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In Situ Stress Measurements in the Lhasa Terrane, Tibetan Plateau, China
Author(s) -
MENG Wen,
GUO Changbao,
ZHANG Yongshuang,
DU Yuben,
ZHANG Min,
BAO Linhai,
ZHANG Peng
Publication year - 2016
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13019
Subject(s) - borehole , geology , terrane , tectonics , stress (linguistics) , plateau (mathematics) , seismology , geotechnical engineering , linguistics , philosophy , mathematical analysis , mathematics
Tectonic activities are frequent in the Lhasa terrane because of the ongoing collision between the India and Eurasia plates. Knowledge of the stress state is critical to evaluate the crustal stability and the design of underground excavations. Because of the limitations imposed by natural conditions, little research has been performed on the present crustal in situ stress in the Tibetan Plateau, and further study is imperative. In this study, hydraulic fracturing measurements were conducted in Nyching County (LZX) and Lang County (LX), Lhasa terrane to characterize the shallow crustal stress state. The results indicate that the stress state in the LZX borehole is markedly different from that in the LX borehole, in both magnitude and orientation. At the same measurement depths, the magnitudes of horizontal principal stresses in the LX borehole are 1.5–3.0 times larger than those in the LZX borehole. The stress regime in the LX borehole favors reverse faulting characterized by S H > S h > S v , where S H , S h , and S v are maximum horizontal, minimum horizontal, and vertical principal stresses, respectively. The S H and S h values are approximately three and two times greater than S v . Fracture impression results reveal that S H in the LX borehole are predominantly N–S, while in the LZX borehole the maximum horizontal principal stress is mainly in the NNE‐direction. The heterogeneity of the regional stress state might be a result of the population and distribution of local structures and seismic activities. The stress state in the LX borehole has exceeded the critical state of failure equilibrium, and there is an optimally orientated pre‐existing fault near the borehole. It can be concluded that the optimally orientated fault is likely to be active when the stress has built up sufficiently to destroy the frictional equilibrium; it is suggested that research focus should be placed on this in future. The stress states in boreholes LZX and LX indicate uniformity of the regional stress field and diversity of the local stress fields resulting from the interactions among regional dynamic forces, tectonic stress field, and geological structures.