Distribution law of in situ stress field and regional stress field assessments in the Jiaodong Peninsula, China

The Jiaodong Peninsula has a complex evolution process in terms of its geological structure. The Tanlu fault zone, Penglai-Qixia fault system, Muping-Jimo fault zone, and Penglai-Weihai fault zone have a noticeable control effect on the seismic activity of the region. A number of medium-strong earthquakes occurred in the past, where Yantai coastal earthquakes are relatively concentrated, with a clustering phenomenon. The distribution law of the in situ stress field is analyzed based on 86 sets of measured data at depths from 109 m to 970 m after optimization in the Sanshandao gold mine of Laizhou, Xincheng gold mine of Laizhou, Linglong gold mine of Zhaoyuan, Pingdu, Qingdao, and Wendeng sub-areas of the region. The fault activity in accordance with the Coulomb friction failure criterion and relationship between the stress field and geological structures is discussed. The results indicate that the in situ stress state of the region is dominated by horizontal tectonic stresses. The stress regime is primarily dominated by the strike-slip regime within the range of the measured depths. The maximum horizontal principal stress is predominantly oriented in the NWW-SEE or near-EW direction, which is generally in agreement with the orientation interpreted by focal mechanism solutions and is basically consistent with those of the regional tectonic stress field generated from the movement of the surrounding tectonic plates. The stress state of the region is basically consistent with the crustal frictional strength range that is predicated using the Coulomb friction failure criterion, with a friction coefficient of 0.2-1.0.