# A New Look at the Stress State Across the Bohai Strait, China
## 4 Results
### Stress Magnitudes
The fitting results of these four parameters are plotted in Figure 6. It should be noted here that these fitting equations were not applied to the CD borehole because of the insufficient data availability but are presented as points in the corresponding figure. Undoubtedly, this may raise uncertainties on the comparison, but given that these parameters usually show a relatively large distribution pattern near the surface, this may not overturn the findings drawn in this study. \[K_{\rm av}=\frac{S_{H}+S_{h}}{S_{\rm p}} \tag{4}\]  
\[K_{\rm Hv}=\frac{S_{H}}{S_{\rm p}} \tag{5}\]  
\[K_{\rm Hv}=\frac{S_{h}}{S_{\rm p}} \tag{6}\]  
Figure 5: Profile of principal stresses versus depths in the Bohai Strait region. The results indicate that \(K_{\rm av}\) values for the PD, CD, and GZ boreholes gradually increase with depth and finally approach 0.37, 0.41, and 1.37, respectively (Figure 6a). Comparison between these three boreholes and the North China Block, which approaches 0.69 [61], reveals that the \(K_{\rm av}\) values for the GZ and PD boreholes were only 53.7% and 59.4% of those in the North China Block, respectively, while the XL exhibits a \(K_{\rm av}\) value 1.99 times higher than that of the North China Block. It can also be seen that the \(K_{\rm av}\) values in the CD site are larger than the North China Block, even though they were just plotted in scatter form in Figure 6b. The \(K_{\rm av}\) features obtained here are consistent with those of \(S_{\rm H}\) and \(S_{\rm h}\) values. As shown in Figure 6b, the \(K_{\rm Hv}\) values are mainly in the range of 0.68-2.26, with a best-fitting constant of 0.46 in the PD borehole, and the \(K_{\rm Hv}\) values are mainly in 0.62-3.46,  
Figure 6: Profile of the parameters (**a**) \(K_{\rm av}\), (**b**) \(K_{\rm Hv}\), (**c**) \(K_{\rm uv}\), and (**d**) \(K_{\rm th}\) versus depths across the Bohai Strait. with a best-fitting constant of 0.49 in the GZ borehole. However, the \(K_{\rm Hv}\) values are mainly in 1.09-3.90, with a best-fitting constant of 1.72 in the XL borehole, which is larger than those of the PD and GZ boreholes. The \(K_{\rm Hv}\) values in the CD borehole are mainly in 1.85-2.97, also larger than those in PD and GZ. The \(K_{\rm hv}\) values are mainly in 0.53-1.57, with a best-fitting constant of 0.38 in the PD borehole, and \(K_{\rm Hv}\) values are mainly in 0.53-2.37, with a best-fitting constant of 0.41 in the GZ borehole, while the \(K_{\rm Hv}\) values are mainly in 0.58-2.29, with a best-fitting constant of 1.02 in the XL borehole. The \(K_{\rm hv}\) values are mainly in 1.20-1.82 in the CD borehole (Figure 6c), larger than the other three sites. It can be seen here that the distributions of the \(K_{\rm Hv}\) and \(K_{\rm hv}\) show similar features to those of the stress values of \(S_{\rm H}\) and \(S_{\rm h}\), and the parameter \(K_{\rm av}\), that is, the closer to the intersection of the TLFZ and ZBFZ, the larger the values. \(K_{\rm Hh}\) shows different features and cannot be fitted using the approach used for the above three parameters because they are considerably scattered, as shown in Figure 6d. Therefore, we adopted the mean values to analyze their distribution patterns. The mean values of \(K_{\rm Hh}\) of the GZ, PD, XL, and CD boreholes are 1.32, 1.36, 1.56, and 1.64, respectively, revealing a similar feature as the above-mentioned parameters. This reflects that the differential stress in the horizontal direction increases as it approaches the intersection of the two large faults.