A New Look at the Stress State Across the Bohai Strait, China

The Bohai Strait is a special tectonic region in North China, characterized by strong fault activity and frequent seismic events. In this study, we analyzed the stress state across the Bohai Strait in detail by integrating the stress data derived from the hydraulic fracturing measurements in four boreholes along the strait (i.e., Pingdu, Xiangli, Changdao, and Gaizhou from south to north) and evaluated its implications for seismicity. The results reveal that the gradient coefficients of the maximum (SH) and minimum horizontal stresses (Sh) with depth in Xiangli and Changdao are over 1.59 and 1.87 times the corresponding stresses of the North China Block. However, the SH and Sh in Pingdu and Gaizhou do not exceed 50.2% and 59.4% of those of the North China Block. The stress values increase as the distance approaches the interaction of the regional faults in the Bohai Strait. The SH orientation in the Bohai Strait region is N68.67 ± 9.30° E, consistent with the prevailing NEE–E-W regional stress direction. According to the Coulomb friction failure criterion, the friction coefficients of the four boreholes range from 0.24 to 0.52, lower than the theoretically critical limit for inducing fault slip in the upper crust (i.e., Byerlee’s law). The faults in the strait region are considered to be contemporarily stable but need to be further evaluated, considering more influencing factors. This study provides a new, instructive understanding of the variations in the stress state in the Bohai Strait region.