Focal Mechanism and Tectonic Stress Field Characteristics of the Lincheng M_L3.9 Earthquake in March 2023

On March 25, 2023, a M_L3.9 earthquake occured in Lincheng. The focal mechanism and focal depth of the earthquake were inverted by the CAP method. Based on the focal mechanisms with the M_L≥2.0 from 2002 to 2021, the characteristics of the regional tectonic stress field were inverted by using the feature of principal stress axis and linear damping inverse method (DRSSI). The inversion results show that this earthquake is a right-lateral strike-slip and EW-trending hidden fault. The moment magnitude is 3.6. The seismogenic fault is the nodal I, and the best double couple solution is 271.0°, 62.0° and −30.0° for strike, dip and slip angles, respectively. In terms of tectonic stress, the focal mechanism solutions in the whole study area are mainly strike-slip type, P axis is NEE-SWW-direction, T axis is NWW-SEE-direction. The plunge of P and T axis is mostly within 30°, while the vertical plunge is less, mainly near horizontal, which is affected by horizontal tectonic stress. The directions of maximum principal compressive stress in the study area are mainly NNE-direction and NE-direction. A clockwise rotation from NNE to NW occurred in southern Hebei and the central Hengshui and Cangzhou regions, which may be related to the complex tectonic environment of Taihang Mountain piedmont fault.