Determining In-Situ Stress State by Anelastic Strain Recovery Method Beneath Xiamen: Implications for the Coastal Region of Southeastern China

The in-situ stress state in the shallow crust of the coastal region of Southeastern China (CRSC) remains poorly understood. We conducted anelastic strain recovery measurements in a 2 km deep geothermal borehole to investigate the in-situ stress state. Four high-quality granite core samples were employed to successfully estimate the full stress tensors. The results show that the maximum principal stress sigma(1) is nearly vertical, implying an extensional shallow crust that is controlled by normal faulting. From similar to 1865 to similar to 1959 m in depth, the maximum and minimum horizontal principal stresses (S-Hmax and S-hmin) are 36.1-48.7 MPa and 34.0-38.5 MPa, respectively. Based on the paleomagnetic analysis, the orientation of the maximum horizontal compressive stress S-Hmax determined as N43 degrees +/- 19 degrees W and aligned with the subduction direction of the Philippine Sea plate. According to the compiled stress data, the SH m orientations in the CRSC rotate counterclockwise towards the Chinese mainland, which are consistent with those of the earthquake focal mechanisms and regardless of earthquake type, indicating a heterogeneous stress field dominancy in the CRSC. Our findings manifest that there is a lower horizontal compressive stress state in the upper crust in the study region. We also discussed the possible influence of in-situ stress on wellbore stability and fracture propagation in hot dry rock exploration and further quantitatively analyzed the reactivation possibility of natural fractures under different injection pressures. This study will provide scientific data for geodynamic research, fault seismicity, and geothermal development in the region in the future.

Automated summary

This study investigated the in-situ stress state in the shallow crust of the coastal region of Southeastern China and found an extensional shallow crust controlled by normal faulting. The study also analyzed the characteristics of the stress field in the region and its possible effects on exploration and fracture propagation.