Present in situ stress measurement in the eastern segment of Yarlung Zangbo River fault and fault activity analysis

Abstract

In order to determine the in situ stress state of the newly built hydropower station project in Jiacha county, and understand the activity of the eastern segment of the Yarlung Zangbo River fault zone, we obtained the in situ stress data in the engineering field by using the self-developed deep-hole stress measuring equipment based on the hydraulic fracturing method. We analyzed the fault activity by employing the Mohr-Coulomb failure criterion and the collected in situ stress data along the eastern segment of the Yarlung Zangbo River fault zone. The results showed that: (1) The magnitudes of the maximum horizontal principal stress SH ranged from 6.07 MPa to 37.62 MPa, the values of the minimum horizontal principal stress Sh were from 3.13 MPa to 20.33 MPa at the depth from 122.75 m to 418.75 m, and the dominant direction of the measured maximum horizontal principal stress was nearly NNE.(2) The stress regime was mainly characterized by SH＞Sh＞Sv (Sv is the vertical principal stress), which was prone to reverse faulting.(3) Most of the measured and collected Mohr stress circles intersected the failure threshold line with friction coefficient equal to 0.6, which indicated that the eastern segment of the Yarlung Zangbo River fault zone was in a high level of fault slip instability. Furthermore, the fault slip risk of the west section from Gongga to Langxian was higher than that of the east section near Linzhi along the eastern segment of the Yarlung Zangbo River fault zone.