantly higher than that from the non-fault development model. According to the identification results of strike-slip faults in the cratonic basin with root mean square amplitude attributes, the main faults of the strike-slip faults are relatively clear, but the branch faults are not clear (Figure 4a).