# A New Look at the Stress State Across the Bohai Strait, China
## 4 Results
### Stress Magnitudes
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Borehole** & \(P_{\rm b}\) & \(P_{\rm r}\) & \(P_{\rm s}\) & \(P_{\rm p}\) & \(S_{\rm H}\) & \(S_{\rm h}\) & \(S_{\rm v}\) & \(K_{\rm uv}\) & \(K_{\rm IN}\) & \(S_{\rm H}\) \\  & **(m)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **K** \\ \hline  & 164.35 & 13.05 & 4.73 & 4.00 & 1.64 & 5.63 & 4.00 & 4.36 & 1.11 & 1.29 & 0.92 & 1.41 & N55\({}^{\circ}\) E \\  & 209.60 & 18.69 & 8.43 & 7.46 & 2.10 & 11.85 & 7.46 & 5.55 & 1.74 & 2.13 & 1.34 & 1.59 & \\  & 220.45 & 12.05 & 7.12 & 6.41 & 2.20 & 9.91 & 6.41 & 5.84 & 1.40 & 1.70 & 1.10 & 1.55 & \\  & 234.13 & 15.34 & 8.04 & 6.35 & 2.34 & 8.67 & 6.35 & 6.20 & 1.21 & 1.40 & 1.02 & 1.37 & \\  & 279.60 & 15.77 & 6.69 & 5.58 & 2.80 & 7.25 & 5.58 & 7.41 & 0.87 & 0.98 & 0.75 & 1.30 & \\  & 295.65 & 12.60 & 5.71 & 5.06 & 2.96 & 6.51 & 5.06 & 7.83 & 0.74 & 0.83 & 0.65 & 1.29 & \\  & 305.81 & 17.38 & 6.05 & 4.90 & 3.06 & 5.59 & 4.90 & 8.10 & 0.65 & 0.69 & 0.60 & 1.14 & N81\({}^{\circ}\) E \\  & 340.73 & 15.87 & 6.72 & 6.18 & 3.41 & 8.41 & 6.18 & 9.03 & 0.81 & 0.93 & 0.68 & 1.36 & \\ GZ [23] & 363.40 & 14.77 & 7.67 & 6.37 & 3.63 & 7.81 & 6.37 & 9.63 & 0.74 & 0.81 & 0.66 & 1.23 & \\  & 382.20 & 21.89 & 9.89 & 8.54 & 3.82 & 11.91 & 8.54 & 10.13 & 1.01 & 1.18 & 0.84 & 1.39 & \\  & 402.00 & 17.16 & 8.94 & 7.10 & 4.02 & 8.34 & 7.10 & 10.65 & 0.72 & 0.78 & 0.67 & 1.17 & N57\({}^{\circ}\) E \\  & 444.90 & 16.29 & 8.85 & 7.66 & 4.45 & 9.68 & 7.66 & 11.79 & 0.74 & 0.82 & 0.65 & 1.26 & \\  & 483.71 & 22.25 & 10.06 & 9.78 & 4.84 & 14.44 & 9.78 & 12.82 & 0.94 & 1.13 & 0.76 & 1.48 & \\  & 513.27 & 13.00 & 8.14 & 7.25 & 5.13 & 8.48 & 7.25 & 13.60 & 0.58 & 0.62 & 0.53 & 1.17 & \\  & 532.20 & 17.90 & 8.30 & 7.60 & 5.32 & 9.18 & 7.60 & 14.10 & 0.59 & 0.65 & 0.54 & 1.21 & N68\({}^{\circ}\) E \\  & 553.90 & 17.82 & 8.65 & 7.88 & 5.54 & 9.45 & 7.88 & 14.68 & 0.59 & 0.64 & 0.54 & 1.20 & \\  & 591.00 & 15.56 & 9.42 & 9.27 & 5.91 & 12.48 & 9.27 & 15.66 & 0.69 & 0.80 & 0.59 & 1.35 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._We compared the depth-dependent variations of stress in the Bohai Strait with the North China Block, where \(S_{\rm H}\) and \(S_{\rm h}\) exhibit gradients of 2.29 MPa/100 m and 1.70 MPa/100 m, respectively. It was found that the gradients of \(S_{\rm H}\) and \(S_{\rm h}\) for the PD borehole is only 39.3% and 50.6% of those of the North China Block, respectively. The gradients of \(S_{\rm H}\) and \(S_{\rm h}\) for the GZ borehole are approximately 50.2% and 59.4% of those of the North China Block. In contrast, the gradients of \(S_{\rm H}\) and \(S_{\rm h}\) for the XL and CD boreholes are 187.3% and 158.8% and 331.0% and 235.8% larger than the North China Block, respectively. This indicates that the stress values in the XL and CD sites are higher than those of the PD and GZ within the same depth range. Moreover, the stress level gradually increases from the PD to the XL and then to the CD, i.e., from south to north. In detail, the gradients of \(S_{\rm H}\) for the CD and XL boreholes are 8.42 and 4.77 times that of the PD borehole, and the gradients of \(S_{\rm h}\) for the CD and XL boreholes are 4.66 and 3.14 times that of the PD borehole. Considering the tectonic framework and fault pattern in the Bohai Strait (Figure 1), it is evident that the stress value gradually increases from the outer region of the strait to the inner area of the strait. We further analyzed the stress state across the Bohai Strait using several commonly adopted parameters, including the lateral stress coefficient \(K_{\rm av}\), as shown in Equation (4) [60], the horizontal stress ratios \(K_{\rm Hv}\) (Equation (5)) and \(K_{\rm Hv}\) (Equation (6)), and the parameter \(K_{\rm Hh}\) (Equation (7)), which indirectly reflects the stress difference in the horizontal direction.