In Situ Stress State of the Northwest Region of the Jiaodong Peninsula, China from Overcoring Stress Measurements in Three Gold Mines

The northwest region of the Jiaodong Peninsula has a complex geological environment that experiences frequent microseismic activity. In situ stress magnitudes and orientations in three underground gold mines (i.e., Sanshandao, Xincheng, and Linglong gold mines) were obtained by an improved overcoring technique with a hollow inclusion strain gauge from 53 measuring points, and the distribution characteristics of the in situ stress field were analyzed. The results show that the stress field is characterized by σ_H > σ_h > σ_v and σ_H > σ_v > σ_h (where σ_H, σ_h, and σ_v are maximum horizontal, minimum horizontal, and vertical principal stresses, respectively). The regional stress field is dominated by the horizontal principal stress in the measurement depth ranges. The σ_H is dominantly oriented in the NWW–SEE or near E–W direction, which is, in general, in agreement with those interpreted by focal mechanism solutions, geodesic leveling analysis, and GPS data. The stress accumulation in the study area is at moderate and low levels under the present tectonic stress state, and the superficial crust is in a relatively stable state. The stress accumulation in the thrust stress state and the strike-slip stress state are mostly moderate.