Based on two-dimensional hydraulic fracture and overcoring in-situ stress measurement data in China, and the resulting depth-variation curves of lateral pressure coefficient of good quality, we analyzed the range of the maximum and minimum horizontal principal stress in the upper crust, which was taken as the stress magnitude range of crust in stable state. Then, based on Zoback's (1992) idea for estimating crustal tectonic stress magnitude and two assumptions, we deduced the formulae of three principal stresses varying with depth in strike-slip faulting regime, and analyzed the influence of friction coefficient, pore pressure coefficient, and stress shape factor on stress value. The maximum principal stress (or the slope of stress increasing linearly with depth) is positively related with the friction coefficient and negatively with the pore pressure coefficient, while the minimum principal stress (or the slope with depth) is negatively related to the friction coefficient, and positively to the pore pressure. Then, the possible magnitude range of the maximum and minimum horizontal principal stress for crustal rock rupturing is estimated. The result shows that the maximum horizontal principal stress in stable crust is below the range of maximum stress of rock rupturing and the minimum stress is approximately the same as the minimum stress range of rupturing.
In-situ stress measurement is an effective means to learn the stress state in the crust. Because of the technical difficulties and high costs, the number and measuring depth of in-situ stress measurements are very limited; particularly, it is difficult to acquire the stress magnitude in the deep part of the crust, and the available in-situ measurement data is not sufficient for analyzing the distribution of crustal stress state. Therefore, utilizing various information from the deep crust and deducing the deep stress state by inversion methods has become one of the major ways for people to understand the stress state in deep crust. By the slip direction fitting method put forward in the 1980s based on the fault slipping theory (Angelier, 1979; Gephart et al., 1984) we can invert for the crustal tectonic stress utilizing focal mechanism solution, fault slickenlines, and other data, and obtain the directions of three principal stresses and the stress shape factor which indicates the relative magnitudes of principal stresses (Xie et al., 1993; Cui et al., 2006; Hardebeck et al., 2006; Zhang et al., 2014). At the end of the twentieth century, utilizing the stress shape factor given by slip fitting method, Zoback (1992) proposed a method for estimating crustal stress magnitude based on the criterion of preferential fault friction orientation, which became one of the effective ways for estimating tectonic crustal stress magnitude and has been used to study the stress magnitude in a number of regions (Pienefisch et al., 1997; Zhao et at., 2002).
