NUMERICAL MODELING OF THE PRESENT TECTONIC STRESS FIELD IN THE CENTRAL QINGHAI-TIBET PLATEAU

Considering crustal rocks as viscous fluids,the tectonic stress field and velocity field of the central segment of the Qinghai-Tibet Plateau are modeled by using the finite element method.The results of modeling indicate that the Qinghai-Tibet Plateau is generally displaced toward the north and east.The velocity of north-directed displacement is highest in the south and gradually decreases form south to north.The velocity of east-directed displacement is highest near the Tanggula fault and gradually decreases toward the south and north sides,showing an "extrusion phenomenon".The maximum principal stress is oriented mainly in a NNW direction in the south and in a NNE direction in the north,generally in a N-S direction.Comparison of the modeling results with the results of tectonic survey and earthquake activity and GPS measurements shows that they are in good agreement.This well reveals the characteristics of tectonic activity,intensity of fault activity and driving mechanism of east-directed displacement in the Qinghai-Tibet Plateau.The present activity of the Qinghai-Tibet Plateau is the results of combined action of northward push and compression of the Indian plate and eastward flow of deep materials.