# A New Look at the Stress State Across the Bohai Strait, China
## 6 Conclusions  
In this study, we determined the stress state across the Bohai Strait using stress data derived from hydraulic fracturing measurements in four boreholes, followed by a discussion on implications for potential fault reactivation. The main conclusions are drawn below.  
The gradients for \(S_{\rm H}\) and \(S_{\rm h}\) values versus depth in the PD and GZ boreholes are only 39.3-50.2% and 50.6-59.4% of those of the North China Block (i.e., 2.29 MPa/100 m and 1.70 MPa/100 m), respectively. The gradients for \(S_{\rm H}\) and \(S_{\rm h}\) values versus depth in the XL and CD boreholes are 187.3-331.0% and 158.8-235.8% of the North China background level. This indicates that the stress value gradually increases from the outer region (PD and GZ sites) to the inner region (XL and CD sites) of the Bohai Strait. Moreover, the stress on the southern side of the Bohai Strait gradually increases as it approaches the intersection of the TLFZ and ZBFZ. The variation in the stress values across the Bohai Strait is preliminarily attributed to the interaction between the ZBFZ and TLFZ.  
The PD and GZ boreholes, which are far from the strait, exhibit stress regimes changing from the reverse or strike-slip faulting to normal faulting. However, the XL and CD boreholes, which are near the Strait core, consistently show a reverse faulting stress regime. The changes in stress regime reveal a stress increase pattern as one approaches the strait from south to north. The mean azimuth of the \(S_{\rm H}\) orientations derived from HF tests across  
Figure 11: Estimation of the in-situ stress analysis in the Bohai Strait according to the Coulomb frictional failure criterion with [PERSON]’s law.  
the Bohai Strait is N68.67 \(\pm\) 9.30\({}^{\circ}\) E, that is, in the NEE direction. This is consistent with the regional stress field in North China determined using multiple stress indicators.  
The stress state across the Bohai Strait is estimated by using the Coulomb friction criterion, incorporating [PERSON]'s law, but without considering the potential influence arising from variations in pore pressure and thermal conditions, and the fault heterogeneity. The results indicate that the stress values in the PD and GZ sites are lower than the limit determined using a friction coefficient of ~0.27, while the stress values in the XL and CD boreholes range between 0.41 and 0.52. The stress values in the four boreholes are all lower than the theoretical limit that induces fault slip, indicating that the faults in the Bohai Strait region exhibit low reactivation potential but need to be further evaluated, considering more influencing factors.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15126708/s1](https://www.mdpi.com/article/10.3390/app15126708/s1)]([https://www.mdpi.com/article/10.3390/app15126708/s1](https://www.mdpi.com/article/10.3390/app15126708/s1)).  
Conceptualization, Z.L. and X.Q.; methodology, X.Q., G.Y. and C.Z.; formal analysis, Z.L., Y.Z., Z.G. and Y.C.; investigation, X.Q. and C.Z.; writing--original draft preparation, Z.L.; writing--review and editing, Z.L. and X.Q.; project administration, X.Q.; funding acquisition, X.Q. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Science and Technology Major Project (grant number 2024 ZD1000706), the Central Public-interest Scientific Institution Basal Research Fund (grant number DZLQJK202408), and the China Geology Survey Projects (grant number DD20230014).  
Not applicable.  
The original contributions presented in this study are included in the article.  
The authors declare no conflicts of interest.