With the purpose of studying Chinese mainland shallow crustal stress state, we have built a spherical shell finite element model including main active faults, tectonic blocks, topography, and Moho discontinuity with the consideration of lithospheric heterogeneity. In this model, we deem gravity and plate tectonic stress as the main influential factors, and use the in-situ stress as the main constraints to make the simulation results and in-situ stress measurement comparable. By this way, we obtain the absolute value estimations of China mainland stress field.
Numerical results are:
the general directions of maximum horizontal stress are distributed radially with the center of Tibetan Plateau. From east to west, the directions of maximum horizontal stress gradually rotate clockwise from NS to NNE, NE, NEE, SE, consistent with previous results of focal mechanism solution;
the stress states in different study regions vary greatly. Stress is obviously lower in the center of Qinghai-Tibet active block and higher in its surrounding areas;
the maximum and minimum tectonic stress σΗ and σh are mainly compressive at the depth of 2000 meters in the shallow crust of Chinese mainland, and the magnitude range are 14.5MPa < σΗ<58.0MPa and 3.8MPa < σh<26.7MPa respectively.
The in-situ stress measurement method is a primary means to understand the present-day state of stress, but due to the measurement restriction, we can only measure the shallow crust stress state. How to take advantage of various known data to analyze the regional crustal stress state quantitatively is a complex problem involving geology, mechanics, mathematics and many other disciplines. The formation of tectonic stress field is determined by many factors such as tectonic movements, geological lithology, topography, rock weight, etc. In-situ stress is the result of the combined effects of these factors. Based on the measured data of stress, the deduction of stress in non-measured region can be regarded as a process of simulating the effects of these factors. In this paper, finite element method is applied to calculate the absolute stress of the shallow crust in China. The fundamental concept of our research is following:
Establish our finite element model with the consideration of previous studies concerning geology, geophysics, rock mechanics, etc.;
Use gravitational field as the initial field and apply horizontal boundary loading based on results of previous related researches;
Adjust physical parameters and boundary conditions to make the simulated shell surface stress directions and value close to the in-situ stress measurement results as possible, and eventually obtain the current Chinese land shallow stress field.