Present-day stress state and fault stability analysis in the capital area of China constrained by in situ stress measurements and focal mechanism solutions

This work proposes to determine the present-day in situ stress state across both known and suspected faults in the capital area of China and to assess fault stability and consequent seismic hazards. The population of main active faults in the capital area is summarized, and 168 sets of hydraulic fracturing and overcoring data and 84 sets of earthquake focal mechanism solutions are gathered and studied. The available data indicate that reverse and strike-slip faulting stress regimes are favored at reservoir depths in this region. The ratio of maximum horizontal stress to vertical stress (K-H) and the ratio of minimum horizontal stress to vertical stress (K-h) at a depth of 500 m show complex spatial variations in stress magnitudes. Generally, K-H appears to increase southward, which might suggest that stress is accumulating in the southern part of the region. The relative stress magnitude R appears independent of the depth and mainly varies between 0.5 and 1.0. The observation of stress data suggests a relatively uniform direction (nearly E-W) for the maximum horizontal principal stress. The influence of hydrostatic pore pressure on critical stresses is discussed, and the presence of hydrostatic pore pressure makes faults more conducive to reactivation. Most locations in this region are critically stressed based on the Coulomb frictional failure criterion and Byerlee's law with hydrostatic pore pressure; thus, the present-day stress state appears to be high enough to initiate slip. In addition, the relationship between the tectonic stress field and earthquakes is discussed.