ANALYSIS OF THE FORMATION SYSTEM OF THE PRESENT TECTONIC STRESS FIELD IN THE HEAD AREA OF THE THREE GORGES RESERVOIR

The present tectonic stress field in the head area of the Three Gorges reservoir was systematically analyzed and verified in the geological,seismological,deformation and in situ stress contexts and checked by numerical modeling.The authors think that the present tectonic stress field in the study area belongs to a pure shear system,i.e.the superimposition of the NE-SW principal compressional stress from the west is superimposed by the WNW-ESE principal tensional stress resulting from extension of the Jianghan-Dongting basin.The axes of the two stresses intersect nearly perpendicularly to each other;so they can act as the principal compressive stress(σ₁) and the principal tensional stress(σ₃) of present tectonic stress field in the study area respectively.