Contemporary stress field in and around a gold mine area adjacent to the Bohai Sea, China, and its seismological implications

Current Tectonic Stress State in an Iron Mine District, North China, Based on Overcoring, Hydraulic Fracturing, and Acoustic Emission Stress Measurements

“…Additionally, the evolution of the fitting lines indicates that the influence of the vertical stress is enhanced. Notably, the stress value at the surface is not zero but very small, which is a common phenomenon and may be associated with the erosion of materials on the surface [13]. Moreover, over the past decades, many studies have been performed on the relationship between the principal stresses in the crust and the depth [35][36][37][38], and most of them suggest that there exists an approximately linear relationship between the horizontal and vertical stresses and the depth.…”

“…This method is limited to certain depths and requires an accessible test site, such as a tunnel, but can be suitably used in underground facilities. According to the acceptable layout principles for OC measurement points [12,13], three measuring points (A1, A2, and A3) used for OC measurements were arranged in a transport tunnel of the iron mine. The horizontal projection positions of these three measuring points are shown in Figure 2.…”

Comparison and evaluation of overcoring and hydraulic fracturing stress measurements

“…On the other hand, for the OC and HF stress data in the two mines, the difference between σ H and σ v increases with increasing depth, which reflects that σ H dominates the modern stress field, and further supports the view that the formation and evolution of stress field are controlled by horizontal tectonic movement. Also, both types of horizontal stress data from the two mines show that the surface stress level is not zero, which is a pathological phenomenon that may be related to the erosion of crustal surface materials 36 . The high constant term and gradient amplitude in the derived linear regression equations show that the surface tectonic action is strong, and the horizontal tectonic stress increases sharply with the increase of depth.…”

“…Based on the recorded original data, the stress-related hydraulic pressure parameters (i.e., breakdown pressure P b , shut-in pressure P s , and reopening pressure P r ), tensile strength ( T ) of the rocks, and the corresponding stress magnitudes and directions in the two mines were derived and presented in Table 3 and Table 4 , respectively. The relevant calculation or determination methods can be found in the introduction by Li et al 19 , 36 . According to the WSM quality ranking system 27 , the HF stress data quality in the Shuichang iron mine can be ranked into the B, C, and D categories and that in the Sanshandao gold mine can be ranked as category C, revealing effective and significant information on the contemporary stress field.…”

“…The stress orientation is a crucial component of stress tensors and a useful evaluation index. The maximum principal stress normally regulates the modern crustal stress environment in the shallow part 36 . The maximum principal stress orientations measured in the two mines using the two techniques are visualized by rose diagrams, as illustrated in Fig.…”